Treatment method of sodium sulfate crystallization solid waste

Abstract

The invention discloses a method for treating sodium sulfate crystallization solid waste, which comprises the following steps of: uniformly mixing the sodium sulfate crystallization solid waste with reduced carbon powder, preparing blocks or particles by using paper paste as a binder, and putting the blocks or particles into a microwave oven; heating to 800-1000 DEG C by microwave radiation, and carrying out carbon thermal reduction reaction; after the reduction reaction is finished, introducing air or oxygen-enriched air into the microwave oven, and carrying out microwave oxidizing roasting under the condition of 1000 + / -50 DEG C; after oxidizing roasting is finished, the temperature is reduced to 200 DEG C or below, and an oxidizing roasting product is taken out and placed in clear water for a hydrothermal reaction; a Na0H solution or a concentrated and crystallized Na0H solid is obtained. According to the method, comprehensive recovery and treatment of the sodium sulfate crystallization solid waste with very low economic value are realized, the obtained Na0H and the crystallization product thereof are wide in application, the economic value is far higher than that of Na2S04 crystallization, and meanwhile, carbon monoxide and sulfur dioxide can be recovered.

Description

Technical Field

[0001] The invention belongs to the field of environmental protection management and comprehensive recovery of metallurgical and chemical solid wastes, and specifically relates to a method for treating sodium sulfate crystal solid wastes, namely, microwave carbon thermal reduction and microwave oxidative roasting of the sodium sulfate crystal solid wastes, and hydrothermal reaction of the oxidative roasting products to recover NaOH. Background Art

[0002] In metallurgical chemical industry, rotary kiln is used for redox volatilization, sulfur-containing tail gas after dust collection, boiling roasting tail gas of sulfide minerals or sulfur-containing tail gas of acid production, sulfur-containing tail gas after dust collection of fuming furnace, when tail gas washing and desulfurization are carried out with sodium carbonate or NaOH dilute solution, a large amount of sodium sulfate waste water will be produced, and sodium sulfate crystal solid waste will be obtained by concentration and crystallization. Hydrometallurgical waste water contains a large amount of sodium sulfate components, and sodium sulfate crystal solid waste is also obtained by concentration and crystallization. In particular, germanium is extracted by solvent extraction, and acid-base neutralization and hydrolysis precipitation must be carried out after stripping germanium to produce germanium concentrate. The hydrolysis residual liquid mainly contains sodium sulfate components, and relatively pure sodium sulfate crystal solid waste is obtained by concentration and crystallization.

[0003] At present, sodium sulfate and its crystallization are all a kind of solid waste in industrial and agricultural production, with no economic value, and are difficult to be recycled and stored in the warehouse. Because sodium sulfate is a strong acid and strong base salt, it is almost impossible to realize that sodium sulfate is causticized by calcium, magnesium, barium, etc. to recycle NaOH. Sodium sulfate is soluble in water, so sodium sulfate crystal solid waste cannot be buried underground. Sulfur element is the highest price in sulfate ion, and the combination with oxygen is very firm. It is impossible to destroy its structure and disintegrate by hydrometallurgical method to carry out redox reaction, so the redox reaction of sulfate can only be carried out by pyrometallurgy. For example, the smelting of lead sulfate slag (mud) mainly adopts redox roasting first at present, obtains lead oxide, then performs carbon thermal reduction smelting to metal crude lead, and then performs lead silicofluoride electrolysis to obtain refined lead. Because the redox pyrometallurgy of current sulfate is carried out in general pyrometallurgy furnace, and does not carry out segmented smelting treatment, the waste gas produced is a mixture of SO2, CO, CO2 air, etc., which is not conducive to governance and comprehensive recovery. However, there has been no report on the comprehensive recovery of low-value sodium sulfate crystal solid waste by pyrometallurgy. Summary of the invention

[0004] Based on the reality that sodium sulfate crystal solid waste cannot be treated after long-term storage and comprehensive recovery is not carried out, the invention proposes a process flow in which microwave radiation carbon thermal reduction smelting is first carried out in a microwave oven to obtain Na2S and relatively pure carbon monoxide, then the Na2S is subjected to microwave air or oxygen-enriched air oxidation roasting to obtain a mixture of Na2O or sodium peroxide or sodium superoxide and SO2 waste gas, and then the mixture of sodium oxide or sodium peroxide or sodium superoxide is subjected to hydrothermal reaction to obtain a Na0H solution or a Na0H crystal solid. The invention can realize comprehensive recovery and environmental protection management of sodium sulfate crystal solid waste.

