A process for extracting chromium residue

Abstract

The application discloses a chromium residue extraction process and belongs to the technical field of waste resource conversion.The chromium residue is fully extracted by multiple times of alkali leaching, solid-liquid separation, pH adjustment of the filtrate, evaporation concentration and cooling crystallization; the valuable elements (such as iron, phosphorus, nickel, chromium and the like) in the chromium residue can be completely separated by further high-temperature oxidation and water extraction of the residue, iron and nickel are used for smelting steel and iron, and the resource utilization rate is remarkably improved; meanwhile, soda ash is not needed to be added, and calcination at a high temperature above 1000 DEG C is not needed, so that the cost of the chromium residue resource conversion is reduced.

Description

Technical Field

[0001] This article relates to the field of waste resource conversion technology, specifically to a chromium slag extraction process. Background Technology

[0002] In the production of nickel compounds such as nickel sulfate, nickel chloride, and nickel nitrate using ferronickel alloys, nickel matte, nickel briquettes, or nickel powder as raw materials, chromium removal is necessary to meet the purity requirements of nickel salt compounds. This chromium removal process generates chromium slag. The main components of chromium slag are compounds composed of cations such as iron, nickel, and chromium, along with phosphorus-containing anions. Since chromium slag is a residue generated during the smelting process, valuable metals and impurities undergo recombination and distribution during slag formation, resulting in stable, mixed compounds. Conventional ore beneficiation methods are insufficient to purify the various compounds in the chromium slag or extract valuable elements (iron, phosphorus, nickel, and chromium). Therefore, although chromium slag contains high levels of ferric phosphate and valuable elements, its resource utilization is challenging.

[0003] Regarding the resource utilization of chromium slag, related technologies extract chromium from chromium slag through oxidative leaching of hexavalent chromium. This mainly employs a method of using soda ash and high-temperature oxidation to convert low-valent chromium into hexavalent chromium, which is then extracted through water washing. For example, in patent CN101058853A, "Method for Recovering Chemical Products from Industrial Slag Containing Vanadium, Chromium, Iron and Phosphorus," trivalent chromium is converted into hexavalent chromium through alkaline roasting. Firstly, calcination consumes a large amount of energy, and secondly, it is difficult to guarantee the complete extraction of hexavalent chromium from the slag during the leaching process. The hexavalent chromium remaining in the slag greatly increases the toxicity of the leaching residue, thereby increasing its environmental and health safety risks.

[0004] Therefore, this paper is presented. Summary of the Invention

[0005] The purpose of this paper is to overcome the shortcomings of existing technologies and provide a chromium slag extraction process that can maximize the conversion and utilization of resources in chromium slag with less energy consumption, while also avoiding environmental and health safety risks.

[0006] To achieve the above objectives, the technical solution adopted in this paper is as follows:

[0007] A chromium slag extraction process includes the following steps:

[0008] S1 primary solid-liquid separation

[0009] After alkali leaching, the chromium slag is separated into solid and liquid components to obtain the first filter residue and the first filtrate.

[0010] S2 Secondary Solid-Liquid Separation

[0011] The first filtrate obtained in step S1 is adjusted to pH 8-13, and after solid-liquid separation, a second filter residue and a second filtrate are obtained.

[0012] The first filter residue obtained in step S1 is oxidized by calcination at 700-800℃, extracted with water, and the solid obtained by solid-liquid separation is denoted as the first product and the liquid is denoted as the third filtrate.

[0013] S3 three-stage solid-liquid separation

[0014] After the second filter residue is washed with water, the solid-liquid separation is followed by alkaline leaching of the washing liquid, and the washing residue is converted into the first filter residue.

[0015] After the second filtrate is heated and cooled to crystallize, the phosphate solid obtained by solid-liquid separation is recorded as the second product, and the resulting liquid is further processed in the same way as the first filtrate.

