Method for purifying chromium electrolyte to improve yield

Abstract

The invention relates to a method for purifying chromium electrolyte to improve yield, which comprises the following steps of: putting chromium electrolyte waste liquid to be purified and recycled into a stirring tank, starting a reaction tank for stirring, adding a sulfur-containing substance into the chromium electrolyte waste liquid, stirring and reacting at 40-60 DEG C, removing Fe and Cu metal ions in the waste liquid, carrying out solid-liquid separation, adding an oxidizing agent, and oxidizing part of trivalent chromium in the chromium electrolyte waste liquid into hexavalent chromium, and a strontium salt additive is added, the content of sulfate radicals is reduced, solid-liquid separation is conducted, purified chromium electrolyte is obtained, direct current is introduced, and electrolytic chromium is produced in an electro-deposition mode. The method has the advantages of short process flow, low energy consumption, strong operability, high production efficiency, high yield and short production period, the purified electrolyte returns to the system for reuse, the product yield is increased by more than 2%, no pollutant is discharged, and the production cost is effectively reduced.

Description

Technical Field

[0001] The invention discloses a method for purifying chromium electrolyte and improving yield, and relates to the technical field of electrodeposition. Background Art

[0002] Electrolytic chromium is an efficient electroplating technology. It is applied as a thin film to the surface of copper, steel, copper and other metals to make the surface wear-resistant, corrosion-resistant, beautiful and atmospheric. Chromium has good chemical stability and is widely used in the fields of chemical industry, refractory materials and metal materials. Chromium added to steel can also change the characteristics of steel and improve its toughness.

[0003] At present, the production methods of electrolytic chromium mainly include molten salt electrolysis and aqueous solution electrolysis. The common aqueous solution electrolysis is hexavalent chromium electrolysis and trivalent chromium electrolysis. After the electrolyte has been used for a period of time, the impurity concentration in the solution has been enriched, which makes the product quality index decline, and the product weight also decreases. In order to ensure the quality and weight of the product, the electrolyte can only be replaced partially or completely, which affects the production operation. The replaced electrolyte cannot be used anymore. Because it contains hexavalent chromium, it must be discharged after professional treatment, and the chromium loss is large. In order to avoid environmental pollution, reduce chromium loss, and reduce production costs, it is necessary to recycle the chromium in the replaced electrolyte. The common treatment and recovery method is to use cation exchange resin. The disadvantage is that the treatment is not thorough and the resin is easy to age, and the treatment cost is high. You can also use a reducing agent to reduce the hexavalent chromium in the electrolyte to trivalent chromium, and then adjust the solution to alkaline to recover the trivalent chromium in the form of chromium hydroxide precipitation. The disadvantage is that the yield is low cost and the COD in the treated solution is high and cannot be discharged directly. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for purifying chromium electrolyte and improving the yield in view of the deficiencies in the prior art. The method has the advantages of short process flow, low energy consumption, strong operability, high production efficiency, high yield and short production cycle. The purified electrolyte is returned to the system for repeated use, the product yield is increased by more than 2%, no pollutants are discharged, and the production cost is effectively reduced.

[0005] The technical solution of the present invention is: A method for purifying chromium electrolyte and improving yield comprises the following steps: (1) placing the chromium electrolysis waste liquid to be purified and recovered in a stirring tank, starting the reaction tank for stirring, adding sulfur-containing substances to the chromium electrolysis waste liquid, stirring and reacting at 40-60° C., removing Fe and Cu metal ions in the waste liquid, and performing solid-liquid separation to obtain the chromium electrolysis waste liquid from which metal ion impurities are removed; The sulfur-containing substance is metallic sulfur powder or hydrogen sulfide gas, and the amount of the sulfur-containing substance added is 0.3-0.6 times the total mass of the metal impurities Fe and Cu in the chromium electrolyte waste; (2) adding an oxidant to the chromium electrolysis waste liquid from which metal ion impurities have been removed in step (1) to oxidize part of the trivalent chromium in the chromium electrolysis waste liquid into hexavalent chromium; The oxidant is hydrogen peroxide or oxygen, and the amount of the oxidant added is 0.2-0.3 times the mass of the trivalent chromium to be oxidized to the hexavalent chromium in the electrolytic waste liquid; (3) adding a strontium salt additive to the chromium electrolysis waste liquid oxidized in step (2) to reduce the sulfate content by 55%-75%, so that the mass ratio of the residual sulfate in the chromium electrolysis waste liquid to the hexavalent chromium in the electrolyte is 1:40-1:60, and performing solid-liquid separation to obtain a purified chromium electrolyte; The strontium salt is strontium carbonate or strontium chloride, and the amount of strontium salt added is 1.4-2.2 times the mass of sulfate to be reduced in the chromium electrolysis waste liquid subjected to oxidation treatment in step (2). Barium salt has a good effect in controlling the reduction of sulfate. Barium salt is not used here because it will cause hexavalent chromium loss in the solution. (4) Direct current is passed through the purified chromium electrolyte to produce electrolytic chromium in the form of electrodeposition.

