Method for pretreating desulfurized gypsum and co-producing ammonium sulfate

Abstract

The invention belongs to the technical field of solid waste resource utilization and separation and purification, and particularly relates to a method for pretreating desulfurized gypsum and co-producing ammonium sulfate. The method for pretreating the desulfurized gypsum and co-producing ammonium sulfate comprises the following steps: (1) carrying out pyrogenic pretreatment on the desulfurized gypsum to obtain primarily pretreated desulfurized gypsum; (2) adding the primary pretreated desulfurized gypsum, an acid reagent and water into a reaction tank, mixing, carrying out acid leaching treatment, carrying out solid-liquid separation after the acid leaching treatment, and drying the solid to obtain secondary pretreated desulfurized gypsum; (3) adding the secondarily pretreated desulfurized gypsum, carbonate, ammonia water and water into a reaction tank for stirring reaction, and after the reaction is finished, carrying out solid-liquid separation by using a plate-and-frame filter press to obtain a leaching solution and leaching residues; (4) carrying out evaporative crystallization and cooling separation on the leachate to obtain an ammonium sulfate product, and collecting and recycling CO2 and NH3 generated in the evaporative crystallization process for the previous procedure; the leaching residues are used for preparing light calcium carbonate.

Description

Technical Field

[0001] This invention belongs to the fields of solid waste resource utilization technology and separation and purification technology, specifically relating to a method for pretreatment of desulfurized gypsum and co-production of ammonium sulfate. Background Technology

[0002] Given that my country's energy structure is dominated by coal and this situation is unlikely to change fundamentally in the short term, coal-fired power generation will continue to occupy an important position in electricity production. Against the backdrop of increasingly stringent environmental policies, thermal power plants have generally installed flue gas desulfurization (FGD) devices, effectively reducing sulfur dioxide emissions and significantly improving regional air quality.

[0003] The wet limestone-gypsum process, currently the most widely used flue gas desulfurization technology, generates a large amount of byproduct—desulfurized gypsum—during its large-scale implementation. Statistics show that the total annual production of desulfurized gypsum in China has exceeded 100 million tons, with an average annual growth rate exceeding 5%. The main component of desulfurized gypsum is CaSO4·2H2O, accounting for approximately 90%. It has a high water content, approximately 10-17%, and its main ash components are Fe2O3 and SiO2. It contains a variety of impurities, with a high chlorine content, primarily in the form of soluble salts. Impurities are present both inside and on the surface of its crystals. my country's sintering flue gas desulfurization industry is still in its developmental stage, and a complete industrial chain for the utilization of desulfurization byproducts has not yet been formed.

[0004] Although the main components of desulfurized gypsum are similar to those of natural gypsum, its high impurity content and large quality fluctuations lead to problems in practical applications, such as inconsistent standards, low market awareness, and insufficient supporting industrial chains. A large amount of desulfurized gypsum has failed to achieve effective resource utilization, and long-term stockpiling not only causes serious resource waste but also poses potential environmental risks. At the same time, the state has set higher requirements for the resource utilization of solid waste. Policy documents such as the "Pilot Program for the Construction of Waste-Free Cities" and the "Guiding Opinions on Accelerating the Resource Utilization of Construction Solid Waste" clearly point out that the high-value utilization of industrial by-product gypsum should be promoted to facilitate the green and low-carbon transformation of the building materials industry.

[0005] Currently, the main ways to utilize desulfurized gypsum as a resource are through two main approaches: building material application and the preparation of high-value-added products. While the technology for building material application is relatively mature and the consumption volume is large, the added value of the products is low, market competition is fierce, and the industry is heavily reliant on the boom-bust cycle of the construction industry. This results in weak risk resistance and limited economic benefits for the desulfurized gypsum resource utilization industry. On the other hand, the preparation of high-value-added products such as α-high-strength gypsum and calcium sulfate whiskers generally suffers from complex processes, high energy consumption and costs, and weak market competitiveness, directly limiting the large-scale promotion and application of this technology.

[0006] Therefore, there is an urgent need to find a new method and path that is simple in process, controllable in cost, and low in energy consumption, so as to achieve large-scale and stable consumption of desulfurized gypsum and promote its transformation into high value-added and high-performance products. Summary of the Invention

[0007] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a method for the pretreatment of desulfurized gypsum and the co-production of ammonium sulfate.

