Method for resource utilization of calcium fluoride residue and fluorine-containing wastewater

Abstract

A method for the resource utilization of calcium fluoride residue and fluorine-containing wastewater. The method comprises: subjecting a leaching solution obtained by acid leaching of calcium fluoride residue to spray roasting, and dissolving and slurrying the resulting solid product to obtain a calcium salt solution; using a calcium salt solution, a sulfate solution, and a fluorine salt solution to prepare a first fluorine removal agent; subjecting the first fluorine removal agent and first fluorine-containing wastewater to a first-stage fluorine removal reaction to obtain first-stage fluorine-removed water and a second fluorine removal agent; and subjecting the second fluorine removal agent and second fluorine-containing wastewater to a second-stage fluorine removal reaction to obtain second-stage fluorine-removed water and a crude calcium fluoride product, wherein the fluorine concentration of the first fluorine-containing wastewater is less than the fluorine concentration of the second fluorine-containing wastewater. This method can not only obtain calcium fluoride products with relatively high purity, but also make the fluoride-containing wastewater meet discharge standards, realizing resource utilization of calcium fluoride residue and fluoride-containing wastewater, reducing the disposal cost of solid waste residue. The method has extensive economic and social benefits.

Description

Method for resource utilization of calcium fluoride slag and fluorine-containing wastewater Technical Field

[0001] The present disclosure relates to the technical field of wastewater and waste residue treatment, and in particular to a method for resource utilization of calcium fluoride residue and fluorine-containing wastewater. Background Art

[0002] Calcium fluoride, a colorless crystal or white powder with the chemical formula CaF2, is insoluble in water but slightly soluble in inorganic acids. It reacts with hot concentrated sulfuric acid to form hydrofluoric acid, a widely used chemical in industries such as metallurgy, chemicals, building materials, light industry, optics, and defense. Currently, low-purity calcium fluoride slag is difficult to directly utilize and is typically disposed of through landfill or in the production of building materials such as red bricks and cement. This results in low throughput and high costs, as well as environmental pollution. The calcium fluoride content in low-purity calcium fluoride slag is generally around 50%. Utilizing this calcium fluoride as a resource would not only address fluorine pollution but also have broad economic and social benefits.

[0003] Currently, treatment methods for fluoride-containing wastewater mainly include adsorption, precipitation, membrane, electrochemical, 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 is the earliest method used to treat fluoride-containing solutions. It has the advantages of a simple process flow, convenient operation, low fixed investment, and low cost, and is therefore widely used. Currently, calcium salt precipitation is the main method used in industry to treat fluoride-containing solutions. This involves adding calcium salts such as lime and calcium chloride to the fluoride-containing solution to form an insoluble calcium fluoride precipitate that can be removed.

[0004] Therefore, how to treat calcium fluoride slag and fluoride-containing wastewater more economically and environmentally friendly is a problem that needs to be solved at present.

[0005] Summary of the Invention

[0006] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0007] In response to the above problems, the purpose of the present disclosure is to provide a method for resource utilization of calcium fluoride slag and fluorine-containing wastewater. Compared with the existing technology, the method provided by the present disclosure can not only obtain calcium fluoride products with higher purity, but also ensure that fluorine-containing wastewater meets discharge standards, thereby realizing resource utilization of calcium fluoride slag and fluorine-containing wastewater, reducing the disposal cost of solid waste residue, and having broad economic and social benefits.

[0008] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0009] The present disclosure provides a method for resource utilization of calcium fluoride slag and fluorine-containing wastewater, the method comprising the following steps:

[0010] sequentially performing acid leaching and first solid-liquid separation on the calcium fluoride slag to obtain a leachate;

[0011] The leachate is spray-roasted to obtain a solid product, and the solid product is sequentially subjected to dissolution and pulping and a second solid-liquid separation to obtain a calcium salt solution;

[0012] mixing the calcium salt solution, sulfate solution and fluoride salt solution, and sequentially performing a reaction and a third solid-liquid separation to obtain a first defluoridating agent;

[0013] The first defluoridation agent and the first fluorine-containing wastewater are sequentially subjected to a first defluoridation reaction and a fourth solid-liquid separation to obtain a first defluoridated water and a second defluoridation agent;

[0014] The second defluoridating agent and the second fluorine-containing wastewater are sequentially subjected to a two-stage defluoridation reaction and a fifth solid-liquid separation to obtain two-stage defluoridated water and a crude calcium fluoride product; the fluorine concentration of the first fluorine-containing wastewater is less than the fluorine concentration of the second fluorine-containing wastewater.

[0015] In the present disclosure, firstly, the calcium fluoride slag is subjected to acid leaching to fully leach fluoride ions; then the leachate is spray-roasted to obtain a solid product (mainly containing calcium salt) and hydrogen fluoride gas, thereby achieving preliminary separation of fluorine and calcium in the calcium fluoride slag; the solid product is dissolved and pulped and subjected to a second solid-liquid separation to further remove impurities to obtain a calcium salt solution; then, the calcium salt, sulfate and fluoride salt are reacted to prepare a first defluoridation agent (calcium sulfate dihydrate doped with calcium fluoride); finally, the first defluoridation agent is used to perform a first defluoridation reaction on a first fluorine-containing wastewater with a lower fluorine concentration to obtain a defluoridation agent. Using the first-stage defluoridated water that meets the discharge standards and the second defluoridating agent (containing calcium fluoride and unreacted calcium sulfate dihydrate), the second defluoridating agent and the second fluorine-containing wastewater with a higher fluorine concentration are used to carry out a two-stage defluoridation reaction to obtain the second-stage defluoridated water and a crude calcium fluoride product. The above two-stage defluoridation reaction against the concentration gradient can effectively promote the reaction, and can obtain both the first-stage defluoridated water that meets the discharge standards and the crude calcium fluoride product with a higher purity, thereby realizing the resource utilization of calcium fluoride slag and fluorine-containing wastewater, reducing the discharge of solid waste slag, and increasing product benefits.

