阅读说明：本技术 废铬催化剂制备醋酸铬的工艺 (Process for preparing chromium acetate by using waste chromium catalyst ) 是由 徐友良 周保学 李金花 于 2021-10-08 设计创作，主要内容包括：一种废铬催化剂制备醋酸铬的工艺,通过将废铬催化剂进行三段热解处理后溶于硝酸溶液中,通过向滤液中缓慢加入NaOH,滤液pH由2.0调至4.0,反应形成氢氧化铬沉淀,再将其溶解在冰醋酸中制备得到的醋酸铬溶液,经喷雾干燥,得固体无水醋酸铬。采用废铬催化剂热解、酸溶、铬沉淀分离制备醋酸易溶的Cr(OH)-(3),然后制备醋酸铬溶液,经喷雾干燥获得无水醋酸铬；本发明通过系统性地解决热解过程的完全氧化工艺、酸溶过程的有机物去除,醋酸易溶的Cr(OH)-(3)制备,防止水解的微酸性气态和固态干燥环境的构建等,实现了废铬催化剂向醋酸铬的转化；得到的醋酸铬,回收率高、产品纯度高。(A process for preparing chromium acetate from waste chromium catalyst includes such steps as three-stage pyrolysis of waste chromium catalyst, dissolving in nitric acid solution, slowly adding NaOH to filtrate, regulating pH value of filtrate to 4.0 from 2.0, reaction to obtain chromium hydroxide deposit, dissolving in glacial acetic acid to obtain chromium acetate solution, and spray drying. Preparing readily soluble Cr (OH) acetic acid by adopting waste chromium catalyst pyrolysis, acid dissolution and chromium precipitation separation 3 Then preparing a chromium acetate solution, and spray-drying to obtain anhydrous chromium acetate; the invention systematically solves the problems of complete oxidation process in the pyrolysis process, organic matter removal in the acid dissolution process and soluble Cr (OH) in acetic acid 3 Preparation, construction of a slightly acidic gaseous and solid drying environment for preventing hydrolysis and the like, and conversion of the waste chromium catalyst to chromium acetate is realized; the obtained chromium acetate has high recovery rate and high product purity.)

1. A process for preparing chromium acetate from waste chromium catalyst is characterized in that the waste chromium catalyst is subjected to three-stage pyrolysis treatment and then dissolved in nitric acid solution, NaOH is slowly added into filtrate, the pH value of the filtrate is adjusted from 2.0 to 4.0, chromium hydroxide precipitate is formed through reaction, the chromium hydroxide precipitate is dissolved in glacial acetic acid to prepare chromium acetate solution, and solid anhydrous chromium acetate is obtained through spray drying.

2. The process for preparing chromium acetate from the waste chromium catalyst as claimed in claim 1, wherein the three-stage pyrolysis treatment comprises: air flow rate of 3.0m³Min, the heating rate is 30 ℃/min; the first-stage pyrolysis temperature is 150-180 ℃, and the heat preservation time is 45-60 min; the second-stage pyrolysis temperature is 450-500 ℃, and the heat preservation time is 60-90 min; the third-stage pyrolysis temperature is 650-700 ℃, and the heat preservation time is 90-120 min.

3. The process for preparing chromium acetate from waste chromium catalyst as claimed in claim 1, wherein the slow addition is: the adding amount and the adding speed of NaOH are controlled according to the pH rising rate of 0.25-0.40 delta pH/h per hour, and the adding time of NaOH is 5-8 h.

4. The process for preparing chromium acetate from waste chromium catalyst as claimed in claim 1 or 3, wherein the slow addition is carried out by diluting the filtrate to Cr content³⁺The amount is 1-3%.

5. The process for preparing chromium acetate from the spent chromium catalyst as claimed in claim 1 or 3, wherein the addition is carried out slowly while stirring at a rate of 10 rpm.

