CN114702071A - Method for preparing chromium sesquioxide by utilizing high-chromium sludge generated by chromium electroplating rinsing wastewater treatment - Google Patents

Method for preparing chromium sesquioxide by utilizing high-chromium sludge generated by chromium electroplating rinsing wastewater treatment Download PDF

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CN114702071A
CN114702071A CN202210398647.9A CN202210398647A CN114702071A CN 114702071 A CN114702071 A CN 114702071A CN 202210398647 A CN202210398647 A CN 202210398647A CN 114702071 A CN114702071 A CN 114702071A
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陈天虎
张雪妹
孙付炜
刘海波
邹雪华
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Hefei University of Technology
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Abstract

The invention discloses a method for preparing chromium sesquioxide by utilizing high-chromium sludge generated by chromium electroplating rinsing wastewater treatment, which decomposes the high-chromium sludge into green chromium ore (Cr) by high-temperature roasting2O3) And sodium sulfate. The method of the invention converts the high-chromium sludge as hazardous waste into Cr with high added value2O3The product is simple to operate, has obvious benefits, and solves the problem that the high-chromium sludge cannot be subjected to resource treatment.

Description

Method for preparing chromium sesquioxide by utilizing high-chromium sludge generated by chromium electroplating rinsing wastewater treatment
Technical Field
The invention belongs to the technical field of electroplating high-chromium sludge treatment, relates to a process for recycling high-chromium sludge, and particularly relates to a method for preparing chromium sesquioxide by using high-chromium sludge generated by chromium electroplating rinsing wastewater treatment.
Background
Electroplating parks typically produce two types of chromium sludge: one type is called low chromium sludge, which is chromium-containing sludge generated by electroplating comprehensive wastewater treatment; the sludge is produced by reduction and precipitation of chromium plating rinsing water by sodium pyrosulfite, the rinsing water has less impurities, and the obtained sludge dry basis has high chromium content. No matter which chromium sludge is used, the chromium sludge is managed as hazardous waste because of the lack of resource utilization technology and ways, and the improper disposal of the chromium sludge not only brings harm to the environment, but also wastes the non-renewable resource chromium, so that the important research on how to achieve the purposes of reduction, stabilization, harmlessness and resource utilization of the chromium sludge is realized.
The conventional common technology for recycling chromium sludge mainly comprises the following steps: the heavy metals in the sludge are extracted and recycled by the fire method and the wet method, and the chromium sludge is converted into common solid waste. However, the above conventional methods are only suitable for treating low-chromium sludge, and if the high-chromium sludge is treated by the same treatment technique to transfer all chromium from the solid phase to the liquid phase, a large amount of reagents and energy are consumed, which results in high operation cost. Therefore, a resource treatment method of the high-chromium sludge needs to be researched.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a method for preparing chromium sesquioxide by utilizing high-chromium sludge generated by the treatment of chromium electroplating rinsing wastewater, so as to realize the resource utilization of the high-chromium sludge.
In order to realize the purpose, the invention adopts the following technical scheme:
the research of the invention discovers that the main compound component of the high-chromium sludge formed by reducing hexavalent chromium and precipitating trivalent chromium by using sodium pyrosulfite in the chromium electroplating rinsing wastewater is NaCr3(SO4)2(OH)6In an amorphous or very low crystallinity state. High temperature heat treatment can make NaCr3(SO4)2(OH)6Decomposed into green chromium ore (Cr)2O3) And sodium sulfate.
