Comprehensive utilization method of red gypsum

Abstract

The invention discloses a comprehensive utilization method of red gypsum. The method comprises the steps that red gypsum is leached through an ammonium citrate solution and then subjected to solid-liquid separation, calcium-rich leaching liquid and iron-containing leaching residues are obtained, the calcium-rich leaching liquid is subjected to standing aging and solid-liquid separation, calcium citrate precipitates are obtained, the calcium citrate precipitates are mixed with water, then the pH value of the solution is adjusted to be alkaline through ammonia water, and the iron-containing leaching residues are obtained. Introducing carbon dioxide to carry out carbonation reaction, and carrying out solid-liquid separation to obtain a calcium carbonate product and filtrate containing ammonium citrate; the filtrate containing ammonium citrate can be recycled for red gypsum leaching; the iron-based catalyst is obtained by carrying out co-carbonization reaction on the iron-containing leaching residues and a biomass material. According to the method, ammonium citrate is utilized to leach active calcium components in the red gypsum for carbon dioxide sequestration and a byproduct calcium carbonate product, the iron-based catalyst is prepared through co-carbonization of iron-rich leaching residues and biomass, organic pollutants can be effectively catalyzed and degraded, resource utilization of red gypsum waste is achieved, and the purpose of treating waste with waste is achieved.

Description

Technical Field

[0001] The invention relates to a solid waste treatment method, in particular to a red gypsum comprehensive utilization method, and belongs to the field of solid waste resource utilization. Background Art

[0002] Red gypsum is a typical industrial solid waste produced by adding lime (or carbide slag) to neutralize a large amount of acidic wastewater in order to treat acidic wastewater when producing titanium dioxide by sulfuric acid method. According to statistics, 6 to 10 tons of red gypsum will be produced for 1 ton of titanium dioxide produced by sulfuric acid method, and the production of red gypsum in my country has increased year by year. Due to the high content of free water and impurities, poor mechanical properties and high viscosity of red gypsum, the recycling of red gypsum is difficult and its utilization is poor, and its comprehensive utilization rate is only about 20%. As of 2021, the production of red gypsum in my country has exceeded 200 million tons. Most red gypsum can only be piled up as solid waste in large quantities. On the one hand, it occupies a large area of ​​land, and on the other hand, it may flow into the surrounding environment in the form of pollutants through rainwater and atmosphere, posing an environmental risk. At present, the treatment of red gypsum has become an economic burden for titanium dioxide processing enterprises, which seriously restricts the development of enterprises.

[0003] Therefore, developing a comprehensive utilization method of red gypsum is of great significance for solving the difficulties in red gypsum treatment in titanium dioxide processing enterprises and solving the environmental pollution problems caused by red gypsum waste. Summary of the invention

[0004] In view of the problems of red gypsum treatment difficulty and environmental pollution in the prior art, the purpose of the present invention is to improve a method for comprehensive utilization of red gypsum. The method can effectively separate calcium and iron in red gypsum, use calcium-rich components to achieve carbon sequestration and by-produce calcium carbonate products, and prepare iron-based catalysts for the degradation of organic pollutants through iron-rich components, ultimately realizing the resource utilization of red gypsum waste and achieving the purpose of "waste treatment with waste".

[0005] In order to achieve the above technical purpose, the present invention provides a method for comprehensive utilization of red gypsum, which comprises leaching the red gypsum through an ammonium citrate solution, and then performing solid-liquid separation to obtain a calcium-rich leachate and an iron-containing leach residue, wherein the calcium-rich leachate is subjected to static aging and solid-liquid separation to obtain a calcium citrate precipitate, the calcium citrate precipitate is mixed with water, ammonia water is used to adjust the pH value of the solution to be alkaline, carbon dioxide is introduced for carbonation reaction, and then solid-liquid separation is performed to obtain a calcium carbonate product and a filtrate containing ammonium citrate; the filtrate containing ammonium citrate can be recycled for leaching of red gypsum; the iron-containing leaching residue is subjected to a co-carbonization reaction with a biomass material to obtain an iron-based catalyst.

