Waste gypsum treatment method

Abstract

The invention provides a waste gypsum treatment method. The treatment method comprises the following steps: S1, carrying out reduction reaction on waste gypsum and a reducing agent to obtain a product containing CaS; s2, the product containing CaS and chlorine are subjected to a chlorination reaction, and CaCl2 and flue gas are obtained; and S3, the flue gas is subjected to fractional condensation, and sulfur and FeCl3 are obtained. In the step S2, the product containing CaS and chlorine are subjected to a chlorination reaction, CaS and chlorine react to generate CaCl2 and sulfur, the iron element in the product containing CaS is chlorinated to form FeCl3, and both sulfur and FeCl3 are separated from CaCl2 along with flue gas. By consuming the waste gypsum and chlorine, the problem of stockpiling of the waste gypsum at present is solved, chlorine consumption in the chlor-alkali industry is achieved, products such as sulfur, anhydrous calcium chloride and ferric chloride with high value can be obtained, and the recovery rate of calcium, sulfur and iron is high.

Description

Technical Field

[0001] The invention relates to the technical field of waste treatment, and in particular to a method for treating waste gypsum. Background Art

[0002] At present, desulfurized gypsum, phosphogypsum, fluorinated gypsum, titanium gypsum, etc. are mainly stored in the form of solid waste. It is difficult to dispose of and utilize waste gypsum, and there is no gypsum disposal production process that can be applied on a large scale. A large amount of waste gypsum is used as a building material and added to cement, but this method has limited disposal capacity, and because waste gypsum may contain harmful substances and the use environment is restricted, it is difficult to promote and use it on a large scale.

[0003] It is reported that gypsum is pyrolyzed into CaO and SO2 under high temperature conditions. The produced calcium oxide can be recycled and SO2 can be used for subsequent production of sulfuric acid. However, this method has high reaction temperature and high energy consumption, and the value of the products calcium oxide and sulfuric acid is low, resulting in poor economic efficiency. Although studies have shown that the decomposition temperature of calcium sulfate can be lowered by controlling a weak oxidizing atmosphere, it is difficult to implement due to many side reactions and difficulty in controlling product components. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for treating waste gypsum to solve the problem of low recovery rates of calcium, sulfur and iron in the prior art methods for treating waste gypsum.

[0005] In order to achieve the above-mentioned object, according to one aspect of the present invention, a method for treating waste gypsum is provided, and the method comprises the following steps: step S1, subjecting the waste gypsum and a reducing agent to a reduction reaction to obtain a product containing CaS; step S2, subjecting the product containing CaS to a chlorination reaction with chlorine to obtain CaCl2 and flue gas; step S3, subjecting the flue gas to graded condensation to obtain sulfur and FeCl3.

[0006] Furthermore, the temperature of the reduction reaction is 800-1000° C.; and / or the time of the reduction reaction is 0.5-2 h; and / or the mass content of the carbon element in the reducing agent is 55-90%.

[0007] Furthermore, the mass ratio of the above-mentioned waste gypsum and the reducing agent is 70-100:30-60; and / or the atmosphere of the reduction reaction contains CO, CO2, H2 and H2O, and the volume ratio of CO to CO2 is 1:1-10; the volume ratio of H2 to H2O is 1:1-10; and / or the mass content of free carbon in the product of the reduction reaction is 5-10%.

[0008] Furthermore, the above reduction reaction is carried out in a rotary kiln or a boiling furnace; and / or, the water content of the waste gypsum does not exceed 2.16%; and / or, the average particle size of the waste gypsum is 1 to 10 mm; and / or, the average particle size of the reducing agent is 1 to 10 mm.

[0009] Furthermore, the chlorination reaction is carried out in a boiling furnace; and / or the temperature of the chlorination reaction is 450-650° C.; and / or the time of the chlorination reaction is 0.1-1 h.

[0010] Furthermore, the ratio of the volume of the chlorine gas to the mass of CaS is 11700-16100 Nm 3 :52.5~70.2t.

[0011] Furthermore, the above-mentioned graded condensation includes primary condensation and secondary condensation performed in sequence; the temperature of the primary condensation is 350-400°C; and / or the time of the primary condensation is 0.5-2h; and / or the temperature of the secondary condensation is 150-200°C; and / or the time of the secondary condensation is 0.5-2h.

[0012] Furthermore, the waste gypsum to be treated is granulated and dehydrated in sequence to obtain waste gypsum; preferably, the dehydration is carried out in a rotary kiln or a boiling furnace; and / or the dehydration temperature is 300-900°C.

[0013] Furthermore, the chlorinated residue obtained by the chlorination reaction is washed, evaporated, crystallized and dehydrated in sequence to obtain CaCl2; washing is performed with a washing liquid, and the mass ratio of the chlorinated residue to the washing liquid is 1:2-10; and / or the evaporation and crystallization temperature is 60-110°C; and / or the evaporation and crystallization time is 1-3h; and / or the dehydration temperature is 200-400°C; and / or the dehydration time is 0.5-3h.