The method for preparing chromium sesquioxide by utilizing high-chromium sludge generated by chromium electroplating rinsing wastewater treatment provided by the invention has three optional technical routes:
the first technical route is as follows: the technical route is characterized in that Na is removed by' primary acid leaching treatment, air roasting treatment, secondary acid leaching treatment, water washing treatment and drying and crushing2SO4And heavy metal impurities, product Cr2O3The purity can reach 99%. The method comprises the following steps:
(1) primary acid leaching treatment: fully mixing 0.5-2 mol/L acid solution and the high-chromium sludge for reaction for 10-60 min, and carrying out solid-liquid separation and drying to obtain high-chromium sludge subjected to acid pretreatment; wherein the mass ratio of the volume of the acid solution to the high-chromium sludge is 1-3L: 1 kg;
(2) roasting treatment: roasting the high-chromium sludge pretreated by acid at 400-700 ℃ in air atmosphere to ensure that the main phase NaCr in the sludge3(SO4)2(OH)6Decomposed into green chromium ore (Cr)2O3) And sodium sulfate;
(3) secondary acid leaching treatment: fully mixing 1-5 mol/L acid solution and the roasted high-chromium sludge for reaction for 10-60 min, and carrying out solid-liquid separation; wherein the mass ratio of the volume of the acid solution to the roasted high-chromium sludge is 1-5L: 1 kg;
(4) and (3) water washing treatment: washing the solid subjected to secondary acid leaching treatment by using water for countercurrent rinsing or filter pressing so as to completely remove dissolved salts in the solid; wherein the mass ratio of the volume of the used water to the solid after the secondary acid leaching treatment is 1-5L: 1 kg;
(5) drying and crushing: and further drying and crushing the solid after the water washing treatment to obtain the target product chromium sesquioxide.
Further, the acid in the step (1) and the step (3) is hydrochloric acid, acetic acid, sulfuric acid or nitric acid.
And (3) further neutralizing the wastewater discharged in the step (1), the step (3) and the step (4), carrying out vulcanization precipitation, filtering to remove heavy metal impurities, and carrying out evaporation crystallization to obtain a byproduct sodium sulfate. Specifically, the washing is carried out multistage (like 4 ~ 6 levels) washing to setting up a plurality of washing ponds against current rinsing, and the material carries out reverse flow with the lotion, and the salt content in the solid reduces along with the washing of multilevel gradually, wherein: the discharged water after the first-stage water washing has high salt content and is used for producing sodium sulfate crystal salt. And adding pure water or tap water into the last-stage water washing tank, and recycling the residual washing liquid to the previous-stage washing.
The second technical route is as follows: the technical route is characterized in that heavy metals are precipitated step by step at the treatment source of the chromium electroplating rinsing wastewater, and the wastewater generated in the acid leaching treatment process is reduced, and the method specifically comprises the following steps:
(1) and (3) hexavalent chromium reduction: adding sodium pyrosulfite into the chromium electroplating rinsing wastewater to reduce hexavalent chromium in the wastewater, wherein the adding amount of the sodium pyrosulfite is calculated according to the concentration of the hexavalent chromium in the wastewater, and the Cr concentration is calculated according to the concentration of the hexavalent chromium in the wastewater6+The molar ratio of the sodium pyrosulfite to the sodium pyrosulfite is 1-4: 1-3;
(2) primary precipitation separation: performing acid-base neutralization on the wastewater treated in the step (1) to ensure that the pH of the solution is 4.5-5, and trivalent chromium in the solution generates NaCr3(SO4)2(OH)6Precipitating, and carrying out solid-liquid separation to obtain high-chromium sludge basically free of Cu, Ni and Pb impurities, wherein the phase of the sludge is basically NaCr3(SO4)2(OH)6Cu, Ni and Pb are basically remained in the solution;
(3) secondary precipitation of wastewater: further neutralizing the solution treated in the step (2) to pH 8-9 with a sodium hydroxide solution and a sodium sulfide solution to form precipitates of Cu, Ni, Pb and Cr in the solution, and reusing the water after heavy metal removal for water washing and desalting in the step (5); wherein, the molar quantity of the added sodium sulfide is 100 to 120 percent of the total molar quantity of the heavy metal ions in the solution;
(4) primary precipitate solid roasting: roasting the high-chromium sludge obtained in the step (2) at 400-700 ℃ in air atmosphere to ensure that the main phase NaCr in the sludge3(SO4)2(OH)6Decomposed into green chromium ore (Cr)2O3) And sodium sulfate;
(5) and (3) water washing treatment: washing the roasted high-chromium sludge by using water for countercurrent rinsing or filter pressing so as to completely remove dissolved salts in the high-chromium sludge; wherein the mass ratio of the volume of the used water to the roasted high-chromium sludge is 1-5L: 1 kg;
(6) drying and crushing: and further drying and crushing the solid after the water washing treatment to obtain the target product chromium sesquioxide.
