A method for preparing chromium trioxide powder using electroplating chromium wastewater as raw material

Abstract

The invention provides a method for preparing chromium trioxide powder using electroplating chromium wastewater as raw material, which belongs to the technical field of sewage treatment. The chromium-containing wastewater is first subjected to a first precipitation pretreatment to remove impurity metal ions in the wastewater. During the impurity removal process, an electrolytic oxidation method is used to oxidize Cr(OH)3 in the precipitate into CrO4. 2‑ Thereby further improving the recovery rate of chromium; CrO4 2‑ Through acid reduction, alkali is added to convert it into a high-purity Cr(OH)3 precipitate; the salt carried by the high-purity Cr(OH)3 precipitate is washed away and then modified by adding water and lauric acid, so that a layer of carbon chain is adsorbed on the outermost surface of the Cr(OH)3 grains to become hydrophobic. After modification, the Cr(OH)3 colloid is powdery, with low degree of agglomeration and low water content. The Cr2O3 powder obtained after calcination is pigment grade, without agglomeration, high purity, uniform particle size, and no additional crushing is required.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment, and in particular to a method for preparing chromium trioxide powder by taking chromium electroplating wastewater as raw material. Background Art

[0002] Chromium trioxide (Cr2O3), as a chemical raw material, plays a very important role in chromium salt chemical industry. Cr2O3 is green and crystalline, resistant to high temperature and corrosion, and exhibits good light resistance and chemical stability. Its product quality is mainly divided into two categories: industrial grade and pigment grade, and has different technical requirements in different application fields. Industrial grade Cr2O3 is mainly used in relatively low-end fields such as metallurgy and refractory materials, while pigment grade Cr2O3, also known as chromium oxide green, is a high-end product and is mostly used in coatings, inks and other fields.

[0003] At present, the domestic Cr2O3 is mainly produced by the thermal decomposition method of chromic anhydride (CrO3). Its preparation process is relatively complicated, the operating environment is harsh, and dust containing hexavalent chromium is discharged during the roasting process. This method is extremely harmful to the environment. The thermal decomposition method of sodium dichromate and ammonium sulfate is the main process for producing chromium oxide green abroad. This process produces a full range of products and does not produce harmful gases during the production process. However, the products prepared by this process have a high sulfur content, and the by-product sodium sulfate containing chromium is difficult to recycle and reuse. The Institute of Process Engineering of the Chinese Academy of Sciences has developed a method for preparing hydroxyl chromium oxide by low-temperature hydrogen reduction of potassium chromate, and then calcining and dehydrating the hydroxyl chromium oxide to obtain chromium oxide green. This method uses a hydrogen reduction process to eliminate impurity infection and the emission of waste gas and waste residue. At the same time, it has the ability to prepare a variety of chromium oxide greens, but this process has high requirements for equipment and hydrogen is a flammable and explosive gas, which is difficult to industrialize. Patent CN201811555377.8 mentions a chromium oxide and a preparation method thereof. This method uses a reducing gas to reduce a hexavalent chromium salt solution with seed crystals under hydrothermal conditions to obtain hydroxy chromium oxide. The hydroxy chromium oxide precipitate obtained by calcination, filtration and separation can obtain chromium oxide. This process has high requirements on equipment and is not easy to commercialize.

[0004] Chromium metal has good corrosion resistance, can maintain its gloss for a long time, good wear resistance, heat resistance, high hardness and other properties. Therefore, chromium metal is widely used in electroplating, such as hard chromium electroplating, decorative chromium electroplating, zinc chromium passivation, etc. In the electroplating process, due to the rinsing of plated parts, the scrapping of bath liquid, the replacement and cleaning of filter cloth filter element of plating liquid filter, etc., a certain amount of chromium-containing wastewater will be generated. The main pollutants in chromium-containing wastewater are Cr2O7 2- Cr 3+ 、Zn 2+ , Cu 2+ , Fe 3+ 、Ni 2+The conventional method for treating chromium water is reduction and flocculation. First, under acidic conditions, a reducing agent is added to convert Cr2O7 2- Reduction to Cr 3+ Then, alkali is added to adjust the pH value of the wastewater so that the metal ions are converted into corresponding hydroxide precipitation and removed. The chromium mud obtained by this method has complex components and low chromium content, which is not easy to reuse. Patent CN1373094A uses a solution containing lead ions to treat hexavalent chromium-containing wastewater and recover hexavalent chromium in the form of chrome yellow (PbCrO4), but it produces lead-containing wastewater, which needs further treatment.

