A method for desulfurization of coal-fired flue gas using phosphorus tailings and simultaneously producing enriched phosphorus concentrate, high-quality calcium sulfate and magnesium hydroxide

Abstract

The present application relates to the inorganic chemical technology field, specifically to a method for using phosphorus tailings for flue gas desulfurization and simultaneously preparing enriched phosphorus concentrate, high-quality calcium sulfate and magnesium hydroxide. The present application uses phosphorus tailings after calcination, ammonium nitrate solvent leaching once to separate calcium and magnesium, and then uses magnesium to remove SO2 in flue gas, which has high desulfurization rate and fast reaction speed. Through the desulfurization process, enriched phosphorus concentrate, high-quality calcium sulfate and magnesium hydroxide are obtained, realizing the perfect combination of flue gas environmental protection desulfurization, comprehensive utilization of phosphorus tailings and high-value-added product manufacturing.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inorganic chemical industry, and particularly relates to a method for using phosphor tailings for flue gas desulfurization and simultaneously preparing phosphor concentrate, high-quality calcium sulfate and magnesium hydroxide. BACKGROUND

[0002] With the continuous development of society and industry, the degree of industrialization is higher and higher, the production scale is continuously expanded, and the flue gas discharged into the atmosphere is also more and more. Among various gaseous pollutants affecting the quality of the atmosphere, the amount of SO2 flue gas is the largest, and it has the greatest impact. It causes acid rain, destroys the ecological environment and affects human health. Therefore, before these industrial flue gas is discharged into the atmosphere, it needs to be treated, and the desulfurization treatment is particularly important.

[0003] Regarding flue gas desulfurization: at present, most domestic enterprises adopt the calcium carbonate-gypsum method to remove SO2 in flue gas. Inexpensive calcium carbonate powder or lime milk is used to react and absorb SO2 in flue gas, and the generated CaSO3 is oxidized to generate CaSO4. However, the product gypsum has low quality and large output, and only a small part of the market can be digested, and a large amount of storage is required, so not only the cost of desulfurization is increased, but also secondary pollution is caused, especially in high-sulfur coal production areas, the desulfurization of coal-fired power plants becomes a huge economic burden for the power generation industry.

[0004] At present, although there is a technical scheme of selecting dolomite which is cheap and easy to obtain in various places as a desulfurizing agent, for example, patent application 201710768665.0 (combined method of flue gas desulfurization and gas desulfurization pollutant resourceization to treat waste with waste) uses magnesium oxide obtained by calcining dolomite as raw material. This technical scheme needs a large amount of input ammonia gas, and is mainly aimed at the ammonia-containing gas generated by coke oven gas or coal chemical industry or petroleum chemical industry various gas making furnaces, etc. When the downstream user of ammonia gas is close, the separated magnesium sulfate solution can be directly transported; if the user is far away, the magnesium sulfate solution needs to be dehydrated before being transported, at this time, the energy consumption and process required for drying and packaging are relatively large costs. Since the power plants generating coal are often far away from the coking plants, this method is restricted by certain objective conditions.

[0005] Phosphorite resources are important strategic resources of the country and the material basis of the phosphor chemical industry. With the large-scale development and utilization of phosphorite resources, a large amount of tailings will be generated in the process of mining phosphorite. Phosphorite tailings refer to products that cannot enter the concentrate after crushing, grinding, flotation and other processes in the process of phosphorite beneficiation, mainly including phosphorite and gangue minerals. The existing beneficiation method has low phosphor resource utilization rate, and a large amount of tailings will bring great environmental risks. Exploring the comprehensive utilization of phosphor tailings and converting them into valuable resources are of great significance to promote the efficient and clean utilization of phosphorite resources in the phosphor chemical industry and realize sustainable development.

