A method for resource recovery and utilization of rare earth industrial precipitation wastewater

Abstract

The present invention provides a method for resource recovery and utilization of rare earth industrial precipitation wastewater. Through processes such as cooling and clarifying rare earths from the wastewater, extracting and separating hydrochloric acid with a chelating extractant mixed system enhanced by isoamyl alcohol for coextraction, converting oxalate radicals into oxalic acid by precipitation, and extracting and purifying oxalic acid, etc., the present invention conducts resource recovery and utilization of a large amount of complex precipitation wastewater in the rare earth industry, realizes the recycling of complex wastewater in the rare earth industry. This method has a simple process, high resource utilization efficiency, high purity of the obtained products which can be directly applied in the process, can greatly reduce pollutant emissions in the wastewater, and can effectively reduce the production cost of rare earths.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth metallurgical industrial wastewater treatment, and particularly relates to a method for resource recovery and utilization of rare earth industrial precipitation wastewater. Background Art

[0002] Rare earths are a collective term for 15 elements such as lanthanides and yttrium in the periodic table. They are non-renewable scarce strategic resources for the development of high-tech and national defense cutting-edge technologies, and are strategic emerging industries that the country focuses on developing. Rare earths have a series of special physical and chemical properties such as light, magnetism, and catalysis. Due to their special atomic structure and extremely rich electron energy levels, they are widely used in industries such as electronic information, petrochemical, metallurgy, machinery, and energy. Moreover, due to their applications in military high-tech such as missiles, smart weapons, navigators, and jet engines, they have attracted much attention and are called the "industrial monosodium glutamate" and the magical "mother of new materials".

[0003] The separation and purification of rare earth elements from each other and the removal of impurities are the main technological processes in the extraction and processing of rare earths. During the rare earth smelting and separation process, carbonate and oxalic acid are used as precipitants for rare earth chloride solution. After the precipitation reaction, insoluble rare earth carbonate and rare earth oxalate are separated from the solution and calcined at high temperature to obtain rare earth oxide products. A large amount of precipitation mother liquor and precipitation washing water are generated during the rare earth chloride precipitation process, collectively referred to as rare earth industrial precipitation wastewater, which accounts for about 80% of the total wastewater volume in the rare earth hydrometallurgy process and is difficult to treat and comprehensively utilize. The disposal prevention and resource utilization of rare earth industrial precipitation wastewater have always been bottleneck problems that particularly require technological breakthroughs in the rare earth industry.

[0004] Rare earth industrial precipitation wastewater is a mixed solution of inorganic acid hydrochloric acid and organic acid oxalic acid. In addition, it also contains a certain amount of rare earths and other soluble metal salts. Among them, the hydrochloric acid concentration is 30 - 90 g / L, the rare earth REO concentration is 50 - 1500 mg / L, and the oxalate concentration is 2 - 50 g / L. The wastewater has strong acidity and complex composition, and oxalic acid belongs to moderately toxic organic substances. Therefore, the pollution index of rare earth industrial precipitation wastewater is very high.

[0005] Currently, for the characteristics of rare earth precipitation wastewater, domestic and foreign rare earth industries have developed treatment methods such as lime neutralization precipitation method, evaporation crystallization method, and ozone oxidation method, mainly for technical routes such as eliminating toxicity and reducing pollution emissions. There is still an urgent need for multi-dimensional breakthroughs in traditional technical methods for the resource recycling of rare earth industrial wastewater.

[0006] ZL201610479890.8 discloses a method for treating rare earth industrial wastewater, which includes the treatment of sodium salt wastewater, magnesium salt wastewater, carbonate precipitation mother liquor, oxalate precipitation mother liquor, and other process wastewater. This method does not involve a method for resource recovery and utilization of rare earth industrial wastewater.

[0007] CN110776128B discloses a treatment and recovery process for rare earth wastewater. The rare earth wastewater is filtered through a quartz sand filter, a microporous filter, and an ultrafiltration device, and operations such as enrichment of rare earth and nitrogen ammonia, rare earth recovery, and nitrogen ammonia absorption are carried out, realizing the enrichment of rare earth ions and nitrogen ammonia in the rare earth wastewater, the recovery of rare earth ions and nitrogen ammonia, and the up-to-standard discharge of the wastewater. This method focuses on the disposal of ammonia nitrogen pollution factors.

