CN113274687A - Co-treatment method of chromium slag and acidic arsenic-containing wastewater - Google Patents

Co-treatment method of chromium slag and acidic arsenic-containing wastewater Download PDF

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CN113274687A
CN113274687A CN202110484560.9A CN202110484560A CN113274687A CN 113274687 A CN113274687 A CN 113274687A CN 202110484560 A CN202110484560 A CN 202110484560A CN 113274687 A CN113274687 A CN 113274687A
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arsenic
chromium slag
containing wastewater
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acidic
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CN113274687B (en
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王鑫
王琳玲
李鸿博
陈静
李瑜玥
戴子文
张虹丽
张玉超
吴小龙
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Huazhong University of Science and Technology
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    • A—HUMAN NECESSITIES
    • A62—LIFE-SAVING; FIRE-FIGHTING
    • A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
    • A62D3/00—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances
    • A62D3/30—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents
    • A62D3/37—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents by reduction, e.g. hydrogenation
    • A—HUMAN NECESSITIES
    • A62—LIFE-SAVING; FIRE-FIGHTING
    • A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
    • A62D3/00—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances
    • A62D3/30—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents
    • A—HUMAN NECESSITIES
    • A62—LIFE-SAVING; FIRE-FIGHTING
    • A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
    • A62D3/00—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances
    • A62D3/30—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents
    • A62D3/36—Detoxification by using acid or alkaline reagents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/28—Treatment of water, waste water, or sewage by sorption
    • C02F1/281—Treatment of water, waste water, or sewage by sorption using inorganic sorbents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/72—Treatment of water, waste water, or sewage by oxidation
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/103—Arsenic compounds

Abstract

The invention belongs to the technical field of harmless treatment of chromium slag and arsenic-containing wastewater, and particularly relates to a co-treatment method of chromium slag and acidic arsenic-containing wastewater. The method for co-processing the chromium slag and the acidic arsenic-containing wastewater provided by the invention fully utilizes the inherent characteristics and complementarity of the chromium slag and the acidic arsenic-containing wastewater, synchronously realizes the neutralization of alkali in the chromium slag and the reduction/stabilization of hexavalent chromium and the neutralization of acid in the acidic arsenic-containing wastewater and the removal of arsenic, and reduces the processing cost of the chromium slag and the acidic arsenic-containing wastewater by the idea of treating waste by waste. A large amount of strong acid substances exist in the acidic arsenic-containing wastewater used by the method, so that the mineral occurrence state Cr (VI) in the chromium slag can be effectively converted into water-soluble state Cr (VI), and the mass transfer limit in the reduction and stabilization process of Cr (VI) is reduced; meanwhile, a large amount of mineral components with arsenic adsorption capacity exist in the used chromium slag, so that arsenic in the wastewater can be effectively fixed, and the use and treatment cost of the medicament is greatly reduced.

Description

Co-treatment method of chromium slag and acidic arsenic-containing wastewater
Technical Field
The invention belongs to the technical field of harmless treatment of chromium slag and arsenic-containing wastewater, and particularly relates to a co-treatment method of chromium slag and acidic arsenic-containing wastewater.
Background
The chromium slag is high-alkalinity industrial waste slag containing hexavalent chromium (Cr (VI)) generated in the process of producing chromium salt by adopting chromite as a raw material. Because hexavalent chromium has strong toxicity and oxidative corrosivity and is an internationally recognized carcinogen, chromium slag is listed in the national records of hazardous wastes. The chromium slag discharged by the chromium salt industry of China is about millions of tons every year, and the reasonable and safe disposal of the chromium slag is directly related to the healthy development of the chromium salt industry and the construction quality of beautiful China. Wet detoxification is an effective harmless treatment method for chromium slag, and chromium slag detoxification is realized by applying a chemical reducing agent to reduce Cr (VI) with high toxicity and high mobility into Cr (III) with low toxicity and low mobility. The Cr (VI) form in the chromium slag can be divided into a water-soluble state and a mineral occurrence state, wherein the mineral occurrence state Cr (VI) is difficult to contact and react with a reducing agent due to mass transfer limitation, so that the detoxification effect is influenced. At present, the mineral occurrence state Cr (VI) is dissolved and released by adopting an acid adding mode so as to ensure the sufficient reduction of the Cr (VI) and the complete detoxification of the chromium slag. Patent documents CN111437561A, CN110812773A, CN110404226A, CN103934256B, CN102614620B, CN101816829B, etc. all adopt an auxiliary treatment mode of adding a large amount of strong acid, and the concentrated sulfuric acid dosage disclosed in CN110812773A is even as high as 700kg/t of chromium slag, so the high acid consumption makes the running cost of the wet detoxification technology of chromium slag high.
