阅读说明：本技术 一种从氟碳铈碱转工艺回收氢氧化钠和联产氟化钠的方法 (Method for recycling sodium hydroxide and co-producing sodium fluoride from fluorine carbon cerium alkali conversion process ) 是由 王先荣 许思玉 朱光荣 冯新瑞 吴仕伦 于 2020-12-18 设计创作，主要内容包括：本发明公开了一种从氟碳铈碱转工艺回收氢氧化钠和联产氟化钠的方法,包括以下步骤：(1)将氟碳铈精矿焙烧、冲洗并使用盐酸溶液酸浸；(2)在浸渣中加入碱溶液搅拌升温；(3)碱转后加入絮凝剂进行固液分离；(4)采用不同含量的固体氢氧化钠生产高质量浓度或低质量浓度的氢氧化钠溶液和生产氟化钠产品；(5)将低质量浓度的氢氧化钠溶液蒸发熬浓得到预定质量浓度的氢氧化钠溶液或氢氧化钠固体。通过该方法回收制得不同浓度的氢氧化钠溶液,可用于氟碳铈精矿碱转工序或其他领域里,而得到氟化钠产品,品质高,纯度≥98％,可作产品销售。降低了生产成本和减轻废水处理困难,避免环境污染和氟资源浪费,适合工业化生产。(The invention discloses a method for recycling sodium hydroxide and co-producing sodium fluoride from a fluorine-carbon cerium alkali conversion process, which comprises the following steps: (1) roasting, washing and acid leaching the bastnaesite concentrate by using a hydrochloric acid solution; (2) adding alkali solution into the leaching residue, stirring and heating; (3) adding a flocculating agent for solid-liquid separation after the alkali conversion; (4) adopting solid sodium hydroxide with different contents to produce sodium hydroxide solution with high quality concentration or low quality concentration and produce sodium fluoride products; (5) evaporating and concentrating the sodium hydroxide solution with low mass concentration to obtain the sodium hydroxide solution or sodium hydroxide solid with preset mass concentration. The sodium hydroxide solution with different concentrations recovered by the method can be used in the alkali conversion process of the bastnaesite concentrate or other fields to obtain sodium fluoride products, the quality is high, the purity is more than or equal to 98%, and the sodium fluoride products can be sold as products. Reduces the production cost, lightens the difficulty of wastewater treatment, avoids environmental pollution and fluorine resource waste, and is suitable for industrial production.)

1. A method for recycling sodium hydroxide and co-producing sodium fluoride from a fluorine carbon cerium alkali conversion process is characterized by comprising the following steps:

(1) roasting and washing the bastnaesite concentrate, and performing acid leaching by using a hydrochloric acid solution to obtain a feed liquid and leaching residues; wherein the roasting temperature is 400-600 ℃, and the roasting time is 30-90 min;

(2) mixing the leaching residue obtained in the step (1) with water, stirring, heating, and adding a sodium hydroxide solution to obtain a mixed solution; wherein the temperature after heating is 90-130 ℃, and the stirring time is 0.3-2 h;

(3) adding a flocculating agent into the mixed solution obtained in the step (2), stopping stirring, carrying out solid-liquid separation after layering occurs, collecting filtrate, adding water to wash solids, repeating the washing process for more than 5 times, and finally transferring the previous 2 times of water washing liquid into the filtrate;

(4) adding 250-300g of solid sodium hydroxide into the filtrate obtained in the step (3) by stirring, cooling to normal temperature or below 15 ℃ below zero to prepare a sodium hydroxide solution with the concentration range of 20-70%, and simultaneously preparing sodium fluoride solid with the yield value of 17.0-17.35 g/L;

(5) and (3) evaporating and concentrating the sodium hydroxide solution with the mass concentration range of 20-70% prepared in the step (4) to obtain a sodium hydroxide solution with a preset mass concentration, or decocting and concentrating in an evaporator to obtain a sodium hydroxide solid.

2. The method for recovering sodium hydroxide and co-producing sodium fluoride from the alkali-transfer process of fluorine-carbon cerium as claimed in claim 1, wherein the concentration of the hydrochloric acid solution in the step (1) is 4-8mol/L, the solid-liquid mass ratio of the hydrochloric acid to the concentrate is 1:2-4, and the acid leaching time is 20-40 min.