6. The process for preparing chromium acetate from the waste chromium catalyst as claimed in any one of claims 1 to 5, which comprises the following steps:

step 1) pyrolysis of waste chromium catalyst: putting the waste chromium catalyst into a pyrolysis furnace, and adopting a three-stage pyrolysis process, wherein the air flow is 3.0m³Min, the heating rate is 30 ℃/min; the first-stage pyrolysis temperature is 150-180 ℃, and the heat preservation time is 45-60 min; the second-stage pyrolysis temperature is 450-500 ℃, and the heat preservation time is 60-90 min; the third-stage pyrolysis temperature is 650-700 ℃, and the heat preservation time is 90-120 min, so that chromium ash A is obtained;

step 2) chromium ash dissolution and organic matter removal: dissolving the chromium ash A obtained in the step 1) in a nitric acid solution, controlling the dissolving pH value to be 1.0-2.0, controlling the dissolving temperature to be 70-85 ℃, stirring and reacting for 5-8 hours, oxidizing and damaging residual trace organic components in the fly ash by nitric acid, and then slowly adjusting the pH value to 2.0; filtering to obtain filtrate B containing trivalent chromium and other metal ion impurities;

step 3) preparation of chromium hydroxide precipitate and separation of impurity ions: diluting the filtrate B obtained in the step 2) to Cr content³⁺Adding 1-3% of NaOH solution, increasing the pH from 2.0 to the final pH of 4.0, stirring at the speed of 10 r/min, and slowly and uniformly adding NaOH; the adding amount and speed of NaOH are controlled according to the rate of pH rise per hour of 0.25-0.40 delta pH/h, the adding time of NaOH is 5-8 h, chromium hydroxide precipitate is finally formed, and the precipitate is washed and filter-pressed to obtain chromium hydroxide precipitate D with uniformly dispersed particles, good crystallinity, low impurity content and readily soluble acetic acid;

step 4) dissolution of the chromium hydroxide precipitate: according to the weight ratio of chromium hydroxide: dissolving the chromium hydroxide precipitate D obtained in the step 3) in glacial acetic acid at a molar ratio of 1: 3.05-3.10, controlling the dissolving temperature at 70 ℃, stirring for 3-5 h, and cooling to room temperature after dissolving to obtain a trivalent chromium acetic acid solution E;

step 5) preparation of solid chromium acetate: and 4) carrying out spray drying on the chromium acetate solution E obtained in the step 4) to obtain solid anhydrous chromium acetate.

Technical Field

The invention relates to a technology in the field of heavy metal waste recovery, in particular to a process for preparing chromium acetate by using a waste chromium catalyst.

Background

The waste chromium catalyst is mainly from organic synthesis industry, and the activity of the catalyst is gradually reduced along with the prolonging of the service time in the organic synthesis reaction process. The reason for deactivation is primarily carbon deposits on the catalyst surface causing it to coke and become obsolete. The waste chromium catalyst is prepared into a chemical product with wide application and high added value, so that the problem of environmental pollution can be solved, and the resource utilization level of the chromium-containing sludge can be improved. The incineration of the waste chromium catalyst for landfill is the main disposal mode in the prior art, thereby causing serious waste of chromium resources. In the prior art, the waste chromium catalyst is converted into chromium oxide by oxygen-enriched calcination, then the chromium oxide is converted into a dichromate by an excessive concentrated alkali solution, and then the chromium oxide is converted into hydrated chromium oxide by a dichromate hydrochloric acid.

