Method for desulfurizing coal-fired flue gas and simultaneously preparing enriched phosphate concentrate, high-quality calcium sulfate and magnesium hydroxide by using phosphate tailings

Abstract

The invention relates to the technical field of inorganic chemical industry, in particular to a method for desulfurizing coal-fired flue gas by using phosphate tailings and simultaneously preparing enriched phosphate concentrate, high-quality calcium sulfate and magnesium hydroxide. According to the method, after the phosphate tailings are calcined, calcium and magnesium are separated through one-time leaching of the ammonium nitrate solvent, then SO2 in the flue gas is removed through magnesium, the desulfurization rate is high, the reaction speed is high, and enriched phosphate concentrate and high-quality calcium sulfate and magnesium hydroxide are obtained by taking the desulfurization process as a medium; and perfect combination of environment-friendly desulfurization of flue gas, comprehensive utilization of phosphate tailings and manufacturing of high-added-value products is realized.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic chemical industry, in particular to a method for using phosphate tailings for coal-fired flue gas desulfurization and simultaneously preparing enriched phosphate concentrate, high-quality calcium sulfate and magnesium hydroxide. Background Art

[0002] With the continuous development of social industry, the degree of industrialization is getting higher and higher, the scale of production is expanding, and the flue gas discharged into the atmosphere is also increasing. Among the various gaseous pollutants that affect the air quality, SO2 flue gas has the largest amount and the greatest impact. It causes acid rain, damages the ecological environment, and affects human health. Therefore, before these industrial flue gases are discharged into the atmosphere, they need to be treated, among which the more important one is desulfurization treatment.

[0003] About flue gas desulfurization: At present, most domestic enterprises use calcium carbonate-gypsum method to remove SO2 from flue gas. Cheap calcium carbonate powder or lime milk is used to absorb SO2 in flue gas, and the generated CaSO3 is oxidized to generate CaSO4. However, due to the low quality and large output of the resulting gypsum, the market can only absorb a small part of it and a large amount of it is stored. Therefore, it not only increases the cost of desulfurization, but also causes secondary pollution. In particular, desulfurization of coal-fired power plants in high-sulfur coal producing areas has become a huge economic burden for the power generation industry.

[0004] Although there is a technical solution that uses cheap and easily available dolomite from various places as a desulfurizer, for example, patent application 201710768665.0 (a combined method for flue gas desulfurization and gas deammonification pollutant resource utilization to treat waste) uses magnesium oxide obtained after calcining dolomite as a raw material. This technical solution requires a large amount of input ammonia, mainly for coke oven gas or ammonia-containing gas produced by various gasification furnaces in coal chemical industry or petrochemical industry. When the downstream users of ammonia are relatively close, the separated magnesium sulfate solution can still be directly transported; if the users are particularly far away, it needs to be dehydrated before transportation. At this time, the energy consumption and processes required for drying and packaging are relatively large costs. Since the power plants that currently produce coal-fired delays are often far away from the coking plants, this method is restricted by certain objective conditions.

[0005] Phosphate resources are important national strategic resources and the material basis of the phosphorus chemical industry. With the large-scale development and utilization of phosphate resources, a large amount of tailings will be generated during the mining process of phosphate. Phosphate tailings refer to the products that fail to enter the concentrate after crushing, grinding, flotation and other processes in the phosphate ore beneficiation process, mainly including phosphate minerals and gangue minerals. The existing beneficiation methods have low utilization rates of phosphorus resources, and the large amount of tailings produced brings huge environmental risks. Exploring the comprehensive utilization of phosphate tailings and converting them into valuable resources is of great significance to promoting the efficient and clean utilization of phosphate resources in the phosphorus chemical industry and achieving sustainable development.

