Sodium thiosulfate wastewater and chromium-containing wastewater resource comprehensive utilization technology

Abstract

The invention discloses a comprehensive utilization technology of sodium thiosulfate wastewater and chromium-containing wastewater resources, which comprises the following steps: uniformly mixing sodium thiosulfate wastewater and hexavalent chromium wastewater in proportion, adding sulfuric acid to adjust the pH value, heating to a certain temperature through steam, and keeping the temperature for reduction reaction; adding caustic soda flakes into the completely reacted materials to adjust the pH value, then stirring and precipitating, and carrying out heat preservation for curing reaction; and carrying out plate-frame pressure filtration on the completely cured material, and washing to obtain a chromium hydroxide product, wherein the hexavalent chromium in the filtered water reaches the specified index. The method has the beneficial effects that the comprehensive value cost of two kinds of wastewater is fully utilized, comprehensive utilization of resources is realized, and the treatment cost is greatly reduced; the generated chromium hydroxide is used for calcining to produce 99% metallurgical grade chromium oxide green products, so that chromium resources in the wastewater are completely recovered and productized; a dispersing agent is added in the precipitation process, microwave and ultrasonic dispersion treatment is carried out at the same time to prevent precipitation from gathering, a calcined product is ground, and the nanoscale chromium oxide green is obtained.

Description

Technical Field

[0001] The invention belongs to the field of chromium salts, and specifically relates to a comprehensive utilization technology of sodium thiosulfate wastewater and chromium-containing wastewater resources. Background Art

[0002] At present, chromium-containing wastewater mainly comes from metal electroplating industry, steel manufacturing industry and other metal processing enterprises. Domestic metallurgy and chemical industry discharge about 200,000 to 300,000 tons of chromium slag every year. The harmful components in chromium slag are mainly hexavalent chromium ions such as soluble sodium chromate and acid-soluble calcium chromate. These hexavalent chromium and its loss and diffusion constitute pollution hazards to the ecological environment. The second is the strong alkalinity of chromium slag. When chromium slag is stored in the open air, after long-term rain, a large amount of hexavalent chromium ions will be dissolved, lost and infiltrated into the surface with rainwater, thereby polluting groundwater, rivers and lakes, and then endangering farmland, aquatic products and human health.

[0003] Wastewater containing sodium thiosulfate and wastewater containing hexavalent chromium are treated separately, which has the problems of high cost of auxiliary materials, high labor cost, and complicated process. For example, patent CN104386850A discloses a method for simultaneously removing hexavalent chromium and cyanide from electroplating wastewater, which uses traditional sodium pyrosulfite to treat hexavalent chromium wastewater, which is costly; another example is patent CN106477766A discloses a method for treating electroplating chromium-containing wastewater, which uses sodium thiosulfate to treat hexavalent chromium wastewater, but needs to add other auxiliary materials such as ascorbic acid, oxalic acid and glucose, and the process is complicated.

[0004] In order to improve the above problems, according to the physical and chemical properties of the two wastewaters, in theory, we can make full use of the properties of sodium thiosulfate in reducing hexavalent chromium under acidic conditions for combined treatment, realize comprehensive utilization of resources and reduce treatment costs. Summary of the invention

[0005] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0006] In order to achieve these purposes and other advantages according to the present invention, a technology for comprehensive utilization of sodium thiosulfate wastewater and chromium-containing wastewater resources is provided, characterized in that it comprises the following steps:

[0007] Step 1: Mix the sodium thiosulfate wastewater and the chromium-containing wastewater in a uniform ratio, add sulfuric acid to adjust the pH, and then heat them to a certain temperature by steam, and then keep them warm for reduction reaction;

[0008] Step 2: adding caustic soda to the reacted material to adjust the pH, stirring and precipitating, and keeping warm for aging reaction;

[0009] Step 3: The fully matured material is filtered through a plate and frame filter press and washed with hot water until the hexavalent chromium in the filtered water reaches the specified index to obtain a chromium hydroxide product, and the chromium hydroxide is calcined at high temperature to obtain chromium oxide green.

