A method for recovering and reusing fluorine in fluorine-containing acidic wastewater and its application

Abstract

The present invention discloses a method for recovering and reusing fluorine in fluorine-containing acidic wastewater and the application of the method in the preparation of low-sodium alumina products. In the present invention, the fluorine-containing acidic wastewater is removed by steps, and according to the acidic characteristics of the aluminum-containing flocculant, the pH of the wastewater is adjusted to achieve continuous neutralization, so as to obtain a coarse-grained, easy-to-filter aluminum fluoride product, which can be used as a high-quality de-sodium agent for the roasting of industrial aluminum hydroxide without introducing other harmful elements, solving the problems of difficult process control, large waste gas emissions, high energy consumption, and limited product application performance in the production process of low-sodium alumina, and fully realizing the high-value utilization of fluorine and aluminum resources; at the same time, the filtrate after separating the aluminum fluoride product is treated as qualified wastewater, which can meet the discharge standards. The method for preparing aluminum fluoride from fluorine-containing acidic wastewater in the present invention has simple steps, short reaction time, low production cost, and is suitable for industrial application.

Description

Technical Field

[0001] The invention relates to the technical field of fluorine-containing acidic wastewater treatment, and in particular to a method and application of fluorine recovery and reuse in fluorine-containing acidic wastewater. Background Art

[0002] With the rapid development of my country's photovoltaic industry in recent years, the discharge of fluorine-containing acidic wastewater has increased. At present, the main technologies for treating fluorine-containing acidic wastewater include chemical precipitation, coagulation and sedimentation, adsorption, reverse osmosis, electrodialysis and other technologies. Among them, chemical precipitation and coagulation and sedimentation are widely used due to their simplicity, effectiveness, low operating cost, high removal efficiency and mature process technology. The removal of fluorine is mainly through flocculation and precipitation to form fluorine-containing sludge. Since fluorine-containing sludge has corrosive, toxic and other dangerous characteristics, and there are problems such as difficulty in disposal and low utilization rate, it is necessary to explore the resource utilization of fluorine-containing acidic wastewater from the source to reduce the generation of fluorine-containing sludge.

[0003] Chinese patent CN104649391B discloses a method for preparing polyaluminum using fluorine-containing waste acid, wherein calcium chloride and calcium aluminate powder are added to the fluorine-containing waste acid, stirred for reaction, and then aged, and fluorine-containing solid waste residue is removed by filtration to obtain a polyaluminum solution. However, the purity of the polyaluminum chloride prepared by this technology is low, and the application scope of the obtained polyaluminum chloride in wastewater is limited to a certain extent.

[0004] Chinese patent CN111170352B discloses a method for preparing rare earth fluoride particles using fluorine-containing waste acid, that is, adding rare earth metal stock solution to fluorine-containing waste acid to obtain rare earth fluoride particles through reaction. This technology utilizes rare earth metal salt solution to utilize fluorine-containing waste acid. Rare earth metal resources are limited and the cost is high. In actual engineering applications, there is still a high cost problem.

[0005] Therefore, how to recover the fluorine resources in the fluorine-containing acidic wastewater at low cost while ensuring that the treatment of the fluorine-containing acidic wastewater meets the standards, and efficiently apply the recovered fluorine products in industry to improve economic benefits and realize the comprehensive utilization of fluorine resources in the fluorine-containing acidic wastewater has become a key issue in the treatment of fluorine-containing acidic wastewater. Summary of the invention

[0006] The purpose of the present invention is to solve the problems of high cost and low economic benefit of fluorine recovery and reuse in fluorine-containing acidic wastewater in the prior art, and to provide a method and application of fluorine recovery and reuse in fluorine-containing acidic wastewater.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: a method for recovering and reusing fluorine in fluorine-containing acidic wastewater, comprising the following steps:

[0008] S1. Adding a polymer flocculation desiliconizing agent to the fluorine-containing acidic wastewater to obtain silicon-free fluorine-containing acidic wastewater;

[0009] S2, adding alkali to adjust the pH to weak alkalinity, and obtaining silicon-free fluorine-containing alkaline wastewater;