[0006] Therefore, finding a method that can make full use of phosphate tailings through the desulfurization process to obtain phosphate concentrate and high-quality calcium sulfate and magnesium hydroxide, achieve a perfect combination of environmentally friendly flue gas desulfurization, comprehensive utilization of phosphate tailings, and high value-added product manufacturing, and be able to combine the large amount of solid waste phosphate tailings in phosphate mining areas with the efficient desulfurization needs of coal-fired flue gas from surrounding coal-fired kilns (mainly power plants) is the current key research direction of "treating waste with waste". Summary of the invention

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

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

[0009] (1) calcining the phosphate tailings to obtain calcined ore powder;

[0010] (2) adding calcined ore powder and ammonium nitrate solution into a reaction tank for stirring and reacting, generating ammonia gas and effectively recovering it, and filtering and separating to obtain leachate A and leach residue a, wherein the leachate A is a mixed solution of calcium nitrate and a small amount of ammonium nitrate, and the leach residue a is a mixture of fluoroapatite and magnesium hydroxide;

[0011] (3) The leached residue a is slurried with water and then enters a circulation tank and is pumped into a desulfurization tower for countercurrent mixing with the dust-removed coal-fired flue gas to remove SO2 from the flue gas. At this time, slightly soluble MgSO3 is generated. During this process, a proper amount of air is introduced for oxidation to obtain a MgSO4 solution, which is separated by plate and frame filter press to obtain a filtrate B and filtered residue b; the filtrate B is a magnesium sulfate solution, and the filtered residue b is washed to obtain a phosphate concentrate containing a small amount of calcium sulfate (fluoroapatite does not participate in the reaction);

[0012] (4) adding the filtrate A to the reaction tank to react with the purified filtrate B, and performing a stirring reaction. After the reaction is completed, the filtrate C and the filter cake C are separated by plate and frame filter pressing; 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) Adding ammonia water to the filtrate C in a reaction tank and stirring the mixture to generate ammonia gas for effective recovery. After the reaction is completed, the filtrate D and filter cake d are separated by plate and frame filter press. The filtrate D is an ammonium nitrate solution containing a small amount of magnesium nitrate. The filter cake d is washed and dried to obtain high-quality magnesium hydroxide.

[0014] Furthermore, the phosphate tailings are solid wastes discarded from phosphate ore flotation, containing 55-10% P2O, 28-35% CaO, and 15-21% MgO (mass fraction).

[0015] Furthermore, the calcination in step (1) is carried out at 750-1100° C. for 1-2 hours. In this case, the calcination has a better effect of decomposing calcium carbonate and magnesium carbonate in the phosphate tailings.

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

[0017] Furthermore, in step (2), the concentration of the ammonium nitrate solution is 10-40%, the reaction temperature is 35-70°C, and the reaction time is 30-120 minutes. In this case, the reaction efficiency is high and the reaction effect is good.

[0018] Furthermore, the step (3) is to slurry the leached slag a with water to 10-40%, and control the liquid-gas ratio in the desulfurization tower to 5-10 L / 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 fully with the SO2 in the flue gas, and the obtained MgSO3 is oxidized by air to obtain MgSO4 solution B.

[0019] Furthermore, in step (4), filtrate B is added to filtrate A in a reaction tank for stirring and reacting, and the reaction temperature is controlled at 30-120° C. and the reaction time is controlled at 30-90 min. Under this condition, high-quality calcium sulfate is obtained with good economic value.

[0020] Furthermore, the ammonia water in step (5) is prepared from the ammonia gas effectively recovered in step (2). The recycling of ammonia gas in the present application can theoretically achieve a non-consumption ammonia cycle without the need for adding ammonia gas. Although there will be some losses in actual production, it is still not necessary to add a large amount of ammonia gas as a whole. The technical solution of the present application successfully does not require a large amount of external ammonia gas input, and gets rid of the dependence on coking plants and the like.