[0010] Preferably, in the step 1, the mixing ratio of the sodium thiosulfate wastewater and the chromium-containing wastewater is: sodium thiosulfate and hexavalent chromium are measured in a mass ratio of 1 to 3:1, and sulfuric acid is added to adjust the pH to 1.0 to 4.0.

[0011] Preferably, in the step 1, the temperature for the reduction reaction is 60 to 100° C., and the reduction reaction is performed for 1 to 8 hours.

[0012] Preferably, in the step 2, caustic soda flakes are added to adjust the pH to 6.0-9.0, the stirring speed is 30-100 r / min, and the stirring time is 1-8 h.

[0013] Preferably, in the step 2, the temperature of the heat preservation and aging reaction is 60-100° C., and the aging time is 1-8 hours.

[0014] Preferably, in step three, the calcination conditions are: an oxygen atmosphere with a concentration of 2 to 10 vol%, a calcination temperature of 900 to 1300° C., and a calcination time of 6 to 24 hours.

[0015] Preferably, after the reduction reaction in step 1 is completed, the reaction product is further treated by first adding a dispersant thereto, stirring evenly, then adding caustic soda to adjust the pH, then microwave treatment, then ultrasonic dispersion, then heat preservation and aging reaction, and then step 3 after aging is completed.

[0016] Preferably, the dispersant is one or more of isopropanol, ethylene glycol, ethylene glycol methyl ether, triethylene glycol divinyl ether or dodecylphenol polyoxyethylene ether.

[0017] Preferably, the amount of dispersant added is 1-5wt% of the total amount of sodium thiosulfate and hexavalent chromium, the microwave power is 600-800w, the microwave treatment is 3-9h, the ultrasonic frequency is 40-120Hz, and the ultrasonic dispersion is 2-4h.

[0018] Preferably, after calcining the chromium oxide green product in step three, the chromium oxide green is ground, the grinding medium is a zirconium oxide ball with a diameter of 0.1 to 0.3 mm, the grinding speed is 100 to 550 rpm, and the grinding time is 2 to 8 hours.

[0019] The present invention has at least the following beneficial effects:

[0020] (1) The present invention uses sodium thiosulfate-containing wastewater to treat hexavalent chromium wastewater without using sodium metabisulfite, a conventional agent for treating hexavalent chromium. At the same time, sodium thiosulfate wastewater is also treated, and the comprehensive value cost of the two types of wastewater is fully utilized, thereby achieving comprehensive utilization of resources and significantly reducing treatment costs.

[0021] (2) The chromium hydroxide produced by the present invention is used for calcination to produce 99% metallurgical grade chromium oxide green products, thereby realizing the complete recovery and productization of chromium resources in wastewater.

[0022] (3) The present invention adds a dispersant during the precipitation process, and simultaneously performs microwave and ultrasonic dispersion treatment to prevent the precipitation from agglomerating, and grinds the calcined product to reduce the particle size of the final product to obtain nano-scale chromium oxide green.

[0023] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. DETAILED DESCRIPTION

[0024] The present invention is described in further detail below so that those skilled in the art can implement it according to the description.

[0025] Example 1

[0026] A technology for comprehensive utilization of sodium thiosulfate wastewater and chromium-containing wastewater resources comprises the following steps:

[0027] Step 1: Pump 30m3 into the reaction tank 3 Wastewater with a sodium thiosulfate content of 10 g / L is then pumped into 40 m 3 Wastewater with a hexavalent chromium content of 3g / L was stirred and mixed evenly, and sulfuric acid was gradually added to adjust the pH value to 2.0, and then the steam valve was opened to heat it to 70℃ and keep it for reduction reaction for 3h;

[0028] Step 2: Add caustic soda flakes to the reacted material to adjust the pH value to 7.0, stir at 80 r / min for 2 h, and after stirring evenly, open the steam valve and heat to 70°C for 3 h;