[0014] Furthermore, the waste gypsum comprises, by mass fraction, 0.17-8.69% Fe2O3, 0.05-13.25% Al2O3, 0-0.8% P2O5, 0.60-6.37% SiO2, 0-0.99% F, 0-1.42% MgO, 71.03-96.30% CaSO4 and the remainder water; preferably, the waste gypsum is selected from any one or more of waste desulfurization gypsum, waste phosphogypsum, waste titanium gypsum, waste salt gypsum and waste fluorine gypsum; and / or the reducing agent is selected from any one or more of lignite, petroleum coke, coke and anthracite.

[0015] Applying the technical solution of the present application, in step S1, waste gypsum and a reducing agent undergo a reduction reaction, and calcium sulfate, the main chemical substance in the waste gypsum, is reduced to CaS under the action of the reducing agent. In step S2, a CaS-containing product and chlorine are subjected to a chlorination reaction, CaS reacts with chlorine to generate CaCl2 and sulfur, and the iron element in the CaS-containing product is chlorinated to form FeCl3, and sulfur and FeCl3 are separated from CaCl2 along with flue gas. In step S3, flue gas is graded and condensed according to the different condensation points of sulfur and FeCl3, thereby obtaining sulfur and FeCl3 with higher purity. The present application solves the current storage problem of waste gypsum by consuming waste gypsum and chlorine, realizes the consumption of chlorine in the chlor-alkali industry, and can also obtain high-value products such as sulfur, anhydrous calcium chloride, and ferric chloride, and the recovery rate of calcium, sulfur and iron is high. DETAILED DESCRIPTION

[0016] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0017] As analyzed in the background technology of this application, the existing waste gypsum treatment method has the problem of low recovery rate of calcium, sulfur and iron. In order to solve this problem, this application provides a waste gypsum treatment method.

[0018] In a typical embodiment of the present application, a method for treating waste gypsum is provided, and the method comprises the following steps: step S1, subjecting the waste gypsum and a reducing agent to a reduction reaction to obtain a product containing CaS; step S2, subjecting the CaS-containing product to a chlorination reaction with chlorine to obtain CaCl2 and flue gas; step S3, subjecting the flue gas to graded condensation to obtain sulfur and FeCl3.

[0019] In step S1, waste gypsum and a reducing agent undergo a reduction reaction, and calcium sulfate, the main chemical substance in the waste gypsum, is reduced to CaS under the action of the reducing agent. In step S2, a CaS-containing product and chlorine are subjected to a chlorination reaction, and CaS reacts with chlorine to generate CaCl2 and sulfur, and the iron element in the CaS-containing product is chlorinated to form FeCl3, and sulfur and FeCl3 are separated from CaCl2 along with flue gas. In step S3, flue gas is graded and condensed according to the different condensation points of sulfur and FeCl3, thereby obtaining sulfur and FeCl3 with higher purity. This application solves the current storage problem of waste gypsum by consuming waste gypsum and chlorine, realizes the consumption of chlorine in the chlor-alkali industry, and can also obtain high-value sulfur, anhydrous calcium chloride, ferric chloride and other products, and the recovery rate of calcium, sulfur and iron is high.

[0020] In one embodiment of the present application, the temperature of the above-mentioned reduction reaction is 800-1000°C, specifically 800°C, 850°C, 900°C, 950°C, 1000°C and a range value between any two values; and / or, the reduction reaction time is 0.5-2h; and / or, the mass content of carbon element in the reducing agent is 55-90%.

[0021] Controlling the temperature and time of the reduction reaction within the above ranges helps promote the chemical reaction between the carbon element and calcium sulfate, thereby helping to increase the generation ratio of CaS and helping to reduce the occurrence of side reactions. Controlling the mass content of the carbon element in the reducing agent within the above range helps promote sufficient contact between the carbon element and calcium sulfate, thereby helping to improve the efficiency of the reduction reaction, and further helping to improve the recovery rate of calcium, sulfur and iron.

[0022] In one embodiment of the present application, the mass ratio of the above-mentioned waste gypsum and the reducing agent is 70-100:30-60; and / or, the atmosphere of the reduction reaction contains CO, CO2, H2 and H2O, and the volume ratio of CO to CO2 is 1:1-10, specifically 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10 and the range value between any two ratios; the volume ratio of H2 to H2O is 1:1-10, specifically 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10 and the range value between any two ratios; and / or, the mass content of free carbon in the product of the reduction reaction is 5-10%.