[0006] Therefore, it is a key research direction to find a medium for desulfurization process, fully utilize phosphorus tailings to obtain phosphorus concentrate and high-quality calcium sulfate and magnesium hydroxide, realize perfect combination of flue gas environmental desulfurization, comprehensive utilization of phosphorus tailings and high value-added product manufacturing, and combine a large amount of solid waste phosphorus tailings in phosphorus mine area with the flue gas desulfurization demand of surrounding coal-fired furnaces (mainly power plants). SUMMARY

[0007] In order to solve the above technical problems existing in the prior art, the present application provides a method for using phosphorus tailings for flue gas desulfurization and simultaneously preparing phosphorus concentrate, high-quality calcium sulfate and magnesium hydroxide, comprising the following steps:

[0008] A method for using phosphorus tailings for flue gas desulfurization and simultaneously preparing phosphorus concentrate, high-quality calcium sulfate and magnesium hydroxide, comprising the following steps:

[0009] (1) calcining the phosphorus tailings to obtain calcined mineral powder;

[0010] (2) stirring and reacting the calcined mineral powder and ammonium nitrate solution in a reaction tank to generate ammonia and effectively recover, and obtaining leaching solution A and leaching residue a through filtration separation, the leaching solution A being a mixed solution of calcium nitrate and a small amount of ammonium nitrate, and the leaching residue a being a mixture of fluorapatite and magnesium hydroxide;

[0011] (3) after the leaching residue a is slurried with water, it is pumped into a desulfurization tower and fully mixed with the dedusted flue gas in countercurrent to remove SO2 in the flue gas, at this time, a slightly soluble MgSO3 is generated, and the MgSO4 solution is obtained by introducing appropriate air for oxidation in the process, and the filtrate B and the filtration residue b are obtained through plate and frame pressure filtration separation; the filtrate B is a magnesium sulfate solution, and the filtration residue b is washed to obtain phosphorus concentrate containing a small amount of calcium sulfate (fluorapatite does not participate in the reaction);

[0012] (4) stirring and reacting the clarified and purified filtrate B with the filtrate A in a reaction tank, and obtaining the filtrate C and the filter cake c through plate and frame pressure filtration separation after the reaction is completed; the filtrate C is a magnesium nitrate solution containing a small amount of ammonium nitrate, and the filter cake c is washed and dried to obtain high-quality calcium sulfate;

[0013] (5) stirring and treating the filtrate C with ammonia water in a reaction tank to generate ammonia and effectively recover, and obtaining the filtrate D and the filter cake d through plate and frame pressure filtration separation after the reaction is completed; the filtrate D is an ammonium nitrate solution containing a small amount of magnesium nitrate, and the filter cake d is washed and dried to obtain high-quality magnesium hydroxide.

[0014] Further, the phosphorus tailings are solid waste discarded by phosphorus flotation, containing P2O5 5-10%, CaO 28-35%, and MgO 15-21% (mass fraction).

[0015] Further, the calcination in step (1) is performed at 750-1100℃ for 1-2h. At this time, the calcination has a good effect on the decomposition of calcium carbonate and magnesium carbonate in the phosphorus tailings.

[0016] Further, in step (2), the calcined ore powder and the ammonium nitrate solution are added in an amount of 120-150% of the theoretical amount of ammonium nitrate required for the mass fraction of MgO in the calcined ore powder.

[0017] Further, in step (2), the ammonium nitrate solution has a concentration of 10-40% ammonium nitrate solution, a reaction temperature of 35-70℃, and a reaction time of 30-120min. At this time, the reaction efficiency is high and the reaction effect is good.

[0018] Further, in step (3), the leaching residue a is slurried with water to 10-40%, the liquid-gas ratio in the desulfurization tower is controlled to 5-10L / m 3 , the reaction temperature is 40-100℃, and the reaction time is 30-90min. At this time, the magnesium hydroxide in the slurry reacts sufficiently with SO2 in the flue gas, and the obtained MgSO3 is oxidized by air to obtain MgSO4 solution B.

[0019] Further, in step (4), the filtrate B is added to the filtrate A in the reaction tank and stirred to control the reaction temperature to 30-120℃ and the reaction time to 30-90min. Under this condition, high-quality calcium sulfate is obtained, which has good economic value.

[0020] Further, the ammonia water in step (5) is prepared from the ammonia gas effectively recovered in step (2). In this application, the recovery and utilization of ammonia gas can theoretically achieve an ammonia cycle without consumption, and no additional ammonia gas is needed. Although there may be some loss in actual production, the overall still does not need to add a large amount of ammonia gas, which successfully makes the technical solution of the present application not need a large amount of input ammonia gas from the outside, and gets rid of the dependence on coking plants and the like.

