A process for purifying and concentrating dilute fluorosilicic acid solution by chemical extraction

Abstract

This invention discloses a process for purifying and concentrating dilute fluorosilicic acid solution using chemical extraction. The main steps are as follows: 1. Extraction: Dilute fluorosilicic acid and extractant are mixed in a certain ratio for chemical extraction. After extraction, the aqueous phase and the organic phase are separated. 2. Back-extraction: The organic phase and back-extraction solution are mixed in a certain ratio. Under certain operating conditions, fluorosilicic acid is back-extracted from the organic phase to obtain a concentrated fluorosilicic acid solution and raffinate. 3. Raffinate treatment: A saturated solution of soluble heavy metal salt is added to the raffinate in a certain ratio, and a chemical reaction is carried out under certain operating conditions. After the reaction is completed, centrifugation is performed to obtain heavy metal sulfate, which is recovered as a byproduct. The organic phase is then subjected to vacuum distillation to separate the extraction aid. The remaining organic matter is further decomposed by vacuum heating to obtain an organic extractant and inorganic acid vapor. The organic extractant is reused, and the inorganic acid vapor is condensed and recovered. This invention has good purification effect, simple process, and the extractant can be recycled.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering, specifically relating to the recycling of fluorosilicic acid, a byproduct of phosphorus chemical enterprises. Background Technology

[0002] Fluorine in the natural environment exists primarily in the form of fluorite and associated phosphate rock. As of 2009, the world's basic fluorite reserves reached 470 million tons, with proven recoverable reserves of 230 million tons (calculated as 100% CaF2). However, the fluorite resources in the United States, Japan, and Western Europe, currently major fluorite consumers, are depleted. my country has proven basic fluorite reserves of 110 million tons, ranking first in the world; and recoverable reserves of approximately 21 million tons, ranking third. However, my country's fluorite mines are characterized by a scarcity of high-grade ore, a prevalence of low-grade ore, a high proportion of difficult-to-process ore, and a scarcity of easily processed ore. Fluorine in phosphate rocks mainly exists as fluorapatite [Ca]. 10 F2(PO4)6] contains fluorine, with a fluorine content between 3% and 4%. According to data from the U.S. Geological Survey in 2017, global phosphate rock reserves are approximately 70 billion tons. Assuming a 3% fluorine content, the fluorine reserves within this rock would be at least 2.1 billion tons, far exceeding fluorite reserves. Therefore, fluorine resources associated with phosphate rock have promising application prospects and strategic value.

[0003] In the wet-process phosphoric acid and phosphate fertilizer industries, fluorine in phosphate rock is mainly recovered in the form of fluorosilicic acid. Fluorosilicic acid is used not only to produce fluoride salts such as sodium fluoride, hydrogen fluoride, aluminum fluoride, and cryolite, but also to prepare silicon-containing compounds such as silicon tetrafluoride and silicon dioxide. In particular, the production of anhydrous hydrogen fluoride using fluorosilicic acid has been industrialized at Guizhou Wengfu Group, reaching an internationally leading level.

[0004] As the main raw material for the production of anhydrous hydrogen fluoride, the concentration of fluorosilicic acid directly affects the cost and energy consumption of the anhydrous hydrogen fluoride production process. The commonly used method for concentrating fluorosilicic acid in production is the concentrated sulfuric acid dehydration method. The lower the concentration of fluorosilicic acid, the more concentrated sulfuric acid is required, the larger the amount of dilute sulfuric acid produced, and the greater the pressure on the company's acid balance and water balance. In addition, other methods reported in literature and patents include phosphoric acid concentration (German patents 1,243,802 and 1,095,859), vacuum falling film evaporation (Chinese patent ZL 2014 1.0062860.8), dry air dehydration and concentration (Chinese patent 202111226699.X), and solvent extraction (Chinese patents 200910264464.2, 201410756767.7, 201510956068.1, 201510955081, 201711337356.4), etc.