[0016] After adding a reducing agent to the third filtrate and reacting, solid chromium hydroxide solid is obtained by solid-liquid separation and is recorded as the third product. The resulting filtrate is recorded as the fourth filtrate. The fourth filtrate is further processed according to the method of the second filtrate.

[0017] This paper describes a process involving multiple alkaline leaching processes, solid-liquid separation, pH adjustment of the filtrate, evaporation and concentration, and cooling crystallization to fully extract phosphorus from chromium slag. Further high-temperature oxidation and water extraction of the filter residue can completely separate valuable elements (such as iron, phosphorus, nickel, and chromium) from the chromium slag. Specifically, during alkaline leaching, chromium remains in the solid phase (i.e., the first filter residue) and is not leached into the alkaline solution. At this point, chromium maintains a divalent or trivalent valence state. Therefore, after further high-temperature oxidation of the filter residue, chromium is oxidized to chromate, iron to iron oxide, and nickel to nickel oxide. After water extraction, elements such as iron and nickel can be completely separated from chromium. Iron and nickel can then be used in steelmaking, significantly improving resource utilization.

[0018] Furthermore, the extraction process used in this paper does not require the addition of soda ash or calcination at temperatures above 1000℃, thus reducing the cost of chromium slag resource conversion.

[0019] In one embodiment, the chromium slag is a byproduct of the nickel salt production process of nickel-iron alloys. The compounds forming the chromium slag include: chromium, iron, and nickel as cations; and phosphorus-containing anions, including at least one of orthophosphate, hypophosphate, phosphite, metaphosphate, polyphosphate, and pyrophosphate.

[0020] In one embodiment, the chromium ions in the chromium slag include Cr. 2+ Cr 3+ At least one of the following; the chromium ion content in the chromium slag is 0.1-8 wt%.

[0021] In one embodiment, the chromium slag contains iron ions including Fe. 2+ Fe 3+At least one of the following; the iron ion content in the chromium slag is 10-50 wt%.

[0022] In one embodiment, the nickel ions in the chromium slag are Ni. 2+ The nickel ion content in the chromium slag is 0.1-10 wt%.

[0023] In one embodiment, the alkali leaching solution is an aqueous solution of an alkali, wherein the alkali refers to an alkali that can ionize into OH radicals in water. - The alkali includes, but is not limited to, at least one of liquid ammonia, ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium phosphate, potassium carbonate, and potassium phosphate.

[0024] In one embodiment, the pH of the alkaline leaching solution is 11-14.

[0025] In one embodiment, the temperature of the alkaline leaching treatment is 60-90°C.

[0026] In one embodiment, the alkaline immersion treatment time is 0.5-24 hours.

[0027] In one embodiment, the alkaline leaching process also requires stirring to ensure that the chromium slag and the alkaline leaching solution are fully in contact and mixed evenly.

[0028] In this paper, alkaline leaching first precipitates the cations to separate them from phosphorus. The main component of the first filtrate is phosphorus-containing anions.

[0029] In one embodiment, in step S2, the pH value of the first filtrate needs to be adjusted according to the specific type of the target phosphate product (i.e., the second product described in step S3). Specifically:

[0030] a. When the second product is a third-generation phosphate, in step S2, the pH of the first filtrate is adjusted to ≥11.5;

[0031] b. When the second product is a second-generation phosphate or a first-generation phosphate, in step S2, 4 ≤ adjust the pH of the first filtrate to <11.5.

[0032] Acidic or alkaline reagents used in this art to adjust the pH of a solution may be used herein.

[0033] In one embodiment, the acidic reagent used to adjust the pH includes, but is not limited to, at least one of phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid, formic acid, acetic acid, and sodium dihydrogen phosphate.

[0034] In one embodiment, the acidic reagent used to adjust the pH includes, but is not limited to, sodium hydroxide.

[0035] In one embodiment, after the pH of the first filtrate is adjusted, a flocculant is added to improve the solid-liquid separation efficiency. The flocculant includes, but is not limited to, polyacrylamide (PAM).

