CN1772345A - Waste gas desulfurizing method with composite absorbant comprising pyrolusite and pH buffering agent - Google Patents

Abstract

The invention is a method combining resource removal of sulfur dioxide waste gas and improvement of added value of pyrolusite comprehensive utilization. The method is to use the compound absorbent made of pyrolusite pulp and pH buffer agent to carry out redox and neutralization reaction with waste gas containing sulfur dioxide (SO ₂ ) to remove sulfur dioxide in the waste gas, and discharge the waste gas after it reaches the standard after purification, and absorb the tail liquid (Containing manganese sulfate) After purification and removal of impurities, manganese sulfate products can be directly obtained through evaporation and crystallization; electrolytic metal manganese products can also be obtained at the cathode through DC electrolysis, and sulfuric acid and a small amount of manganese sulfate contained in the anolyte can be obtained by adding carbonic acid After carbonization of ammonium bicarbonate or ammonium carbonate, high-purity manganese carbonate product is obtained after removing impurities from the precipitate, and ammonium sulfate product is obtained after concentrating and crystallizing the supernatant of the precipitate, thus realizing waste treatment by waste, recovery of sulfur resources and comprehensive utilization of soft The purpose of manganese ore. The method of the invention has reasonable technology and no secondary pollution, and is an ideal method for treating waste gas containing sulfur dioxide (SO ₂ ) and improving the added value of comprehensive utilization of pyrolusite.

Description

Method for waste gas desulfurization using pyrolusite and pH buffer as composite absorbent

1. Technical field

The invention relates to a method for absorbing sulfur dioxide in exhaust gas based on pyrolusite as an absorbent, which is used for the treatment of exhaust gas containing sulfur dioxide and the development and utilization of pyrolusite, and is a method for recycling sulfur resources and comprehensively utilizing manganese resources.

2. Background technology

Electrolytic manganese metal has a wide range of uses. In addition to being mainly used in the iron and steel industry for refining alloy steel, such as stainless steel, special alloy steel, stainless steel electrodes, etc., it can also be used in non-ferrous alloys, chemicals, medicine, food, analysis, scientific research, etc., so manganese deficiency Most countries usually reserve it as a strategic material. The production process of traditional electrolytic manganese metal mainly includes two steps of preparation of manganese sulfate electrolyte and electrolysis. Wherein the production method of manganese sulfate electrolyte mainly contains two kinds: (1) rhodochrosite method: generally need rhodochrosite powder with manganese content greater than 20%, react with dilute sulfuric acid under the condition of 80～90 ℃, generate manganese sulfate solution, Then the manganese sulfate electrolyte is obtained after purification and removal of impurities. This process method is the most important production method of manganese sulfate electrolyte. (2) pyrolusite method: it mixes pyrolusite powder containing more than 65% _MnO2 with white coal powder in a mass ratio of 100:20, and performs reduction roasting at 700°C-850°C in a reduction roaster to produce MnO, and then cool the MnO to room temperature under the condition of isolating the air, dissolve the cooled MnO with about 15% dilute sulfuric acid, and then purify and remove impurities to prepare the manganese sulfate electrolyte. These two manganese sulfate electrolyte production methods all consume a large amount of sulfuric acid, resulting in higher production costs of traditional electrolytic manganese metal. The manganese sulfate electrolyte is electrolyzed by direct current electrolysis, and the electrolytic metal manganese product can be obtained at the cathode, while dilute sulfuric acid is generated at the anode. In the traditional electrolytic manganese industry, the anolyte containing dilute sulfuric acid and part of Mn ²⁺ is usually recycled as supplementary dilute sulfuric acid in the production process of manganese sulfate electrolyte.

Manganese sulfate is an important chemical product. In addition to being used as chemical and metallurgical raw materials, it can also be used in medicine, papermaking, ceramics, catalysts, ore flotation, feed additives, production of electrolytic manganese and other manganese salts. The traditional manganese sulfate production method is relatively complicated. The main method is to prepare the manganese sulfate solution by the rhodochrosite method and the pyrolusite method, and then purify and remove impurities, stand still, evaporate and crystallize, and centrifuge. In addition to hot air drying to obtain manganese sulfate, there are two following methods: (1) ferrous sulfate method, the mixed solution of manganese sulfate and ferric sulfate is generated by the reaction of pyrolusite and ferrous sulfate, and then purified to remove iron, stand still, Manganese sulfate is obtained by evaporating crystallization, centrifuging, and drying with hot air. (2) The acid-adding method of two ores, using pyrolusite and pyrite to react under the condition of sulfuric acid to generate a mixed solution of manganese sulfate and ferric sulfate, after the mixed solution is purified and removed, left to stand, evaporated and crystallized, and centrifuged , and then dried with hot air to obtain manganese sulfate. The production of manganese sulfate by rhodochrosite method and pyrolusite method will consume a large amount of sulfuric acid, resulting in higher production cost of traditional manganese sulfate; The iron impurity content of the input is relatively high, resulting in complex impurity removal process, high cost, and the quality of manganese sulfate product is affected.

