Method for deep defluorination and resource recovery of bastnaesite washing alkali liquor

Abstract

The invention relates to the technical field of bastnaesite washing alkali liquor recycling, in particular to a bastnaesite washing alkali liquor deep fluorine removal and resource recovery method which comprises the following steps that S1, bastnaesite washing alkali liquor is pretreated, and large-particle suspended solids in the washing alkali liquor are removed; s2, adjusting the pH value to be neutral, adding an impurity removing agent to remove impurity ions, and filtering to obtain an adjusting solution; s3, a calcium precipitator is added into the adjusting liquid, stirring and filtering are conducted, and an industrial-grade calcium fluoride product and supernate are obtained; s4, calcium salt is added into the supernate for a precipitation reaction, then a coagulant aid is added for sedimentation, filtering is conducted, and filtrate and a calcium fluoride crude product are obtained; the calcium precipitant in the step S2 comprises the calcium fluoride crude product. By adopting the method of combining calcium salt precipitation and flocculation precipitation, the removal efficiency of the fluorine ions is remarkably improved, and the concentration of the fluorine ions in the wastewater can be reduced to be below the discharge standard.

Description

Technical Field

[0001] The invention relates to the technical field of recycling and utilizing bastnaesite washing alkali solution, and in particular to a method for deep defluorination and resource recovery of bastnaesite washing alkali solution. Background Art

[0002] In the rare earth smelting process, especially when fluorine-containing raw materials such as bastnaesite are used for smelting, a large amount of fluorine-containing wastewater will be generated. The main process of bastnaesite is oxidation roasting-hydrochloric acid leaching, which is derived from the chemical treatment process to produce rare earth products. This process is to oxidize and roast bastnaesite, then use hydrochloric acid to leach to obtain a rare earth chloride solution with less cerium. The tetravalent cerium, thorium and fluorine enter the slag. The process of decomposing the slag with caustic soda is called the alkali conversion process. The cerium-rich slag obtained by alkali conversion is filtered and washed. The wastewater produced is strongly alkaline, contains a large amount of fluoride ions, and is radioactive, which is the alkali washing solution. The concentration of fluoride in these wastewaters is high. If it is directly discharged, it will pose a serious threat to human health and the water environment. Rare earth smelting enterprises generally face huge challenges in the treatment of fluorine-containing wastewater. Research on defluorination treatment and fluorine resource recycling technology will help reduce treatment costs and improve economic benefits, and can effectively promote the sustainable development of the rare earth smelting industry.

[0003] Although there are many technical methods for treating fluoride-containing wastewater from rare earth smelting and recovering calcium fluoride, there are still some challenges. For example, although the chemical precipitation method is low-cost, the treatment effect is limited, the adsorption method has a good treatment effect but the adsorbent is difficult to regenerate, and the membrane technology has the problem of high operating costs.

[0004] CN105836866B discloses a process for inducing crystallization of calcium fluoride from high-fluorine wastewater in rare earth metal smelting, but it uses fluidized bed crystallization, and it is also necessary to apply an electromagnetic field and introduce helium, resulting in a long processing time and high cost. CN103570161B discloses a method for removing fluoride ions from fluorocerium carbon ore rare earth smelting wastewater, which uses calcium chloride and rare earth element reagents to carry out primary and secondary defluorination, but there are still problems of high cost and low recovery rate of calcium fluoride. Therefore, it is necessary to further study and develop more efficient and economical treatment technologies and recovery processes. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for deep defluorination and resource recovery of bastnaesite washing solution to at least achieve

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] A method for deep defluorination and resource recovery of bastnaesite washing liquor, comprising the following steps:

[0008] S1: pre-treating the bastnaesite washing solution to remove large suspended particles in the washing solution;

[0009] S2: Adjust the pH to 6-8, add an impurity remover to remove impurity ions, filter, and obtain a regulated solution;

[0010] S3: adding the regulating solution to a calcium precipitant, stirring and filtering to obtain an industrial-grade calcium fluoride product and a supernatant;

[0011] S4: adding calcium salt to the supernatant to carry out precipitation reaction, then adding a coagulant to carry out sedimentation, filtering, and obtaining a filtrate and a crude calcium fluoride product;

[0012] The calcium precipitant in step S3 includes the crude calcium fluoride product.