[0036] In one embodiment, the calcination oxidation time in step S2 is 1-24 hours.

[0037] In one embodiment, the oxidizing atmosphere for the ablation oxidation in step S2 is an air atmosphere, an oxygen atmosphere, an ozone atmosphere, or an atmosphere formed by a mixture of oxygen and ozone. Oxygen and ozone in the air participate in the oxidation reaction as oxidants.

[0038] In one embodiment, the crystallization process in step S3 is as follows: within 24 hours, the temperature is raised to 40-140°C for evaporation and concentration, and then cooled to 20-30°C.

[0039] In one embodiment, the reducing agent in step S3 includes at least one of elemental sulfur and water-soluble sulfides.

[0040] In one embodiment, the water-soluble sulfide includes, but is not limited to, at least one of sodium sulfide, potassium sulfide, calcium sulfide, and magnesium sulfide. To improve the purity of the extracted product, the cations in the water-soluble sulfide are consistent with the cations of the alkali in the alkaline leaching solution in step S1.

[0041] In this article, the first product is iron ore with a phosphorus content ≤0.15wt%; the second product is phosphate; and the third product is chromium hydroxide.

[0042] This article does not limit the method of solid-liquid separation. Any method that can achieve solid-liquid separation in the art can be used in this article. The solid-liquid separation method includes, but is not limited to, filtration, centrifugation, and sedimentation.

[0043] In one embodiment, the solid-liquid separation method is pressure filtration.

[0044] The beneficial effects of this article are:

[0045] This paper describes a process that involves multiple alkaline leaching, solid-liquid separation, pH adjustment of the filtrate, evaporation and concentration, and cooling crystallization to fully extract phosphorus from chromium slag. Further processes such as high-temperature oxidation and water extraction of the filter residue can completely separate valuable elements (such as iron, phosphorus, nickel, and chromium) from the chromium slag. Iron and nickel can then be used for steelmaking, thus greatly improving resource utilization.

[0046] The extraction process used in this paper does not require the addition of soda ash or calcination at temperatures above 1000℃, thus reducing the cost of chromium slag resource conversion. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the chromium slag extraction process in Example 1. Detailed Implementation

[0048] To better illustrate the purpose, technical solutions, and advantages of this document, the following description will be provided in conjunction with specific embodiments, comparative examples, and accompanying drawings. The purpose of this description is to provide a detailed understanding of the content of this document, rather than to limit it.

[0049] Unless otherwise specified, all components and raw materials used in the embodiments and comparative examples in this article are commercially available, and the same type of components and raw materials were used in each parallel experiment.

[0050] Example 1

[0051] A chromium slag extraction process includes the following steps:

[0052] 100g of chromium slag sample was mixed with 74.8g of sodium hydroxide, 400mL of water was added, and the mixture was stirred and mixed. Then the mixture was heated to 80℃ and kept at that temperature for 3h. After filtration, the first filtrate and the first filter residue were obtained.

[0053] Add 15 mol / L concentrated phosphoric acid to the first filtrate to adjust the pH to 12, then add flocculant PAM and stir, then filter to obtain the second filter residue and the second filtrate.

[0054] The second filter residue is washed with water and filtered to obtain washing water and washing residue. The washing water is reused for one alkali leaching, and the washing residue is transferred to the first filter residue. The second filtrate is heated to 140℃ and evaporated, then concentrated to a relative density ρ = 1.24 g / cm³. 3 Heating was stopped, and the concentrated evaporation solution was cooled to room temperature (25°C) within 24 hours to crystallize. The crystals were separated from the liquid by filtration, and trisodium dodecahydrate crystals and crystallization mother liquor were obtained. Trisodium dodecahydrate was dried at 40°C and recorded as the second product. The crystallization mother liquor was returned to the first filtrate for recycling.

