Synergistic fluorine removal method for fluorine-containing silicon slag

Abstract

The invention belongs to the technical field of industrial solid waste treatment, and particularly discloses a synergistic fluorine removal method for fluorine-containing silicon slag. The fluorine removal method for the fluorine-containing silicon slag comprises the following steps: adding water into the fluorine-containing silicon slag, and stirring to obtain fluorine-containing silicon slag slurry; adding calcium hydroxide into the fluorine-containing silicon slag slurry, stirring, adding a La-Z adsorbent, and stirring; and standing for reaction, and carrying out solid-liquid separation to obtain supernate and precipitate. According to the method, fluorine in the fluorine-silicon slag solid waste is efficiently removed, the fluorine is stabilized in the precipitator and the adsorbent, free fluorine ions are prevented from being dissolved out, environmental hazards are reduced, and the method is particularly suitable for recycling and innocent treatment of fluorine-containing silicon slag generated by recycling fluorine through silicon dioxide in the phosphorus chemical industry; the contradiction between efficient fluorine removal and limitation of fluorine precipitation caused by silicon dissolution in fluorine-containing silicon slag treatment is solved.

Description

Technical Field

[0001] This invention relates to the field of industrial solid waste treatment technology, and in particular to a method for synergistic defluorination of fluorinated silicon slag. Background Technology

[0002] The wet process for producing phosphoric acid involves decomposing phosphate rock powder (mainly fluorapatite Ca5(PO4)3F) with sulfuric acid to obtain phosphoric acid and phosphogypsum as a byproduct. The core chemical reaction is: Ca5(PO4)3F + 5H2SO4 + 10H2O → 3H3PO4 + 5CaSO4·2H2O + HF. The chemical reaction produces HF (hydrogen fluoride) as a byproduct. In the reaction tank or subsequent waste gas scrubbing system, HF reacts with SiO2 to generate fluorosilicic acid (H2SiF6). Fluorosilicone slag (fluorosilicone slag) is mainly generated from the production of downstream fluoride salts (especially sodium fluorosilicate) using fluorosilicic acid. During the production process, in the reaction that generates sodium fluorosilicate (or aluminum fluoride, cryolite), silicon in the fluorosilicic acid precipitates out as hydrated silicon dioxide (SiO2·nH2O). Fluorosilica slag is mainly composed of amorphous silicon dioxide, but it contains soluble fluorine (0.5%~3% or higher), phosphorus, trace heavy metals, etc., and is classified as hazardous waste (because the concentration of leached toxic fluorine may exceed the standard).

[0003] Fluorosilica slag has a complex composition, typically containing a large amount of silica (SiO2) in addition to fluorides. Currently, related technologies for treating this special material generally face the following challenges: 1. The contradiction between pH sensitivity and silica leaching: When using strongly alkaline precipitants (such as calcium hydroxide) for fluoride removal, the system pH rises sharply, causing a large amount of silica in the silica slag to dissolve, generating silicate ions. This not only interferes with the precipitation purity and settling performance of calcium fluoride (CaF2), but may also form difficult-to-handle silica gel, clogging pipelines and causing significant difficulties in subsequent wastewater treatment. 2. The bottleneck of single-method effectiveness: If only adsorption methods (such as La-Z adsorbents) are used to treat silica slag solutions with high fluoride loads, a large amount of adsorbent needs to be added to meet emission standards, leading to a sharp increase in costs. Furthermore, adsorbent regeneration is difficult and easily generates secondary solid waste. 3. Process integration and cost issues: Existing combined processes such as "sedimentation followed by neutralization" or "multi-stage adsorption" have long flow rates, high reagent consumption, and high operating costs. Furthermore, they are difficult to stably control the pH of the effluent, failing to meet the dual requirements of economic efficiency and stability in the treatment of fluorosilica slag. 4. After leaching from fluorosilica slag, fluorine is mainly released as fluorosilicate (SiF6). 2- It exists in the form of complexed ions (rather than as a single F). - ), SiF6 2- Its chemical stability is much higher than that of free F. - Conventional precipitants have weak binding ability to it, and SiF6 2-Larger molecular size makes it difficult for them to enter the micropores / active sites of the adsorbent, resulting in a much lower removal efficiency of adsorption methods compared to free F. 5. Fluorine-silicon synergistic interference effect: The high proportion of SiO2 in fluorosilicone slag will dissolve with pH fluctuations during the treatment process. The dissolved silicate ions will further complex with fluorine to form more stable fluorine-containing silicon complexes, which not only reduces the treatability of fluorine, but also generates silica gel, exacerbating system blockage and making solid-liquid separation difficult.