[0013] Further, the F in the alkali washing solution - The concentration is 3200~4500mg / L, PO4 3- Concentration is 45~155mg / L, SO4 2- The concentration is 502-1460 mg / L, the SiO2 concentration is 211-439 mg / L, and the pH of the alkali washing solution is 13-14.

[0014] Further, in step S1, the pre-processing includes filtering;

[0015] Further, in step S2, the pH is adjusted using a neutralizing agent including hydrochloric acid;

[0016] Preferably, the mass fraction of hydrochloric acid is 36-38%.

[0017] Furthermore, in step S2, the impurity remover includes ferric chloride or aluminum chloride.

[0018] Preferably, in step S3, the reaction temperature is maintained at 20-70° C. during the stirring and filtering; the stirring time is 1-4 h, and the stirring speed is 150-240 r / min.

[0019] Furthermore, in step S4, the calcium salt includes calcium chloride or quicklime.

[0020] Furthermore, in step S4, the reaction temperature of the precipitation reaction is 20-70°C.

[0021] Preferably, in step S4, the amount of calcium salt added is calculated by: calculating according to the molar amount of F in the supernatant, and adding at a molar ratio of Ca:F=0.5 to 1:1.

[0022] Preferably, in step S4, the precipitation reaction is continuously stirred for 0.5 to 2 h at a stirring speed of 150 to 240 r / min.

[0023] Furthermore, in step S4, the coagulant aid includes polyacrylamide and polyvinylamide.

[0024] Preferably, the added amount of the polyacrylamide is 2-5 mg / L.

[0025] Furthermore, in step S4, the sedimentation time is 10 to 60 minutes.

[0026] Furthermore, the precipitant also includes a calcium fluoride product prepared by the following method:

[0027] S5: pre-treating the bastnaesite washing solution to remove large suspended particles in the washing solution;

[0028] S6: adjusting the pH to neutral, adding an impurity remover to remove impurity ions, filtering, and obtaining a regulated solution;

[0029] S7: adding the regulating liquid to calcium salt for precipitation reaction, then adding a coagulant aid for sedimentation, filtering, and obtaining a filtrate and a calcium fluoride product.

[0030] In the first cycle process, step S3 uses the calcium fluoride product obtained in S5-S7 as a calcium precipitant;

[0031] In the second or more circulation steps, step S3 uses the crude calcium fluoride product obtained in step S4 in the previous cycle as a calcium precipitant, and subsequently only the process of steps S1-S4 needs to be repeated continuously to continuously recover the fluorine in the alkali washing solution.

[0032] The invention removes large suspended solids in the alkali washing solution by pretreating the bastnaesite alkali washing solution; adjusts the pH value to a suitable range and adds an impurity remover to remove part of the impurity ions so as not to affect the subsequent calcium fluoride grade; adds an appropriate amount of calcium salt to precipitate fluoride ions, adds a small amount of coagulant to precipitate to prepare a crude calcium fluoride product, and evaporates and crystallizes the filtered solution to meet the requirements of chlor-alkali chemical industry; returns the crude calcium fluoride to the adjusted alkali washing solution, and stirs it at a certain temperature for a period of time to obtain an industrial-grade calcium fluoride product, and the filtered supernatant is the mother liquor for preparing the crude calcium fluoride product.