[0010] S3, preparing an aluminum-containing inorganic flocculant solution;

[0011] S4, adding the silicon-free fluorine-containing weakly alkaline wastewater and the aluminum-containing inorganic flocculant solution into the stirring reactor at a uniform speed, adjusting the pH in the reactor to neutral, and obtaining a neutral slurry after the reaction;

[0012] S5. The neutral slurry of S4 is subjected to solid-liquid separation. The filter cake is washed with clean water to obtain pure aluminum fluoride precipitate. The pure aluminum fluoride precipitate is dried and powdered to obtain ultrafine aluminum fluoride powder.

[0013] Preferably, the fluorine-containing acidic wastewater in S1 is fluorine-containing acidic wastewater directly taken from the drainage outlet of the photovoltaic enterprise workshop after filtering and removing impurities; a polymer flocculation desiliconizing agent is added, and magnetic stirring is used to stir for 30 minutes to form a mixed liquid, which is then allowed to stand for 2 hours, filtered to remove silicon, and obtain silicon-free fluorine-containing acidic wastewater.

[0014] Preferably, in S2, alkali is added with stirring at room temperature and pressure to adjust the pH to 7-8.

[0015] Preferably, the aluminum-containing inorganic flocculant is polyaluminum chloride or polyaluminum sulfate.

[0016] Preferably, in S4, the reaction conditions of the silicon-free fluorine-containing weakly alkaline wastewater and the aluminum-containing inorganic flocculant solution are normal temperature and pressure, the stirring speed is 20-300r / min, the stirring reaction time is 5-10min, and the pH in the stirring reactor is 6.8-7.2.

[0017] Preferably, the silicon-free fluorine-containing weakly alkaline wastewater and the aluminum-containing inorganic flocculant solution enter the bottom of the stirred reactor from two diagonally arranged feed pipes respectively, and the neutral slurry after the reaction flows out from the overflow discharge port arranged at 1 / 4-1 / 5 of the upper part of the reactor.

[0018] Preferably, the SO4 in the pure aluminum fluoride precipitate 2- ≤0.05%、Cl - ≤0.02%,Fe 3+ ≤0.01%.

[0019] Further preferably, in S5, the pure aluminum fluoride precipitate is dried by air flow, the temperature is maintained at 200° C., and the particle size of the aluminum fluoride is controlled in the range of 2-10 um.

[0020] The present invention also provides an application of the above method in the preparation of a low-sodium alumina product, wherein ultrafine aluminum fluoride powder and ultrafine industrial aluminum hydroxide powder are mixed and roasted to obtain a low-sodium alumina product, wherein Na + ≤0.05%.

[0021] Preferably, industrial aluminum hydroxide is pulverized by ultrasound, and the ultrasonic treatment frequency is 60 to 80 kHz to obtain industrial aluminum hydroxide ultrafine powder with a particle size range of 2-10 um.

[0022] The process of the above method and its application in the preparation of low sodium alumina products is shown in the attached Figure 1 shown.

[0023] The beneficial effects of the present invention are:

[0024] (I) In the present invention, the fluorine-containing acidic wastewater is removed from impurities in steps, and according to the acidic characteristics of the aluminum-containing flocculant, the pH value of the wastewater is adjusted to achieve continuous neutralization, thereby obtaining an aluminum fluoride product with coarse particles that is easy to filter and wash; at the same time, the filtrate after separating the aluminum fluoride product is treated as qualified wastewater and can meet the discharge standards.

[0025] (ii) The method for preparing aluminum fluoride from fluorine-containing acidic wastewater in the present invention has simple steps, short reaction time, low production cost, and is suitable for industrial application.