The acidic arsenic-containing wastewater is industrial wastewater containing a large amount of arsenic generated in pyrite and polymetallic sulphide mineral smelting and flue gas acid making, and has extremely high danger and corrosivity. The currently common arsenic-containing wastewater treatment methods mainly comprise a sulfuration method, a lime neutralization and precipitation method and a lime ferric salt method. Patent document CN102992505B discloses a method for treating high-arsenic contaminated acid wastewater, wherein arsenic sulfide residues are generated by adding sodium sulfide solution under strong acid condition to remove about 90% of arsenic in wastewater, but the wastewater after the sulfuration treatment needs to be further neutralized in acidity and deeply removed with lime method and iron salt method, and the arsenic sulfide residues have high environmental risk. Patent document CN105417767B discloses a method for removing arsenic from sulfuric acid waste acid wastewater, which adopts calcium carbonate and lime milk to neutralize the acidity of wastewater, simultaneously removes more than 98% of arsenic by calcium-arsenic precipitation reaction, and finally realizes the deep removal of arsenic by ferric salt flocculation precipitation method. Therefore, the acid neutralization with alkaline materials is an essential link for the treatment of acidic arsenic-containing wastewater, and the consumption of alkali is extremely high, for example, the lime dosage in the gypsum precipitation-arsenic oxidation-neutralization iron salt coprecipitation acid-leaching method disclosed in patent document CN101830583B is as high as 182kg/m3. The high agent consumption and the complicated arsenic removal process result in high cost for treating the acidic arsenic-containing wastewater.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a method for detoxifying chromium slag and discharging arsenic-containing wastewater to reach the standard, which is simple in treatment method and low in cost, and aims to solve the technical problems that a large amount of acid is required to be consumed when chromium slag is treated alone, a large amount of alkaline agent is required to be consumed when arsenic-containing wastewater is treated alone, and the like in the prior art.
In order to realize the aim, the invention provides a co-treatment method of chromium slag and acidic arsenic-containing wastewater, which comprises the following steps:
(1) mixing the chromium slag and the acidic arsenic-containing wastewater, and fully stirring to obtain a first suspension; wherein the chromium slag reacts with the acidic arsenic-containing wastewater to release solid phase Cr (VI) in the chromium slag into a solution phase to form water soluble Cr (VI); part of As (III) in the arsenic-containing wastewater and part of water-soluble Cr (VI) released by the chromium slag are subjected to redox reaction, the As (III) is oxidized into As (V), and meanwhile, the Cr (VI) is reduced into Cr (III) and is precipitated in a precipitation form; meanwhile, arsenic in the acidic arsenic-containing wastewater is adsorbed and fixed by the lamellar minerals in the chromium slag;
(2) mixing the first suspension with a low-valence iron reducing agent, and fully stirring for reaction to obtain a second suspension; wherein the low-valence iron reducing agent and water-soluble Cr (VI) released by the chromium slag are subjected to redox reaction, and the Cr (VI) is reduced into Cr (III) and precipitated;
(3) adjusting the pH value of the second suspension to 6-9 by adopting alkali, and exposing to oxygen to react to obtain a third suspension; wherein the inherent minerals in the chromium slag and Cr (VI) generated by reduction and precipitation of Cr (VI)III(OH)3And FeIII 0.75CrIII 0.25(OH)3Arsenic is fixed through adsorption, so that the arsenic is transferred from a solution phase to a solid phase, and the concentration of the arsenic in the wastewater reaches the discharge standard;
(4) and carrying out solid-liquid separation on the third suspension to obtain the detoxified chromium slag and the discharged water with the water quality reaching the standard.
Preferably, the pH value of the chromium slag is more than 10, and the content of hexavalent chromium is 100-20000 mg/kg; the pH value of the arsenic-containing wastewater is less than 2, the total arsenic concentration is 10-10000 mg/L, and the content of As (III) in the total arsenic is not less than 20%.
Further preferably, the pH value of the chromium slag is more than 10, and the content of hexavalent chromium is 10000-15000 mg/kg; the pH value of the arsenic-containing wastewater is less than 2, the total arsenic concentration is 1000-5000 mg/L, and the content of As (III) in the total arsenic is not less than 50%.
Preferably, H in the arsenic-containing wastewater+The concentration of (b) is more than 0.1 mol/L.
Preferably, in the step (1), the chromium slag and the acidic arsenic-containing wastewater are mixed, the solid-to-liquid ratio is controlled to be 0.01-5: 10, and the pH value is controlled to be 4-8 by regulating the solid-to-liquid ratio.