And (3) further, carrying out vulcanization precipitation and filtration on the discharged water subjected to water washing treatment in the step (5) to remove heavy metal impurities, and carrying out evaporation crystallization to obtain a by-product sodium sulfate. Specifically, the washing is carried out multistage (like 4 ~ 6 levels) washing to setting up a plurality of washing ponds against current rinsing, and the material carries out reverse flow with the lotion, and the salt content in the solid reduces along with the washing of multilevel gradually, wherein: the discharged water after the first-stage water washing has high salt content and is used for producing sodium sulfate crystal salt. And adding pure water or tap water into the last-stage water washing tank, and recycling the residual washing liquid to the previous-stage washing.
The technical route is three: the technical route is characterized in that the industrial Cr is obtained by directly roasting, washing and desalting the high-chromium sludge generated by the treatment of chromium electroplating rinsing wastewater2O3The product with the purity of more than 97 percent is specifically carried out according to the following steps:
(1) roasting the high-chromium sludge at 400-700 ℃ in air atmosphere to ensure that the main phase NaCr in the sludge3(SO4)2(OH)6Decomposing into green chromium ore and sodium sulfate;
(2) rinsing the roasted high-chromium sludge by using water in a countercurrent way to remove dissolved salts in the high-chromium sludge so as to obtain a target product chromium sesquioxide; wherein the mass ratio of the volume of the water to the roasted high-chromium sludge is 1L:1 kg;
(3) and (4) carrying out vulcanization precipitation and filtration on the discharged water of the counter-current rinsing to remove heavy metal impurities, and then carrying out evaporation crystallization to obtain a by-product sodium sulfate. Specifically, the washing is carried out multistage (like 4 ~ 6 levels) washing to a plurality of washing ponds of setting up against the current rinsing, and the material carries out reverse flow with the lotion, and the salt content in the solid reduces along with the washing of multilevel gradually, wherein: the discharged water after the first-stage water washing has high salt content (the concentration of sodium sulfate is close to a saturation value), and is used for producing sodium sulfate crystal salt. Pure water or tap water is added into the last stage of washing pool, and the rest washing liquid is recycled to the previous stage of washing. In order to further improve the purity, the number of times of the countercurrent rinsing can be 1-3 times.
Compared with the prior art, the invention has the beneficial effects that:
(1) researches show that the once acid washing is carried out before roasting, so that the removal efficiency of heavy metal impurities such as copper in the high-chromium sludge can be improved, and the purity of a final product is improved. The acid washing mode can also control the pH value to be about 5 when hexavalent chromium is reduced and precipitated, and heavy metals such as chromium, copper and the like are separated; or washing the precipitated chromium sludge once by using dilute acid solution during dehydration of the precipitated chromium sludge to reduce the content of heavy metals such as copper in the chromium sludge.
(2) Researches show that the main compound component of the high-chromium sludge formed by reducing hexavalent chromium and precipitating trivalent chromium by using sodium pyrosulfite in the chromium electroplating rinsing wastewater is NaCr3(SO4)2(OH)6A compound in an amorphous state, cannot be separated from chromium and sulfate radicals by washing with water. The system research finds that the high-temperature heat treatment at the temperature of more than 400 ℃ can lead the NaCr3(SO4)2(OH)6Decomposed into green chromium ore and sodium sulfate. The temperature is required to be lower than 700 ℃ because experiments show that the wall and ring formation of the roasting furnace can be caused by the phenomenon that the roasting furnace is formed when the sodium sulfate is molten at an overhigh roasting temperature, and the operation of the furnace can be influenced.
(3) And (3) recycling the hazardous waste: the electroplating high-chromium sludge is not only a dangerous solid waste with complex components, but also a renewable resource with large yield. The high-chromium sludge contains high-value chromium, and Na in the high-chromium sludge can be realized by treating the high-chromium sludge by the method2SO4High-efficiency removal of 99% to obtain high-purity Cr2O3And (5) producing the product.
(4) Product Cr2O3The application field is wide: cr prepared by the method of the invention2O3The product has the particle size of 5-100nm and the average particle size of about 40nm, belongs to nano powder, can be used as a coloring pigment in the paint and ceramic industry, and can also be used as a raw material of plasma spraying, metallurgy, refractory materials and metal oxide-based catalysts.
(5) The economic benefit is high: because the high-chromium sludge has dual attributes of pollution and resource, relevant advanced treatment and disposal processes and equipment are researched and developed, the problem of chromium resource shortage can be well solved while the environment is protected, and better economic benefits are created for high-chromium sludge treatment and disposal enterprises. Produced on the basis of the inventionOf Cr (C)2O3Through simple cost analysis and calculation, the method estimates that Cr is obtained by resourceful treatment of 1 ton of dried high-chromium sludge2O310960 yuan/ton can be gained.