3. The method for recycling sodium hydroxide and co-producing sodium fluoride from a bastnaesite alkaline conversion process as claimed in claim 1, wherein the mass concentration of the sodium hydroxide solution in the step (2) is 45-80% and the amount of the sodium hydroxide solution is 20-80% of the mass of the bastnaesite concentrate.

4. The method for recycling sodium hydroxide and co-producing sodium fluoride from a fluorine-carbon cerium alkaline conversion process according to claim 1, wherein the flocculant in the step (3) is polyacrylamide, polyaluminum chloride, polyaluminum sulfate, polyaluminum/ferric silicate or polyaluminum/ferric phosphate, the mass concentration of the flocculant is 15% -20%, and the addition amount is 0.01-1% of the volume of the system.

5. The method for recycling sodium hydroxide and co-producing sodium fluoride from the alkali-transfer process of fluorine-carbon cerium as claimed in claim 4, wherein the flocculant in the step (3) is a polyacrylamide flocculant, the mass concentration of which is preferably 15-18%, and the addition amount of which is 0.02-0.1% of the volume of the system.

6. The method for recovering sodium hydroxide and co-producing sodium fluoride from a fluorocarbon cerium alkaline conversion process as claimed in claim 1, wherein the solid-liquid separation method in the step (3) is siphon, cascading or filtration.

7. The method for recovering sodium hydroxide and co-producing sodium fluoride from the alkali-transfer process of fluorine-carbon cerium as claimed in claim 6, wherein the solid-liquid separation method in the step (3) is filtration.

8. The method for recovering sodium hydroxide and co-producing sodium fluoride from a fluorocarbon cerium alkaline conversion process as claimed in claim 1, wherein the washing in step (3) is ended by a water washing solution having a pH value of 7.0.

9. The method for recovering sodium hydroxide and co-producing sodium fluoride from a fluorocarbon cerium alkaline conversion process as claimed in claim 1, wherein the step (3) further comprises transferring the water washing solution of last 3 times or more to the next alkaline conversion process as an initial washing solution.

Technical Field

The invention relates to the technical field of mineral recovery, in particular to a method for recovering sodium hydroxide and co-producing sodium fluoride from a fluorine-carbon cerium alkali conversion process.

Background

Bastnaesite is known as the most abundant rare earth mineral in the world, and the exploitation amount and the usage amount are the largest at present, about 70% of rare earth raw materials are from bastnaesite, and bastnaesite belongs to light rare earth minerals, mainly contains a series of 7 elements such as lanthanum and cerium, and has been widely used in the traditional industry and high-tech industry due to unique properties. Although bastnaesite has the characteristics of less non-rare earth impurities, small mineral particles and the like, the problems of difficult recycling of other valuable elements, serious three-waste pollution and the like exist in the smelting process all the time.

In the smelting process of bastnaesite concentrate, fluorine of bastnaesite is generated in the form of fluorine gas or fluoride, comprehensive recovery treatment is needed, fluoride impurities are more in the whole, or the treatment process time of fluorine is long. The prior art introduces a technology for refining rare earth of fluorine carbon and cerium, and the method comprises the following specific steps: in the high-temperature roasting process or in acid leaching, a decomposition auxiliary agent or a fluorine-fixing agent is added to form corresponding fluoride, and then the fluoride is separated from the rare earth. Wherein, in the roasting process, part of fluorine can be removed by washing with water, but the emulsification problem in the extraction process cannot be solved fundamentally, a complexing agent is still needed to be added for elimination, the cost of the decomposition auxiliary agent (about 20-25% of the concentrate amount of the decomposition auxiliary agent) is increased, the washing amount is large, a large amount of other impurities are accompanied, and the recovery is difficult; and when the fluoride is added in acid leaching, although a stable fluorine complex can be formed, the fluoride still has influence on the later extraction process, the market demand of the recycled partial fluoride is small, and the product backlog is easy to form, so certain resistance exists in the decision and implementation of treatment engineering.