[0006] Furthermore, the hexavalent chromium content in the chromium electrolysis waste liquid is ≥70 g / L, the trivalent chromium content is ≥5 g / L, the sulfate content is ≥5 g / L, the iron content is ≥8 g / L, and the copper content is ≥0.5 g / L.

[0007] Furthermore, during the stirring in step (1), the stirring time is 3-4 hours.

[0008] Furthermore, during the stirring in step (2), the stirring time is 1-2 hours.

[0009] Furthermore, during the stirring in step (3), the stirring time is 4-6 hours. Furthermore, in step (2), 67%-70% of the trivalent chromium in the chromium electrolysis waste liquid is oxidized to hexavalent chromium.

[0010] Furthermore, in the purified chromium electrolyte, the hexavalent chromium content is ≥80 g / L, the trivalent chromium content is ≤2.0 g / L, the iron content is ≤0.5 g / L, and the copper content is ≤0.1 g / L.

[0011] Furthermore, the sulfate content in the purified chromium electrolyte is ≤2.5g / L.

[0012] Furthermore, the yield index of the electrolytic chromium product obtained by electroplating using the purified chromium electrolyte is increased by more than 2%.

[0013] Conventional addition of reagents to waste chromium electrolyte removes various impurities and achieves the purpose of purifying the electrolyte. Using the chromium electrolyte from which metal ion impurities have been removed for electrodeposition treatment can improve product quality indicators, but the use time will not be extended and regular discharge still occurs, which increases production costs and affects the production cycle.

[0014] The present invention effectively removes metal ion impurities by controlling the addition sequence, time and removal parameters of the impurity remover, reduces the concentration of sulfate ions and trivalent chromium ions, balances the ion concentration in the electrolyte, extends the service life of the electrolyte, reduces the amount of raw materials used, and does not require additional waste electrolyte treatment costs, thereby reducing production costs and improving product yields.

[0015] Its beneficial effects are: The process flow is short, the operability is strong, the reaction process is easy to control, the production efficiency is high, the electrolyte impurity purification rate is more than 95%, which effectively extends the electrolyte service life and enables the electrolyte to be effectively recycled for a long time, avoiding delays in the production cycle due to electrolyte replacement, reducing the cost of electrolyte environmental protection treatment, and reducing production costs. DETAILED DESCRIPTION

[0016] The components of the chromium electrolysis waste liquid used in Examples 1-3 of the present invention and Comparative Examples 1-3 are shown in the following table