Further preferably, in the step (1), the chromium slag and the acidic arsenic-containing wastewater are mixed, the solid-to-liquid ratio is controlled to be 0.1-2: 10, the pH value is controlled to be 5-7 by regulating the solid-to-liquid ratio, and the stirring time is 12-24 hours.
Preferably, the granularity of the chromium slag in the step (1) is less than 200 meshes.
Preferably, the low-valent iron reducing agent in step (2) is one or more of ferrous sulfate heptahydrate, ferrous sulfate tetrahydrate, ferrous sulfate monohydrate, ferrous sulfate pentahydrate, ferrous sulfate hexahydrate, ferrous chloride tetrahydrate, ferrous chloride dihydrate, anhydrous ferrous chloride, zero-valent iron and iron powder.
Preferably, the addition amount of the low-valence iron reducing agent in the step (2) is 1-100 kg/m3(ii) a The reaction time is 12-24 hours.
Preferably, the alkali in step (3) is one or more of quicklime, slaked lime, milk of lime, sodium hydroxide, calcium hydroxide and calcium oxide.
Preferably, the alkali in the step (3) is lime milk, and the content of calcium hydroxide in the lime milk is 5-8%; the addition amount of the lime milk is 0.1-5 kg/m3。
Preferably, in the step (3), the pH of the second suspension is adjusted to 7-9 by using alkali; the reaction time is 12-24 hours.
Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:
(1) the method for co-processing the chromium slag and the acidic arsenic-containing wastewater provided by the invention fully utilizes the inherent characteristics and complementarity of the chromium slag and the acidic arsenic-containing wastewater, synchronously realizes the neutralization of alkali in the chromium slag and the reduction/stabilization of hexavalent chromium and the neutralization of acid in the acidic arsenic-containing wastewater and the removal of arsenic, and reduces the processing cost of the chromium slag and the acidic arsenic-containing wastewater by the idea of treating waste by waste. The acidic arsenic-containing wastewater used by the invention contains a large amount of strong acid substances, can effectively dissolve and convert mineral occurrence state Cr (VI) in the chromium slag into water-soluble state Cr (VI), greatly reduces mass transfer limitation in the reduction and stabilization process of Cr (VI), removes an additional acid step in the traditional wet detoxification method of chromium slag, and effectively reduces the use and treatment cost of medicaments.
(2) The acid arsenic-containing wastewater used by the invention contains abundant oxyanions (including sulfate radicals, arsenate radicals and the like), and chromate ions in an existing mineral structure of Cr (VI) can be efficiently replaced through ion exchange, so that the existing state Cr (VI) in the chromium slag is promoted to be fully released to a solution phase, the mass transfer limit between Cr (VI) and a reducing agent is reduced, and the purpose of fully reducing Cr (VI) is finally achieved.
(3) The acid arsenic-containing wastewater used by the invention contains a large amount of reducing substances (such as As (III)), and Cr (VI) can be directly reduced into Cr (III) to promote the detoxification of the chromium slag, thereby greatly reducing the consumption of an external reducing agent and saving the medicament cost.
(4) The chromium slag used in the method has strong basicity, and can effectively neutralize acid in the acidic arsenic-containing wastewater, thereby avoiding the step of adding alkali in the traditional acidic arsenic-containing wastewater treatment technology and effectively reducing the use and treatment cost of medicaments.
(5) The chromium slag used in the invention contains a large amount of Cr (VI) with strong oxidizing property, and can oxidize low-valent arsenic (As (III)) in the acid arsenic-containing wastewater into high-valent arsenic (As (V)), thereby reducing the treatment difficulty of the arsenic-containing wastewater. Since As (III) is at pH<9 is mainly in molecular form (H)3AsO3) The existing method is not beneficial to the occurrence of reactions such as precipitation/adsorption; as (V) is mainly in the form of anion in a wide range of pH 2-14, and is more easily adsorbed or precipitated.
(6) The chromium slag used in the method contains a large amount of active mineral components (including iron/aluminum metal oxide, layered double hydroxides and the like), can effectively reduce the concentration of arsenic in the acidic arsenic-containing wastewater by directly adsorbing free arsenic, avoids the step of adding an arsenic removal agent in the traditional arsenic-containing wastewater treatment method, and effectively reduces the treatment cost.
(7) The invention makesThe chromium slag used forms a large amount of chromium hydroxide (Cr) after reduction detoxificationIII(OH)3) And ferrochrome hydroxide (Fe)III 0.75CrIII 0.25(OH)3) The arsenic adsorbent can be used as an effective arsenic adsorbent to enhance the removal effect of arsenic in arsenic-containing wastewater, and finally the purpose of standard-reaching discharge of the wastewater is achieved.