In China, with the rapid development of the economy, soot-type air pollution is also _becoming more and more serious. In 1999, China's SO ₂ emissions had reached 27.3 million tons, ranking first in the world. The direct economic loss caused by the disaster amounted to more than 100 billion yuan. According to the "21st Century Agenda" and the needs of China's sustainable development strategy, China's National Environmental Protection Agency has divided the coal-burning pollution area into two areas in China, namely the SO ₂ emission control area and the acid rain control area. In 2020 and 2020, the standard will be achieved, and the total amount control and SO ₂ emission charging system will be implemented accordingly. For small and medium-sized coal-fired boilers that do not meet emission standards, they will be forced to shut down. Since 1998, each province in the country has successively formulated specific implementation rules and implemented them gradually. On the other hand, China's national economic structure and economic development level determine that China's coal-based energy structure will be difficult to change for a long time. Therefore, enterprises urgently need flue gas desulfurization technology suitable for China's national conditions.

The traditional sulfur dioxide-containing waste gas treatment process mainly uses alkaline absorbents such as calcium-based, sodium-based and amino to absorb sulfur dioxide in the waste gas. These methods play a certain role in reducing industrial SO ₂ pollution to the atmosphere, but these methods are in In terms of the supply of absorbent and the sales of by-products, there are high costs or limited sources of desulfurization raw materials, such as the consumption of ammonia water in ammonia desulfurization, the consumption of sodium carbonate or sodium hydroxide in sodium alkali method, and the consumption of magnesium oxide in magnesium oxide method. Consumption, the source of phosphate rock in the ammonium phosphate fertilizer method, and the source of limestone in the gypsum method; second, there are secondary pollution problems to varying degrees. Therefore, it is of great significance to seek a new sulfur dioxide-containing exhaust gas treatment method with high efficiency, less secondary pollution, and significant economic benefits to promote the control of air pollution.

The use of pyrolusite slurry for flue gas desulfurization, commonly known as wet flue gas desulfurization, has recently attracted widespread attention and has become a popular research field, and has achieved many research results. The method utilizes the oxidation-reduction property of SO ₂ in exhaust gas and MnO ₂ in pyrolusite to desulfurize, and utilizes the absorption tail liquid to by-produce MnSO ₄ . As far as flue gas desulfurization is concerned, this process can not only effectively remove SO ₂ in flue gas, but also make sulfur be resourced in the form of marketable MnSO ₄ . For the production of manganese sulfate, this process saves the high-temperature reduction process and sulfuric acid raw materials of the traditional production process, which has a significant role in promoting the development of manganese products. Therefore, the desulfurization process of pyrolusite resources is very important for the development and utilization of pyrolusite resources in western China. , the control of coal-fired sulfur-containing flue gas pollution has realistic environmental and economic benefits. A number of Chinese patents have been applied for the research results of using pyrolusite pulp for flue gas desulfurization. The applicant disclosed in the Chinese Patent Gazette is Guangxi University, and the patent application number is 89107720.0 "A new method for producing industrial manganese sulfate by absorbing sulfur dioxide from pyrolusite pulp", the process absorption process clearly recorded in the patent application documents, which is used to absorb the absorption of sulfur dioxide The agent is pyrolusite pulp only, and no other absorbent components are mentioned. The patent application number published in the Chinese Patent Gazette is 89104140.0, and the title is "Desulfurization method for sulfur-containing flue gas or tail gas". For desulfurization, the sulfur-containing gas is converted into water-soluble manganese sulfate after contacting with the desulfurizer. The manganese oxides disclosed in it are insoluble or insoluble manganese oxides, essentially mainly pyrolusite containing manganese dioxide, and no other absorbent components are mentioned. The patent application number disclosed in the Chinese Patent Gazette is 200420033268.7, and the name is "flue gas desulfurization resource utilization equipment". The process absorption process clearly recorded in the application document, the pulp entering the reactor is pure pyrolusite pulp, that is, only pyrolusite The pulp is absorbent and no additives of other ingredients are added. The patent application number published in the Chinese Patent Gazette is 03135926.4.0, and the title is "A method for absorbing sulfur dioxide from flue gas and producing manganese sulfate with pyrolusite pulp and rhodochrosite pulp". The process absorption process clearly recorded in the application document is, enter The pulp in the absorption tower is pure pyrolusite pulp, and only rhodochrosite is added to the pulp tank to adjust the pH value. The rhodochrosite pulp is only used as a pH regulator for the absorption tail liquid, instead of entering the absorber together with the pyrolusite pulp for desulfurization absorption. agent.