With the rare earth resource being less and less, the environmental protection requirement and awareness are higher and higher, and more attention and attention are paid to people. Intensive and detailed research on the rare earth hydrometallurgy process needs a large amount of chemical raw materials (such as a roasting agent, a dissolving agent, a conversion agent, an extracting agent and the like) as assistance, generates a large amount of other byproducts and original excessive chemical raw materials, cannot be directly discharged, generates secondary pollution and causes serious harm to the environment.

Disclosure of Invention

The invention aims to provide a method for recovering sodium hydroxide and co-producing sodium fluoride from a fluorine carbon cerium alkali conversion process, which can produce rare earth chloride solution in a fluorine carbon cerium concentrate process, can also utilize fluorine in the fluorine carbon cerium concentrate to produce sodium fluoride and simultaneously recover unconsumed sodium hydroxide.

In order to achieve the purpose, the invention provides a method for recovering sodium hydroxide and co-producing sodium fluoride from a fluorine-carbon cerium alkali conversion process, which comprises the following steps:

(1) roasting and washing the bastnaesite concentrate, and performing acid leaching by using a hydrochloric acid solution to obtain a feed liquid and leaching residues; wherein the roasting time is 30-90min, and the roasting temperature is 400-600 ℃;

(2) mixing the leaching residue obtained in the step (1) with water, stirring, heating, and adding a sodium hydroxide solution to obtain a mixed solution; wherein the temperature is raised to 90-130 ℃ after stirring, and the stirring time is 0.3-2 h;

(3) adding a flocculating agent into the mixed solution obtained in the step (2), stopping stirring, performing solid-liquid separation after obvious layering occurs, collecting filtrate, adding water to repeatedly wash the solid for more than 5 times, and transferring the previous 2 times of washing liquid into the filtrate;

(4) adding 300g of solid sodium hydroxide 250-250 g into the filtrate obtained in the step (3) by stirring, cooling to normal temperature or below 15 ℃ below zero to obtain a sodium hydroxide solution with the concentration range of 20-70% and a sodium fluoride solid, wherein the yield value of the sodium fluoride solid is 17.0-17.35 g/L;

(5) and (4) evaporating and concentrating the sodium hydroxide solution with the mass concentration range of 20-70% prepared in the step (4) to obtain a sodium hydroxide solution with a preset mass concentration, or decocting and concentrating in an evaporator to obtain a sodium hydroxide solid.

The beneficial effect who adopts above-mentioned scheme is: firstly, oxidizing and roasting bastnaesite concentrate to generate rare earth oxide, rare earth oxyfluoride and rare earth fluoride, washing the bastnaesite concentrate by counter-current water to remove non-rare earth impurities soluble in water, and then carrying out hydrochloric acid leaching to form rare earth chloride feed liquid (containing impurities soluble in hydrochloric acid) and rare earth fluoride acid leaching residue insoluble in hydrochloric acid; decomposing the acid leaching residue by using a sodium hydroxide solution, wherein rare earth fluoride can be separated from the acid leaching residue and dissolved in the sodium hydroxide solution, the alkali-transition temperature is controlled to be 90-130 ℃, the temperature is too low, the rare earth fluoride is not completely decomposed, the temperature is higher than 130 ℃, part of cerium in a rare earth fluoride decomposition product is oxidized and can possibly cause local overheating to generate insoluble matters, so that the concentration and the dosage of subsequent hydrochloric acid are increased, the alkali-transition time is controlled to be 0.3-2h, when the time is lower than 0.3h, the rare earth fluoride and the sodium hydroxide solution are not completely reacted, but the alkali-transition time is too long, the efficiency is low, the moisture is gradually reduced at high temperature, the viscosity is too high, and the alkali-transition is influenced; then flocculating the solution by using a flocculating agent, and separating out solids and impurities by using the obtained mixed solution containing solids in a filtration mode and the like to leave a fluorine-containing water solution; adding water for repeated washing, wherein the fluorine content in the water washing liquid is more than or equal to 3g/L, F^-、Na⁺And OH^-Has high mass concentration, so the filtrate is required to be recovered together with the retained filtrate; and adding sodium hydroxide solid into the filtrate, reducing the stability of the saturated sodium fluoride solution under the stirring action, separating out sodium fluoride crystals, namely the sodium hydroxide solution, evaporating or decocting the sodium hydroxide solution to be concentrated to obtain the sodium hydroxide solution or the sodium hydroxide solid with the preset concentration, and recycling the obtained sodium hydroxide solution or the obtained sodium hydroxide solid in the whole process flow.