[0008] CN109293049A discloses a method for recovering oxalic acid and hydrochloric acid from rare earth wastewater with oxalic acid precipitation. This method includes steps such as waste liquid collection, detection, extraction-separation reaction, reuse of oxalic acid, and reuse of hydrochloric acid. By carrying out an extraction-separation reaction between the rare earth wastewater with oxalic acid and hydrochloric acid and the waste liquid of the P204 and TBD mixed organic phase, oxalic acid and hydrochloric acid products are obtained respectively. After preferentially extracting oxalic acid using the P204 mixed system in this method, the raffinate is used as the hydrochloric acid product, which has the defects of low concentration, high impurity content, and difficulty in utilization.

[0009] CN106892479B discloses a method for recovering oxalic acid and hydrochloric acid from rare earth wastewater with oxalic acid precipitation. First, N235 and octanol are used as extractants to simultaneously extract oxalic acid and hydrochloric acid from the rare earth wastewater with oxalic acid precipitation to obtain a mixed solution of oxalic acid and hydrochloric acid, and then TBP is used as the extractant to extract and separate oxalic acid. This application uses the N235 extraction system to simultaneously extract two acids with completely different properties, oxalic acid and hydrochloric acid. One acid belongs to the easily extractable component, and the other acid belongs to the difficult-to-extract component. Inevitably, there will be problems such as difficulty in extracting or back-extracting one of the acids to be extracted, affecting the resource recovery efficiency. Moreover, N235 belongs to amine extractants, and usually an alkali is required as the back-extracting agent. Using water as the back-extracting agent has limited effect and will cause the accumulation and failure of the organic phase.

[0010] In the process of disposing and utilizing rare earth industrial wastewater, there are mainly defects such as complex process, high cost, and traditional and backward technical routes. The common neutralization precipitation method mainly uses lime milk to be added to adjust the wastewater from acidic to neutral for discharge. The residual rare earth, heavy metal ions, etc. in the wastewater are simultaneously precipitated as neutralization slag, and the beneficial components in the wastewater cannot be recycled resourcefully, and new pollutants, neutralization slag, are generated, and the pollutants change from the liquid phase to the solid phase. Similarly, when treating rare earth wastewater by the oxidation method, an oxidant is added to oxidize the oxalate in the wastewater to carbon dioxide, and the expensive oxalic acid cannot be fully utilized. Some modern methods developed in recent years, including extraction, adsorption and other process methods, usually also have defects such as complex process, no recovery of residual rare earth, low recovery rate of oxalic acid, poor quality and low concentration of the recovered products, and cannot meet the quality control requirements required by the process. Summary of the Invention

[0011] The object of the present invention is to provide a method for the resource recovery and utilization of rare earth industrial precipitation wastewater. The method proposed by the present invention can realize the step-by-step resource recovery of rare earth, hydrochloric acid, and oxalic acid in the wastewater through a series of systematic processes, such as cooling and clarifying the rare earth industrial wastewater to recover the residual rare earth, using a chelating extractant to strengthen the co-extraction system to maximize the recovery and concentration of hydrochloric acid, using calcium compounds to precipitate and recover oxalate and convert calcium oxalate into crude oxalic acid, and purifying oxalic acid with a neutral phosphorus extraction system, so as to realize the comprehensive utilization of complex precipitation wastewater in the rare earth industry and the process cycle.