Chromium acetate Cr (CH)₃CO₂)₃Belongs to a chemical product with high added value, and is an important organic synthesis catalyst, mordant and electroplating additive. The prior art is carried out by using chromium trichloride hexahydrate CrCl₃·(H₂O)₆The method is characterized in that dilute ammonia water is added into a dilute solution to prepare chromium hydroxide, then the chromium hydroxide reacts with excessive acetic acid to prepare chromium acetate through concentration and crystallization, but the chromium acetate obtained by the method is hydrated chromium acetate instead of anhydrous chromium acetate, and meanwhile, the prepared chromium hydroxide is easy to crosslink and agglomerate to form part of chromium hydroxide which is difficult to dissolve in acetic acid, and the problems of nitrogen-containing wastewater and ammonia pollution are caused. In the prior art, a chromic anhydride solution is reduced by a reducing agent in an acetic acid environment for preparation, but a product is chromium acetate containing crystal water; the chromium acetate has high solubility and is easy to form crystal water, and the spray drying causes the strong hydrolysis of the chromium acetate, so that the high-purity anhydrous chromium acetate is difficult to obtain. In addition, the chromium acetate is prepared by using the waste chromium catalyst as a starting material, and the impurities of the chromium acetate can further influence the production of the chromium acetateThe purity of the product.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a process for preparing chromium acetate by using a waste chromium catalyst, which adopts pyrolysis, acid dissolution and chromium precipitation separation of the waste chromium catalyst to prepare Cr (OH) with easily soluble acetic acid₃Then preparing a chromium acetate solution, and spray-drying to obtain anhydrous chromium acetate; by systematically solving the complete oxidation process of the pyrolysis process, the removal of organic matters in the acid dissolution process, and the Cr (OH) which is easy to dissolve in acetic acid₃Preparation, construction of a slightly acidic gaseous and solid drying environment for preventing hydrolysis and the like, and conversion of the waste chromium catalyst to chromium acetate is realized; the obtained chromium acetate has high recovery rate and high product purity.

The invention is realized by the following technical scheme:

the invention relates to a process for preparing chromium acetate from a waste chromium catalyst, which comprises the steps of dissolving the waste chromium catalyst in a nitric acid solution after three-section pyrolysis treatment, slowly adding NaOH into filtrate, adjusting the pH value of the filtrate from 2.0 to 4.0, reacting to form chromium hydroxide precipitate, dissolving the chromium hydroxide precipitate in glacial acetic acid to prepare a chromium acetate solution, and performing spray drying to obtain solid anhydrous chromium acetate.

The three-stage pyrolysis treatment refers to: air flow rate of 3.0m³Min, the heating rate is 30 ℃/min; the first-stage pyrolysis temperature is 150-180 ℃, and the heat preservation time is 45-60 min; the second-stage pyrolysis temperature is 450-500 ℃, and the heat preservation time is 60-90 min; the third-stage pyrolysis temperature is 650-700 ℃, and the heat preservation time is 90-120 min.

The slow addition is as follows: the adding amount and the adding speed of NaOH are controlled according to the pH rising rate of 0.25-0.40 delta pH/h per hour, and the adding time of NaOH is 5-8 h.

The slow addition is preferably carried out by diluting the filtrate to Cr content³⁺The amount is 1-3%.

The slow addition is preferably carried out while stirring at a rate of 10 revolutions per minute.

The process specifically comprises the following steps:

step 1) pyrolysis of waste chromium catalyst: putting the waste chromium catalyst into a pyrolysis furnace, and adopting three-section pyrolysis processProcess, wherein the air flow is 3.0m³Min, the heating rate is 30 ℃/min; the first-stage pyrolysis temperature is 150-180 ℃, and the heat preservation time is 45-60 min; the second-stage pyrolysis temperature is 450-500 ℃, and the heat preservation time is 60-90 min; the third-stage pyrolysis temperature is 650-700 ℃, and the heat preservation time is 90-120 min, so that chromium ash A is obtained;

step 2) chromium ash dissolution and organic matter removal: dissolving the chromium ash A obtained in the step 1) in a nitric acid solution, controlling the dissolving pH value to be 1.0-2.0, controlling the dissolving temperature to be 70-85 ℃, stirring and reacting for 5-8 hours, oxidizing and damaging residual trace organic components in the fly ash by nitric acid, and then slowly adjusting the pH value to 2.0; filtering to obtain filtrate B containing trivalent chromium and other metal ion impurities;

step 3) preparation of chromium hydroxide precipitate and separation of impurity ions: diluting the filtrate B obtained in the step 2) to Cr content³⁺Adding 1-3% of NaOH solution, increasing the pH from 2.0 to the final pH of 4.0, stirring at the speed of 10 r/min, and slowly and uniformly adding NaOH; the adding amount and speed of NaOH are controlled according to the rate of pH rise per hour of 0.25-0.40 delta pH/h, the adding time of NaOH is 5-8 h, chromium hydroxide precipitate is finally formed, and the precipitate is washed and filter-pressed to obtain chromium hydroxide precipitate D with uniformly dispersed particles, good crystallinity, low impurity content and readily soluble acetic acid;