[0023] Controlling the mass ratio of waste gypsum and reducing agent within the above range helps to improve the yield of CaS and reduce the occurrence of side reactions. Controlling the volume ratio of CO to CO2 and the volume ratio of H2 to H2O in the atmosphere of the reduction reaction within the above range helps to make the reduction reaction in a reducing atmosphere, which is beneficial to the conversion of calcium sulfate to calcium sulfide, and helps to regulate the direction and speed of the reaction, reduce unnecessary side reactions, and thus help to improve the purity and yield of calcium sulfide. In the present application, the volume ratio of CO, CO2, H2 and H2O can be regulated by introducing an appropriate amount of air. Excessive carbon residue will not only reduce the purity of the product, but also increase the complexity and cost of subsequent processing. An appropriate amount of free carbon helps to reduce the occurrence of side reactions such as the generation of H2S, S2, SO2, etc., thereby helping to improve the yield of CaS.

[0024] In one embodiment of the present application, the above-mentioned reduction reaction is carried out in a rotary kiln or a boiling furnace; and / or the water content of the waste gypsum does not exceed 2.16%; and / or the average particle size of the waste gypsum is 1 to 10 mm; and / or the average particle size of the reducing agent is 1 to 10 mm.

[0025] Both rotary kiln and fluidized bed furnace are high-temperature reaction equipment. They can provide good heat and mass exchange conditions, so that waste gypsum and reducing agent are evenly heated during the reaction process, thereby improving the conversion rate. Waste gypsum with low water content can reduce water evaporation during the reaction process, save energy, and thus help improve reaction efficiency and speed up the reaction. Gypsum with high water content is prone to equipment corrosion and blockage. Controlling water content helps to extend the service life of the equipment and reduce maintenance costs. In addition, the reduction of water content helps to improve the purity of the product and reduce the purification steps and costs in the subsequent treatment process. Controlling the average particle size of waste gypsum and reducing agent within the above range helps to increase the contact area between waste gypsum and reducing agent, promote the reaction, and improve the reaction rate and conversion rate.

[0026] In one embodiment of the present application, the CaS-containing product is cooled under nitrogen protection and then subjected to a chlorination reaction with chlorine.

[0027] In one embodiment of the present application, the chlorination reaction is carried out in a boiling furnace; and / or the temperature of the chlorination reaction is 450-650°C, specifically 450°C, 500°C, 550°C, 600°C, 650°C and a range value between any two values; and / or the chlorination reaction time is 0.1-1h.

[0028] The fluidized bed furnace can make the materials form a boiling state under high temperature conditions, enhance the heat and mass exchange between the materials, and promote the full contact between the reactants and the chlorine, thereby helping to improve the rate and conversion efficiency of the chlorination reaction. Controlling the temperature and time of the chlorination reaction within the above range helps to improve the yield of calcium chloride, while helping to reduce the probability of CaCl2 melting due to excessive temperature, and helping to reduce the generation of by-products. The temperature of the chlorination reaction of the present application is relatively low, which helps to reduce energy consumption.

[0029] In one embodiment of the present application, the ratio of the volume of the chlorine gas to the mass of CaS is 11700-16100 Nm 3 :52.5~70.2t.

[0030] Controlling the volume ratio of chlorine to the mass ratio of CaS within the above range helps to improve the utilization rate of chlorine and reduce the excess of chlorine. Excess chlorine not only increases production costs, but also increases the complexity and safety of subsequent treatment due to its strong oxidizing properties and environmental toxicity.

[0031] In one embodiment of the present application, the above-mentioned graded condensation includes primary condensation and secondary condensation performed sequentially; the temperature of the primary condensation is 350-400°C; and / or the time of the primary condensation is 0.5-2h; and / or the temperature of the secondary condensation is 150-200°C; and / or the time of the secondary condensation is 0.5-2h.

[0032] Controlling the temperature and time of the primary condensation within the above range is helpful to separate sulfur from the flue gas to obtain liquid sulfur. Controlling the temperature and time of the secondary condensation within the above range is helpful to separate FeCl3 from the flue gas to obtain FeCl3.

[0033] In one embodiment of the present application, the waste gypsum to be treated is granulated and dehydrated in sequence to obtain waste gypsum; preferably, the dehydration is carried out in a rotary kiln or a boiling furnace; and / or the dehydration temperature is 300-900°C.

[0034] The granulated waste gypsum has better fluidity, which is conducive to its uniform distribution and stable operation in subsequent processing equipment. Granular waste gypsum helps to increase the surface area of ​​the waste gypsum, making the subsequent reduction reaction more sufficient. Controlling the dehydration temperature within the above range helps to improve the dehydration efficiency while controlling the gypsum to prevent side reactions. The water content of the waste gypsum after the above dehydration is less than 1%.

[0035] In one embodiment of the present application, the flue gas used in dehydration is the flue gas discharged after the reduction reaction is completed, which helps to improve the utilization rate of energy, reduce energy consumption, and reduce the number of flue gas treatment units. The sulfur-containing flue gas generated in the present application can be absorbed by the desulfurization tower and then returned as a raw material for recycling. The desulfurization process does not generate new solid waste emissions, which helps to improve the sulfur recovery rate.