[0055] The first filter residue was added to a high-temperature atmosphere furnace, air was introduced, and the temperature was raised to 700°C. It was then calcined at this temperature for 5 hours. Water was then added and stirred until homogeneous. The mixture was filtered to obtain iron ore as the first product. The liquid obtained after filtration was designated as the third filtrate. Sodium sulfide, a reducing agent, was added to the third filtrate. After a complete reaction, it was filtered to obtain solid chromium hydroxide (designated as the third product) and a phosphorus-containing filtrate (also known as the fourth filtrate). This filtrate was processed in the same way as the second filtrate. After evaporation, concentration, cooling, and crystallization, trisodium phosphate dodecahydrate (designated as the second product) was obtained.

[0056] In this embodiment, (1) the composition of the selected chromium slag is shown in Table 1:

[0057] Table 1 Composition of chromium slag

[0058] Element types iron phosphorus chromium nickel quality score 33.36％ 15.29％ 0.65％ 1.35％

[0059] (2) The composition of the extracted product—iron ore—is shown in Table 2:

[0060] Table 2 Composition of Iron Ore Products

[0061] Element types iron phosphorus chromium nickel sulfur copper Zinc mass fraction % 66.32 0.017 0.025 1.567 0.076 0.001 0.001 Element types aluminum silicon lead arsenic cobalt manganese mass fraction % 0.001 0.481 0.000 0.000 0.000 0.004

[0062] (3) The extracted product, trisodium phosphate dodecahydrate, contains less than 0.001% iron and less than 0.001% chromium, which meets the standard of "HG / T2517-2009 Industrial Trisodium Phosphate".

[0063] Example 2

[0064] A chromium slag extraction process includes the following steps:

[0065] 100g of chromium slag sample (same as in Example 1) was mixed with 74.8g of potassium hydroxide, 400mL of water was added, and the mixture was stirred and mixed. Then the mixture was heated to 80℃ and kept at that temperature for 3h. After filtration, the first filtrate and the first filter residue were obtained.

[0066] Add 15 mol / L concentrated phosphoric acid to the first filtrate to adjust the pH to 12, then add flocculant PAM and stir, then filter to obtain the second filter residue and the second filtrate.

[0067] The second filter residue is washed with water and filtered to obtain washing water and washing residue. The washing water is reused for one alkali leaching, and the washing residue is transferred to the first filter residue. The second filtrate is heated to 140℃ and evaporated, then concentrated to a relative density ρ = 1.24 g / cm³. 3 Heating was stopped, and the concentrated evaporation solution was cooled to room temperature (25°C) within 24 hours to crystallize. The crystals were separated from the liquid by filtration, and tripotassium dodecahydrate and crystallization mother liquor were obtained. Tripotassium dodecahydrate was dried at 40°C and recorded as the second product. The crystallization mother liquor was returned to the first filtrate for recycling.

[0068] The first filter residue was added to a high-temperature atmosphere furnace, oxygen was introduced, and the temperature was raised to 700°C. It was then calcined at this temperature for 5 hours. Water was then added and stirred until homogeneous. The mixture was filtered to obtain iron ore as the first product. The liquid obtained after filtration was designated as the third filtrate. Potassium sulfide, a reducing agent, was added to the third filtrate. After a complete reaction, it was filtered to obtain solid chromium sulfide (designated as the third product) and a phosphorus-containing filtrate (also known as the fourth filtrate). This filtrate was processed in the same way as the second filtrate. After evaporation, concentration, cooling, and crystallization, tripotassium dodecahydrate (designated as the second product) was obtained.

[0069] In this embodiment, (1) the composition of the extracted iron ore is shown in Table 3:

[0070] Table 3 Composition of Iron Ore Products

[0071] Element types iron phosphorus chromium nickel sulfur copper Zinc mass fraction % 66.72 0.019 0.015 1.681 0.096 0.001 0.001 Element types aluminum silicon lead arsenic cobalt manganese mass fraction % 0.001 0.481 0.000 0.000 0.000 0.004

[0072] (2) The extracted product, tripotassium dodecahydrate, contains less than 0.001% iron and less than 0.001% chromium, which meets the standard of GB / T 2925-2008 Industrial Tripotassium Phosphate.