[0021] Furthermore, in step (5), the filtrate C is added with ammonia water in the reaction tank and stirred at a reaction temperature of 60-120° C. and a reaction time of 30-90 min. Under these conditions, high-quality magnesium hydroxide is obtained with 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 phosphate tailings begins to decompose at a high temperature above 750°C. The specific equation is as follows:

[0024] CaCO3·MgCO3=CaO+MgO+2CO2

[0025] In step (2), the equation for 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 invention uses ammonium nitrate solvent to leach calcium and magnesium after calcining phosphate tailings, and then uses magnesium to remove SO2 in the flue gas. The desulfurization rate is high and the reaction speed is fast. The desulfurization process is used as a medium to obtain enriched phosphate concentrate and high-quality calcium sulfate and magnesium hydroxide, thereby achieving a perfect combination of environmentally friendly flue gas desulfurization, comprehensive utilization of phosphate tailings, and manufacturing of high value-added products.

[0037] Compared with the prior art, the technical effects created by the present invention are embodied in:

[0038] 1. The present invention uses phosphate tailings as a desulfurizing agent for the removal of SO2 in the flue gas of coal-fired kilns and power plant boilers. Compared with the existing calcium carbonate-gypsum method, it has the characteristics of fast reaction speed, high desulfurization rate, low investment cost and low operating cost, and completely solves the problem that the desulfurization gypsum is of low quality and difficult to utilize. It cleverly combines the unique calcium and magnesium properties of a large amount of discarded phosphate tailings produced by phosphate ore dressing with flue gas desulfurization to produce high-value-added calcium sulfate and magnesium hydroxide, while recovering precious phosphorus resources, realizing the transformation of flue gas desulfurization and environmental protection treatment from negative economic output to high returns.

[0039] 2. The present invention achieves flue gas desulfurization under more optimized conditions through a reasonable division of labor between the functions of calcium and magnesium in phosphate tailings, while avoiding the risk of secondary environmental pollution and the burden of high disposal costs caused by the production of low-quality desulfurization gypsum.

[0040] 3. The present invention uses phosphate tailings instead of limestone or light-burned magnesium oxide to treat flue gas desulfurization, which can basically achieve "waste treatment with waste" for phosphorus chemical waste and SO2 in coal-fired flue gas, and at the same time solve the major problem of phosphate tailings and flue gas desulfurization restricting the development of two industries (mainly phosphate mining and coal power generation), so that flue gas desulfurization can be changed from a burden on enterprises to an economic growth point, which effectively promotes the enthusiasm of enterprises for environmental protection investment and improves the social benefits of ecological environmental protection.

[0041] 4. In the process of the present invention, the ammonia produced in steps (2) and (5) is recycled in the system, which not only saves the cost of raw materials, but also makes full use of the gas produced in the process, avoiding waste of resources and environmental pollution. In the process of the present invention, since 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. The technical solution of the present application does not require a large amount of external ammonia input to produce magnesium hydroxide products. There is no need to dehydrate and dry the magnesium sulfate product and transfer it to a place where ammonia is produced and then re-prepared into magnesium hydroxide products. There is no dilemma of only being able to produce magnesium sulfate products with low economic value when there is no ammonia input.

[0043] 6. The high-quality calcium sulfate obtained by the present invention has a purity of more than 98% and a whiteness of more than 97%, and the market price is about 1,200 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 4,500 yuan / ton. The low-value phosphorus tailings are processed by the flue gas desulfurization high-efficiency combination to obtain high value-added products and double the value, which has good economic benefits. The high-quality calcium sulfate obtained by this application is in short supply in the market, which solves the current desulfurization product, low-quality gypsum, which can only be digested by the market due to excessive production. Therefore, it not only increases the desulfurization cost, but also causes a major problem of secondary pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0045] The technical solution of the present invention is further defined below in conjunction with specific implementation methods, but the scope of protection required is not limited to the description.