Drawings
FIG. 1 is a schematic flow chart of the co-treatment method of chromium slag and acidic arsenic-containing wastewater according to the present invention;
FIG. 2 is an XRD pattern of chromium slag No. I treated in the examples of the present invention;
FIG. 3 shows the reaction product Fe (II) of Fe (II) and Cr (VI) in example 7 of the present inventionIII 0.75CrIII 0.25(OH)3Adsorption condition of arsenic.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The co-treatment method of the chromium slag and the acidic arsenic-containing wastewater provided by the invention comprises the following steps as shown in figure 1:
(1) mixing the chromium slag and the acidic arsenic-containing wastewater, and fully stirring to obtain a first suspension; wherein the chromium slag reacts with the acidic arsenic-containing wastewater to release solid phase Cr (VI) in the chromium slag into a solution phase to form water soluble Cr (VI); part of As (III) in the arsenic-containing wastewater and part of water-soluble Cr (VI) released by the chromium slag undergo redox reaction, the As (III) is oxidized into As (V), and the Cr (VI) is reduced into Cr (III) and precipitated, for example, the Cr (III) can be precipitatedIII(OH)3Form precipitation; meanwhile, arsenic in the acid arsenic-containing wastewater is adsorbed and fixed in the layered minerals;
(2) mixing the first suspension with a low-valence iron reducing agent, and fully stirring for reaction to obtain a second suspension; the low-valence iron reducing agent and water-soluble Cr (VI) released by the chromium slag undergo oxidation-reduction reaction, and the Cr (VI) is reduced intoCr (III) and precipitated in the form of precipitates, e.g. FeIII 0.75CrIII 0.25(OH)3Form precipitation;
(3) adjusting the pH value of the second suspension to 6-9 by adopting alkali, and carrying out oxygen exposure reaction to obtain a third suspension; inherent minerals in the chromium slag and Cr generated by reduction and precipitation of Cr (VI)III(OH)3And FeIII 0.75CrIII 0.25(OH)3Arsenic is fixed through adsorption, so that the arsenic is transferred from a solution phase to a solid phase, and the concentration of the arsenic in the wastewater reaches the discharge standard;
(4) and carrying out solid-liquid separation on the third suspension to obtain the detoxified chromium slag and the discharged water with the water quality reaching the standard.
Specifically, the technical principle of the present invention is as follows:
reacting acid in the acidic arsenic-containing wastewater with alkaline minerals in the chromium slag, adjusting the pH of the system to be a weak acid to neutral condition (pH 5-8), and simultaneously dissolving a large amount of alkaline minerals to release Cr (VI) which is generated by the alkaline minerals from a solid phase to a solution phase (formula 1); oxyanions in wastewater (e.g. HAsO)4 2–、SO4 2–) Interlaminar CrO of lamellar mineral in chromium slag4 2-Ion exchange reaction, CrO4 2-Is displaced into the solution to be water-soluble Cr (VI), and part of arsenic is fixed in the layered minerals to be removed from the wastewater (formulas 2 and 3); as (III) in the arsenic-containing wastewater and water-soluble Cr (VI) released by the chromium slag undergo redox reaction, the As (III) is oxidized into As (V), and the Cr (VI) is reduced into Cr (III) and CrIII(OH)3Precipitating (formula 4); the added low-valence iron reducing agent and the water-soluble Cr (VI) released by the chromium slag undergo redox reaction, the Cr (VI) is reduced into Cr (III) and FeIII 0.75CrIII 0.25(OH)3Form precipitation (formula 5), and finally realize chromium slag detoxification; inherent minerals (including iron-aluminum metal oxide, layered double hydroxide and the like) in the chromium slag and Cr (VI) generated by reduction and precipitation of CrIII(OH)3And FeIII 0.75CrIII 0.25(OH)3All can pass through the adsorptionThe arsenic in the wastewater is removed under the action of the formula 6, 7 and 8, so that the concentration of the arsenic in the wastewater reaches the discharge standard.