[0073] Example 3

[0074] A chromium slag extraction process includes the following steps:

[0075] 100g of chromium slag sample (same as in Example 1) was mixed with 74.8g of sodium hydroxide, 400mL of water was added, and the mixture was stirred and mixed. Then the mixture was heated to 80℃ and kept at that temperature for 3h. After filtration, the first filtrate and the first filter residue were obtained.

[0076] Add 15 mol / L concentrated phosphoric acid to the first filtrate to adjust the pH to 8.5, then add flocculant PAM and stir, then filter to obtain the second filter residue and the second filtrate.

[0077] The second filter residue is washed with water and filtered to obtain washing water and washing residue. The washing water is reused for one alkali leaching, and the washing residue is transferred to the first filter residue. The second filtrate is heated to 50-140℃ for evaporation and concentrated to a relative density ρ = 1.24 g / cm³. 3 Heating was stopped, and the concentrated evaporation solution was cooled to room temperature (25°C) within 24 hours to crystallize. The crystals were separated from the liquid by filtration, and disodium hydrogen phosphate and crystallization mother liquor were obtained. Sodium hydrogen phosphate was dried at 40°C and recorded as the second product. The crystallization mother liquor was returned to the first filtrate for recycling.

[0078] The first filter residue was added to a high-temperature atmosphere furnace, air was introduced, and the temperature was raised to 700°C. It was then calcined at this temperature for 5 hours. Water was then added and stirred until homogeneous. The mixture was filtered to obtain iron ore as the first product. The liquid obtained after filtration was designated as the third filtrate. Hydrazine hydrate, a reducing agent, was added to the third filtrate. After a complete reaction, it was filtered to obtain solid chromium hydroxide (designated as the third product) and a phosphorus-containing filtrate (also known as the fourth filtrate). This filtrate was processed in the same way as the second filtrate. After evaporation, concentration, cooling, and crystallization, disodium hydrogen phosphate (designated as the second product) was obtained.

[0079] In this embodiment, (1) the composition of the extracted iron ore is shown in Table 4:

[0080] Table 4 Composition of Iron Ore Products

[0081] Element types iron phosphorus chromium nickel sulfur copper Zinc mass fraction % 66.19 0.014 0.021 1.554 0.068 0.001 0.001 Element types aluminum silicon lead arsenic cobalt manganese mass fraction % 0.001 0.481 0.000 0.000 0.000 0.004

[0082] (2) The extracted product, disodium hydrogen phosphate, has an iron content of less than 0.001% and a chromium content of less than 0.001%, which meets the standard of "HG / T 2965-2009 Industrial Disodium Hydrogen Phosphate".

[0083] Example 4

[0084] A chromium slag extraction process includes the following steps:

[0085] 100g of chromium slag sample (same as in Example 1) was mixed with 74.8g of sodium hydroxide, 400mL of water was added, and the mixture was stirred and mixed. Then the mixture was heated to 80℃ and kept at that temperature for 3h. After filtration, the first filtrate and the first filter residue were obtained.

[0086] Add 15 mol / L concentrated phosphoric acid to the first filtrate to adjust the pH to 4.3, then add flocculant PAM and stir, then filter to obtain the second filter residue and the second filtrate.

[0087] The second filter residue is washed with water and filtered to obtain washing water and washing residue. The washing water is reused for one alkali leaching, and the washing residue is transferred to the first filter residue. The second filtrate is heated to 50°C and evaporated, then concentrated to a relative density ρ = 1.24 g / cm³. 3 Heating was stopped, and the concentrated evaporation solution was cooled to room temperature (25°C) within 24 hours to crystallize. After filtration, sodium dihydrogen phosphate and crystallization mother liquor were obtained. Sodium dihydrogen phosphate was dried at 40°C and recorded as the second product. The crystallization mother liquor was returned to the first filtrate for recycling.