Further, the concentration of the hydrochloric acid solution in the step (1) is 4-8mol/L, and the solid-liquid mass ratio of the hydrochloric acid solution to the concentrate is 1:2-4, and the acid leaching time is 20-40 min.

The beneficial effect who adopts above-mentioned scheme is: the hydrochloric acid solution has small influence on subsequent processes, has low impurity content and is beneficial to recovery. If the dosage is more than the range of 4-8mol/L, resource waste is caused, and the recycling or environmental pollution is increased; if the dosage is less than the range of 4-8mol/L, the recovery rate of the rare earth is low, and the alkali transfer pressure is increased.

Further, in the step (2), the mass concentration of the sodium hydroxide solution is 45-80%, and the dosage of the sodium hydroxide solution is 20-80% of the mass fraction of the bastnaesite concentrate.

The beneficial effect who adopts above-mentioned scheme is: if the mass concentration of the sodium hydroxide solution is lower than 45%, the decomposition rate of the concentrate and the preferential dissolution rate of the rare earth are incomplete, and the acid dissolution rate of iron is increased along with the incomplete decomposition rate of the concentrate and the preferential dissolution rate of the rare earth, so that impurities are increased; if the mass concentration of the sodium hydroxide is higher than 80%, the viscosity is high, the solid-liquid contact is insufficient, the conversion rate is low, and part of rare earth fluoride remains in the slag.

Further, in the step (3), the flocculating agent is polyacrylamide, polyaluminium chloride, polyaluminium sulfate, polyaluminium silicate/iron or polyaluminium phosphate/iron, the mass concentration of the flocculating agent is 15-20%, and the addition amount is 0.01-1% of the volume of the system.

Further, the flocculant in the step (3) is a polyacrylamide flocculant, the preferable mass concentration is 15-18%, and the addition amount is 0.02-0.1% of the volume of the system.

Further, the solid-liquid separation method in the step (3) is siphoning, inclined draining or filtering.

Further, the solid-liquid separation method in the step (3) is filtration.

Further, the end point of the washing in the step (3) is that the pH value of the water washing liquid is 7.0.

Further, the step (3) also comprises transferring the water washing liquid for the last 3 times or more to the next alkali-transferring process to be used as the initial washing liquid.

The beneficial effect who adopts above-mentioned scheme is: can play a role of accumulating F^-、Na⁺And OH^-The mass concentration of the water also saves water resources.

In summary, the invention has the following advantages:

1. the method recovers and prepares the sodium hydroxide solution with different concentrations, can be used in the alkali conversion process of the bastnaesite concentrate or other fields to obtain the sodium fluoride product, has high quality and purity of more than or equal to 98 percent, and can be sold as a product;

2. in the whole process, no three wastes are generated, the sodium hydroxide solution can be efficiently recovered and prepared and the sodium fluoride product can be efficiently produced, the production cost is reduced, the difficulty in wastewater treatment is reduced, the environmental pollution and the fluorine resource waste are avoided, and the method is suitable for industrial production.

Detailed Description

The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.

The invention provides a method for recycling sodium hydroxide and co-producing sodium fluoride from a fluorine-carbon cerium alkali conversion process, which comprises the following steps of: putting the bastnaesite concentrate with the REO of more than or equal to 65 percent into an eight-section Hesch multi-hearth roasting furnace for oxidizing roasting for 60min, controlling the temperature to be 500 ℃, generating products such as rare earth oxide, rare earth oxyfluoride, rare earth fluoride and the like, washing the products by using counter-current water, and carrying out acid leaching by using 5mol/L hydrochloric acid, wherein the solid-to-liquid ratio of the hydrochloric acid to the concentrate is 1:2, the time is 40min, then solid-liquid separation is carried out, rare earth chloride feed liquid (containing impurities of soluble hydrochloric acid) and rare earth fluoride acid leaching residue which is insoluble in hydrochloric acid are obtained, wherein the Rare Earth Oxide (REO) with the weight of about 30 percent is contained, and the further separation and purification can be carried out only by alkali conversion.