[0004] Therefore, there is an urgent need to develop new treatment technologies for fluorosilicone slag solid waste, and to provide economical, efficient and simple solutions for the treatment of fluorosilicone slag, thereby solving the technical problems existing in traditional technologies. Summary of the Invention

[0005] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention provides a method for the synergistic removal of fluorine from fluorinated silicon slag. This invention is particularly applicable to the resource recovery and harmless treatment of fluorinated silicon slag generated from fluorine recovery using silica in the phosphate chemical industry, resolving the contradiction between "efficient fluorine removal" and "limited fluorine precipitation due to silicon leaching" in the treatment of fluorinated silicon slag, and providing an economical, efficient, and streamlined integrated solution.

[0006] This invention provides a method for removing fluoride from fluorine-containing silicon slag, characterized by comprising the following steps:

[0007] S1. Add water to the fluorinated silicon slag and stir to obtain a fluorinated silicon slag slurry;

[0008] S2. Add calcium hydroxide to the fluorine-containing silicon slag slurry, stir for 0-10 min, then add La-Z adsorbent and stir for 5-20 min.

[0009] S3. Allow the reaction to stand for 10-25 hours, then separate the solid and liquid to obtain the supernatant and precipitate.

[0010] According to a specific embodiment of the present invention, in the process of defluorination of fluoride-containing silicon slag system, it is difficult to control the pH by relying solely on calcium oxide, and the economic cost and poor defluorination effect of relying solely on La-Z adsorbents are high. The present invention innovatively couples the precipitation effect of calcium hydroxide with the adsorption-buffering effect of La-Z adsorbents, and takes "controlling the pH at the reaction endpoint" as the core linking index and optimization goal to achieve efficient synergy between the two.

[0011] According to some embodiments of the present invention, in step S2, calcium hydroxide is added to the fluorine-containing silicon slag slurry and stirred for 0-5 minutes.

[0012] According to some embodiments of the present invention, the mass fraction of SiO2 in the fluorinated silicon slag is 80%~90%.

[0013] According to some embodiments of the present invention, in step S1, the concentration of fluorine in the fluorine-containing silicon slag slurry is 300~500 mg / L, the pH is 2~3.5, and the mass fraction of SiO2 is 20%~40%.

[0014] According to some embodiments of the present invention, in step S2, the calcium hydroxide is calcium hydroxide powder with a particle size ≤100μm.

[0015] According to some embodiments of the present invention, in step S2, the La-Z adsorbent is prepared by combining modified zeolite and lanthanum chloride.

[0016] According to some embodiments of the present invention, in step S2, the ratio of fluorine in the calcium hydroxide and fluorine-containing silica slurry is (2.5~3.2):1, measured by molar ratio.

[0017] In this invention, calcium hydroxide is used as the main precipitant, and its dosage is calculated based on the fluorine concentration in the fluorinated silica slurry to ensure sufficient Ca is provided. 2+ It is used to precipitate most fluoride ions.

[0018] According to some embodiments of the present invention, in step S2, the mass ratio of the La-Z adsorbent to calcium hydroxide is (0.75~3.5):1.

[0019] This invention uses La-Z adsorbent as a synergistic adsorption-buffer. Its dosage is not determined independently, but is coupled with the dosage of calcium hydroxide, and the key determination criterion is "to make the pH of the system at the reaction endpoint fall in the range of 6.0 to 8.5".

[0020] According to some preferred embodiments of the present invention, the mass ratio of La-Z adsorbent to calcium hydroxide is (1.25~3):1; more preferably, the mass ratio of La-Z adsorbent to calcium hydroxide is (2~3):1.