[0088] The first filter residue was added to a high-temperature atmosphere furnace, air was introduced, and the temperature was raised to 700°C. It was then calcined at this temperature for 4 hours. Water was then added and stirred until homogeneous. The mixture was filtered to obtain iron ore as the first product. The liquid obtained after filtration was designated as the third filtrate. Sodium sulfide, a reducing agent, was added to the third filtrate. After a complete reaction, it was filtered to obtain solid chromium sulfide (designated as the third product) and a phosphorus-containing filtrate (also known as the fourth filtrate). This filtrate was processed in the same way as the second filtrate. After evaporation, concentration, cooling, and crystallization, sodium dihydrogen phosphate (designated as the second product) was obtained.

[0089] In this embodiment, the composition of the extracted iron ore is similar to that of Example 3; the iron content in the sodium dihydrogen phosphate is less than 0.05%, and the chromium content is less than 0.001%, which meets the standard of "HG / T 2965-2009 Industrial Sodium Dihydrogen Phosphate".

[0090] Example 5

[0091] A chromium slag extraction process is performed according to the steps of Example 1, except that the alkaline leaching temperature is 60°C and the alkaline leaching time is 4 hours. The elemental composition of the obtained product is similar to that of Example 1.

[0092] Example 6

[0093] A chromium slag extraction process is performed according to the steps of Example 1, except that the alkaline leaching temperature is 90°C and the alkaline leaching time is 2 hours. The elemental composition of the obtained product is similar to that of Example 1.

[0094] Example 7

[0095] A chromium slag extraction process, following the steps of Example 1, differs from Example 1 only in that: the first filter residue is added to a high-temperature atmosphere furnace, air is introduced, the temperature is raised to 800°C, and then calcined at this temperature for 3 hours. The composition of the obtained iron ore product is shown in Table 5 below.

[0096] Table 5 Composition of Iron Ore Products

[0097] Element types iron phosphorus chromium nickel sulfur copper Zinc mass fraction % 66.81 0.011 0.011 1.597 0.052 0.001 0.001 Element types aluminum silicon lead arsenic cobalt manganese mass fraction % 0.001 0.481 0.000 0.000 0.000 0.004

[0098] Comparative Example 1

[0099] A chromium slag extraction process was performed according to the steps of Example 1, except that the first filter residue was added to a high-pressure reactor, oxygen was introduced at 0.6 MPa, the temperature was raised to 140°C, and the reaction was carried out at this temperature for 3 hours. The composition of the obtained iron ore product is shown in Table 6 below.

[0100] Table 6 Composition of Iron Ore Products

[0101] Element types iron phosphorus chromium nickel sulfur copper Zinc mass fraction % 53.99 0.61 0.536 1.344 0.017 0.004 0.002 Meta-type aluminum silicon lead arsenic cobalt manganese mass fraction % 0.001 0.478 0.000 0.000 0.000 0.002

[0102] Comparative Example 2

[0103] A chromium slag extraction process, following the steps of Example 1, differs from Example 1 only in that: the first filter residue is added to a high-pressure reactor, oxygen is introduced at 0.6 MPa, the temperature is raised to 200°C, and the reaction is carried out at this temperature for 3 hours. The composition of the obtained iron ore product is shown in Table 6 below:

[0104] Table 6 Composition of Iron Ore Products

[0105] Element types iron phosphorus chromium nickel sulfur copper Zinc mass fraction % 54.86 0.57 0.502 1.361 0.025 0.004 0.002 Meta-type aluminum silicon lead arsenic cobalt manganese mass fraction % 0.001 0.478 0.000 0.000 0.000 0.002

[0106] The comparison of the above embodiments and comparative examples further demonstrates that, using the extraction process described herein, through multiple alkaline leaching, solid-liquid separation, and pH adjustment, evaporation concentration, and cooling crystallization of the filtrate, phosphorus can be fully extracted from the chromium slag. Further high-temperature oxidation and water extraction of the filter residue can completely separate valuable elements (such as iron, phosphorus, nickel, and chromium) from the chromium slag. Iron and nickel can then be used in steelmaking, significantly improving resource utilization. This process can convert environmentally harmful chromium slag into phosphate, chromium hydroxide, and iron ore products, realizing the resource utilization of chromium slag and turning waste into treasure.