[0006] The present invention uses ammonium citrate to leach active calcium components in red gypsum, while iron components are retained in the leached residue, thereby realizing the separation of calcium and iron in the red gypsum. The calcium-rich leaching solution realizes carbon sequestration through carbonation and produces a calcium carbonate product as a by-product. The iron-rich leaching residue can be used to prepare an iron-based catalyst to treat organic wastewater, thereby ultimately realizing the resource utilization of red gypsum and achieving the purpose of "treating waste with waste". The calcium leaching process fully exposes the iron component in the red gypsum leaching residue, so that the iron component is more fully reduced in the co-carbonization process. At the same time, based on the uniqueness of the red gypsum leaching residue component, the red gypsum leaching residue contains titanium, and the titanium component in the form of titanium dioxide has photocatalytic activity, can photocatalytically degrade organic pollutants, and is helpful to improve the catalytic effect of the iron / carbon composite catalyst.

[0007] As a preferred solution, the concentration of the ammonium citrate solution is 0.02-2 mol / L, more preferably 0.1-1 mol / L, and most preferably 0.1-0.5 mol / L.

[0008] As a preferred solution, the leaching conditions are: liquid-solid mass ratio of 10-100:1, temperature of 10-40°C, and time of 10-60 min. A further preferred liquid-solid mass ratio is 10-50:1.

[0009] As a preferred solution, the particle size of the calcium carbonate product is 2-5 μm.

[0010] As a preferred solution, the static aging time is 6 to 24 hours.

[0011] As a preferred solution, ammonia water is used to adjust the pH value of the system to 9.5-12.

[0012] As a preferred solution, the pH value of the filtrate containing ammonium citrate is adjusted to 6.5-7.5 and then recycled for red gypsum leaching.

[0013] As a preferred solution, the mass ratio of the iron-containing leaching residue to the biomass material is 1-5:1-2. In the present invention, the red gypsum leaching residue and the biomass material are co-carbonized. During the carbonization process, the biomass can reduce the trivalent iron in the red gypsum to low-valent iron, so that the prepared catalyst has a higher catalytic activity. The principles involved in the relevant process are as follows:

[0014] C + 3Fe 2 O 3 → 2Fe 3 O 4 + CO;

[0015] CO + 3Fe 2 O 3 → 2Fe3 O 4 + CO 2 ;

[0016] C + Fe 3 O 4 → 3Fe 0 + 4CO.

[0017] As a preferred solution, the mass content of carbon in the biomass material is not less than 50%.

[0018] As a preferred solution, the particle sizes of the iron-containing leaching slag and the biomass material are both 0.15-0.25 mm.

[0019] As a preferred solution, the biomass material is waste biomass material.

[0020] As a preferred solution, the waste biomass material includes at least one of straw, wood chips, fallen leaves, food residues, sludge, biomass processing waste, and livestock manure.

[0021] As a preferred solution, the conditions of the co-carbonization reaction are: the atmosphere is a protective atmosphere, the temperature is 400-1000°C, the time is 1-3 h, and the heating rate is 5-10°C / min.

[0022] As a preferred solution, the protective atmosphere is nitrogen and / or an inert gas, and the inert gas is argon.

[0023] As a preferred solution, in the co-carbonization reaction, the biomass material is added in multiple times. By adding the biomass into the leached residue in multiple times, the uniform mixing of the two can be promoted.

[0024] As a preferred solution, the biomass material is added in 10 times.

[0025] As a preferred solution, after the co-carbonization reaction is completed, the obtained product is cleaned with a cleaning agent and water.

[0026] As a preferred solution, the cleaning agent includes at least one of methanol, ethanol and acetone.

[0027] The present invention also provides an application of an iron-based catalyst, which is used for catalyzing an oxidant to degrade organic pollutants. The iron-based catalyst is prepared by the above method.