step 4) dissolution of the chromium hydroxide precipitate: according to the weight ratio of chromium hydroxide: dissolving the chromium hydroxide precipitate D obtained in the step 3) in glacial acetic acid at a molar ratio of 1: 3.05-3.10, controlling the dissolving temperature at 70 ℃, stirring for 3-5 h, and cooling to room temperature after dissolving to obtain a trivalent chromium acetic acid solution E;

step 5) preparation of solid chromium acetate: and 4) carrying out spray drying on the chromium acetate solution E obtained in the step 4) to obtain solid anhydrous chromium acetate.

Drawings

FIG. 1 is a schematic view of the preparation process of the present invention.

Detailed Description

Example 1

The embodiment specifically comprises the following steps:

step 1) pyrolysis of waste chromium catalyst: putting the waste chromium catalyst into a pyrolysis furnace, and adopting three-section pyrolysis processProcess, wherein the air flow is 3.0m³Min, the heating rate is 30 ℃/min; the first stage pyrolysis temperature is 160 ℃, and the heat preservation time is 50 min; the second-stage pyrolysis temperature is 480 ℃, and the heat preservation time is 890 min; the third-stage pyrolysis temperature is 680 ℃, and the heat preservation time is 100min, so that chromium ash A is obtained;

step 2) chromium ash dissolution and organic matter removal: dissolving the chromium ash A obtained in the step 1) in a nitric acid solution, controlling the dissolving pH value to be 1.5, controlling the dissolving temperature to be 80 ℃, stirring and reacting for 6 hours, oxidizing and damaging residual trace organic components in the fly ash by nitric acid, and then slowly adjusting the pH value to be 2.0; filtering to obtain filtrate B containing trivalent chromium and other metal ion impurities;

step 3) preparation of chromium hydroxide precipitate and separation of impurity ions: diluting the filtrate B obtained in the step 2) to Cr content³⁺Adding NaOH solution, increasing the pH from 2.0 to the final pH of 4.0, stirring at 10 r/min, and slowly and uniformly adding NaOH; the adding amount and the adding speed of NaOH are controlled according to the pH rising rate of 0.30 delta pH/h per hour, the adding time of the NaOH is about 7h, chromium hydroxide precipitate is finally formed, and the precipitate is washed and filter-pressed to obtain chromium hydroxide precipitate D with uniformly dispersed particles, good crystallinity, low impurity content, acid solubility and good solubility;

step 4) dissolution of the chromium hydroxide precipitate: according to the weight ratio of chromium hydroxide: dissolving the chromium hydroxide precipitate D obtained in the step 3) in glacial acetic acid at the molar ratio of 1:3.08, controlling the dissolving temperature at 70 ℃, stirring for 4 hours, and cooling to room temperature after dissolving to obtain a trivalent chromium acetic acid solution E;

step 5) preparation of solid chromium acetate: and 4) carrying out spray drying on the chromium acetate solution E obtained in the step 4) to obtain solid anhydrous chromium acetate.

The purity of the chromium acetate prepared in this example>99 percent and the recovery rate of the waste chromium catalyst chromium is 98 percent; the chromium ash A has complete appearance pyrolysis without carbon deposition and is dissolved in HNO₃TOC 150ppm and TOC 5ppm of the filtrate B were measured.

Comparative example 1

The comparative example differs from example 1 in that:

pyrolysis of the waste chromium catalyst: the waste chromium catalyst is put into a pyrolysis furnace, and the air flow is 3.0m³Min, the heating rate is 30 ℃/min; heating to 680 ℃, and keeping the temperature for 100min to obtain chromium ash A;

in the example, the chromium ash A has the appearance of incomplete pyrolysis and carbon deposition and is dissolved in HNO₃TOC 1400ppm was measured.