[0008] The method for pretreatment of desulfurized gypsum and co-production of ammonium sulfate according to embodiments of the present invention includes the following steps: (1) The desulfurized gypsum is subjected to pyrometallurgical pretreatment to obtain pretreated desulfurized gypsum; (2) The primary pretreated desulfurized gypsum, acid reagent and water obtained in step (1) are added to the reaction tank and mixed for acid leaching treatment. After acid leaching treatment, solid and liquid are separated, and the solid is dried to obtain secondary pretreated desulfurized gypsum. (3) The secondary pretreated desulfurized gypsum, carbonate, ammonia and water obtained in step (2) are added to the reaction tank for stirring and reaction. After the reaction is completed, a plate and frame filter press is used for solid-liquid separation to obtain leachate and leachate residue. (4) The leachate obtained in step (3) is evaporated, crystallized, cooled and separated to obtain ammonium sulfate product. The CO2 and NH3 generated during the evaporation and crystallization process are collected and reused in the previous process. The leachate residue is used to prepare light calcium carbonate.

[0009] The advantages and technical effects of the desulfurized gypsum pretreatment and co-production of ammonium sulfate in this invention are as follows: 1. The method of this invention uses calcination-acid leaching pretreatment of desulfurized gypsum to increase its grade and whiteness; 2. The method of this invention uses a carbonate system, which is beneficial for the co-production of high-purity ammonium sulfate and calcium carbonate; 3. The method of this invention achieves green, low-carbon, and circular processes, with advantages such as low energy consumption, simple operation, readily available equipment, and mild reaction conditions. Simultaneously, the separation and recycling of valuable components in the desulfurized gypsum provides a new path for the high-value treatment of desulfurized gypsum.

[0010] In some embodiments, in step (1), the temperature of the pyrometallurgical pretreatment is 300~500℃, the time of the pyrometallurgical pretreatment is 100~150min, and the pyrometallurgical pretreatment is carried out in a calcining furnace.

[0011] In some embodiments, in step (2), the acid reagent includes at least one of hydrochloric acid, nitric acid or citric acid; the concentration of the acid reagent is 0.2~0.6 mol / L.

[0012] In some embodiments, in step (2), the solid-liquid ratio of the primary pretreated desulfurized gypsum to water is 1:(2~6), and the mass ratio of the primary pretreated desulfurized gypsum to acid reagent is 1:(0.154~0.461).

[0013] In some embodiments, in step (2), the acid leaching time is 6-14 hours, the acid leaching temperature is 40-60°C, and the acid leaching is carried out under stirring at a speed of 300-500 r / min.

[0014] In some embodiments, in step (3), the mass ratio of the secondary pretreated desulfurized gypsum to carbonate is 1:(0.4~0.8); the carbonate includes at least one of ammonium carbonate or ammonium bicarbonate.

[0015] In some embodiments, in step (3), the mass ratio of the secondary pretreatment desulfurization gypsum to ammonia water is 1:(0.56~0.83).

[0016] In some embodiments, in step (3), the solid-liquid ratio of the secondary pretreated desulfurized gypsum to water is 1:(2~6).

[0017] In some embodiments, in step (3), the stirring speed of the stirring reaction is 50~200 r / min, the temperature of the stirring reaction is 25~50 ℃, and the stirring reaction time is 30~150 min.

[0018] In some embodiments, in step (4), the temperature of evaporation and crystallization is 80~110 ℃, and the temperature after cooling is 10~50 ℃. Detailed Implementation

[0019] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0020] The method for pretreatment of desulfurized gypsum and co-production of ammonium sulfate according to embodiments of the present invention includes the following steps: (1) The desulfurized gypsum is subjected to pyrometallurgical pretreatment to obtain pretreated desulfurized gypsum; (2) The primary pretreated desulfurized gypsum, acid reagent and water obtained in step (1) are added to the reaction tank and mixed for acid leaching treatment. After acid leaching treatment, solid and liquid are separated, and the solid is dried to obtain secondary pretreated desulfurized gypsum. (3) The secondary pretreated desulfurized gypsum, carbonate, ammonia and water obtained in step (2) are added to the reaction tank for stirring and reaction. After the reaction is completed, a plate and frame filter press is used for solid-liquid separation to obtain leachate and leachate residue. (4) The leachate obtained in step (3) is evaporated, crystallized, cooled and separated to obtain ammonium sulfate product. The CO2 and NH3 generated during the evaporation and crystallization process are collected and reused in the previous process. The leachate residue is used to prepare light calcium carbonate.