[0046] Example 1

[0047] Example 1

[0048] (1) calcining the phosphate tailings at 950° C. for 1.5 h to obtain calcined ore powder;

[0049] (2) adding calcined ore powder and 25% ammonium nitrate solution into a reaction tank for stirring and reacting at a reaction temperature of 45° C. for a reaction time of 60 min, generating ammonia gas and effectively recovering it, and filtering and separating to obtain leachate A and leach residue a, wherein the leachate A is a mixed solution of calcium nitrate, magnesium nitrate and ammonium nitrate, and the leach residue a is a mixture of calcium fluorophosphate and magnesium hydroxide;

[0050] (3) The leached slag a (mainly a mixture of calcium fluorophosphate and magnesium hydroxide) is slurried with water to a concentration of about 20% to absorb SO2 in the flue gas and control the liquid-gas ratio in the desulfurization tower to 5L / m 3 The reaction temperature is 50°C and the reaction time is 60 min. After the reaction is completed, air is introduced for oxidation to obtain calcium fluorophosphate and MgSO4. After filtration and separation, magnesium sulfate solution B and phosphate concentrate b (containing a small amount of calcium sulfate) are obtained.

[0051] (4) The magnesium sulfate solution B and the leaching solution A are stirred for reaction, the reaction temperature is controlled to be 60° C., the reaction time is controlled to be 60 min, and the mixture is filtered, washed and separated. 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.

[0052] (5) The filtrate C is treated with ammonia water to precipitate magnesium hydroxide. The temperature is controlled at 60° C. and the reaction time is 60 min. The filter is filtered, washed and separated. The filter cake d is dried to obtain Mg(OH)2. The ammonium nitrate solution in the filtrate D is returned for recycling.

[0053] Example 2

[0054] (1) calcining the phosphate tailings at 900° C. for 2 h to obtain calcined ore powder;

[0055] (2) adding calcined ore powder and 10% ammonium nitrate solution into a reaction tank for stirring reaction at a reaction temperature of 70° C. for a reaction time of 120 min, generating ammonia gas and effectively recovering it, and filtering and separating to obtain leachate A and leach residue a, wherein the leachate A is a mixed solution of calcium nitrate, magnesium nitrate and ammonium nitrate, and the leach residue a is a mixture of calcium fluorophosphate and magnesium hydroxide;

[0056] (3) The leached slag a (mainly a mixture of calcium fluorophosphate and magnesium hydroxide) is slurried with water to a concentration of about 10% to absorb SO2 in the flue gas and control the liquid-gas ratio in the desulfurization tower to 6L / m 3 The reaction temperature is 100°C and the reaction time is 120 min. After the reaction is completed, air is introduced for oxidation to obtain calcium fluorophosphate and MgSO4. After filtration and separation, magnesium sulfate solution B and phosphate concentrate b (containing a small amount of calcium sulfate) are obtained.

[0057] (4) The magnesium sulfate solution B and the leaching solution A are stirred for reaction, the temperature is controlled at 50° C., the reaction time is 90 min, and the mixture is filtered, washed and separated. The filter cake c is dried to obtain high-quality CaSO4·2H2O. The filtrate is a magnesium nitrate solution C containing a small amount of ammonium nitrate.

[0058] (5) The filtrate C is treated with ammonia water to precipitate magnesium hydroxide. The temperature is controlled at 60° C. and the reaction time is 60 min. The filter is filtered, washed and separated. The filter cake d is dried to obtain Mg(OH)2. The ammonium nitrate solution in the filtrate D is returned for recycling.

[0059] Example 3

[0060] (1) calcining the phosphate tailings at 1100° C. for 2 h to obtain calcined ore powder;

[0061] (2) adding calcined ore powder and 40% ammonium nitrate solution into a reaction tank for stirring reaction at a reaction temperature of 45° C. for a reaction time of 30 min, generating ammonia gas and effectively recovering it, and filtering and separating to obtain leachate A and leach residue a, wherein the leachate A is a mixed solution of calcium nitrate, magnesium nitrate and ammonium nitrate, and the leach residue a is a mixture of calcium fluorophosphate and magnesium hydroxide;

[0062] (3) The leached slag a (mainly a mixture of calcium fluorophosphate and magnesium hydroxide) is slurried with water to a concentration of about 30% to absorb SO2 in the flue gas and control the liquid-gas ratio in the desulfurization tower to 10L / m 3 The reaction temperature is 80°C and the reaction time is 30 min. After the reaction is completed, air is introduced for oxidation to obtain calcium fluorophosphate and MgSO4. After filtration and separation, magnesium sulfate solution B and phosphate concentrate b (containing a small amount of calcium sulfate) are obtained.