[0028] The present invention utilizes the low-valent iron in the catalyst prepared from the red gypsum leaching residue to react with an oxidant to generate a strong oxidizing hydroxyl radical or sulfate radical, thereby oxidizing and degrading organic pollutants. The free radicals are non-selective for the degradation of organic pollutants. The strong oxidizing free radicals can basically degrade most organic pollutants, and the degree of mineralization of organic pollutants is relatively high. For example, hydrogen peroxide is used as an oxidant, and the principle is as follows:

[0029] Fe 2+ + H 2 O 2 → Fe 3+ + OH - + •OH, k = 76 M -1 S -1 ;

[0030] Fe 3+ + H 2 O 2 → Fe 2+ + H + + •OOH, k = 0.02 M -1 S -1 .

[0031] As a preferred embodiment, the oxidant includes at least one of hydrogen peroxide, peroxymonosulfate, and peroxydisulfate.

[0032] As a preferred embodiment, the peroxymonosulfate includes at least one of sodium peroxymonosulfate, potassium peroxymonosulfate and ammonium peroxymonosulfate.

[0033] As a preferred embodiment, the peroxodisulfate includes at least one of sodium peroxodisulfate, potassium peroxodisulfate and ammonium peroxodisulfate.

[0034] As a preferred solution, the organic pollutants include drugs, pesticides, dyes, etc.

[0035] As a preferred solution, the iron-based catalyst is used to catalyze the degradation of organic pollutants in the oxidant solution.

[0036] As a preferred solution, the solution is water.

[0037] As a preferred solution, the concentration of the iron-based catalyst is 1-10 g / L.

[0038] As a preferred solution, the concentration of the organic pollutants is 10-200 mg / L.

[0039] As a preferred solution, when the oxidant is hydrogen peroxide, the concentration of the oxidant is 0.02-0.2 mol / L.

[0040] As a preferred embodiment, when the oxidant is peroxymonosulfate, the concentration of the oxidant is 0.1-2.0 mmol / L.

[0041] As a preferred solution, when the oxidant is peroxydisulfate, the concentration of the oxidant is 0.5-4.0 mmol / L.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) Red gypsum is an industrial solid waste rich in calcium and iron components. The present invention uses ammonium citrate to leach the active calcium component in the red gypsum for carbon dioxide sequestration and produces a by-product of calcium carbonate. The leached residue is then co-carbonized with biomass to prepare an iron-based catalyst that can be used to catalyze and degrade organic pollutants. This achieves the comprehensive utilization of red gypsum, improves resource utilization, effectively solves the problems of red gypsum being difficult to manage and polluting the environment, and realizes "turning waste into treasure".

[0044] (2) The ammonium citrate leaching agent used in the present invention has a small dosage, low corrosiveness, environmental friendliness, and good selectivity. Compared with the prior art, the present invention uses ammonium citrate to leach red gypsum to obtain a calcium-containing leachate, which is then placed and aged to separate calcium citrate precipitate, so that impurities in the leachate are separated from calcium, and then the calcium carbonate product prepared by carbonation reaction has good morphology, high purity, and good quality. The obtained ammonium citrate can be recycled, which solves the problems of incomplete separation of impurities in red gypsum, insufficient leaching, large dosage of leaching agent, and secondary wastewater pollution.

[0045] (3) The carbon dioxide storage capacity of the present invention can reach 176 kg CO 2 / t red gypsum, the by-product calcium carbonate product has high yield, high purity, uniform particles and good quality. Among them, the calcium carbonate production capacity can reach 400 kg CaCO 3 / t red gypsum;

[0046] (4) The iron-based catalyst prepared by the present invention using red gypsum leaching residue has high catalytic activity and strong stability. In the calcium leaching process of the present invention, calcium leaching can fully expose the iron components in the red gypsum leaching residue, thereby ensuring that the iron is fully reduced when the red gypsum leaching residue is co-carbonized with the biomass. At the same time, the components of the red gypsum leaching residue are unique (for example, containing titanium), which is beneficial to improving the catalytic activity of the obtained iron / carbon catalyst, so that the iron-based catalyst can effectively catalyze the degradation of organic pollutants by oxidants, with high degradation efficiency and a high degree of mineralization of the organic pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0048] Figure 1 This is a process flow chart for comprehensive utilization of red gypsum in Example 1 of the present invention. DETAILED DESCRIPTION

[0049] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] The chemical composition of the red gypsum selected in the present invention is shown in Table 1:

[0051]

[0052] Example 1

[0053] The specific process of comprehensive utilization of red gypsum is as follows:

[0054] Step 1: Prepare a 0.5 mol / L ammonium citrate solution as a leaching agent for red gypsum, add 5 g of red gypsum and ammonium citrate solution into a reaction vessel at a liquid-solid mass ratio of 10, and stir at 300 rpm for 10 min. After the reaction is completed, filter to obtain calcium-rich leaching solution and leaching residue.