[0021] The method for pretreatment of desulfurized gypsum and co-production of ammonium sulfate in this embodiment of the invention employs calcination-acid leaching pretreatment of desulfurized gypsum to increase its grade and whiteness. The method utilizes a carbonate system, which facilitates the co-production of high-purity ammonium sulfate and calcium carbonate. Furthermore, the entire process system of this method achieves green, low-carbon, and circular operation, with advantages such as low energy consumption, simple operation, readily available equipment, and mild reaction conditions. Simultaneously, the separation and recycling of valuable components in the desulfurized gypsum provides a new pathway for the high-value treatment of desulfurized gypsum.

[0022] In some embodiments, preferably, in step (1), the temperature of the pyrometallurgical pretreatment is 300~500℃, the time of the pyrometallurgical pretreatment is 100~150 min, and the pyrometallurgical pretreatment is carried out in a calcining furnace.

[0023] In this embodiment of the invention, the temperature and time of the pyrometallurgical pretreatment are limited to balance the decomposition of impurities and the stability of gypsum. If the temperature of the pyrometallurgical pretreatment is too low or the time is too short, silicate impurities cannot be fully decomposed, resulting in more impurity residues, limited improvement in whiteness, and reduced removal efficiency of impurities such as Fe in subsequent acid leaching. If the temperature of the pyrometallurgical pretreatment is too high or the time is too long, it may cause excessive dehydration or phase transformation of the gypsum matrix (such as CaSO4·2H2O), affecting the product structure and strength properties, and may also cause impurity recrystallization or the formation of new compounds.

[0024] In some embodiments, preferably, in step (2), the acid reagent includes at least one of hydrochloric acid, nitric acid or citric acid; the concentration of the acid reagent is 0.2~0.6 mol / L.

[0025] In this embodiment of the invention, the concentration of the acid reagent is limited to achieve the best impurity removal efficiency and process economy; if the acid concentration is too low, the target impurities cannot be fully dissolved and removed; if the acid concentration is too high, it may change the crystal morphology of gypsum and increase the cost of subsequent neutralization or wastewater treatment.

[0026] In some embodiments, preferably, in step (2), the solid-liquid ratio of the primary pretreated desulfurized gypsum to water is 1:(2~6), and the mass ratio of the primary pretreated desulfurized gypsum to acid reagent is 1:(0.154~0.461).

[0027] In some embodiments, preferably, in step (2), the acid leaching time is 6-14 hours, the acid leaching temperature is 40-60°C, and the acid leaching is carried out under stirring at a speed of 300-500 r / min.

[0028] In some embodiments, preferably, in step (3), the mass ratio of the secondary pretreated desulfurized gypsum to carbonate is 1:(0.4~0.8); the carbonate includes at least one of ammonium carbonate or ammonium bicarbonate.

[0029] In this embodiment of the invention, the mass ratio of secondary pretreatment desulfurization gypsum to carbonate is limited to ensure efficient conversion while achieving economic balance; if the amount of carbonate is too low, the CO3 provided in the reaction system will be insufficient. 2- Insufficient ion concentration weakens the driving force of the carbonation reaction, reduces the reaction rate, and prevents the conversion efficiency from reaching the expected target; if the amount of carbonate is too high, it will cause ammonia escape and excessive consumption of reagents.

[0030] In some embodiments, preferably, in step (3), the mass ratio of the secondary pretreatment desulfurization gypsum to ammonia water is 1:(0.56~0.83).

[0031] In this embodiment of the invention, the mass ratio of the secondary pretreatment desulfurization gypsum to ammonia water is limited to construct a suitable alkaline environment for the reaction. If the amount of ammonia water is too low, the pH value of the system will be too low, resulting in insufficient alkalinity and inability to effectively suppress NH4. + Hydrolysis is detrimental to crystal aggregation and recrystallization; if the amount of ammonia water is too high, the excess free ammonia will greatly increase the risk and extent of ammonia escape, and increase the possibility of other side reactions.

