Method for preparing high-purity chromium chloride through alkali circulation

Abstract

The invention discloses a method for preparing high-purity chromium chloride through alkali circulation, which comprises the following steps: mixing ferrochromium and an alkali solution for liquid-phase oxidation leaching, carrying out solid-liquid separation on a leaching solution to obtain a chromate solution and leaching residues, adding a certain amount of organic reducing agent into the leaching solution to reduce hexavalent chromium in the solution into trivalent chromium, and carrying out solid-liquid separation on the trivalent chromium to obtain the high-purity chromium chloride. And carrying out solid-liquid separation on the reduced slurry to obtain a filter cake and filtrate. And washing the reduced filter cake, and performing acid dissolution to obtain the high-purity chromium chloride. And adding a certain amount of calcium oxide into the reduced filtrate for causticization reaction, and returning the causticized solution to liquid-phase oxidation. According to the method, oxidation-reduction of ferrochrome is achieved under the liquid phase condition to prepare trivalent chromium, then high-purity chromium chloride is prepared through acid dissolution, only a very small amount of alkali needs to be supplemented in the whole process, aluminum-silicon impurities in the trivalent chromium can be effectively removed, and the method has the advantages of being simple in technological process, clean, environmentally friendly, low in production cost and the like.

Description

Technical Field

[0001] The invention belongs to the field of chromium salt production, and specifically relates to a method for preparing high-purity chromium chloride by alkali circulation. Background Art

[0002] CrCl3·6H2O is a commonly used raw material for the preparation of other inorganic and organic chromium compounds. It is often used as a raw material for the production of chromium compounds for medical treatment, food additives, and oil fields. It can be used to prepare catalysts, mordants, polymer adhesives, trivalent chromium electroplating, iron-chromium flow battery electrolytes and other products. In particular, with the rapid development of the energy storage industry in recent years, the demand for high-purity chromium chloride has continued to increase.

[0003] The production methods of chromium chloride include chromic anhydride ethanol reduction method, chlorination of carbon ferrochrome to produce chromium chloride, chlorination of chromium oxide green to produce chromium chloride and direct acid leaching method, among which the chlorination method can only produce anhydrous chromium chloride, and the direct hydrochloric acid acid leaching method has not yet been industrialized due to the difficulty of the impurity removal process. The most important production method is chromic anhydride ethanol reduction method. The production cost of raw material chromic anhydride is high, and chromic anhydride is prepared from sodium chromate by high-temperature roasting of chromium-containing raw materials, and further prepared by removing aluminum silicon impurities, acidification and other processes. The production process is long and energy consumption is high. A large amount of chromium-containing sodium hydrogen sulfate and chromium-containing waste residue will be generated during the production process, resulting in high chromium belt loss and serious environmental pollution. Chinese patent CN201310755600.4 uses hydrochloric acid to dissolve ferrochrome to prepare high-purity chromium chloride. The production process is complicated, and the impurity removal process requires the addition of compounds such as sodium fumer or sulfide, yellow blood salt or red blood salt, which is difficult to remove impurities. Chinese patent CN202010100978.0 adds desiliconizing agent and flocculant to remove impurities in chromium leaching solution, with a long production process and complicated operation. Chinese patent CN201410433325.9 uses sodium chromate aqueous solution to reduce chromium chloride, but does not explain the source of sodium chromate. Moreover, the reduction and acidification are always carried out in a chlorine-containing system, which leads to severe equipment corrosion. The high-value sodium in sodium chromate is not utilized and is discharged in the form of sodium chloride waste liquid.

[0004] Therefore, it is necessary to develop a process for directly preparing chromium chloride from chromium-containing resources by wet method, simplify the impurity removal process, improve the production environment, and increase resource utilization and economic benefits. Summary of the invention

[0005] Aiming at the problems of complicated impurity removal process, low utilization rate of alkali resources and serious environmental pollution in the existing chromium chloride production process, the present invention proposes a method for preparing high-purity chromium chloride by alkali circulation. The method realizes ferrochromium oxidation-reduction to prepare trivalent chromium under liquid phase conditions, and then prepares high-purity chromium chloride by acid dissolution. Only a very small amount of alkali needs to be added in the whole process, and aluminum and silicon impurities therein can be effectively removed. The method has the characteristics of simple process flow, clean and environmental protection, low production cost and the like.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing high-purity chromium chloride by alkali circulation comprises the following steps:

[0008] (1) mixing the ground ferrochrome powder with the alkaline solution returned from the causticizing process, and adding a certain amount of alkali to a high-pressure reactor, the amount of alkali added being 0.01-0.2 times the mass of the alkali metal in the solution, and continuously introducing an oxidant into the reactor for liquid-phase oxidation reaction, the liquid-phase oxidation reaction temperature being 260-350° C., the reaction time being 1-6 h, and the stirring speed being ≥600 rpm;

[0009] (2) After the reaction in step (1) is completed, the temperature is cooled to less than 100° C., the reactor is opened, and the reaction liquid is subjected to solid-liquid separation to obtain a chromate solution and iron slag;

[0010] (3) adding a certain amount of reducing agent to the chromate solution obtained in step (2), adding the solution to a high-pressure reactor, and performing a liquid-phase reduction reaction at 170-250° C. After the reaction is completed, the slurry is cooled to below 100° C., and the slurry is subjected to solid-liquid separation to obtain a trivalent chromium filter cake and a filtrate;

[0011] (4) adding calcium oxide in an amount of 0.1-0.55 times the amount of sodium in the solution to the filtrate obtained in step (3), stirring the reaction at a reaction temperature of 60-105° C. for a reaction time of 1-8 h, adding a flocculant after the reaction is completed to flocculate and settle for 1-8 h, and then filtering, calcining the filter cake and returning it for next use, and returning the filtrate to step (1) for continued use as a leaching agent;

[0012] (5) The filter cake obtained in step (3) is washed, dissolved in hydrochloric acid, and evaporated to obtain high-purity chromium chloride.

[0013] Preferably, the added alkali is one or a mixture of at least two of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate.

[0014] Preferably, the oxidant is oxygen or oxygen-enriched air.

[0015] Preferably, the reducing agent is one or at least two of glucose, sucrose, fructose or starch; or one or more of the derivatives of the above reducing agents.

[0016] The flocculant is one of anionic polyacrylamide, cationic polyacrylamide, nonionic polyacrylamide or hydrolyzed polyacrylamide.

[0017] The liquid phase oxidation reaction of the present invention can be carried out at a reaction pressure of 6-10 MPa, and the liquid phase reduction reaction can be carried out at a reaction pressure of 1-4 MPa.

[0018] The alkali liquor circulation of the present invention is realized by partial causticization, and ferrochrome is used as raw material, and chromate does not need to be purified and can be directly used in the production of high-purity chromium chloride. In the prior art, the reduction reaction occurs in the chlorine-containing system, the equipment is corroded greatly, there is no impurity removal step in the middle, and high-purity sodium chromate is required as raw material to produce high-purity chromium chloride.

[0019] The high-purity chromium chloride produced by the invention is high-purity CrCl3·6H2O, which is mainly used for preparing electrolyte of iron-chromium liquid flow battery.

[0020] The present invention aims at the problems in the existing chromium chloride production and proposes a method for preparing high-purity chromium chloride by alkali circulation using ferrochrome as raw material, which mainly has the following advantages:

[0021] (1) The oxidation and reduction of chromium are both carried out under liquid phase conditions, without high-temperature calcination process. The production process is simple, the process is short, the operability is strong, and the cost is low.

[0022] (2) The reduced filtrate is causticized and returned for use to avoid the loss of high-value alkali metal ions in the form of waste, which not only reduces production costs but also has good environmental benefits.

[0023] (3) The small amount of calcium remaining in the caustic solution is returned to the leaching process, which can cause the aluminum and silicon in the ferrochrome to react with the calcium, thereby removing it in the form of calcium aluminosilicate, avoiding the subsequent tedious impurity removal process.

[0024] (4) After the reduction filtrate is causticized, some carbonate and organic matter still remain in the solution, which can generate carbon dioxide in the liquid phase oxidation process, playing a good acidification role, avoiding the need for acidification when using sodium chromate as a raw material or the need for pH adjustment when using sodium dichromate as a raw material during liquid phase reduction.