[0036] In order to improve the purity of CaCl2, in one embodiment of the present application, the chlorinated residue obtained by the chlorination reaction is washed, evaporated, crystallized and dehydrated in sequence to obtain CaCl2; washing is performed using a washing liquid, and the mass ratio of the chlorinated residue to the washing liquid is 1:2-10; preferably, the washing liquid is selected from any one or more of water, methanol and ethanol; and / or, the evaporation crystallization temperature is 60-110°C; and / or, the evaporation crystallization time is 1-3h; and / or, the dehydration temperature is 200-400°C; and / or, the dehydration time is 0.5-3h. The purity of the CaCl2 of the present application is greater than 95%.

[0037] In order to enrich the selectivity of materials, in one embodiment of the present application, the waste gypsum includes, by mass fraction, 0.17-8.69% Fe2O3, 0.05-13.25% Al2O3, 0-0.8% P2O5, 0.60-6.37% SiO2, 0-0.99% F, 0-1.42% MgO, 71.03-96.30% CaSO4 and the remainder water; preferably, the waste gypsum is selected from any one or more of waste desulfurization gypsum, waste phosphogypsum, waste titanium gypsum, waste salt gypsum and waste fluorine gypsum; and / or the reducing agent is selected from any one or more of lignite, petroleum coke, coke and anthracite.

[0038] The beneficial effects of the present application will be further illustrated below in conjunction with embodiments.

[0039] The components of the waste gypsum used in the embodiments and comparative examples, except water, are shown in Table 1 in terms of mass percentage.

[0040] Table 1

[0041]

[0042] Example 1

[0043] 100 tons of phosphogypsum is used as raw material, which is crushed and granulated to obtain phosphogypsum particles with an average particle size of 7mm. The granular materials are put into the rotary kiln for roasting and dehydration. The flue gas of the rotary kiln is countercurrent with the materials. The material temperature at the feed port is room temperature, the flue gas temperature is 200℃, the material temperature at the discharge port is 700℃, and the flue gas temperature in the high temperature zone is 900℃. The water content of the phosphogypsum particles after roasting is 0.1%. The mass of anhydrous gypsum that can be produced is 79.3t, and the flue gas volume of the rotary kiln is 81,700Nm 3 .

[0044] After roasting, the anhydrous gypsum is cooled and mixed with anthracite particles. The average particle size of the anthracite particles is 7 mm, the carbon content of the anthracite is 55%, and the mass of the anthracite material is 39.4 t. After mixing, the materials are put into a boiling furnace for reduction and sulfidation. Air is blown into the bottom to maintain incomplete combustion of carbon, and the temperature in the furnace is maintained at 900°C. The reduction reaction time is 0.5, and a reducing atmosphere is maintained in the boiling furnace so that the volume ratio of CO to CO2 in the flue gas is 1:1, and the volume ratio of H2 to H2O is 1:1. At this time, most of the calcium sulfate in the furnace is reduced to CaS by excess coal, and the residual free carbon mass percentage is 5%.

[0045] After reduction and sulfidation, 52.5t of material mainly composed of CaS was produced. After cooling under nitrogen protection, it entered the boiling chlorination furnace for chlorination. The temperature in the boiling furnace was maintained at 500℃. The chlorination reaction time was 1h, so that CaS was converted into CaCl2, and sulfur entered the 500℃ flue gas in the form of a single substance. The chlorine consumption during the chlorination process was 11,700 Nm 3 , nitrogen consumption is about 2900 Nm 3 . The output was 71.6t of chlorinated slag mainly composed of CaCl2.

[0046] The chlorinated slag mainly composed of CaCl2 is washed, evaporated, crystallized and dehydrated to obtain anhydrous calcium chloride. The purity of CaCl2 is 96%. Washing liquid is used for washing. The mass ratio of chlorinated slag to washing liquid is 1:2. The washing liquid is water. The evaporation and crystallization temperature is 110°C, the evaporation and crystallization time is 3h, the dehydration temperature is 200°C, and the dehydration time is 3h.

[0047] The sulfur-containing high-temperature flue gas is cooled to 350°C and kept warm for 0.5h. The sulfur is collected and the flue gas is further cooled to 200°C and kept warm for 0.5h. FeCl3 is collected and the tail gas is discharged after treatment.

[0048] Example 2

[0049] The difference from Example 1 is that 100 tons of desulfurized gypsum is used as raw material, which is crushed and granulated to obtain desulfurized gypsum particles with an average particle size of 5 mm. The granular material is put into a first-stage oxidation rotary kiln for roasting and dehydration. The rotary kiln flue gas and the material are countercurrent. The material temperature at the feed inlet is room temperature, the flue gas temperature is 200°C, the material temperature at the discharge port is 600°C, and the flue gas temperature in the high temperature zone is 800°C. The moisture content of the gypsum after roasting is 0.7%, and the rotary kiln flue gas volume is 36,600 Nm 3 , the output quality of anhydrous gypsum is 93.06t.