[0012] To achieve the object of the invention, the technical solution adopted by the present invention is: a method for the resource recovery and utilization of rare earth industrial precipitation wastewater, comprising the following steps:

[0013] S1. After adsorbing and degreasing the rare earth industrial precipitation wastewater with activated carbon, it is injected into a cooling and sedimentation tank to cool down and stand for clarification. Control the cooling temperature and the standing clarification time to precipitate and crystallize the rare earth contained in the wastewater. Perform liquid-solid separation on the rare earth compound obtained by cooling crystallization, and recover the filter residue to obtain rare earth products;

[0014] S2. For the wastewater after clarification, crystallization, and separation to recover rare earth products, perform solvent extraction to recover the hydrochloric acid contained therein; use a mixed co-extraction system with a chelating extractant as the main body to extract hydrochloric acid, and use deionized water to back-extract the loaded organic phase to obtain a concentrated high-purity hydrochloric acid solution;

[0015] S3. For the wastewater after extraction and separation of hydrochloric acid, precipitate and regenerate oxalic acid; add a precipitant to the wastewater to cause a precipitation chemical reaction between the oxalate in the wastewater and the calcium cation in the precipitant to form calcium oxalate precipitation. After suction filtration, dry the calcium oxalate filter cake, add 10M sulfuric acid, control the temperature condition at 70-80 °C, and perform a ripening reaction to decompose calcium oxalate. After the decomposition of calcium oxalate is complete, filter while it is hot, wash the filter residue with water twice to recover the soluble oxalic acid filtrate, and the filter residue is calcium sulfate product;

[0016] S4. Perform solvent extraction and purification on the filtrate containing oxalic acid after separating calcium sulfate; use a tributyl phosphate extraction system to extract oxalic acid, with isooctanol as a phase regulator, and use deionized water to back-extract the loaded organic phase to obtain a high-purity oxalic acid solution.

[0017] Preferably, in step S1, after adsorbing and degreasing the precipitation wastewater with activated carbon, it is injected into a cooling and sedimentation tank to cool down, control the cooling temperature at 0-20 °C, and the standing clarification time at 2-10 days.

[0018] Preferably, the mixed co-extraction system with a chelating extractant as the main body in step S2 is composed of, by volume percentage: LIX64N or LIX65N 10-25%, co-extractor isoamyl alcohol 5-15%, and diluent sulfonated kerosene 60-85%.

[0019] Preferably, the specific steps of solvent extraction for recovering hydrochloric acid in step S2 are as follows: multi-stage countercurrent extraction, with the phase ratio O / A = 1:1 - 3 during the extraction process, temperature < 20°C, time 3 min - 10 min, clarification time 3 - 8 min. After the two-phase separation, the loaded organic phase is subjected to five-stage countercurrent stripping with deionized water. The stripping phase ratio O / A = 6 - 1:1, stripping temperature 30 - 60°C, stripping time 4 min - 8 min, clarification time 3 min. After the two-phase separation, a hydrochloric acid solution is obtained.

[0020] Preferably, the precipitant in step S3 is one or more of calcium oxide, calcium hydroxide, and calcium carbonate.

[0021] Preferably, the specific steps of precipitating and regenerating oxalic acid in step S3 are as follows: adding a precipitant to the wastewater after separating hydrochloric acid, with the addition amount of the precipitant being 1.1 times the stoichiometric ratio, and controlling the stirring time and standing time to be 120 min respectively.

[0022] Preferably, the specific steps of purifying the filtrate containing oxalic acid by solvent extraction in step S4 are as follows: three-stage countercurrent extraction, with the extraction system composed of the following volume percentages: tributyl phosphate 35%, isooctanol 5%, sulfonated kerosene; the phase ratio O / A = 2:1 during the extraction process, extraction time 3 min - 10 min, clarification time 3 - 8 min. After the two-phase separation, the loaded organic phase containing oxalic acid is subjected to three-stage countercurrent stripping with deionized water. The stripping phase ratio O / A = 1:1, stripping temperature 60 - 80°C, stripping time 5 min - 10 min, clarification time 3 min. Finally, a pure oxalic acid solution is obtained.

