CN114029333A - Novel method for repairing soil polluted by heavy metals of cadmium, lead, mercury and chromium - Google Patents

Abstract

The invention discloses a new method for restoring soil polluted by heavy metals of cadmium, lead, mercury and chromium, which comprises the steps of restoring soil polluted by heavy metals of cadmium, lead, mercury, chromium and the like by 2 steps, wherein the first step is to add a composite material of a sulfur-containing material, a phosphorus-containing material and the like, to strengthen the release of heavy metal cations of cadmium, lead, mercury and the like through a soil acidification process, to reduce hexavalent chromium into harmless trivalent chromium through an oxidation-reduction reaction in the soil acidification process, and the second step is to add a composite material and a passivation material for improving the pH value of soil, to realize the passivation and fixation of heavy metals of cadmium, lead, mercury, chromium and the like in the process of improving the pH value of the soil. The method has the outstanding advantages of rapid acidification, accurate acidification, thorough restoration, high safety, simple restoration link and the like. The combined material and the method can realize the complete restoration of single element pollution or compound pollution of heavy metals such as cadmium, lead, mercury, chromium and the like.

Description

Novel method for repairing soil polluted by heavy metals of cadmium, lead, mercury and chromium

Technical Field

The invention relates to the technical field of heavy metal contaminated soil remediation, in particular to a novel method for remediating heavy metal cadmium, lead, mercury and chromium contaminated soil.

Background

The pollution of heavy metals such as cadmium, lead, mercury, chromium and the like is a main pollution source of cultivated land soil in China, wherein the cadmium, lead and mercury pollution sources enter plant bodies in a cation form and are accumulated in agricultural products to form overproof pollution of cadmium, lead and mercury elements; the chromium element is hexavalent chromium which harms plants and agricultural products. Heavy metal pollution is not only standard exceeding pollution of single heavy metal elements, but also compound pollution of 2 or more than 2 heavy metal elements. The soil heavy metal pollution of the cultivated land of China occupies a large area, Song Wei and the like (2013) measure the soil heavy metal pollution profile of the cultivated land of China, and the result shows that (1) the probability of the soil heavy metal pollution of the cultivated land of China is 16.67 percent and the soil heavy metal pollution accounts for about 1/6 percent of the total amount of the cultivated land; (2) in the categories of heavy metal pollution of farmland soil and the like, the specific weights of light pollution, medium pollution and heavy pollution are 14.49%, 1.45% and 0.72% respectively; (3) among 8 soil heavy metal elements, the Cd pollution probability is 25.20 percent and far exceeds that of other soil heavy metal elements, and Ni, Hg, As and Pb soil pollution exists in some areas, but the pollution probability of Zn, Cr and Cu elements is lower. Studies of Shang Er Lian et al (2018) show that the standard exceeding rate of heavy metal point of soil in cultivated land of China grain main producing area is 21.49%, wherein the proportion of mild, moderate and severe pollution is respectively 13.97%, 2.50% and 5%.02 percent; the standard exceeding rates of the cultivated land points of the Sichuan basin, the Yangtze river midstream and the Jianghuai region, the Huang-Huai-Hai plain, the Song-Nei plain and the Sanjiang plain are 43.55%, 30.64%, 12.22%, 9.35% and 1.67% respectively, the pollution of the cultivated land in the south is heavier than that in the north, the main pollutants are Cd, Ni, Cu, Zn and Hg, and the standard exceeding rates are 17.39%, 8.41%, 4.04%, 2.84% and 2.56% respectively; since the 80 s of the last century, the heavy metal content of the cultivated land soil tends to increase, and the point exceeding rate is increased by 14.91 percent on the whole. The heavy metal pollution of soil is related to artificial activities such as industrial production, agricultural production and the like, and also related to a matrix weathering process. Chua Ma Fang et al (2014) report that background values of As, Cd, Cr, Hg and Pb of national soil are averagely 9.2, 0.061, 52.8, 0.026 and 22.3mg/kg respectively, wherein the background value of heavy metals of soil in Guizhou province is the highest (except Pb), and the background values of the 5 heavy metals are 21.3, 0.2681, 114.7, 0.1205 and 31.1mg/kg respectively; exogenous heavy metal pollution is formed by factors such as atmospheric sedimentation, sewage irrigation, fertilizer application, electronic waste dumping and disassembling and the like. According to the investigation of China Ministry of agriculture on national pollution irrigation areas, the irrigation depth is about 140 ten thousand hm²The land area polluted by heavy metals in the sewage irrigation area accounts for 64.8 percent of the area of the sewage irrigation area. Aiming at the research and investigation results, the development of the restoration and treatment of the heavy metal pollution of the farmland soil becomes a major key technical problem to be urgently broken through and solved in the current agricultural environment protection work.

In recent 20 years, Chinese scholars have carried out a great deal of research on the aspects of heavy metal pollution remediation and treatment and have made a lot of important progress, and the research is mainly reflected in the aspects of bioremediation, passivation remediation, leaching remediation, site remediation and the like of heavy metal polluted soil.

1. The bioremediation related patent technology of the heavy metal contaminated soil is as follows:

the invention patent ZL 200810239918.6 discloses a method for restoring cadmium pollution of soil through passivation. The method is to add plant residues rich in sulfydryl into soil, and specifically comprises the following three steps: firstly, crushing plant residues rich in sulfydryl to enable the length of the residues to be less than 10 cm; secondly, adding the plant residues obtained in the first step into the soil to be repaired and mixing, wherein the plant residues at least equal to 0.001 weight part of fresh plant residues are added into the soil to be repaired in a proportion of 1 weight part; and thirdly, keeping the water content of the soil added with the plant residues to be more than 50% of the maximum field water capacity within 20-40 days. The plant residue rich in sulfhydryl is cruciferous plant residue or gramineous plant residue.

The invention patent ZL 201910667304.6 discloses a cadmium-polluted soil composite passivator and application thereof. The soil passivator comprises a soil passivator with pseudomonas as a main active ingredient, and the required soil composite passivator can be prepared by using the soil passivator and a carrier passivation material. The soil passivator and the soil composite passivator provided by the invention can passivate heavy metals in soil, can block the heavy metals, and effectively prevent plants from absorbing metal Cd.

The invention patent ZL 201910573872.X discloses a method for restoring cadmium-polluted farmland soil by rape-medium rice crop rotation. The method comprises the following steps: in the first year, soil preparation is carried out on farmland soil to be repaired, activated base fertilizer is applied to the soil, and rape seeds with high enrichment of cadmium are sown; spraying a leaf surface activator to the rapes in the bolting period and the flowering period of the rapes; in the second year, harvesting rape; after harvesting, applying a passivation conditioner into soil, uniformly harrowing and flooding, directly sowing the medium rice seeds with low cadmium accumulation into the cadmium-polluted farmland soil, and carrying out cultivation management; spraying a leaf surface resistance control agent to the medium rice at the tillering stage, the booting stage and the filling stage of the medium rice; after ripening, the medium rice was harvested. The invention adopts a high-enrichment rape and low-accumulation medium-rice crop rotation system, and is matched with an activated base fertilizer, a leaf surface activating agent, a passivation conditioner and a leaf surface resistance and control agent, so that the absorption amount of cadmium in soil to be repaired of rape and rice is obviously improved, and the modification effect of cadmium-polluted farmland soil is improved.