(6) After the washing wastewater is purified to remove heavy metals, the washing wastewater is evaporated and crystallized by MVR to obtain a byproduct sodium sulfate product. The whole process has no wastewater discharge, and secondary pollution is avoided. And countercurrent rinsing is adopted, so that the washing water consumption is reduced, the concentration of sodium sulfate in washing wastewater is improved, the evaporation water amount is reduced, and the treatment cost is reduced.
(7) The second technical route realizes the separation of chromium from heavy metals such as copper, nickel, lead and the like from the source, reduces the steps of acid pretreatment and secondary acid leaching, greatly reduces the generation amount of wastewater, and reduces the subsequent wastewater evaporation concentration treatment cost.
(8) The third technical route is suitable for the condition that the content of copper, nickel, lead and the like in the high-chromium sludge is very low or the product Cr2O3When the requirement is not high, the step of acid treatment twice in the first technical route or the step-by-step precipitation step in the second technical route is omitted, and the treatment cost is further reduced.
Drawings
FIG. 1 is a flow chart of a first embodiment of the present invention;
FIG. 2 is a flow chart of a second embodiment of the present invention;
FIG. 3 is a flow chart of a third embodiment of the present invention;
FIG. 4 is an XRD pattern of the high chromium sludge of the present invention after freeze drying.
Fig. 5 is an XRD chart of the high chromium sludge after calcination at different temperatures, wherein fig. 5a corresponds to the sample calcined without leaching only and fig. 5b corresponds to the sample calcined with 2 times leaching treatment.
FIG. 6 shows Cr, a target product obtained in example 1 of the present invention2O3Particle size distribution diagram of (c).
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention more comprehensible, specific embodiments thereof will be described in detail with reference to the following examples. The following is merely exemplary and illustrative of the inventive concept and various modifications, additions and substitutions of similar embodiments may be made to the described embodiments by those skilled in the art without departing from the inventive concept or exceeding the scope of the claims defined thereby.
The high-chromium sludge used in the following examples is the high-chromium sludge generated by the treatment of chromium electroplating rinsing wastewater, the composition characteristic analysis is performed after the freeze drying treatment, and the X-ray diffraction (XRD) pattern is shown in fig. 4, so that it can be seen that the high-chromium sludge only has a weak characteristic diffraction peak of sodium sulfate, and other components do not have corresponding diffraction peaks, which indicates that a small amount of sodium sulfate phase exists therein, and the chromium compound as the main component has extremely low crystallinity or exists in an amorphous state.
Example 1
As shown in fig. 1, in the present embodiment, the method for preparing chromium sesquioxide by using high-chromium sludge adopts a first technical route, which specifically includes the following steps:
(1) primary acid leaching treatment: fully mixing 1mol/L hydrochloric acid solution and the high-chromium sludge for reaction for 40min, and carrying out solid-liquid separation and drying to obtain high-chromium sludge subjected to acid pretreatment; wherein the mass ratio of the volume of the hydrochloric acid solution to the high-chromium sludge is 2L:1 kg.
(2) Roasting treatment: roasting the high-chromium sludge pretreated by acid at 500 ℃ for 2h in air atmosphere to ensure that the main phase NaCr in the sludge3(SO4)2(OH)6Decomposed into green chromium ore and sodium sulfate.
(3) Secondary acid leaching treatment: fully mixing 3mol/L hydrochloric acid solution and the roasted high-chromium sludge for reaction for 60min, and carrying out solid-liquid separation; wherein the mass ratio of the volume of the hydrochloric acid solution to the roasted high-chromium sludge is 2L:1 kg.
(4) And (3) water washing treatment: rinsing the solid subjected to the secondary acid leaching treatment by using water in a counter-current manner to completely remove dissolved salts in the solid; wherein, the countercurrent rinsing is to set 4 water washing pools for 4-level washing, the materials and the washing liquid flow in the reverse direction, and the salt content in the solid is gradually reduced along with the multilevel washing. The discharged water after the 1 st stage water washing has high salt content and is used for producing sodium sulfate crystal salt. Pure water (the mass ratio of the volume of the water to the solid after the secondary acid leaching treatment is 3L:1kg) is added into the 4 th-stage washing tank, and the residual washing liquid is recycled to the previous stage for washing.
