Process method for co-processing chromic anhydride waste and waste zinc phosphide

Abstract

The invention relates to the technical field of hazardous waste disposal and utilization, in particular to a technological method for co-disposal of chromic anhydride waste and waste zinc phosphide, which comprises the following steps: dissolving chromic anhydride waste in a dissolving tank according to a certain solid-to-liquid ratio, and hydrolyzing chromic anhydride to generate chromic acid; the method comprises the following steps: adding a certain proportion of an inorganic acid solution into a chromic acid solution, and combining chromate ions with hydrogen ions to generate dichromate ions under an acidic condition; transferring the solution into a closed first-stage reactor, and slowly stirring; according to the method, firstly, the method is suitable for chromic anhydride waste and zinc phosphide waste, waste chromate, dichromate waste and aluminum phosphide waste can be used, harmless treatment of the hazardous waste can be completed, secondly, reagents used in the treatment process only need phosphoric acid, hydrogen peroxide and sodium hydroxide, ferrous sulfate is not used as a reducing agent, and the method is environmentally friendly. The production of a large amount of iron mud is avoided, and finally, the produced secondary waste can be recycled, so that the aim of turning waste into wealth is fulfilled.

Description

Technical Field

[0001] The invention relates to the technical field of hazardous waste disposal and utilization, and in particular to a process for the coordinated disposal of chromic anhydride waste and waste zinc phosphide. Background Art

[0002] Chromic anhydride and zinc phosphide are two chemicals widely used in industrial and agricultural fields. Chromic anhydride, also known as chromic acid, is an important industrial oxidant widely used in electroplating, dye and pigment manufacturing, etc. Zinc phosphide is mainly used as a rodenticide and insecticide, with high efficiency and rapid poisoning effect.

[0003] Chromic anhydride is a strong oxidant widely used in metal surface treatment and electroplating industries. Like many other metals, chromium can only be dissolved in water and absorbed by the body after it becomes a metal ion. Hexavalent chromium is a highly toxic substance that is carcinogenic, teratogenic, and mutagenic. It is 100 times more toxic than trivalent chromium and is listed as a Class I controlled pollutant by the state. If waste containing chromic anhydride is not treated, it will have a great impact on human health and the ecological environment.

[0004] Zinc phosphide is one of the commonly used fumigants and rodenticides in agriculture due to its high toxicity. Zinc phosphide will slowly decompose when it comes into contact with water and humid air, and will violently decompose and release highly toxic phosphine gas when it comes into contact with acid. Zinc phosphide can not only kill rats, but is also highly toxic to humans and livestock. When zinc phosphide enters the stomach through the mouth, it will produce phosphine gas when it comes into contact with stomach acid, which has a corrosive and irritating effect on the gastrointestinal tract. Phosphine is absorbed into the blood in the gastrointestinal tract and circulates throughout the body with the blood, stimulating nerve endings and receptors, causing the central nervous system to be excited first and then inhibited. Zinc phosphide mainly damages the central nervous system, heart, liver, kidneys, etc.

[0005] In industrial production, chromic anhydride and zinc phosphide raw materials are often stored out of date. For product quality reasons, these expired raw materials are usually scrapped as hazardous waste. How to dispose of these hazardous wastes harmlessly is particularly important.

[0006] The present invention provides a method for the coordinated disposal of chromic anhydride waste and waste zinc phosphide, which utilizes the strong reducing property of phosphine generated by the decomposition of zinc phosphide to reduce hexavalent chromium to trivalent chromium, and then converts the trivalent chromium and zinc in the solution into chromium hydroxide and zinc hydroxide sludge under alkaline conditions, and the sludge is handed over to a qualified enterprise for recycling, so as to achieve the purpose of harmless treatment of chromic anhydride waste and zinc phosphide. Summary of the invention