Acid dissolution:
[COPR≡CrO4 2-](s)+H+→[COPR*](s)+CrO4 2– (1)
ion exchange:
[COPR≡CrO4 2-](s)+HAsO4 2–→[COPR≡HAsO4 2-](s)+CrO4 2– (2)
[COPR≡CrO4 2-](s)+SO4 2–→[COPR≡SO4 2-](s)+CrO4 2– (3)
oxidation and reduction:
3H3AsIIIO3+2CrO4 2-+2OH-→3HAsVO4 2-+2[CrIII(OH)3](s)+H2O (4)
3Fe2++CrO4 2-+4OH-+4H2O-→4[FeIII 0.75CrIII 0.25(OH)3](s) (5)
arsenic adsorption:
[COPR](s)+As→[COPR≡As](s) (6)
[CrIII(OH)3](s)+As→[CrIII(OH)3≡As](s) (7)
[FeIII 0.75CrIII 0.25(OH)3](s)+As→[FeIII 0.75CrIII 0.25(OH)3≡As](s) (8)
in the formulas (1) to (8), COPR represents an inherent mineral in the chromium slag; COPR represents chromium slag after acid dissolutionThe remaining intrinsic minerals in (1); COPR ≡ CrO4 2-Indicating the occurrence state of the minerals CrO in the chromium slag4 2-；COPR≡HAsO4 2-Showing HAsO adsorbed and fixed in the inherent mineral of chromium slag in arsenic-containing wastewater4 2-；COPR≡SO4 2-Indicating SO fixed in the mineral inherent in the chromium slag4 2-(ii) a COPR ≡ As represents As (including As (V) and As (III)) in arsenic-containing wastewater adsorbed and fixed in inherent minerals of chromium slag; cr (chromium) componentIII(OH)3As represents Cr As a precipitateIII(OH)3Adsorbing As in the arsenic-containing wastewater; feIII 0.75CrIII 0.25(OH)3As represents Fe to be precipitatedIII 0.75CrIII 0.25(OH)3Adsorbing As in the arsenic-containing wastewater.
In some embodiments of the invention, the pH of the chromium slag is more than 10, the content of hexavalent chromium is 100-20000 mg/kg, the pH of the arsenic-containing wastewater is less than 1, and the concentration of arsenic is 10-10000 mg/L.
In some embodiments, the chromium slag and the acidic arsenic-containing wastewater are mixed in the step (1), the solid-to-liquid ratio is controlled to be 0.01-5: 10, and the pH value is controlled to be 4-8. In the preferred embodiment, the chromium slag and the acidic arsenic-containing wastewater are mixed in the step (1), the solid-to-liquid ratio is controlled to be 0.1-2: 10, the pH value is controlled to be 5-7, and the stirring time is 12-24 hours. In the step, the solid-liquid ratio and the pH value are controlled, so that the acid in the acidic arsenic-containing wastewater and the alkaline minerals in the chromium slag generate physical and chemical changes including dissolution, acid-base neutralization reaction, ion exchange, oxidation-reduction reaction, adsorption and the like, the reaction is sufficient due to the proper pH value, and a foundation is laid for chromium slag detoxification and wastewater arsenic removal.
In order to promote the full reaction of the chromium slag and the arsenic-containing wastewater, in some embodiments, the chromium slag is crushed and ground to have a particle size of less than 200 meshes so as to reduce mass transfer limitation and promote the full release of hexavalent chromium in the solid phase of the chromium slag into the liquid phase.
In some embodiments, the low-valent iron reducing agent in step (2) is ferrous sulfate heptahydrate, ferrous sulfate tetrahydrate, ferrous sulfate monohydrate, ferrous sulfate pentahydrate, ferrous sulfate hexahydrate, ferrous chloride tetrahydrate, or ferrous chloride dihydrateOne or more of ferrous chloride hydrate, anhydrous ferrous chloride, zero-valent iron and iron powder. The added low-valence iron reducing agent and the water-soluble Cr (VI) released by the chromium slag undergo redox reaction, the Cr (VI) is reduced into Cr (III) and FeIII 0.75CrIII 0.25(OH)3The form is precipitated (formula 5), and finally the chromium slag detoxification is realized. In some embodiments, the amount of the low-valence iron reducing agent added in the step (2) is 1-100 kg/m3(ii) a The reaction time is between 12 and 24 hours.
In some embodiments, the alkali of step (3) is one or more of quicklime, slaked lime, milk of lime, sodium hydroxide, calcium oxide.
In a preferred embodiment, the alkali is lime milk, and the content of calcium hydroxide in the lime milk is 5-8%; the addition amount of the lime milk is 0.1-5 kg/m3(ii) a The pH is 7-9; the reaction time is between 12 and 24 hours.
The purpose of oxygen exposure in the step (3) is to accelerate iron removal and enhance arsenic removal.