[0026] (III) The aluminum fluoride prepared and purified in the present invention can be used as a high-quality sodium removal agent for the roasting of industrial aluminum hydroxide without introducing other harmful elements, thereby solving the problems of difficult process control, large waste gas emissions, high energy consumption, and limited product application performance in the production process of low-sodium alumina (low sodium means less than 0.1%), and fully realizing the high-value utilization of fluorine and aluminum resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a flow chart of the method and application of fluorine recovery and reuse in fluorine-containing acidic wastewater. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] Take 5m 3 Fluoride-containing acidic wastewater, after testing F -The content is 1.2g / l and the silicon content (in terms of SiO2) is 0.48g / l; 1kg of anionic polyacrylamide (pre-prepared into a solution with 100 liters of water) as a high molecular flocculant is added, stirred for 30 minutes, allowed to stand for 2 hours, and the silicon slag is removed by filtration; sodium hydroxide is added to the silicon removal wastewater to adjust the pH to 7.5; the alkali-adjusted wastewater and polyaluminium chloride solution (containing AlCl3 100g / l) are respectively fed into a 1m3 feed pipe through two diagonally arranged feed pumps. 3 The bottom of the neutralization stirring reactor is adjusted to stabilize the pH in the reactor within the range of 6.8-7.2, and the stirring speed is controlled at 100r / min. The neutralization completed liquid overflows from the overflow port set at 1 / 4-1 / 5 of the upper part of the neutralization reactor to the transfer tank. After the neutralization is completed, it is filtered and the filtrate is wastewater that meets the discharge standards. After testing, F - The content was 5.7 mg / l. The filter cake was washed with clean water and dried at 200℃ to obtain 8.8 kg of aluminum fluoride product. The SO4 in aluminum fluoride was detected. 2- 0.04%, Cl - 0.02%, Fe 3+ 0.008%, particle size D50 = 3.2um; 100kg of aluminum hydroxide was crushed to a particle size D50 = 5um at an ultrasonic frequency of 65kHZ, and then mixed with 8.8kg of aluminum fluoride, and calcined at 1200℃ for 2 hours to obtain 70.1kg of low-sodium alumina product. The Na + =0.03%, which meets the product standard of low sodium alumina.

[0031] Example 2

[0032] Take 3m 3 Fluoride-containing acidic wastewater, after testing F - The content is 7.6g / l and the silicon content (in terms of SiO2) is 0.2g / l; 0.6kg of anionic polyacrylamide (preliminarily prepared into a solution with 100 liters of water) as a high molecular flocculant is added, stirred for 30 minutes, allowed to stand for 2 hours, and the silicon slag is filtered out; sodium hydroxide is added to the silicon removal wastewater to adjust the pH to 7.8; the alkali-adjusted wastewater and polyaluminium chloride solution (containing AlCl3 100g / l) are respectively fed into a 1m3 feed pipe through two diagonally arranged feed pumps. 3 The bottom of the neutralization stirring reactor is adjusted to stabilize the pH in the reactor within the range of 6.8-7.2, and the stirring speed is controlled at 120r / min. The neutralization completed liquid overflows from the overflow port set at 1 / 4-1 / 5 of the upper part of the neutralization reactor to the transfer tank. After the neutralization is completed, it is filtered and the filtrate is wastewater that meets the discharge standards. After testing, F - The content is 6.8mg / l. The filter cake is washed with clean water and dried at 200℃ to obtain 33.8kg of aluminum fluoride product. The SO4 in aluminum fluoride is detected.2- 0.04%, Cl - 0.01%, Fe 3+ 500 kg of aluminum hydroxide was crushed to a particle size of D50 = 7.2 um at an ultrasonic frequency of 65 kHz, and then mixed with 33.8 kg of aluminum fluoride and calcined at 1200 ° C for 2 hours to obtain 335.5 kg of low sodium alumina product. + =0.008%, which meets the product standard of low sodium alumina.