[0005] From the above, it can be seen that pigment-grade chromium oxide has high requirements and is difficult to prepare, while chromium-containing wastewater contains a large amount of chromium resources, which have not been effectively utilized. Summary of the invention

[0006] In view of this, the object of the present invention is to provide a method for preparing chromium trioxide powder using electroplating chromium wastewater as raw material. The preparation method provided by the present invention uses electroplating chromium wastewater as raw material, effectively utilizes waste chromium resources, and the obtained chromium trioxide powder has excellent color, no agglomeration, high purity, uniform particle size, and meets the requirements of pigment-grade chromium oxide.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing chromium trioxide powder by using electroplating chromium wastewater as raw material, comprising the following steps:

[0009] 1) mixing the electrochromium plating wastewater with an alkali to perform a first precipitation reaction to obtain a first suspension;

[0010] 2) subjecting the first suspension in step 1) to direct current electrolytic oxidation and then first solid-liquid separation to obtain a sodium chromate solution and comprehensive sludge;

[0011] 3) mixing the sodium chromate solution in step 2) with an acid and a reducing agent, and performing an acidification reduction reaction to obtain an acidification reduction reaction solution;

[0012] 4) mixing the acidified reduction reaction solution in step 3) with a base to perform a second precipitation reaction to obtain a second suspension;

[0013] 5) subjecting the second suspension in step 4) to a second solid-liquid separation and water washing in sequence to obtain a chromium hydroxide mud cake;

[0014] 6) mixing the chromium hydroxide mud cake, water and lauric acid in step 5) and performing a neutralization reaction, and performing a third solid-liquid separation on the obtained reaction solution to obtain modified chromium hydroxide;

[0015] 7) calcining the modified chromium hydroxide in step 6) to obtain chromium trioxide powder;

[0016] The total chromium content of the electroplating chromium wastewater is 0.1-5 g / L. 3+ The concentration of is 0.01~1g / L, and the content of other impurity metal ions is 0.01~1g / L.

[0017] Preferably, the pH value of the first precipitation reaction in step 1) is 8.5 to 10.5.

[0018] Preferably, the current density of the electrolytic oxidation in step 2) is 50 to 500 A / m 2 The electrolytic oxidation time is Cr 3+ Oxidized to CrO4 2- 2 to 4 times the theoretical electrolysis time required.

[0019] Preferably, in step 3), the reducing agent is at least one of sodium sulfite, sodium bisulfite and sodium pyrosulfite.

[0020] Preferably, the pH value of the acidification reduction reaction in step 3) is 2-3, the time of the acidification reaction is 0.45-0.55 h, the ORP value of the acidification reaction liquid is controlled to be 230-270 mv, and the reaction time is controlled to be about 0.5 h.

[0021] Preferably, the pH value of the second precipitation reaction in step 4) is 9.5-10.5.

[0022] Preferably, in step 5), the water washing is performed until the conductivity of the obtained washing liquid is lower than 200 us / cm.

[0023] Preferably, in step 6), the weight ratio of the chromium hydroxide mud cake to lauric acid is 100:10-30; and the dosage ratio of the chromium hydroxide mud cake to water is 20-80 g:1000 mL.

[0024] Preferably, the neutralization reaction temperature in step 6) is 60-90° C. and the time is 2-4 hours.

[0025] Preferably, the calcination temperature in step 7) is 900-1300° C., and the calcination time is 2-5 hours.