[0005] The technical solution of the present invention:

[0006] A method for treating sodium sulfate crystal solid waste, the specific implementation steps are as follows:

[0007] Step 1. Evenly mix the sodium sulfate crystal solid waste and the reduced carbon powder, and use paper pulp paste as a binder to form agglomerates or particles;

[0008] Step 2. placing the sodium sulfate crystal solid waste agglomerates or particles prepared in step 1 in a microwave oven for carbon thermal reduction smelting to obtain sodium sulfide solid and carbon monoxide gas; the smelting end point is when the carbon monoxide gas discharged from the microwave oven through the gas duct no longer burns;

[0009] Step 3. After the carbon thermal reduction smelting in step 2 is completed, air or oxygen-enriched air is introduced into the microwave oven to perform oxidative roasting of sodium sulfide to obtain a mixture of sodium oxide, sodium peroxide, sodium superoxide and a mixed waste gas of SO2 and air; the end point of oxidative roasting is that the discharged waste gas contains SO2 ≤ 100 mg / m 3 until;

[0010] Step 4. After the oxidation roasting in step 3 is completed, the temperature is lowered to below 200° C., and the oxidation roasting product is taken out and placed in clean water at room temperature for hydrothermal reaction; after filtering, a NaOH solution or a concentrated crystalline NaOH solid is obtained.

[0011] Furthermore, the sodium sulfate crystal solid waste in step 1 is solid waste with sodium sulfate crystals as the main component and a sodium sulfate content of ≥90%; the reducing carbon powder is coke powder or activated carbon powder or carbon black powder, and the added amount is 1.2 to 1.3 times the theoretical amount required according to the chemical reaction equation Na2S04+4C=Na2S+4C0; the amount of paper pulp paste binder is 6 to 8% of the total mass.

[0012] Furthermore, the conditions of the microwave carbon thermal reduction smelting in step 2 are: microwave radiation frequency of 1 to 10 GHz, temperature of 800 to 1000° C., time of more than 30 minutes, and until the carbon thermal reduction reaction waste gas discharged from the microwave oven through the gas duct no longer burns.

[0013] Furthermore, the oxidation roasting conditions of step 3 are: microwave radiation frequency 5-10 GHz, the flow rate of air or oxygen-enriched air is 60-120 L / min, the oxygen content of oxygen-enriched air is ≥30%, and the oxidation roasting temperature is 1000±50°C.

[0014] Furthermore, the hydrothermal reaction conditions of step 4 are: placing the oxidative roasting product below 200° C. in clean water at room temperature at a liquid / solid ratio of 1 to 2, reacting for more than 2 hours, filtering, and then cooling to room temperature to obtain a NaOH solution or a concentrated crystalline NaOH solid.

[0015] Working principle and features of the present invention:

[0016] The first chemical reaction involved in the present invention is the carbon thermal reduction reaction of sodium sulfate crystals, that is, Na2S04+4C=Na2S+4C0. When there is no or little oxygen in the microwave oven, the red-hot reducing carbon will mainly capture the oxygen in the sulfate radical and make S 6+ Restore to S or S 2- , while Na + It will quickly react with the reduced sulfur component to generate Na2S. In the case of no artificial introduction of air or other oxygen-containing gases into the microwave oven, the reduced carbon absorbs a large amount of microwaves to generate instantaneous high temperature, mainly taking away oxygen from the sulfate ion to produce carbon thermal reduction reaction. Since microwave heating does not require heat-conducting materials and there is no temperature gradient, and the reduced carbon is an excellent material for absorbing microwaves, it can absorb microwaves uniformly and simultaneously from the inside and outside of the material to quickly generate heat, and at the same time consume the oxygen remaining in the air in the microwave oven, promote the carbon thermal reduction reaction of sodium sulfate, and the reaction speed is fast. In addition, due to the addition of excessive reduced carbon, the carbon thermal reduction reaction of sodium sulfate can be carried out more thoroughly, and only Na2S and carbon monoxide can be generated in the end.