[0016] In one embodiment, before acid leaching, the calcium fluoride slag is crushed and sieved in sequence to obtain calcium fluoride powder.

[0017] In one embodiment, the liquid-to-solid ratio of the acid solution to the calcium fluoride powder is (1-10):1 mL / g, for example, 1:1 mL / g, 2:1 mL / g, 3:1 mL / g, 4:1 mL / g, 5:1 mL / g, 6:1 mL / g, 7:1 mL / g, 8:1 mL / g, 9:1 mL / g or 10:1 mL / g, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0018] In the present disclosure, it is preferred to control the liquid-to-solid ratio of the acid solution to the calcium fluoride powder within a specific range, which can avoid the problem of too low a leaching rate of calcium fluoride due to too small a liquid-to-solid ratio, and at the same time avoid the problem of too large a liquid-to-solid ratio resulting in solution waste.

[0019] In one embodiment, the acid solution used in the acid leaching includes hydrochloric acid.

[0020] In one embodiment, the acid solution used in the acid leaching contains H + The concentration is 1.5-3moL / L, for example, it can be 1.5moL / L, 1.8moL / L, 2moL / L, 2.2moL / L, 2.4moL / L, 2.6moL / L, 2.8moL / L or 3moL / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] In the present disclosure, it is preferred to control the H + The concentration of hydrochloric acid is within a specific range, which can not only promote the full leaching of calcium fluoride, but also avoid problems such as increased costs, equipment corrosion and environmental pollution caused by excessive hydrochloric acid concentration.

[0022] In one embodiment, aluminum chloride is further added to the acid solution.

[0023] In the present disclosure, it is preferred to control the addition of aluminum chloride to the acid solution so as to fully utilize the aluminum ions and fluoride ions in the solution to generate AlF6 3- To dissolve calcium fluoride and increase the leaching rate of calcium fluoride.

[0024] In one embodiment, the concentration of aluminum ions in the acid solution is 1.5-3 moL / L, for example, 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, and other values ​​not listed within the numerical range are also applicable.

[0025] In the present disclosure, an increase in the concentration of aluminum ions promotes the reaction to continuously move in the positive direction, thereby increasing the leaching rate of calcium fluoride. The present disclosure preferably controls the concentration of aluminum ions in the acid solution within a specific range, thereby avoiding the situation in which the increase rate of calcium fluoride leaching rate is significantly slowed down and the cost is excessively high when the concentration of aluminum ions is too high.

[0026] In one embodiment, the temperature of the spray roasting is 200-400°C, for example, 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 numerical range are also applicable.

[0027] In the present disclosure, it is preferred to control the temperature of the spray roasting within a specific range to avoid excessively low temperatures that may cause AlF6 3- It cannot be fully decomposed and thus cannot be converted into hydrogen fluoride gas. At the same time, it can prevent the aluminum chloride in the solution from being unable to be converted into aluminum oxide solid due to the temperature being too low, which in turn causes the chloride ions to be unable to be fully transferred to the calcium chloride. It can also prevent the calcium chloride solid from reaching its melting point due to the temperature being too high, which causes energy waste.

[0028] In one embodiment, hydrogen fluoride gas is obtained after the spray roasting, and 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 and reused in the reaction or used to adjust the fluorine concentration of fluoride-containing wastewater.

[0029] In the present disclosure, fluorine and calcium in calcium fluoride slag are separated by spray roasting to obtain hydrogen fluoride gas with high purity. The hydrogen fluoride gas is preferably recovered using a sodium hydroxide solution to prepare a sodium fluoride product, which can improve the recovery rate of fluorine in the calcium fluoride slag. The obtained sodium fluoride can be added to the reaction as a fluoride salt and can also be used as a regulator for fluorine-containing wastewater raw water, providing a stable fluorine source for the subsequent output of calcium fluoride products and the defluorination of fluorine-containing wastewater raw water, providing a basis for ensuring the stable discharge of water after defluorination and the stable purity of calcium fluoride products meeting standards, and realizing the resource utilization of fluorine sources.

[0030] In one embodiment, aluminum slag is obtained after the second solid-liquid separation, and the aluminum slag is leached with hydrochloric acid to obtain aluminum chloride solution which is reused in the acid leaching.

[0031] In the present 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 leached with hydrochloric acid to prepare an aluminum chloride solution, which can realize the recycling of aluminum chloride, reduce the cost of aluminum chloride, and avoid environmental pollution.

[0032] In one embodiment, the calcium salt solution comprises a calcium chloride solution.

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

[0034] In one embodiment, the fluoride salt solution comprises a sodium fluoride solution.

[0035] In one embodiment, the concentrations of the calcium salt solution, sulfate solution, and fluoride salt 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, and other values ​​not listed within the numerical range are also applicable.