[0026] Beneficial technical effect: The present invention provides a method for preparing chromium trioxide powder using electroplating chromium wastewater as raw material, firstly subjecting the chromium-containing wastewater to a first precipitation pretreatment to remove impurity metal ions in the wastewater, and in the impurity removal process, using an electrolytic oxidation method to oxidize Cr(OH)3 in the precipitate into CrO4 2- Thereby further improving the recovery rate of chromium; CrO4 2-Through acid reduction, alkali is added to convert it into a high-purity Cr(OH)3 precipitate; the salt carried by the high-purity Cr(OH)3 precipitate is washed away and then modified by adding water and lauric acid, so that a layer of carbon chain is adsorbed on the outermost surface of the Cr(OH)3 grains to become hydrophobic. After modification, the Cr(OH)3 colloid is powdery, with low degree of agglomeration and low water content. The Cr2O3 powder obtained after calcination is pigment grade, without agglomeration, high purity, uniform particle size, and no additional crushing is required. DETAILED DESCRIPTION

[0027] The present invention provides a method for preparing chromium trioxide powder by using electroplating chromium wastewater as raw material, comprising the following steps:

[0028] 1) mixing the electrochromium plating wastewater with an alkali to perform a first precipitation reaction to obtain a first suspension;

[0029] 2) subjecting the first suspension in step 1) to direct current electrolytic oxidation and then first solid-liquid separation to obtain a sodium chromate solution and comprehensive sludge;

[0030] 3) mixing the sodium chromate solution in step 2) with an acid and a reducing agent, and performing an acidification reduction reaction to obtain an acidification reduction reaction solution;

[0031] 4) mixing the acidified reduction reaction solution in step 3) with a base to perform a second precipitation reaction to obtain a second suspension;

[0032] 5) subjecting the second suspension in step 4) to a second solid-liquid separation and water washing in sequence to obtain a chromium hydroxide mud cake;

[0033] 6) mixing the chromium hydroxide mud cake, water and lauric acid in step 5) and performing a neutralization reaction, and performing a third solid-liquid separation on the obtained reaction solution to obtain modified chromium hydroxide;

[0034] 7) calcining the modified chromium hydroxide in step 6) to obtain chromium trioxide powder;

[0035] The total chromium content of the electroplating chromium wastewater is 0.1-5 g / L. 3+ The concentration of is 0.01~1g / L, and the content of other impurity metal ions is 0.01-1g / L.

[0036] The present invention mixes electrochromium plating wastewater with alkali to carry out a first precipitation reaction to obtain a first suspension.

[0037] In the present invention, the total chromium content in the chromium electroplating wastewater is preferably 0.1 to 5 g / L, more preferably 1 to 3 g / L; Cr 3+The concentration of is preferably 0.01 to 1 g / L, more preferably 0.5 to 0.8 g / L; the content of other impurity metal ions is preferably 0.01 to 1 g / L, more preferably 0.5 to 0.8 g / L. The other impurity ions of the present invention preferably include Zn 2+ , Cu 2+ , Fe 3+ and Ni 2+ At least one of .

[0038] In the present invention, the alkali is preferably sodium carbonate or sodium hydroxide. The present invention has no particular limitation on the amount of the alkali, and the pH value of the mixed solution of the electrochromium plating wastewater and the alkali can be adjusted to the pH value required for the first precipitation reaction. In the present invention, the pH value of the first precipitation reaction is preferably 8.5 to 10.5, more preferably 9 to 10. The present invention removes impurity metal ions in the wastewater by precipitation reaction between the electrochromium plating wastewater and the alkali.

[0039] After obtaining the first suspension, the present invention performs direct current electrolytic oxidation on the first suspension and then performs first solid-liquid separation to obtain a sodium chromate solution and comprehensive sludge.