[0063] (4) The magnesium sulfate solution B and the leachate A are stirred for reaction, the reaction temperature is controlled to be 120° C., the reaction time is controlled to be 30 min, and the mixture is filtered, washed and separated. 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 filtrate C is treated with ammonia water to precipitate magnesium hydroxide. The temperature is controlled at 60° C. and the reaction time is 60 min. The filter is filtered, washed and separated. The filter cake d is dried to obtain Mg(OH)2. The ammonium nitrate solution in the filtrate D is returned for recycling.

[0065] Example 4

[0066] (1) calcining the phosphate tailings at 950° C. for 1.5 h to obtain calcined ore powder;

[0067] (2) Calcined ore powder and 25% ammonium nitrate solution are added to a reaction tank and stirred for reaction. The reaction temperature is 60° C. and the reaction time is 60 min. Ammonia gas is generated and effectively recovered. Leachate A and leaching residue a are obtained by filtration and separation. Leachate A is a mixed solution of calcium nitrate, magnesium nitrate and ammonium nitrate. Leaching residue a is a mixture of calcium fluorophosphate and magnesium hydroxide.

[0068] (3) Leaching slag a (mainly magnesium hydroxide and a small amount of calcium hydroxide) is slurried with water to a concentration of about 20% to absorb SO2 in the flue gas and control the liquid-gas ratio in the desulfurization tower to 7L / m 3 The reaction temperature is 90°C and the reaction time is 60 min. After the reaction is completed, air is introduced for oxidation to obtain calcium fluorophosphate and MgSO4. After filtration and separation, magnesium sulfate solution B and phosphate concentrate b (containing a small amount of calcium sulfate) are obtained.

[0069] (4) The magnesium sulfate solution B and the leaching solution A are stirred for reaction, the reaction temperature is controlled to be 60° C., the reaction time is controlled to be 60 min, and the mixture is filtered, washed and separated. 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 aqueous ammonia to precipitate magnesium hydroxide. The temperature is controlled at 60° C. and the reaction time is 60 min. The filter cake d is dried to obtain Mg(OH)2. The ammonium nitrate solution in the filtrate D is returned for recycling.

[0071] The composition of the phosphorus tailings used in the embodiment is as follows:

[0072]

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

[0074]

[0075] The calcium sulfate and magnesium hydroxide products obtained in each embodiment of the present invention have a calcium sulfate content of more than 98% and a whiteness of more than 97%, and a magnesium hydroxide content of more than 98% and a whiteness of more than 95%, all of which are excellent products.

[0076] Finally, it should be pointed out that the above embodiments are only representative examples of the present invention. Obviously, the technical solution of the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by ordinary technicians in this field should be considered as the protection scope of the present invention.

Claims

1. A method for using phosphate tailings for coal-fired flue gas desulfurization and simultaneously preparing enriched phosphate concentrate, high-quality calcium sulfate and magnesium hydroxide, characterized in that: The steps include: (1) calcining the phosphate tailings to obtain calcined ore powder; (2) adding calcined ore powder and ammonium nitrate solution into a reaction tank for stirring and reacting, generating ammonia gas and effectively recovering it, and filtering and separating to obtain leachate A and leach residue a, wherein the leachate A is a mixed solution of calcium nitrate and a small amount of ammonium nitrate, and the leach residue a is a mixture of fluoroapatite (Ca5F(PO4)3) and magnesium hydroxide; (3) The leached residue a is slurried with water and then enters a circulation tank and is pumped into a desulfurization tower for countercurrent mixing with the dust-removed coal-fired flue gas to remove SO2 from the flue gas. At this time, slightly soluble MgSO3 is generated. During this process, a proper amount of air is introduced for oxidation to obtain a MgSO4 solution, which is separated by plate and frame filter press to obtain a filtrate B and filtered residue b; the filtrate B is a magnesium sulfate solution, and the filtered residue b is washed to obtain a phosphate concentrate containing a small amount of calcium sulfate; (4) adding the filtrate A to the reaction tank to react with the purified filtrate B, and performing a stirring reaction. After the reaction is completed, the filtrate C and the filter cake C are separated by plate and frame filter pressing; 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 ammonia water to the filtrate C in a reaction tank and stirring the mixture to generate ammonia gas for effective recovery. After the reaction is completed, the filtrate D and filter cake d are separated by plate and frame filter press. The filtrate D is an ammonium nitrate solution containing a small amount of magnesium nitrate. The filter cake d is washed and dried to obtain high-quality magnesium hydroxide.