[0029] Step 3: The fully matured material is filtered through a plate and frame filter press and washed in a secondary countercurrent until the hexavalent chromium in the filtered water reaches the specified index (<0.5 mg / L) to obtain a chromium hydroxide product. The produced chromium hydroxide has a main content of 47% in terms of chromium trioxide and a sodium content of 0.05%. The chromium hydroxide is then calcined in an atmosphere of 4 vol% oxygen concentration at a calcination temperature of 1000°C for 10 hours to obtain a metallurgical grade chromium oxide green product with a purity of 99%, and the particle size of the chromium oxide green is D90=30 um.

[0030] Example 2

[0031] A technology for comprehensive utilization of sodium thiosulfate wastewater and chromium-containing wastewater resources comprises the following steps:

[0032] Step 1: Pump 30m3 into the reaction tank 3 Wastewater with a sodium thiosulfate content of 11 g / L is then pumped into 40 m 3 Wastewater with a hexavalent chromium content of 4g / L was stirred and mixed evenly, and sulfuric acid was gradually added to adjust the pH value to 3.0, and then the steam valve was opened to heat it to 80℃ and keep it for 6h for reduction reaction;

[0033] Step 2: Add caustic soda to the reacted material to adjust the pH value to 8.0, stir at 80 r / min for 2 h, and after stirring evenly, open the steam valve and heat to 80 ° C and keep warm for 6 h;

[0034] Step 3: The fully matured material is filtered through a plate and frame filter press and washed in a secondary countercurrent manner until the hexavalent chromium in the filtered water reaches the specified index (<0.5 mg / L), thereby obtaining a chromium hydroxide product. The produced chromium hydroxide has a main content of 46% in terms of chromium trioxide and a sodium content of 0.05%. The chromium hydroxide is then calcined in an atmosphere of 4 vol% oxygen concentration at a calcination temperature of 1000°C for 10 hours to obtain a metallurgical grade chromium oxide green product with a purity of 99%, and the particle size of the chromium oxide green is D90=30 um.

[0035] Example 3

[0036] A technology for comprehensive utilization of sodium thiosulfate wastewater and chromium-containing wastewater resources comprises the following steps:

[0037] Step 1: Pump 50m3 into the reaction tank 3 Wastewater with a sodium thiosulfate content of 12 g / L is then pumped into a 60m 3 Wastewater with a hexavalent chromium content of 5g / L was stirred and mixed evenly, and sulfuric acid was gradually added to adjust the pH value to 4.0, and then the steam valve was opened to heat it to 100℃ for a reduction reaction of 9h;

[0038] Step 2: Add caustic soda flakes to the reacted material to adjust the pH value to 9.0, stir at 80 r / min for 2 h, and after stirring evenly, open the steam valve and heat to 100 ° C and keep warm for 9 h;

[0039] Step 3: The fully matured material is filtered through a plate and frame filter press and washed in a secondary countercurrent manner until the hexavalent chromium in the filtered water reaches the specified index (<0.5 mg / L), thereby obtaining a chromium hydroxide product. The chromium hydroxide produced has a main content of 47% in terms of chromium trioxide and a sodium content of 0.05%. The chromium hydroxide is then calcined in an atmosphere of 4 vol% oxygen concentration at a calcination temperature of 1000°C for 10 hours to obtain a metallurgical grade chromium oxide green product with a purity of 99%, and a particle size of the chromium oxide green of D90=30 um.

