A method for resource utilization of calcium fluoride slag and fluoride-containing wastewater

Abstract

This disclosure relates to a method for the resource utilization of calcium fluoride slag and fluoride-containing wastewater. The method includes: spray-firing the leachate obtained from acid leaching of calcium fluoride slag; dissolving and pulping the resulting solid product to obtain a calcium salt solution; preparing a first defluorinating agent using the calcium salt solution, sulfate solution, and fluoride solution; subjecting the first defluorinating agent and the first fluoride-containing wastewater to a first-stage defluorination reaction to obtain first-stage defluorinated water and a second defluorinating agent; subjecting the second defluorinating agent and the second fluoride-containing wastewater to a second-stage defluorination reaction to obtain second-stage defluorinated water and crude calcium fluoride product; wherein the fluoride concentration of the first fluoride-containing wastewater is less than that of the second fluoride-containing wastewater. The method provided by this disclosure not only yields high-purity calcium fluoride products but also ensures that the fluoride-containing wastewater meets discharge standards, realizing the resource utilization of calcium fluoride slag and fluoride-containing wastewater, reducing the disposal cost of solid waste, and possessing broad economic and social benefits.

Description

Technical Field

[0001] This disclosure relates to the field of wastewater and waste residue treatment technology, specifically to a method for the resource utilization of calcium fluoride slag and fluoride-containing wastewater. Background Technology

[0002] Calcium fluoride is a colorless crystal or white powder with the chemical formula CaF2. It is sparingly soluble in water, slightly soluble in inorganic acids, and reacts with hot concentrated sulfuric acid to form hydrofluoric acid. It is widely used in metallurgy, chemical industry, building materials, light industry, optics, and defense. Currently, low-purity calcium fluoride slag is difficult to utilize directly and is usually disposed of through landfilling or the production of building materials such as bricks and cement. This method is not only inefficient and costly but also prone to environmental pollution. The calcium fluoride content in low-purity calcium fluoride slag is generally around 50%. If the calcium fluoride contained within it could be utilized as a resource, it would not only solve the problem of fluoride pollution but also bring extensive economic and social benefits.

[0003] Currently, the main methods for treating fluoride-containing wastewater include adsorption, precipitation, membrane methods, electrochemical methods, and ion exchange methods, with adsorption and precipitation being the most commonly used. Precipitation methods mainly include chemical precipitation, crystallization precipitation, and coagulation precipitation. Chemical precipitation was the earliest method used to treat fluoride-containing solutions, and it has advantages such as simple process flow, convenient operation, low fixed investment, and low cost, making it widely used. Currently, in industry, calcium salt precipitation is mainly used to treat fluoride-containing solutions, that is, calcium salts such as lime and calcium chloride are added to the fluoride-containing solution to form insoluble calcium fluoride precipitate, which is then removed.

[0004] Therefore, how to treat calcium fluoride slag and fluoride-containing wastewater in a more economical and environmentally friendly manner is a problem that needs to be solved. Summary of the Invention

[0005] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0006] To address the above problems, the purpose of this disclosure is to provide a method for the resource utilization of calcium fluoride slag and fluoride-containing wastewater. Compared with the prior art, the method provided by this disclosure can not only obtain calcium fluoride products with high purity, but also ensure that the fluoride-containing wastewater meets the discharge standards, thereby realizing the resource utilization of calcium fluoride slag and fluoride-containing wastewater, reducing the disposal cost of solid waste residue, and having broad economic and social benefits.

[0007] To achieve this objective, the present disclosure adopts the following technical solution:

[0008] This disclosure provides a method for the resource utilization of calcium fluoride slag and fluoride-containing wastewater, the method comprising the following steps:

[0009] The calcium fluoride slag was subjected to acid leaching and first solid-liquid separation in sequence to obtain leachate;

[0010] The leachate is spray-calcined to obtain a solid product, which is then subjected to dissolution and pulping followed by a second solid-liquid separation to obtain a calcium salt solution.

[0011] The calcium salt solution, sulfate solution, and fluoride solution are mixed and reacted sequentially, followed by a third solid-liquid separation, to obtain the first defluorinating agent.

[0012] The first defluorinating agent and the first fluoride-containing wastewater are subjected to a first-stage defluorination reaction and a fourth-stage solid-liquid separation to obtain water after first-stage defluorination and a second defluorinating agent.

[0013] The second defluorinating agent and the second fluoride-containing wastewater are subjected to a two-stage defluorination reaction and a fifth solid-liquid separation to obtain water after two-stage defluorination and crude calcium fluoride product; the fluoride concentration of the first fluoride-containing wastewater is less than the fluoride concentration of the second fluoride-containing wastewater.

[0014] In this disclosure, fluoride ions are first fully leached from calcium fluoride slag through acid leaching. Then, the leachate is spray-roasted to obtain a solid product (mainly containing calcium salts) and hydrogen fluoride gas, thus achieving preliminary separation of fluoride and calcium in the calcium fluoride slag. The solid product is then dissolved and pulped, followed by a second solid-liquid separation to further remove impurities, yielding a calcium salt solution. Subsequently, a first defluorinating agent (calcium sulfate dihydrate doped with calcium fluoride) is prepared by reacting calcium salts, sulfates, and fluoride salts. Finally, the first defluorinating agent is used to perform a first-stage defluorination reaction on a first fluoride-containing wastewater with a low fluoride concentration, yielding a solution that can... Using first-stage defluorination water that meets emission standards and a second defluorinating agent (containing calcium fluoride and unreacted calcium sulfate dihydrate), a two-stage defluorination reaction is carried out with the second defluorinating agent and second fluoride-containing wastewater with a higher fluoride concentration. This yields second-stage defluorination water and crude calcium fluoride product. Through the above two-stage defluorination reaction against the concentration gradient, the reaction can be effectively promoted. This method can obtain both first-stage defluorination water that meets emission standards and crude calcium fluoride product with high purity. It realizes the resource utilization of calcium fluoride slag and fluoride-containing wastewater, reduces the discharge of solid waste, and increases product revenue.