[0040] In the present invention, the current density of the electrolytic oxidation is preferably 50 to 500 A / m 2 , more preferably 100 to 400 A / m 2 , the most preferred is 200~250A / m 2 The electrolytic oxidation time is preferably 2 to 4 times the theoretical electrolytic time; the theoretical electrolytic time is based on Cr 3+ Content and Cr 3+ The electrochemical equivalent of 0.67g / Ah is calculated, and the anode material of the electrolytic oxidation is preferably titanium-coated lead dioxide, titanium-coated ruthenium-iridium, titanium-coated tantalum-iridium or graphite; the cathode material of the electrolytic oxidation is preferably a stainless steel plate or a stainless steel mesh; when the cathode material is preferably a stainless steel mesh, the pore size of the stainless steel mesh is preferably 20 to 200 meshes, more preferably 50 to 150 meshes. The present invention does not specifically limit the area of ​​the cathode or anode, and it is appropriately adjusted according to the volume of the solution required for electrolysis.

[0041] The present invention oxidizes Cr(OH)3 in the precipitate into CrO4 by electrolytic oxidation. 2- Thereby further improving the chromium recovery rate without adding additional oxidant.

[0042] The method for solid-liquid separation in the present invention is preferably filtration. The present invention has no particular limitation on the specific method of filtration, and any method well known to those skilled in the art can be selected.

[0043] After obtaining the sodium chromate solution and the comprehensive sludge, the present invention mixes the sodium chromate solution with an acid and a reducing agent to carry out an acidification reduction reaction to obtain an acidification reduction reaction liquid.

[0044] In the present invention, the acid is preferably hydrochloric acid or sulfuric acid; the present invention has no special limitation on the amount of the acid used, and the pH value of the solution obtained by mixing the sodium chromate solution with the acid and the reducing agent can be adjusted to the pH value required for the acidification reduction reaction.

[0045] In the present invention, the reducing agent is preferably at least one of sodium sulfite, sodium bisulfite and sodium pyrosulfite; the amount of the reducing agent is preferably CrO4 2- Reduction to Cr 3+ 1-2 times of the theoretical amount.

[0046] In the present invention, the pH value of the acidification reduction reaction is preferably 2-3, more preferably 2.5; the reducing agent is added to control the ORP value of the acidification reaction liquid to 230-270 mv, preferably 240-260 mv, and most preferably 250-255 mv. The reaction time is controlled to be about 0.5 h.

[0047] The present invention converts CrO4 into 2- Reduction to Cr 3+ .

[0048] After obtaining the acidified reduction reaction solution, the present invention mixes the acidified reduction reaction solution with a base to perform a second precipitation reaction to obtain a second suspension.

[0049] In the present invention, the alkali is preferably sodium carbonate or sodium hydroxide; the pH value of the second precipitation reaction is preferably 9.5 to 10.5, more preferably 10. 3+ Converted into Cr(OH)3 precipitate.

[0050] After obtaining the second suspension, the present invention sequentially performs second solid-liquid separation and water washing on the second suspension to obtain a chromium hydroxide mud cake.

[0051] In the present invention, the second solid-liquid separation is preferably filter press separation. The present invention has no particular limitation on the specific method of filter press separation, and any method well known to those skilled in the art can be used.

[0052] The present invention has no particular limitation on the method of water washing, and any water washing method known to those skilled in the art can be used. The water washing of the present invention is preferably stopped when the conductivity of the obtained water washing liquid is less than 200 us / cm. The present invention removes the salt in the mud cake obtained by the second solid-liquid separation by water washing.

[0053] In the present invention, the filtrate obtained from the second solid-liquid separation and the washing liquid obtained from water washing are preferably introduced into a wastewater treatment system.

[0054] After the chromium hydroxide mud cake is obtained, the present invention modifies the chromium hydroxide mud cake after mixing with water and lauric acid, and performs a third solid-liquid separation on the obtained reaction liquid to obtain modified chromium hydroxide.

[0055] In the present invention, the weight ratio of the chromium hydroxide mud cake to lauric acid is preferably 100:10-30, more preferably 100:15-25, and most preferably 100:20; the dosage ratio of the chromium hydroxide mud cake to water is preferably 20-80 g:1000 mL, more preferably 30-70 g:1000 mL, and most preferably 40-50 g:1000 mL.

[0056] In the present invention, the modification temperature is preferably 60 to 90° C., more preferably 70 to 80° C.; the modification time is preferably 2 to 4 hours, more preferably 3 to 3.5 hours.