[0023] In the present invention, for the resource recovery process of residual hydrochloric acid in wastewater, a mixed system with a chelating extractant as the main body and enhanced synergistic extraction as the auxiliary is used. The chelating extractant is LIX64N or LIX65N, which can directly chelate and intercept hydrogen chloride molecules with low molecular weight. Oxalic acid molecules are difficult to extract. It has the process advantages of high chelating extraction efficiency in the easy extraction phase, high separation coefficient between the easy and the difficult, low water solubility, low toxicity, and low price. Isoamyl alcohol is an enhanced synergistic extractant for residual hydrochloric acid, which has a natural affinity for chloride ions in the aqueous phase and can accelerate the chelating extraction process and loading capacity of hydrogen chloride molecules. The loaded organic phase containing hydrochloric acid is stripped and dissociated at a higher temperature to obtain a pure hydrochloric acid with a higher concentration.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: A method for resource recovery and utilization of rare earth industrial precipitation wastewater proposed by the present invention utilizes the principle that the solubility of rare earth decreases synchronously with the decrease in temperature in the solution. Rare earth is separated and recovered from the wastewater by the cooling clarification method, and a chelating extractant mixed system with isopentyl alcohol enhanced co-extraction is prepared to extract and separate hydrochloric acid, convert oxalate precipitation into oxalic acid and extract and purify oxalic acid, etc. The resource recovery and utilization of a large amount of complex precipitation wastewater in the rare earth industry is realized, and the recycling of complex wastewater in the rare earth industry is achieved. The method has a simple process, high resource utilization efficiency, and the obtained product has high purity and can be directly applied in the process, which can greatly reduce the production cost of rare earth. Detailed implementation mode

[0025] The present invention will be further elaborated below in conjunction with embodiments. These embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions noted in the following embodiments are usually carried out according to the conventional conditions in the art or according to the conditions recommended by the manufacturer; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as conventional markets. Any non-substantive changes and substitutions made by those skilled in the art based on the present invention fall within the scope claimed by the present invention.

[0026] Example 1:

[0027] After subjecting rare earth industrial precipitation wastewater with a hydrochloric acid concentration of 45 g / L, a rare earth REO concentration of 180 mg / L, and an oxalate concentration of 28 g / L to activated carbon adsorption and oil separation, it is injected into a cooling sedimentation tank for cooling and static clarification. The cooling temperature is controlled at 15 °C and the static clarification time is 5 days to recover the rare earth products obtained by cooling crystallization and liquid-solid separation. The remaining wastewater is subjected to solvent extraction to recover the hydrochloric acid it contains. The extraction system is prepared as follows: LIX64N + isopentanol + sulfonated kerosene (volume ratios are 15% + 10% + 75% respectively). Five-stage countercurrent extraction is used to extract hydrochloric acid from the wastewater, with the extraction process ratio O / A = 1:2, temperature < 20 °C, extraction time 5 min, and clarification time 5 min. After phase separation, deionized water is used for five-stage countercurrent stripping of the loaded organic phase, with the stripping ratio O / A = 4:1, stripping temperature 50 °C, stripping time 5 min, and clarification time 3 min. After phase separation, a hydrochloric acid solution with a mass concentration of 25% is obtained. For the wastewater after extracting and separating hydrochloric acid, calcium carbonate with a stoichiometric ratio of oxalate of 1.1 times is added as a precipitant, and the stirring time and static time are controlled at 120 min respectively. After the calcium oxalate filter cake is dried, 10 M sulfuric acid is added and the temperature condition is controlled at 80 °C for a ripening reaction to decompose calcium oxalate. After the calcium oxalate is completely decomposed, it is filtered while hot, and the filter residue is washed with water 2 times for recovery. The obtained crude oxalic acid filtrate is subjected to three-stage countercurrent extraction and purification. The extraction system is prepared as follows: tributyl phosphate + isooctanol + sulfonated kerosene (volume ratios are 35% + 5% + 60% respectively). The extraction ratio O / A = 2:1, extraction time 8 min, and clarification time 5 min are controlled. After phase separation, deionized water is used for three-stage countercurrent stripping of the loaded oxalic acid organic phase, with the stripping ratio O / A = 1:1, stripping temperature 70 °C, stripping time 5 min, and clarification time 3 min to obtain a high-purity oxalic acid solution for the rare earth precipitation process.