[0033] Example 3

[0034] Take 6m 3 Fluoride-containing acidic wastewater, after testing F - The content is 3.3g / l and the silicon content (in terms of SiO2) is 1.3g / l; 1.5kg of anionic polyacrylamide (pre-prepared into a solution with 100 liters of water) as a high molecular flocculant is added, stirred for 30 minutes, allowed to stand for 2 hours, and the silicon residue is filtered out; sodium hydroxide is added to the silicon removal wastewater to adjust the pH to 7.7; the alkali-adjusted wastewater and polyaluminum sulfate solution (containing Al2(SO4)3120g / l) are respectively fed into a 1m3 feed pipe through two diagonally arranged feed pumps. 3 The bottom of the neutralization stirring reactor is adjusted to stabilize the pH in the reactor within the range of 6.8-7.0, and the stirring speed is controlled to 65r / min. The neutralization completed liquid overflows from the overflow port set at 1 / 4-1 / 5 of the upper part of the neutralization reactor to the transfer tank. After the neutralization is completed, it is filtered and the filtrate is wastewater that meets the discharge standards. After testing, F - The content was 2.7 mg / l. The filter cake was washed with clean water and dried at 200℃ to obtain 17.2 kg of aluminum fluoride product. The SO4 in aluminum fluoride was detected. 2- 0.02%, Cl - 0.01%, Fe 3+ 0.002%, particle size D50 = 6.7um; 200kg of aluminum hydroxide was crushed to a particle size D50 = 3.7um at an ultrasonic frequency of 65kHZ, and then mixed with 17.2kg of aluminum fluoride, and calcined at 1200℃ for 2 hours to obtain 130.5kg of low-sodium alumina product. The Na + =0.011%, which meets the product standard of low sodium alumina.

[0035] The specification and drawings of the present invention are considered to be illustrative rather than restrictive. On the basis of the present invention, those skilled in the art can make some substitutions and modifications to some of the technical features according to the disclosed technical content without creative labor, all of which are within the protection scope of the present invention.

Claims

1. A method for recovering and reusing fluorine in fluorine-containing acidic wastewater, characterized in that: The following steps are involved: S1. Add a polymer flocculation desiliconization agent to the fluorine-containing acidic wastewater to obtain silicon-free fluorine-containing acidic wastewater; the fluorine-containing acidic wastewater is directly taken from the drainage outlet of the photovoltaic enterprise workshop and filtered and impurities removed; add the polymer flocculation desiliconization agent, stir with magnetic force, stir for 30 minutes to form a mixed solution, let it stand for 2 hours, filter and remove silicon, and obtain silicon-free fluorine-containing acidic wastewater S2. At normal temperature and pressure, add alkali to adjust the pH to weak alkalinity, pH 7-8, to obtain silicon-free fluorine-containing alkaline wastewater; S3, preparing an aluminum-containing inorganic flocculant solution; the aluminum-containing inorganic flocculant is polyaluminum chloride or polyaluminum sulfate; S4, the silicon-free fluorine-containing weak alkaline wastewater and the aluminum-containing inorganic flocculant solution are respectively introduced into the bottom of the stirred reactor from two diagonally arranged feed pipes, the reaction conditions are normal temperature and pressure, the stirring speed is 20-300r / min, the stirring reaction time is 5-10min, the pH in the stirred reactor is 6.8-7.2, and a neutral slurry is obtained after the reaction; the neutral slurry after the reaction flows out from the overflow discharge port arranged at 1 / 4-1 / 5 of the upper part of the reactor; S5, the neutral slurry of S4 is subjected to solid-liquid separation, and the filter cake is washed with clean water to obtain pure aluminum fluoride precipitate, wherein SO4 2- ≤0.05%、Cl - ≤0.02%,Fe 3+ ≤0.01%; the pure aluminum fluoride precipitate is dried and powdered to obtain ultrafine aluminum fluoride powder.

2. The method according to claim 1, characterized in that: In S5, the pure aluminum fluoride precipitate is dried by air flow, the temperature is maintained at 200° C., and the particle size of the aluminum fluoride is controlled in the range of 2-10 um.

3. Application of the method according to claim 1 or 2 in the preparation of low sodium alumina products, characterized in that: The ultrafine aluminum fluoride powder and the ultrafine industrial aluminum hydroxide powder are mixed and roasted to obtain a low-sodium alumina product, wherein the Na + ≤0.05%.

4. The use according to claim 3, characterized in that Industrial aluminum hydroxide is crushed by ultrasound with an ultrasonic treatment frequency of 60 to 80 kHz to obtain industrial aluminum hydroxide ultrafine powder with a particle size range of 2 to 10 um.

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