The invention patent ZL 201910313402.X discloses a modification method of biochar and application of biochar in soil remediation. Comprises the following steps: 1) carrying out oxygen-limited pyrolysis on wheat straws and fresh whole cattail plants to obtain biochar and crushing the biochar; 2) soaking the prepared biochar in hydrogen peroxide, then soaking in aqueous solution of maleic acid and polyethylene glycol, cooling and filtering to obtain a solid phase A; 3) dispersing the solid phase A in ethanol to form a suspension, and respectively adding 2,2,6, 6-tetramethylpiperidine-nitrogen-oxide and methacrylic acid into the suspension to obtain a solid phase B; 4) soaking the solid phase B into an acetic acid aqueous solution, and adding potassium periodate into the solution to obtain a solid phase C; 5) and soaking the solid phase C in a mixed solution of dimethylformamide and N-methyl pyrrolidone to obtain the modified biochar. The method optimizes the modification process of the biochar, has a very obvious Cd remediation effect, and remarkably reduces the heavy metal toxicity of the soil.

The invention patent ZL 201810309290.6 discloses a method for biochemically and jointly repairing mercury pollution. It comprises the following steps: step 1, sowing euphorbia pekinensis seeds in soil polluted by mercury to be repaired; step 2, fully and uniformly mixing the soil conditioner; step 3, applying the uniformly mixed soil conditioner to the soil around the root system of the euphorbia pekinensis; and 4, harvesting the euphorbia pekinensis in the mature period. The method can effectively reduce the content of mercury in the soil, promote the plant root system to absorb mercury from the soil and transfer the mercury to the overground part of the plant, and effectively improve the overall repair efficiency and range.

The invention patent ZL 200710070622.1 discloses a technology for simultaneously producing and repairing heavy metal moderately and slightly polluted vegetable field soil. The method comprises the following steps: 1) planting sedum alfredii and elsholtzia haichowensis in spring in vegetable field soil polluted by heavy metals such as cadmium, copper and zinc in an intercropping manner, wherein the planting density is 10-15cm, and the row spacing is 30 cm; 2) periodically harvesting the sedum alfredii, wherein the sedum alfredii is harvested for 3-4 months for the first time, and then harvested once every 3 months or 30-40cm high, and the stem at the upper part of the harvested time is 2-3cm high; elsholtzia haichowensis is harvested in 10 months; 3) after being harvested, elsholtzia haichowensis seeds are planted with cadmium-enriched rapes, the plant spacing is 15-20cm, and the elsholtzia haichowensis seeds are harvested in 4 months in the next year; 4) after the rape is harvested, cucumber is planted, the plant spacing is 20-25cm, after the cucumber in 9 months is harvested, Chinese cabbage is planted, after the Chinese cabbage is harvested, the elsholtzia splendens is planted, and a repair cycle is completed. The invention utilizes hyper-accumulator plants to carry a large amount of heavy metals from soil, thereby achieving the purpose of reducing the content of heavy metals in vegetables.

The invention patent ZL 201110411889.9 discloses application of Trifolium repens in repairing heavy metal contaminated soil. The method comprises the following steps: planting trifolium repens in the heavy metal contaminated soil; when the Trifolium repens grows to the initial flowering stage, carrying out first cutting on the overground part of the plant; when the plants continue to grow to be grown and buds appear, carrying out secondary mowing on the overground parts of the plants; removing the whole plant when the plant continues to grow to the full-bloom stage; wherein the heavy metal is one or more of copper, cadmium and lead. According to the invention, the trifolium repens is planted in the heavy metal contaminated soil, the trifolium repens can absorb and accumulate heavy metals in the soil in the growing process, the aim of reducing the content of the heavy metals in the soil can be achieved by periodically harvesting the overground part and the underground part, and planting the trifolium repens for several times in a circulating manner, so that the heavy metal contaminated soil can be repaired.

The invention patent ZL 201610033411.X discloses a bioremediation agent for treating composite polluted soil and an application thereof. The bioremediation agent is prepared by mixing the following raw materials in parts by mass: 10-35 parts of microbial agent, 5-25 parts of nano-scale shell powder, 2-10 parts of nano-active silicon fertilizer and 40-55 parts of aronia melanocarpa residue powder. The application method of the bioremediation agent is to apply the bioremediation agent into acid farmland soil polluted by heavy metals, wherein the heavy metals are lead, cadmium and zinc, the concentration of lead is 300mg/Kg, the concentration of cadmium is 0.3-0.4mg/Kg, and the concentration of zinc is 200-230 mg/Kg.

The invention patent ZL 201210014161.7 discloses a bioremediation method of heavy metal contaminated soil. The method comprises the following steps: applying earthworm feed to the heavy metal contaminated soil, turning soil, mixing uniformly, and putting earthworms for breeding; after 28-35 days of cultivation, collecting earthworm casts in upper soil, collecting earthworm casts by a natural illumination method, and keeping young earthworms and earthworm eggs in the soil; planting plants in a strip planting mode, cutting the overground part of the plants when the plants grow for 78-90 days, and removing the whole plants after the plants grow for 50-70 days; collecting earthworm and earthworm cast for 1-3 days by a field collection method every 28-35 days during the period of planting plants; after the whole plant is removed, all adult earthworms and young earthworms are collected by a natural illumination method, and earthworm feces and earthworm eggs are collected. The invention adopts the combination of animals, plants and microorganisms, realizes the remediation of the soil through a proper remediation sequence and a remediation period, and is particularly suitable for mild or moderate copper, cadmium and lead compound contaminated soil.

The invention patent ZL 201910417099.8 discloses a method for in-situ remediation of cadmium-polluted soil by using a microbial nano material. The method mainly comprises the following steps: A. preparing compound bacteria: preparing the vibrio desulfurates, the enterobacter desulfurates, the bacillus desulfurates and the streptococcus desulfurates into composite bacteria according to the mass ratio of 35-55:10-15:30-60: 7-10; B. culturing the compound bacteria: carrying out anaerobic culture on the composite bacteria by using a sulfate reducing bacteria culture; C. preparation of a suspending agent: taking the composite bacteria, metabolites thereof and nutrients as the microbial nano-materials, adding water to prepare a microbial nano-material suspending agent with the thallus number of (0.8-1.2) multiplied by 107/ml; D. repairing cadmium-polluted soil: ploughing the cadmium-polluted soil, simultaneously pouring the suspending agent according to the pouring amount of 50-500L per square meter of soil, and repeatedly ploughing and pouring after 7-15 days, wherein the total times of ploughing and pouring are 2-4 times.

2. The related patent technologies for the passivation and remediation of the heavy metal contaminated soil are as follows:

the invention patent ZL 200910227135.0 discloses a passivation method for reducing the bioavailability of cadmium in acid cadmium polluted soil. The passivating agent adopted by the passivating method is industrial waste obtained after white lime is utilized by a paper mill to recover pulp alkali liquor. The industrial waste generally contains 0.8g/kg-3.0g/kg of available silicon, 0.6g/kg-2.0g/kg of available iron and 100.0mg/kg-400.0mg/kg of available phosphorus. The passivation method can effectively treat the heavy metal pollution of the soil and reduce the bioavailability of cadmium in the acid cadmium polluted soil.

The invention patent ZL 201110078053.1 discloses a soil heavy metal composite passivator containing humic acid minerals and a preparation method thereof. It is prepared from humic acid mineral powder, calcium magnesium phosphate fertilizer and quicklime according to a certain proportion, and comprises the following steps: A. preparation of humic acid mineral powder: selecting raw humic acid ore, ball-milling and sieving with a sieve of 110-140 meshes for later use; B. uniformly mixing the raw materials prepared in the step (A), a calcium magnesium phosphate fertilizer and quicklime, regulating the water content of the mixture to 10% by H2O, and retting and piling for 5-7 days to obtain the soil heavy metal composite passivator containing humic acid minerals. The method reduces the content of cadmium in the soil with the total cadmium content of 10mg/kg (added by external sources) by 0.36-2.25mg/kg within 90 days of culture time, and the reduction amplitude reaches 4.7-25.7%.