[0021] According to some embodiments of the present invention, in step S3, after the reaction is allowed to stand, the pH of the system is 6.0~8.5;

[0022] According to some preferred embodiments of the present invention, the pH of the system is 6.0~7.5 after the static reaction is completed.

[0023] In this invention, the synergistic effect of calcium hydroxide and La-Z adsorbent, and their connection mechanism with the system pH, are as follows: First stage: Precipitation and defluorination dominated by calcium hydroxide and initial pH increase, Ca(OH)2 dissolution and release of Ca... 2+ and OH - Ca 2+ With F - CaF2 precipitate is generated, achieving rapid removal of fluoride; simultaneously, OH... -The first stage raises the system pH; the second stage utilizes the synergistic "adsorption-buffering" dual function of the La-Z adsorbent, which highly overlaps with the first stage in time and space, and is the core of achieving pH transition; the adsorption function of the La-Z adsorbent: the La active sites on its surface strongly adsorb residual fluoride ions, achieving deep purification; the buffering function: the La in La-Z... 3+ Its hydrolysis products (such as La(OH)3) have acid-base buffering capacity and can effectively consume excess OH- introduced by calcium hydroxide in the system. - To prevent excessive pH increases, the reaction endpoint pH of this invention is within the range of 6.0 to 8.5, achieving triple optimization: 1. Optimal defluorination efficiency: This pH range is conducive to complete CaF2 precipitation and is within the optimal pH window for fluorine adsorption at the La active sites; 2. Inhibition of silicon leaching: This pH range is far below the critical pH for large-scale silicon dioxide leaching (usually >9.5), fundamentally avoiding secondary problems caused by large-scale silicon leaching from silicon slag due to defluorination; Minimizing adsorbent dosage: Excess alkali is precisely "neutralized" through the buffering effect of La-Z, ensuring that the dosage is just sufficient to adjust the pH from the high point after precipitation reaction (possibly >10) to the target range, avoiding blindly increasing the adsorbent dosage in pursuit of deep defluorination, thus achieving economic optimization.

[0024] According to some embodiments of the present invention, in step S3, the concentration of fluoride in the supernatant is <6 mg / L.

[0025] According to some preferred embodiments of the present invention, the concentration of fluoride in the supernatant is <3 mg / L.

[0026] According to some embodiments of the present invention, in step S3, the precipitate comprises silica slag, calcium fluoride precipitate, and adsorbed F. - La-Z adsorbent.

[0027] The present invention ultimately yields a supernatant with a low fluoride ion concentration and a precipitate of fixed fluoride, wherein calcium fluoride is a crystalline precipitate, and calcium hydroxide dissolves and releases Ca2+. 2+ F dissociated from fluorosilicate in fluorosilicone slurry - A chemical reaction occurs to form calcium fluoride precipitate; after precipitation with calcium hydroxide, the residual F - (And incompletely dissociated fluorosilicate ions) will be strongly adsorbed by the La active sites on the surface of the La-Z adsorbent. This part of the fluorine will enter the precipitation during solid-liquid separation with the La-Z adsorbent, achieving deep purification and fixation of fluorine. Moreover, the adsorbed fluorine is highly stable and will not easily dissolve and cause secondary pollution.

[0028] According to some embodiments of the present invention, steps S1 to S3 are performed at room temperature (20 to 30°C).

[0029] The beneficial effects of this invention are:

[0030] 1) This invention can target fluoride removal, with a stronger ability to remove fluoride from fluorosilicate complex ions in fluorosilicone slag, achieving highly efficient fluoride removal (removal rate ≥99%). Simultaneously, through precise pH range control, it effectively inhibits silica leaching, avoiding secondary pollution. 2) The method of this invention can achieve pH self-balancing, with the treated system's pH automatically stabilizing in the optimal range of 6.0~8.5. This range ensures both efficient fluoride removal and maximum inhibition of silica leaching, eliminating the need for additional acid-base neutralization units. It achieves a three-in-one system of "fluoride removal-silicon inhibition-pH stabilization" without additional steps. 3) This invention also has economic and efficiency advantages. Through "waste-to-waste" treatment and collaborative design, it significantly reduces the dosage of expensive adsorbents (La-Z) (by more than 50%), optimizes overall operating costs, and eliminates the need for a separate neutralization unit. This shortens the process, reduces control points, and facilitates automated control and large-scale application. 4) The process of the present invention has strong adaptability, and the method can be directly applied to the treatment of fluorine-containing silicon slag slurry, and is easy to integrate with existing slag treatment facilities.