[0015] In one embodiment, the calcium fluoride slag is crushed and sieved sequentially before acid leaching to obtain calcium fluoride powder.

[0016] In one embodiment, the liquid-to-solid ratio of the acid solution to the calcium fluoride powder is (1-10):1mL / g, for example, it can be 1:1mL / g, 2:1mL / g, 3:1mL / g, 4:1mL / g, 5:1mL / g, 6:1mL / g, 7:1mL / g, 8:1mL / g, 9:1mL / g or 10:1mL / g, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] In this disclosure, it is preferable to control the liquid-solid ratio of acid solution to calcium fluoride powder within a specific range, which can avoid the problem of excessively low leaching rate of calcium fluoride due to an insufficient liquid-solid ratio, while also avoiding the problem of solution waste due to an excessively high liquid-solid ratio.

[0018] In one embodiment, the acid solution used for the acid leaching includes hydrochloric acid.

[0019] In one embodiment, the acid leaching uses an acid solution containing H... + The concentration is 1.5-3 mol / L, for example, it can be 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.8 mol / L or 3 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] In this disclosure, it is preferable to control the H in the acid solution. + When the concentration is within a specific range, it can promote the full leaching of calcium fluoride while avoiding problems such as increased costs, equipment corrosion, and environmental pollution caused by excessive hydrochloric acid concentration.

[0021] In one embodiment, aluminum chloride is also added to the acid solution.

[0022] In this disclosure, aluminum chloride is preferably added to the acid solution to fully utilize the reaction between aluminum ions and fluoride ions in the solution to generate AlF6. 3- To dissolve calcium fluoride and increase the leaching rate of calcium fluoride.

[0023] In one embodiment, the concentration of aluminum ions in the acid solution is 1.5-3 mol / L, for example, it can be 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.8 mol / L or 3 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] In this disclosure, an increase in the concentration of aluminum ions will promote the reaction to move continuously in the positive direction, thereby increasing the leaching rate of calcium fluoride. This disclosure preferably controls the concentration of aluminum ions in the acid solution within a specific range, which can avoid the situation where the rate of increase in calcium fluoride leaching rate slows down significantly and the cost is too high when the concentration of aluminum ions is too high.

[0025] In one embodiment, the spray calcination temperature is 200-400°C, for example, it can be 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, 320°C, 340°C, 360°C, 380°C or 400°C, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0026] In this disclosure, it is preferable to control the spray calcination temperature within a specific range to avoid excessively low temperatures causing AlF6 to... 3- It cannot be fully decomposed, thus failing to convert into hydrogen fluoride gas. At the same time, it avoids the situation where aluminum chloride in the solution cannot be converted into solid alumina due to excessively low temperature, which would prevent chloride ions from being fully transferred to calcium chloride. It also avoids the situation where the temperature is too high, causing the solid calcium chloride to reach its melting point and resulting in energy waste.

[0027] In one embodiment, hydrogen fluoride gas is obtained after the spray roasting. The hydrogen fluoride gas is absorbed by a sodium hydroxide solution to obtain sodium fluoride. The sodium fluoride is used to prepare a fluoride salt solution for reuse in the reaction or to adjust the fluoride concentration of the raw fluoride wastewater.

[0028] In this disclosure, fluorine and calcium are separated from calcium fluoride slag by spray roasting to obtain hydrogen fluoride gas with high purity. Preferably, sodium hydroxide solution is used to recover the hydrogen fluoride gas to prepare sodium fluoride product, which can improve the fluorine recovery rate in calcium fluoride slag. The obtained sodium fluoride can be added to the reaction as a fluoride salt and can also be used as a conditioner for fluoride-containing wastewater. This provides a stable fluoride source for the subsequent production of calcium fluoride products and the defluorination of fluoride-containing wastewater, and provides a foundation for ensuring the stable discharge of defluorinated water and the stable purity of calcium fluoride products, thus realizing the resource utilization of fluoride source.

[0029] In one embodiment, aluminum slag is obtained after the second solid-liquid separation, and the aluminum slag is leached with hydrochloric acid to obtain an aluminum chloride solution that is reused in the acid leaching.

[0030] In this disclosure, the aluminum ions introduced after spray roasting are converted into aluminum oxide, and then the aluminum slag obtained after the second solid-liquid separation is preferably prepared by leaching with hydrochloric acid, which can realize the recycling of aluminum chloride, reduce the cost of using aluminum chloride, and avoid environmental pollution.

[0031] In one embodiment, the calcium salt solution comprises a calcium chloride solution.

[0032] In one embodiment, the sulfate solution comprises a sodium sulfate solution.

[0033] In one embodiment, the fluoride salt solution comprises a sodium fluoride solution.

[0034] In one embodiment, the concentrations of the calcium salt solution, sulfate solution, and fluoride solution are each independently 0.5-2.5 mol / L, for example, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, or 2.5 mol / L, but are not limited to the listed values; other unlisted values ​​within the range are also applicable.

[0035] In this disclosure, it is preferable to control the concentrations of calcium salt solution, sulfate solution and fluoride solution within a specific range, which can avoid the formation of calcium sulfate dihydrate being affected by too low a concentration, and can also avoid the increase in cost due to too high a concentration.

[0036] In one embodiment, the reaction temperature is 55-75°C, for example, 55°C, 56°C, 58°C, 60°C, 62°C, 64°C, 68°C, 70°C, 72°C, 74°C or 75°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] In one embodiment, the reaction time is 0.5-1.5h, for example, it can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1h, 1.2h, 1.4h or 1.5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] In this disclosure, it is preferable to control the temperature and time of the reaction within a specific range, so as to obtain calcium sulfate dihydrate doped with calcium fluoride of a specific crystal form and to control the uniformity of the particle size of calcium sulfate dihydrate.