The invention patent ZL 201910832023.1 discloses a soil conditioner for rapidly and long-term repairing cadmium pollution of farmland and a preparation method thereof. The soil conditioner comprises: 60-80 parts of silicon-calcium-potassium-magnesium fertilizer; 5-10 parts of anhydrous calcium sulphoaluminate; 5-15 parts of alum; 10-15 parts of sodium carbonate. The silicon-calcium-potassium-magnesium fertilizer contains nutrient components which can be absorbed by plants, and the mass percentage of the nutrient components is as follows: more than or equal to 30 percent of available silicon, more than or equal to 28 percent of available calcium, more than or equal to 4 percent of available magnesium and more than or equal to 5 percent of available potassium. The soil conditioner not only can rapidly passivate heavy metal cadmium in polluted farmland soil and reduce the mobility and toxicity of the heavy metal cadmium, but also can slowly release ions and radicals which form solid precipitate substances with the heavy metal cadmium for a long time.

The invention patent ZL 201610309437.2 discloses a chromium-contaminated soil remediation improver and a remediation method thereof. The material consists of the following raw materials in percentage by weight: 5-25% of ferrous sulfate, 5-25% of calcium polysulfide, 5-30% of humic acid resin, 1-25% of cow dung and 1-25% of mushroom dregs; the humic acid resin is prepared by activating after the sulfonated sodium humate, the phenolic resin and the calcium acetate are crosslinked and solidified. The repairing modifier is mainly used for repairing chromium in soil, has high hexavalent chromium removing efficiency and can improve the content of residue chromium.

The invention patent ZL 201710556724.8 discloses a method for repairing hexavalent chromium polluted soil by biological iron. The method is realized by the following steps: firstly, sponge iron is placed in activated sludge to be cultured to obtain a biological iron microbial inoculum; and then, fully mixing the biological iron microbial inoculum and the hexavalent chromium polluted soil, and removing the hexavalent chromium in the soil through the combined action of electrochemistry, oxidation reduction, adsorption and microorganisms.

The invention patent ZL 201710449175.4 discloses a mercury-polluted soil remediation agent and application thereof. The soil repairing agent comprises 30-70 parts of gypsum and 30-50 parts of carbide slag, wherein the water content of the carbide slag is 10% -20%. The application method of the mercury-polluted soil remediation agent in remediation of mercury-polluted soil comprises the steps of mixing the mercury-polluted soil remediation agent with the mercury-polluted soil, controlling the water content to be 20% -40% by adding water, and maintaining for 3-10 days. Compared with the existing mercury-polluted soil remediation agent which can achieve the equivalent effect, the mercury-polluted soil remediation agent has the advantages that solid wastes are recycled, and the efficiency is high and the economy is realized.

The invention patent ZL 201810125460.5 discloses a soil remediation agent and a method for remediating organically-polluted or mercury-polluted soil. The soil remediation agent comprises ferrous chloride solution with pH of 4-5 and mass concentration of 3-5%, and the method for remediating organic contaminated or mercury contaminated soil comprises the following steps: taking organic polluted or mercury polluted soil to be repaired; preparing a soil remediation agent; adding the soil remediation agent into the organic polluted or mercury polluted soil to be remediated, mixing and stirring to obtain a mixture; and placing the mixture in a microwave reactor for reaction to obtain the repaired soil.

The invention patent ZL 201510933830.4 discloses a curing agent for repairing lead-polluted soil and a repairing method. The curing agent is composed of the following substances in parts by mass: 3-5 parts of cement, 1-2 parts of quicklime and 1-2 parts of sodium dihydrogen phosphate. The method for restoring the lead-polluted soil by using the curing agent has the advantage that the content of lead in the restored soil is lower than the national standard.

The invention patent ZL 201611108051.1 discloses a repairing composition and a repairing method for lead-polluted soil. The restoration composition comprises sodium phosphate, slaked lime, liquid sodium silicate and active humic acid, wherein the mass ratio of the sodium phosphate to the slaked lime to the liquid sodium silicate to the active humic acid is (0.8-1.1): 2.9-3.1): 3.8-4.2): 1. After the stabilization treatment is carried out for 3 days, the lead content of the leachate in the lead-containing polluted soil is lower than the maximum concentration limit value of 0.25mg/L in the pollution control standard of the domestic garbage landfill. And with the increase of the stabilization time, the lead content of the soil leaching solution is reduced to a certain extent.

The invention patent ZL 201110059264.0 discloses a heavy metal composite passivator for paddy soil and a preparation method thereof. It is prepared from sepiolite ore powder, ferro-manganese oxide and quicklime according to the proportion, and comprises the following steps: A. preparing sepiolite ore powder; B. preparing iron-manganese oxide; C. and (4) uniformly mixing the raw material prepared in the step (A, B) with quicklime to obtain the composite passivator. The material has multiple functions of passivating soil heavy metals, restoring acidified soil and the like, so that the content of cadmium and lead in the soil active state in the polluted rice field is respectively reduced by 39.7-53.8% and 49.9-59.1%, the content of cadmium and lead in agricultural products is reduced by 35.1-46.9% and 35.3-53.1%, and the pH value of the soil is increased by 0.22-0.43.

The invention patent ZL 201310106543.7 discloses a lead-cadmium composite modifier for paddy soil and a preparation method and an application method thereof. The modifier consists of the following raw materials in percentage by mass: 30% -50% of calcium carbonate; 5% -10% of hydroxyapatite; 20% -30% of sepiolite; 20% -30% of zeolite; the method comprises the following steps: 1) analyzing the total lead and cadmium content and the exchange lead and cadmium content in the rice field; 2) determining the soil pollution degree of the rice field by applying an evaluation model; 3) applying a lead-cadmium composite modifier according to the lead and cadmium pollution degree in the rice field, applying 100-150 kg/mu in a slightly polluted rice field, applying 150-300 kg/mu in a slightly polluted rice field, applying 300-600 kg/mu in a moderately polluted rice field, and balancing and stabilizing for 10-15 days; 4) analyzing and measuring the content of lead and cadmium in the exchange state in the rice field, and if the fixation rate is lower than 90%, supplementing 100-150 Kg/mu.

The invention patent ZL 201410382463.9 discloses a composite soil passivator for reducing cadmium and lead contents and a preparation method and a use method thereof. The fertilizer comprises the following components in percentage by weight: 5 to 15 weight percent of decomposed chicken manure, 5 to 15 weight percent of unite bran, 5 to 15 weight percent of grass carbon, 10 to 20 weight percent of silicon-calcium-magnesium-potassium fertilizer, 5 to 15 weight percent of talcum powder, 25 to 35 weight percent of sepiolite, 10 to 20 weight percent of stacked fermented sugarcane filter mud and 1.5 to 2.5 percent of microbial fermentation liquor. The composite soil passivator can be widely applied to light and medium cadmium and lead polluted rice fields, can respectively reduce the content of cadmium and lead in the soil active state of the heavy metal polluted rice field by 51.5-51.6 percent and 52.6-58.8 percent, respectively reduce the content of cadmium and lead in polished rice by 48.8-51.6 percent and 52.7-56.0 percent, and simultaneously improve the pH value of the soil by 0.97-1.04.