[0031] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Detailed Implementation

[0032] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0033] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0034] Example 1

[0035] This embodiment provides a method for defluorination treatment of fluorine-containing silicon slag, and the specific steps are as follows:

[0036] 1) Add water to the fluorinated silicon slag and stir to prepare a fluorinated silicon slag slurry;

[0037] The mass fraction of SiO2 in the fluorinated silica slag is 86%, and the initial concentration of fluoride ions in the fluorinated silica slag slurry is 358.6 mg / L (including SiF6). 2- F and free F in -The initial pH was 2.73, the mass fraction of SiO2 was 25%, and the initial leaching potential of SiO2 was ≥80mg / L.

[0038] 2) Place 10 mL of the slurry into a centrifuge tube, weigh 0.04 g of calcium hydroxide powder and add it to the tube, then stir magnetically for 5 min. At this time, Ca(OH)2 dissolves and releases Ca. 2+ With OH - Ca 2+ Preliminary reaction with SiF6 in liquid 2- F dissociated - The reaction produces CaF2 precipitate, and the pH of the system initially rises to 8.5-9.0;

[0039] The calcium hydroxide used was analytical grade, with a particle size ≤100μm, which ensured the Ca... 2+ Efficiently releases fluorine from precipitated fluorosilicone slag liquid;

[0040] 3) Immediately add 0.1g of weighed La-Z adsorbent to the system and continue stirring for 10 minutes: At this point, the La-Z surface... 3+ Its hydrolysis product (La(OH)3) rapidly consumes excess OH. - This allows for precise pH control; subsequently, the mixture is placed in a 25°C environment and allowed to stand for 20 hours to ensure the SiF6... 2- Complete dissociation and adsorption;

[0041] Among them, the La-Z adsorbent is lanthanum-supported modified zeolite, which is prepared by combining modified zeolite and lanthanum chloride at a mass ratio of 5:1 according to existing conventional methods, with a particle size of 50~80μm. In this embodiment, the La-Z adsorbent is used to meet the "fluorine removal-silicon inhibition" requirements of fluorosilicone slag liquid by utilizing its dual functions of fluorine adsorption and pH buffering.

[0042] 4) After the reaction is complete, take the supernatant and measure the fluoride ion concentration and pH value.

[0043] The results showed that the fluoride ion concentration in the supernatant after treatment was 2.12 mg / L, and the fluoride ion removal rate was 99.4%. The pH of the system was 6.19, with no adsorbent aggregation. Solid-liquid separation was convenient and met the engineering treatment requirements.

[0044] In this embodiment, Ca(OH)2 and La-Z work synergistically, Ca 2+ Fully precipitate F - La-Z efficiently adsorbs residual F - It buffers pH, has high fluoride removal efficiency, keeps pH stable within a suitable range, and does not exhibit adsorbent aggregation; subsequent solid-liquid separation is convenient (takes approximately 15 minutes).

[0045] Example 2

[0046] This embodiment provides a method for defluorination treatment of fluorinated silicon slag.

[0047] This embodiment is basically the same as Embodiment 1, except that 0.05g of La-Z adsorbent is added in step 3) of this embodiment, which is consistent with the steps in Embodiment 1.

[0048] The results showed that the fluoride ion concentration in the supernatant after treatment was 2.45 mg / L, and the fluoride ion removal rate was 99.3%. The pH of the system was 7.73, which means it can be discharged directly without neutralization. The process has good stability and there is no risk of silica gel formation or pipeline blockage.

[0049] This embodiment ensures both fluoride removal efficiency and silicon inhibition effect while further reducing reagent costs, making it suitable for fluorosilicone slag treatment scenarios where treatment costs are sensitive.

[0050] Example 3

[0051] This embodiment provides a method for defluorination treatment of fluorinated silicon slag.