[0033] The beneficial effects of the present invention are:

[0034] Compared with the prior art, the method of combining calcium salt precipitation with flocculation precipitation proposed in the present invention significantly improves the removal efficiency of fluoride ions and can reduce the fluoride ion concentration in wastewater to below the discharge standard. At the same time, the fluorine resources in the wastewater are recovered, and industrial-grade calcium fluoride can be obtained with a high fluorine recovery rate. The process also has the advantages of simple process and low processing cost, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a process flow chart of step S1 to step S4 of the present invention;

[0036] Figure 2 It is a process flow chart of steps S5-S7 of the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0038] Example 1

[0039] Collect 1L of bastnaesite washing solution, filter to remove large suspended particles, and detect the F - The concentration is 3280mg / L, PO4 3- The concentration is 64mg / L, SO4 2- The concentration is 789 mg / L, the SiO2 concentration is 295 mg / L, and the pH of the washing solution is 14. The following method is used for recovery:

[0040] ① Use hydrochloric acid to adjust the pH value of the washing solution to 7, and add 0.1g / L ferric chloride for filtration and precipitation.

[0041] ② Add 20wt% calcium chloride solution, the amount of calcium chloride added is the molar ratio of Ca:F=0.6:1, the reaction temperature is 40°C, the stirring time is 1h, and the stirring speed is 150r / min.

[0042] ③ Add polyacrylamide (PAM) as a coagulant at an amount of 3 mg / L, settling time 10 min, filter to obtain filtrate and calcium fluoride.

[0043] Sampling and testing showed that the calcium fluoride was 9.96 g in total and the grade of calcium fluoride was 87.31%.

[0044] Example 2

[0045] Collect 1L of bastnaesite washing solution, filter to remove large suspended particles, and detect the F - The concentration is 3280mg / L, PO4 3- The concentration is 64mg / L, SO4 2- The concentration is 789 mg / L, the SiO2 concentration is 295 mg / L, and the pH of the washing solution is 14. The following method is used for recovery:

[0046] ① Use hydrochloric acid to adjust the pH value of the washing solution to 7, and add 0.1g / L ferric chloride for filtration and precipitation.

[0047] ② Add 9.96 g of calcium fluoride prepared in Example 1, reaction temperature 40°C, stirring time 1 h,

[0048] The stirring speed is 150r / min, and the mixture is stirred and filtered to obtain industrial-grade calcium chloride product and supernatant.

[0049] ③ Add 20wt% calcium chloride solution to the supernatant for chemical precipitation, the added amount is the molar ratio of Ca:F=0.6:1, the reaction temperature is 40°C, the stirring time is 1h, and the stirring speed is 150r / min.

[0050] ④ Add PAM for flocculation precipitation, the addition amount is, the sedimentation time is 30min, and filter to obtain the crude calcium fluoride product and filtrate.

[0051] After sampling and testing, the industrial-grade calcium chloride product obtained had a grade of 95.28%, a total of 9.18 g;

[0052] The crude calcium fluoride product obtained has a grade of 86.55%, with a total amount of 9.83 g.

[0053] The fluoride ion concentration in the filtrate is 9.5 mg / L.

[0054] Example 3

[0055] Collect 1L of bastnaesite washing solution, remove large suspended particles by filtration, and detect the F - The concentration is 3280mg / L, PO4 3- The concentration is 64mg / L, SO4 2- The concentration is 789 mg / L, the SiO2 concentration is 295 mg / L, and the pH of the washing solution is 14. The following method is used for recovery:

[0056] ① Use hydrochloric acid to adjust the pH value of the washing solution to 7, and add 0.1g / L ferric chloride for filtration and precipitation.

[0057] ② Add the crude calcium fluoride product obtained in Example 2, the amount of calcium fluoride added is 9.83 g, the reaction temperature is 40° C., the stirring time is 1 h, the stirring speed is 150 r / min, and the mixture is stirred and filtered to obtain an industrial-grade calcium chloride product and a supernatant.

[0058] ③ Add 20wt% calcium chloride solution to the supernatant for chemical precipitation, the added amount is the molar ratio of Ca:F=0.6:1, the reaction temperature is 40°C, the stirring time is 1h, and the stirring speed is 150r / min.

[0059] ④ Add PAM for flocculation precipitation, the addition amount is, the sedimentation time is 20min, filter to obtain the crude calcium fluoride product and filtrate.