The invention patent ZL 201510056406.6 discloses a repairing agent for reducing the content of cadmium and lead in effective states of soil. The repairing agent comprises the following components: the quick lime, the calcium sulfate, the charcoal, the ferric chloride and the water, wherein the weight ratio of the quick lime to the calcium sulfate to the charcoal to the ferric chloride is 1-2: 1-2: 1-2: 0.5-1, and the weight of water is 30-45% of the weight of soil. The invention can be used for treating heavily polluted soil, acid soil and soil with neutral pH. The method has high efficiency of repairing cadmium-polluted soil, the reaction mechanism relates to chemical precipitation and physical adsorption, and the method has a certain control effect on the effective state content of lead in the polluted soil.

The invention patent ZL 201710124748.6 discloses a soil oxidation-solidification stabilization repairing agent and a using method thereof. The repairing agent comprises independently packaged zero-valent iron, silicate and calcium oxide. According to the invention, through the molecular oxygen activation process in the zero-valent iron and disilicate system, the organic matters in the polluted soil are oxidized and removed, the interference of the organic matters on the soil solidification and stabilization process is reduced, and meanwhile, the mobility of the heavy metal polluted soil is greatly reduced through oxidation on the reductive substances such as arsenite radicals, selenite radicals and sulfide ions which may exist in the heavy metal polluted soil. Then, calcium oxide/calcium hydroxide is added, and the heavy metal ions (copper, lead, cadmium, mercury and the like) are stabilized and immobilized through iron minerals formed by residual zero-valent iron, calcium silicate compounds and the like.

3. Leaching remediation related patent technology for heavy metal contaminated soil

The invention patent ZL 201080067809.6 discloses a method for purifying cadmium-containing paddy field soil. The method is an in-situ purification method for extracting cadmium by washing cadmium-containing paddy field soil with a pharmaceutical aqueous solution, separating the cadmium-containing paddy field soil into soil and supernatant water by standing, discharging the extracted cadmium as the supernatant water, further diluting and washing with water, concentrating the cadmium-containing washing drainage water to a part of a paddy field to be washed, and carrying out neutralization or alkali treatment on the drainage water at the position to accumulate cadmium. The purification method can efficiently purify the cadmium-containing paddy field soil.

The invention patent ZL 201310302660.0 discloses a composite chemical leaching method for repairing heavy metal contaminated soil. And leaching the heavy metal contaminated soil 1-3 times by using a composite leacheate prepared from ferric chloride and organic acid, then continuously leaching for 1-3 times by using distilled water, and finally separating the leacheate from the soil. The removal rate of cadmium can reach more than 80% and lead more than 55%, and the method finally uses water for leaching, so that the content of metal ions in the soil after remediation and the residual amount of leacheate are reduced, and the method is favorable for cultivating crops in the later period.

The invention patent ZL 201510117369.5 discloses a chemical leaching-plant absorption combined remediation method for cadmium heavily-polluted acidic soil in nonferrous metal mining and metallurgy areas in southern China. Grinding and sieving the heavy metal contaminated soil, and filling the soil into a soil column; pouring ferric chloride solution above the soil body, and naturally flowing out liquid from the bottom of the soil column along with gravity to remove most of active cadmium in the soil; after the leacheate above the soil body completely permeates into the soil, pouring deionized water above the soil body, and naturally flowing out the liquid from the bottom of the soil column along with gravity to remove the residual cadmium and the leacheate in the soil body; drying, grinding and sieving the washed soil, and adding quicklime, sepiolite, commercial organic fertilizer and 0.2-1.2 g kg-1 total nutrient (N + P2O5+ K2O) for improvement; continuously planting the Sedum plumbizincicola for 1-5 seasons, and harvesting the overground part to finish the restoration.

The invention patent ZL 201710382106.6 discloses a stabilizer for synchronously and efficiently repairing lead-cadmium composite polluted red soil. The lead-oriented stabilizer comprises the following components in percentage by weight of a soil sample: the 1 st alkaline substance a is 3.3, the phosphorus-containing material B is 7, the 2 nd alkaline substance C is 2, the polysaccharide D is 0.04, the sulfur-containing material E is 10, the organic material F is 0.5, and the organic acid G is 0.03; the cadmium stabilizer comprises the following components in percentage by weight of a soil sample: the 1 st basic substance a is 3.3, the phosphorus-containing substance B is 7, the 2 nd basic substance C is 2.5, the polysaccharide D is 0.1, the sulfur-containing substance E is 2.5, the organic substance-containing substance F is 0.1, and the organic acid G is 0.02. The stabilizer aims at lead-cadmium composite polluted soil of red loam, has high-efficiency stability, and achieves the highest stabilization rates of 69.51% and 76.09% respectively when lead and cadmium are optimally combined at 24 d.

The invention patent ZL 201710702248.6 discloses a method for efficiently repairing mercury-polluted soil by leaching and a leaching agent. The leaching agent consists of an oxidant, a leaching solution I and a leaching solution II; the oxidant is persulfate solution; the eluent I solute is composed of organic acid, iodine salt and chlorine salt; the solute of the leacheate II consists of sodium sulfide and sodium hydroxide; the method for leaching mercury contaminated soil by using leaching agent comprises the following steps: and (3) oxidizing the mercury-polluted soil, and then sequentially leaching by using a leaching solution I and a leaching solution II. The method can efficiently elute various valence states of mercury in the mercury-polluted soil, and has low mercury residue.

The invention patent ZL 201910284576.8 discloses a method for leaching and repairing cadmium-polluted soil. The invention takes amino acid-hydrochloric acid ionic liquid aqueous solution as an eluting agent, adds the eluting agent into cadmium contaminated soil according to the water-soil ratio of more than 2:1, oscillates, and carries out solid-liquid separation, thus completing the elution. Compared with the existing eluent, the eluent used in the soil leaching method has the advantages that the loss of soil nutrients is less, the quick-acting phosphorus and nitrogen elements in the soil can be increased, the leaching efficiency is high, and the removal rate of cadmium is as high as 84%.

4. Site remediation related patent technology for heavy metal contaminated soil

The invention patent ZL 201210570480.6 discloses a soil conditioning method capable of reducing cadmium accumulation of rice. The method comprises the following steps: before ploughing and fertilizing the soil polluted by the acidic heavy metal cadmium, uniformly spreading a soil conditioner sulfite on the surface of the soil polluted by the acidic heavy metal cadmium, then applying a base fertilizer, and fully and uniformly stirring; and in combination with soil flooding conditioning, the soil is in a flooded state during the growth period of rice, the Eh of the acid heavy metal cadmium-polluted soil is in a reducing environment with low electrochemical potential of-150 mV to-300 mV, and the generated reduction product is utilized to effectively adsorb cadmium in the soil and generate chemical precipitation, thereby completing the conditioning process of the soil.

The invention patent ZL 201210485714.7 discloses a physicochemical remediation method for copper-cadmium composite polluted soil. Carrying out physicochemical remediation on heavy metal contaminated soil by adopting a complexing evaporation absorption enrichment mode, wherein the concrete remediation steps are as follows: firstly, adding a complexing repair reagent into polluted soil, then fully turning and uniformly mixing the soil, adding water, covering a layer of natural cellulose adsorption medium after the soil surface is flat, placing the mixture in an environment system at 35-45 ℃ and naturally evaporating to dryness to finish repairing. By using the method, the removal rates of the total Cu and Cd in the soil can reach over 37 percent and 56.9 percent respectively in a relatively short time (8-12 hours), and the removal rates of the Cu and Cd in the hydrochloric acid extractable state in the soil can reach over 60.7 percent and 69.4 percent respectively.