[0050] After roasting, anhydrous gypsum directly enters the second-stage reduction sulfide rotary kiln at high temperature. 42.3 tons of lignite is added into the second-stage kiln. The carbon content of lignite is 80%. The average particle size of lignite particles is 5 mm. The outlet of the first-stage rotary kiln is connected to the inlet of the second-stage rotary kiln. The high-temperature reducing gas discharged from the second-stage kiln directly enters the first-stage kiln for combustion and heating. The flue gas temperature is 600°C, so that the volume ratio of CO to CO2 in the flue gas is 1:10, and the volume ratio of H2 to H2O is 1:10. The temperature of the high-temperature zone in the kiln is 1000°C, and the reduction reaction time is 1h. The material discharged from the second-stage kiln is mainly CaS, and the mass percentage of residual free carbon is 10%.

[0051] The second stage kiln produces 59.0t of material mainly composed of CaS. After cooling under nitrogen protection, it enters the boiling chlorination furnace for chlorination. The temperature in the boiling furnace is maintained at 650℃. The chlorination reaction time is 0.1h, so that CaS is converted into CaCl2, and sulfur enters the 650℃ flue gas in the form of a single substance. The chlorine consumption during the chlorination process is 14,900 Nm 3 , nitrogen consumption is about 3700 Nm 3 . 81.2t of chlorinated slag mainly composed of CaCl2 was produced.

[0052] The chlorinated slag mainly composed of CaCl2 is washed, evaporated, crystallized and dehydrated to obtain anhydrous calcium chloride. The washing liquid is used for washing. The mass ratio of the chlorinated slag to the washing liquid is 1:5. The washing liquid is methanol. The evaporation and crystallization temperature is 60°C, the evaporation and crystallization time is 1h, the dehydration temperature is 200°C, and the dehydration time is 0.5h.

[0053] The sulfur-containing high-temperature flue gas is cooled to 400℃ and kept warm for 1 hour. The sulfur is collected and the flue gas is further cooled to 200℃ and kept warm for 1 hour. FeCl3 is collected and the tail gas is discharged after treatment.

[0054] Example 3

[0055] The difference from Example 1 is that 100 tons of fluorgypsum is used as raw material, which is crushed and granulated to obtain fluorgypsum particles with an average particle size of 10 mm. Since the water content of fluorgypsum itself is 1.57%, it can be directly mixed with anthracite particles without roasting and dehydration. The average particle size of anthracite particles is 6 mm, and the coke powder material ratio is 53.6 tons. After mixing, the materials are put into a boiling furnace for reduction and sulfurization. Air is blown into the lower part to keep the carbon in the furnace from being fully burned. The temperature in the furnace is 800°C, the reduction reaction time is 0.5h, and the reducing atmosphere is maintained in the boiling furnace so that the volume ratio of CO to CO2 in the flue gas is 1:1, and the volume ratio of H2 to H2O is 1:1. At this time, most of the calcium sulfate in the furnace is reduced to CaS by excess coal, and the residual free carbon mass percentage is 5%.

[0056] After reduction and sulfidation, 61.3t of material mainly composed of CaS was produced. After cooling under nitrogen protection, it entered the boiling chlorination furnace for chlorination. The temperature in the boiling furnace was maintained at 500℃. The chlorination reaction time was 0.3h, so that CaS was converted into CaCl2, and sulfur entered the 500℃ flue gas in the form of a single substance. The chlorine consumption during the chlorination process was 16,100 Nm 3 , nitrogen consumption is about 4000 Nm 3 . 87.7t of chlorinated slag mainly composed of CaCl2 was produced.

[0057] The chlorinated slag mainly composed of CaCl2 is washed, evaporated, crystallized and dehydrated to obtain anhydrous calcium chloride. The washing liquid is used for washing. The mass ratio of the chlorinated slag to the washing liquid is 1:5. The washing liquid is ethanol. The evaporation and crystallization temperature is 80°C, the evaporation and crystallization time is 1h, the dehydration temperature is 400°C, and the dehydration time is 0.5h.

[0058] The sulfur-containing high-temperature flue gas is cooled to 350°C and kept warm for 1 hour. The sulfur is collected and the flue gas is further cooled to 150°C and kept warm for 2 hours. FeCl3 is collected and the tail gas is discharged after treatment.