Example 1

Recovering the high-quality concentration sodium hydroxide solution:

putting the rare earth fluoride acid leaching residue containing 100kg of REO into an alkali transfer tank, starting stirring, uniformly mixing, adding 230kg of sodium hydroxide solution with the mass concentration of 50%, starting heating, controlling the temperature to be 100 ℃, supplementing a small amount of water during the period, wherein the specific dosage is determined according to the water loss condition, stopping stirring after the duration time is 60min, standing for 30min, transferring the supernatant into a storage tank A, heating the water to the original liquid level, starting stirring, washing, repeating the washing for more than 5 times to ensure that the pH value of the washing liquid is 7, judging the washing liquid to be qualified, pumping the washing liquid of the previous 2 times into another storage tank A, pumping the washing liquid of the other times into another storage tank B, and pumping the washing liquid of the previous 2 times in the next alkali transfer process as the water for the previous 2 times in the next alkali transfer process, wherein the last 3 times of the washing in the alkali transfer process need new purified water or deionized water for washing. And then starting stirring in the storage tank A, slowly adding solid sodium hydroxide to completely dissolve the sodium hydroxide, cooling to normal temperature or below-15 ℃ when the fluorine content in the water washing liquid is less than or equal to 30mg/L, and carrying out solid-liquid separation.

Example 2

Recovering the low-mass concentration sodium hydroxide solution:

putting the rare earth fluoride acid leaching residue containing 100kg of REO into an alkali transfer tank, starting stirring, uniformly mixing, adding 230kg of sodium hydroxide solution with the mass concentration of 50%, starting heating, controlling the temperature to be 100 ℃, supplementing a small amount of water during the period, wherein the specific dosage is determined according to the water loss condition, stopping stirring after the duration time is 60min, standing for 30min, transferring the supernatant into a storage tank A, heating the water to the original liquid level, starting stirring, washing, repeating the washing for more than 5 times to ensure that the pH value of the washing liquid is 7, judging the washing liquid to be qualified, pumping the washing liquid of the previous 2 times into another storage tank A, pumping the washing liquid of the other times into another storage tank B, and pumping the washing liquid of the previous 2 times in the next alkali transfer process as the water for the previous 2 times in the next alkali transfer process, wherein the last 3 times of the washing in the alkali transfer process need new purified water or deionized water for washing. Then starting the stirring in the tank A, slowly adding solid sodium hydroxide, then cooling the solid sodium hydroxide to below-15 ℃, and recovering and preparing the sodium hydroxide solution with low mass concentration and producing sodium fluoride.

Example 3

And (3) recovering a sodium hydroxide solution with a preset mass concentration:

putting the rare earth fluoride acid leaching residue containing 100kg of REO into an alkali transfer tank, starting stirring, uniformly mixing, adding 230kg of sodium hydroxide solution with the mass concentration of 50%, starting heating, controlling the temperature to be 100 ℃, supplementing a small amount of water during the period, wherein the specific dosage is determined according to the water loss condition, stopping stirring after the duration time is 60min, standing for 30min, transferring the supernatant into a storage tank A, heating the water to the original liquid level, starting stirring, washing, repeating the washing for more than 5 times to ensure that the pH value of the washing liquid is 7, judging the washing liquid to be qualified, pumping the washing liquid of the previous 2 times into another storage tank A, pumping the washing liquid of the other times into another storage tank B, and pumping the washing liquid of the previous 2 times in the next alkali transfer process as the water for the previous 2 times in the next alkali transfer process, wherein the last 3 times of the washing in the alkali transfer process need new purified water or deionized water for washing. And starting stirring in the storage tank A, slowly adding solid sodium hydroxide, cooling to below 15 ℃ below zero to obtain a sodium hydroxide solution with low mass concentration, transferring the sodium hydroxide solution to an enamel evaporator, and evaporating and concentrating the sodium hydroxide solution to a preset mass concentration.