The invention patent ZL 201410648415.X discloses a method for repairing a severe composite pollution site. The method utilizes the iron-carrying attapulgite and microwave-assisted combined treatment of the organic matter and heavy metal composite heavy polluted site. The iron-loaded attapulgite adsorbs organic matters and stabilized heavy metals through self-carried structural charges, lattice defects and hydroxyl complexing chelation, and under the action of microwaves, the activated attapulgite modified by iron has excellent wave-absorbing performance and is beneficial to soil temperature rise and heavy metal fixation to realize long-acting stability; the iron-loaded modified activated attapulgite is subjected to high-temperature degradation in a microwave field, oxygen in air and water in soil are catalyzed, hydroxyl free radicals are excited to perform oxidative degradation to treat organic matters, and meanwhile, the excellent specific surface area of the iron-modified attapulgite is favorable for adsorbing degradation products.

The invention patent ZL 201510156600.1 discloses a layered remediation method for chromium-contaminated soil. The method is based on an actual chromium-polluted site, selects a combined remediation method aiming at the current situation that the pollution degrees of upper-layer soil and bottom-layer soil are different, adopts a chemical reduction stabilization method to remediate surface-layer severe chromium-polluted soil, adopts a chemical or biochemical reduction stabilization method to remediate deep-layer mild chromium-polluted soil, avoids the defects that the soil properties are not distinguished and the same remediation method is uniformly adopted in the past research, combines ex-situ remediation and in-situ remediation, and enables the remediation method to be more reasonably applied.

The invention patent ZL 201610505080.5 discloses a soil composite pollutant remediation system. Comprises a soil restoration column, an electrolysis chamber, a graphite electrode, a direct current power supply and a nanofiber membrane. The anode and cathode pH control technology can well solve the problems of the focusing effect of heavy metals in soil and poor polycyclic aromatic hydrocarbon migration capacity, the chitosan nanofiber membrane has better adsorption performance on the heavy metals and the polycyclic aromatic hydrocarbons, and the electromotion technology and the chitosan nanofiber membrane PRB are combined to achieve better treatment effect on composite pollutants.

Among the above patent technologies, many are relatively effective in remediation of lightly contaminated soil, but have relatively limited remediation capabilities for moderately and heavily contaminated soil; some patent technologies have obvious effects on repairing moderate and severe polluted soil, but have the problems of complex links or high cost, and are difficult to implement in practical application. At present, a technology for repairing heavy metal contaminated soil, which is simple in research and development measures and low in cost, is urgently needed. Accordingly, the inventor proposes a method for radically treating heavy metal pollution by two steps of operations of intensifying soil acidification and adding a composite passivation material according to earlier research.

In view of this, the invention is particularly proposed.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a novel method for repairing soil polluted by heavy metals of cadmium, lead, mercury and chromium.

The invention is realized by the following steps:

the invention provides a method for restoring heavy metal contaminated soil, which comprises the following steps: firstly, acidizing the soil polluted by the heavy metal by using an acidizing material, then adding an alkaline material and a passivating material to passivate the heavy metal, and realizing the restoration of the soil polluted by the heavy metal in the process of improving the pH value of the restored soil, wherein,

the acidizing material is composed of a sulfur-containing material and a phosphorus-containing material. The sulfur-containing material comprises one or more of sulfur, ammonium bisulfate, sulfamic acid and the like, and the phosphorus-containing material comprises one or more of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, phytic acid and the like. The alkaline material for increasing the pH value of the soil comprises one or more of quicklime, hydrated lime, dolomite, caustic sludge, tricalcium phosphate, biochar and the like, and the passivating material comprises one or more of magnesium silicate, sodium silicate, potassium silicate, iron powder, ferric oxide, ferrous sulfate, ferrous chloride, manganese powder and manganese oxide. The mass percentage of the sulfur-containing material is 50-95%, the mass percentage of the phosphorus-containing material is 1-10%, and the balance is the passivation material; the dosage of the alkaline material for improving the pH value of the soil is determined by the pH value range of the acidified soil.

The heavy metal in the heavy metal contaminated soil comprises one or more of cadmium, lead, mercury and chromium.

The invention has the following beneficial effects:

the invention provides a method for restoring heavy metal contaminated soil, which is to firstly carry out acidification treatment on the heavy metal contaminated soil by using an acidification material, wherein ions of heavy metal contaminated elements such as cadmium, lead, mercury and the like absorbed by soil colloid in the acidification process are caused by H⁺The polluted soil is replaced and released in a large amount, so that the content of water-soluble and exchange-state ions in the polluted soil is obviously increased, meanwhile, hexavalent chromium ions are reduced into nontoxic trivalent chromium ions due to violent redox reaction in the acidification process, and then, an alkaline material and a passivation material for improving the pH value of the soil are added, so that cadmium, lead and mercury cations are rapidly and completely passivated.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

Aiming at the powerful measures of rapidly reducing the pH value of soil at home and abroad and aggravating the lack of precision and strong practicability in the aspect of soil acidification, the inventor forms a sulfur-core soil acidification accelerating technology through a large amount of researches, and heavy metal pollution element ions such as cadmium, lead, mercury and the like adsorbed by soil colloid in the acidification process are caused by H⁺A large amount of displacement and release are carried out, so that the content of water-soluble and exchange-state ions in the polluted soil is obviously increased, meanwhile, hexavalent chromium ions are reduced into nontoxic trivalent chromium ions due to violent redox reaction in the acidification process, and then, an alkaline material and a passivation material for improving the pH value of the soil are added, so that cadmium, lead and mercury cations are rapidly and completely passivated, and the 2-step method operation can realize the pollution to cadmium, lead, mercury and chromiumComplete fixation of elements and complete restoration of polluted soil.

The invention aims to provide a composite material for rapidly reducing the pH value of soil and intensifying soil acidification and passivation.

To achieve the object of the present invention, the following scheme is adopted.

In a first aspect, embodiments of the present invention provide a composite material for enhancing soil acidification and passivation.

The composite materials for intensifying soil acidification and passivating comprise sulfur-containing materials, phosphorus-containing materials and passivating materials, wherein the sulfur-containing materials comprise: one or more of materials such as sulfur, ammonium bisulfate, sulfamic acid and the like; the phosphorus-containing material comprises: one or more of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, phytic acid and other materials; the passivation material includes: one or more of magnesium silicate, sodium silicate, potassium silicate, iron powder, ferric oxide, ferrous sulfate, ferrous chloride, manganese powder, manganese oxide and the like; the mass fraction of the sulfur-containing material accounts for 50-95% by taking the total amount of the combined material as one hundred percent; the amount of the phosphorus-containing material accounts for 1-10 percent; the mass fraction of the passivation material is 4-40%.

In a second aspect, an embodiment of the present invention further provides a method for preparing a composite material for enhancing soil acidification and passivation, wherein the method comprises: the method is realized in two steps, wherein in the first step, a sulfur-containing material, a phosphorus-containing material and a passivation material are respectively crushed or ground to be below 100 meshes; and secondly, weighing the sulfur-containing material, the phosphorus-containing material and the passivation material according to the mass fraction, then fully and uniformly mixing the sulfur-containing material, the phosphorus-containing material and the passivation material in a stirrer, and packaging the mixture into two types of materials to obtain the composite material for intensifying soil acidification and passivation.