The above-mentioned methods of absorbing and removing sulfur dioxide in the flue gas with pyrolusite pulp in the above-mentioned prior art all have such a deficiency, that is, in the absorption reaction system of pyrolusite pulp absorbing _SO2 in the waste gas, the sulfuric acid formed has affected the SO2 in the waste gas. ₂ absorption and leaching of manganese in pyrolusite, the absorption rate of SO ₂ and the leaching rate of manganese in pyrolusite are not high, which leads to the low purification rate of exhaust gas desulfurization and the low utilization rate of manganese. In addition, as far as the inventor knows, the current method of absorbing and removing sulfur dioxide in the flue gas with pyrolusite pulp is to only obtain the manganese sulfate product after the absorption tail liquid containing manganese sulfate after desulfurization is processed, and for further utilization of it The research results of preparing electrolytic manganese and other products have not been reported. As we all know, the added value of manganese sulfate products is far lower than that of electrolytic manganese products. The market value of 1 ton of manganese sulfate is only equivalent to 1/4 of that of 1 ton of electrolytic manganese.

3. Contents of the invention

In view of the defects existing in the wet flue gas desulfurization method of the prior art, the purpose of the present invention is to propose a new combination of waste gas desulfurization and pyrolusite comprehensive utilization, with high desulfurization efficiency, high manganese utilization rate, and secondary A wet waste gas desulfurization method with less pollution and significant economic benefits can reduce and control the pollution of sulfur dioxide in the waste gas to the atmosphere, promote the development of wet waste gas desulfurization technology, and increase the added value of the comprehensive utilization of pyrolusite.

Aiming at the defects existing in the existing pyrolusite pulp flue gas desulfurization method, the basic idea of the present invention is to provide a kind of using pyrolusite and pH buffer as a new composite absorbent to absorb sulfur dioxide in the waste gas, and discharge the waste gas after the purification reaches the standard, absorbing After the tail liquid (containing manganese sulfate) is purified and removed, qualified manganese sulfate can be obtained directly through evaporative crystallization and drying; it can also be further subjected to direct current electrolysis to obtain electrolytic metal manganese products at the cathode. Manganese, after carbonization by adding ammonium bicarbonate, remove impurities from the precipitate to obtain high-purity manganese carbonate product, and obtain ammonium sulfate product after concentrating and crystallizing the supernatant of the precipitate, thus realizing waste treatment by waste, recovery of sulfur resources and comprehensive The purpose of using pyrolusite.

The purpose of the present invention is achieved by the technical solution consisting of the following measures:

A method for desulfurizing waste gas by using pyrolusite and a pH buffer as a composite absorbent comprises the following process steps:

(1) mix pyrolusite and pH buffering agent according to the mass ratio of 20:1～5:1, and then mix with water to form a composite absorbent with a liquid-solid mass ratio of 10:1～2:1;

(2) The prepared composite absorbent is in direct contact with the sulfur-containing waste gas for absorption and desulfurization reaction to remove SO ₂ in the waste gas, and the desulfurized gas is discharged into the atmosphere, and the tail liquid after the reaction enters the next process;

(3) Absorb the tail liquid through solid-liquid separation, and the gained liquid phase is water-soluble manganese sulfate, then add the impurity removal agent to carry out the impurity removal reaction, carry out the solid-liquid separation again after the impurity removal reaction ends, the gained liquid phase can be further carried out Processed manganese sulfate solution.

Said pH buffering agent in above-mentioned scheme is the buffering agent that suppresses sulfuric acid formation speed, can be selected from carbonate, the alkali metal oxide that can form pH buffering system with dilute sulfuric acid, hydroxide. Preference is given to MnCO ₃ , NH ₄ HCO ₃ , (NH ₄ ) ₂ CO ₃ .