[0021] Further, in step (5), the filtrate C is added to the ammonia water in the reaction tank and stirred to control the reaction temperature to 60-120℃ and the reaction time to 30-90min. Under this condition, high-quality magnesium hydroxide is obtained, which has high economic value. The filtrate D in step (5) is reused in step (2).

[0022] Chemical reaction principle of each step:

[0023] In step (1), CaCO3·MgCO3 in the phosphorus tailings begins to decompose at a high temperature of 750℃ or higher, and the specific equation is as follows:

[0024] CaCO3·MgCO3=CaO+MgO+2CO2

[0025] In step (2), the equation of ammonium nitrate leaching is as follows:

[0026] CaO + 2NH4NO3 = Ca(NO3)2 + 2NH3 + H2O

[0027] MgO + H2O = Mg(OH)2

[0028] In step (3), the specific equation is as follows:

[0029] SO2 + Mg(OH)2 = MgSO3 + H2O

[0030] 2MgSO3 + O2 = 2MgSO4

[0031] 2Ca(OH)2 + 2SO2 + O2 + 2H2O = 2CaSO4·2H2O

[0032] In step (4), the specific equation is as follows:

[0033] MgSO4 + Ca(NO3)2 + 2H2O = CaSO4·2H2O + Mg(NO3)2

[0034] In step (5), the specific equation is as follows:

[0035] Mg(NO3)2 + 2NH4OH = Mg(OH)2 + 2NH4NO3

[0036] The present application adopts phosphorus tailings after calcination, and then separates calcium and magnesium by one-time leaching with ammonium nitrate solvent, and then uses magnesium to remove SO2 in flue gas, so that the desulfurization rate is high, the reaction speed is fast, and through the desulfurization process, the enriched phosphorus concentrate, high-quality calcium sulfate and magnesium hydroxide are obtained, and the perfect combination of flue gas environmental protection desulfurization, comprehensive utilization of phosphorus tailings and high-value-added product manufacturing is realized.

[0037] Compared with the prior art, the technical effects of the present application are embodied in:

[0038] 1. The present application uses phosphorus tailings as a desulfurizer for removing SO2 in flue gas of coal-fired kiln and boiler of power plant, and compared with the existing calcium carbonate-gypsum method, the present application has the characteristics of fast reaction speed, high desulfurization rate, low investment cost, and low operation cost, completely solves the problem of low-quality desulfurization gypsum which is difficult to utilize, ingeniously combines the calcium and magnesium characteristics of a large amount of abandoned phosphorus tailings produced by phosphorus ore dressing with flue gas desulfurization to produce high-value-added calcium sulfate and magnesium hydroxide, and simultaneously recovers valuable phosphorus resources, and realizes the transformation of flue gas desulfurization environmental protection treatment from negative economic output to high income.

[0039] 2. The present application reasonably divides the functions of calcium and magnesium in phosphorus tailings, so that flue gas desulfurization is completed under more optimized conditions, and at the same time, the secondary environmental pollution risk and high disposal cost burden caused by low-quality desulfurization gypsum are avoided.

[0040] 3、The application uses phosphor tailings to replace limestone or light-burned magnesium oxide to treat flue gas desulfurization, which can basically achieve "waste treatment with waste" of phosphorus chemical waste and SO2 in coal-fired flue gas, and simultaneously solve the major problems restricting the development of two industries (mainly the phosphor mining and selection industry and the coal power generation industry), so that flue gas desulfurization changes from an enterprise burden to an economic growth point, and effectively promotes the enthusiasm of enterprise environmental protection investment and the social benefits of ecological environmental protection.

[0041] 4、In the process of the application, the ammonia gas generated in steps (2) and (5) is recycled in the system, which not only saves the cost of raw materials, but also fully utilizes the gas generated by the process, avoiding waste of resources and environmental pollution. In the process of the application, the liquid-gas ratio of the desulfurization tower is greatly reduced, the water consumption is reduced, and the washing water is fully recycled, which has significant environmental protection significance.