[0059] Example 4

[0060] The difference from Example 1 is that 100 tons of titanium gypsum with a water content of 2.16% is used as raw material, and it is pulverized and granulated with 45.6 tons of anthracite to obtain a mixed material with an average particle size of 3 mm. The molded material particles enter the rotary kiln for reduction and sulfurization, the rotary kiln flue gas and the material are countercurrent, the temperature of the material at the feed inlet is room temperature, the temperature of the flue gas is 300°C, the temperature of the material at the discharge port is 600°C, the volume ratio of CO to CO2 in the flue gas in the high-temperature zone is 1:1, the volume ratio of H2 to H2O is 1:1, the temperature of the high-temperature zone in the kiln is 1000°C, the reduction reaction time is 2h, the discharged material is mainly CaS, and the residual free carbon mass percentage is 10%.

[0061] The rotary kiln produces 70.2t of material, mainly CaS. After cooling under nitrogen protection, it enters the boiling chlorination furnace for chlorination. The temperature in the boiling furnace is maintained at 450℃. The chlorination reaction time is 0.5h, so that CaS is converted into CaCl2, and sulfur enters the 450℃ flue gas in the form of a single substance. The chlorine consumption during the chlorination process is 15,900 Nm 3 , nitrogen consumption is about 4000 Nm 3 . 82.4t of chlorinated slag mainly composed of CaCl2 was produced.

[0062] The chlorinated slag mainly composed of CaCl2 is washed, evaporated, crystallized and dehydrated to obtain anhydrous calcium chloride. The washing liquid is used for washing, the mass ratio of the chlorinated slag to the washing liquid is 1:2, the washing liquid is water, the evaporation and crystallization temperature is 110°C, the evaporation and crystallization time is 1h, the dehydration temperature is 400°C, and the dehydration time is 0.5h.

[0063] The sulfur-containing high-temperature flue gas is cooled to 350°C and retained for 1 hour to collect sulfur. The flue gas is further cooled to 200°C and retained for 0.5 hours to collect FeCl3. The tail gas is discharged after treatment.

[0064] Example 5

[0065] The difference from Example 1 is that 100 tons of salt gypsum is used as raw material, crushed and granulated to obtain salt gypsum particles with an average particle size of 5 mm, and the granular material is put into a first-stage oxidation rotary kiln for roasting and dehydration. The rotary kiln flue gas and the material are countercurrent. The material temperature at the feed inlet is room temperature, the flue gas temperature is 300°C, the material temperature at the discharge port is 600°C, and the flue gas temperature in the high-temperature zone is 800°C. The moisture content of the salt gypsum particles after roasting is 0.4%, and the rotary kiln flue gas volume is 70,000 Nm 3 , the output mass of anhydrous gypsum is 84.27t.

[0066] After roasting, anhydrous gypsum directly enters the second-stage reduction sulfide rotary kiln at high temperature. 41.7 tons of petroleum coke is added to the second-stage kiln. The average particle size of the petroleum coke is 8 mm, and the carbon content of the petroleum coke is 90%. The outlet of the first-stage rotary kiln is connected to the inlet of the second-stage rotary kiln. The high-temperature reducing gas discharged from the second-stage kiln directly enters the first-stage kiln for combustion and heating. The flue gas temperature is 600°C, and the volume ratio of CO to CO2 in the flue gas is 1:5, and the volume ratio of H2 to H2O is 1:5. The temperature of the high-temperature zone in the kiln is 900°C, and the reduction reaction time is 1h. The material discharged from the second-stage kiln is mainly CaS, and the mass percentage of residual free carbon is 10%.

[0067] The second stage kiln produces 55.1t of material mainly composed of CaS. After cooling under nitrogen protection, it enters the boiling chlorination furnace for chlorination. The temperature in the boiling furnace is maintained at 450℃. The chlorination reaction time is 0.5h, so that CaS is converted into CaCl2, and sulfur enters the 450℃ flue gas in the form of a single substance. The chlorine consumption during the chlorination process is 13,200 Nm 3 , nitrogen consumption is about 3300 Nm 3 . The output was 76.5t of chlorinated slag mainly composed of CaCl2.

[0068] The chlorinated slag mainly composed of CaCl2 is washed, evaporated, crystallized and dehydrated to obtain anhydrous calcium chloride. The washing liquid is used for washing. The mass ratio of the chlorinated slag to the washing liquid is 1:5. The washing liquid is methanol. The evaporation and crystallization temperature is 60°C, the evaporation and crystallization time is 1h, the dehydration temperature is 200°C, and the dehydration time is 2h.

[0069] The sulfur-containing high-temperature flue gas is cooled to 400°C and retained for 0.5h to collect sulfur. The flue gas is further cooled to 200°C and retained for 1h to collect FeCl3. The tail gas is discharged after treatment.

[0070] Example 6

[0071] The difference from Example 1 is that the temperature of the reduction reaction is 800° C., the time of the reduction reaction is 2 h, and anhydrous calcium chloride, sulfur and FeCl3 are finally obtained.

[0072] Example 7

[0073] The difference from Example 1 is that the temperature of the reduction reaction is 1000° C., the time of the reduction reaction is 0.5 h, and anhydrous calcium chloride, sulfur and FeCl3 are finally obtained.