[0028] Example 2:

[0029] The rare earth industrial precipitation wastewater with a hydrochloric acid concentration of 35 g / L, a rare earth REO concentration of 650 mg / L, and an oxalate concentration of 10 g / L is subjected to activated carbon adsorption and oil separation, and then injected into a cooling sedimentation tank for cooling and static clarification. The cooling temperature is controlled at 10 °C and the static clarification time is 3 days to recover the rare earth products obtained by cooling crystallization and liquid-solid separation. The remaining wastewater is subjected to solvent extraction to recover the hydrochloric acid contained therein. The extraction system is prepared as follows: LIX65N + isopentanol + sulfonated kerosene (volume ratios are 10% + 8% + 82% respectively). Four-stage countercurrent extraction is used to extract hydrochloric acid from the wastewater, and the phase ratio O / A during the extraction process is controlled at 1:3, the temperature is <20 °C, the extraction time is 4 min, and the clarification time is 6 min. After phase separation, deionized water is used for five-stage countercurrent stripping of the loaded organic phase. The stripping phase ratio O / A is 6:1, the stripping temperature is 40 °C, the stripping time is 4 min, and the clarification time is 3 min. After phase separation, a hydrochloric acid solution with a mass concentration of 18% is obtained. For the wastewater after hydrochloric acid extraction and separation, calcium carbonate and calcium oxide composite precipitants with a stoichiometric ratio of oxalate of 1.1 times are added, and the stirring time and static time are controlled at 120 min respectively. After the calcium oxalate filter cake is dried, 10 M sulfuric acid is added and the temperature condition is controlled at 70 °C for a ripening reaction to decompose calcium oxalate. After the calcium oxalate is completely decomposed, it is filtered while it is hot, and the filter residue is washed with water 2 times for recovery. The obtained crude oxalic acid filtrate is subjected to three-stage countercurrent extraction and purification. The extraction system is prepared as follows: tributyl phosphate + isooctanol + sulfonated kerosene (volume ratios are 35% + 5% + 60% respectively). The extraction phase ratio O / A is controlled at 2:1, the extraction time is 4 min, and the clarification time is 4 min. After phase separation, deionized water is used for three-stage countercurrent stripping of the loaded oxalic acid organic phase. The stripping phase ratio O / A is 1:1, the stripping temperature is 60 °C, the stripping time is 7 min, and the clarification time is 3 min. A high-purity oxalic acid solution is obtained for the rare earth precipitation process.

[0030] Example 3:

[0031] After the activated carbon adsorption and oil separation of rare earth industrial precipitation wastewater with a hydrochloric acid concentration of 60 g / L, a rare earth REO concentration of 300 mg / L, and an oxalate concentration of 33 g / L, it is injected into a cooling sedimentation tank for cooling and static clarification. The cooling temperature is controlled at 8 °C and the static clarification time is 8 days to recover the rare earth products obtained by cooling crystallization and liquid-solid separation. The remaining wastewater is subjected to solvent extraction to recover the hydrochloric acid it contains. The extraction system is prepared as follows: LIX64N + isopentanol + sulfonated kerosene (with volume ratios of 22% + 13% + 65% respectively). Seven-stage countercurrent extraction is used to extract hydrochloric acid from the wastewater, and the phase ratio O / A in the extraction process is controlled at 1:1, the temperature is <20 °C, the extraction time is 9 min, and the clarification time is 7 min. After the two-phase separation, deionized water is used for five-stage countercurrent stripping of the loaded organic phase. The stripping phase ratio O / A is 2:1, the stripping temperature is 55 °C, the stripping time is 7 min, and the clarification time is 3 min. After the two-phase separation, a hydrochloric acid solution with a mass concentration of 21% is obtained. For the wastewater after the extraction and separation of hydrochloric acid, a composite precipitant of calcium carbonate and calcium hydroxide with a stoichiometric ratio of oxalate of 1.1 times is added, and the stirring time and static time are controlled at 120 min respectively. After the calcium oxalate filter cake is dried, 10 M sulfuric acid is added and the temperature condition is controlled at 75 °C for the ripening reaction to decompose calcium oxalate. After the complete decomposition of calcium oxalate, it is filtered while it is hot, and the filter residue is washed with water 2 times for recovery. The obtained crude oxalic acid filtrate is subjected to three-stage countercurrent extraction and purification. The extraction system is prepared as follows: tributyl phosphate + isooctanol + sulfonated kerosene (with volume ratios of 35% + 5% + 60% respectively). The extraction phase ratio O / A is controlled at 2:1, the extraction time is 4 min, and the clarification time is 4 min. After the two-phase separation, deionized water is used for three-stage countercurrent stripping of the loaded oxalic acid organic phase. The stripping phase ratio O / A is 1:1, the stripping temperature is 75 °C, the stripping time is 9 min, and the clarification time is 3 min. A high-purity oxalic acid solution is obtained for the rare earth precipitation process.