[0036] In the present disclosure, it is preferred to control the concentrations of the calcium salt solution, sulfate solution, and fluoride salt solution within a specific range, which can avoid the formation of calcium sulfate dihydrate due to too low a concentration, and can also avoid the cost increase due to too high a concentration.

[0037] 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, and other unlisted values ​​within the numerical range are also applicable.

[0038] In one embodiment, the reaction time is 0.5-1.5 h, for example, 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1 h, 1.2 h, 1.4 h or 1.5 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] In the present disclosure, it is preferred to control the reaction temperature and time within a specific range, so as to obtain calcium sulfate dihydrate doped with calcium fluoride of a specific crystal form and to control the particle size of the calcium sulfate dihydrate to be uniform.

[0040] In one embodiment, a calcium ion chelating agent is added during the reaction.

[0041] 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.

[0042] In one embodiment, the concentration of the calcium ion chelator is 0.01-10 mol / L, for example, 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, and other values ​​not listed within the numerical range are also applicable.

[0043] In the present disclosure, it is preferred to add a calcium ion chelating agent, 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 short rod-shaped, thereby making the calcium sulfate dihydrate evenly distributed, increasing the contact area with fluoride-containing wastewater, and facilitating improving the purity of the calcium fluoride product.

[0044] In one embodiment, the first defluoridating agent contains 55-80 wt% of 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, and other values ​​not listed within the numerical range are also applicable.

[0045] In the present disclosure, it is preferred to control the mass percentage of dihydrate sulfuric acid in the first defluorinating agent, which can further improve the defluorinating effect.

[0046] In one embodiment, in the first stage of the defluorination reaction, the first defluorination agent is added in excess relative to the first fluorine-containing wastewater.

[0047] In one embodiment, in the second-stage defluorination reaction, the second fluorine-containing wastewater is added in excess relative to the second defluorination agent.

[0048] In the present disclosure, a one-stage defluorination reaction and a two-stage defluorination reaction are used to carry out multi-stage defluorination against the concentration gradient. The excess of calcium sulfate dihydrate is controlled in the one-stage defluorination reaction, and the excess of fluorine element is controlled in the two-stage defluorination reaction. This can effectively promote the reaction, ensure that the water after defluorination meets the discharge standards, and obtain a high-purity calcium fluoride product.

[0049] In one embodiment, the first fluorine-containing wastewater includes diluted fluorine-containing wastewater raw water and / or water after secondary defluorination.

[0050] In one embodiment, the second fluorine-containing wastewater includes fluorine-containing wastewater raw water and / or fluorine-containing wastewater raw water after fluorine concentration adjustment; the regulator for adjusting the fluorine concentration includes sodium fluoride.

[0051] In one embodiment, the fluorine concentration of the first fluorine-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, and other unlisted values ​​within the numerical range are also applicable.

[0052] In one embodiment, the fluorine concentration of the second fluorine-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, and other unlisted values ​​within the numerical range are also applicable.

[0053] In one embodiment, the fluorine concentration of the fluorine-containing wastewater raw water 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, and other unlisted values ​​within the numerical range are also applicable.

[0054] In this disclosure, the fluorine-containing wastewater source is preferably high-salt fluorine-containing wastewater from the lithium battery recycling industry. Due to the influence of front-end processes, the fluorine concentration generally ranges from 1.4 to 3 g / L and fluctuates greatly, which is not conducive to the subsequent defluorination reaction. In this disclosure, sodium fluoride is preferably added to the fluorine-containing wastewater source to stabilize the fluorine concentration in the fluorine-containing wastewater source, thereby facilitating the subsequent defluorination reaction.

[0055] In one embodiment, the crude calcium fluoride product is sequentially washed and dried to obtain a calcium fluoride product.

[0056] In the present 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 may be, for example, filtration.

[0057] As an optional technical solution of the present disclosure, the method includes the following steps:

[0058] The calcium fluoride slag is crushed and sieved in sequence to obtain calcium fluoride powder, and the calcium fluoride powder is 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 H + The concentration of aluminum ions in 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, and then a first solid-liquid separation is performed to obtain a leachate;

[0059] The leachate is spray-roasted at a temperature of 200-400° C. to obtain a solid product and hydrogen fluoride gas. The solid product is sequentially subjected to dissolution and pulping and 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 which is reused in the acid leaching. 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 which is reused in the reaction or used to adjust the fluorine concentration of the fluorine-containing wastewater.

[0060] mixing the calcium salt solution, sulfate solution, and fluoride salt solution, adding a calcium ion chelating agent with a concentration of 0.01-10 mol / L, reacting at a temperature of 55-75° C. for 0.5-1.5 hours, and then performing a third solid-liquid separation to obtain a first defluoridating agent, wherein the concentrations of the calcium salt solution, sulfate solution, and fluoride salt solution are each independently 0.5-2.5 mol / L, and the calcium ion chelating agent comprises any one or a combination of at least two of EDTA, sodium pyrophosphate, sodium tripolyphosphate, potassium oxalate, sodium citrate, or sodium gluconate;

[0061] performing a first defluorination reaction and a fourth solid-liquid separation on the first defluoridating agent and the first fluorine-containing wastewater in sequence to obtain first-stage defluoridated water and a second defluoridating agent, wherein the first defluoridating agent contains 55-80 wt% of calcium sulfate dihydrate by weight, and the first defluoridating agent is added in excess relative to the first fluoride-containing wastewater in the first defluoridation reaction, and the first fluoride-containing wastewater includes diluted fluoride-containing wastewater raw water and / or second-stage defluoridated water;

[0062] sequentially subjecting the second defluorinating agent and the second fluorine-containing wastewater to a two-stage defluorination reaction and a fifth solid-liquid separation to obtain second-stage defluoridated water and a crude calcium fluoride product, wherein the second fluorine-containing wastewater is added in excess relative to the second defluorinating agent in the two-stage defluoridation reaction, the second fluorine-containing wastewater comprises raw fluorine-containing wastewater and / or raw fluorine-containing wastewater after fluorine concentration adjustment, and the fluorine concentration adjustment agent comprises sodium fluoride;

[0063] The crude calcium fluoride product is washed and dried in sequence to obtain a calcium fluoride product.