[0025] The process of the invention not only has significant economic benefits, but also meets environmental protection requirements, can greatly improve the production environment and environmental protection problems of the chromium salt industry, and is a good method for producing high-purity chromium chloride. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a flow chart of the method for preparing high-purity chromium chloride by alkali circulation. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0028] Example 1

[0029] like Figure 1As shown, a method for preparing high-purity chromium chloride by alkali circulation comprises the following steps:

[0030] The ground ferrochrome powder is mixed with the alkaline solution returned from the causticizing process, and solid sodium hydroxide is added in an amount of 0.01 times the mass of the sodium substance in the solution, and the mixture is added to a high-pressure reactor. At the same time, oxygen is continuously introduced into the reactor for liquid-phase oxidation reaction, and the reaction temperature is 260°C, the reaction time is 1 hour, and the stirring speed is 600 rpm. After the oxidation reaction is completed, the temperature is cooled, the solid-liquid separation is performed, and a certain amount of starch is added to the obtained chromate solution as a reducing agent, and the mixture is added to the high-pressure reactor for liquid-phase reduction reaction at 170°C. After the reaction is completed, the slurry is cooled and separated to obtain a trivalent chromium filter cake and a filtrate. Calcium oxide is added to the reduced filtrate in an amount of 0.15 times the mass of the sodium substance in the solution, and the mixture is stirred and reacted at a reaction temperature of 60°C and a reaction time of 8 hours. After the reaction is completed, an anionic polyacrylamide flocculant is added to keep warm and flocculate for 1 hour, and then filtered. The filtered filter cake is calcined and returned for next use, and the filtrate is returned to the oxidation process for continued use. After the reduced filter cake is washed, it is dissolved in hydrochloric acid and evaporated and crystallized to prepare high-purity chromium chloride. The results showed that the liquid phase chromium oxide conversion rate was 92.53%, the liquid phase reduction conversion rate was 98.13%, the purity of chromium chloride was 99.28%, the aluminum content in chromium chloride was 3.1 μg / g, and the silicon content was 3.8 μg / g.

[0031] Example 2

[0032] like Figure 1 As shown, a method for preparing high-purity chromium chloride by alkali circulation comprises the following steps:

[0033] The ground ferrochrome powder is mixed with the alkaline solution returned from the causticizing process, and solid sodium hydroxide is added in an amount of 0.05 times the mass of the sodium substance in the solution, and the mixture is added to a high-pressure reactor. At the same time, oxygen is continuously introduced into the reactor for liquid-phase oxidation reaction. The reaction temperature is 280°C, the reaction time is 4 hours, and the stirring speed is 800 rpm. After the oxidation reaction is completed, the mixture is cooled and cooled, and the solid-liquid separation is performed. A certain amount of glucose is added to the obtained chromate solution as a reducing agent, and the mixture is added to the high-pressure reactor for liquid-phase reduction reaction at 200°C. After the reaction is completed, the slurry is cooled and separated to obtain a trivalent chromium filter cake and a filtrate. Calcium oxide is added to the reduced filtrate in an amount of 0.15 times the mass of the sodium substance in the solution, and the mixture is stirred and reacted at a reaction temperature of 80°C and a reaction time of 2 hours. After the reaction is completed, a cationic polyacrylamide flocculant is added to keep warm and flocculate for 3 hours, and then the mixture is filtered. After the filtered filter cake is calcined, it is returned for next use, and the filtrate is returned to the oxidation process for continued use. After the reduced filter cake is washed, it is dissolved in hydrochloric acid and evaporated and crystallized to prepare high-purity chromium chloride. The test showed that the liquid phase chromium oxide conversion rate was 98.16%, the liquid phase reduction conversion rate was 99.29%, the purity of chromium chloride was 99.51%, the aluminum content in chromium chloride was 2.3 μg / g, and the silicon content was 2.9 μg / g.

[0034] Example 3

[0035] like Figure 1 As shown, a method for preparing high-purity chromium chloride by alkali circulation comprises the following steps:

[0036] The ground ferrochrome powder is mixed with the alkaline solution returned from the causticizing process, and solid sodium carbonate is added in an amount of 0.10 times the mass of the sodium substance in the solution, and the mixture is added to a high-pressure reactor. At the same time, oxygen is continuously introduced into the reactor for liquid-phase oxidation reaction. The reaction temperature is 280°C, the reaction time is 6 hours, and the stirring speed is 900 rpm. After the oxidation reaction is completed, the mixture is cooled and cooled, and the solid-liquid separation is performed. A certain amount of starch is added to the obtained chromate solution as a reducing agent, and the mixture is added to the high-pressure reactor for liquid-phase reduction reaction at 220°C. After the reaction is completed, the slurry is cooled and separated to obtain a trivalent chromium filter cake and a filtrate. Calcium oxide is added to the reduced filtrate in an amount of 0.55 times the mass of the sodium substance in the solution, and the mixture is stirred and reacted at a reaction temperature of 80°C and a reaction time of 3 hours. After the reaction is completed, an anionic polyacrylamide flocculant is added to keep warm and flocculate for 3 hours, and then filtered. The filtered filter cake is calcined and returned for next use, and the filtrate is returned to the oxidation process for continued use. The reduced filter cake is washed, and then dissolved in hydrochloric acid and evaporated and crystallized to prepare high-purity chromium chloride. The test showed that the liquid phase chromium oxide conversion rate was 98.91%, the liquid phase reduction conversion rate was 99.85%, the purity of chromium chloride was 99.17%, the aluminum content in chromium chloride was 3.2 μg / g, and the silicon content was 3.0 μg / g.

[0037] Example 4

[0038] like Figure 1 As shown, a method for preparing high-purity chromium chloride by alkali circulation comprises the following steps:

[0039] The ground ferrochrome powder is mixed with the alkaline solution returned from the causticizing process, and solid potassium hydroxide is added in an amount of 0.2 times the mass of potassium in the solution, and the mixture is added to a high-pressure reactor. At the same time, oxygen is continuously introduced into the reactor for liquid-phase oxidation reaction. The reaction temperature is 300°C, the reaction time is 4 hours, and the stirring speed is 1000 rpm. After the oxidation reaction is completed, the mixture is cooled and cooled, and the solid-liquid separation is performed. A certain amount of starch is added to the obtained chromate solution as a reducing agent, and the mixture is added to the high-pressure reactor for liquid-phase reduction reaction at 250°C. After the reaction is completed, the slurry is cooled and separated to obtain a trivalent chromium filter cake and a filtrate. Calcium oxide is added to the reduced filtrate in an amount of 0.4 times the mass of potassium in the solution, and the mixture is stirred and reacted at a reaction temperature of 90°C and a reaction time of 4 hours. After the reaction is completed, a non-ionic polyacrylamide flocculant is added to keep warm and flocculate for 4 hours, and then filtered. The filtered filter cake is calcined and returned for next use, and the filtrate is returned to the oxidation process for continued use. The reduced filter cake is washed, and then dissolved in hydrochloric acid and evaporated and crystallized to obtain high-purity chromium chloride. The test showed that the liquid phase chromium oxide conversion rate was 99.29%, the liquid phase reduction conversion rate was 99.91%, the purity of chromium chloride was 99.29%, the aluminum content in chromium chloride was 2.2 μg / g, and the silicon content was 4.0 μg / g.

[0040] Example 5

[0041] like Figure 1 As shown, a method for preparing high-purity chromium chloride by alkali circulation comprises the following steps:

[0042] The ground ferrochrome powder is mixed with the alkaline solution returned from the causticizing process, and solid potassium bicarbonate is added in an amount 0.1 times the amount of potassium in the solution, and then added to a high-pressure reactor. At the same time, oxygen-rich gas with an oxygen content of 60% is continuously introduced into the reactor for liquid-phase oxidation reaction. The reaction temperature is 290°C, the reaction time is 5 hours, and the stirring speed is 700 rpm. After the oxidation reaction is completed, the temperature is cooled, the solid and the liquid are separated, and a certain amount of starch + glucose is added to the obtained chromate solution as a reducing agent, and then added to the high-pressure reactor. The reaction is continued at 24 The liquid phase reduction reaction is carried out at 0°C. After the reaction is completed, the slurry is cooled and separated to obtain a trivalent chromium filter cake and a filtrate; calcium oxide is added to the reduced filtrate according to 0.25 times the mass of potassium in the solution, and the reaction is stirred at a reaction temperature of 105°C and a reaction time of 2h. After the reaction is completed, a hydrolyzed polyacrylamide flocculant is added and flocculated for 2h before filtration. The filter cake is calcined and returned for the next use, and the filtrate is returned to the oxidation process for continued use; the reduced filter cake is washed, and then dissolved in hydrochloric acid and evaporated and crystallized to obtain high-purity chromium chloride. The liquid phase chromium oxide conversion rate is 95.08%, the liquid phase reduction conversion rate is 99.22%, the purity of chromium chloride is 99.17%, the aluminum content in chromium chloride is 2.7μg / g, and the silicon content is 3.2μg / g.