[0057] In the present invention, preferably, the chromium hydroxide mud cake is first mixed with water and then stirred to form a slurry, and the obtained slurry is heated to the modification temperature and then lauric acid is added for modification. In the present invention, lauric acid is used to modify the chromium hydroxide so that a layer of carbon chains is adsorbed on the outermost surface of the chromium hydroxide crystal grains to become hydrophobic. The modified chromium hydroxide colloid is powdery, has a low degree of agglomeration, and has a low water content.

[0058] The third solid-liquid separation method of the present invention is preferably filter press separation. The present invention has no particular limitation on the specific method of filter press separation, and any method well known to those skilled in the art can be used.

[0059] In the present invention, the filtrate obtained from the third solid-liquid separation preferably enters a wastewater treatment system.

[0060] After obtaining the modified chromium hydroxide, the present invention calcines the modified chromium hydroxide to obtain chromium trioxide powder.

[0061] In the present invention, the temperature of the modified chromium hydroxide is preferably 900-1300°C, more preferably 1000-1200°C, and most preferably 1100-1150°C; the calcination time is preferably 2-5h, more preferably 3-4h. The present invention converts the modified chromium hydroxide into chromium trioxide by calcination. During the calcination process, the chromium hydroxide undergoes thermal decomposition, chemically bound water and volatile impurities (CO2, NO2, NH3, etc.) are removed, and finally chromium oxide powder is obtained.

[0062] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0063] Example 1

[0064] 1) Take 5L of hard chrome electroplating rinse water (total chromium 2.4g / L, Cr 3+0.4g / L, the rest of the metal ion concentrations are 0.1-0.5g / L) were placed in a beaker, and 100g / L of soda ash solution was added to adjust the solution pH to 9.5, so that the metal ions (Zn 2+ Cr 3+ , Cu 2+ , Fe 3+ 、Ni 2+ etc.) to form a corresponding hydroxide precipitate to obtain a first suspension;

[0065] 2) The first suspension obtained in step 1) is placed in an electrolytic cell, the anode is made of titanium-based lead dioxide, the cathode is made of stainless steel plate, and the effective area of ​​the cathode and cathode is 300 cm 2 , direct current electrolysis, the current density is set to 220A / m 2 The DC electrolysis time was set to twice the theoretical electrolysis time, i.e. 0.9 h. After the electrolysis was completed, the suspension was filtered and separated to obtain Na2CrO4 solution and comprehensive sludge.

[0066] 3) First, add hydrochloric acid to the Na2CrO4 solution to control the pH value at 2-2.5, add sodium bisulfite to control the ORP value at 230-270mv, and carry out acidification reduction reaction. The reaction time is about 0.5h. When the ORP value is basically stable, it means that the reduction has been complete;

[0067] 4) After the reduction is completed, add liquid alkali to control the pH value between 9.5-10.5. 3+ Neutralization converts into Cr(OH)3 precipitation to obtain a second suspension;

[0068] 5) filtering and separating the second suspension, washing the salt in the Cr(OH)3 mud cake with medium water after the filtration, and stopping washing when the conductivity of the washing water is lower than 200us / cm to obtain the Cr(OH)3 mud cake;

[0069] 6) Add a certain amount of pure water to the Cr(OH)3 mud cake and stir to form a slurry, and control the solid concentration in the slurry to 40g / L. Heat the slurry to adjust the temperature to 75°C, add lauric acid at 25% of the weight of Cr(OH)3, stir for 2h, and filter again to obtain modified Cr(OH)3;

[0070] 7) The modified Cr(OH)3 is sent to a calcining furnace for calcination. The calcination temperature is controlled at 1200°C and the calcination time is set to 3 hours. After the calcination, the Cr2O3 powder obtained is of pigment grade, dark green in color, uniform in particle size, and has a purity of 99.5 (based on Cr2O3).