[0032] In some embodiments, preferably, in step (3), the solid-liquid ratio of the secondary pretreated desulfurized gypsum to water is 1:(2~6).

[0033] In some embodiments, preferably, in step (3), the stirring speed of the stirring reaction is 50~200 r / min, the temperature of the stirring reaction is 25~50 ℃, and the stirring reaction time is 30~150 min.

[0034] In some embodiments, preferably, in step (4), the evaporation and crystallization temperature is 80~110 ℃, and the temperature after cooling is 10~50 ℃.

[0035] The technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0036] Example 1 (1) Weigh out desulfurized gypsum and place it in a calcining furnace. After calcining at 400℃ for 120 min, cool it to room temperature to obtain pretreated desulfurized gypsum. (2) Weigh 5 kg of primary pretreated desulfurized gypsum and place it in a reaction tank. Add 1.536 kg of 0.4 mol / L citric acid and 20 L of water. Adjust the water bath temperature to 60 ℃ and stir for 12 h at a stirring speed of 400 r / min for acid leaching treatment. After acid leaching treatment, the mixture is separated into solid and liquid. The solid is dried at 60 ℃ to obtain secondary pretreated desulfurized gypsum.

[0037] (3) Weigh 5 kg of secondary pretreatment desulfurization gypsum, 3 kg of ammonium bicarbonate and 3.9 kg of ammonia water and place them in the reaction tank. Add 25 L of water and adjust the water bath temperature to 25 ℃. Stir for 120 min at a stirring speed of 200 r / min to make the reaction uniform. After the reaction is completed, use a plate and frame filter press to separate the solid and liquid to obtain leachate and leach residue. The pH of the leachate is 9.43, and the sulfur leaching rate is calculated to be 93.74%. (4) After the leachate is evaporated and crystallized at 105 °C, it is cooled to room temperature to obtain ammonium sulfate product. The leachate residue is used to prepare light calcium carbonate.

[0038] In this embodiment, the whiteness of the desulfurized gypsum ore was 32.5%, the grade (calculated as CaSO4·2H2O) was 89.19%, the SiO2 content was 5.08%, the iron impurities (calculated as Fe2O3) were 1.23%, and the aluminum impurities (calculated as Al2O3) were 1.90%. After two pretreatments, the whiteness of the secondary pretreated desulfurized gypsum increased to 73%, the grade (calculated as CaSO4·2H2O) increased to 98.2%, the SiO2 content decreased to 0.80%, the iron impurities (calculated as Fe2O3) decreased to 0.25%, and the aluminum impurities (calculated as Al2O3) decreased to 0.36%.

[0039] The ammonium sulfate product obtained in this example has an N content of 20.41% and an S content of 24.4%, which meets the Type II index of fertilizer-grade ammonium sulfate. The remaining ions also meet the standards. The whiteness of calcium carbonate is 85%.

[0040] Comparative Example 1 The method of Comparative Example 1 is the same as that of Example 1, except that step (1) is omitted.

[0041] In this comparative example, the whiteness of the desulfurized gypsum after one pretreatment was increased to 60.8%, the grade (calculated as CaSO4·2H2O) was increased to 92.17%, the SiO2 content was reduced to 1.06%, the iron impurities (calculated as Fe2O3) were reduced to 0.35%, and the aluminum impurities (calculated as Al2O3) were reduced to 0.44%.

[0042] The ammonium sulfate product obtained in this comparative example has an N content of 19.3% and an S content of 23.4%, which meets the Type II index of fertilizer-grade ammonium sulfate. The remaining ions also meet the standards. The whiteness of calcium carbonate is 64%.

[0043] Comparative Example 2 The method of Comparative Example 1 is the same as that of Example 1, except that step (2) is omitted.

[0044] In this comparative example, the whiteness of the desulfurized gypsum after one pretreatment was increased to 54%, the grade (calculated as CaSO4·2H2O) was increased to 94.31%, the SiO2 content was reduced to 0.95%, the iron impurities (calculated as Fe2O3) were reduced to 0.48%, and the aluminum impurities (calculated as Al2O3) were reduced to 0.47%.