(5) Drying and crushing: and further drying and crushing the solid after the water washing treatment to obtain the target product chromium sesquioxide.
In order to compare the change of the selective leaching rate of heavy metals in the high-chromium sludge under the hydrochloric acid leaching conditions with different concentrations, the concentrations of the hydrochloric acid solution in the step (1) are respectively set to be 0.5mol/L, 1mol/L, 2mol/L, 3mol/L, 4mol/L and 8mol/L, and solid-liquid separation is carried out. The results show that: when the concentration of the hydrochloric acid solution is 3mol/L, 4mol/L and 8mol/L, the chromium dissolution rate is too high, which is not beneficial to the separation of chromium and heavy metal impurities; when the concentration of the hydrochloric acid solution is 0.5mol/L, 1mol/L and 2mol/L, the impurities of copper, lead, iron and nickel can be respectively removed, and the dissolution of chromium can be reduced.
In order to compare the influence of different roasting temperatures on the decomposition efficiency of the high-chromium sludge, the roasting temperatures in the step (2) are respectively set to be 200, 300, 400, 500, 600 and 700 ℃. And (3) carrying out leaching desalination treatment on the roasted high-chromium sludge for 2 times by using pure water. Fig. 5 is an XRD chart of the high chromium sludge after calcination at different temperatures, wherein fig. 5a corresponds to the sample calcined without leaching only and fig. 5b corresponds to the sample calcined with 2 times leaching treatment. The high-chromium sludge can be completely decomposed into green chromium ore and sodium sulfate through high-temperature treatment at 400-700 ℃, and the green chromium ore and the sodium sulfate can be completely separated through washing.
In order to verify the influence of different acids on the secondary acid leaching treatment, hydrochloric acid, sulfuric acid, acetic acid and nitric acid are respectively set in the acid in the step (3), and solid-liquid separation is carried out. The results show that four different acids have better removal effect on copper, nickel, iron and lead, wherein the acid washing effect of 3mol/L hydrochloric acid is the best, and Cr is obtained2O3The product has the highest purity.
The results of the examination of the high purity chromium sesquioxide obtained in the present example according to the above steps (1) to (5) are shown in Table 1 and FIG. 6, referring to the industrial standard for chromium sesquioxide (HG/T2775-2010). As can be seen from Table 1, the prepared nano-scale Cr2O3Class I priorityIndex requirements of the product. As can be seen from FIG. 6, the particle size distribution of chromium sesquioxide is 8-100 nm, and the average particle size is 40nm, which meets the particle size requirement of the plasma spraying material.
TABLE 1 preparation of product Cr from high-chromium sludge2O3Composition and technical grade Cr2O3Index requirement
Figure BDA0003598629700000051
Figure BDA0003598629700000061
Example 2
As shown in fig. 2, in the method for preparing chromium sesquioxide by using high-chromium sludge in the embodiment, a second technical route is adopted, and the specific steps are as follows:
(1) reduction of hexavalent chromium: adding sodium pyrosulfite into the chromium electroplating rinsing wastewater to reduce hexavalent chromium in the wastewater, wherein the adding amount of the sodium pyrosulfite is calculated according to the concentration of the hexavalent chromium in the wastewater, and the Cr concentration is calculated according to the concentration of the hexavalent chromium in the wastewater6+The molar ratio to sodium metabisulfite was 1.2: 1.
(2) Primary precipitation separation: performing acid-base neutralization on the wastewater treated in the step (1) to ensure that the pH of the solution is 4.5-5, and trivalent chromium in the solution generates NaCr3(SO4)2(OH)6Precipitating and carrying out solid-liquid separation to obtain the high-chromium sludge basically free of Cu, Ni and Pb impurities, wherein the Cu, Ni and Pb are basically remained in the solution.
(3) Secondary precipitation of wastewater: further neutralizing the solution treated in the step (2) with a sodium hydroxide solution and a sodium sulfide solution to pH 8-9 to completely precipitate Cu, Ni, Pb and Cr in the solution, and reusing the water from which heavy metals are removed in the step (5) for washing and desalting; wherein the molar amount of the added sodium sulfide is 110 percent of the total molar amount of the heavy metal ions in the solution.