The following are examples:
example 1
The chromium slag I (from Changsha of Hunan province, a chromium salt plant) and the arsenic-containing wastewater I (from great smelting of North lake, a sulfuric acid plant) are co-treated, and the components of the treated objects are shown in tables 1 and 2. The XRD pattern of the chromium slag is shown in figure 2, and the chromium slag contains unreacted raw ore (chromite), minerals (brownmillerite, periclase and wollastonite) formed in the high-temperature roasting process and minerals (brucite, calcite, hydrocalumite, hydrotalcite and ettringite) formed by environmental weathering in the stacking process, wherein metal oxides such as chromite and the like and layered minerals such as hydrocalumite, hydrotalcite, ettringite and the like have potential arsenic adsorption capacity.
Weighing 10g of chromium slag sample, adding 150mL of wastewater sample according to the solid-to-liquid ratio of 0.67:10, stirring for 24 hours to obtain a first suspension, wherein the pH value of the supernatant is 6.4; then 25kg/m3Adding ferrous sulfate heptahydrate, and stirring to react for 24 hours to obtain a second suspension; then according to 3kg/m3Adding lime milk, and reacting for 24 hr under oxygen to obtain a third suspensionThe supernatant had a pH of 8.3. And filtering the third suspension liquid to separate a solid phase and a liquid phase to obtain the treated chromium slag and the treated wastewater. The leaching toxicity test result of the treated chromium slag shows that the leaching concentration of Cr (VI) is less than 0.1mg/L, which meets the requirements of technical specifications for environmental protection and protection for chromium slag pollution control (HJ/T301-2007); the analysis result of the components of the treated wastewater shows that the pH value is 8.3, the As concentration is 0.2mg/L, Cr (VI) concentration is less than 0.1mg/L, and the requirements of Integrated wastewater discharge Standard (GB L, Cr-1996) are met.
TABLE 1 ingredient list of No. I chromium slag
pH Cr(VI)(wt.％) Cr(tot)(wt.％) Ca(wt.％) Mg(wt.％) Fe(wt.％)
12.1 1.2 2.4 16.9 11.0 4.3
Al(wt.％) Si(wt.％) Ba(wt.％) Mn(wt.％) Ni(wt.％) S(wt.％)
2.3 7.6 0.1 0.08 0.06 0.06
TABLE 2 ingredient table of arsenic-containing wastewater
Figure BDA0003049793890000081
Figure BDA0003049793890000091
Example 2
In order to compare the difference of the dosage and the cost of the medicament in the co-treatment and the single treatment, the No. I chromium slag and the No. I arsenic-containing wastewater are respectively and independently treated. The dosage of sulfuric acid required for independently treating the chromium slag I is 750g/kg, the dosage of ferrous sulfate heptahydrate is 380g/kg, and the leaching concentration of Cr (VI) in the treated chromium slag is less than 0.1mg/L, so that the requirements of technical specifications of chromium slag pollution treatment and environmental protection (HJ/T301-2007) are met. The arsenic-containing wastewater I is separately treated, and the required lime consumption is 60kg/m3The required ferrous sulfate heptahydrate is 36kg/m3The pH value of the treated wastewater is 8.5, and the concentration of As is 0.3mg/L, which meets the requirements of Integrated wastewater discharge Standard (GB 8978 & 1996). As described in example 1, the co-treatment of the No. I chromium slag and the No. I arsenic-containing wastewater requires only 25kg/m of ferrous sulfate heptahydrate3Only 3kg/m lime milk is needed3Greatly reduces the dosage of sulfuric acid, lime and ferrous salt required by single treatment. The cost of the medicament required for separately treating 1 ton of chromium slag is calculated according to the market price of 400 yuan/ton sulfuric acid, 200 yuan/ton ferrous sulfate heptahydrate and 300 yuan/ton limeAbout 380 yuan, 1m of the powder is treated alone3The cost of the agent required by the arsenic-containing wastewater is about 25 yuan, and 1 ton of chromium slag and 1m are co-processed3The cost of the medicament required by the arsenic-containing wastewater is about 80 yuan, and is only 1/5 which is treated separately.
Example 3
The samples of No. II chromium slag (from a chromium salt plant in south of Ji, Shandong) and No. II arsenic-containing wastewater (from a sulfuric acid plant in North Da, lake) were co-processed, and the compositions of the processed objects are shown in tables 3 and 4. Weighing 10g of chromium slag sample, adding 1200mL of wastewater sample according to a solid-to-liquid ratio of 0.083:10, stirring for 24 hours to obtain first suspension, wherein the pH value of the supernatant is 6.8; then 3.1kg/m3Adding ferrous chloride tetrahydrate, and stirring to react for 24 hours to obtain a second suspension; then according to 0.6kg/m3Adding lime milk, and performing oxygen exposure reaction for 12 hours to obtain a third suspension, wherein the pH of the supernatant is 7.5. And filtering the third suspension liquid to separate a solid phase and a liquid phase to obtain the treated chromium slag and the treated wastewater. The leaching toxicity test result of the treated chromium slag shows that the leaching concentration of Cr (VI) is 0.1mg/L, which meets the requirements of technical Specification for environmental protection and pollution control of chromium slag (HJ/T301-2007); the analysis result of the components of the treated wastewater shows that the pH value is 7.5, the As concentration is 0.3mg/L, Cr (VI) concentration is less than 0.1mg/L, and the requirements of Integrated wastewater discharge Standard (GB L, Cr-1996) are met.