[0055] Step 2: The calcium-rich leaching solution obtained in step 1 is allowed to stand for 6 hours to obtain calcium citrate precipitation. After the reaction is completed, calcium citrate is obtained by filtration.

[0056] Step 3: The calcium citrate obtained in step 2 and water are added into a reaction container at a liquid-to-solid mass ratio of 50, and after being fully mixed and reacted for 10 minutes, ammonia water is added to adjust the pH of the solution to 9.5 to obtain a mixed solution.

[0057] Step 4: Add CO to the mixed solution obtained in step 3 at a flow rate of 100 mL / min. 2The gas was carbonated and the reaction was terminated after 60 min. The reaction product was filtered and the liquid phase was used as the raw material for the red gypsum leaching reaction cycle. The solid phase was dried, ground and tested to show that the solid product was calcite calcium carbonate with an impurity content of less than 0.1%. The carbon dioxide storage capacity was 145 kg CO 2 / t red gypsum, calcium carbonate production capacity: 340 kg CaCO 3 / t Red Gypsum.

[0058] Step 5: The biomass obtained in step 1 is added to the leaching residue in 10 portions, and mixed evenly to obtain a mixture. The mass ratio of the leaching residue to the biomass is 2:1, the particle size of the leaching residue is 0.15 mm, and the particle size of the biomass is 0.2 mm.

[0059] Step 6: The mixture obtained in step 5 was heated to 1000°C at a heating rate of 10°C / min under a nitrogen atmosphere and kept at this temperature for 1.5 h to obtain a reaction product.

[0060] Step 7: The reaction product obtained in step 6 is cooled in sequence, washed with ethanol and deionized water, and dried to obtain a catalyst. The catalyst yield is 80.50%, and the catalyst particle size is 0.15-0.2 mm.

[0061] The leached residue catalyst obtained in step 7 is added to the aqueous solution of organic pollutants and mixed. First, 50wt% hydrogen peroxide is added to the catalyst and the aqueous solution of organic pollutants, and then the remaining 50wt% hydrogen peroxide is added to the catalyst and the aqueous solution of organic pollutants. The amount of catalyst is 1 g and the amount of hydrogen peroxide is 0.1 mol per liter of the aqueous solution of organic pollutants. The mixture is stirred and reacted for 40 minutes to degrade the organic pollutants in the aqueous solution of organic pollutants. Among them, the organic pollutants are acid orange dye or rhodamine B, and the degradation rate of acid orange dye (concentration of 20 mg / L) is 96.52%; the degradation rate of rhodamine B dye (concentration of 20 mg / L) is 99.75%; the total organic carbon removal rate is greater than 68.4%.

[0062] Example 2

[0063] The specific process of comprehensive utilization of red gypsum is as follows:

[0064] Step 1: Prepare a 0.1 mol / L ammonium citrate solution as a leaching agent for red gypsum, add 5 g of red gypsum and ammonium citrate solution into a reaction vessel at a liquid-solid mass ratio of 20, and stir at 500 rpm for 20 min. After the reaction is completed, filter to obtain calcium-rich leaching solution and leaching residue.

[0065] Step 2: The calcium-rich leaching solution obtained in step 1 is allowed to stand for 12 hours to obtain calcium citrate precipitate. After the reaction is completed, calcium citrate is obtained by filtration.

[0066] Step 3: The calcium citrate obtained in step 2 and water are added into a reaction container at a liquid-to-solid mass ratio of 100, and after being fully mixed and reacted for 10 minutes, ammonia water is added to adjust the pH of the solution to 10.5 to obtain a mixed solution.