[0107] It also eliminates the need for adding soda ash and calcination at temperatures above 1000℃, thus reducing the cost of chromium slag resource conversion.

[0108] Even more advantageously, the phosphorus content in the iron ore obtained after high-temperature oxidation can be as low as 0.15 wt%, while the phosphorus and chromium contents in the iron ore in Comparative Examples 1 and 2 are both relatively high.

Claims

1. A chromium slag extraction process, characterized in that, Includes the following steps: S1 Single solid-liquid separation After alkali leaching, the chromium slag is separated into solid and liquid components to obtain the first filter residue and the first filtrate. The alkaline leaching solution used is an aqueous solution of alkali, and the pH of the alkaline leaching solution is 11-14. The alkaline immersion temperature is 60-90℃; the alkaline immersion time is 0.5-24h; S2 Secondary Solid-Liquid Separation The first filtrate obtained in step S1 is adjusted to pH 8-13, and after solid-liquid separation, a second filter residue and a second filtrate are obtained. The first filter residue obtained in step S1 is oxidized by calcination at 700-800℃, extracted with water, and the solid obtained by solid-liquid separation is denoted as the first product and the liquid is denoted as the third filtrate. S3 Three-stage solid-liquid separation After the second filter residue is washed with water, the solid-liquid separation is followed by alkaline leaching of the washing liquid, and the washing residue is converted into the first filter residue. After the second filtrate is heated and cooled to crystallize, the phosphate solid obtained by solid-liquid separation is recorded as the second product, and the resulting liquid is further processed in the same way as the first filtrate. After adding a reducing agent to the third filtrate and reacting, solid chromium hydroxide solid is obtained by solid-liquid separation and is recorded as the third product. The resulting filtrate is recorded as the fourth filtrate. The fourth filtrate is further processed according to the method of the second filtrate.

2. The chromium slag extraction process according to claim 1, characterized in that, The chromium slag contains ionic compounds, wherein the ionic compounds include: Cationic elements include chromium, iron, and nickel; The anion contains phosphorus, and the anion includes at least one of orthophosphate, hypophosphate, phosphite, metaphosphate, polyphosphate, and pyrophosphate.

3. The chromium slag extraction process according to claim 1, characterized in that, The alkali leaching solution used is an aqueous solution of alkali, and the alkali includes at least one of liquid ammonia, ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium phosphate, potassium carbonate, and potassium phosphate.

4. The chromium slag extraction process according to claim 1, characterized in that, satisfy: a. When the second product is a third-generation phosphate, in step S2, the pH of the first filtrate is adjusted to ≥11.5; b. When the second product is a second-generation phosphate or a first-generation phosphate, in step S2, 4 ≤ adjust the pH of the first filtrate to <11.

5.

5. The chromium slag extraction process according to claim 1, characterized in that, The calcination oxidation time in step S2 is 1-24 hours.

6. The chromium slag extraction process according to claim 1, characterized in that, The oxidant used in step S2 for combustion oxidation includes at least one gas selected from air, oxygen, and ozone.

7. The chromium slag extraction process according to claim 1, characterized in that, The crystallization process described in step S3 is as follows: within 48 hours, the temperature is raised to 40-140℃ for evaporation and concentration, and then cooled to 20-30℃ for crystallization and separation.

8. The chromium slag extraction process according to claim 1, characterized in that, The reducing agent mentioned in step S3 includes at least one of elemental sulfur and water-soluble sulfides.

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