[0071] Example 1 Calculation method of theoretical electrolysis time of trivalent chromium oxidation:

[0072] Trivalent chromium mass M(Cr 3+ )=0.4*5=2g,Cr 3+ The electrochemical equivalent is 0.67g / Ah, the current I=220*0.03=6.6A, then the theoretical electrolysis time T=2 / 0.67 / 6.6=0.45h.

[0073] Example 2

[0074] 1) Take 10L of zinc-plated hexavalent chromium passivation waste bath solution (total chromium 1.5g / L, Cr 3+ 0.7g / L, the concentration of other metal ions is 0.1-0.3g / L) in a reaction barrel, add 20% liquid alkali to adjust the solution pH to 10.0, so that the metal ions (Zn 2 + Cr 3+ , Cu 2+ , Fe 3+ 、Ni 2+ etc.) to form a corresponding hydroxide precipitate to obtain a first suspension;

[0075] 2) The first suspension obtained in step 1) is placed in an electrolytic cell, the anode is made of titanium-coated ruthenium-iridium material, the cathode is made of a stainless steel mesh, the aperture of the stainless steel mesh is 100 mesh, and the effective area of ​​the cathode and cathode is 500 cm 2 , direct current electrolysis, the current density is set to 200A / m 2 The DC electrolysis time is set to 2.5 times the theoretical electrolysis time, i.e. 2.7h. After the electrolysis is completed, the suspension is filtered and separated to obtain Na2CrO4 solution and comprehensive sludge;

[0076] 3) First, add sulfuric acid to the Na2CrO4 solution, control the pH value at 2-2.5, add sodium metabisulfite to control the ORP value at 230-270mv, and carry out acidification reduction reaction. The reaction time is about 0.5h. When the ORP value is basically stable, it means that the reduction has been complete;

[0077] 4) After the reduction is completed, add liquid alkali to control the pH value between 9.5-10.5. 3+ Neutralization converts into Cr(OH)3 precipitation to obtain a second suspension;

[0078] 5) The second suspension is subjected to filter press separation. After the filter press is completed, the salt contained in the obtained mud cake is washed away with medium water. When the conductivity of the washing water is lower than 200 us / cm, the washing is stopped to obtain a Cr(OH)3 mud cake;

[0079] 6) Add a certain amount of pure water to the Cr(OH)3 mud cake, stir to form a slurry, control the solid concentration in the slurry to 60g / L, heat the slurry to adjust the temperature to 55°C, add lauric acid at 20% of the weight of Cr(OH)3, stir for 4h, and then filter and separate again to obtain modified Cr(OH)3;

[0080] 7) The modified Cr(OH)3 is sent to a calcining furnace for calcination. The calcination temperature is controlled at 1300°C and the calcination time is set to 4 hours. After the calcination, the Cr2O3 powder obtained is of pigment grade, dark green in color, uniform in particle size, and has a purity of 99.6 (based on Cr2O3).

[0081] Example 3

[0082] 1) Take 50L of electroplating decorative chrome rinsing water (total chromium 1.7g / L, Cr 3+ 0.8g / L, the concentration of other metal ions is 0.05-0.5g / L) in a reaction barrel, and 30% liquid alkali is added to adjust the pH of the solution to 9.5, so that the metal ions (Zn 2+ Cr 3 + , Cu 2+ , Fe 3+ 、Ni 2+ etc.) to form a corresponding hydroxide precipitate to obtain a first suspension;

[0083] 2) The suspension obtained in step 1) is placed in an electrolytic cell, the anode is made of graphite, the cathode is made of a stainless steel mesh, the pore size of the stainless steel mesh is 150 mesh, and the effective area of ​​the cathode and cathode is 5000 cm 2 , direct current electrolysis, the current density is set to 180A / m 2 The DC electrolysis time was set to 3 times of the theoretical electrolysis time, i.e. 2.06 h. After the electrolysis was completed, the suspension was filtered and separated to obtain Na2CrO4 solution and comprehensive sludge.