[0039] In one embodiment, a calcium ion chelating agent is added during the reaction.

[0040] In one embodiment, the calcium ion chelating agent includes any one or a combination of at least two of EDTA, sodium pyrophosphate, sodium tripolyphosphate, potassium oxalate, sodium citrate, or sodium gluconate.

[0041] In one embodiment, the concentration of the calcium ion chelating agent is 0.01-10 mol / L, for example, it can be 0.01 mol / L, 0.05 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L or 10 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] In this disclosure, a calcium ion chelating agent is preferably added, and the type and concentration of the calcium ion chelating agent are preferably controlled, which can further adjust the crystal morphology of calcium sulfate dihydrate to make it into a short rod shape, thereby making the calcium sulfate dihydrate uniformly distributed, increasing the contact area with fluoride-containing wastewater, and helping to improve the purity of calcium fluoride products.

[0043] In one embodiment, the first defluorinating agent contains 55-80 wt% calcium sulfate dihydrate by mass percentage, for example, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, or 85 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] In this disclosure, it is preferable to control the mass percentage of sulfuric acid dihydrate in the first defluorinating agent, which can further improve the defluorination effect.

[0045] In one embodiment, the first defluorinating agent is added in excess relative to the first fluoride-containing wastewater during the defluorination reaction.

[0046] In one embodiment, the second fluoride-containing wastewater is added in excess relative to the second defluorinating agent in the two-stage defluorination reaction.

[0047] In this disclosure, a multi-stage defluorination process with a reverse concentration gradient is adopted, consisting of a first-stage defluorination reaction and a second-stage defluorination reaction. In the first-stage defluorination reaction, the excess of calcium sulfate dihydrate is controlled, and in the second-stage defluorination reaction, the excess of fluorine is controlled. This effectively promotes the reaction, ensuring that the defluorinated water meets discharge standards and that a high-purity calcium fluoride product is obtained.

[0048] In one embodiment, the first fluoride-containing wastewater includes diluted raw fluoride-containing wastewater and / or water after two-stage defluorination.

[0049] In one embodiment, the second fluoride-containing wastewater includes raw fluoride-containing wastewater and / or raw fluoride-containing wastewater with adjusted fluoride concentration; the fluoride concentration adjusting agent includes sodium fluoride.

[0050] In one embodiment, the fluoride concentration of the first fluoride-containing wastewater is 0.6-1.5 g / L, for example, it can be 0.6 g / L, 0.8 g / L, 1 g / L, 1.2 g / L, 1.4 g / L or 1.5 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] In one embodiment, the fluoride concentration of the second fluoride-containing wastewater is 2-3 g / L, for example, it can be 2 g / L, 2.2 g / L, 2.4 g / L, 2.6 g / L, 2.8 g / L or 3 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0052] In one embodiment, the fluoride concentration of the raw fluoride wastewater is 1.4-3 g / L, for example, it can be 1.4 g / L, 1.6 g / L, 1.8 g / L, 2 g / L, 2.2 g / L, 2.4 g / L, 2.6 g / L, 2.8 g / L or 3 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] In this disclosure, the fluoride-containing wastewater source is preferably high-salt fluoride-containing wastewater from the lithium battery recycling industry. Due to the influence of upstream processes, the fluoride concentration is generally between 1.4-3 g / L and fluctuates significantly, which is unfavorable for subsequent defluorination reactions. In this disclosure, sodium fluoride is preferably added to the fluoride-containing wastewater source to stabilize the fluoride concentration, thereby facilitating the subsequent defluorination reaction.

[0054] In one embodiment, the crude calcium fluoride product is sequentially washed and dried to obtain the calcium fluoride product.

[0055] In this disclosure, the methods of the first solid-liquid separation, the second solid-liquid separation, the third solid-liquid separation, the fourth solid-liquid separation, and the fifth solid-liquid separation are not particularly limited, and for example, they can be filtration.

[0056] As an optional technical solution of this disclosure, the method includes the following steps:

[0057] The calcium fluoride slag is crushed and sieved sequentially to obtain calcium fluoride powder. The calcium fluoride powder is then acid-leached with an acid solution, wherein the liquid-to-solid ratio of the acid solution to the calcium fluoride powder is (1-10):1 mL / g, and the acid solution contains H+. + The concentration of the acid solution is 1.5-3 mol / L, and the concentration of aluminum ions in the acid solution is 1.5-3 mol / L. Then, a first solid-liquid separation is performed to obtain the leachate.

[0058] The leachate is spray-roasted at a temperature of 200-400℃ to obtain a solid product and hydrogen fluoride gas. The solid product is then subjected to dissolution and pulping followed by a second solid-liquid separation to obtain aluminum slag and a calcium salt solution. The aluminum slag is leached with hydrochloric acid to obtain an aluminum chloride solution that is reused in the acid leaching process. The hydrogen fluoride gas is absorbed by a sodium hydroxide solution to obtain sodium fluoride. The sodium fluoride is used to prepare a fluoride salt solution that is reused in the reaction or to adjust the fluoride concentration in the raw fluoride-containing wastewater.

[0059] The calcium salt solution, sulfate solution, and fluoride solution are mixed, and a calcium ion chelating agent with a concentration of 0.01-10 mol / L is added. The mixture is reacted at a temperature of 55-75℃ for 0.5-1.5 h, followed by a third solid-liquid separation to obtain the first defluorinating agent. The concentrations of the calcium salt solution, sulfate solution, and fluoride solution are each independently 0.5-2.5 mol / L. The calcium ion chelating agent includes any one or a combination of at least two of EDTA, sodium pyrophosphate, sodium tripolyphosphate, potassium oxalate, sodium citrate, or sodium gluconate.