[0064] Compared with the prior art, the present disclosure has the following beneficial effects:

[0065] (1) In the present disclosure, the calcium fluoride slag is leached with acid solution and aluminum chloride solution, thereby improving the leaching effect of calcium fluoride and reducing the leaching cost. In addition, the introduced aluminum ions are finally converted into aluminum slag and the aluminum chloride solution obtained after leaching with hydrochloric acid can be recycled, thereby reducing the use cost of aluminum chloride and avoiding environmental pollution.

[0066] (2) In the present disclosure, a sodium fluoride product is prepared by separating the fluorine source from the calcium fluoride slag. The obtained sodium fluoride product can be used as a fluorine concentration regulator for fluorine-containing wastewater raw water and as a fluorine source basis for preparing calcium fluoride products, providing a stable fluorine source for subsequent fluorine-containing wastewater defluorination treatment and the output of calcium fluoride products, ensuring the stable discharge of subsequent defluorinated water and the stable purity of the calcium fluoride product.

[0067] (3) In the present disclosure, a single-stage defluorination reaction and a second-stage defluorination reaction are used to carry out multi-stage defluorination against the concentration gradient. In the first-stage defluorination reaction, the amount of calcium sulfate dihydrate is controlled excessively, and in the second-stage defluorination reaction, the amount of fluorine element is controlled excessively. This can effectively promote the reaction, so that the water after defluorination meets the discharge standards and a high-purity calcium fluoride product can be obtained.

[0068] (4) In the present disclosure, calcium sulfate dihydrate doped with calcium fluoride is used as the first defluoridation agent. The particle size of the calcium sulfate dihydrate is 2-22 μm, and the particles are small and uniform. The doped calcium fluoride can serve as a crystal seed and has the effect of inducing precipitation during the defluoridation process. The present disclosure controls the crystal morphology of calcium sulfate dihydrate by using a calcium ion chelating agent, making it short rod-shaped, which is conducive to the subsequent defluoridation reaction.

[0069] (5) The method provided by the present invention can obtain a calcium chloride-containing solid product with a purity of more than 74.56%, sodium fluoride with a purity of more than 72.34%, and a calcium fluoride product with a purity of more than 56.35%. The fluorine concentration in the water after the first stage of defluoridation by the method can reach below 132 mg / L, and the fluorine recovery rate can reach above 94.26%. Under better conditions, the present invention can obtain a calcium chloride-containing solid product with a purity of more than 97.67%, sodium fluoride with a purity of more than 95.36%, and a calcium fluoride product with a purity of more than 85.3%. The fluorine concentration in the water after the first stage of defluoridation by the method can reach below 49 mg / L and meet the emission standards, and the fluorine recovery rate can reach above 97.75%, thereby realizing the resource utilization of calcium fluoride slag and fluorine-containing wastewater, reducing the discharge of solid waste slag, and increasing product benefits.

[0070] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0072] FIG1 is a flow chart of the method described in Example 1 of the present disclosure;

[0073] FIG2 is a SEM image of the first defluorination agent of Example 1 of the present disclosure;

[0074] FIG3 is a SEM image of the calcium fluoride product described in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0075] The technical solution of the present disclosure is further described below through specific implementation methods. It should be understood by those skilled in the art that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0076] In the present disclosure, the acid leaching time, the concentration of the sodium hydroxide solution, the stirring speed, the stirring time, the standing time, the addition time of the second defluorinating agent, the amount of washing water, etc. are all conventional operations in this field. Conventional operating parameters in this field can be used without affecting the final treatment effect.

[0077] Example 1

[0078] This embodiment provides a method for resource utilization of calcium fluoride slag and fluoride-containing wastewater, as shown in FIG1 , the method comprising the following steps:

[0079] The calcium fluoride slag was crushed and sieved in sequence to obtain calcium fluoride powder. 100 g of the calcium fluoride powder was acid-leached for 2 h using 1 L 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 H + The concentration of ions is 1.5 moL / L, the concentration of aluminum ions is 1.5 moL / L, and then filtered to obtain a leachate;

[0080] The leachate is spray-roasted at a temperature of 300° C. to obtain a solid product at the bottom of the roasting furnace and hydrogen fluoride gas at the top of the roasting furnace. The solid product is sequentially dissolved, pulped, and filtered to obtain aluminum slag and a calcium chloride solution. The aluminum slag is leached with hydrochloric acid to obtain an aluminum chloride solution which is reused in the acid leaching for preparing an acid solution. The hydrogen fluoride gas is absorbed by a sodium hydroxide solution with a concentration of 10 g / L 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 fluorine concentration of the fluorine-containing wastewater.