[0052] This embodiment is basically the same as Embodiment 1, except that 0.03g of La-Z adsorbent is added in step 3) of this embodiment, which is consistent with the steps in Embodiment 1.

[0053] Results: The concentration of fluoride ions in the supernatant after treatment was 5.59 mg / L, and the fluoride ion removal rate was calculated to be 98.44%; the pH of the system was 8.45.

[0054] Comparative Example 1

[0055] This comparative example provides a method for defluorination treatment of fluorinated silicon slag.

[0056] This comparative example is basically the same as Example 1, except that 0.02g of calcium hydroxide powder is added in step 2) of this comparative example, and La-Z adsorbent is not added in step 3). The steps are consistent with those of Example 1.

[0057] The results showed that the fluoride ion concentration in the supernatant after treatment was 192.5 mg / L, and the fluoride ion removal rate was only 46.3%; the pH of the system was 3.31, which did not reach the critical pH for SiO2 dissolution, and no silica gel was generated.

[0058] Comparative Example 2

[0059] This comparative example provides a method for defluorination treatment of fluorinated silicon slag.

[0060] This comparative example is basically the same as Example 1, except that 0.04g of calcium hydroxide powder is added in step 2) of this comparative example, and La-Z adsorbent is not added in step 3). The steps are consistent with those of Example 1.

[0061] The results showed that the fluoride ion concentration in the supernatant after treatment was 6.28 mg / L, and the fluoride ion removal rate was 98.2%. The pH of the system was 10.57, which is far above the critical value for the large-scale dissolution of SiO2 (pH 9.5).

[0062] Comparative Example 3

[0063] This comparative example provides a method for defluorination treatment of fluorinated silicon slag.

[0064] This comparative example is basically the same as Example 1, except that 0.06g of calcium hydroxide powder is added in step 2) of this comparative example, and La-Z adsorbent is not added in step 3). The steps are consistent with those of Example 1.

[0065] The results showed that the fluoride ion concentration in the supernatant after treatment was 8.81 mg / L, and the fluoride ion removal rate was 97.5%. The pH of the system was 11.47, which is far above the critical value for the large-scale dissolution of SiO2 (pH 9.5).

[0066] Comparative Example 4

[0067] This comparative example provides a method for defluorination treatment of fluorinated silicon slag.

[0068] This comparative example is basically the same as Example 1, except that calcium hydroxide was not added in step 2) of this comparative example, and 0.05g of La-Z adsorbent was added in step 3), which is consistent with the steps in Example 1.

[0069] The results showed that the fluoride ion concentration in the supernatant after treatment was 215.55 mg / L, and the fluoride ion removal rate was only 39.9%; the pH of the system was 3.29, and there was no risk of silicon leaching.

[0070] Comparative Example 5

[0071] This comparative example provides a method for defluorination treatment of fluorinated silicon slag.

[0072] This comparative example is basically the same as Example 1, except that calcium hydroxide was not added in step 2) of this comparative example, and 0.1g of La-Z adsorbent was added in step 3), which is consistent with the steps in Example 1.

[0073] The results showed that the fluoride ion concentration in the supernatant after treatment was 63.89 mg / L, and the fluoride ion removal rate was only 82.2%; the pH of the system was 3.6, and there was no risk of silicon leaching.

[0074] Comparative Example 6

[0075] This comparative example provides a method for defluorination treatment of fluorinated silicon slag.

[0076] This comparative example is basically the same as Example 1, except that calcium hydroxide was not added in step 2) of this comparative example, and 0.2g of La-Z adsorbent was added in step 3), which is consistent with the steps in Example 1.

[0077] Results: The concentration of fluoride ions in the supernatant after treatment was 18.78 mg / L, and the fluoride ion removal rate was calculated to be 94.8%; the pH of the system was 3.96, indicating no risk of silica leaching.

[0078] Comparative Example 7

[0079] This comparative example provides a method for defluorination treatment of fluorinated silicon slag.

[0080] This comparative example is basically the same as Example 1, except that calcium hydroxide was not added in step 2) of this comparative example, and 0.3g of La-Z adsorbent was added in step 3), which is consistent with the steps in Example 1.