[0007] The purpose of the present invention is to provide a process method for the coordinated disposal of chromic anhydride waste and waste zinc phosphide. The process method has a reasonable and simple process flow, realizes the harmless disposal of two highly dangerous wastes, chromic anhydride waste and zinc phosphide, and secondary wastes such as sludge generated during the disposal process can be used as raw materials for resource recycling.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: A process for the coordinated disposal of chromic anhydride waste and waste zinc phosphide comprises the following steps: Step 1: dissolving chromic anhydride waste in a dissolving tank according to a certain solid-liquid ratio, and hydrolyzing chromic anhydride to generate chromic acid; Step 2: Add a certain proportion of inorganic acid solution to the chromic acid solution. Under acidic conditions, chromate ions can combine with hydrogen ions to form dichromate ions; Step 3, transferring the solution to a closed primary reactor and slowly stirring it, opening the nitrogen protection valve, using nitrogen to replace the air in the reactor, and when the oxygen concentration in the reactor is lower than the set value, closing the reactor inlet and outlet valves and the nitrogen protection valve in sequence to maintain an oxygen-free environment in the reactor, and ensuring that the reactor is under a slightly positive pressure state; slowly adding a certain amount of zinc phosphide into the reactor through a powder feeding device, and the zinc phosphide directly reacts with the phosphoric acid solution to generate phosphine gas and zinc phosphate; Step 4: After the reaction is completed, the solution is transferred to a secondary reactor, and hydrogen peroxide solution is added to remove the remaining small amount of Cr 6+ Completely reduced to Cr 3+ Cr in the solution to be tested 6+ < 0.5 (mg / L), using 30% liquid alkali to adjust the solution pH to 5.0-5.5, after the reaction is completed, pumping the solid-liquid mixture into a plate-frame filter press to obtain chromium hydroxide sludge and filtrate 1; Step 5: Transfer the filtrate 1 to the tertiary reactor, continue to use 30% liquid caustic soda to adjust the pH to 8, and after sufficient reaction, filter the solid-liquid mixture through a plate and frame filter press to obtain zinc hydroxide sludge and filtrate 2; Step 6: The filtrate 2 in step 5 enters an evaporation crystallization device to prepare trisodium phosphate, and the distillate water produced by the evaporation crystallization device can be reused to dissolve chromic anhydride waste.

[0009] As a further description of the above technical solution: The solid-to-liquid ratio of chromic anhydride to water in step 1 is 1-1.5:20.

[0010] As a further description of the above technical solution: The inorganic acid added in the step 2 is a phosphoric acid solution with a concentration of 30-50%, and the amount of phosphoric acid added is 10-15% of the volume of the solution.

[0011] As a further description of the above technical solution: The amount of zinc phosphide powder added in step 3 is 0.8-0.9 times the mass of chromic anhydride, and the insufficient amount of zinc phosphide added to the reaction system ensures that the phosphine produced in the reaction is completely absorbed, thereby preventing excessive phosphine gas from escaping the reactor and causing adverse effects on the environment and personnel.

[0012] As a further description of the above technical solution: The amount of hydrogen peroxide added in step 4 needs to be determined based on the amount of Cr in the filtrate detected after the reaction in step 3. 6+ The content is determined, and the amount added is Cr 6+ The content is 1.1-1.5 times.

[0013] As a further description of the above technical solution: The primary reactor is provided with a gas external circulation device, which pumps the gas in the upper part of the reactor into the aeration device at the bottom of the reactor through an air pump to improve the absorption and utilization rate of the phosphine gas and prevent the residual phosphine in the gas in the upper part of the reactor.

[0014] As a further description of the above technical solution: A phosphine gas concentration alarm is arranged outside the primary reactor to monitor the phosphine gas concentration in the environment.

[0015] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. The present invention is not only applicable to chromic anhydride waste and zinc phosphide waste, but also can be used to treat waste chromate, dichromate and aluminum phosphide waste to complete the harmless treatment of such hazardous wastes.

[0016] 2. In the present invention, the reagents used in the treatment process only need phosphoric acid, hydrogen peroxide and sodium hydroxide, and ferrous sulfate is not used as a reducing agent, thereby avoiding the generation of a large amount of iron mud.