[0042] 5、In the technical scheme of the application, magnesium hydroxide products can be produced without a large amount of external ammonia gas input, and the magnesium sulfate products do not need to be dehydrated and dried and then transferred to a place where ammonia gas is generated to be re-prepared into magnesium hydroxide products, and there is no dilemma of being able to only produce low-value magnesium sulfate products without ammonia gas input.

[0043] 6、The high-quality calcium sulfate obtained by the application has a purity of more than 98% and a whiteness of more than 97%, and the market price is about 1200 yuan / ton; the high-purity magnesium hydroxide has a purity of more than 98% and a whiteness of more than 95%, and the market price is about 4500 yuan / ton, the low-value phosphor tailings are multiplied in value by being treated by flue gas desulfurization and high-efficiency combination, and have good economic benefits. The high-quality calcium sulfate obtained by the application is in short supply in the market, and solves the major problem that the low-quality gypsum produced by current desulfurization has a large output, and only a small part of the market can be digested, so not only the desulfurization cost is increased, but also secondary pollution is caused. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 is a flowchart of the application. DETAILED DESCRIPTION

[0045] The technical scheme of the application will be further limited in combination with specific embodiments, but the scope of protection is not limited to the description.

[0046] Example 1

[0047] Example 1

[0048] (1) The phosphor tailings are calcined at 950℃ for 1.5h to obtain calcined mineral powder;

[0049] (2) The calcined mineral powder and the 25% ammonium nitrate solution are added into the reaction tank for stirring reaction, the reaction temperature is 45°C, the reaction time is 60 min, ammonia gas is generated and effectively recovered, and leaching solution A and leaching residue a are obtained by filtration separation, the leaching solution A is a mixed solution of calcium nitrate, magnesium nitrate and ammonium nitrate, and the leaching residue a is a mixture containing calcium fluoro-phosphate and magnesium hydroxide;

[0050] (3) The leaching residue a (mainly a mixture of calcium fluoro-phosphate and magnesium hydroxide) is added into water for slurry adjustment to about 20% concentration for absorbing SO2 in flue gas, the liquid-gas ratio in the desulfurization tower is controlled to be 5 L / m 3 , the reaction temperature is 50°C, the reaction time is 60 min, after the reaction is completed, air is introduced for oxidation to obtain calcium fluoro-phosphate and MgSO4, and magnesium sulfate solution B and phosphate concentrate b (containing a small amount of calcium sulfate) are obtained by filtration separation.

[0051] (4) The magnesium sulfate solution B is stirred with the leaching solution A, the reaction temperature is controlled to be 60°C, the reaction time is 60 min, and the filter cake c is obtained by filtration washing separation, and high-quality CaSO4·2H2O is obtained by drying the filter cake c, and the filtrate is a magnesium nitrate solution C containing a small amount of ammonium nitrate.

[0052] (5) The filtrate C is treated with ammonia water to precipitate magnesium hydroxide, the temperature is controlled to be 60°C, the reaction time is 60 min, the filter cake d is obtained by filtration washing separation, and Mg(OH)2 is obtained by drying the filter cake d, and the filtrate D is an ammonium nitrate solution which is returned for recycling.

[0053] Example 2

[0054] (1) The phosphorus tailings are calcined at 900°C for 2 h to obtain calcined mineral powder;

[0055] (2) The calcined mineral powder and the 10% ammonium nitrate solution are added into the reaction tank for stirring reaction, the reaction temperature is 70°C, the reaction time is 120 min, ammonia gas is generated and effectively recovered, and leaching solution A and leaching residue a are obtained by filtration separation, the leaching solution A is a mixed solution of calcium nitrate, magnesium nitrate and ammonium nitrate, and the leaching residue a is a mixture containing calcium fluoro-phosphate and magnesium hydroxide;

[0056] (3) The leaching residue a (mainly a mixture of calcium fluoro-phosphate and magnesium hydroxide) is added into water for slurry adjustment to about 10% concentration for absorbing SO2 in flue gas, the liquid-gas ratio in the desulfurization tower is controlled to be 6 L / m 3 , the reaction temperature is 100°C, the reaction time is 120 min, after the reaction is completed, air is introduced for oxidation to obtain calcium fluoro-phosphate and MgSO4, and magnesium sulfate solution B and phosphate concentrate b (containing a small amount of calcium sulfate) are obtained by filtration separation.