TABLE 3 ingredient list of No. II chromium slag
pH Cr(VI)(wt.％) Cr(tot)(wt.％) Ca(wt.％) Mg(wt.％) Fe(wt.％)
11.0 1.6 3.5 25.1 10.3 3.7
Al(wt.％) Si(wt.％) Ba(wt.％) Mn(wt.％) Ni(wt.％) S(wt.％)
6.1 7.7 0.2 0.08 0.05 0.09
TABLE 4 ingredient table of As-containing wastewater No. II
H+(mol/L) SO4 2–(mg/L) As(tot)(mg/L) As(III)(mg/L) As(V)(mg/L) Cd(mg/L)
0.13 6200 410 210 200 23
Cu(mg/L) Pb(mg/L) Zn(mg/L) Fe(mg/L) F–(mg/L) Cl–(mg/L)
160 14 55 970 32 440
Example 4
The second suspension obtained in example 1 was mixed at a ratio of 3kg/m3After the lime milk is added, if the oxygen exposure reaction is not carried out to obtain a third suspension, the concentration of ferrous ions in the treated wastewater obtained after solid-liquid separation can reach 1600mg/L, and the wastewater is slowly oxidized to generate ferric iron in the standing process to further form iron oxide particles, so that suspended matters in the treated wastewater gradually rise and cannot meet the requirements of Integrated wastewater discharge Standard (GB 8978-. On the contrary, the present invention is not limited to the above-described embodiments,the oxygen exposure reaction is increased, the concentration of ferrous ions in the treated wastewater is lower than 1mg/L, and the problem of suspended matters caused by ferrous oxidation is avoided. In addition, the oxygen exposure reaction accelerates the oxidation of ferrous iron to generate iron oxide, so that more adsorbent is provided for arsenic, and the arsenic concentration in the wastewater is further reduced. Therefore, the oxygen exposure reaction has double effects of accelerating iron removal and strengthening arsenic removal.
Example 5
For No. I chromium slag and simulated No. III arsenic-containing wastewater (the components are shown in Table 5) only containing As (V), 10g of chromium slag sample is weighed, 140mL of wastewater sample is added according to the solid-to-liquid ratio of 0.7:10, a first suspension is obtained after stirring for 24 hours, the pH of the supernatant is 6.9, the concentration of Cr (VI) is increased from 0 to 1220mg/L, As and is reduced from 2100 to 170mg/L, and the fixing effect of the inherent minerals of the chromium slag on As is embodied. If the sulfuric acid solution with the same volume and the same concentration is directly added to react with the chromium slag, the concentration of Cr (VI) in the obtained supernatant is 660mg/L, which is far lower than the condition that No. III arsenic-containing wastewater reacts with the chromium slag, and the existence of As (V) anions can strengthen the release of Cr (VI) in the chromium slag from a solid phase to a liquid phase, so that the subsequent reduction and stabilization are facilitated.
TABLE 5 ingredient table of arsenic-containing wastewater
H+(mol/L) SO4 2–(mg/L) As(tot)(mg/L) As(III)(mg/L) As(V)(mg/L)
1.10 53000 2100 0 2100
Example 6
For No. I chromium slag and simulated No. IV arsenic-containing wastewater containing only As (III) (see Table 6), 10g of chromium slag sample is weighed, 140mL of wastewater sample is added according to the solid-to-liquid ratio of 0.7:10, after stirring for 24 hours, a first suspension is obtained, and the pH of the supernatant is measured to be 6.8, and the concentration of Cr (VI) is measured to be 90 mg/L. If the same volume of sulfuric acid solution with the same concentration is directly added to react with the chromium slag, the concentration of Cr (VI) in the obtained supernatant is 660mg/L, which is far higher than the case that No. IV arsenic-containing wastewater reacts with the chromium slag, and the result shows that As (III) can directly reduce and stabilize Cr (VI).