[0017] The second chemical reaction involved in the present invention is the oxidation roasting of Na2S, i.e., 2Na2S+302=2Na20+2S02 or Na2S+202=Na202 (sodium peroxide)+S02 or Na2S+302=Na02 (sodium superoxide)+S02. Since Na2S is a substance that highly absorbs microwaves, the oxidation roasting of sodium sulfide can also be carried out uniformly and rapidly inside and outside. As long as the air or oxygen-enriched air introduced is promoted, the oxidation roasting of sodium sulfide can be carried out thoroughly. The obtained oxidation roasting product is mainly sodium oxide, and even if it contains some sodium peroxide or sodium superoxide, it will not affect the subsequent hydrothermal reaction of sodium oxide.

[0018] The third chemical reaction involved in the present invention is the hydrothermal reaction of sodium oxide, that is, Na20+H20=2Na0H or Na202+H20=2Na0H+1 / 20 or 2Na02+H20=2Na0H+03,03→1 / 20+02. Since the hydrothermal reaction of sodium oxide is an exothermic reaction, the temperature of the hydrothermal reaction can reach about 100°C. The present invention controls the liquid / solid of the hydrothermal reaction of sodium oxide to be 1-2, which is conducive to obtaining a Na0H solution with a higher concentration and a concentrated cooling crystallized Na0H solid.

[0019] Through the control and operation of the above three chemical reaction mechanisms, the present invention converts the sodium sulfate crystal solid waste into high-value, widely used NaOH for recycling, eliminating the environmental hazards and warehouse storage of the sodium sulfate crystal solid waste.

[0020] The beneficial effects of the present invention are: achieving comprehensive recovery and treatment of sodium sulfate crystal solid waste with very low economic value, the obtained NaOH and its crystal products have wide applications, the economic value is much greater than that of Na2S04 crystals, and carbon monoxide and sulfur dioxide can be recovered at the same time. DETAILED DESCRIPTION

[0021] The present invention will be further described below by way of examples.

[0022] Example: A method for treating sodium sulfate crystal solid waste, the specific implementation scheme is as follows:

[0023] Step 1. Add reducing carbon powder to sodium sulfate crystal solid waste and mix them evenly; then add pulp paste as a binder to make the mixture into agglomerates or particles; the sodium sulfate crystal solid waste is solid waste containing sodium sulfate components ≥ 90%; the reducing carbon powder is coke powder or activated carbon powder or carbon black powder, and its added amount is 1.2 to 1.3 times the theoretical required amount according to the chemical reaction equation: Na2S04+4C=Na2S+4C0; the added amount of pulp paste is 6 to 8% of the total mass of the material.

[0024] Step 2. placing the sodium sulfate crystal solid waste agglomerates or particles in step 1 in a microwave oven to first perform a carbon thermal reduction reaction to obtain Na2S solid and CO gas; the microwave carbon thermal reduction reaction conditions are: microwave radiation frequency of 1 to 10 GHz, carbon thermal reduction reaction temperature of 800 to 1000° C., reaction time of more than 30 minutes, and the end point of the reduction reaction is that the waste gas discharged through the gas duct is slightly burned or not burned;

[0025] Step 3. After the carbon thermal reduction reaction in step 2 reaches the end point, air or oxygen-enriched air is introduced into the microwave oven through the air inlet pipe to carry out oxidative roasting of Na2S; a solid mixture of sodium oxide, sodium peroxide or sodium superoxide is obtained, and the generated SO2-containing waste gas is recycled through the air guide pipe; the oxygen-enriched air is air containing ≥30% oxygen; the conditions for the oxidative roasting of Na2S are: microwave radiation frequency 5-10GHz, the flow rate of air or oxygen-enriched air is 60-120L / min, the oxidative roasting temperature is 1000±50℃, and the end point of oxidative roasting is that the discharged waste gas contains SO2≤100mg / m 3 ;