[0017] 3. In the present invention, the generated inferior waste can be utilized as resources, thus achieving the purpose of turning waste into treasure. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] The present invention provides a technical solution: a process for the coordinated disposal of chromic anhydride waste and waste zinc phosphide, comprising the following steps: The first step is to dissolve the chromic anhydride waste in water in a dissolving tank at a solid-liquid ratio of 1-1.5:20, and the chromic anhydride is hydrolyzed to generate chromic acid. The reaction equation is as follows: CrO3+H2O→H2CrO4 Chromic acid (H2CrO4) is a dibasic weak acid that can further dissociate in water to form chromate ions (CrO4 2- ), the reaction equation is as follows: H2CrO4↔H + +HCrO4 - HCrO4 - ↔H + +CrO4 2- The second step is to add an inorganic acid solution to the chromic acid solution. The concentration of phosphoric acid solution is 30-50%. The amount of phosphoric acid added is 10-15% of the volume of the solution. Under acidic conditions, chromate ions (CrO4 2- ) can react with hydrogen ions (H + ) combines to form dichromate ions (Cr2O7 2- ), the reaction equation is as follows: 2CrO4 2- +2H + ↔Cr2O7 2- +H2O Step 3: Transfer the solution to a sealed primary reactor and stir slowly. Open the nitrogen protection valve and use nitrogen to replace the air in the reactor. When the oxygen concentration in the reactor reaches the set value, close the reactor inlet and outlet valves and the nitrogen protection valve in sequence to maintain an oxygen-free environment in the reactor and ensure that the reactor is under a slightly positive pressure. Among them, the first-level reactor is equipped with a gas external circulation device, which pumps the gas above the reactor into the aeration device at the bottom of the reaction through an air pump to improve the absorption and utilization rate of phosphine gas, and at the same time prevent residual phosphine in the gas above the reactor. At the same time, a phosphine gas concentration alarm is installed outside the first-level reactor to monitor the phosphine gas concentration in the environment.

[0020] Zinc phosphide is slowly added into the reactor through a powder feeding device, and the amount of zinc phosphide powder is controlled to be 0.8-0.9 times the mass of chromic anhydride. Zinc phosphide directly reacts with phosphoric acid solution to generate phosphine gas and zinc phosphate. The reaction equation is as follows: Zn3P2+2H3PO4→2PH3+Zn3(PO4)2 Phosphine (PH3) and dichromate (Cr2O7 2- ) reacts in an acidic aqueous solution, a redox reaction occurs, and the specific reaction principle is as follows: 3PH3+2Cr2O72- +16H + →3H3PO4+4Cr 3+ +8H2O In the third step, insufficient amount of zinc phosphide is added to the reaction system to ensure that the phosphine produced in the reaction is completely absorbed, thereby preventing excessive phosphine gas from escaping from the reactor and causing adverse effects on the environment and personnel.

[0021] Step 4: The amount of hydrogen peroxide added should be based on the amount of Cr in the filtrate detected after the reaction in step 3. 6+ The content is determined, and the amount added is Cr 6+ The sodium hydroxide solution should be added slowly, and the pH should be monitored in real time. When the pH is 5.0±0.2, stop adding alkali and stir to fully precipitate the chromium hydroxide.

[0022] Step 5: Transfer the filtrate 1 to a tertiary reactor, slowly add sodium hydroxide solution, adjust the pH to 8.0±0.2, and stir thoroughly during the pH adjustment process.

[0023] Step 6: The filtrate 2 in step 5 enters an evaporation crystallization device to prepare trisodium phosphate, and the distillate water produced by the evaporation crystallization device can be reused to dissolve chromic anhydride waste.

[0024] The present invention is further described in detail below in conjunction with implementation cases.