TABLE 6 ingredient table of arsenic-containing wastewater
H+(mol/L) SO4 2–(mg/L) As(tot)(mg/L) As(III)(mg/L) As(V)(mg/L)
1.10 53000 2200 2200 0
Example 7
Preparing Fe (II) and Cr (VI) solution for reaction to obtain precipitate FeIII 0.75CrIII 0.25(OH)3And used for arsenic adsorption experiments, and the results are shown in fig. 3. At pH 7, FeIII 0.75CrIII 0.25(OH)3The adsorption capacity to As can reach 110mg/g, which shows that the reaction product of Fe (II) and Cr (VI) has extremely strong arsenic adsorption capacity.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A co-treatment method of chromium slag and acidic arsenic-containing wastewater is characterized by comprising the following steps:
(1) mixing the chromium slag and the acidic arsenic-containing wastewater, and fully stirring to obtain a first suspension; wherein the chromium slag reacts with the acidic arsenic-containing wastewater to release solid phase Cr (VI) in the chromium slag into a solution phase to form water soluble Cr (VI); part of As (III) in the arsenic-containing wastewater and part of water-soluble Cr (VI) released by the chromium slag are subjected to redox reaction, the As (III) is oxidized into As (V), and meanwhile, the Cr (VI) is reduced into Cr (III) and is precipitated in a precipitation form; meanwhile, arsenic in the acidic arsenic-containing wastewater is adsorbed and fixed by the lamellar minerals in the chromium slag;
(2) mixing the first suspension with a low-valence iron reducing agent, and fully stirring for reaction to obtain a second suspension; wherein the low-valence iron reducing agent and water-soluble Cr (VI) released by the chromium slag are subjected to redox reaction, and the Cr (VI) is reduced into Cr (III) and precipitated;
(3) adjusting the pH value of the second suspension to 6-9 by adopting alkali, and exposing to oxygen to react to obtain a third suspension; wherein the inherent minerals in the chromium slag and Cr (VI) generated by reduction and precipitation of Cr (VI)III(OH)3And FeIII 0.75CrIII 0.25(OH)3Arsenic is fixed through adsorption, so that the arsenic is transferred from a solution phase to a solid phase, and the concentration of the arsenic in the wastewater reaches the discharge standard;
(4) and carrying out solid-liquid separation on the third suspension to obtain the detoxified chromium slag and the discharged water with the water quality reaching the standard.
2. The co-treatment method according to claim 1, wherein the chromium slag has a pH of more than 10, a hexavalent chromium content of 100 to 20000 mg/kg; the pH value of the arsenic-containing wastewater is less than 2, and H in the arsenic-containing wastewater is preferably selected+The concentration of (A) is more than 0.1 mol/L; the total arsenic concentration is 10-10000 mg/L, wherein the content of As (III) in the total arsenic is not less than 20%.
3. The co-treatment method according to claim 1, wherein the chromium slag and the acidic arsenic-containing wastewater are mixed in the step (1), the solid-to-liquid ratio is controlled to be 0.01-5: 10, and the pH value is controlled to be 4-8 by adjusting the solid-to-liquid ratio.
4. The co-treatment method according to claim 1, wherein the chromium slag and the acidic arsenic-containing wastewater are mixed in the step (1), the solid-to-liquid ratio is controlled to be 0.1-2: 10, the pH value is controlled to be 5-7 by regulating the solid-to-liquid ratio, and the stirring time is 12-24 hours.
5. The co-processing method according to claim 1, wherein the grain size of the chromium slag in the step (1) is less than 200 meshes.
6. The co-processing method according to claim 1, wherein the low-valent iron reducing agent in step (2) is one or more of ferrous sulfate heptahydrate, ferrous sulfate tetrahydrate, ferrous sulfate monohydrate, ferrous sulfate pentahydrate, ferrous sulfate hexahydrate, ferrous chloride tetrahydrate, ferrous chloride dihydrate, anhydrous ferrous chloride, zero-valent iron, and iron powder.
7. The co-processing method according to claim 1, wherein the amount of the low-valent iron reducing agent added in the step (2) is 1 to 100kg/m3(ii) a The reaction time is 12Between 24 hours.
8. The co-processing method of claim 1, wherein the alkali of step (3) is one or more of quicklime, slaked lime, milk of lime, sodium hydroxide, calcium hydroxide, and calcium oxide.
9. The co-processing method according to claim 1, wherein the alkali in the step (3) is lime milk, and the content of calcium hydroxide in the lime milk is 5-8%; the addition amount of the lime milk is 0.1-5 kg/m3。
10. The co-processing method according to claim 1, wherein in the step (3), the pH of the second suspension is adjusted to 7-9 by using alkali; the reaction time is 12-24 hours.
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