[0017] Example 1 1) Remove metal ion impurities Take 1m 3 The chromium waste electrolyte is put into a reaction tank, the reaction tank is started to stir, 2.838 kg of metal sulfur powder is added to the reaction tank, the temperature is raised to 40° C., and after stirring and reacting at this temperature for 3 hours, stirring is stopped, and the chromium waste electrolyte is filtered and separated. The concentrations of Fe and Cu metal ions in the chromium waste electrolyte are 0.5 g / L and 0.1 g / L respectively, and a low-iron and low-copper chromium electrolytic waste liquid is obtained; 2) Oxidation reaction The low-iron and low-copper chromium electrolysis waste liquid of step (1) is returned to the reaction tank, the reaction tank is started for stirring, 551 mL of hydrogen peroxide is added to the reaction tank, the temperature is raised to 40° C., and the reaction is stirred at this temperature for 1 hour. After testing, the trivalent chromium concentration in the chromium waste electrolyte after the trivalent chromium oxidation reaction is 2.0 g / L, the hexavalent chromium concentration is 102.5 g / L, and 67% wt of the trivalent chromium in the chromium waste electrolyte is oxidized to hexavalent chromium; 3) Reduce the sulfate concentration: Add 5.023 kg of strontium carbonate to the reaction tank, stir and react at 40° C. for 4 hours, stop stirring and perform solid-liquid separation. The hexavalent chromium concentration in the chromium electrolyte after separation is 102.4 g / L, and the sulfate concentration is 2.56 g / L. The sulfate content in the chromium waste electrolyte is reduced by 57% wt to obtain a purified chromium electrolyte. The mass ratio of the remaining sulfate content in the solution to the hexavalent chromium content in the electrolyte is 1:40. The solid obtained is a strontium sulfate by-product, which is sold as a by-product after washing. 4) Electrolysis The purified electrolyte is placed in an electrolytic cell, and a current of 15000A is passed for electrolysis for 16 hours, and the Cr content in the product is 99.99%; the Fe element content is 0.003%, which is 25% lower than the previous product of 0.004%; the copper element content is 0.002%, which is 33% lower than the previous product of 0.003%; the strontium content in the product is 0.0001%; ​​the product yield is 95.5%, which is 2.0% higher than the previous yield of 93.5%. 5) Electrolyte life: The purified electrolyte can be recycled continuously without adverse effects. When the impurities in the liquid increase after 2 years of use, it can be purified again and continued to be used, avoiding delays in the production cycle due to electrolyte replacement. At the same time, it saves the cost of processing waste electrolyte and reduces the labor intensity of employees.

[0018] Comparative Example 1 1) Remove metal ion impurities Take 1m 3 The chromium waste electrolyte was put into a reaction tank, stirring was started, 2.838 kg of metallic sulfur powder was added to the reaction tank, and the temperature was raised to 40°C. After reacting for 3 hours, stirring was stopped and the reaction tank was filtered. After separation, the concentrations of iron and copper in the liquid were 0.5 g / L and 0.1 g / L respectively, which was a low-iron and low-copper chromium electrolytic waste liquid; 2) Oxidation reaction The low-iron and low-copper chromium electrolysis waste liquid of step (1) is returned to the reaction tank, 551 mL of hydrogen peroxide is added, and the mixture is stirred and reacted at 40° C. for 1 hour to oxidize 67% of the trivalent chromium to hexavalent chromium. After the reaction, the concentration of trivalent chromium in the solution is 2.0 g / L, and the concentration of hexavalent chromium is 102.5 g / L; 3) Reduce the sulfate concentration by adding 5.023 kg of barium carbonate to the reaction tank, stirring the reaction at 40°C for 4 hours, stopping stirring to perform solid-liquid separation. The hexavalent chromium concentration in the separated chromium electrolyte is 86.1 g / L, and the sulfate concentration is 2.28 g / L. The amount of sulfate in the solution is reduced by 62%, and the purified chromium electrolyte is obtained. The mass ratio of the remaining sulfate in the solution to the hexavalent chromium in the electrolyte is 1:40. The solid obtained is a barium sulfate by-product. During the purification process, the sulfate concentration decreases significantly, but the hexavalent chromium content in the electrolyte drops from 102.5 g / L to 86.1 g / L, and the hexavalent chromium loss is 16%; 4) Electrolysis The purified electrolyte was placed in an electrolytic cell and electrolyzed with a current of 15000A for 16 hours, and the Cr content in the product was 99.98%; the Fe content was 0.003%, which was 25% lower than the previous product of 0.004%; the copper content was 0.002%, which was 33% lower than the previous product of 0.003%; the barium content in the product was 0.0005%; the product yield was 90.2%, which was 3.3% lower than the previous product; 5) Electrolyte life The purified electrolyte can be recycled continuously, but this method is not advisable because the loss rate of hexavalent chromium in the electrolyte is large and the product yield is reduced, resulting in increased production costs.