[0081] Results: The concentration of fluoride ions in the supernatant after treatment was 5.61 mg / L, and the fluoride ion removal rate was calculated to be 98.4%; the pH of the system was 5.84, indicating no risk of silicon leaching.

[0082] Comparative Example 8

[0083] This comparative example provides a method for defluorination treatment of fluorinated silicon slag.

[0084] This comparative example is basically the same as Example 1, except that 0.02g of calcium hydroxide powder is added in step 2) and 0.05g of La-Z adsorbent is added in step 3), which is consistent with the steps in Example 1.

[0085] Results: The concentration of fluoride ions in the supernatant after treatment was 23.25 mg / L, and the fluoride ion removal rate was calculated to be 93.5%; the pH of the system was 3.82, and there was no risk of silicon leaching.

[0086] Comparative Example 9

[0087] This comparative example provides a method for defluorination treatment of fluorinated silicon slag.

[0088] This comparative example is basically the same as Example 1, except that 0.02g of calcium hydroxide powder is added in step 2) and 0.1g of La-Z adsorbent is added in step 3), which is consistent with the steps in Example 1.

[0089] Results: The concentration of fluoride ions in the supernatant after treatment was 10.37 mg / L, and the fluoride ion removal rate was calculated to be 97.1%; the pH of the system was 11.69.

[0090] Comparative Example 10

[0091] This comparative example provides a method for defluorination treatment of fluorinated silicon slag.

[0092] This comparative example is basically the same as Example 1, except that 0.02g of calcium hydroxide powder is added in step 2) and 0.2g of La-Z adsorbent is added in step 3), which is consistent with the steps in Example 1.

[0093] Results: The concentration of fluoride ions in the supernatant after treatment was 2.24 mg / L, and the fluoride ion removal rate was calculated to be 99.4%; the pH of the system was 8.64.

[0094] Comparative Example 11

[0095] This comparative example provides a method for defluorination treatment of fluorinated silicon slag.

[0096] This comparative example is basically the same as Example 1, except that 0.04g of calcium hydroxide powder is added in step 2) and 0.2g of La-Z adsorbent is added in step 3), which is consistent with the steps in Example 1.

[0097] Results: The concentration of fluoride ions in the supernatant after treatment was 4.56 mg / L, and the fluoride ion removal rate was calculated to be 98.7%; the pH of the system was 9.35.

[0098] Comparative Example 12

[0099] This comparative example provides a method for defluorination treatment of fluorinated silicon slag.

[0100] This comparative example is basically the same as Example 1, except that 0.06g of calcium hydroxide powder is added in step 2) and 0.1g of La-Z adsorbent is added in step 3), which is consistent with the steps in Example 1.

[0101] Results: The concentration of fluoride ions in the supernatant after treatment was 1.89 mg / L, and the fluoride ion removal rate was calculated to be 99.47%; the pH of the system was 10.37.

[0102] Comparative Example 13

[0103] This comparative example provides a method for defluorination treatment of fluorinated silicon slag.

[0104] This comparative example is basically the same as Example 1, except that 0.08g of calcium hydroxide powder is added in step 2) and 0.1g of La-Z adsorbent is added in step 3), which is consistent with the steps in Example 1.

[0105] Results: The concentration of fluoride ions in the supernatant after treatment was 1.55 mg / L, and the fluoride ion removal rate was calculated to be 99.57%; the pH of the system was 11.69.

[0106] In summary, the method provided by this invention can achieve efficient defluorination treatment of industrial solid waste containing fluorinated silica slag. This invention effectively solves the contradiction between defluorination and silica suppression by precisely controlling the endpoint pH, maintaining the environment within a low silica leaching range while efficiently removing fluoride. This invention is a coupled process specifically designed based on the characteristics of the fluorinated silica slag system (high silica). Its pH control target (6.0~8.5) directly serves the specific need for silica suppression, exhibiting significant targeting and unexpected synergistic effects. This invention utilizes the built-in buffering function of La-Z, eliminating the need for a separate neutralization process and neutralizing agent. Furthermore, because pre-precipitation removes most of the fluoride, the La-Z dosage is only 30%-50% of that used when treating the same concentration of purely fluorinated wastewater, significantly reducing costs.