[0067] Step 4: Add CO to the mixed solution in step 3 at a flow rate of 200 mL / min. 2 The gas was carbonated and the reaction was terminated after 90 min. The reaction product was filtered and the liquid phase was used as the raw material for the red gypsum leaching reaction cycle. The solid phase was dried, ground and tested to show that the solid product was calcite calcium carbonate with an impurity content of less than 0.2%. The carbon dioxide storage capacity was 176 kg CO 2 / t red gypsum, calcium carbonate production capacity: 400 kg CaCO 3 / t Red Gypsum.

[0068] Step 5: The leached residue obtained in step 1 and the biomass are evenly mixed to obtain a mixture, wherein the mass ratio of the leached residue to the biomass is 1:1, the particle size of the leached residue is 0.15 mm, and the particle size of the biomass is 0.25 mm.

[0069] Step 6: The mixture obtained in step 5 is heated to 800°C at a heating rate of 5°C / min under an argon atmosphere and kept at this temperature for 2 hours to obtain a reaction product.

[0070] Step 7: The reaction product obtained in step 6 is cooled in sequence, washed with methanol and deionized water, and dried to obtain a catalyst. The catalyst yield is 68.45%, and the catalyst particle size is 0.15-0.25 mm.

[0071] The leached residue catalyst obtained in step 7 is added to the organic pollutant aqueous solution and mixed, 50wt% potassium permonosulfate is first added to the catalyst and the organic pollutant aqueous solution, and then the remaining 50wt% potassium permonosulfate is added to the catalyst and the organic pollutant aqueous solution. The amount of the leached residue heterogeneous catalyst is 5 g and the amount of potassium permonosulfate is 1.5 mmol per liter of the organic pollutant aqueous solution. The mixture is stirred for 150 minutes to degrade the organic pollutants in the organic pollutant aqueous solution, wherein the organic pollutants are carbamazepine or methylene blue dye, and the degradation rate of carbamazepine (concentration of 20 mg / L) is 97.63%; the degradation rate of methylene blue dye is 94.31%; and the total organic carbon removal rate is greater than 62.21%.

[0072] Example 3

[0073] Step 1: Prepare a 0.2 mol / L ammonium citrate solution as a leaching agent for red gypsum, add 5 g of red gypsum and ammonium citrate solution into a reaction vessel at a liquid-solid mass ratio of 40, and stir at 800 rpm for 30 min. After the reaction is completed, filter to obtain calcium-rich leaching solution and leaching residue.

[0074] Step 2: The calcium-rich leaching solution obtained in step 1 is allowed to stand for 24 hours to obtain calcium citrate precipitate. After the reaction is completed, calcium citrate is obtained by filtration.

[0075] Step 3: The calcium citrate obtained in step 2 and water are added into a reaction container at a liquid-to-solid mass ratio of 200, and after being fully mixed and reacted for 10 minutes, ammonia water is added to adjust the pH of the solution to 11.5 to obtain a mixed solution.

[0076] Step 4: Add CO to the mixed solution obtained in step 3 at a flow rate of 300 mL / min. 2 The gas was carbonated and the reaction was terminated after 120 min. The reaction product was filtered and the liquid phase was used as the raw material for the red gypsum leaching reaction cycle. The solid phase was dried, ground and tested to show that the solid product was calcite calcium carbonate with an impurity content of less than 0.15%. The carbon dioxide storage capacity was 158 kg CO 2 / t red gypsum, calcium carbonate production capacity: 360 kg CaCO 3 / t Red Gypsum.

[0077] Step 5: The leaching residue obtained in step 1 and the biomass are evenly mixed to obtain a mixture, wherein the mass ratio of the leaching residue to the biomass is 1:2, the particle size of the leaching residue is 0.25 mm, and the particle size of the biomass is 0.15 mm.

[0078] Step 6: The mixture obtained in step 5 was heated to 600° C. at a heating rate of 10° C. / min under an argon atmosphere and kept at this temperature for 1 h to obtain a reaction product.

[0079] Step 7: The reaction product obtained in step 6 is cooled in sequence, washed with ethanol and deionized water, and dried to obtain a catalyst. The catalyst yield is 60.01%, and the catalyst particle size is 0.15-0.25 mm.