Example 4

Recovering sodium hydroxide solid:

putting the rare earth fluoride acid leaching residue containing 100kg of REO into an alkali transfer tank, starting stirring, uniformly mixing, adding 230kg of sodium hydroxide solution with the mass concentration of 50%, starting heating, controlling the temperature to be 100 ℃, supplementing a small amount of water during the period, wherein the specific dosage is determined according to the water loss condition, stopping stirring after the duration time is 60min, standing for 30min, transferring the supernatant into a storage tank A, heating the water to the original liquid level, starting stirring, washing, repeating the washing for more than 5 times to ensure that the pH value of the washing liquid is 7, judging the washing liquid to be qualified, pumping the washing liquid of the previous 2 times into another storage tank A, pumping the washing liquid of the other times into another storage tank B, and pumping the washing liquid of the previous 2 times in the next alkali transfer process as the water for the previous 2 times in the next alkali transfer process, wherein the last 3 times of the washing in the alkali transfer process need new purified water or deionized water for washing. And then starting stirring in the storage tank A, slowly adding solid sodium hydroxide to completely dissolve the solid sodium hydroxide, cooling to below-15 ℃ when the fluorine content in the water washing liquid is less than or equal to 30mg/L, performing solid-liquid separation, continuously transferring the recovered sodium hydroxide solution to an enamel evaporator to further concentrate the sodium hydroxide solution to obtain sodium hydroxide solid.

Example 5

And (3) recovering a sodium hydroxide solution with a preset mass concentration:

putting the rare earth fluoride acid leaching residue containing 100kg of REO into an alkali transfer tank, starting stirring, uniformly mixing, adding 200kg of sodium hydroxide solution with the mass concentration of 70%, starting heating, controlling the temperature to be 95 ℃, supplementing a small amount of water during the period, wherein the specific dosage is determined according to the water loss condition, stopping stirring after the duration time is 50min, standing for 30min, transferring the supernatant into a storage tank A, heating the water to the original liquid level, starting stirring, washing, repeating the washing for more than 6 times to ensure that the pH value of the washing liquid is 7, judging the washing liquid to be qualified, pumping the washing liquid of the previous 2 times into another storage tank A, pumping the washing liquid of the other times into another storage tank B, and using the washing liquid of the previous 2 times in the next alkali transfer process, wherein the last 3 times of the washing in the alkali transfer process need new purified water or deionized water for washing. And starting stirring in the storage tank A, slowly adding solid sodium hydroxide, cooling to below 15 ℃ below zero to obtain a sodium hydroxide solution with low mass concentration, transferring the sodium hydroxide solution into an enamel evaporator, and evaporating and concentrating the sodium hydroxide solution to a sodium hydroxide solution with a preset mass concentration.

Example 6

Recovering the high-quality concentration sodium hydroxide solution:

putting the rare earth fluoride acid leaching residue containing 100kg of REO into an alkali transfer tank, starting stirring, uniformly mixing, adding 200kg of a sodium hydroxide solution with the mass concentration of 65%, starting heating, controlling the temperature to be 100 ℃, supplementing a small amount of water during the period, wherein the specific dosage is determined according to the water loss condition, stopping stirring after the duration time is 60min, standing for 30min, transferring the supernatant into a storage tank A, heating the water to the original liquid level, starting stirring, washing, repeating the washing for more than 5 times to ensure that the pH value of the washing liquid is 7, judging the washing liquid to be qualified, pumping the washing liquid of the previous 2 times into another storage tank A, pumping the washing liquid of the other times into another storage tank B, and using the washing liquid of the previous 2 times in the next alkali transfer process, wherein the last 3 times of the washing in the alkali transfer process need new purified water or deionized water for washing. And then starting stirring in the storage tank A, slowly adding solid sodium hydroxide to completely dissolve the sodium hydroxide, and cooling to below-15 ℃ when the fluorine content in the water washing liquid is less than or equal to 30mg/L, and then carrying out solid-liquid separation.