[0060] The first defluorinating agent and the first fluoride-containing wastewater are subjected to a first-stage defluorination reaction and a fourth solid-liquid separation in sequence to obtain first-stage defluorinated water and a second defluorinating agent. The first defluorinating agent contains 55-80 wt% calcium sulfate dihydrate by mass percentage. In the first-stage defluorination reaction, the first defluorinating agent is added in excess relative to the first fluoride-containing wastewater. The first fluoride-containing wastewater includes diluted raw fluoride-containing wastewater and / or second-stage defluorinated water.

[0061] The second defluorinating agent and the second fluoride-containing wastewater are subjected to a two-stage defluorination reaction and a fifth solid-liquid separation in sequence to obtain water and crude calcium fluoride product after two-stage defluorination. In the two-stage defluorination reaction, the second fluoride-containing wastewater is added in excess relative to the second defluorinating agent. The second fluoride-containing wastewater includes raw fluoride-containing wastewater and / or raw fluoride-containing wastewater with adjusted fluoride concentration. The fluoride concentration adjustment agent includes sodium fluoride.

[0062] The crude calcium fluoride product is successively washed and dried to obtain the final calcium fluoride product.

[0063] Compared with the prior art, this disclosure has the following beneficial effects:

[0064] (1) In this disclosure, calcium fluoride slag is leached with acid and aluminum chloride solution, which improves the leaching effect of calcium fluoride, reduces the leaching cost, and the introduced aluminum ions are eventually converted into aluminum slag and then leached with hydrochloric acid to obtain aluminum chloride solution for recycling, which reduces the cost of using aluminum chloride and avoids environmental pollution.

[0065] (2) In this disclosure, sodium fluoride products are prepared by separating the fluoride source from the calcium fluoride slag. The obtained sodium fluoride products can be used as a fluoride concentration regulator for the raw water of fluoride-containing wastewater and as a fluoride source basis for the preparation of calcium fluoride products. This provides a stable fluoride source for the subsequent defluorination treatment of fluoride-containing wastewater and the production of calcium fluoride products, ensuring the stable discharge of defluorinated water and the stable purity of calcium fluoride products.

[0066] (3) In this disclosure, a multi-stage defluorination process with a reverse concentration gradient is carried out by using a first-stage defluorination reaction and a second-stage defluorination reaction. In the first-stage defluorination reaction, the excess of calcium sulfate dihydrate is controlled, and in the second-stage defluorination reaction, the excess of fluorine is controlled. This can effectively promote the reaction, so that the defluorinated water meets the discharge standards and high-purity calcium fluoride products can be obtained.

[0067] (4) In this disclosure, calcium sulfate dihydrate doped with calcium fluoride is used as the first defluorinating agent. Its particle size is 2-22 μm, and the particles are small and uniform. The doped calcium fluoride can be used as a seed crystal and has the effect of inducing precipitation during the defluorination process. In this disclosure, the crystal morphology of calcium sulfate dihydrate is controlled by calcium ion chelating agent so that it is in the shape of short rods, which is beneficial to the subsequent defluorination reaction.

[0068] (5) The method provided in this disclosure can obtain a calcium chloride solid product with a purity of 74.56% or higher, sodium fluoride with a purity of 72.34% or higher, and calcium fluoride product with a purity of 56.35% or higher. After the first stage of defluorination treatment by the method, the fluoride concentration in the water can reach below 132 mg / L, and the fluoride recovery rate can reach above 94.26%. Under better conditions, this disclosure can obtain a calcium chloride solid product with a purity of 97.67% or higher, sodium fluoride with a purity of 95.36% or higher, and calcium fluoride product with a purity of 85.3% or higher. After the first stage of defluorination treatment by the method, the fluoride concentration in the water can reach below 49 mg / L and meet the discharge standards. The fluoride recovery rate can reach above 97.75%, realizing the resource utilization of calcium fluoride slag and fluoride-containing wastewater, reducing the discharge of solid waste residue, and increasing product revenue.

[0069] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0070] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0071] Figure 1 This is a flowchart of the method described in Embodiment 1 of this disclosure;

[0072] Figure 2 This is a SEM image of the first defluorinating agent in Embodiment 1 of this disclosure;

[0073] Figure 3 This is a SEM image of the calcium fluoride product described in Embodiment 1 of this disclosure. Detailed Implementation

[0074] The technical solutions of this disclosure will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of this disclosure and should not be construed as specific limitations thereof.

[0075] In this disclosure, the acid leaching time, sodium hydroxide solution concentration, stirring speed, stirring time, settling time, addition time of the second defluorinating agent, and amount of washing water are all conventional operations in the art. Conventional operating parameters in the art can be used without affecting the final treatment effect.

[0076] Example 1

[0077] This embodiment provides a method for the resource utilization of calcium fluoride slag and fluoride-containing wastewater, such as... Figure 1 As shown, the method includes the following steps:

[0078] The calcium fluoride slag was crushed and sieved sequentially to obtain calcium fluoride powder. 100g of the calcium fluoride powder was then acid-leached for 2 hours in 1L of an acid solution containing hydrochloric acid and aluminum chloride. The liquid-to-solid ratio of the acid solution to the calcium fluoride powder was 10:1 mL / g. The acid solution contained H... + The concentration of the solvent was 1.5 mol / L, the concentration of aluminum ions was 1.5 mol / L, and then the solution was filtered to obtain the leachate.

[0079] The leachate is spray-roasted at 300°C, resulting in a solid product at the bottom of the roasting furnace and hydrogen fluoride gas at the top. The solid product is then dissolved, pulped, and filtered to obtain aluminum slag and calcium chloride solution. The aluminum slag is leached with hydrochloric acid to obtain aluminum chloride solution, which is reused in the acid leaching process to prepare the acid solution. The hydrogen fluoride gas is absorbed by a 10 g / L sodium hydroxide solution to obtain sodium fluoride. The sodium fluoride is used to prepare a sodium fluoride solution, which is reused in the reaction or used to adjust the fluoride concentration in the raw fluoride wastewater.