[0026] Step 4. Cool the sodium oxide, sodium peroxide or sodium superoxide mixture in step 3 to below 200° C., take it out and place it in clean water at room temperature for hydrothermal reaction to obtain a NaOH solution; the liquid / solid ratio of the hydrothermal reaction is 1 to 2, and the temperature is the natural temperature of the reaction;

[0027] Step 5. Filter the NaOH solution in step 4 and cool the crystallized NaOH or re-concentrate the crystallized NaOH; the crystallization mother liquor is returned to step 4 for hydrothermal reaction.

[0028] Example 1. A certain enterprise uses sodium carbonate solution to absorb and wash the sulfur-containing tail gas of the rotary kiln, and produces a mixture of sodium sulfate and sodium sulfite. After concentration and crystallization, the purity of sodium sulfate is 91.5%. The sulfate mixture is added with coke powder according to 1.3 times the theoretical amount of carbon required by the Na2S04+4C→Na2S+4C0 reduction reaction equation. After mixing evenly, 8% of paper pulp paste binder is added to granulate into soybean-sized particles. Then put it into a microwave oven with a power of 2KW, turn on the microwave radiation, and perform carbon thermal reduction smelting at a frequency of 2GHz and a temperature of 850℃. The CO2 waste gas is ignited through the outlet of the microwave oven gas duct. After 40 minutes, the CO2 burns out. Then air is introduced through the microwave oven air intake duct for oxidative roasting, the microwave radiation frequency is controlled to 5GHz, the oxidative roasting temperature is 900±50℃, and the oxidative roasting is 60 minutes. The oxidative roasting waste gas contains 112mg / m2 of SO2 through the gas duct sampling test. 3 The microwave radiation was turned off, the temperature was lowered to 150°C, the air was stopped, the oxidation roasting product was taken out, and it was placed in a normal temperature clear water pool for hydrothermal reaction at a liquid / solid ratio of 1. The water temperature was lowered to below 70°C, the hydrothermal reaction residue was filtered, and the NaOH solution was measured to contain 38.5% NaOH.

[0029] Example 2. A company uses N 235 Kerosene extractant extracts germanium from the germanium-containing zinc sulfate solution, and 30% NaOH solution is used to strip germanium. The germanium-containing stripping solution is then neutralized with sulfuric acid and hydrolyzed to precipitate to produce germanium concentrate. The solution after hydrolysis and precipitation is concentrated and crystallized with sodium sulfate to obtain a sodium sulfate crystal solid waste with a purity of 95.4%. The solid waste is added with carbon black powder at 1.2 times the theoretical amount required by the carbon thermal reduction reaction equation, mixed evenly, and then 6% of paper pulp paste is added. The pellets are granulated into bean size and first subjected to microwave carbon thermal reduction reaction. The microwave power is 2KW, the microwave radiation frequency is 3GHz, the carbon thermal reduction reaction temperature is 850±50℃, the carbon thermal reduction reaction time is 60 minutes, and the CO at the outlet of the microwave oven air duct is tested to be extinguished. Oxygen-enriched air containing 30% oxygen is introduced through the microwave oven air intake pipe, the microwave radiation frequency is adjusted to 5GHz, the oxidation roasting temperature is 950±10℃, and the exhaust gas is tested after 30 minutes to contain SO2120mg / m 3 After 40 minutes, the exhaust gas contains SO290mg / m 3 The microwave radiation was turned off, and the air was continued to be introduced to cool down to 210°C. The oxidative roasting product was taken out and hydrothermal reaction was carried out at a liquid / solid ratio of 0.8 to obtain a NaOH solution containing 46.5% NaOH. The solution was continued to be cooled down to room temperature for crystallization to obtain NaOH crystals with a proportion of 20.5%.