[0057] (4) Magnesium sulfate solution B is stirred and reacted with leaching solution A, the reaction temperature is controlled at 50°C, the reaction time is 90 min, and filtration and washing are performed to separate, the filter cake c is dried to obtain high-quality CaSO4-2H2O, and the filtrate is a magnesium nitrate solution C containing a small amount of ammonium nitrate.

[0058] (5) The filter cake d is dried to obtain Mg(OH)2, and the filtrate D is an ammonium nitrate solution which is returned to the recycling use.

[0059] Example 3

[0060] (1) The phosphorus tailings are calcined at 1100°C for 2h to obtain calcined mineral powder;

[0061] (2) The calcined mineral powder and the ammonium nitrate solution with a concentration of 40% are added into a reaction tank and stirred and reacted, the reaction temperature is 45°C, the reaction time is 30 min, ammonia gas is generated and effectively recovered, and leaching solution A and leaching residue a are obtained through filtration and separation, the leaching solution A is a mixed solution of calcium nitrate, magnesium nitrate and ammonium nitrate, and the leaching residue a is a mixture containing calcium fluophosphate and magnesium hydroxide;

[0062] (3) The leaching residue a (mainly a mixture of calcium fluophosphate and magnesium hydroxide) is slurried with water to a concentration of about 30% and used to absorb SO2 in flue gas, the liquid-gas ratio in the desulfurization tower is controlled at 10 L / m 3 , the reaction temperature is 80°C, the reaction time is 30 min, air is introduced after the reaction is completed to obtain calcium fluophosphate and MgSO4, and magnesium sulfate solution B and phosphorus concentrate b (containing a small amount of calcium sulfate) are obtained through filtration and separation.

[0063] (4) Magnesium sulfate solution B is stirred and reacted with leaching solution A, the reaction temperature is controlled at 120°C, the reaction time is 30 min, and filtration and washing are performed to separate, the filter cake c is dried to obtain high-quality CaSO4-2H2O, and the filtrate is a magnesium nitrate solution C containing a small amount of ammonium nitrate.

[0064] (5) The filter cake d is dried to obtain Mg(OH)2, and the filtrate D is an ammonium nitrate solution which is returned to the recycling use.

[0065] Example 4

[0066] (1) The phosphorus tailings are calcined at 950°C for 1.5h to obtain calcined mineral powder;

[0067] (2) The calcined ore powder and the 25% ammonium nitrate solution are added into the reaction tank for stirring reaction, the reaction temperature is 60°C, the reaction time is 60 min, ammonia gas is generated and effectively recovered, and the leaching solution A and the leaching residue a are obtained through filtration separation, the leaching solution A is a mixed solution of calcium nitrate, magnesium nitrate and ammonium nitrate, and the leaching residue a is a mixture containing calcium fluoro-phosphate and magnesium hydroxide.

[0068] (3) The leaching residue a (mainly magnesium hydroxide and a small amount of calcium hydroxide) is added into water for slurry adjustment to about 20% concentration for absorbing SO2 in flue gas, the liquid-gas ratio in the desulfurization tower is controlled to be 7L / m 3 , the reaction temperature is 90°C, the reaction time is 60 min, after the reaction is completed, air is introduced for oxidation to obtain calcium fluoro-phosphate and MgSO4, and the magnesium sulfate solution B and the phosphate concentrate b (containing a small amount of calcium sulfate) are obtained through filtration separation.

[0069] (4) The magnesium sulfate solution B is stirred with the leaching solution A, the reaction temperature is controlled to be 60°C, the reaction time is controlled to be 60 min, and the filter cake c is obtained through filtration washing separation, and the filter cake c is dried to obtain high-quality CaSO4·2H2O, and the filtrate is a magnesium nitrate solution C containing a small amount of ammonium nitrate.

[0070] (5) The filtrate D is treated with ammonia water to precipitate magnesium hydroxide, the temperature is controlled to be 60°C, the reaction time is controlled to be 60 min, the filter cake d is obtained through filtration washing separation, and the filter cake d is dried to obtain Mg(OH)2, and the filtrate D is returned to be recycled and utilized.