Comparative example 2

The comparative example differs from example 1 in that:

pyrolysis of the waste chromium catalyst: putting the waste chromium catalyst into a pyrolysis furnace, and adopting a two-stage pyrolysis process, wherein the air flow is 3.0m³Min, the heating rate is 30 ℃/min; the first stage pyrolysis temperature is 160 ℃, and the heat preservation time is 50 min; the second-stage pyrolysis temperature is 680 ℃, and the heat preservation time is 100min, so that chromium ash A is obtained;

in the example, the chromium ash A has the appearance of incomplete pyrolysis and carbon deposition and is dissolved in HNO₃TOC 1100ppm was measured.

Comparative example 3

The comparative example differs from example 1 in that:

step 1) pyrolysis of waste chromium catalyst: putting the waste chromium catalyst into a pyrolysis furnace, and adopting a three-stage pyrolysis process, wherein the air flow is 3.0m³Min, the heating rate is 30 ℃/min; the first stage pyrolysis temperature is 160 ℃, and the heat preservation time is 50 min; the second-stage pyrolysis temperature is 480 ℃, and the heat preservation time is 890 min; the third-stage pyrolysis temperature is 680 ℃, and the heat preservation time is 100min, so that chromium ash A is obtained;

step 2) chromium ash dissolution and organic matter removal: dissolving the chromium ash A obtained in the step 1) in an HCl solution, controlling the pH value of the solution to be 1.5, dissolving the chromium ash A at room temperature, and then slowly adjusting the pH value to be 2.0; obtaining filtrate B;

filtrate B of this example had a TOC of 103 ppm.

Comparative example 4

The comparative example specifically included the following steps:

step 1) pyrolysis of waste chromium catalyst: putting the waste chromium catalyst into a pyrolysis furnace, and adopting a three-stage pyrolysis process, wherein the air flow is 3.0m³Min, the heating rate is 30 ℃/min; the first stage pyrolysis temperature is 160 ℃, and the heat preservation time is 50 min; the second-stage pyrolysis temperature is 480 ℃, and the heat preservation time is 890 min; the third stage pyrolysis temperature is 680 ℃,keeping the temperature for 100min to obtain chromium ash A;

step 2) chromium ash dissolution and organic matter removal: dissolving the chromium ash A obtained in the step 1) in a nitric acid solution, controlling the dissolving pH value to be 1.5, controlling the dissolving temperature to be 80 ℃, stirring and reacting for 6 hours, oxidizing and damaging residual trace organic components in the fly ash by nitric acid, and then slowly adjusting the pH value to be 2.0; filtering to obtain filtrate B containing trivalent chromium and other metal ion impurities;

step 3) preparation of chromium hydroxide precipitate and separation of impurity ions: diluting the filtrate B obtained in the step 2) to Cr content³⁺Adding 20% NaOH solution to a pH value of 4, stirring and reacting for 0.5h to form chromium hydroxide precipitate, washing and filter-pressing to obtain chromium hydroxide precipitate D;

step 4) dissolution of the chromium hydroxide precipitate: according to the weight ratio of chromium hydroxide: and (3) reacting the chromium hydroxide precipitate D obtained in the step 3) with glacial acetic acid at the molar ratio of 1:3.08, stirring and dissolving for 4 hours at room temperature, and filtering to obtain a trivalent chromium acetic acid solution E and an undissolved chromium hydroxide precipitate.

The dissolution rate of the chromium hydroxide precipitate D in the comparative example was 35%.

Comparative example 5

Step 1), step 2), and step 3) of this comparative example were the same as in example 1;

step 4) dissolution of the chromium hydroxide precipitate: according to the weight ratio of chromium hydroxide: dissolving the chromium hydroxide precipitate D obtained in the step 3) in glacial acetic acid at the molar ratio of 1:3, controlling the dissolving temperature at 70 ℃, stirring for 4 hours, and cooling to room temperature after dissolving to obtain a trivalent chromium acetic acid solution E;

step 5) preparation of solid chromium acetate: and 4) carrying out spray drying on the chromium acetate solution E obtained in the step 4) to obtain solid anhydrous chromium acetate.

The purity of the chromium acetate prepared in this comparative example was > 85%.