[0080] The calcium chloride solution, sodium sulfate solution, and sodium fluoride solution were mixed, and a 0.05 mol / L EDTA solution was added. The mixture was reacted at 65°C for 0.5 h with a stirring speed of 150 r / min. The mixture was then filtered to obtain the first defluorinating agent, the SEM image of which is shown below. Figure 2 As shown, the concentrations of the calcium chloride solution, sodium sulfate solution, and sodium fluoride solution are each independently 1.5 mol / L;

[0081] 14.87g of the first defluorinating agent (containing 70wt% calcium sulfate dihydrate by mass percentage) and 1L of the first fluoride-containing wastewater (diluted raw fluoride-containing wastewater with a fluoride concentration of 0.6g / L) were subjected to a first-stage defluorination reaction and stirred for 1.5h at a speed of 150r / min. After standing for 1h, the mixture was filtered to obtain water after the first-stage defluorination with a fluoride concentration of 47mg / L and a second defluorinating agent. The water after the first-stage defluorination met the discharge standards. In the first-stage defluorination reaction, the first defluorinating agent was added in excess relative to the first fluoride-containing wastewater.

[0082] The second defluorinating agent was added to 1L of the second fluoride-containing wastewater (the raw fluoride wastewater was adjusted to a fluoride concentration of 2.3g / L with sodium fluoride) and added slowly over 1.5 hours. After addition, the mixture was stirred for 4 hours to carry out the second-stage defluorination reaction at a speed of 150r / min. Then, the mixture was filtered to obtain the water after the second-stage defluorination and the crude calcium fluoride product. The water after the second-stage defluorination can be reused as the first fluoride-containing wastewater in the first-stage defluorination reaction. In the second-stage defluorination reaction, the second fluoride-containing wastewater was added in excess of the second defluorinating agent.

[0083] The crude calcium fluoride product was washed with 100 mL of pure water and then dried to obtain the calcium fluoride product. Its SEM image is shown below. Figure 3 As shown.

[0084] Example 2

[0085] This embodiment provides a method for the resource utilization of calcium fluoride slag and fluoride-containing wastewater, the method comprising the following steps:

[0086] The calcium fluoride slag was crushed and sieved sequentially to obtain calcium fluoride powder. 150g of the calcium fluoride powder was then acid-leached for 2 hours in an acid solution containing hydrochloric acid and aluminum chloride. The liquid-to-solid ratio of the acid solution to the calcium fluoride powder was 5:1 mL / g. The acid solution contained H... + The concentration of the solvent was 2 mol / L, the concentration of aluminum ions was 2 mol / L, and then the solution was filtered to obtain the leachate.

[0087] The leachate is spray-roasted at 200°C, resulting in a solid product at the bottom of the roasting furnace and hydrogen fluoride gas at the top. The solid product is then dissolved, pulped, and filtered to obtain aluminum slag and calcium chloride solution. The aluminum slag is leached with hydrochloric acid to obtain aluminum chloride solution, which is reused in the acid leaching process to prepare the acid solution. The hydrogen fluoride gas is absorbed by a 10 g / L sodium hydroxide solution to obtain sodium fluoride. The sodium fluoride is used to prepare a sodium fluoride solution, which is reused in the reaction or used to adjust the fluoride concentration in the raw fluoride wastewater.

[0088] The calcium chloride solution, sodium sulfate solution, and sodium fluoride solution were mixed, and a sodium gluconate solution with a concentration of 0.01 mol / L was added. The mixture was reacted at a temperature of 55°C for 1 hour, with the stirring speed at 150 r / min during the reaction. The mixture was then filtered to obtain the first defluorinating agent. The concentrations of the calcium chloride solution, sodium sulfate solution, and sodium fluoride solution were each 1 mol / L.

[0089] 11.32g of the first defluorinating agent (containing 80wt% calcium sulfate dihydrate by mass percentage) and 1L of the first fluoride-containing wastewater (diluted raw fluoride-containing wastewater with a fluoride concentration of 1g / L) were subjected to a first-stage defluorination reaction and stirred for 1.5h at a speed of 150r / min. After standing for 1h, the mixture was filtered to obtain water after the first-stage defluorination with a fluoride concentration of 45mg / L and a second defluorinating agent. The water after the first-stage defluorination met the discharge standards. In the first-stage defluorination reaction, the first defluorinating agent was added in excess relative to the first fluoride-containing wastewater.

[0090] The second defluorinating agent was added to 1L of the second fluoride-containing wastewater (the raw fluoride wastewater was adjusted to a fluoride concentration of 2g / L with sodium fluoride) and added slowly over 1.5 hours. After addition, the mixture was stirred for 4 hours to carry out the second-stage defluorination reaction at a speed of 150r / min. Then, the mixture was filtered to obtain the water after the second-stage defluorination and the crude calcium fluoride product. The water after the second-stage defluorination can be reused as the first fluoride-containing wastewater in the first-stage defluorination reaction. In the second-stage defluorination reaction, the second fluoride-containing wastewater was added in excess of the second defluorinating agent.

[0091] The crude calcium fluoride product was washed with 100 mL of pure water and then dried to obtain the calcium fluoride product.

[0092] Example 3

[0093] This embodiment provides a method for the resource utilization of calcium fluoride slag and fluoride-containing wastewater, the method comprising the following steps:

[0094] The calcium fluoride slag was crushed and sieved sequentially to obtain calcium fluoride powder. 200g of the calcium fluoride powder was then acid-leached for 2 hours in an acid solution containing hydrochloric acid and aluminum chloride. The liquid-to-solid ratio of the acid solution to the calcium fluoride powder was 1:1 mL / g. The acid solution contained H... + The concentration of the solvent was 3 mol / L, the concentration of aluminum ions was 3 mol / L, and then the solution was filtered to obtain the leachate.