[0074] Example 8

[0075] The difference from Example 1 is that the temperature of the reduction reaction is 1100° C., the time of the reduction reaction is 0.3 h, and anhydrous calcium chloride, sulfur and FeCl3 are finally obtained.

[0076] Example 9

[0077] The difference from Example 1 is that the mass of the anthracite material is 20 t, the mass ratio of phosphogypsum to the anthracite material is 79.3:20, and anhydrous calcium chloride, sulfur and FeCl3 are finally obtained.

[0078] Example 10

[0079] The difference from Example 1 is that the volume ratio of CO to CO2 is 1:10; the volume ratio of H2 to H2O is 1:10, and anhydrous calcium chloride, sulfur and FeCl3 are finally obtained.

[0080] Embodiment 11

[0081] The difference from Example 1 is that the volume ratio of CO to CO2 is 1:15; the volume ratio of H2 to H2O is 1:15, and anhydrous calcium chloride, sulfur and FeCl3 are finally obtained.

[0082] Example 12

[0083] The difference from Example 1 is that the consumption of chlorine is 0.84 Nm 3 , and finally obtain anhydrous calcium chloride, sulfur and FeCl3.

[0084] Example 13

[0085] The difference from Example 1 is that the temperature of the chlorination reaction is 450° C., the time of the chlorination reaction is 1 h, and anhydrous calcium chloride, sulfur and FeCl3 are finally obtained.

[0086] Embodiment 14

[0087] The difference from Example 1 is that the temperature of the chlorination reaction is 650° C., the time of the chlorination reaction is 0.1 h, and anhydrous calcium chloride, sulfur and FeCl3 are finally obtained.

[0088] Embodiment 15

[0089] The difference from Example 1 is that the temperature of the chlorination reaction is 700° C., the time of the chlorination reaction is 0.05 h, and anhydrous calcium chloride, sulfur and FeCl3 are finally obtained.

[0090] Comparative Example 1

[0091] The difference from Example 1 is that 100 tons of phosphogypsum are treated by the method of Example 1 in the Chinese patent application with the patent application publication number CN106745145A. Specifically, (1) gypsum pretreatment: the dihydrate gypsum is firstly decontaminated and then dried and dehydrated, the drying temperature is 90°C, the drying time is 8h, the total moisture content of the dehydrated gypsum after drying and dehydration is 2-8%, the dehydrated gypsum is sent to a grinding device to produce dehydrated gypsum powder with an average particle size of not more than 800μm; (2) gypsum decomposition: the obtained dehydrated gypsum powder and sulfur-containing process gas are sent to a high-temperature reaction device, the molar ratio of S to CaSO4 is 1.0, the reaction temperature is controlled at 1200°C, calcium oxide and sulfur dioxide gas are obtained, the gypsum decomposition rate is not less than 99%, and the purity of the by-product calcium oxide is ≥85%;

[0092] (3) Sulfur dioxide reduction: The prepared sulfur dioxide gas and the carbonaceous reducing agent are fed into a reduction furnace together, and the reaction temperature is controlled at 1000°C. The sulfur dioxide gas and the carbonaceous reducing agent undergo a reduction reaction to obtain a sulfur-containing process gas, wherein the carbonaceous reducing agent is one or a combination of coal, coke, activated carbon, petroleum coke, natural gas, and coal gas; the sulfur-containing process gas is the product of a high-temperature reaction between sulfur dioxide and the carbonaceous reducing agent, and its composition includes sulfur vapor and one or a combination of SO2, H2S, COS, and CS2; the reduction furnace discharges the sulfur-containing process gas, which is firstly subjected to impurity and dust removal and then divided into two streams by a splitter, one of which is used for the gypsum decomposition reaction in step (2), and the other is taken out, and finally produces commercial sulfur after a series of processes including condensation, catalytic reduction, and granulation, with a sulfur purity of ≥98%, and the reduction tail gas is discharged after treatment.

[0093] The other sulfur-containing process gas in step (3) is first condensed in a first sulfur condenser to collect sulfur, and then discharged from the first sulfur condenser into a catalytic reactor; the sulfide in the sulfur-containing process gas in the catalytic reactor is reduced and converted into elemental sulfur under the action of the catalyst, and the catalytic process gas enters a second sulfur condenser to condense and separate elemental sulfur and tail gas, and the elemental sulfur is discharged from the bottom of the second sulfur condenser into a liquid sulfur pool, and the tail gas is discharged from the top of the second sulfur condenser into a tail gas treatment system, and is discharged after being treated to meet the emission standards; the elemental sulfur entering the liquid sulfur pool is sent to a liquid sulfur forming system for sulfur granulation, and then stored in a solid sulfur storage device to obtain sulfur.