[0043] Example 6

[0044] like Figure 1 As shown, a method for preparing high-purity chromium chloride by alkali circulation comprises the following steps:

[0045] The ground ferrochrome powder is mixed with the alkaline solution returned from the causticizing process, and solid sodium bicarbonate is added in an amount of 0.1 times the mass of the sodium substance in the solution, and added to the autoclave, while oxygen is continuously introduced into the autoclave for liquid-phase oxidation reaction, the reaction temperature is 290°C, the reaction time is 4 hours, and the stirring speed is 1000 rpm; after the oxidation reaction is completed, the temperature is cooled, the solid-liquid separation is performed, a certain amount of starch + sucrose is added to the obtained chromate solution as a reducing agent, and the autoclave is added to perform liquid-phase reduction reaction at 230°C. After the reaction is completed, the slurry is cooled and separated to obtain a trivalent chromium filter cake and a filtrate; calcium oxide is added to the reduced filtrate in an amount of 0.5 times the mass of the sodium substance in the solution, and the reaction is stirred at a reaction temperature of 80°C and a reaction time of 4 hours. After the reaction is completed, an anionic polyacrylamide flocculant is added to keep warm and flocculate for 2 hours, and then filtered, the filtered filter cake is calcined and returned for next use, and the filtrate is returned to the oxidation process for continued use; the reduced filter cake is washed, and then dissolved in hydrochloric acid and evaporated and crystallized to prepare high-purity chromium chloride. The test showed that the liquid phase chromium oxide conversion rate was 98.81%, the liquid phase reduction conversion rate was 99.11%, the purity of chromium chloride was 99.42%, the aluminum content in chromium chloride was 1.6 μg / g, and the silicon content was 2.7 μg / g.

[0046] The process parameters (such as temperature, time, etc.) of the present invention can realize the method by taking upper and lower limits and interval values, and the embodiments are not listed one by one here.

[0047] Any contents not described in detail in the present invention can be based on the conventional technical knowledge in the art.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention and should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing high-purity chromium chloride by alkali circulation, the method comprising the following steps: (1) Mixing ferrochrome powder with an alkaline solution returned from a causticizing process in a high-pressure reactor, adding a certain amount of alkali to the high-pressure reactor, and introducing an oxidant into the reactor to carry out a liquid-phase oxidation reaction; (2) After the reaction in step (1) is completed, the temperature is cooled and the reaction liquid is subjected to solid-liquid separation to obtain a chromate solution and iron slag; (3) adding a certain amount of reducing agent to the chromate solution obtained in step (2), adding the solution to a high-pressure reactor to carry out a liquid-phase reduction reaction, and cooling and solid-liquid separation after the reaction to obtain a trivalent chromium filter cake and a filtrate; (4) adding a certain amount of calcium oxide to the filtrate obtained in step (3) and stirring the mixture for a period of time for causticization, filtering the mixture, and returning the filtrate to step (1) as a leaching agent; (5) The trivalent chromium filter cake obtained in step (3) is washed, acid-dissolved, and evaporated to prepare high-purity chromium chloride.

2. The method according to claim 1, characterized in that The alkali added in step (1) is one or a mixture of at least two of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate, and the amount of the added alkali is 0.01-0.2 times the amount of the alkali metal in the solution in terms of alkali metal.

3. The method according to claim 1, characterized in that The oxidant described in step (1) is oxygen or oxygen-enriched air, and the introduction method is continuous ventilation.

4. The method according to claim 1, characterized in that: The reaction temperature of the liquid phase oxidation reaction in step (1) is 260-350° C., and the reaction time is 1-6 h.

5. The method according to claim 1, characterized in that The reducing agent in step (3) is one or at least two of glucose, sucrose, fructose and starch.

6. The method according to claim 1, characterized in that The reduction reaction temperature of the liquid phase reduction reaction in step (3) is 170-250°C.

7. The method according to claim 1, characterized in that In step (4), the amount of calcium oxide added is 0.1-0.55 times the amount of sodium in the solution, the reaction temperature is 60-105° C., and the reaction time is 1-8 h.

8. The method according to claim 1, characterized in that After the calcium oxide reaction in step (4) is completed, a flocculant is added to flocculate for 1-8 hours.

9. The method according to claim 8, characterized in that The flocculant is one of anionic polyacrylamide, cationic polyacrylamide, nonionic polyacrylamide or hydrolyzed polyacrylamide.

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