In a third aspect, an embodiment of the present invention further provides a method for repairing heavy metal contaminated soil by using the above composite material, including the following steps: the method comprises the steps of firstly, carrying out soil acidification treatment on heavy metal contaminated soil by using an acidification material, and then adding an alkaline improving material and a passivation material to carry out heavy metal passivation treatment, so as to realize remediation of the heavy metal contaminated soil, wherein heavy metals in the heavy metal contaminated soil comprise one or more of cadmium, lead, mercury and chromium.

In an alternative embodiment, the method comprises the following steps: calculating the addition amount of the acidizing material in an expected soil pH range through a soil simulation test, then fully and uniformly mixing the acidizing material and the heavy metal contaminated soil, adding water, standing for 2 months to ensure that the pH value of the soil is basically stable, and measuring the pH value of the soil to obtain acidized soil meeting the pH requirement range; then, according to the pH value of the acidified soil and the design dosage of the alkaline material for improving the pH value of the soil, adding the alkaline material for improving the pH value, uniformly mixing the alkaline material for improving the pH value, the passivation material and the heavy metal contaminated soil again, adding water, standing for 2 weeks, and measuring the pH value of the soil and the content of heavy metal ions to realize the thorough remediation of the heavy metal contaminated soil.

In an optional embodiment, the heavy metal contaminated soil is a site heavy metal contaminated soil, and the remediation method comprises the following steps: calculating the addition amount of the acidizing material in an expected soil pH range through a soil simulation test, then, fully and uniformly mixing the acidizing material and the heavy metal contaminated soil, adding water to a saturated water holding capacity, standing for 2 months, and measuring the pH value of the soil to obtain acidized soil meeting the pH requirement range; then, adding an alkaline material and a passivation material which can improve the pH value, uniformly mixing the alkaline material and the passivation material with the heavy metal contaminated soil again, and adding water to measure the pH value of the soil and the content of heavy metal ions after 2 weeks.

In an optional embodiment, the heavy metal contaminated soil is farmland heavy metal contaminated soil, and the remediation comprises the following steps: calculating the addition amount of the acidizing material in an expected soil pH range through a soil simulation test, uniformly spreading the acidizing material on the surface of the soil, deeply ploughing the soil, keeping the field surface flat, then irrigating in a proper amount, standing for 2 months, and then measuring the pH of the soil to obtain acidized soil meeting the pH requirement range; standing for 2 months to determine the pH value of the soil, then adding an alkaline material and a passivation material for increasing the pH value, further performing deep ploughing, continuous harrowing and irrigation operations, adding water, standing for 2 weeks, and determining the pH value of the soil and the content of heavy metal ions.

In an optional embodiment, the addition amount of the acidification material is used for reducing the pH value of the heavy metal contaminated soil by 1.5-2.5 units as a preset value, so that more adsorbed or fixed heavy metal ions are released;

preferably, when the pH of the heavy metal contaminated soil is 5.0-5.5, the acidifying material is added according to the weight ratio of the sulfur-containing composite material to the soil of 3.0-5.0 per thousand, 1.0-3.0 per thousand, 0.5-1.0 per thousand and 0.1-0.5 per thousand respectively, so that the soil with the original pH of 5.0-5.5 can be further acidified to the pH of less than 3.3, 3.4 of less than 3.8, 3.9 of less than 4.4 and 4.5 of less than 4.9.

In an optional embodiment, the alkaline material for increasing the pH of the soil is calculated according to the pH value of the acidified soil to determine the addition amount;

preferably, the alkaline material for increasing the pH of the soil comprises one or more of quicklime, slaked lime, dolomite, caustic sludge, tricalcium phosphate and biochar;

pH<2.5 hours per hm²The addition amount is 10.0 to 15.0 tons;

pH of 2.5-3.5 per hm²The addition amount is 8.5 to 10.0 tons;

pH of 3.5-4.0 per hm²The addition amount is 7.0 to 8.5 tons;

pH of 4.0-4.5 per hm²The addition amount is 6.0 to 7.5 tons;

pH of 4.5-5.0 per hm²The addition amount is 4.5 to 6.0 tons;

pH of 5.0-5.5 per hm²The addition amount is 3.0 to 4.5 tons.

The clay soil is preferably selected to have a high limit, and the sandy soil is preferably selected to have a low limit. The addition amount can increase the pH value of the corresponding soil to more than 5.5.

In an optional embodiment, the adding amount of the passivation material is determined according to the content of heavy metal elements in the heavy metal contaminated soil;

preferably, when the total effective contents of cadmium and mercury in the heavy metal contaminated soil are respectively more than 2.0mg/kg, 1.5-2.0mg/kg, 1.0-1.5mg/kg and 0.3-1.0mg/kg, the cadmium and mercury are added according to the weight ratio of the passivation material to the heavy metal contaminated soil of 0.5-1.0 thousandth, 0.25-0.5 thousandth, 0.1-0.25 thousandth and 0.05-0.1 thousandth respectively;

preferably, when the total effective content of other heavy metal compound pollution in the heavy metal contaminated soil is respectively 500-1000mg/kg, 250-500mg/kg, 100-250mg/kg and 30-100mg/kg, the passivation material is added according to the weight ratio of the passivation material to the heavy metal contaminated soil being 2.5-5.0 thousandths, 1.25-2.5 thousandths, 0.75-1.25 thousandths and 0.3-0.75 thousandths respectively.

The method for intensifying the soil acidification and the heavy metal pollution of cadmium, lead, mercury, chromium and the like is realized by two steps, wherein the first step is to fully and uniformly mix 2 types of packaged composite materials with the polluted soil according to the design dosage, add water to the saturated water holding capacity, or firstly uniformly spread the 2 types of composite materials on the soil surface, deeply plough the soil, fully and uniformly mix 0-15cm soil by using a rotary cultivator and keep the field surface smooth, then, irrigate in proper amount, and measure the pH value of the soil after 2 months; and secondly, weighing the improved composite material according to the pH value of the acidified soil and the recommended dosage of the composite material for improving the pH value of the soil, uniformly spreading the improved composite material on the field surface, carrying out deep ploughing and harrowing, and planting the target crops after 2 weeks.

The features and properties of the present invention are described in further detail below with reference to examples.

Example 1

The pH value of certain cadmium-mercury composite polluted soil is 5.7, the effective cadmium content and the effective mercury content are respectively 1.40mg/kg and 0.67mg/kg, 10kg of the soil is taken, crushed, sieved by a 5mm sieve, 30g of a sulfur-containing and phosphorus-containing combined material is added, the soil is fully and uniformly mixed, 2.2L of deionized water is added, the soil is placed for 2 months, the pH value of the soil is measured to be 3.0, then 50g of the pH-increasing combined material and 10g of a passivation combined material are added, the soil is uniformly mixed again, 1.5L of deionized water is added, the pH value of the soil is measured to be 5.8 after 2 weeks, the effective cadmium content is 0.17mg/kg, and the effective mercury content is 0.15 mg/kg.

Example 2

Taking 10kg of soil with the pH value of 6.1, the effective cadmium content of 0.87mg/kg and the effective lead content of 220mg/kg, crushing the soil, sieving the soil by a 5mm sieve, adding 35g of a sulfur-containing and phosphorus-containing combined material, fully and uniformly mixing the soil, adding 2.2L of deionized water, standing for 2 months, measuring the pH value of the soil to be 3.2, then adding 60g of a pH-increasing combined material and 12g of a passivation combined material, uniformly mixing the soil again, adding 1.5L of deionized water, measuring the pH value of the soil to be 5.5 after 2 weeks, measuring the effective cadmium content of 0.14mg/kg and the effective lead content of 62 mg/kg.