[0019] Example 2 1) Remove metal ion impurities Take 1m 3 The chromium waste electrolyte is put into a reaction tank, the reaction tank is started for stirring, 5.676 kg of metallic sulfur powder is added to the reaction tank, the temperature is raised to 60° C., and after stirring and reacting at this temperature for 4 hours, stirring is stopped, and the chromium waste electrolyte is filtered and separated. The concentrations of Fe and Cu metal ions in the chromium waste electrolyte are 0.4 g / L and 0.09 g / L, respectively, to obtain a chromium electrolytic waste liquid with low iron and low copper; 2) Oxidation reaction The low-iron and low-copper chromium electrolysis waste liquid of step (1) is returned to the reaction tank, the reaction tank is started to stir, 865 mL of hydrogen peroxide is added to the reaction tank, and the reaction is stirred at 60° C. for 2 hours, and 70% wt of the trivalent chromium in the chromium waste electrolyte is oxidized to hexavalent chromium. After testing, the trivalent chromium concentration in the chromium waste electrolyte after the trivalent chromium oxidation reaction is 1.81 g / L, and the hexavalent chromium concentration is 102.69 g / L, and 70% wt of the trivalent chromium in the chromium waste electrolyte is oxidized to hexavalent chromium; 3) Reduce sulfate concentration Continue to add 7.894 kg of strontium carbonate to the reaction tank, stir and react at 60°C for 6 hours, stop stirring, and separate the solid and liquid. The hexavalent chromium concentration in the chromium electrolyte after separation is 102.6 g / L, and the sulfate concentration is 1.71 g / L. The sulfate content in the chromium waste electrolyte is reduced by 71%wt to obtain a purified chromium electrolyte. The mass ratio of the remaining sulfate content in the solution to the hexavalent chromium content in the electrolyte is 1:60. The solid obtained is a strontium sulfate by-product, which is sold as a by-product after washing. 4) Electrolysis The purified electrolyte was placed in an electrolytic cell and electrolyzed with a current of 23000A for 22 hours. The Cr content of the product was 99.99%; the Fe content was 0.003%, which was 25% lower than the previous product of 0.004%; the copper content was 0.0015%, which was 50% lower than the previous product of 0.003%; the strontium content of the product was 0.0001%; ​​the product yield was 96.1%, which was 2.6% higher than the previous yield of 93.5%; 5) Electrolyte life The purified electrolyte can be recycled continuously without adverse effects. When the impurities in the liquid increase after 2 years of use, it can be purified again in this way and continued to be used, avoiding delays in the production cycle due to electrolyte replacement. At the same time, it saves the cost of processing waste electrolyte and reduces the labor intensity of employees.

[0020] Comparative Example 2 1) Remove metal ion impurities Take 1m 3 The chromium waste electrolyte was put into a reaction tank, stirring was started, 5.676 kg of metallic sulfur powder was added to the reaction tank, and the temperature was raised to 60°C. After reacting for 4 hours, stirring was stopped and the reaction tank was filtered. After separation, the concentrations of iron and copper in the liquid were 0.4 g / L and 0.09 g / L respectively, which was a low-iron and low-copper chromium electrolytic waste liquid; 2) Oxidation reaction The low-iron and low-copper chromium electrolysis waste liquid of step (1) is returned to the reaction tank, 865 mL of hydrogen peroxide is added, and the mixture is stirred and reacted at 60° C. for 2 hours to oxidize 70% of the trivalent chromium to hexavalent chromium. After the reaction, the concentration of trivalent chromium in the solution is 1.81 g / L, and the concentration of hexavalent chromium is 102.69 g / L; 3) Reduce the sulfate concentration by adding 7.894 kg of barium carbonate to the reaction tank, stirring and reacting at 60°C for 6 hours, stopping stirring and performing solid-liquid separation. The hexavalent chromium concentration in the separated chromium electrolyte is 83.2 g / L, and the sulfate concentration is 2.12 g / L. The amount of sulfate in the solution is reduced by 65%, and the purified chromium electrolyte is obtained. The mass ratio of the remaining sulfate in the solution to the hexavalent chromium in the electrolyte is 1:39. The solid obtained is a barium sulfate by-product. During the purification process, the sulfate concentration decreases significantly, but the hexavalent chromium content in the electrolyte drops from 102.69 g / L to 83.2 g / L, and the hexavalent chromium loss is 19%; 4) Electrolysis The purified electrolyte was placed in an electrolytic cell and electrolyzed with a current of 23000A for 22 hours. The Cr content of the product was 99.96%, the Fe content was 0.003%, which was 25% lower than the previous product of 0.004%, the copper content was 0.0015%, which was 50% lower than the previous product of 0.003%, and the barium content of the product was 0.0010%. The product yield was 89.2%, which was 4.3% lower than the previous product. 5) Electrolyte life The purified electrolyte can be recycled continuously, but this method is not advisable because the loss rate of hexavalent chromium in the electrolyte is large and the product yield is reduced by 3.6%, resulting in increased production costs.