[0081] The calcium chloride solution, sodium sulfate solution and sodium fluoride solution were mixed, and an EDTA solution with a concentration of 0.05 mol / L was added. The mixture was reacted at a temperature of 65° C. for 0.5 h, with a stirring speed of 150 r / min during the reaction. The mixture was then filtered to obtain a first defluoridating agent, the SEM image of which is shown in FIG2 . The concentrations of the calcium chloride solution, sodium sulfate solution and sodium fluoride solution were each independently 1.5 mol / L.

[0082] 14.87 g of the first defluoridant (containing 70 wt % of calcium sulfate dihydrate by mass percentage) and 1 L of the first fluorine-containing wastewater (diluted fluorine-containing wastewater raw water, with a fluorine concentration of 0.6 g / L) were subjected to a first defluoridation reaction and stirred for 1.5 hours at a speed of 150 r / min, and then allowed to stand for 1 hour and then filtered to obtain a first defluoridated water with a fluorine concentration of 47 mg / L and a second defluoridant, wherein the first defluoridated water met the discharge standard, and the first defluoridant was added in excess relative to the first fluoride-containing wastewater in the first defluoridation reaction;

[0083] The second defluoridating agent is added to 1L of the second fluorine-containing wastewater (the raw fluorine-containing wastewater is adjusted to a fluorine concentration of 2.3g / L by sodium fluoride), and the addition time is 1.5 hours. After the addition, the mixture is stirred for 4 hours to perform a second-stage defluoridation reaction at a rotation speed of 150r / min, and then filtered to obtain second-stage defluoridated water and a crude calcium fluoride product. The second-stage defluoridated water can be reused as the first fluoride-containing wastewater in the first-stage defluoridation reaction. In the second-stage defluoridation reaction, the second fluoride-containing wastewater is added in excess relative to the second defluoridating agent.

[0084] The crude calcium fluoride product was washed with 100 mL of pure water and then dried to obtain a calcium fluoride product, a SEM image of which is shown in FIG3 .

[0085] Example 2

[0086] This embodiment provides a method for resource utilization of calcium fluoride slag and fluorine-containing wastewater, the method comprising the following steps:

[0087] The calcium fluoride slag was crushed and sieved in sequence to obtain calcium fluoride powder. 150 g of the calcium fluoride powder was acid-leached for 2 h using 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 H + The concentration of ions is 2moL / L, the concentration of aluminum ions is 2moL / L, and then filtered to obtain a leachate;

[0088] The leachate is spray-roasted at a temperature of 200° C. to obtain a solid product at the bottom of the roasting furnace and hydrogen fluoride gas at the top of the roasting furnace. The solid product is sequentially dissolved, pulped, and filtered to obtain aluminum slag and a calcium chloride solution. The aluminum slag is leached with hydrochloric acid to obtain an aluminum chloride solution which is reused in the acid leaching for preparing an acid solution. The hydrogen fluoride gas is absorbed by a sodium hydroxide solution with a concentration of 10 g / L 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 fluorine concentration of the fluorine-containing wastewater.

[0089] mixing the calcium chloride solution, sodium sulfate solution, and sodium fluoride solution, adding a sodium gluconate solution having a concentration of 0.01 mol / L, reacting at a temperature of 55° C. for 1 hour with a stirring speed of 150 r / min during the reaction, and then filtering to obtain a first defluoridating agent, wherein the concentrations of the calcium chloride solution, sodium sulfate solution, and sodium fluoride solution are each independently 1 mol / L;

[0090] 11.32 g of the first defluoridant (containing 80 wt % of calcium sulfate dihydrate by mass percentage) and 1 L of the first fluorine-containing wastewater (diluted fluorine-containing wastewater raw water, with a fluorine concentration of 1 g / L) were subjected to a first defluoridation reaction and stirred for 1.5 hours at a speed of 150 r / min, and then allowed to stand for 1 hour and then filtered to obtain a first defluoridated water with a fluorine concentration of 45 mg / L and a second defluoridant, wherein the first defluoridated water met the discharge standard, and the first defluoridant was added in excess relative to the first fluoride-containing wastewater in the first defluoridation reaction;

[0091] The second defluoridating agent is added to 1L of the second fluorine-containing wastewater (the raw fluorine-containing wastewater is adjusted to a fluorine concentration of 2g / L by sodium fluoride), and the addition time is 1.5 hours. After the addition, the mixture is stirred for 4 hours to perform a second-stage defluoridation reaction at a rotation speed of 150r / min, and then filtered to obtain second-stage defluoridated water and a crude calcium fluoride product. The second-stage defluoridated water can be reused as the first fluoride-containing wastewater in the first-stage defluoridation reaction. In the second-stage defluoridation reaction, the second fluoride-containing wastewater is added in excess relative to the second defluoridating agent.

[0092] The crude calcium fluoride product was washed with 100 mL of pure water and then dried to obtain a calcium fluoride product.