[0107] In Comparative Example 1, the amount of Ca(OH)2 added was insufficient, resulting in the release of Ca... 2+ Unable to fully integrate with SiF6 2- dissociated F - In combination, the defluorination efficiency was extremely low and could not meet basic treatment requirements; in Comparative Example 2, the Ca(OH)2 dosage met the defluorination requirements, but the excess OH... - The pH exceeded the critical value, resulting in turbidity of the supernatant and the adhesion of gelatinous precipitates (silica gel) to the container walls. This posed a serious risk of pipeline blockage and required additional acid to neutralize the pH, increasing process complexity and the risk of secondary pollution. In Comparative Example 3, excessive Ca(OH)2 addition not only failed to improve the defluorination rate (but also slightly increased fluoride residue due to CaF2 precipitation and agglomeration) but also exacerbated SiO2 leaching and silica gel formation. Furthermore, reagent waste increased costs, rendering the method completely impractical for engineering applications. Therefore, the method of using calcium hydroxide alone for defluorination suffers from the problem of ineffective defluorination when the dosage is insufficient, while sufficient or excessive dosage leads to pH exceeding the critical value and causing silica leaching. This presents an irreconcilable contradiction between "defluorination efficiency" and "silicon inhibition requirements," an inherent defect of the traditional lime method for treating fluorinated silica slag, which cannot be solved by adjusting the dosage of a single reagent.

[0108] In Comparative Example 4, the amount of La-Z added was too small, resulting in insufficient active sites and inability to effectively adsorb SiF6. 2- and the dissociated F - The defluorination efficiency was extremely poor. In Comparative Example 5, the defluorination rate improved after increasing the La-Z dosage, but it still did not meet the engineering requirements (too much residual fluorine). Furthermore, the single adsorbent was ineffective against SiF6. 2- The dissociation-promoting effect of La-Z is weak, the adsorption rate is slow, and deep defluorination cannot be achieved. In Comparative Example 6, the defluorination rate was further improved by increasing the dosage of La-Z, but there was still obvious fluoride residue. Moreover, the dosage of La-Z was twice that of Example 1, resulting in a significant increase in reagent cost and poor economic efficiency. In Comparative Example 7, although a relatively high defluorination rate was achieved, the dosage of La-Z was three times that of Example 1, leading to a sharp increase in cost. Furthermore, the adsorbent adsorbed SiF6...2- The subsequent surface charge imbalance led to significant agglomeration (particle size ≥ 500 μm), and the solid-liquid separation took 45 minutes (three times that of Example 1), which does not meet the requirements for efficient engineering treatment. Therefore, a significant increase in the La-Z dosage is needed to approach the effective defluorination rate, resulting in soaring costs and difficulties in solid-liquid separation, while also preventing the utilization of Ca. 2+ For F - Its rapid sedimentation effect results in low processing efficiency, and its use alone makes it difficult to balance economy and practicality.

[0109] In Comparative Example 8, Ca(OH)₂ and La-Z were added synergistically, but the amounts were relatively insufficient. 2+ F cannot be fully precipitated - The limited adsorption capacity of La-Z resulted in suboptimal defluorination efficiency, with the post-treatment fluoride ion concentration remaining high and failing to meet the stringent defluorination requirements of engineering projects. In Comparative Example 9, Ca(OH)2 and La-Z were added synergistically, but the amount of Ca(OH)2 was insufficient, leading to F... - Insufficient precipitation, high concentration of F - Inhibiting La-Z surface La 3+ Hydrolysis prevents the system from functioning as a pH buffer, resulting in an excessively high pH that does not meet engineering pH stability requirements, necessitating additional neutralization. In Comparative Example 10, the synergistic addition of Ca(OH)2 and La-Z achieved optimal defluorination efficiency, with the pH within the acceptable engineering range, satisfying treatment requirements. However, the La-Z dosage was twice that of Example 1, leading to higher reagent costs, making it suitable for scenarios with extremely high defluorination efficiency requirements and low cost sensitivity. In Comparative Example 11, the Ca(OH)2 dosage was appropriate, but the excessive La-Z dosage not only resulted in reagent waste and increased costs but also posed a risk due to the weak alkalinity of La-Z and the excess La-Z. 3+ Hydrolysis caused the system pH to be slightly high. Although it did not exceed the standard, it required slight neutralization, adding to the engineering steps. In Comparative Examples 12 and 13, the excessive amount of Ca(OH)2 led to an excessively high pH, ​​creating a strongly alkaline environment. This not only increased the cost of subsequent acid neutralization but also potentially caused equipment corrosion and secondary pollution risks.