[0021] Example 3 1) Remove metal ion impurities Take 1m 3 The chromium waste electrolyte was placed in a reaction tank, the reaction tank was stirred, and 2.77 m 3 The hydrogen sulfide gas is heated to 50°C and stirred at this temperature for 3.5 hours, and then filtered. After separation, the concentrations of Fe and Cu metal ions in the chromium waste electrolyte are 0.45 g / L and 0.095 g / L respectively, and a low-iron and low-copper chromium electrolytic waste liquid is obtained; 2) Oxidation reaction The low-iron and low-copper chromium electrolysis waste liquid of step (1) is returned to the reaction tank, the reaction tank is stirred, and 0.72 m 3 Oxygen, heated to 40°C, and stirred at this temperature for 1.5 hours. After testing, the trivalent chromium concentration in the chromium waste electrolyte after the trivalent chromium oxidation reaction was 1.93g / L, the hexavalent chromium concentration was 102.6g / L, and 68%wt of the trivalent chromium in the chromium waste electrolyte was oxidized to hexavalent chromium; 3) Reduce the sulfate concentration by adding 6.997 kg of strontium carbonate to the reaction tank, stirring and reacting at 50° C. for 5 hours, stopping stirring and performing solid-liquid separation. The hexavalent chromium concentration in the chromium electrolyte after separation is 102.5 g / L, and the sulfate concentration is 2.11 g / L. The sulfate content in the chromium waste electrolyte is reduced by 65% ​​wt to obtain a purified chromium electrolyte. The mass ratio of the remaining sulfate content in the solution to the hexavalent chromium content in the electrolyte is 1:49. The obtained solid is a strontium sulfate by-product, which is sold as a by-product after washing. 4) Electrolysis The purified electrolyte was placed in an electrolytic cell and electrolyzed with a current of 20,000A for 19 hours, and the Cr content of the product was 99.99%; the Fe content was 0.003%, which was 25% lower than the previous product of 0.004%; the copper content was 0.0018%, which was 40% lower than the previous product of 0.003%; the strontium content of the product was 0.0001%; ​​the product yield was 95.7%, which was 2.2% higher than the previous yield of 93.5%; 5) Electrolyte life The purified electrolyte can be recycled continuously without adverse effects. When the impurities in the liquid increase after 2 years of use, it can be purified again in this way and continued to be used, avoiding delays in the production cycle due to electrolyte replacement. At the same time, it saves the cost of processing waste electrolyte and reduces the labor intensity of employees.

[0022] Comparative Example 3 1) Remove metal ion impurities Take 1m 3 The chromium waste electrolyte was placed in a reaction tank, stirring was started, and 2.77 m 3 The hydrogen sulfide gas was heated to 50°C, and the stirring was stopped after the reaction for 3.5 hours. The liquid was filtered and the concentrations of iron and copper in the separated liquid were 0.45 g / L and 0.095 g / L respectively, which was a chromium electrolysis waste liquid with low iron and copper content; 2) Oxidation reaction The low-iron and low-copper chromium electrolysis waste liquid from step (1) is returned to the reaction tank and introduced into 0.72m 3 Oxygen, stirred at 50°C for 1.5 hours, 67% of trivalent chromium was oxidized to hexavalent chromium. After the reaction, the concentration of trivalent chromium in the solution was 1.93 g / L, and the concentration of hexavalent chromium was 102.6 g / L; 3) Reduce the sulfate concentration by adding 3.887 kg of barium carbonate to the reaction tank, stirring the reaction at 50°C for 5 hours, stopping stirring to perform solid-liquid separation. The hexavalent chromium concentration in the separated chromium electrolyte is 84.9 g / L, and the sulfate concentration is 2.21 g / L. The amount of sulfate in the solution is reduced by 63%, and the purified chromium electrolyte is obtained. The mass ratio of the remaining sulfate in the solution to the hexavalent chromium in the electrolyte is 1:38. The solid obtained is a barium sulfate by-product. During the purification process, the sulfate concentration decreases significantly, but the hexavalent chromium content in the electrolyte drops from 102.6 g / L to 84.9 g / L, and the hexavalent chromium loss is 17%; 4) Electrolysis The purified electrolyte was placed in an electrolytic cell and electrolyzed with a current of 20,000A for 19 hours, and the Cr content of the product was 99.97%; the Fe content was 0.003%, which was 25% lower than the previous product of 0.004%; the copper content was 0.0018%, which was 40% lower than the previous product of 0.003%; the barium content of the product was 0.0007%; the product yield was 90.0%, which was 3.5% lower than the previous product; 5) Electrolyte life The purified electrolyte can be recycled continuously, but this method is not advisable because the loss rate of hexavalent chromium in the electrolyte is large and the product yield is reduced by 3.6%, resulting in increased production costs.