(4) Primary precipitation solid roasting: roasting the high-chromium sludge obtained in the step (2) for 30min at 600 ℃ in air atmosphere to ensure that the main phase NaCr in the sludge3(SO4)2(OH)6Decomposed into green chromium ore and sodium sulfate.
(5) And (3) water washing treatment: loading the roasted high-chromium sludge into a filter bag, and rinsing the filter bag by using water in a counter-current manner to completely remove dissolved salts in the high-chromium sludge; wherein, the countercurrent rinsing of countercurrent rinsing sets up 4 washing ponds and carries out 4 levels of washing, and the material carries out countercurrent flow with the lotion, and the salt content in the solid reduces along with multilevel washing gradually. The discharged water after the 1 st-stage water washing has high salt content and is used for producing sodium sulfate crystal salt. Pure water (the mass ratio of the volume of the water to the solid after the secondary acid leaching treatment is 3L:1kg) is added into the 4 th-stage washing tank, and the residual washing liquid is recycled to the previous stage for washing.
(6) Drying and crushing: and further drying and crushing the solid after the water washing treatment to obtain the target product chromium sesquioxide.
Through tests, the high-purity chromium sesquioxide prepared by the embodiment also meets the index requirements of I-class high-class products of industrial chromium sesquioxide industry standard (HG/T2775-2010).
Example 3
As shown in fig. 3, in the method for preparing chromium sesquioxide by using high-chromium sludge in the embodiment, a third technical route is adopted, and the specific steps are as follows:
(1) the content of impurities of copper, lead and nickel in the high-chromium sludge is detected to be lower than 0.5 percent. The chromium sludge is directly roasted at 600 ℃ in the air atmosphere, so that the main phase NaCr in the sludge3(SO4)2(OH)6Decomposed into green chromium ore (Cr)2O3) And sodium sulfate.
(2) The roasted high-chromium sludge is rinsed by water in a countercurrent way to remove dissolved salts in the high-chromium sludge, and Cr with the purity of 97 percent is obtained2O3Can be used as a metal material protective layer; specifically, the countercurrent rinsing is to set 4 water washing tanks for 4-level washing, the materials and the washing liquid flow in the countercurrent direction, and the salt content in the solid is gradually reduced along with the multilevel washing. The discharged water after the 1 st-stage water washing has high salt content and is used for producing sodium sulfate crystal salt. Adding pure water (the mass ratio of the volume of the water to the solid after the secondary acid leaching treatment is 1L:1kg) into a 4-stage water washing tank, and recycling the residual washing liquid to the previous stage for washing。
(3) And (3) carrying out vulcanization precipitation (adding sodium sulfide for precipitation), filtering to remove heavy metal impurities, and carrying out evaporation crystallization to obtain a byproduct sodium sulfate, wherein the concentration of sodium sulfate in the discharged water after the 1 st-stage washing is close to a saturation value. The evaporated condensed water is reused for washing the roasted high-chromium sludge, and basically no wastewater is discharged.
The present invention is not intended to be limited to the exemplary embodiments but rather to cover all modifications, equivalents, and improvements falling within the spirit and scope of the present invention.

Claims (7)

1. A method for preparing chromium sesquioxide by utilizing high-chromium sludge generated by chromium electroplating rinsing wastewater treatment is characterized by comprising the following steps:
(1) primary acid leaching treatment: fully mixing 0.5-2 mol/L acid solution and the high-chromium sludge for reaction for 10-60 min, and carrying out solid-liquid separation and drying to obtain high-chromium sludge subjected to acid pretreatment; wherein the mass ratio of the volume of the acid solution to the high-chromium sludge is 1-3L: 1 kg;
(2) roasting treatment: roasting the high-chromium sludge pretreated by acid at 400-700 ℃ in air atmosphere to ensure that the main phase NaCr in the sludge3(SO4)2(OH)6Decomposing into green chromium ore and sodium sulfate;
(3) secondary acid leaching treatment: fully mixing 1-5 mol/L acid solution and the roasted high-chromium sludge for reaction for 10-60 min, and carrying out solid-liquid separation; wherein the mass ratio of the volume of the acid solution to the roasted high-chromium sludge is 1-5L: 1 kg;
(4) and (3) water washing treatment: washing the solid subjected to secondary acid leaching treatment by using water for countercurrent rinsing or filter pressing so as to completely remove dissolved salts in the solid; wherein the mass ratio of the volume of the used water to the solid after the secondary acid leaching treatment is 1-5L: 1 kg;
(5) drying and crushing: and further drying and crushing the solid after the water washing treatment to obtain the target product chromium sesquioxide.