[0110] The process of this invention involves a complex adjustment of the system's pH, which affects the dissociation characteristics of fluorosilicate and the system's F... - The result is a synergistic effect between concentration and the La-Z adsorbent mechanism. Fluorosilicate (SiF6) 2- It will stably dissociate and release F. - Its dissociation process consumes some Ca. 2+ Indirectly affecting the release of OH from Ca(OH)2 - Consumption efficiency; while the key to pH change depends on the system's F - Regulation of La-Z buffering capacity by concentration – F -Excessive concentration will inhibit La 3+ Hydrolysis leads to OH - Unable to be effectively buffered, pH rises; F - After being fully settled, La 3+ It can be hydrolyzed normally to achieve pH stability; at the same time, the amount of La-Z added will further adjust the pH of the system through factors such as adsorption capacity and its own weak alkalinity.

[0111] This invention is the first to explicitly propose and solve the treatment problem of fluorinated silica slag, a special type of waste, specifically targeting the key interfering factor of "silica leaching." Furthermore, the technical solution of this invention goes beyond a simple physical combination of "precipitation + adsorption," innovatively utilizing and enhancing the pH buffering function of La-Z materials, using them as the core hub connecting the precipitation and adsorption stages to achieve the goal of "silica suppression." Ultimately, this invention achieves an ultra-high fluoride removal rate (≥99%) while simultaneously suppressing silica leaching, achieving self-stabilization of effluent pH, and significantly reducing the amount of adsorbent required.

[0112] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for removing fluoride from fluorine-containing silicon slag, characterized in that, Includes the following steps: S1. Add water to the fluorinated silicon slag and stir to obtain a fluorinated silicon slag slurry; S2. Add calcium hydroxide to the fluorine-containing silicon slag slurry, stir for 0-10 min, then add La-Z adsorbent and stir for 5-20 min. S3. Allow the reaction to stand for 10-25 hours, then separate the solid and liquid to obtain the supernatant and precipitate.

2. The method for removing fluoride from fluorinated silicon slag according to claim 1, characterized in that, The mass fraction of SiO2 in the fluorinated silicon slag is 80%~90%.

3. The method for removing fluoride from fluorinated silicon slag according to claim 1, characterized in that, In step S1, the fluorine concentration in the fluorine-containing silicon slag slurry is 300~500 mg / L, the pH is 2~3.5, and the mass fraction of SiO2 is 20%~40%.

4. The method for removing fluoride from fluorinated silicon slag according to claim 1, characterized in that, In step S2, the calcium hydroxide is calcium hydroxide powder with a particle size ≤100μm.

5. The method for removing fluoride from fluorinated silicon slag according to claim 1, characterized in that, In step S2, the La-Z adsorbent is prepared by combining modified zeolite and lanthanum chloride.

6. The method for removing fluoride from fluorinated silicon slag according to claim 1, characterized in that, In step S2, the ratio of fluorine in the calcium hydroxide and fluorine-containing silica slurry is (2.5~3.2):1, measured by molar ratio.

7. The method for removing fluoride from fluorinated silicon slag according to claim 1, characterized in that, In step S2, the mass ratio of the La-Z adsorbent to calcium hydroxide is (0.75~3.5):

1.

8. The method for removing fluoride from fluorinated silicon slag according to claim 7, characterized in that, The mass ratio of the La-Z adsorbent to calcium hydroxide is (1.25~3):

1.

9. The method for removing fluoride from fluorinated silicon slag according to claim 1, characterized in that, In step S3, after the reaction is allowed to stand, the pH of the system is 6.0~8.

5.

10. The method for removing fluoride from fluorinated silicon slag according to claim 1, characterized in that, In step S3, the concentration of fluoride in the supernatant is <6 mg / L.