Example 3

The pH of the soil of a certain cadmium-lead combined polluted farmland is 5.3, and the effective cadmium content is 1.23mg/kg, effective lead content 280mg/kg per hm²Uniformly spreading 6.0t of sulfur-containing and phosphorus-containing composite material, then carrying out deep ploughing and harrowing operation, then carrying out irrigation, standing for 2 months, measuring the pH value of the soil to be 3.7, and then every hm²Adding 7.5t of the pH-increasing composite material and 2.5t of the passivation composite material, carrying out deep ploughing, harrowing and irrigation again, and measuring the pH of the soil to be 6.0, the effective cadmium content to be 0.22mg/kg and the effective lead content to be 55mg/kg after 2 weeks.

Example 4

The pH value of soil in a cadmium-mercury-chromium combined polluted farmland is 6.0, the effective cadmium content is 2.3mg/kg, the effective mercury content is 0.89mg/kg, the total Cr (VI) content is 460mg/kg, the Cr (VI) concentration in a soil leachate is 23.3mg/L, and the concentration is calculated according to the formula of per hm²Uniformly spreading a sulfur-containing and phosphorus-containing composite material for 7.5t, then carrying out deep ploughing and harrowing operation, then carrying out irrigation, standing for 2 months, measuring the pH of the soil to be 3.5, and then, every hm²Adding 9.0t of the pH-increasing combination material and 3.0t of the passivation combination material, carrying out deep ploughing, harrowing and irrigation again, measuring that the pH of the soil is 5.8 after 2 weeks, the effective cadmium content is 0.28mg/kg, the effective mercury content is 0.24mg/kg, the total Cr (VI) content is reduced to 1.5mg/kg, and the Cr (VI) concentration in the soil leachate is reduced to 0.08 mg/L.

Example 5

The soil of the paddy field in one place of Guangdong Meizhou is the soil of the cadmium-mercury combined polluted cultivated land, the pH value is 5.9, the effective cadmium content is 1.05mg/kg, the effective mercury content is 0.74mg/kg, the cadmium content in the planted rice is 0.67mg/kg, and the mercury content is 0.43 mg/kg. For restoring the paddy field, per hm²Uniformly spreading 6.75t of sulfur-containing and phosphorus-containing composite material, deep ploughing for 1 time, continuously harrowing for 3 times, irrigating, standing for 2 months, measuring pH of soil to 3.4, and measuring pH per hm²Adding 7.5t of pH-increasing composite material and 1.8t of passivation composite material, carrying out deep ploughing for 1 time, continuously harrowing for 3 times, and irrigating again, and measuring the pH of the soil to be 5.7, the effective cadmium content to be 0.18mg/kg and the effective mercury content to be 0.14mg/kg after 2 weeks. Then transplanting rice, applying fertilizer and other management are identical to conventional operation, the tillering, growth vigor, spike development and grain filling of rice in whole growth period are identical to those of rice in past growth period, and rice sample is taken in harvest period to make test, and the cadmium content and mercury content in rice are respectively0.17mg/kg and 0.12mg/kg, which shows that the cadmium and mercury pollution of the rice field is thoroughly solved through rapid acidification treatment and improved repair.

Comparative example 1

Similar to the procedure of example 1, except that: if the amount of the acidizing material is reduced to 15g, the pH value of the soil is 4.42 after 2 months, 50g of the pH-increasing combination material and 10g of the passivation combination material are added and mixed with the soil again, 1.5L of deionized water is added, the pH value of the soil is measured to be 6.4 after 2 weeks, the content of effective cadmium is 0.15mg/kg, and the content of effective mercury is 0.12 mg/kg. If 30g of the pH-increasing combination material and 6g of the passivation combination material are added, the mixture is uniformly mixed with the soil again, 1.5L of deionized water is added, and the pH value of the soil is measured to be 5.1 after 2 weeks, the content of effective cadmium is 0.27mg/kg, and the content of effective mercury is 0.22 mg/kg.

Comparative example 2

Similar to the procedure of example 1, except that: if the amount of the acidizing material is increased to 50g, the pH value of the soil is 2.58 after 2 months, 50g of the pH-increasing combination material and 10g of the passivation combination material are added to be uniformly mixed with the soil again, 1.5L of deionized water is added, the pH value of the soil is measured to be 4.2 after 2 weeks, the content of effective cadmium is 0.35mg/kg, and the content of effective mercury is 0.24 mg/kg. If 30g of the combination material for increasing the pH and 6g of the passivation combination material are added, the mixture is uniformly mixed with the soil again, 1.5L of deionized water is added, the pH of the soil is 3.6 after 2 weeks, the content of effective cadmium is 0.49mg/kg, and the content of effective mercury is 0.34 mg/kg.

Comparative example 3

Similar to the procedure of example 1, except that: if the sulfur-containing substances in the acidizing material are changed into 24ml of 1M hydrochloric acid and 6g of phosphorus-containing materials, the pH value of the soil is reduced to 2.5 after 2 months, but the soil is pulverized completely, the structure is damaged, and the damage is not beneficial to the planting of crops later. If the sulfur-containing and phosphorus-containing composite material is inconvenient to use, the material for increasing the pH is changed into 1M sodium hydroxide, the usage amount is 50ml, 8g of the passivation composite material is still used, the passivation composite material is uniformly mixed with the soil again, 1.5L of deionized water is added, the pH of the soil is measured to rise to 7.6 after 2 weeks, the effective cadmium content is 0.47mg/kg, and the effective mercury content is 0.36 mg/kg.

The results of the examples and comparative examples of the present invention were analyzed, and if the acidifying material, the pH raising material, and the passivating material were used in the appropriate ranges, the effect of remedying heavy metal contamination could be achieved according to the recommended amounts. If the use of acidifying materials, pH raising materials and passivating materials is too high or too low, the healing effect will be compromised. If the peracid or the overbase material is used for replacement, the heavy metal repair is not facilitated, and the physical and chemical properties or the structural damage of the soil is formed.

In conclusion, the method aims at the current situations that the pH value of the soil is rapidly reduced at home and abroad, precise and strong powerful measures are lacked in the aspect of aggravating soil acidification, and the heavy metal polluted soil such as moderate and severe cadmium, lead, mercury, chromium and the like is lack of a repair technology with low cost and simple links. The embodiment of the invention provides a combined material and a method for rapidly acidifying heavy metal pollution such as cadmium, lead, mercury, chromium and the like by combining soil, wherein the combined material comprises an acidifying material for reducing the pH value of the soil and a passivating material for passivating the heavy metal, the sulfur-containing material comprises one or more of materials such as sulfur, ammonium bisulfate, sulfamic acid and the like, and the phosphorus-containing material comprises one or more of materials such as ammonium dihydrogen phosphate, sodium dihydrogen phosphate, phytic acid and the like; the passivation material comprises one or more of magnesium silicate, sodium silicate, potassium silicate, iron powder, ferric oxide, ferrous sulfate, ferrous chloride, manganese powder, manganese oxide and the like; the composite material of the sulfur-containing material accounts for 50-95% by mass, the composite material of the phosphorus-containing material accounts for 1-10% by mass, and the composite material of the passivating material accounts for 4-40% by mass.