Example 2

The embodiment specifically comprises the following steps:

step 1) pyrolysis of waste chromium catalyst: putting the waste chromium catalyst into a pyrolysis furnace, and adopting a three-stage pyrolysis process, wherein the air flow is 3.0m³Min, the heating rate is 30 ℃/min; first stageThe pyrolysis temperature is 150 ℃, and the heat preservation time is 60 min; the second-stage pyrolysis temperature is 450 ℃, and the heat preservation time is 90 min; the third-stage pyrolysis temperature is 650 ℃, and the heat preservation time is 120min, so that chromium ash A is obtained;

step 2) chromium ash dissolution and organic matter removal: dissolving the chromium ash A obtained in the step 1) in a nitric acid solution, controlling the dissolving pH value to be 1.0, controlling the dissolving temperature to be 85 ℃, stirring and reacting for 5 hours, oxidizing and damaging residual trace organic components in the fly ash by nitric acid, and then slowly adjusting the pH value to be 2.0; filtering to obtain filtrate B containing trivalent chromium and other metal ion impurities;

step 3) preparation of chromium hydroxide precipitate and separation of impurity ions: diluting the filtrate B obtained in the step 2) to Cr content³⁺Adding NaOH solution, increasing the pH from 2.0 to the final pH of 4.0, stirring at a speed of 10 r/min, and slowly and uniformly adding NaOH; the adding amount and the adding speed of NaOH are controlled according to the pH rising rate of 0.25 delta pH/h per hour, the adding time of NaOH is 8 hours, chromium hydroxide precipitate is finally formed, and the precipitate is washed and filter-pressed to obtain chromium hydroxide precipitate D with uniformly dispersed particles, good crystallinity, low impurity content, acid solubility and good solubility;

step 4) dissolution of the chromium hydroxide precipitate: according to the weight ratio of chromium hydroxide: dissolving the chromium hydroxide precipitate D obtained in the step 3) in glacial acetic acid at the molar ratio of 1:3.05, controlling the dissolving temperature at 70 ℃, stirring for 5 hours, and cooling to room temperature after dissolution to obtain a trivalent chromium acetic acid solution E;

step 5) preparation of solid chromium acetate: and 4) carrying out spray drying on the chromium acetate solution E obtained in the step 4) to obtain solid anhydrous chromium acetate.

The purity of the chromium acetate prepared by the embodiment is 98.5%, and the recovery rate of the waste chromium catalyst chromium is 96%.

Example 3

The embodiment specifically comprises the following steps:

step 1) pyrolysis of waste chromium catalyst: putting the waste chromium catalyst into a pyrolysis furnace, and adopting a three-stage pyrolysis process, wherein the air flow is 3.0m³Min, the heating rate is 30 ℃/min; the first stage pyrolysis temperature is 180 ℃, and the heat preservation time is 45 min; the second stage pyrolysis temperature is 500 ℃, and the heat preservation time is 60 min; the third stage pyrolysis temperature is 700 ℃, and the temperature is keptKeeping for 90min to obtain chromium ash A;

step 2) chromium ash dissolution and organic matter removal: dissolving the chromium ash A obtained in the step 1) in a nitric acid solution, controlling the dissolving pH value to be 2.0, controlling the dissolving temperature to be 70 ℃, stirring and reacting for 8 hours, and oxidizing and damaging residual trace organic components in the fly ash by nitric acid; filtering to obtain filtrate B containing trivalent chromium and other metal ion impurities;

step 3) preparation of chromium hydroxide precipitate and separation of impurity ions: diluting the filtrate B obtained in the step 2) to Cr content³⁺Adding NaOH solution, increasing the pH from 2.0 to the final pH of 4.0, stirring at 10 r/min, and slowly and uniformly adding NaOH; the adding amount and the adding speed of NaOH are controlled according to the pH rising rate of 0.40 delta pH/h per hour, the adding time of NaOH is 5h, chromium hydroxide precipitate is finally formed, and the precipitate is washed and filter-pressed to obtain chromium hydroxide precipitate D with uniformly dispersed particles, good crystallinity, low impurity content, acid solubility and good solubility;

step 4) dissolution of the chromium hydroxide precipitate: according to the weight ratio of chromium hydroxide: dissolving the chromium hydroxide precipitate D obtained in the step 3) in glacial acetic acid at the molar ratio of 1:3.10, controlling the dissolving temperature at 70 ℃, stirring for 3 hours, and cooling to room temperature after dissolving to obtain a trivalent chromium acetic acid solution E;

step 5) preparation of solid chromium acetate: and 4) carrying out spray drying on the chromium acetate solution E obtained in the step 4) to obtain solid anhydrous chromium acetate.