[0080] The leached residue catalyst obtained in step 7 is added to the organic pollutant aqueous solution and mixed. First, 50wt% potassium permonosulfate is added to the catalyst and the organic pollutant aqueous solution, and then the remaining 50wt% potassium permonosulfate is added to the catalyst and the organic pollutant aqueous solution. The amount of the leached residue heterogeneous catalyst is 8 g and the amount of potassium permonosulfate is 2 mmol per liter of the organic pollutant aqueous solution. The mixture is stirred for 200 min to degrade the organic pollutants in the organic pollutant aqueous solution. The organic pollutants are tetracycline or rhodamine b dye, and the degradation rate of tetracycline (concentration of 20 mg / L) is 97.68%, and the degradation rate of rhodamine b dye (concentration of 50 mg / L) is 99.28%; the total organic carbon removal rate is greater than 69.32%.

[0081] Comparative Example 1

[0082] Step 1: Prepare a 0.1 mol / L ammonium citrate solution as a leaching agent for red gypsum, add 5 g of red gypsum and ammonium citrate solution into a reaction vessel at a liquid-solid mass ratio of 20, and stir at 500 rpm for 20 min. After the reaction is completed, filter to obtain calcium-rich leaching solution and leaching residue.

[0083] Step 2: Add ammonia water to the calcium-rich leaching solution obtained in step 1 to adjust the pH of the solution to 10.5 to obtain a mixed solution.

[0084] Step 3: Add CO to the mixed solution in step 2 at a flow rate of 200 mL / min. 2 The gas was carbonated and the reaction was terminated after 90 min. The reaction product was filtered and the liquid phase was used as the raw material for the red gypsum leaching reaction cycle. The solid phase was dried, ground and tested to show that the solid product was calcite and vaterite calcium carbonate. The impurity content of calcium carbonate was 0.5%. The carbon dioxide storage capacity was: 172 kg CO 2 / t red gypsum, calcium carbonate production capacity: 394 kg CaCO 3 / t red gypsum. In this comparative example, since there are impurities in the leaching solution, these impurities directly affect the carbonation process, resulting in impure crystal system of calcium carbonate product, poor stability and reduced purity.

[0085] Comparative Example 2

[0086] Step 1: Prepare an ammonium acetate solution with a concentration of 0.1 mol / L as a leaching agent for red gypsum, add 5 g of red gypsum and ammonium acetate solution into a reaction vessel at a liquid-solid mass ratio of 20, and stir at 500 rpm for 20 minutes. After the reaction is completed, filter to obtain the calcium-rich leaching solution and leaching residue.

[0087] Step 2: Add ammonia water to the calcium-rich leaching solution obtained in step 1 to adjust the pH of the solution to 10.5 to obtain a mixed solution.

[0088] Step 3: Add CO to the mixed solution in step 2 at a flow rate of 200 mL / min. 2 The gas was carbonated and the reaction was terminated after 90 min. The reaction product was filtered and the liquid phase was used as the raw material for the red gypsum leaching reaction cycle. The solid phase was dried, ground and tested to show that the solid product was vaterite calcium carbonate with an impurity content of 0.62%. The carbon dioxide storage capacity was 18 kg CO 2 / t red gypsum, calcium carbonate production capacity: 40 kg CaCO 3 / t red gypsum. Due to the molecular structure (different number of carboxylic acid groups) and solution chemistry (different solution ionic strength) of ammonium acetate and ammonium citrate, ammonium acetate cannot fully leach calcium from red gypsum, and the impurities in the leachate directly affect the unstable calcium carbonate crystals generated, which have low purity and significantly reduced carbon fixation capacity. In addition, due to insufficient calcium leaching when using ammonium acetate to leach red gypsum, the iron in the leached residue is wrapped by residual calcium sulfate, so that the iron cannot fully react when the leached residue is co-carbonized with biomass, resulting in a reduction in the surface active sites of the prepared catalyst and a decrease in catalytic performance.