[0025] Implementation Case 1: Add 400L of water to the dissolution tank, then slowly add 20kg of chromic anhydride waste, stir for 1h, then slowly add 60L of 50% phosphoric acid solution to the dissolution tank, stir thoroughly and pump the solution into the primary reactor. Turn on the stirring and gas circulation device in the primary reactor, slowly add 20kg of zinc phosphide powder (effective content is 80%) into the reactor, fully react for 4-6h, and pump the liquid into the secondary reactor for temporary storage. Detect Cr in the filtrate 6+ 30.50 mg / L, add 45 mL of 30% hydrogen peroxide solution to the secondary reactor, stir and react for 2 hours, and the Cr in the solution 6+ No detection was made, and 30% liquid alkali was added to the secondary reactor to control the pH to 5.3. After stirring and reacting for 2 hours, the chromium hydroxide sludge after plate-frame solid-liquid separation was handed over to the resource-based enterprise for reuse. Filtrate 1 was transferred to the tertiary reactor to continue adjusting the pH to 8.0, and the zinc hydroxide sludge after plate-frame solid-liquid separation was handed over to the resource-based enterprise for utilization. After testing, the Cr content in filtrate 2 was less than 0.1 mg / L, and Zn was not detected. Filtrate 2 entered the evaporation crystallization device to prepare trisodium phosphate, and the evaporated distillate water was collected and reused to dissolve chromic anhydride waste.

[0026] Implementation Case 2: Add 1000L of water to the dissolution tank, then slowly add 50kg of chromic anhydride waste, stir for 1h, then slowly add 200L of 50% phosphoric acid solution to the dissolution tank, stir thoroughly and pump the solution into the primary reactor. Turn on the stirring and gas circulation device in the primary reactor, slowly add 50kg of zinc phosphide powder (effective content is 80%) into the reactor, fully react for 4-6h, and then pump the liquid into the secondary reactor for temporary storage. Detect Cr in the filtrate 6+ The concentration of Cr in the solution was 25.00 mg / L. 100 mL of hydrogen peroxide solution was added to the secondary reactor and stirred for 2 h. 6+ The concentration is less than 0.01 mg / L. Continue to add 30% liquid alkali to the secondary reactor, control the pH to 5.5, and stir the reaction for 2 hours. The chromium hydroxide sludge after plate-frame solid-liquid separation is handed over to the resource enterprise for reuse. Filtrate 1 is transferred to the tertiary reactor to continue to adjust the pH to 8.0. The zinc hydroxide sludge after plate-frame solid-liquid separation is handed over to the resource enterprise for utilization. After testing, no Cr and no Zn were detected in filtrate 2. Filtrate 2 enters the evaporation crystallization device to prepare trisodium phosphate, and the evaporated distillate water is collected and reused to dissolve chromic anhydride waste.

[0027] Implementation Case 3: Add 2000L of water to the dissolving tank, then slowly add 100kg of chromic anhydride waste, stir for 1h, then slowly add 400L of 50% phosphoric acid solution to the dissolving tank, stir thoroughly and pump the solution into the primary reactor. Turn on the stirring and gas circulation device in the primary reactor, slowly add 100kg of zinc phosphide powder (effective content is 80%) into the reactor, fully react for 4-6h, and then pump the liquid into the secondary reactor for temporary storage. Detect Cr in the filtrate 6+ The pH value of zinc hydroxide sludge after plate-frame solid-liquid separation was 21.62 mg / L. 30% liquid alkali was added to the secondary reactor to control the pH value to 5.3. After stirring and reacting for 2 hours, the chromium hydroxide sludge after plate-frame solid-liquid separation was handed over to the resource-based enterprise for reuse. Filtrate 1 was transferred to the tertiary reactor to continue adjusting the pH value to 8.0. The zinc hydroxide sludge after plate-frame solid-liquid separation was handed over to the resource-based enterprise for utilization. After testing, no Cr and no Zn were detected in filtrate 2. Filtrate 2 entered the evaporation crystallization device to prepare trisodium phosphate, and the evaporated distillate water was collected and reused to dissolve chromic anhydride waste.

[0028] The pH, total chromium, and chemical oxygen demand (COD) of the filtrate after the tertiary reaction obtained in Examples 1-3 and the recovered water after evaporation and crystallization were tested to obtain the data shown in Table 1. The specific data are shown in the following table: Table 1 By analyzing the data in Table 1, we can draw the following conclusions: By adopting the method for co-disposal of chromic anhydride waste and waste zinc phosphide provided by the present invention, hazardous components can be completely removed, and the pH of the obtained recycled water can be controlled near neutral, the total chromium can be controlled below the limit value in the "Comprehensive Sewage Discharge Standard" (GB8978-1996), and the chemical oxygen demand (COD) can be controlled at 30 mg / L, which is of great significance for the coordinated treatment of hazardous wastes.