The purity of the chromium hydroxide prepared by the embodiment is 99 percent, and the recovery rate of the chromium of the waste chromium catalyst is 98 percent.

Compared with the prior art, the invention designs a three-stage oxygen-enriched environment pyrolysis process aiming at the characteristics that the waste chromium catalyst mainly comprises an organic chromium complex structure, organic matters and organic solvents containing carbon deposition pollution and the like, wherein the volatile organic matters and organic solvents in the catalyst are removed in the first stage, the chromium complex structure is destroyed in the second stage, and the carbon deposition and the organic matters are oxidized in the third stage, so that the problems of incomplete oxidation, local carbonization and difficult oxidation of carbon deposition of the chromium catalyst caused by one-time heating pyrolysis are solved, and the obtained chromium ash is thoroughly oxidized and has few residues. The invention further utilizes nitric acid to dissolve chromium ash, and controls the dissolution reaction temperatureAnd the temperature is 70-85 ℃ and the reaction lasts for 5-8 hours, so that trace organic impurities in the chromium ash can be effectively eliminated and reduced, and the purity of subsequent chromium hydroxide is improved. In the acetic acid dissolution of the chromium hydroxide precipitate, according to the weight ratio of chromium hydroxide: the theoretical molar ratio of the glacial acetic acid is 1:3, and the actual molar ratio is 1: 3.05-3.10, namely the glacial acetic acid is slightly excessive; the slightly excessive glacial acetic acid mainly provides slightly acidic gaseous and solid environments for the spray drying process in the step 5), and prevents the chromium acetate from being hydrolyzed in the high-temperature drying process. The excessive amount of glacial acetic acid has a decisive role in controlling the high-temperature hydrolysis of the chromium acetate, too little glacial acetic acid cannot play a role in inhibiting the hydrolysis, and too high glacial acetic acid can cause the waste of the acetic acid and the corrosion to drying equipment. According to the invention, the low heavy metal ion concentration and the low alkali concentration are adopted, the precipitation pH is controlled to be always within the range of 2-4, the increase change of the pH is further controlled by controlling the addition amount and the speed of NaOH according to the metal ion concentration and the reaction process of each stage, the chromium hydroxide precipitate is prepared according to the long-time and slow pH increase process, the pH fluctuation is small, the reaction is slow and mild, the crystallization time is long, the wide pH change range, the overhigh local concentration, the uneven distribution and the local severe pH change of a precipitator in the reverse process in the prior art are effectively controlled, particularly the pH change in the later reaction stage is severe, and the alkali concentration and the Cr concentration are controlled³⁺Concentration mismatch, causing interparticle aggregation, cross-linking, aging and Cr³⁺With Fe³⁺、Ni²⁺、Cu²⁺The problems of low purity, large particles, difficult dissolution of weak acid and the like of chromium hydroxide precipitate caused by coprecipitation; despite the use of low Cr concentration³⁺Reacting with low-concentration alkali solution or mixing alkali solution with Cr³⁺Simultaneously adding into water is beneficial to reducing the cross-linking and aggregation of chromium hydroxide precipitate, but the Cr with too low concentration³⁺And alkali liquor consumes a large amount of water, and the problems of cross-linking and aggregation caused by uneven concentration distribution in the reaction process or the later stage of the reaction still cannot be solved; and the ammonia (amine) precipitator is adopted, so that the problem of ammonia nitrogen sewage discharge is caused. The method adopts the chromium hydroxide prepared by the waste catalyst with fine granularity, uniform dispersion, high purity and good acid solubility as the raw material to prepare the chromium acetate, and has high purity and high recovery rate of chromium.

The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.