[0005] Extraction, as a unit operation for separating liquid mixtures, is widely used in industries such as petrochemicals, hydrometallurgy, rare earth extraction and purification, nuclear industry, industrial wastewater treatment, and pharmaceuticals due to its advantages of high separation efficiency, large processing capacity, and low energy consumption. For example, in the gold industry, extraction technology can be used to purify gold and silver; in the electroplating industry, extraction technology is used to recover copper and zinc from cyanide-containing waste liquids; sulfuric acid can be purified and recovered from rare earth extracts and titanium dioxide hydrolysis waste acid; in the nuclear industry, uranium, plutonium, and thorium are extracted from nuclear materials such as uranium, plutonium, and thorium, and nitric acid is recovered; penicillin extraction, and so on.

[0006] Studies on the extraction of fluorosilicic acid, a byproduct of wet-process phosphoric acid production, are frequently found in Chinese patents. The Nanjing Institute of Soil Science, Chinese Academy of Sciences (Chinese Patent 200910264464.2) used an extractant to purify fluorosilicic acid, removing phosphorus from the acid and indirectly concentrating it. Yunnan Chemical Research Institute and Yunnan Tianan Chemical Co., Ltd. (Chinese Patents 201410756767.7, 201510956068.1, 201510955081, 201711337356.4) used tertiary amines as extractants and alkanes as diluents for solvent extraction of fluorosilicic acid. The extracted organic phase was obtained through thermal decomposition. The extracted quaternary ammonium fluorosilicic acid quaternary salt was dehydrated under reduced pressure, then decomposed under reduced pressure and heat to obtain hydrogen fluoride and silicon tetrafluoride; or ammonia was added to prepare ammonium fluoride and silicon dioxide. Similar to the Nanjing Institute of Soil Science, Chinese Academy of Sciences, Do-Fluoride Chemicals Co., Ltd. (Chinese Patent 201010232881.1) uses C4-10 alcohols (n-butanol, isoamyl alcohol, n-octanol, etc.) as extractants, primarily to extract phosphorus from fluorosilicic acid. The aqueous phase is a low-phosphorus fluorosilicic acid solution. Calcium salts are then added to the aqueous phase to obtain calcium fluorosilicate. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a process technology for purifying and concentrating dilute fluorosilicic acid with readily available raw materials, few auxiliary reagents, simple process, and feasible operation.

[0008] The technical solution of this invention is: a process for concentrating dilute fluorosilicic acid by using an organic base or modified organic base as an extractant and an inorganic acid as a back-extraction agent through chemical extraction and chemical back-extraction, the specific steps of which are as follows:

[0009] (1) Chemical extraction of dilute fluorosilicic acid is performed using an organic base or a modified organic base as an extractant; the organic base is trioctylmethylammonium chloride, triisooctylamine, trioctylamine, or diisooctylamine.

[0010] (2) Chemical extraction of dilute fluorosilicic acid with or without the addition of additives;

[0011] (3) Use inorganic acids as back-extraction agents to chemically back-extract fluorosilicic acid from the extract;

[0012] (4) Add polar or non-polar organic compounds as auxiliaries to the back-extraction agent to chemically back-extract fluorosilicic acid in the extract;

[0013] (5) Treat the raffinate with a chemical treatment method using soluble salts of heavy metals;

[0014] (6) The auxiliary agent is recovered by vacuum distillation;

[0015] (7) The extractant was recovered by decomposition under reduced pressure.

[0016] The dilute fluorosilicic acid comes from a phosphorus chemical production enterprise, with a concentration ranging from 2% to 18%.

[0017] In step (1), the modifier used for the modified organic base is sulfuric acid, nitric acid, hydrochloric acid or phosphoric acid; the operating conditions for modification are: the concentration of the modifier is 1-30%, the ratio of the modifier to the organic base is 2:1-2:5, the temperature is 5-40℃, the rotation speed is 100-600 rpm, the mixing time is 0.5-4h, and the standing time is 1-5h.

[0018] Preferably, the extraction operating conditions are as follows: the concentration of the extractant in the extract solution is 20-100%, the ratio of dilute fluorosilicic acid to the extract solution is 5:1-1:5, the mixing time is 0.5-4h, the standing time is 1-5h, the rotation speed is 100-600 rpm, the temperature is 5-50℃, and the extraction rate is >95% for dilute fluorosilicic acid with a concentration of 2-18%.

[0019] In step (2), the auxiliary agent is carbon tetrachloride, benzene, chloroform, cyclohexane, TBP, MIBK or kerosene.

[0020] In step (3), the stripping agent is nitric acid, hydrochloric acid, phosphoric acid or sulfuric acid.