The impurity remover mentioned in the above scheme is at least one of oxidizing agent, lye and vulcanizing agent. The oxidizing agent is selected from manganese oxide (MnO), hydrogen peroxide (H ₂ O ₂ ), etc.; the lye is selected from lime water, ammonia water, etc.; the vulcanizing agent is selected from barium sulfide, ammonia sulfide, copper reagent, etc. Impurities in manganese sulfate solution are removed by adding impurity remover to react with impurities in the solution to form precipitates, and then remove impurities by solid-liquid separation. Therefore, the type and amount of impurity remover added depend on the type and amount of impurities contained in pyrolusite pulp.

The purified manganese sulfate solution prepared by the above scheme can further produce manganese sulfate products. The specific method is to heat the purified manganese sulfate solution to make it evaporate and crystallize. After the crystallization reaction is completed, solid-liquid separation is carried out, and the obtained solid phase is dried to be the finished manganese sulfate to be produced.

The purified manganese sulfate solution prepared by the above scheme can further produce electrolytic manganese products, manganese carbonate products and ammonium sulfate products. The specific method is to electrolyze the purified manganese sulfate solution to produce electrolytic manganese, and then add a carbonizing agent to the electrolytic anolyte for carbonization reaction. The manganese carbonate product, the liquid phase is heated, evaporated, crystallized and dried to obtain the ammonium sulfate product. In order to produce higher-purity manganese carbonate products, a carbonizing agent can be added to the electrolytic anolyte before the carbonization reaction to adjust the pH value to be neutral by adding an ammonia water regulator to further remove impurities. The pH value of the electrolytic anolyte is adjusted to be neutral, and other regulators can also be added for adjustment. After the pH value of the electrolytic anolyte is adjusted to be neutral, the added carbonizing agent can be ammonium bicarbonate, ammonium carbonate and the like. The control conditions for direct current electrolysis of manganese sulfate solution are: the concentration of Mn ²⁺ in the cathode room is 15-20g/L, the concentration of (NH ₄ ) ₂ SO ₄ in the bath is 110-130g/L, the pH value is 7-8.4, and the temperature is 35 ～40℃, cathode current density 350～420A/m ² , anode current density 600～700A/m ² , cell voltage 4.2～5.3V, pole distance of the same name about 100mm, electrolysis cycle 24～48h.

A part of the purified manganese sulfate solution produced by the above scheme can be used to further produce manganese sulfate products, and the remaining part can be further produced to produce electrolytic manganese products, manganese carbonate products and ammonium sulfate product sulfur. The specific preparation method is as above.

The present invention also takes some other technical measures.

The inventors of the present invention have carried out in-depth research on the traditional pyrolusite pulp flue gas desulfurization method. The research results show that when using the traditional pyrolusite pulp flue gas desulfurization method to absorb SO ₂ -containing waste gas, the main reaction in the system is the redox reaction between MnO ₂ in the pyrolusite and SO ₂ absorbed in the pulp. The product is related to the pH value of the system. When the pH value of the system is higher than 3, the reaction mainly generates manganese sulfate and a small amount of sulfuric acid; when the pH value of the system is lower than 3, the reaction also generates a large amount of manganese sulfate Manganese dithionate, and manganese dithionate is unstable and will be decomposed into sulfuric acid and _SO2 gas, which will rapidly reduce the pH value of the pulp to below 1, inhibit the absorption rate of pyrolusite pulp on _SO2 waste gas, and then affect the The leaching of manganese in pyrolusite is limited, which makes it difficult for the traditional pyrolusite pulp flue gas desulfurization method to simultaneously obtain the SO ₂ absorption rate to ensure that SO ₂ meets the emission standard and the leaching rate of manganese that makes full use of pyrolusite. For the technical scheme that the patent No. is 03135926.4.0, adopt rhodochrosite as the adjusting agent of absorbing tail liquid pH value, but because a large amount of other impurity exists in the rhodochrosite, according to the industrial data of traditional rhodochrosite method production manganese sulfate, rhodochrosite The reaction of manganese ore and sulfuric acid can only be carried out normally at a relatively high temperature (generally above 80°C), while the temperature of the absorbing liquid under general flue gas desulfurization conditions does not exceed 50°C, so it is difficult to implement, and it has been confirmed by the inventors that the use of The effect of rhodochrosite as a pH regulator of the absorption tail liquid is indeed not obvious.