[0060] Sampling and testing showed that the grade of industrial-grade calcium chloride product obtained was 95.64%, totaling 9.08 g;

[0061] The crude calcium fluoride product obtained has a grade of 85.59%, totaling 9.88 g.

[0062] The fluoride ion concentration in the filtrate is 8.7 mg / L.

[0063] Comparative Example

[0064] Collect 1L of bastnaesite washing solution, remove large suspended particles by filtration, and detect the F - The concentration is 3280mg / L, PO4 3- The concentration is 64mg / L, SO4 2- The concentration is 789 mg / L, the SiO2 concentration is 295 mg / L, and the pH of the washing alkali solution is 14. The following method is used for recovery, which is different from Example 2 in that flocculation precipitation is not performed:

[0065] ① Use hydrochloric acid to adjust the pH value of the washing solution to 7, and add 0.1g / L ferric chloride for filtration and precipitation.

[0066] ② Add the calcium fluoride prepared in Example 1, the amount of calcium fluoride added is 9.46 g, the reaction temperature is 40° C., the stirring time is 1 h, the stirring speed is 150 r / min, and the mixture is stirred and filtered to obtain an industrial-grade calcium chloride product and a supernatant.

[0067] ③ Add 20wt% calcium chloride solution to the supernatant for chemical precipitation, the added amount is Ca:F=0.8:1, the reaction temperature is 40°C, the stirring time is 1h, the stirring speed is 150r / min, and the crude calcium fluoride product and the filtrate are obtained by filtration.

[0068] Sampling and testing showed that the grade of industrial-grade calcium chloride product obtained was 95.35%, totaling 9.12 g;

[0069] The crude calcium fluoride product obtained has a grade of 84.56%, totaling 9.48 g.

[0070] The fluoride ion concentration in the filtrate is 83.9 mg / L.

[0071] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not deviate from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for deep defluorination and resource recovery of bastnaesite washing solution, comprising the following steps: S1: pre-treating the bastnaesite washing solution to remove large suspended particles in the washing solution; S2: Adjust the pH to neutral, add an impurity remover to remove impurity ions, filter, and obtain a regulated solution; S3: adding the regulating solution to a calcium precipitant, stirring and filtering to obtain an industrial-grade calcium fluoride product and a supernatant; S4: adding calcium salt to the supernatant to carry out precipitation reaction, then adding a coagulant to carry out sedimentation, filtering, and obtaining a filtrate and a crude calcium fluoride product; The calcium precipitant in step S2 includes the crude calcium fluoride product.

2. The recycling method according to claim 1, characterized in that: In step S1, the preprocessing is filtering.

3. The recycling method according to claim 1, characterized in that: In step S2, the pH is adjusted using a neutralizing agent including hydrochloric acid.

4. The recycling method according to claim 1, characterized in that: In step S2, the impurity remover includes ferric chloride or aluminum chloride.

5. The recycling method according to claim 1, characterized in that: In step S4, the calcium salt includes calcium chloride or quicklime.

6. The recycling method according to claim 1, characterized in that: In step S4, the reaction temperature of the precipitation reaction is 20-70°C.

7. The recycling method according to claim 1, characterized in that: In step S4, the coagulant aid includes polyacrylamide.

8. The recycling method according to claim 1, characterized in that: In step S4, the sedimentation time is 10 to 60 minutes.

9. The recycling method according to claim 1, characterized in that: The precipitant also includes a calcium fluoride product prepared by the following method: S5: pre-treating the bastnaesite washing solution to remove large suspended particles in the washing solution; S6: adjusting the pH to neutral, adding an impurity remover to remove impurity ions, filtering, and obtaining a regulated solution; S7: adding the regulating solution to calcium fluoride, stirring and filtering to obtain an industrial-grade calcium fluoride product and a supernatant; S8: adding calcium salt to the supernatant to carry out precipitation reaction, then adding a coagulant to carry out sedimentation, filtering, and obtaining a filtrate and a calcium fluoride product.

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