[0040] Example 4

[0041] A technology for comprehensive utilization of sodium thiosulfate wastewater and chromium-containing wastewater resources comprises the following steps:

[0042] Step 1: Pump 30m3 into the reaction tank 3 Wastewater with a sodium thiosulfate content of 10 g / L is then pumped into 40 m 3 Wastewater with a hexavalent chromium content of 3g / L was stirred and mixed evenly, and sulfuric acid was gradually added to adjust the pH value to 2.0, and then the steam valve was opened to heat it to 70℃ and keep it for reduction reaction for 3h;

[0043] Step 2: first add 5 kg of ethylene glycol to the solution after the reduction reaction, then add caustic soda to adjust the pH to 7.0, then treat with 600 W microwave for 4 hours, then disperse with 100 Hz ultrasound for 4 hours, and stir at 80 r / min until the dispersion is uniform, then open the steam valve to heat to 100 ° C and keep warm for 9 hours;

[0044] Step 3: The fully matured material is filtered through a plate and frame filter press and washed in a secondary countercurrent manner until the hexavalent chromium in the filtered water reaches the specified index (<0.5 mg / L), thereby obtaining a chromium hydroxide product. The generated chromium hydroxide has a main content of 46% in terms of chromium trioxide and a sodium content of 0.05%. The chromium hydroxide is then calcined in an atmosphere of 4 vol% oxygen concentration at a calcination temperature of 1000°C for 10 hours. The calcined chromium oxide green is then placed in a grinder, with 0.2 mm zirconium oxide beads as the grinding medium, and ground at 300 rpm for 2 hours to obtain a metallurgical grade nano chromium oxide green product with a purity of 99%, and a particle size of chromium oxide green of D90=80 nm.

[0045] Comparative Example 1

[0046] This comparative example uses a conventional hexavalent chromium treatment reagent, sodium pyrosulfite, to treat hexavalent chromium wastewater. The method is as follows: Step 1, prepare a sodium pyrosulfite solution with a concentration of 10g / L, add 30m 3 The prepared sodium metabisulfite solution is pumped into the reaction tank, and then 40m 3 Wastewater with a hexavalent chromium content of 3g / L was stirred and mixed evenly, and sulfuric acid was gradually added to adjust the pH value to 2.0, and then the steam valve was opened to heat it to 70℃ and keep it for reduction reaction for 3h;

[0047] Step 2: Add caustic soda flakes to the reacted material to adjust the pH value to 9.0, stir at 80 r / min for 2 h, and after stirring evenly, open the steam valve and heat to 70°C for 3 h;

[0048] Step 3: The fully matured material is filtered through a plate and frame filter press and washed in a secondary countercurrent until the hexavalent chromium in the filtered water reaches the specified index (<0.5 mg / L) to obtain a chromium hydroxide product. The chromium hydroxide produced has a main content of 30% and a sodium content of 1% as calculated as chromium trioxide. The chromium hydroxide is then calcined at a calcination temperature of 1000° C. for 10 hours to obtain chromium oxide green with a purity of 96%, and a particle size of chromium oxide green of D90=30 um.

[0049] Comparative Example 2

[0050] The difference between this comparative example and Example 4 is that after calcining to obtain chromium oxide green in step three, it is not ground, and the remaining steps are consistent with comparative example 4, to obtain chromium oxide green with a purity of 99%, and the particle size of chromium oxide green D90=900nm.

[0051] Comparative Example 3

[0052] The difference between this comparative example and Example 4 is that no dispersant is added in step 2, and no microwave treatment and ultrasonic dispersion are performed. The remaining steps are consistent with comparative example 4, and chromium oxide green with a purity of 99% is obtained, and the particle size of chromium oxide green D90=2um.

[0053] It can be seen from Examples 1 to 4 and Comparative Example 1 that the chromium hydroxide obtained by the mixed treatment of two wastewaters in the present invention has a higher content of chromium trioxide, and the purity of the chromium oxide green obtained by the final calcination is also higher than the chromium oxide green obtained by treating hexavalent chromium wastewater with sodium metabisulfite in the conventional method; it can be seen from Example 4 and Comparative Examples 2 to 3 that the present invention also adopts the method of adding a dispersant and performing microwave and ultrasonic treatment during the precipitation process to disperse the precipitate and prevent aggregation, which can effectively reduce the particle size of the chromium hydroxide, and then reduce the particle size of the chromium oxide green after calcination, and also uses grinding to further reduce the particle size of the chromium oxide green, so as to finally obtain nano-scale chromium oxide green.