[0094] The anhydrous calcium chloride, sulfur and FeCl3 prepared in the examples and comparative examples were tested for quality and the recovery rates of calcium, sulfur and iron. The test results are shown in Table 2.

[0095] Table 2

[0096]

[0097] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0098] In step S1, waste gypsum and a reducing agent undergo a reduction reaction, and calcium sulfate, the main chemical substance in the waste gypsum, is reduced to CaS under the action of the reducing agent. In step S2, a CaS-containing product and chlorine are subjected to a chlorination reaction, and CaS reacts with chlorine to generate CaCl2 and sulfur, and the iron element in the CaS-containing product is chlorinated to form FeCl3, and sulfur and FeCl3 are separated from CaCl2 along with flue gas. In step S3, flue gas is graded and condensed according to the different condensation points of sulfur and FeCl3, thereby obtaining sulfur and FeCl3 with higher purity. This application solves the current storage problem of waste gypsum by consuming waste gypsum and chlorine, realizes the consumption of chlorine in the chlor-alkali industry, and can also obtain high-value sulfur, anhydrous calcium chloride, ferric chloride and other products, and the recovery rate of calcium, sulfur and iron is high.

[0099] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for treating waste gypsum, characterized in that: The processing method comprises the following steps: Step S1, subjecting the waste gypsum and a reducing agent to a reduction reaction to obtain a product containing CaS; Step S2, subjecting the CaS-containing product to a chlorination reaction with chlorine to obtain CaCl2 and flue gas; Step S3, condensing the flue gas in stages to obtain sulfur and FeCl3.

2. The processing method according to claim 1, characterized in that: The temperature of the reduction reaction is 800-1000° C.; and / or, the time of the reduction reaction is 0.5-2 hours; and / or, the mass content of the carbon element in the reducing agent is 55-90%.

3. The processing method according to claim 1 or 2, characterized in that: The mass ratio of the waste gypsum to the reducing agent is 70-100:30-60; And / or, the atmosphere of the reduction reaction contains CO, CO2, H2 and H2O, and the volume ratio of CO to CO2 is 1:1-10; the volume ratio of H2 to H2O is 1:1-10; And / or, the mass content of free carbon in the product of the reduction reaction is 5-10%.

4. The processing method according to any one of claims 1 to 3, characterized in that: The reduction reaction is carried out in a rotary kiln or a fluidized bed furnace; And / or, the water content of the waste gypsum does not exceed 2.16%; and / or, the average particle size of the waste gypsum is 1 to 10 mm; and / or, the average particle size of the reducing agent is 1 to 10 mm.

5. The processing method according to any one of claims 1 to 4, characterized in that: The chlorination reaction is carried out in a boiling furnace; and / or, the temperature of the chlorination reaction is 450-650° C.; and / or, the time of the chlorination reaction is 0.1-1 h.

6. The processing method according to any one of claims 1 to 5, characterized in that: The volume ratio of the chlorine gas to the mass ratio of the CaS is 11700-16100 Nm 3 :52.5~70.2t.

7. The processing method according to any one of claims 1 to 6, characterized in that: The graded condensation includes primary condensation and secondary condensation performed sequentially; The temperature of the first-stage condensation is 350-400°C; and / or, the time of the first-stage condensation is 0.5-2h; And / or, the temperature of the secondary condensation is 150-200° C.; and / or, the time of the secondary condensation is 0.5-2 h.

8. The processing method according to any one of claims 1 to 7, characterized in that: The waste gypsum to be treated is granulated and dehydrated in sequence to obtain the waste gypsum; Preferably, the dehydration is carried out in a rotary kiln or a boiling furnace; and / or the dehydration temperature is 300-900°C.

9. The processing method according to any one of claims 1 to 8, characterized in that: The chlorinated residue obtained by the chlorination reaction is sequentially washed, evaporated, crystallized and dehydrated to obtain the CaCl2; a washing liquid is used for the washing, and the mass ratio of the chlorinated residue to the washing liquid is 1:2-10; And / or, the temperature of the evaporation crystallization is 60-110°C; and / or, the time of the evaporation crystallization is 1-3h; And / or, the dehydration temperature is 200-400° C.; and / or, the dehydration time is 0.5-3 h.

10. The processing method according to any one of claims 1 to 9, characterized in that: The waste gypsum comprises, by mass fraction, 0.17-8.69% of Fe2O3, 0.05-13.25% of Al2O3, 0-0.8% of P2O5, 0.60-6.37% of SiO2, 0-0.99% of F, 0-1.42% of MgO, 71.03-96.30% of CaSO4 and the balance of water; Preferably, the waste gypsum is selected from any one or more of waste desulfurization gypsum, waste phosphogypsum, waste titanium gypsum, waste salt gypsum and waste fluorine gypsum; and / or, the reducing agent is selected from any one or more of lignite, petroleum coke, coke and anthracite.

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