[0071] The phosphor tailings used in the examples have the following composition:

[0072]

[0073] The qualities of the products obtained in Examples 1-4 are as follows:

[0074]

[0075] The calcium sulfate and magnesium hydroxide products obtained in the examples have the following qualities: the content of calcium sulfate is more than 98%, the whiteness is more than 97%, the content of magnesium hydroxide is more than 98%, and the whiteness is more than 95%, all reaching the superior grade.

[0076] Finally, it should be pointed out that the above examples are only more representative examples of the present application. Obviously, the technical solutions of the present application are not limited to the above examples, and there can be many variations. All the variations that can be directly derived or thought of by those skilled in the art from the content disclosed in the present application should be considered as the protection scope of the present application.

Claims

1. A process for the desulphurization of coal combustion flue gases and simultaneously producing enriched phosphatic concentrate, high quality calcium sulphate and magnesium hydroxide using phosphatic tailings, characterized by, The method comprises the following steps: (1) calcining phosphorite tailings to obtain calcined mineral powder; (2) adding the calcined mineral powder and an ammonium nitrate solution into a reaction tank to stir and react, generating ammonia gas and being effectively recovered, and then filtering and separating to obtain leaching solution A and leaching residue a, wherein the leaching solution A is a mixed solution of calcium nitrate and a small amount of ammonium nitrate, and the leaching residue a is a mixture of fluorapatite (Ca5F(PO4)3) and magnesium hydroxide; wherein the ammonium nitrate solution is used in an amount of 120-150% of the theoretical amount of ammonium nitrate required for the MgO mass fraction in the calcined mineral powder; the ammonium nitrate solution has a concentration of 10-40%, the reaction temperature is 35-70℃, and the reaction time is 30-120 min; (3) after the leaching residue a is slurried with water, the slurry is pumped into a desulfurization tower to react with dust-removed coal-fired flue gas in countercurrent to remove SO2 in the flue gas, at this time, a slightly soluble MgSO3 is generated, and the MgSO4 solution is obtained by introducing appropriate air for oxidation in the process, and then the solution is separated by plate and frame pressure filtration to obtain filtrate B and filtration residue b; the filtrate B is a magnesium sulfate solution, and the filtration residue b is washed to obtain a phosphorus concentrate containing a small amount of calcium sulfate; (4) adding the clear and purified filtrate B into the reaction tank to stir and react with the filtrate A, and then separating the reaction product by plate and frame pressure filtration to obtain filtrate C and filter cake c; the filtrate C is a magnesium nitrate solution containing a small amount of ammonium nitrate, and the filter cake c is washed and dried to obtain high-quality calcium sulfate; (5) adding the filtrate C into the reaction tank to stir and treat with ammonia water, generating ammonia gas and being effectively recovered, and then separating the reaction product by plate and frame pressure filtration to obtain filtrate D and filter cake d; the filtrate D is an ammonium nitrate solution containing a small amount of magnesium nitrate, and the filter cake d is washed and dried to obtain high-quality magnesium hydroxide.

2. The method of claim 1, wherein: The phosphorite tailings are solid waste discarded in phosphorite flotation and contain Ca5F(PO4)3, CaCO3 and MgCO3.

3. The method of claim 1, wherein: The calcination in step (1) is performed at 750-1100℃ for 1-2h.

4. The method of claim 1, wherein: The pulp concentration of the leaching residue a in step (3) is 10-40%, and the liquid-gas ratio in the desulfurization tower is 5-10 L / m 3 The reaction temperature is 40-100℃, and the reaction time is 30-120 min.

5. The method of claim 1, wherein: The reaction temperature in step (4) is 30-120℃, and the reaction time is 30-90 min.

6. The method of claim 1, wherein: The ammonia water in step (5) is prepared from the ammonia gas effectively recovered in step (2).

7. The method of claim 1, wherein: In step (5), the filtrate C is added into the reaction tank to stir and treat with ammonia water, and the reaction temperature is controlled to be 30-120℃, and the reaction time is controlled to be 30-90 min.

8. The method of claim 1, wherein: The filtrate D in step (5) is returned to step (2) for reuse.

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