[0021] Preferably, the back-extraction operating conditions are as follows: the concentration of the back-extracting agent in the back-extracting solution is 20-100%, the ratio of the extracting organic phase to the back-extracting solution is 5:1 to 1:5, the temperature is -10 to 30°C, the rotation speed is 100-600 rpm, the mixing time is 0.5-4 h, and the settling time is 1-5 h. This yields a fluorosilicic acid solution with a concentration of 20-40% and raffinate, with a back-extraction rate >50%.

[0022] The specific operation of step (5) is as follows: after back-extraction, the two phases are separated, and barium chloride, barium nitrate, or a saturated solution of lead nitrate soluble heavy metal salt is added to the raffinate for raffinate treatment; the operating conditions are: the liquid-liquid ratio of inorganic phase to organic phase is 1:5 to 5:1, the temperature is 5 to 50°C, the mixing time is 0.2 to 5 h, the rotation speed is 100 to 600 rpm, and the settling time is 0.3 to 5 h; centrifugation is performed to obtain barium sulfate or lead sulfate, which is recovered as a by-product.

[0023] The specific operation of step (6) is as follows: the organic phase is then subjected to vacuum distillation at a vacuum level of 0.08 to 0.1 MPa and a temperature of 50 to 100°C to separate the extraction aid.

[0024] The specific operation of step (7) is as follows: further reduce the pressure and heat to 200~400℃ to decompose organic extractant and inorganic acid vapor. The organic extractant is reused and the inorganic acid vapor is condensed and recovered. The extractant recovery rate is >80%.

[0025] In the above methods, the concentrations are all mass concentrations, and the liquid-liquid ratios are volume ratios.

[0026] This invention can obtain purified fluorosilicic acid with a concentration of 20-50%. The extractant is recyclable and can be used more than 10 times.

[0027] This invention employs an organic base or modified organic base compound to chemically extract a low-concentration fluorosilicic acid solution, and then uses an inorganic acid as a back-extraction agent to extract the fluorosilicic acid through chemical back-extraction. The purified fluorosilicic acid can be directly fed into an anhydrous hydrogen fluoride production unit, thereby reducing the subsequent production cost of anhydrous hydrogen fluoride and the consumption of concentrated sulfuric acid, improving the effectiveness of existing enterprise production processes, reducing acid balance and water balance pressure, and increasing production and revenue. Attached Figure Description

[0028] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation Example 1

[0029] 58.5 g of 13.16% fluorosilicic acid and 40.8 g of extractant TOA were added to an extractor and placed on a magnetic stirrer at 25°C and 420 rpm for 120 min. The mixture was then transferred to a separatory funnel and allowed to stand for 180 min. An aqueous phase and an organic phase were obtained, with the aqueous phase containing 0.71% fluorosilicic acid. The organic phase was then transferred to a back-extractor, and 10 mL of 98% concentrated sulfuric acid was added at 0°C for back-extraction. A 35.08% fluorosilicic acid solution was obtained. After phase separation, a saturated barium chloride solution was added to the raffinate at a 1:1 liquid-liquid ratio at room temperature to obtain barium sulfate and TOA·HCl. The barium sulfate was obtained by centrifugation and filtration, and was recovered as a byproduct. TOA·HCl was heated under reduced pressure to 220°C to decompose and produce TOA and HCl gases. TOA was reused as the extractant, and HCl was condensed and recovered. Example 2

[0030] 58.4 g of 13.16% fluorosilicic acid, 40.7 g of extractant TOA, and 25 mL of benzene were added to an extractor. The mixture was placed on a magnetic stirrer and reacted at 25°C and 420 rpm for 120 min. Afterward, the mixture was transferred to a separatory funnel and allowed to stand for 180 min to separate the phases. An aqueous phase and an organic phase were obtained, with the aqueous phase containing 0.028% fluorosilicic acid. The organic phase solution was poured into a back-extractor, and 10 mL of 98% concentrated sulfuric acid was added at 10°C for back-extraction, yielding a 29.18% fluorosilicic acid solution. After phase separation, a saturated barium chloride solution was added to the raffinate at a 1:1 liquid-liquid ratio at room temperature to obtain barium sulfate and TOA·HCl + benzene. The resulting product was centrifuged and filtered to obtain barium sulfate, which was recovered as a byproduct. The organic phase TOA·HCl + benzene is separated by vacuum distillation at 0.085 MPa and 50 °C to obtain benzene. The temperature is then directly increased to 220 °C to decompose TOA and HCl gases. TOA is recycled as an extractant, and HCl is condensed and recovered.