[0093] Example 3

[0094] This embodiment provides a method for resource utilization of calcium fluoride slag and fluorine-containing wastewater, the method comprising the following steps:

[0095] The calcium fluoride slag was crushed and sieved in sequence to obtain calcium fluoride powder. 200 g of the calcium fluoride powder was acid-leached for 2 h using 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 H + The concentration of ions is 3moL / L, the concentration of aluminum ions is 3moL / L, and then filtered to obtain a leachate;

[0096] The leachate is spray-roasted at a temperature of 380° C. to obtain a solid product at the bottom of the roaster and hydrogen fluoride gas at the top of the roaster. The solid product is sequentially dissolved, pulped, and filtered to obtain aluminum slag and a calcium chloride solution. The aluminum slag is leached with hydrochloric acid to obtain an aluminum chloride solution which is reused in the acid leaching to prepare an acid solution. The hydrogen fluoride gas is absorbed by a sodium hydroxide solution with a concentration of 10 g / L 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 fluorine concentration of the fluorine-containing wastewater.

[0097] Mixing the calcium chloride solution, sodium sulfate solution, and sodium fluoride solution, adding 10 mol / L EDTA solution, reacting at 75° C. for 1.5 hours with a stirring speed of 150 r / min during the reaction, and then filtering to obtain a first defluoridating agent, wherein the concentrations of the calcium chloride solution, sodium sulfate solution, and sodium fluoride solution are each independently 2.5 mol / L;

[0098] 24.68 g of the first defluoridant (containing 55 wt % of calcium sulfate dihydrate by mass percentage) and 1 L of the first fluorine-containing wastewater (diluted fluorine-containing wastewater raw water, with a fluorine concentration of 1.5 g / L) were subjected to a first defluoridation reaction and stirred for 1.5 hours at a speed of 150 r / min, and then allowed to stand for 1 hour and then filtered to obtain a first defluoridated water with a fluorine concentration of 49 mg / L and a second defluoridant, wherein the first defluoridated water met the discharge standard, and the first defluoridant was added in excess relative to the first fluoride-containing wastewater in the first defluoridation reaction;

[0099] The second defluoridating agent is added to 1L of the second fluorine-containing wastewater (the raw fluorine-containing wastewater is adjusted to a fluorine concentration of 3g / L by sodium fluoride), and the addition time is 1.5 hours. After the addition, the mixture is stirred for 4 hours to perform a second-stage defluoridation reaction at a rotation speed of 150r / min, and then filtered to obtain second-stage defluoridated water and a crude calcium fluoride product. The second-stage defluoridated water can be reused as the first fluoride-containing wastewater in the first-stage defluoridation reaction. In the second-stage defluoridation reaction, the second fluoride-containing wastewater is added in excess relative to the second defluoridating agent.

[0100] The crude calcium fluoride product was washed with 100 mL of pure water and then dried to obtain a calcium fluoride product.

[0101] Example 4

[0102] This embodiment provides a method for resource utilization of calcium fluoride slag and fluorine-containing wastewater. The method is different from that of Example 1 only in that aluminum chloride is not added to the acid solution.

[0103] Example 5

[0104] This embodiment provides a method for resource utilization of calcium fluoride slag and fluoride-containing wastewater. The method is different from that of Example 1 only in that no EDTA solution is added during the reaction.

[0105] Example 6

[0106] This embodiment provides a method for resource utilization of calcium fluoride slag and fluorine-containing wastewater. The method is different from that of Example 1 only in that the temperature of the spray roasting is 150°C.

[0107] Example 7

[0108] This embodiment provides a method for resource utilization of calcium fluoride slag and fluorine-containing wastewater. The method is different from that of Example 1 only in that the temperature of the spray roasting is 450°C.

[0109] Comparative Example 1

[0110] This comparative example provides a method for resource utilization of calcium fluoride slag and fluoride-containing wastewater. The method is different from Example 1 only in that no sodium fluoride solution is added in the reaction.

[0111] Comparative Example 2

[0112] This comparative example provides a method for resource utilization of calcium fluoride slag and fluorine-containing wastewater. The method differs from Example 1 only in that no two-stage defluorination reaction is performed, and the second defluorination agent is a crude calcium fluoride product.

[0113] Comparative Example 3

[0114] This comparative example provides a method for resource utilization of calcium fluoride slag and fluorine-containing wastewater. The method differs from Example 1 only in that no defluorination reaction is performed. Instead, a first defluorinating agent is directly reacted with fluorine-containing wastewater raw water having a fluorine concentration of 2.3 g / L to perform a defluorination reaction, and then the defluorinated water and a crude calcium fluoride product are obtained by filtration.

[0115] The purity of the calcium chloride, the purity of the sodium fluoride and the purity of the calcium fluoride product in the solid products obtained in Examples 1-7 and Comparative Examples 1-3 were detected by X-ray fluorescence spectrometry (XRF). The results are shown in Table 1.

[0116] The fluoride concentrations of the water after the first stage of defluoridation in Examples 1-7 and Comparative Examples 1-2, and the fluoride concentration of the water after defluoridation in Comparative Example 3 were measured using a fluoride ion selective electrode method, and the results are shown in Table 1. The fluoride recovery rates of the fluoride-containing wastewater in Examples 1-7 and Comparative Examples 1-3 were calculated based on the fluoride concentrations measured using the fluoride ion selective electrode method, and the results are shown in Table 1, where:

[0117] In Examples 1-7 and Comparative Example 1: Recovery rate = (fluorine concentration of the second fluorine-containing wastewater - fluorine concentration of the water after the first stage of defluoridation) / fluorine concentration of the second fluorine-containing wastewater × 100%;

[0118] In Comparative Example 2: Recovery rate = (fluorine concentration of the first fluorine-containing wastewater - fluorine concentration of the water after the first stage of defluoridation) / fluorine concentration of the first fluorine-containing wastewater × 100%;

[0119] In Comparative Example 3: Recovery rate = (fluorine concentration of the raw water of the fluorine-containing wastewater - fluorine concentration of the water after defluorination) / fluorine concentration of the raw water of the fluorine-containing wastewater × 100%.