The soil polluted by heavy metals such as cadmium, lead, mercury, chromium and the like is repaired by using the composite material in two steps, the first step is to add the composite material such as a sulfur-containing material, a phosphorus-containing material and the like, the release of heavy metal cations such as cadmium, lead, mercury and the like is enhanced through the soil acidification process, hexavalent chromium is reduced into harmless trivalent chromium through the oxidation-reduction reaction in the soil acidification process, and the second step is to add the composite material and the passivation material for improving the soil pH, so that the heavy metals such as cadmium, lead, mercury, chromium and the like are passivated and fixed in the process of improving the soil pH. The method has the outstanding advantages of rapid acidification, accurate acidification, thorough restoration, high safety, simple restoration link and the like. The combined material and the method can realize the complete restoration of the single element pollution or the compound pollution of heavy metals such as cadmium, lead, mercury, chromium and the like.

The combined material and the method provided by the embodiment of the invention have five advantages in the aspects of intensifying acidification and repairing heavy metal pollution such as cadmium, lead, mercury, chromium and the like:

first, acidification is rapid. The composition of the invention can be rapidly oxidized to generate a large amount of H⁺Or released directly to release H⁺And a strong acid environment is formed, so that soil acidification is intensified.

Secondly, acidification is accurate. The physical quantity of the sulfur-containing and phosphorus-containing composite material which should be added in the expected soil pH range can be calculated through a soil simulation test, and the physical quantity is applied to farmlands, so that a reasonable soil pH range can be formed.

Thirdly, the repair is thorough. The invention firstly uses the sulfur-containing and phosphorus-containing composite material, accelerates the release of effective cadmium, lead and mercury ions in soil acidification, quickly converts hexavalent chromium ions into trivalent chromium ions through oxidation-reduction reaction, and then adds an alkaline material for raising the pH value of the soil and a passivation material to quickly fix heavy metal elements such as cadmium, lead, mercury, chromium and the like and thoroughly repair the polluted soil.

Fourthly, the safety is high. Compared with strong acid solution and strong alkali solution such as concentrated sulfuric acid and nitric acid used in the past research, the composition provided by the invention basically has no strong corrosivity or toxicity, and does not form a safety threat to users in farmland use.

And fifthly, the repair link is simple. The invention adopts a two-step method of firstly acidifying and then improving to passivate and repair the heavy metal pollution such as cadmium, lead, mercury, chromium and the like, the process is deep ploughing and harrowing, the process is simple, the cost is low, and the method can be quickly applied to the heavy metal pollution repair practice.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A new method for repairing soil polluted by heavy metals of cadmium, lead, mercury and chromium is characterized by comprising the following steps: firstly, acidizing the soil polluted by heavy metal by using an acidizing material, and then adding an alkaline material and a passivating material to carry out heavy metal passivation treatment to realize the remediation of the soil polluted by the heavy metal, wherein,

the acidizing material is composed of a sulfur-containing material and a phosphorus-containing material, the alkaline material comprises one or more of quick lime, hydrated lime, dolomite, caustic sludge, tricalcium phosphate and biochar, and the passivating material comprises one or more of magnesium silicate, sodium silicate, potassium silicate, iron powder, ferric oxide, ferrous sulfate, ferrous chloride, manganese powder and manganese oxide; the mass percentage of the sulfur-containing material is 50-95%, the mass percentage of the phosphorus-containing material is 1-10%, and the balance is the passivation material;

the heavy metal in the heavy metal contaminated soil comprises one or more of cadmium, lead, mercury and chromium.

2. The new method according to claim 1, characterized in that it comprises the following steps: calculating the addition amount of the acidizing material in an expected soil pH range through a soil simulation test, then fully and uniformly mixing the acidizing material and the heavy metal contaminated soil, adding water, standing for 2 months, and measuring the pH value of the soil to obtain acidized soil meeting the pH requirement range; and then, according to the pH value of the acidified soil and the design dosage of the alkaline material for improving the pH value of the soil, adding the alkaline material for improving the pH value, uniformly mixing the alkaline material for improving the pH value, the passivation material and the heavy metal contaminated soil again, adding water, standing for 2 weeks, and measuring the pH value of the soil and the content of heavy metal ions to realize the thorough remediation of the heavy metal contaminated soil.

3. The new process of claim 1 or 2, wherein the sulphur-containing material comprises one or more of sulphur, ammonium bisulphate and sulphamic acid material; the phosphorus-containing material comprises one or more of ammonium dihydrogen phosphate, sodium dihydrogen phosphate and phytic acid.

4. The new method of claim 3, wherein the sulfur-containing material, phosphorus-containing material, and passivation material have a particle size of 100 mesh or less.

5. The method according to claim 1 or 2, wherein the heavy metal contaminated soil is a site heavy metal contaminated soil, the acidification material and the heavy metal contaminated soil are fully mixed during acidification, water is added to reach a saturated water holding capacity, standing is carried out for 2 months, and then the pH of the soil is measured.

6. The method according to claim 1 or 2, wherein the soil contaminated by heavy metal is soil contaminated by heavy metal in farmland, and during acidification, the acidification material is uniformly spread on the soil surface, the soil is ploughed deeply and the land surface is kept flat, then the soil is irrigated in proper amount, and after standing for 2 months, the pH of the soil is measured.

7. The new method according to claim 1 or 2, characterized in that the addition of said acidifying material lowers the pH of the soil contaminated with heavy metals by a value predetermined to be 1.5-2.5 units, so as to obtain a greater release of the heavy metal ions in adsorbed or immobilized form:

when the pH of the heavy metal contaminated soil is 5.0-5.5, the acidifying material is added according to the weight ratio of the sulfur-containing and phosphorus-containing composite material to the soil of 3.0-5.0 per mill, 1.0-3.0 per mill, 0.5-1.0 per mill and 0.1-0.5 per mill, so that the soil with the original pH of 5.0-5.5 can be further acidified to a pH value of less than 3.3, a pH value of less than 3.4 and a pH value of less than 3.8, a pH value of less than 3.9 and a pH value of less than 4.5 and a pH value of less than 4.9.

8. The new method according to claim 1 or 2, characterized in that the alkaline material for raising the pH of the soil is added in an amount calculated from the pH of the soil after acidification:

when the pH of the heavy metal contaminated soil is lower<2.5 hours per hm²The addition amount is 10.0 to 15.0 tons; pH of 2.5-3.5 per hm²The addition amount is 8.5 to 10.0 tons; pH of 3.5-4.0 per hm²Adding amount of7.0 to 8.5 tons; pH of 4.0-4.5 per hm²The addition amount is 6.0 to 7.5 tons; pH of 4.5-5.0 per hm²The addition amount is 4.5 to 6.0 tons; pH of 5.0-5.5 per hm^-2The addition amount is 3.0-4.5 tons, and the addition amount can increase the corresponding soil pH to more than 5.5.

9. The new method according to claim 1 or 2, characterized in that the amount of the passivating material added is determined according to the content of heavy metal elements in the heavy metal contaminated soil:

when the total effective contents of cadmium and mercury in the heavy metal contaminated soil are respectively more than 2.0mg/kg, 1.5-2.0mg/kg, 1.0-1.5mg/kg and 0.3-1.0mg/kg, the passivating material is added according to the weight ratio of 0.5-1.0 thousandths, 0.25-0.5 thousandths, 0.1-0.25 thousandths and 0.05-0.1 thousandths of the heavy metal contaminated soil;

when the total effective content of other heavy metal compound pollution in the heavy metal polluted soil is respectively 500-1000mg/kg, 250-500mg/kg, 100-250mg/kg and 30-100mg/kg, the passivation material is added according to the weight ratio of the passivation material to the heavy metal polluted soil being 2.5-5.0 thousandths, 1.25-2.5 thousandths, 0.75-1.25 thousandths and 0.3-0.75 thousandths respectively.

10. The new method according to claim 1 or 2, further comprising: and directly planting the target crops on the restored soil.