[0095] The leachate is spray-roasted at 380°C, resulting in a solid product at the bottom of the roasting furnace and hydrogen fluoride gas at the top. The solid product is then dissolved, pulped, and filtered to obtain aluminum slag and calcium chloride solution. The aluminum slag is leached with hydrochloric acid to obtain aluminum chloride solution, which is reused in the acid leaching process to prepare the acid solution. The hydrogen fluoride gas is absorbed by a 10 g / L sodium hydroxide solution to obtain sodium fluoride. The sodium fluoride is used to prepare a sodium fluoride solution, which is reused in the reaction or used to adjust the fluoride concentration in the raw fluoride wastewater.

[0096] The calcium chloride solution, sodium sulfate solution, and sodium fluoride solution were mixed, and a 10 mol / L EDTA solution was added. The mixture was reacted at 75°C for 1.5 h with a stirring speed of 150 r / min. The mixture was then filtered to obtain the first defluorinating agent. The concentrations of the calcium chloride solution, sodium sulfate solution, and sodium fluoride solution were each 2.5 mol / L.

[0097] 24.68g of the first defluorinating agent (containing 55wt% calcium sulfate dihydrate by mass percentage) and 1L of the first fluoride-containing wastewater (diluted raw fluoride-containing wastewater with a fluoride concentration of 1.5g / L) were subjected to a first-stage defluorination reaction and stirred for 1.5h at a speed of 150r / min. After standing for 1h, the mixture was filtered to obtain water after the first-stage defluorination with a fluoride concentration of 49mg / L and a second defluorinating agent. The water after the first-stage defluorination met the discharge standards. In the first-stage defluorination reaction, the first defluorinating agent was added in excess relative to the first fluoride-containing wastewater.

[0098] The second defluorinating agent was added to 1L of the second fluoride-containing wastewater (the raw fluoride wastewater was adjusted to a fluoride concentration of 3g / L with sodium fluoride) and added slowly over 1.5 hours. After addition, the mixture was stirred for 4 hours to carry out the second-stage defluorination reaction at a speed of 150r / min. Then, the mixture was filtered to obtain the water after the second-stage defluorination and the crude calcium fluoride product. The water after the second-stage defluorination can be reused as the first fluoride-containing wastewater in the first-stage defluorination reaction. In the second-stage defluorination reaction, the second fluoride-containing wastewater was added in excess of the second defluorinating agent.

[0099] The crude calcium fluoride product was washed with 100 mL of pure water and then dried to obtain the calcium fluoride product.

[0100] Example 4

[0101] This embodiment provides a method for the resource utilization of calcium fluoride slag and fluoride-containing wastewater. The only difference between this method and Embodiment 1 is that aluminum chloride is not added to the acid solution.

[0102] Example 5

[0103] This embodiment provides a method for the resource utilization of calcium fluoride slag and fluoride-containing wastewater. The only difference between this method and Embodiment 1 is that EDTA solution is not added during the reaction.

[0104] Example 6

[0105] This embodiment provides a method for the resource utilization of calcium fluoride slag and fluoride-containing wastewater. The only difference between this method and Embodiment 1 is that the spray roasting temperature is 150°C.

[0106] Example 7

[0107] This embodiment provides a method for the resource utilization of calcium fluoride slag and fluoride-containing wastewater. The only difference between this method and Embodiment 1 is that the spray roasting temperature is 450°C.

[0108] Comparative Example 1

[0109] This comparative example provides a method for the resource utilization of calcium fluoride slag and fluoride-containing wastewater. The only difference between this method and Example 1 is that sodium fluoride solution is not added in the reaction.

[0110] Comparative Example 2

[0111] This comparative example provides a method for the resource utilization of calcium fluoride slag and fluoride-containing wastewater. The only difference between this method and Example 1 is that a two-stage defluorination reaction is not performed, and the second defluorinating agent is the crude calcium fluoride product.

[0112] Comparative Example 3

[0113] This comparative example provides a method for the resource utilization of calcium fluoride slag and fluoride-containing wastewater. The only difference between this method and Example 1 is that a defluorination reaction is not performed. Instead, the first defluorinating agent is directly reacted with the raw fluoride-containing wastewater with a fluoride concentration of 2.3 g / L, and then filtered to obtain defluorinated water and crude calcium fluoride product.

[0114] The purity of calcium chloride, sodium fluoride, and calcium fluoride products in the solid products obtained in Examples 1-7 and Comparative Examples 1-3 were determined by X-ray fluorescence spectroscopy (XRF), and the results are shown in Table 1.

[0115] The fluoride concentration in the defluoridated water of Examples 1-7 and Comparative Examples 1-2, and the fluoride concentration in the defluoridated water of Comparative Example 3 were determined using the fluoride ion selective electrode method. The results are shown in Table 1. The fluoride recovery rate in the fluoride-containing wastewater of Examples 1-7 and Comparative Examples 1-3 was calculated based on the fluoride concentrations obtained by the fluoride ion selective electrode method. The results are shown in Table 1.

[0116] In Examples 1-7 and Comparative Example 1: Recovery rate = (fluoride concentration of the second fluoride-containing wastewater - fluoride concentration of the water after the first stage of defluorination) / fluoride concentration of the second fluoride-containing wastewater × 100%;

[0117] In Comparative Example 2: Recovery rate = (fluoride concentration of the first fluoride-containing wastewater - fluoride concentration of the water after the first stage of defluorination) / fluoride concentration of the first fluoride-containing wastewater × 100%;

[0118] In Comparative Example 3: Recovery rate = (fluoride concentration of raw fluoride wastewater - fluoride concentration of water after defluorination) / fluoride concentration of raw fluoride wastewater × 100%.