Claims

1. A process for purifying and concentrating dilute fluorosilicic acid solution using chemical extraction, characterized in that, The method is: (1) Chemical extraction of dilute fluorosilicic acid is performed using an organic base or a modified organic base as an extractant; the organic base is trioctylmethylammonium chloride, triisooctylamine, trioctylamine, or diisooctylamine. (2) Chemical extraction of dilute fluorosilicic acid with or without the addition of additives; (3) Use inorganic acids as back-extraction agents to chemically back-extract fluorosilicic acid from the extract; (4) Add polar or non-polar organic compounds as auxiliaries to the back-extraction agent to chemically back-extract fluorosilicic acid in the extract; (5) Treat the raffinate with a chemical treatment method using soluble salts of heavy metals; (6) The auxiliary agent is recovered by vacuum distillation; (7) The extractant was recovered by decomposition under reduced pressure; The modifier used in the modified organic base is sulfuric acid, nitric acid, hydrochloric acid or phosphoric acid; the operating conditions for modification are: the concentration of the modifier is 1-30%, the ratio of the modifier to the organic base is 2:1-2:5, the temperature is 5-40℃, the rotation speed is 100-600 rpm, the mixing time is 0.5-4h, and the standing time is 1-5h. The additives are carbon tetrachloride, benzene, chloroform, cyclohexane, TBP, MIBK, or kerosene; The stripping agent is nitric acid, hydrochloric acid, phosphoric acid, or sulfuric acid; The operating conditions for back-extraction are as follows: the concentration of the back-extracting agent in the back-extraction solution is 20-100%, the ratio of the extracting organic phase to the back-extraction solution is 5:1 to 1:5, the temperature is -10 to 30℃, the rotation speed is 100-600 rpm, the mixing time is 0.5-4h, and the standing time is 1-5h, resulting in a fluorosilicic acid solution with a concentration of 20-40% and raffinate, with a back-extraction rate >50%.

2. The process for purifying and concentrating dilute fluorosilicic acid solution by chemical extraction according to claim 1, characterized in that, The dilute fluorosilicic acid comes from a phosphorus chemical production enterprise, with a concentration ranging from 2% to 18%.

3. The process for purifying and concentrating dilute fluorosilicic acid solution by chemical extraction according to claim 1, characterized in that, The extraction conditions are as follows: the concentration of the extractant in the extract solution is 20-100%, the ratio of dilute fluorosilicic acid to the extract solution is 5:1-1:5, the mixing time is 0.5-4 h, the standing time is 1-5 h, the rotation speed is 100-600 rpm, and the temperature is 5-50℃. The extraction rate is >95% for dilute fluorosilicic acid with a concentration of 2-18%.

4. The process for purifying and concentrating dilute fluorosilicic acid solution by chemical extraction according to claim 1, characterized in that, After back-extraction, the two phases are separated. Barium chloride, barium nitrate, or a saturated solution of lead nitrate soluble heavy metal salt is added to the raffinate for raffinate treatment. The operating conditions are as follows: the liquid-liquid ratio of inorganic phase to organic phase is 1:5 to 5:1, the temperature is 5 to 50℃, the mixing time is 0.2 to 5 h, the rotation speed is 100 to 600 rpm, and the settling time is 0.3 to 5 h. After centrifugation, barium sulfate or lead sulfate is obtained and recovered as a by-product.

5. The process for purifying and concentrating dilute fluorosilicic acid solution by chemical extraction according to claim 1, characterized in that, The specific operation of step (6) is as follows: the organic phase is then subjected to vacuum distillation at a vacuum level of 0.08 to 0.1 MPa and a temperature of 50 to 100°C to separate the extraction aid.

6. The process for purifying and concentrating dilute fluorosilicic acid solution by chemical extraction according to claim 1, characterized in that, The specific operation of step (7) is as follows: further reduce the pressure and heat to 200~400℃ to decompose organic extractant and inorganic acid vapor. The organic extractant is reused and the inorganic acid vapor is condensed and recovered. The extractant recovery rate is >80%.

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