[0120] Table 1

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

[0122] (1) It can be seen from the data of Examples 1-7 that the method provided by the present disclosure can obtain a solid product containing calcium chloride with a purity of more than 74.56%, sodium fluoride with a purity of more than 72.34%, and calcium fluoride with a purity of more than 56.35%. After the method is used to treat the water, the fluorine concentration in the water after the first stage of defluoridation can reach below 132 mg / L, and the fluorine recovery rate can reach above 94.26%. Under better conditions, a solid product containing calcium chloride with a purity of more than 97.67%, sodium fluoride with a purity of more than 95.36%, and calcium fluoride with a purity of more than 85.3% can be obtained. After the method is used to treat the water after the first stage of defluoridation, the fluorine concentration in the water can reach below 49 mg / L and meet the emission standards, and the fluorine recovery rate can reach above 97.75%.

[0123] (2) From the comparison between Example 1 and Example 4, it can be seen 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 solid product containing calcium chloride, sodium fluoride and calcium fluoride products in Example 1 are all higher than those in Example 4, and the fluorine concentration of the water after the first stage of defluoridation in Example 1 is lower than that in Example 4, and the fluorine recovery rate is higher. This shows that the present disclosure preferably adds aluminum chloride to the acid solution, which can further improve the purity of the solid product containing calcium chloride, sodium fluoride and calcium fluoride products, reduce the fluorine concentration of the water after the first stage of defluoridation, make it meet the emission standards, and improve the fluorine recovery rate.

[0124] (3) From the comparison between Example 1 and Example 5, it can be seen 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 solid product containing calcium chloride and the calcium fluoride product in Example 1 are higher than that in Example 5, and the fluorine concentration of the water after the first stage of defluoridation in Example 1 is lower than that in Example 5, and the fluorine recovery rate is higher. This shows that the present disclosure preferably adds EDTA solution in the reaction, which can further improve the purity of the solid product containing calcium chloride and the calcium fluoride product, reduce the fluorine concentration of the water after the first stage of defluoridation, that is, improve the water quality of the effluent, and increase the fluorine recovery rate.

[0125] (4) From the comparison between Example 1 and Examples 6-7, it can be seen that the only difference between Example 6-7 and Example 1 is that the temperature of the spray roasting is not within the preferred range of the present disclosure. The results show that the purity of the calcium chloride-containing solid product, sodium fluoride and calcium fluoride product in Example 1 is higher than that in Example 6-7, and the fluorine concentration of the water after the first stage of defluoridation in Example 1 is lower than that in Examples 6-7, and the fluorine recovery rate is higher. This shows that the present disclosure preferably controls the temperature of the spray roasting, which can further improve the purity of the calcium chloride-containing solid product, sodium fluoride and calcium fluoride products, reduce the fluorine concentration of the water after the first stage of defluoridation, that is, improve the water quality of the effluent, and increase the fluorine recovery rate.

[0126] (5) From the comparison between Example 1 and Comparative Example 1, it can be seen that the only difference between Comparative Example 1 and Example 1 is that no sodium fluoride solution is added during the reaction. The purity of the solid product containing calcium chloride and the calcium fluoride product in Example 1 is higher, the fluorine concentration of the water after the first stage of defluoridation is lower, and the fluorine recovery rate is higher. Therefore, it can be seen that in the present disclosure, calcium fluoride-doped calcium sulfate dihydrate can be formed by adding sodium fluoride solution during the reaction. The doped calcium fluoride can serve as a crystal seed and has the effect of inducing precipitation during the defluoridation process, which can further improve the purity of the solid product containing calcium chloride and the calcium fluoride product and improve the fluorine recovery rate.

[0127] (6) From the comparison between Example 1 and Comparative Examples 2-3, it can be seen that the second-stage defluorination reaction and the first-stage defluorination reaction are not performed in Comparative Examples 2-3 respectively. Compared with Comparative Example 2, the purity of the calcium chloride-containing solid product and the calcium fluoride product in Example 1 is higher. Compared with Comparative Example 3, the purity of the calcium fluoride product in Example 1 is higher. Compared with Comparative Examples 2-3, the fluorine recovery rate in Example 1 is higher and the fluorine content of the effluent water quality is lower. It can be seen that the present disclosure can effectively promote the reaction by combining the first-stage defluorination reaction and the second-stage defluorination reaction to perform two-stage defluorination against the concentration gradient, so that the water after defluorination meets the discharge standards and a high-purity calcium fluoride product can be obtained.

[0128] In summary, the method provided by the present disclosure can not only obtain a calcium fluoride product with high purity, but also ensure that fluorine-containing wastewater is discharged in compliance with discharge standards, thereby realizing the resource utilization of calcium fluoride slag and fluorine-containing wastewater, reducing the disposal cost of solid waste slag, and having broad economic and social benefits.