[0045] The ammonium sulfate product obtained in this comparative example has an N content of 19.54% and an S content of 23.24%, which meets the Type II index of fertilizer-grade ammonium sulfate. The remaining ions also meet the standards. The whiteness of calcium carbonate is 60%.

[0046] Comparative Example 3 The method of Comparative Example 1 is the same as that of Example 1, except that steps (1) and (2) are omitted.

[0047] The ammonium sulfate product obtained in this comparative example has an N content of 19.29% and an S content of 21.85%, which meets the Type II index of fertilizer-grade ammonium sulfate. The remaining ions also meet the standards. The whiteness of calcium carbonate is 39.4%.

[0048] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0049] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for pretreatment of desulfurized gypsum and co-production of ammonium sulfate, characterized in that, Includes the following steps: (1) The desulfurized gypsum is subjected to pyrometallurgical pretreatment to obtain pretreated desulfurized gypsum; (2) The primary pretreated desulfurized gypsum, acid reagent and water obtained in step (1) are added to the reaction tank and mixed for acid leaching treatment. After acid leaching treatment, solid and liquid are separated, and the solid is dried to obtain secondary pretreated desulfurized gypsum. (3) The secondary pretreated desulfurized gypsum, carbonate, ammonia and water obtained in step (2) are added to the reaction tank for stirring and reaction. After the reaction is completed, a plate and frame filter press is used for solid-liquid separation to obtain leachate and leachate residue. (4) The leachate obtained in step (3) is evaporated, crystallized, cooled and separated to obtain ammonium sulfate product. The CO2 and NH3 generated during the evaporation and crystallization process are collected and reused in the previous process. The leachate residue is used to prepare light calcium carbonate.

2. The method for pretreatment of desulfurized gypsum and co-production of ammonium sulfate according to claim 1, characterized in that, In step (1), the temperature of the pyrometallurgical pretreatment is 300~500℃, the time of the pyrometallurgical pretreatment is 100~150 min, and the pyrometallurgical pretreatment is carried out in a calcining furnace.

3. The method for pretreatment of desulfurized gypsum and co-production of ammonium sulfate according to claim 1, characterized in that, In step (2), the acid reagent includes at least one of hydrochloric acid, nitric acid or citric acid, and the concentration of the acid reagent is 0.2~0.6 mol / L.

4. The method for pretreatment of desulfurized gypsum and co-production of ammonium sulfate according to claim 1 or 3, characterized in that, In step (2), the solid-liquid ratio of the primary pre-treated desulfurized gypsum to water is 1:(2~6), and the mass ratio of the primary pre-treated desulfurized gypsum to acid reagent is 1:(0.154~0.461).

5. The method for pretreatment of desulfurized gypsum and co-production of ammonium sulfate according to claim 4, characterized in that, In step (2), the acid leaching time is 6-14 hours and the acid leaching temperature is 40-60°C; the acid leaching is carried out under stirring at a speed of 300-500 r / min.

6. The method for pretreatment of desulfurized gypsum and co-production of ammonium sulfate according to claim 1, characterized in that, In step (3), the mass ratio of the secondary pretreated desulfurized gypsum to carbonate is 1:(0.4~0.8); the carbonate includes at least one of ammonium carbonate or ammonium bicarbonate.

7. The method for pretreatment of desulfurized gypsum and co-production of ammonium sulfate according to claim 1, characterized in that, In step (3), the mass ratio of the secondary pretreatment desulfurization gypsum to ammonia water is 1:(0.56~0.83).

8. The method for pretreatment of desulfurized gypsum and co-production of ammonium sulfate according to any one of claims 1, 6-7, characterized in that, In step (3), the solid-liquid ratio of the secondary pretreatment desulfurization gypsum to water is 1:(2~6).

9. The method for pretreatment of desulfurized gypsum and co-production of ammonium sulfate according to claim 8, characterized in that, In step (3), the stirring speed of the stirring reaction is 50~200 r / min, the stirring temperature is 25~50 ℃, and the stirring time is 30~150 min.

10. The method for pretreatment of desulfurized gypsum and co-production of ammonium sulfate according to claim 1, characterized in that, In step (4), the evaporation and crystallization temperature is 80~110 ℃, and the temperature after cooling is 10~50 ℃.