Example 7

Recovering the high-quality concentration sodium hydroxide solution:

putting the rare earth fluoride acid leaching residue containing 100kg of REO into an alkali transfer tank, starting stirring, uniformly mixing, adding 230kg of sodium hydroxide solution with the mass concentration of 50%, starting heating, controlling the temperature to be 120 ℃, supplementing a small amount of water during the period, wherein the specific dosage is determined according to the water loss condition, stopping stirring after the duration time is 30min, standing for 30min, transferring the supernatant into a storage tank A, heating the water to the original liquid level, starting stirring, washing, repeating the washing for more than 5 times to ensure that the pH value of the washing liquid is 7, judging the washing liquid to be qualified, pumping the washing liquid of the previous 2 times into another storage tank A, pumping the washing liquid of the other times into another storage tank B, and using the washing liquid of the previous 2 times in the next alkali transfer process, wherein the last 3 times of the washing in the alkali transfer process need new purified water or deionized water for washing. And then starting stirring in the storage tank A, slowly adding solid sodium hydroxide to completely dissolve the sodium hydroxide, and cooling to below-15 ℃ when the fluorine content in the water washing liquid is less than or equal to 30mg/L, and then carrying out solid-liquid separation.

Comparative example 1

Putting the rare earth fluoride acid leaching residue containing 100kg of REO into an alkali transfer tank, starting stirring, uniformly mixing, adding 230kg of sodium hydroxide solution with the mass concentration of 50%, starting heating, controlling the temperature to be 120 ℃, supplementing a small amount of water during the period, wherein the specific dosage is determined according to the water loss condition, stopping stirring after the duration time is 30min, standing for 30min, transferring the supernatant into a storage tank A, heating the water to the original liquid level, starting stirring, washing, repeating the washing for more than 4 times to ensure that the pH value of the washing liquid is 8.5, pumping the washing liquid of the first 2 times into a storage tank A, pumping the washing liquid of the other times into another storage tank B, using the washing liquid as the washing water of the first 2 times in the next alkali transfer process, wherein the last 3 times of the washing of the alkali transfer process need new purified water or deionized water. And then starting stirring in the storage tank A, slowly adding solid sodium hydroxide to completely dissolve the sodium hydroxide, and cooling to below-15 ℃ when the fluorine content in the water washing liquid is less than or equal to 30mg/L, and then carrying out solid-liquid separation.

Comparative example 2

Putting the rare earth fluoride acid leaching residue containing 100kg of REO into an alkali transfer tank, starting stirring, uniformly mixing, adding 230kg of sodium hydroxide solution with the mass concentration of 50%, starting heating, controlling the temperature to be 120 ℃, supplementing a small amount of water during the period, wherein the specific dosage is determined according to the water loss condition, stopping stirring after the duration time is 30min, standing for 30min, transferring the supernatant into a storage tank A, heating the water to the original liquid level, starting stirring, washing, repeating the washing for more than 3 times to ensure that the pH value of the washing liquid is 7.5, pumping the washing liquid of the first 2 times into a storage tank A, pumping the washing liquid of the other times into another storage tank B, using the washing liquid as the washing water of the first 2 times in the next alkali transfer process, wherein the last 3 times of the washing of the alkali transfer process need new purified water or deionized water for washing. And then starting stirring in the storage tank A, slowly adding solid sodium hydroxide to completely dissolve the sodium hydroxide, and cooling to below-15 ℃ when the fluorine content in the water washing liquid is less than or equal to 30mg/L, and then carrying out solid-liquid separation.

The concentrations of the respective solutions of examples and comparative examples were measured, and the obtained data are shown in Table 1:

table 1: sodium hydroxide mass concentration and sodium fluoride product purity statistical table

As can be seen from Table 1: the embodiment of the invention recovers sodium hydroxide and fluorine from acid leaching residue in the refining and separating process of bastnaesite concentrate, the recovery rate is higher than 98%, and the requirements on the washing times and the washing end point in the comparative example are reduced, so that the recovery rate of sodium hydroxide and the recovery rate of fluorine are obviously reduced, which shows that the conditions of all parameters of the invention are strictly controlled by technology, and the sodium hydroxide solution can be efficiently recovered and prepared and the sodium fluoride product can be efficiently produced.

While specific embodiments of the invention have been described in detail with reference to tables, these should not be construed as limitations on the scope of this patent. Various modifications and changes may be made by those skilled in the art without inventive step within the scope of the appended claims.