Claims

1. A method for the resource utilization of calcium fluoride slag and fluorine-containing wastewater, comprising the following steps: The calcium fluoride slag is subjected to acid leaching and first solid-liquid separation in sequence to obtain a leaching solution; The leaching solution is subjected to spray roasting to obtain a solid product. The solid product is subjected to dissolution pulping and second solid-liquid separation in sequence to obtain a calcium salt solution; The calcium salt solution, sulfate solution and fluoride salt solution are mixed and subjected to reaction and third solid-liquid separation in sequence to obtain a first defluorinating agent; The first defluorinating agent and the first fluoride-containing wastewater are subjected to first-stage defluorination reaction and fourth solid-liquid separation in sequence to obtain first-stage defluorinated water and a second defluorinating agent; The second defluorinating agent and the second fluoride-containing wastewater are subjected to second-stage defluorination reaction and fifth solid-liquid separation in sequence to obtain second-stage defluorinated water and a crude calcium fluoride product; the fluoride concentration of the first fluoride-containing wastewater < the fluoride concentration of the second fluoride-containing wastewater.

2. The method according to claim 1, wherein, Before the acid leaching, the calcium fluoride slag is subjected to crushing and screening in sequence to obtain calcium fluoride powder.

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

4. The method according to any one of claims 1-3, wherein, The concentration of H + in the acid solution used for acid leaching is 1.5 - 3 moL / L.

5. The method according to any one of claims 1-4, 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 any one of claims 1-6, wherein, The temperature of the spray roasting is 200-400 °C.

8. The method according to any one of claims 1-7, wherein, Hydrogen fluoride gas is also 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 recycling in the reaction or for adjusting the fluoride concentration of the raw water of the fluoride-containing wastewater.

9. The method according to any one of claims 1-8, wherein, Aluminum slag is obtained after the second solid-liquid separation. The aluminum slag is leached with hydrochloric acid to obtain an aluminum chloride solution for recycling in the acid leaching.

10. The method according to any one of claims 1-9, wherein, The concentrations of the calcium salt solution, sulfate solution and fluoride salt solution are each independently 0.5-2.5 mol / L.

11. The method according to any one of claims 1-10, wherein, The temperature of the reaction is 55-75 °C; Optionally, the reaction time is 0.5-1.5 h; Optionally, a calcium ion chelating agent is added during the reaction.

12. The method according to claim 11, 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; Optionally, the concentration of the calcium ion chelating agent is 0.01-10 mol / L.

13. The method according to any one of claims 1-12, wherein, In the first defluorinating agent, by mass percentage, it contains 55-80 wt% of calcium sulfate dihydrate.

14. The method according to any one of claims 1-13, wherein, In the first-stage defluorination reaction, the first defluorinating agent is overdosed relative to the first fluoride-containing wastewater; Optionally, in the second-stage defluorination reaction, the second fluoride-containing wastewater is overdosed relative to the second defluorinating agent; Optionally, the first fluoride-containing wastewater includes diluted raw water of the fluoride-containing wastewater and / or second-stage defluorinated water; Optionally, the second fluoride-containing wastewater includes raw water of the fluoride-containing wastewater and / or raw water of the fluoride-containing wastewater after fluoride concentration adjustment; the regulator for fluoride concentration adjustment includes sodium fluoride.

15. The method according to any one of claims 1-14, wherein, The crude calcium fluoride product is washed and dried in sequence to obtain a calcium fluoride product.

16. According to the method described in any one of claims 1-15, wherein, The method includes the following steps: The calcium fluoride slag is successively crushed and screened to obtain calcium fluoride powder. The calcium fluoride powder is acid-leached with an acid solution. The liquid-solid ratio of the acid solution to the calcium fluoride powder is (1-10):1 mL / g. The concentration of H + in 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, the first solid-liquid separation is carried out to obtain a leaching solution; The leaching solution is subjected to spray roasting at a temperature of 200 - 400 °C to obtain a solid product and hydrogen fluoride gas. The solid product is successively subjected to dissolution pulping and 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 for reuse in the acid leaching; the hydrogen fluoride gas is absorbed by a sodium hydroxide solution to obtain sodium fluoride, and 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 water of the fluoride-containing wastewater; The calcium salt solution, the sulfate solution, and the fluoride salt solution are mixed, and a calcium ion chelating agent with a concentration of 0.01 - 10 mol / L is added. The reaction is carried out at a temperature of 55 - 75 °C for 0.5 - 1.5 h, and then a third solid-liquid separation is carried out to obtain a first defluorinating agent. The concentrations of the calcium salt solution, the sulfate solution, and the fluoride salt 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 successively subjected to a first-stage defluorination reaction and a fourth solid-liquid separation to obtain water after the first-stage defluorination and a second defluorinating agent. The first defluorinating agent contains 55 - 80 wt% of calcium sulfate dihydrate by mass percentage. In the first-stage defluorination reaction, the first defluorinating agent is overdosed relative to the first fluoride-containing wastewater. The first fluoride-containing wastewater includes the diluted raw water of the fluoride-containing wastewater and / or the water after the second-stage defluorination; The second defluorinating agent and the second fluoride-containing wastewater are successively subjected to a second-stage defluorination reaction and a fifth solid-liquid separation to obtain water after the second-stage defluorination and a crude calcium fluoride product. In the second-stage defluorination reaction, the second fluoride-containing wastewater is Overdosed relative to the second defluorinating agent. The second fluoride-containing wastewater includes the raw water of the fluoride-containing wastewater and / or the raw water of the fluoride-containing wastewater with adjusted fluoride concentration. The regulator for the fluoride concentration adjustment includes sodium fluoride; The crude calcium fluoride product is successively washed and dried to obtain a calcium fluoride product.

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