The present invention can combine the production of manganese sulfate, electrolytic metal manganese, high-purity manganese carbonate and ammonium sulfate with the treatment of _SO2- containing waste gas. Compared with the prior art, it not only saves the manganese sulfate in the traditional electrolytic manganese production The electrolyte preparation process saves a lot of sulfuric acid. In addition, because the absorbent used in the present invention is a composite absorbent composed of pyrolusite pulp and pH buffering agent, it can fundamentally solve the problem of sulfuric acid in the _SO2 absorption system existing in the traditional pyrolusite pulp flue gas desulfurization method. ₂ The problem of the absorption rate, so that the absorption rate of SO ₂ in the waste gas can reach more than 90%, and the discharge of SO ₂ waste gas can be achieved. At the same time, the high absorption rate of SO ₂ ensures the high leaching rate of manganese in pyrolusite, which can The leaching rate of manganese can reach more than 85%, and the full utilization of pyrolusite is realized. The electrolytic manganese product obtained by the method of the present invention can reach above the national secondary standard after being processed, and the high-purity manganese carbonate obtained by using the electrolytic manganese anolyte can be recycled and value-added as the preferred additive manganese carbonate on the one hand. , which improves the added value of the comprehensive utilization of pyrolusite; at the same time, the ammonium sulfate obtained enables the resource recovery of sulfur dioxide in the flue gas, and realizes the resource recovery of SO ₂ waste gas. This method combines many sets of traditional processes such as flue gas desulfurization process, electrolytic manganese process, high-purity manganese carbonate production process, ammonium sulfate production process, etc. Technology, new method have reached the purpose of invention.

The method disclosed by the present invention for exhaust gas desulfurization using pyrolusite and pH buffer as a composite absorbent has the following outstanding advantages and effects:

(1) The used raw material pyrolusite of the present invention is natural ore, and reserves are abundant, and price is cheap, and grade requirement is not high (containing manganese 20～25%), and only needs mechanical crushing to 100 order and gets final product during use. The preferred additive is industrial grade manganese carbonate, which is easily available in the market.

(2) The present invention has not only utilized pyrolusite and _SO Oxidation and reduction properties, but also controlled the generation of sulfuric acid in the system by using a pH buffer to control the pH value of the slurry in the reactor, and realized the efficient absorption of sulfur dioxide in the waste gas At the same time, a higher manganese leaching rate is obtained.

(3) The present invention can realize resource recovery, harmlessness and reduction of _SO2 waste gas. The present invention can not only be used for SO ₂ waste gas treatment of coal-fired boilers, including large boilers in thermal power plants, small and medium-sized coal-fired boilers and steam boilers, but also can be used for sintering SO ₂ waste gas treatment in ironworks and SO ₂ waste gas in non-ferrous smelting and chemical plants governance.

(4) The present invention can realize the value-added of the comprehensive utilization of pyrolusite and the value-added of the preferred additives such as manganese carbonate, which can be used for the comprehensive utilization of pyrolusite.

(5) adopt the inventive method, can also combine the exploitation and utilization of high-sulfur coal and pyrolusite, produce manganese sulfate or electrolytic manganese, high Pure manganese carbonate, ammonium sulfate, and the hot steam produced by the combustion of high-sulfur coal and the electricity it produces can supply the steam and electricity required for the above process, thus establishing a cycle that combines the development and utilization of high-sulfur coal and pyrolusite economic model.

4. Description of drawings

Fig. 1 is a schematic block diagram of the process flow of an embodiment of the present invention.

Fig. 2 is a schematic block diagram of a process flow in another embodiment of the present invention.

Fig. 3 is a schematic process flow diagram of a specific embodiment of the present invention.

Fig. 4 is a schematic process flow diagram of another specific embodiment of the present invention.

In accompanying drawing 3 and accompanying drawing 4, the meanings of each diagram label are as follows: 1 is the exhaust gas inlet, 2 is the flue gas desulfurization reactor, 3 is the exhaust gas outlet, 4 is the slurry mixing tank, 5 is the slurry pump, and 6 is the slurry inlet , 7 is the pulp outlet, 8 is the sedimentation separation tank, 9 is the mud pump, 10 is the filter separator, 11 is the impurity removal and purification pool, 12 is the dryer, 13 is the DC electrolytic cell, 14 is the electrolytic cathode, 15 is the electrolytic manganese washing Tank, 16 is an electrolytic manganese drier, 17 is a pH adjustment purification tank, 18 is a carbonization pool, 19 is a centrifugal separator, 20 is a manganese carbonate drier, and 21 is an ammonium sulfate drier.