2. The method for preparing chromium sesquioxide using high chromium sludge produced by chromium electroplating rinse wastewater treatment according to claim 1, wherein: the acid in the step (1) and the step (3) is hydrochloric acid, acetic acid, sulfuric acid or nitric acid.
3. The method for preparing chromium sesquioxide using high chromium sludge produced by chromium electroplating rinse wastewater treatment according to claim 1, wherein: and (4) neutralizing, sulfurizing, precipitating and filtering the wastewater discharged in the steps (1), (3) and (4), and evaporating and crystallizing to obtain a byproduct sodium sulfate.
4. A method for preparing chromium sesquioxide by utilizing high-chromium sludge generated by chromium electroplating rinsing wastewater treatment is characterized by comprising the following steps:
(1) and (3) hexavalent chromium reduction: adding sodium pyrosulfite into the chromium electroplating rinsing wastewater to reduce hexavalent chromium in the chromium electroplating rinsing wastewater;
(2) primary precipitation separation: performing acid-base neutralization on the wastewater treated in the step (1) to ensure that the pH of the solution is 4.5-5, and trivalent chromium in the solution generates NaCr3(SO4)2(OH)6Precipitating and carrying out solid-liquid separation to obtain high-chromium sludge without impurities of Cu, Ni and Pb, so that the Cu, Ni and Pb are kept in the solution;
(3) secondary precipitation of wastewater: further neutralizing the solution treated in the step (2) to pH 8-9 with a sodium hydroxide solution and a sodium sulfide solution to form precipitates of Cu, Ni, Pb and Cr in the solution, and reusing the water after heavy metal removal for water washing and desalting in the step (5); wherein, the molar quantity of the added sodium sulfide is 100 to 120 percent of the total molar quantity of the heavy metal ions in the solution;
(4) primary precipitation solid roasting: roasting the high-chromium sludge obtained in the step (2) at 400-700 ℃ in air atmosphere to ensure that the main phase NaCr in the sludge3(SO4)2(OH)6Decomposing into green chromium ore and sodium sulfate;
(5) and (3) water washing treatment: washing the roasted high-chromium sludge by using water for countercurrent rinsing or filter pressing so as to completely remove dissolved salts in the high-chromium sludge; wherein the mass ratio of the volume of the used water to the roasted high-chromium sludge is 1-5L: 1 kg;
(6) drying and crushing: and further drying and crushing the solid after the water washing treatment to obtain the target product chromium sesquioxide.
5. The method for preparing chromium sesquioxide using high chromium sludge produced by chromium electroplating rinse wastewater treatment according to claim 4, wherein: the adding amount of the sodium pyrosulfite in the step (1) is calculated according to the concentration of hexavalent chromium in water, and Cr6+The molar ratio of the sodium pyrosulfite to the sodium pyrosulfite is 1-4: 1-3.
6. The method for preparing chromium sesquioxide using high chromium sludge produced by chromium electroplating rinse wastewater treatment according to claim 4, wherein: and (5) carrying out vulcanization precipitation and filtration on the discharged water subjected to water washing treatment in the step (5), and carrying out evaporative crystallization to obtain a byproduct sodium sulfate.
7. A method for preparing chromic oxide by utilizing high-chromium sludge generated by chromium electroplating rinsing wastewater treatment is characterized by comprising the following steps:
(1) roasting the high-chromium sludge at 400-700 ℃ in air atmosphere to ensure that the main phase NaCr in the sludge3(SO4)2(OH)6Decomposing into green chromium ore and sodium sulfate;
(2) rinsing the roasted high-chromium sludge by using water in a counter-current manner to remove dissolved salts in the high-chromium sludge so as to obtain a target product chromium sesquioxide; wherein the mass ratio of the volume of the used water to the roasted high-chromium sludge is 1L:1 kg;
(3) and (4) carrying out vulcanization precipitation and filtration on the discharged water of the counter-current rinsing, and then carrying out evaporative crystallization to obtain a by-product sodium sulfate.
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