[0119] Table 1

[0120]

[0121] The following points can be observed from the data in Table 1:

[0122] (1) As can be seen from the data in Examples 1-7, the method provided in this disclosure can obtain a calcium chloride solid product with a purity of 74.56% or higher, sodium fluoride with a purity of 72.34% or higher, and calcium fluoride with a purity of 56.35% or higher. After the first stage of defluorination treatment by the method, the fluoride concentration in the water can reach below 132 mg / L, and the fluoride recovery rate can reach above 94.26%. Under better conditions, a calcium chloride solid product with a purity of 97.67% or higher, sodium fluoride with a purity of 95.36% or higher, and calcium fluoride with a purity of 85.3% or higher can be obtained. After the first stage of defluorination treatment by the method, the fluoride concentration in the water can reach below 49 mg / L and meet the discharge standard, and the fluoride recovery rate can reach above 97.75%.

[0123] (2) A comparison between Example 1 and Example 4 shows that the only difference between Example 4 and Example 1 is that aluminum chloride is not added to the acid solution. The results show that the purity of the calcium chloride solid product, sodium fluoride and calcium fluoride product in Example 1 is higher than that in Example 4. Moreover, the fluoride concentration of the water after the first stage of defluorination in Example 1 is lower than that in Example 4, and the fluoride recovery rate is higher. This indicates that the present disclosure preferably adds aluminum chloride to the acid solution, which can further improve the purity of the calcium chloride solid product, sodium fluoride and calcium fluoride product, reduce the fluoride concentration of the water after the first stage of defluorination, so that it meets the discharge standards, and improve the fluoride recovery rate.

[0124] (3) A comparison between Example 1 and Example 5 shows that the only difference between Example 5 and Example 1 is that EDTA solution is not added in the reaction. The results show that the purity of the calcium chloride solid product and calcium fluoride product in Example 1 is higher than that in Example 5. Moreover, the fluoride concentration of the water after the first stage of defluorination in Example 1 is lower than that in Example 5, and the fluoride recovery rate is higher. This indicates that the present disclosure preferably adds EDTA solution in the reaction, which can further improve the purity of the calcium chloride solid product and calcium fluoride product, reduce the fluoride concentration of the water after the first stage of defluorination, that is, improve the quality of the effluent and improve the fluoride recovery rate.

[0125] (4) A comparison of Examples 1 and 6-7 shows that the only difference between Examples 6-7 and Example 1 is that the spray roasting temperature is not within the preferred range of this disclosure. The results show that the purity of the calcium chloride solid product, sodium fluoride and calcium fluoride product in Example 1 is higher than that in Examples 6-7. Moreover, the fluoride concentration of the water after the first stage of defluorination in Example 1 is lower than that in Examples 6-7, and the fluoride recovery rate is higher. This indicates that controlling the spray roasting temperature in this disclosure can further improve the purity of the calcium chloride solid product, sodium fluoride and calcium fluoride product, reduce the fluoride concentration of the water after the first stage of defluorination, thereby improving the effluent water quality and increasing the fluoride recovery rate.

[0126] (5) As can be seen from the comparison between Example 1 and Comparative Example 1, the only difference between Comparative Example 1 and Example 1 is that sodium fluoride solution is not added in the reaction. The purity of the calcium chloride solid product and calcium fluoride product in Example 1 is higher, the fluoride concentration of water after the first defluorination is lower, and the fluoride recovery rate is higher. It can be seen that by adding sodium fluoride solution in the reaction, calcium sulfate dihydrate doped with calcium fluoride can be formed. The doped calcium fluoride can act as a seed crystal and has the effect of inducing precipitation in the defluorination process, which can further improve the purity of the calcium chloride solid product and calcium fluoride product and improve the fluoride recovery rate.

[0127] (6) From the comparison between Example 1 and Comparative Examples 2-3, it can be seen that Comparative Examples 2-3 do not carry out two-stage defluorination reaction and one-stage defluorination reaction respectively. Compared with Comparative Example 2, Example 1 has higher purity of calcium chloride solid product and calcium fluoride product. Compared with Comparative Example 3, Example 1 has higher purity of calcium fluoride product. Compared with Comparative Examples 2-3, Example 1 has higher fluoride recovery rate and lower fluoride content in effluent. It can be seen that the present disclosure can effectively promote the reaction by using a combination of one-stage defluorination reaction and two-stage defluorination reaction to perform two-stage defluorination against the concentration gradient, so that the defluorinated water meets the discharge standards and high-purity calcium fluoride product can be obtained.

[0128] In summary, the method provided in this disclosure not only yields calcium fluoride products with high purity, but also enables fluoride-containing wastewater to meet discharge standards, realizing the resource utilization of calcium fluoride slag and fluoride-containing wastewater, reducing the disposal cost of solid waste residue, and has broad economic and social benefits.

Claims

1. A method for the resource utilization of calcium fluoride slag and fluoride-containing wastewater, comprising the following steps: The calcium fluoride slag was subjected to acid leaching and first solid-liquid separation in sequence to obtain leachate; The leachate is spray-calcined to obtain a solid product, which is then subjected to dissolution and pulping followed by a second solid-liquid separation to obtain a calcium salt solution. The calcium salt solution, sulfate solution, and fluoride solution are mixed and reacted sequentially, followed by a third solid-liquid separation, to obtain the first defluorinating agent. The first defluorinating agent and the first fluoride-containing wastewater are subjected to a first-stage defluorination reaction and a fourth-stage solid-liquid separation to obtain water after first-stage defluorination and a second defluorinating agent. The second defluorinating agent and the second fluoride-containing wastewater are subjected to a two-stage defluorination reaction and a fifth solid-liquid separation to obtain water after two-stage defluorination and crude calcium fluoride product; the fluoride concentration of the first fluoride-containing wastewater is less than the fluoride concentration of the second fluoride-containing wastewater.