The present invention will be further described in detail below in conjunction with the process flow diagram and examples, but the content of the present invention is not limited to the content involved in the examples.

Example 1:

The exhaust gas treated in this embodiment is coal-fired boiler exhaust gas, and the by-product of production is manganese sulfate. While recovering sulfur resources from the exhaust gas, the value of pyrolusite is increased, and the sulfur and manganese resources are comprehensively utilized to treat a scale of 35T/h. coal-fired boilers as an example. The amount of waste gas to be treated is 60000Nm ³ /h, the content of sulfur dioxide in the waste gas is 3000ppm, and the content of oxygen is 8%. The process flow of this embodiment is shown in Figure 3 . First mix pyrolusite and manganese carbonate in a mass ratio of 9:1, then mix with water in the slurry tank 4 equipped with a stirrer to make a slurry with a liquid-solid ratio (mass ratio) of 3:1, and pass the slurry pump 5 The pulp inlet 6 is pumped into the desulfurization reactor 2, and the exhaust gas containing SO ₂ first passes through the wet dedusting, cooling and humidifying, then enters the gas dispersing device through the exhaust gas inlet 1 of the desulfurization reactor 2, and then enters the pulp from the gas dispersing device absorbed within. The SO ₂ in the flue gas absorbs and reacts with the composite absorbent composed of pyrolusite and manganese carbonate to absorb and remove the SO ₂ in the exhaust gas, and the gas after the absorption reaches the standard is discharged from the gas outlet 3 of the desulfurization reactor.

Manganese carbonate as an absorption additive can also be replaced by carbonates, alkali metal oxides and hydroxides that can form a pH buffer system with dilute sulfuric acid. The desulfurization absorption tail liquid containing manganese sulfate, slag and water is discharged from the pulp outlet 7 of the desulfurization reactor and sent to the sedimentation separation tank 8. After sufficient settlement, the supernatant liquid containing suspended matter is pumped into the filtration separation tank by the mud pump 9 The device 10 separates the water-soluble manganese sulfate from the solid residue, and the liquid phase is an aqueous solution of manganese sulfate. The manganese sulfate aqueous solution is sent to the impurity removal purification pool 11 for purification treatment. In the impurity removal and purification unit, first add MnO ₂ oxidant to the manganese sulfate solution to oxidize the contained Fe ²⁺ impurities to Fe ³⁺ , then add lime water (or ammonia water) to the manganese sulfate solution to lower the pH of the manganese sulfate solution The value is adjusted to about 6.0, so that Fe ³⁺ and Al ³⁺ in the manganese sulfate solution are removed by precipitation; then barium sulfide (or ammonia sulfide, copper reagent) is added to the manganese sulfate solution to make the heavy metal ions Cu ²⁺ , pb ²⁺ , Co ²⁺ , Ni ²⁺ are removed by precipitation; then the manganese sulfate solution is heated until a white flocculent precipitate appears, so that the silicic acid and Mg ²⁺ in the manganese sulfate solution are removed; then the manganese sulfate solution is left standing for 24 After about 1 hour, the Ca ²⁺ in the manganese sulfate solution is removed by precipitation; after the above treatment, a relatively pure manganese sulfate solution is obtained, and then the manganese sulfate is obtained by heating, evaporation, concentration and crystallization reaction, and finally the manganese sulfate is subjected to the conditions of 150 ° C ~ 200 ° C The product manganese sulfate can be obtained by drying under the hood for two hours.

Example 2:

The exhaust gas treated in this embodiment is coal-fired boiler exhaust gas, and the by-products produced include electrolytic manganese, high-purity manganese carbonate and ammonium sulfate, and the value-added comprehensive utilization of pyrolusite is carried out while recovering sulfur resources from the exhaust gas. Taking the treatment of a coal-fired boiler with a scale of 35T/h as an example, the amount of waste gas to be treated is 60000Nm ³ /h, the content of sulfur dioxide in the waste gas is 3000ppm, and the content of oxygen is 8%. The process flow of this embodiment is shown in Figure 4 Show. First mix pyrolusite and manganese carbonate at a mass ratio of 15:1, and then mix them with water in the slurry tank 4 equipped with an agitator to form a slurry with a liquid-solid ratio (mass ratio) of 8:1, and pass the slurry pump 5 from the slurry inlet 6 Injected into the desulfurization reactor 2, the exhaust gas containing SO ₂ first passes through wet dust removal, cooling and humidification, and then enters the gas dispersion device through the exhaust gas inlet 1 of the desulfurization reactor 2, and then enters the pulp to be absorbed by the gas dispersion device . The SO ₂ in the flue gas absorbs and reacts with the composite absorbent composed of pyrolusite and manganese carbonate to absorb and remove the SO ₂ in the exhaust gas, and the gas after the absorption reaches the standard is discharged from the gas outlet 3 of the desulfurization reactor. Manganese carbonate as an absorption additive can also be replaced by carbonates, alkali metal oxides and hydroxides that can form a pH buffer system with dilute sulfuric acid. The desulfurization absorption tail liquid containing manganese sulfate, slag and water is discharged from the pulp outlet 7 of the desulfurization reactor and sent to the sedimentation separation tank 8. After sufficient settlement, the supernatant liquid containing suspended matter is pumped into the filtration separation tank by the mud pump 9 The device 10 separates the water-soluble manganese sulfate from the solid residue, and the liquid phase is an aqueous solution of manganese sulfate. The manganese sulfate aqueous solution is sent to the impurity removal purification pool 11 for purification treatment. In the impurity removal and purification unit, first add MnO ₂ oxidant to the manganese sulfate solution to oxidize the contained Fe ²⁺ impurities to Fe ³⁺ , then add lime water (or ammonia water) to the manganese sulfate solution to lower the pH of the manganese sulfate solution Adjust the value to about 5.5 (control range 5.5-6.0), so that Fe ³⁺ and Al ³⁺ in the manganese sulfate solution are precipitated and removed; then add barium sulfide (or ammonia sulfide, copper reagent) to the manganese sulfate solution to make the heavy metal Cu ²⁺ , Pb ²⁺ , Co ²⁺ , Ni ²⁺ are removed by precipitation; then the manganese sulfate solution is heated until a white flocculent precipitate appears, so that the silicic acid and Mg ²⁺ in the manganese sulfate solution are removed; then Let the manganese sulfate solution stand for about 24 hours to remove Ca ²⁺ in the manganese sulfate solution by precipitation; after the above treatment, a relatively pure manganese sulfate solution is obtained. The manganese sulfate solution is pumped into the electrolytic cell 13 with a centrifugal pump 9 for direct current electrolysis. The controlled electrolysis conditions of DC electrolysis are: the concentration of Mn ²⁺ in the cathode chamber is about 15g/L, the concentration of (NH ₄ ) ₂ SO ₄ in the bath is about 120g/L (control range 110-130g/L), and the pH value is about 8.4 (control Range 7~8.4), temperature about 35°C (control range 35~40°C), selenous acid (calculated as selenium) about 0.03g/L (control range 0.03~0.04g/L), cathode current density 400A/ ^m2 About (control range 350-420A/m ² ), anode current density about 640A/m ² (control range 600-700A/m ² ), cell voltage about 5.0V (control range 4.2-5.3V), electrode spacing of the same name 100mm About, the electrolysis cycle is about 30h (control range 24 ~ 48h). After the electrolysis is completed, the cathode plate 14 is passivated and washed in the passivation and cleaning pool 15, and then dried in the drier 16. After drying, the manganese is peeled off from the cathode plate to obtain qualified electrolytic manganese products. The cathode plates are reused after treatment. After electrolysis, the electrolytic anolyte containing (NH ₄ ) ₂ SO ₄ , MnSO ₄ is sent to the regulating purification tank 17, and ammonia water is added to the regulating purification tank 17 to adjust the pH value of the electrolytic anolyte to be neutral, and further washed and purified Remove traces of Na, Ca, Mg. The treated electrolytic anolyte flows into the carbonization pool 18, and a _NH4HCO3 solution with a concentration of about 6% (mass concentration) is added into the carbonization pool, and the _NH4HCO3 and _{the MnSO4} in the _solution carry out carbonization reaction to generate _MnCO3 precipitation and (NH ₄ ) ₂ SO ₄ , the aqueous precipitate is separated from solid and liquid by a centrifuge 19, and the solid phase precipitate is washed with water and centrifugally dried to obtain a high-purity manganese carbonate product with a manganese carbonate content higher than 98%. The liquid phase is the supernatant liquid containing (NH ₄ ) ₂ SO ₄ after the carbonization reaction, and the ammonium sulfate product whose (NH ₄ ) ₂ SO ₄ content is higher than 98% is obtained through evaporation, concentration, and crystallization and drying.