[0089] Comparative Example 3

[0090] Step 1: Evenly mix red gypsum and biomass to obtain a mixture, wherein the mass ratio of red gypsum to biomass is 1:1, the particle size of the red gypsum is 0.15 mm, and the particle size of the biomass is 0.25 mm.

[0091] Step 2: The mixture obtained in step 1 is heated to 800°C at a heating rate of 5°C / min under an argon atmosphere and kept at this temperature for 2 h to obtain a reaction product.

[0092] Step 3: The reaction product obtained in step 2 is cooled in sequence, washed with methanol and deionized water, and dried to obtain a catalyst. The catalyst yield is 61.19%, and the catalyst particle size is 0.15-0.25 mm.

[0093] The red gypsum catalyst obtained in step 3 is added to the aqueous solution of organic pollutants and mixed. First, 50wt% potassium permonosulfate is added to the catalyst and the aqueous solution of organic pollutants, and then the remaining 50wt% potassium permonosulfate is added to the catalyst and the aqueous solution of organic pollutants. The amount of red gypsum heterogeneous catalyst is 5 g and the amount of potassium permonosulfate is 1.5 mmol per liter of organic pollutant aqueous solution. The mixture is stirred and reacted for 150 min, so that the organic pollutants in the aqueous solution of organic pollutants are degraded, wherein the organic pollutants are carbamazepine or methylene blue dye, and the degradation rate of carbamazepine (concentration of 20 mg / L) is 5.1%; the degradation rate of methylene blue dye (concentration of 20 mg / L) is 3.2%; and the total organic carbon removal rate is less than 2%. It can be seen that when red gypsum is directly used to prepare the catalyst, because the iron therein is wrapped by calcium sulfate, the iron cannot fully react when it is co-carbonized with biomass, resulting in fewer active sites on the catalyst surface and poor catalytic effect.

[0094] Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for comprehensive utilization of red gypsum, characterized in that: The red gypsum is leached with an ammonium citrate solution, and then the solid and liquid are separated to obtain a calcium-rich leachate and an iron-containing leach residue. The calcium-rich leachate is subjected to static aging and solid-liquid separation to obtain a calcium citrate precipitate. The calcium citrate precipitate is mixed with water, and then the pH value of the solution is adjusted to be alkaline using ammonia water. Carbon dioxide is then introduced for carbonation reaction, and solid-liquid separation is performed to obtain a calcium carbonate product and a filtrate containing ammonium citrate. The filtrate containing ammonium citrate can be recycled for red gypsum leaching. The iron-containing leaching residue is subjected to a co-carbonization reaction with a biomass material to obtain an iron-based catalyst.

2. A method for comprehensive utilization of red gypsum according to claim 1, characterized in that: The concentration of the ammonium citrate solution is 0.02-2 mol / L.

3. A method for comprehensive utilization of red gypsum according to claim 1 or 2, characterized in that: The leaching conditions are: liquid-solid mass ratio of 10-100:1, temperature of 10-40°C, and time of 10-60min.

4. A method for comprehensive utilization of red gypsum according to claim 1, characterized in that: The pH value is 9.5~12.

5. A method for comprehensive utilization of red gypsum according to claim 1, characterized in that: The mass ratio of the iron-containing leaching residue to the biomass material is 1-5:1-2.

6. A method for comprehensive utilization of red gypsum according to claim 1 or 5, characterized in that: The mass content of carbon element in the biomass material is not less than 50%.

7. A method for comprehensive utilization of red gypsum according to claim 1 or 5, characterized in that: The biomass material is waste biomass material.

8. A method for comprehensive utilization of red gypsum according to claim 7, characterized in that: The waste biomass material includes at least one of straw, wood chips, fallen leaves, food residues, sludge, biomass processing waste, and livestock manure.

9. A method for comprehensive utilization of red gypsum according to claim 1, characterized in that: The conditions of the co-carbonization reaction are: the atmosphere is a protective atmosphere, the temperature is 400-1000° C., and the time is 1-3 hours.

10. An application of an iron-based catalyst, characterized in that: Used for catalyzing oxidants to degrade organic pollutants, the iron-based catalyst is prepared by the method described in any one of claims 1 to 9.

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