[0084] 3) Add sulfuric acid to the Na2CrO4 solution, control the pH value at 2-2.5, add sodium sulfite to control the ORP value at 230-270mv, and carry out acidification reduction reaction for about 0.5h. When the ORP value is basically stable, it means that the reduction has been complete;

[0085] 4) After the reduction is completed, add liquid alkali to control the pH value between 9.5-10.5. 3+ Neutralization converts into Cr(OH)3 precipitation to obtain a second suspension;

[0086] 5) After the reaction is completed, the Cr(OH)3 suspension is filtered and separated. After the filtration is completed, the salt entrained in the obtained mud cake is washed away with tap water. When the conductivity of the washing water is lower than 200us / cm, the washing is stopped to obtain the Cr(OH)3 mud cake;

[0087] 6) Add a certain amount of pure water to the Cr(OH)3 mud cake, stir to form a slurry, control the solid concentration in the slurry to 45g / L, heat the slurry to adjust the temperature to 50°C, add lauric acid at 30% of the weight of Cr(OH)3, stir for 3.5h, and then filter and separate again to obtain modified Cr(OH)3;

[0088] 7) The modified Cr(OH)3 is sent to a calcining furnace for calcination. The calcination temperature is controlled at 1250°C and the calcination time is set to 3.5 hours. After the calcination, the Cr2O3 powder obtained is pigment grade, dark green in color, with uniform particle size and a purity of 99.3 (calculated as Cr2O3).

[0089] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing chromium trioxide powder using electroplating chromium wastewater as raw material, characterized in that: The following steps are involved: 1) mixing the electrochromium plating wastewater with an alkali to perform a first precipitation reaction to obtain a first suspension; 2) subjecting the first suspension in step 1) to direct current electrolytic oxidation and then first solid-liquid separation to obtain a sodium chromate solution and comprehensive sludge; 3) mixing the sodium chromate solution in step 2) with an acid and a reducing agent, and performing an acidification reduction reaction to obtain an acidification reduction reaction solution; 4) mixing the acidified reduction reaction solution in step 3) with a base to perform a second precipitation reaction to obtain a second suspension; 5) subjecting the second suspension in step 4) to a second solid-liquid separation and water washing in sequence to obtain a chromium hydroxide mud cake; 6) mixing the chromium hydroxide mud cake, water and lauric acid in step 5) and performing a neutralization reaction, and performing a third solid-liquid separation on the obtained reaction solution to obtain modified chromium hydroxide; 7) calcining the modified chromium hydroxide in step 6) to obtain chromium trioxide powder; The total chromium content of the electroplating chromium wastewater is 0.1-5 g / L. 3+ The concentration of is 0.01~1g / L, and the content of other impurity metal ions is 0.01~1g / L; The pH value of the first precipitation reaction in step 1) is 8.5 to 10.5; The current density of the electrolytic oxidation in step 2) is 50 to 500 A / m 2 The electrolytic oxidation time is Cr 3+ Oxidized to CrO4 2- 2 to 4 times the theoretical electrolysis time required.

2. The method according to claim 1, characterized in that In the step 3), the reducing agent is at least one of sodium sulfite, sodium bisulfite and sodium pyrosulfite.

3. The method according to claim 1, characterized in that The pH value of the acidification reduction reaction in step 3) is 2-3, the time of the acidification reaction is 0.45-0.55 h, and the ORP value of the acidification reaction liquid is 230-270 mv.

4. The method according to claim 1, characterized in that: The pH value of the second precipitation reaction in step 4) is 9.5-10.

5.

5. The method according to claim 1, characterized in that In the step 5), the water washing is performed until the conductivity of the obtained water washing liquid is lower than 200 us / cm.

6. The method according to claim 1, characterized in that In the step 6), the weight ratio of the chromium hydroxide mud cake to lauric acid is 100:10-30; the dosage ratio of the chromium hydroxide mud cake to water is 20-80 g:1000 mL.

7. The method according to claim 1, characterized in that The neutralization reaction temperature in step 6) is 60-90° C. and the reaction time is 2-4 hours.

8. The method according to claim 1, characterized in that: In the step 7), the calcination temperature is 900-1300° C., and the calcination time is 2-5 hours.