Claims (10)

1. A method for carrying out exhaust gas desulfurization with pyrolusite and pH buffering agent as a composite absorbent, characterized in that it comprises the following process steps: (1) After mixing pyrolusite and pH buffering agent at a mass ratio of 20:1 to 5:1, they are mixed with water to form a composite absorbent with a liquid-solid mass ratio of 10:1 to 2:1; (2) The prepared composite absorbent is in direct contact with the sulfur-containing waste gas to carry out absorption and desulfurization reaction to remove SO ₂ in the waste gas, and the desulfurized gas is discharged into the atmosphere, and the tail liquid after the reaction enters the next step; (3) Absorb the tail liquid through solid-liquid separation, and the gained liquid phase is water-soluble manganese sulfate, then add the impurity removal agent to carry out the impurity removal reaction, carry out the solid-liquid separation again after the impurity removal reaction ends, the gained liquid phase can be further carried out Processed manganese sulfate solution. 2. The method for desulfurizing waste gas with pyrolusite and pH buffering agent as composite absorbent according to claim 1, characterized in that the obtained manganese sulfate liquid is subjected to heating, evaporation and crystallization reaction, and solid-liquid separation is carried out after the crystallization reaction, and the obtained The solid phase was dried to obtain manganese sulfate. 3. The method for exhaust gas desulfurization using pyrolusite and pH buffering agent as a composite absorbent as claimed in claim 1, characterized in that the obtained manganese sulfate solution is electrolyzed to produce electrolytic manganese, and then a carbonizing agent is added into the electrolytic anolyte The carbonization reaction is carried out, and the solid-liquid separation is carried out after the reaction is completed. The solid phase is washed and dried to obtain the manganese carbonate product, and the liquid phase is heated, evaporated, crystallized and dried to obtain the ammonium sulfate product. 4. The method for exhaust gas desulfurization using pyrolusite and pH buffering agent as a composite absorbent as claimed in claim 3, characterized in that said electrolytic anolyte is added with ammonia water to lower its pH value before adding carbonizing agent to carry out carbonization reaction. Adjust to be neutral, and further remove impurities and purify. 5. The method for exhaust gas desulfurization using pyrolusite and pH buffering agent as composite absorbent as claimed in claim 3, characterized in that said carbonizing agent is selected from ammonium bicarbonate and ammonium carbonate. 6. The method for exhaust gas desulfurization using pyrolusite and pH buffering agent as a composite absorbent as claimed in claim 3, characterized in that said electrolysis is direct current electrolysis, and the electrolysis control conditions are: the concentration of Mn2 ⁺ in the cathode room is 15~ 20g/L, (NH ₄ ) ₂ SO ₄ concentration in the bath solution is 110~130g/L, pH value is 7~8.4, temperature is 35~40℃, cathode current density is 350~420A/m ² , anode current density is 600~700A/m m ² , the cell voltage is 4.2-5.3V, the pole distance of the same name is about 100mm, and the electrolysis cycle is 24-48h. 7. The method for exhaust gas desulfurization using pyrolusite and pH buffering agent as a composite absorbent as claimed in any one of claims 1 to 6, characterized in that said pH buffering agent is selected from carbonates, Alkali metal oxides and hydroxides that form a pH buffer system with dilute sulfuric acid. 8. The method for exhaust gas desulfurization using pyrolusite and pH buffer as composite absorbent as claimed in claim 7, characterized in that said pH buffer is MnCO ₃ , NH ₄ HCO ₃ , (NH ₄ ) ₂ CO ₃ . 9. The resource utilization method for exhaust gas desulfurization using pyrolusite and pH buffering agent as a composite absorbent as claimed in any one of claims 1 to 6, characterized in that the impurity remover is an oxidizing agent, lye and at least one of vulcanizing agents. 10. The method for exhaust gas desulfurization using pyrolusite and pH buffering agent as a composite absorbent as claimed in claim 9, characterized in that said oxidant is selected from manganese oxide and hydrogen peroxide, and the lye is selected from lime water, ammonia water, sulfide The reagent is selected from barium sulfide, ammonia sulfide, copper reagent.

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