[0029] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A process for the coordinated disposal of chromic anhydride waste and waste zinc phosphide, characterized in that: The following steps are involved: Step 1: dissolving chromic anhydride waste in a dissolving tank according to a certain solid-liquid ratio, and hydrolyzing chromic anhydride to generate chromic acid; Step 2: Add a certain proportion of inorganic acid solution to the chromic acid solution. Under acidic conditions, chromate ions can combine with hydrogen ions to form dichromate ions; Step 3, transferring the solution to a closed primary reactor and slowly stirring it, opening the nitrogen protection valve, using nitrogen to replace the air in the reactor, and when the oxygen concentration in the reactor is lower than the set value, closing the reactor inlet and outlet valves and the nitrogen protection valve in sequence to maintain an oxygen-free environment in the reactor, and ensuring that the reactor is under a slightly positive pressure state; slowly adding a certain amount of zinc phosphide into the reactor through a powder feeding device, and the zinc phosphide directly reacts with the phosphoric acid solution to generate phosphine gas and zinc phosphate; Step 4: After the reaction is completed, the solution is transferred to a secondary reactor, and hydrogen peroxide solution is added to remove the remaining small amount of Cr 6+ Completely reduced to Cr 3+ Cr in the solution to be tested 6+ < 0.5 (mg / L), using 30% liquid alkali to adjust the solution pH to 5.0-5.5, after the reaction is completed, pumping the solid-liquid mixture into a plate-frame filter press to obtain chromium hydroxide sludge and filtrate 1; Step 5: Transfer the filtrate 1 to the tertiary reactor, continue to use 30% liquid caustic soda to adjust the pH to 8, and after sufficient reaction, filter the solid-liquid mixture through a plate and frame filter press to obtain zinc hydroxide sludge and filtrate 2; Step 6: The filtrate 2 in step 5 enters an evaporation crystallization device to prepare trisodium phosphate, and the distillate water produced by the evaporation crystallization device can be reused to dissolve chromic anhydride waste.

2. The process for the coordinated disposal of chromic anhydride waste and waste zinc phosphide according to claim 1, characterized in that: The solid-to-liquid ratio of chromic anhydride to water in step 1 is 1-1.5:

20.

3. The process for the coordinated disposal of chromic anhydride waste and waste zinc phosphide according to claim 1, characterized in that: The inorganic acid added in the step 2 is a phosphoric acid solution with a concentration of 30-50%, and the amount of phosphoric acid added is 10-15% of the volume of the solution.

4. The process for the coordinated disposal of chromic anhydride waste and waste zinc phosphide according to claim 1, characterized in that: The amount of zinc phosphide powder added in step 3 is 0.8-0.9 times the mass of chromic anhydride, and the insufficient amount of zinc phosphide added to the reaction system ensures that the phosphine produced in the reaction is completely absorbed, thereby preventing excessive phosphine gas from escaping the reactor and causing adverse effects on the environment and personnel.

5. The process for the coordinated disposal of chromic anhydride waste and waste zinc phosphide according to claim 1, characterized in that: The amount of hydrogen peroxide added in step 4 needs to be determined based on the amount of Cr in the filtrate detected after the reaction in step 3. 6+ The content is determined, and the amount added is Cr 6+ The content is 1.1-1.5 times.

6. The process for the coordinated disposal of chromic anhydride waste and waste zinc phosphide according to claim 1, characterized in that: The primary reactor is provided with a gas external circulation device, which pumps the gas in the upper part of the reactor into the aeration device at the bottom of the reactor through an air pump to improve the absorption and utilization rate of the phosphine gas and prevent the residual phosphine in the gas in the upper part of the reactor.

7. The process for the coordinated disposal of chromic anhydride waste and waste zinc phosphide according to claim 1 or 6, characterized in that: A phosphine gas concentration alarm is arranged outside the primary reactor to monitor the phosphine gas concentration in the environment.

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