Claims

1. A method for purifying chromium electrolyte to improve yield, characterized in that: The following steps are involved: (1) placing the chromium electrolysis waste liquid to be purified and recovered in a stirring tank, starting the reaction tank for stirring, adding sulfur-containing substances to the chromium electrolysis waste liquid, stirring and reacting at 40-60° C., removing Fe and Cu metal ions in the waste liquid, and performing solid-liquid separation to obtain the chromium electrolysis waste liquid from which metal ion impurities are removed; The sulfur-containing substance is metallic sulfur powder or hydrogen sulfide gas, and the amount of the sulfur-containing substance added is 0.3-0.6 times the total mass of the metal impurities Fe and Cu in the chromium electrolyte waste; (2) adding an oxidant to the chromium electrolysis waste liquid from which metal ion impurities have been removed in step (1) to oxidize part of the trivalent chromium in the chromium electrolysis waste liquid into hexavalent chromium; The oxidant is hydrogen peroxide or oxygen, and the amount of the oxidant added is 0.2-0.3 times the mass of the trivalent chromium to be oxidized to the hexavalent chromium in the electrolytic waste liquid; (3) adding a strontium salt additive to the chromium electrolysis waste liquid oxidized in step (2) to reduce the sulfate content by 55%-75%, so that the mass ratio of the residual sulfate in the chromium electrolysis waste liquid to the hexavalent chromium in the electrolyte is 1:40-1:60, and performing solid-liquid separation to obtain a purified chromium electrolyte; The strontium salt is strontium carbonate or strontium chloride, and the amount of strontium salt added is 1.4-2.2 times the mass of sulfate to be reduced in the chromium electrolysis waste liquid subjected to oxidation treatment in step (2). Barium salt has a good effect in controlling the reduction of sulfate. Barium salt is not used here because it will cause hexavalent chromium loss in the solution. (4) Direct current is passed through the purified chromium electrolyte to produce electrolytic chromium in the form of electrodeposition.

2. The method for purifying chromium electrolyte and improving yield according to claim 1, characterized in that: The chromium electrolysis waste liquid has a hexavalent chromium content of ≥70 g / L, a trivalent chromium content of ≥5 g / L, a sulfate content of ≥5 g / L, an iron content of ≥8 g / L, and a copper content of ≥0.5 g / L.

3. The method for purifying chromium electrolyte to improve yield according to claim 1, characterized in that: During the stirring in step (1), the stirring time is 3-4 hours.

4. The method for purifying chromium electrolyte and improving yield according to claim 1, characterized in that: During the stirring in step (2), the stirring time is 1-2 hours.

5. The method for purifying chromium electrolyte and improving yield according to claim 1, characterized in that: During the stirring in step (3), the stirring time is 4-6 hours.

6. The method for purifying chromium electrolyte and improving yield according to claim 1, characterized in that: In step (2), 67%-70% of the trivalent chromium in the chromium electrolysis waste liquid is oxidized to hexavalent chromium.

7. The method for purifying chromium electrolyte and improving yield according to claim 1, characterized in that: The hexavalent chromium content in the purified chromium electrolyte is ≥80g / L, the trivalent chromium content is ≤2.0g / L, the iron content is ≤0.5g / L, and the copper content is ≤0.1g / L.

8. The method for purifying chromium electrolyte and improving yield according to claim 1, characterized in that: The sulfate content in the purified chromium electrolyte is ≤2.5g / L.

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