[0054] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A technology for comprehensive utilization of sodium thiosulfate wastewater and chromium-containing wastewater resources, characterized in that: The following steps are involved: Step 1: Mix the sodium thiosulfate wastewater and the chromium-containing wastewater in a uniform ratio, add sulfuric acid to adjust the pH, and then heat them to a certain temperature by steam, and then keep them warm for reduction reaction; Step 2: adding caustic soda to the reacted material to adjust the pH, stirring and precipitating, and keeping warm for aging reaction; Step 3: The fully matured material is filtered through a plate and frame filter press and washed with hot water until the hexavalent chromium in the filtered water reaches the specified index to obtain a chromium hydroxide product, and the chromium hydroxide is calcined at high temperature to obtain chromium oxide green.

2. The comprehensive utilization technology of sodium thiosulfate wastewater and chromium-containing wastewater resources according to claim 1, characterized in that: In the step 1, the mixing ratio of sodium thiosulfate wastewater and chromium-containing wastewater is: sodium thiosulfate and hexavalent chromium are measured at a mass ratio of 1 to 3:1, and sulfuric acid is added to adjust the pH to 1.0 to 4.

0.

3. The comprehensive utilization technology of sodium thiosulfate wastewater and chromium-containing wastewater resources according to claim 1, characterized in that: In the step 1, the temperature for the reduction reaction is kept at 60 to 100° C., and the reduction reaction is carried out for 1 to 8 hours.

4. The comprehensive utilization technology of sodium thiosulfate wastewater and chromium-containing wastewater resources according to claim 1, characterized in that: In the step 2, caustic soda flakes are added to adjust the pH to 6.0-9.0, the stirring speed is 30-100 r / min, and the stirring time is 1-8 hours.

5. The comprehensive utilization technology of sodium thiosulfate wastewater and chromium-containing wastewater resources according to claim 1 is characterized in that: In the step 2, the temperature of the heat preservation and aging reaction is 60-100° C., and the aging time is 1-8 hours.

6. The comprehensive utilization technology of sodium thiosulfate wastewater and chromium-containing wastewater resources according to claim 1, characterized in that: In the step 3, the calcination conditions are: an oxygen atmosphere with a concentration of 2 to 10 vol%, a calcination temperature of 900 to 1300° C., and a calcination time of 6 to 24 hours.

7. The comprehensive utilization technology of sodium thiosulfate wastewater and chromium-containing wastewater resources according to claim 1, characterized in that: After the reduction reaction in step 1 is completed, the reaction product is further treated by first adding a dispersant thereto, stirring evenly, then adding caustic soda to adjust the pH, then microwave treatment, then ultrasonic dispersion, then heat preservation and aging reaction, and then step 3 after aging is completed.

8. The comprehensive utilization technology of sodium thiosulfate wastewater and chromium-containing wastewater resources according to claim 7, characterized in that: The dispersant is one or more of isopropanol, ethylene glycol, ethylene glycol methyl ether, triethylene glycol divinyl ether or dodecylphenol polyoxyethylene ether.

9. The comprehensive utilization technology of sodium thiosulfate wastewater and chromium-containing wastewater resources according to claim 7, characterized in that: The amount of dispersant added is 1-5wt% of the total amount of sodium thiosulfate and hexavalent chromium, the microwave power is 600-800w, the microwave treatment is 3-9h, the ultrasonic frequency is 40-120Hz, and the ultrasonic dispersion is 2-4h.

10. The comprehensive utilization technology of sodium thiosulfate wastewater and chromium-containing wastewater resources according to claim 1, characterized in that: After calcining in step 3 to obtain the chromium oxide green product, the chromium oxide green is ground, the grinding medium is a zirconium oxide ball with a diameter of 0.1 to 0.3 mm, the grinding speed is 100 to 550 rpm, and the grinding time is 2 to 8 hours.