2. The method for using the phosphate tailings according to claim 1 for desulfurization of coal-fired flue gas and simultaneously preparing enriched phosphate concentrate, high-quality calcium sulfate and magnesium hydroxide, characterized in that: The phosphate tailings are solid wastes discarded from phosphate ore flotation, and contain Ca5F(PO4)3, CaCO3, and MgCO3.

3. The method for using the phosphate tailings according to claim 1 for desulfurization of coal-fired flue gas and simultaneously preparing enriched phosphate concentrate, high-quality calcium sulfate and magnesium hydroxide, characterized in that: The calcination in step (1) is carried out at 750-1100° C. for 1-2 hours.

4. The method for using the phosphate tailings according to claim 1 for desulfurization of coal-fired flue gas and simultaneously preparing enriched phosphate concentrate, high-quality calcium sulfate and magnesium hydroxide, characterized in that: In the 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.

5. The method for using the phosphate tailings according to claim 1 for desulfurization of coal-fired flue gas and simultaneously preparing enriched phosphate concentrate, high-quality calcium sulfate and magnesium hydroxide, characterized in that: In the step (2), the concentration of the ammonium nitrate solution is 10-40%, the reaction temperature is 35-70° C., and the reaction time is 30-120 min.

6. The method for using the phosphate tailings according to claim 1 for desulfurization of coal-fired flue gas and simultaneously preparing enriched phosphate concentrate, high-quality calcium sulfate and magnesium hydroxide, characterized in that: The step (3) is to slurry the leached slag a with water to 10-40%, and control the liquid-gas ratio in the desulfurization tower to 5-10 L / m 3 , the reaction temperature is 40-100℃, and the reaction time is 30-120min. At this time, the magnesium hydroxide in the slurry reacts fully with the SO2 in the flue gas, and the obtained MgSO3 is oxidized by air to obtain MgSO4 solution B.

7. The method for using the phosphate tailings according to claim 1 for desulfurization of coal-fired flue gas and simultaneously preparing enriched phosphate concentrate, high-quality calcium sulfate and magnesium hydroxide, characterized in that: In the step (4), filtrate B is added to filtrate A in a reaction tank for stirring and reacting, and the reaction temperature is controlled at 30-120° C. and the reaction time is 30-90 min. Under this condition, high-quality calcium sulfate is obtained with good economic value.

8. The method for using the phosphate tailings for coal-fired flue gas desulfurization and simultaneously preparing enriched phosphate concentrate, high-quality calcium sulfate and magnesium hydroxide according to claim 1, characterized in that: The ammonia water in step (5) is prepared from the ammonia gas effectively recovered in step (2).

9. The method for using the phosphate tailings for coal-fired flue gas desulfurization and simultaneously preparing enriched phosphate concentrate, high-quality calcium sulfate and magnesium hydroxide according to claim 1, characterized in that: In the step (5), filtrate C is added with ammonia water in a reaction tank and stirred, and the reaction temperature is controlled at 30-120° C. and the reaction time is controlled at 30-90 min.

10. The method for using phosphate tailings for coal-fired flue gas desulfurization and simultaneously preparing enriched phosphate concentrate, high-quality calcium sulfate and magnesium hydroxide according to claim 1, characterized in that: The filtrate D in step (5) is returned to step (2) for reuse.

Images