2. The method according to claim 1, wherein, Before acid leaching, the calcium fluoride slag is crushed and sieved sequentially to obtain calcium fluoride powder.

3. The method according to claim 2, wherein, The liquid-to-solid ratio of the acid solution used for pickling to calcium fluoride powder is (1-10):1mL / g.

4. The method according to claim 1, wherein, The acid solution used in the acid leaching contains H + The concentration is 1.5-3 mol / L.

5. The method according to claim 4, wherein, Aluminum chloride is also added to the acid solution.

6. The method according to claim 5, wherein, The concentration of aluminum ions in the acid solution is 1.5-3 mol / L.

7. The method according to claim 1, wherein, The spray roasting temperature is 200-400℃.

8. The method according to claim 1, wherein, The spray roasting process also yields hydrogen fluoride gas, which is absorbed by a sodium hydroxide solution to obtain sodium fluoride. The sodium fluoride is used to prepare a fluoride salt solution for reuse in the reaction or to adjust the fluoride concentration in the raw fluoride wastewater.

9. The method according to claim 1, wherein, After the second solid-liquid separation, aluminum slag is obtained. The aluminum slag is then leached with hydrochloric acid to obtain an aluminum chloride solution, which is reused in the acid leaching process.

10. The method according to claim 1, wherein, The concentrations of the calcium salt solution, sulfate solution, and fluoride solution are each independently 0.5-2.5 mol / L.

11. The method according to claim 1, wherein, The reaction temperature is 55-75℃.

12. The method according to claim 1, wherein, The reaction time is 0.5-1.5 hours.

13. The method according to claim 1, wherein, A calcium ion chelating agent is added during the reaction.

14. The method according to claim 13, wherein, The calcium ion chelating agent includes any one or a combination of at least two of EDTA, sodium pyrophosphate, sodium tripolyphosphate, potassium oxalate, sodium citrate, or sodium gluconate.

15. The method according to claim 14, wherein, The concentration of the calcium ion chelating agent is 0.01-10 mol / L.

16. The method according to claim 1, wherein, The first defluorinating agent contains 55-80 wt% calcium sulfate dihydrate by mass percentage.

17. The method according to claim 1, wherein, In the aforementioned defluorination reaction, the first defluorinating agent is added in excess relative to the first fluoride-containing wastewater.

18. The method according to claim 1, wherein, In the two-stage defluorination reaction, the second fluoride-containing wastewater is added in excess relative to the second defluorinating agent.

19. The method according to claim 1, wherein, The first fluoride-containing wastewater includes diluted raw fluoride-containing wastewater and / or water after two-stage defluorination.

20. The method according to claim 1, wherein, The second fluoride-containing wastewater includes raw fluoride-containing wastewater and / or raw fluoride-containing wastewater with adjusted fluoride concentration; the fluoride concentration adjusting agent includes sodium fluoride.

21. The method according to claim 1, wherein, The crude calcium fluoride product is successively washed and dried to obtain the final calcium fluoride product.

22. The method according to claim 1, wherein, The method includes the following steps: The calcium fluoride slag is crushed and sieved sequentially to obtain calcium fluoride powder. The calcium fluoride powder is then acid-leached with an acid solution, wherein the liquid-to-solid ratio of the acid solution to the calcium fluoride powder is (1-10):1 mL / g, and the acid solution contains H+. + The concentration of the acid solution is 1.5-3 mol / L, and the concentration of aluminum ions in the acid solution is 1.5-3 mol / L. Then, a first solid-liquid separation is performed to obtain the leachate. The leachate is spray-roasted at a temperature of 200-400℃ to obtain a solid product and hydrogen fluoride gas. The solid product is then subjected to dissolution and pulping followed by a second solid-liquid separation to obtain aluminum slag and a calcium salt solution. The aluminum slag is leached with hydrochloric acid to obtain an aluminum chloride solution that is reused in the acid leaching process. The hydrogen fluoride gas is absorbed by a sodium hydroxide solution to obtain sodium fluoride. The sodium fluoride is used to prepare a fluoride salt solution that is reused in the reaction or to adjust the fluoride concentration in the raw fluoride-containing wastewater. The calcium salt solution, sulfate solution, and fluoride solution are mixed, and a calcium ion chelating agent with a concentration of 0.01-10 mol / L is added. The mixture is reacted at a temperature of 55-75℃ for 0.5-1.5 h, followed by a third solid-liquid separation to obtain the first defluorinating agent. The concentrations of the calcium salt solution, sulfate solution, and fluoride solution are each independently 0.5-2.5 mol / L. The calcium ion chelating agent includes any one or a combination of at least two of EDTA, sodium pyrophosphate, sodium tripolyphosphate, potassium oxalate, sodium citrate, or sodium gluconate. The first defluorinating agent and the first fluoride-containing wastewater are subjected to a first-stage defluorination reaction and a fourth solid-liquid separation in sequence to obtain first-stage defluorinated water and a second defluorinating agent. The first defluorinating agent contains 55-80 wt% calcium sulfate dihydrate by mass percentage. In the first-stage defluorination reaction, the first defluorinating agent is added in excess relative to the first fluoride-containing wastewater. The first fluoride-containing wastewater includes diluted raw fluoride-containing wastewater and / or second-stage defluorinated water. The second defluorinating agent and the second fluoride-containing wastewater are subjected to a two-stage defluorination reaction and a fifth solid-liquid separation in sequence to obtain water and crude calcium fluoride product after two-stage defluorination. In the two-stage defluorination reaction, the second fluoride-containing wastewater is added in excess relative to the second defluorinating agent. The second fluoride-containing wastewater includes raw fluoride-containing wastewater and / or raw fluoride-containing wastewater with adjusted fluoride concentration. The fluoride concentration adjustment agent includes sodium fluoride. The crude calcium fluoride product is successively washed and dried to obtain the final calcium fluoride product.

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