[0030] Example 3. Take 5 kg of sodium sulfate crystal solid waste stored in a warehouse of a certain enterprise, and the sodium sulfate content is 80.6%. According to the conditions of Example 1, microwave carbon thermal reduction reaction is first carried out, and then microwave oxidation roasting is carried out. Take out the roasted product and carry out hydrothermal reaction to obtain a NaOH solution with a concentration of 28.5%.

[0031] Based on the reality that sodium sulfate crystal solid waste cannot be treated after long-term storage and comprehensive recovery is not carried out, the invention proposes a process flow in which microwave radiation carbon thermal reduction smelting is first carried out in a microwave oven to obtain Na2S and relatively pure carbon monoxide, then the Na2S is subjected to microwave air or oxygen-enriched air oxidation roasting to obtain a mixture of Na2O or sodium peroxide or sodium superoxide and SO2 waste gas, and then the mixture of sodium oxide or sodium peroxide or sodium superoxide is subjected to hydrothermal reaction to obtain a Na0H solution or a Na0H crystal solid. The invention can realize comprehensive recovery and environmental protection management of sodium sulfate crystal solid waste.

[0032] The above examples are only used to further illustrate the present invention, and the present invention is not limited thereto.

Claims

1. A method for treating sodium sulfate crystal solid waste, characterized in that: The specific implementation steps are as follows: Step 1. Evenly mix the sodium sulfate crystal solid waste and the reduced carbon powder, and use paper pulp paste as a binder to form agglomerates or particles; Step 2. placing the sodium sulfate crystal solid waste agglomerates or particles prepared in step 1 in a microwave oven for carbon thermal reduction smelting to obtain sodium sulfide solid and carbon monoxide gas; the smelting end point is when the carbon monoxide gas discharged from the microwave oven through the gas duct no longer burns; Step 3. After the carbon thermal reduction smelting in step 2 is completed, air or oxygen-enriched air is introduced into the microwave oven to perform oxidative roasting of sodium sulfide to obtain a mixture of sodium oxide, sodium peroxide, sodium superoxide and a mixed waste gas of SO2 and air; the end point of oxidative roasting is that the discharged waste gas contains SO2 ≤ 100 mg / m 3 until; Step 4. After the oxidation roasting in step 3 is completed, the temperature is lowered to below 200° C., and the oxidation roasting product is taken out and placed in clean water at room temperature for hydrothermal reaction; after filtering, a NaOH solution or a concentrated crystalline NaOH solid is obtained.

2. A method for treating sodium sulfate crystal solid waste as claimed in claim 1, characterized in that: The sodium sulfate crystal solid waste in step 1 is solid waste with sodium sulfate crystals as the main component and a sodium sulfate content of ≥90%; the reducing carbon powder is coke powder or activated carbon powder or carbon black powder, and the added amount is 1.2 to 1.3 times the theoretical amount required according to the chemical reaction equation Na2S04+4C=Na2S+4C0; the amount of paper pulp paste binder is 6 to 8% of the total mass.

3. A method for treating sodium sulfate crystal solid waste as claimed in claim 1, characterized in that: The conditions of the microwave carbon thermal reduction smelting in step 2 are: microwave radiation frequency of 1 to 10 GHz, temperature of 800 to 1000° C., time of more than 30 minutes, and until the carbon thermal reduction reaction waste gas discharged from the microwave oven through the gas duct no longer burns.

4. A method for treating sodium sulfate crystal solid waste as claimed in claim 1, characterized in that: The oxidation roasting conditions of step 3 are: microwave radiation frequency 5-10 GHz, the flow rate of air or oxygen-enriched air is 60-120 L / min, the oxygen content of oxygen-enriched air is ≥30%, and the oxidation roasting temperature is 1000±50°C.

5. A method for treating sodium sulfate crystal solid waste as claimed in claim 1, characterized in that: The hydrothermal reaction conditions of step 4 are: placing the oxidative roasting product below 200° C. in clean water at room temperature at a liquid / solid ratio of 1 to 2, reacting for more than 2 hours, filtering, and then cooling to room temperature to obtain a NaOH solution or a concentrated crystalline NaOH solid.