Claims

1. A method for resource recovery and utilization of rare earth industrial precipitation wastewater, characterized in that, It includes the following steps: S1. After subjecting the rare earth industrial precipitation wastewater to activated carbon adsorption and oil separation, it is injected into a cooling sedimentation tank for cooling and static clarification. Control the cooling temperature and static clarification time to precipitate the rare earth contained in the crystallization wastewater. The rare earth compound obtained by cooling crystallization is subjected to liquid-solid separation, and the filter residue is recovered to obtain rare earth products; S2. For the wastewater after clarification, crystallization and separation and recovery of rare earth products, solvent extraction is carried out to recover the hydrochloric acid contained therein; a mixed synergistic extraction system with a chelating extractant as the main body is used to extract hydrochloric acid, and deionized water is used to back-extract the loaded organic phase to obtain a concentrated high-purity hydrochloric acid solution; S3. For the wastewater after extraction and separation of hydrochloric acid, precipitate and regenerate oxalic acid; add a precipitant to the wastewater to cause a precipitation chemical reaction between the oxalate in the wastewater and the calcium cations in the precipitant to form calcium oxalate precipitate. After suction filtration, the calcium oxalate filter cake is dried, 10M sulfuric acid is added, and the temperature is controlled at 70-80 °C for a ripening reaction to decompose calcium oxalate. After the calcium oxalate is completely decomposed, it is filtered while it is hot. The filter residue is washed with water twice to recover the soluble oxalic acid filtrate, and the filter residue is calcium sulfate product; S4. Solvent extraction and purification is carried out on the filtrate containing oxalic acid after separating calcium sulfate; tributyl phosphate extraction system is used to extract oxalic acid, isooctanol is used as a phase regulator, and deionized water is used to back-extract the loaded organic phase to obtain a high-purity oxalic acid solution; Among them, the mixed synergistic extraction system with a chelating extractant as the main body in step S2 is composed of the following volume percentages: LIX64N or LIX65N 10-25%, synergistic extractant isoamyl alcohol 5-15%, diluent sulfonated kerosene 60-85%; The specific steps of solvent extraction to recover hydrochloric acid in step S2 are: multi-stage countercurrent extraction, the extraction process ratio O / A = 1:1-3, temperature <20 °C, time 3 min - 10 min, clarification time 3-8 min. After the two phases are separated, deionized water is used for five-stage countercurrent back-extraction of the loaded organic phase, the back-extraction ratio O / A = 6-1:1, the back-extraction temperature is 30-60 °C, the back-extraction time is 4 min - 8 min, the clarification time is 3 min, and a hydrochloric acid solution is obtained after the two phases are separated; The specific steps of solvent extraction and purification of the filtrate containing oxalic acid in step S4 are: three-stage countercurrent extraction, the extraction system is composed of the following volume percentages: tributyl phosphate 35%, isooctanol 5%, sulfonated kerosene; the extraction process ratio O / A = 2:1, the extraction time is 3 min - 10 min, the clarification time is 3-8 min. After the two phases are separated, deionized water is used for three-stage countercurrent back-extraction of the loaded oxalic acid organic phase, the back-extraction ratio O / A = 1:1, the back-extraction temperature is 60-80 °C, the back-extraction time is 5 min - 10 min, the clarification time is 3 min, and finally a pure oxalic acid solution is obtained.

2. A method for resource recovery and utilization of rare earth industrial precipitation wastewater according to claim 1, characterized in that, In step S1, after subjecting the precipitation wastewater to activated carbon adsorption and oil separation, it is injected into a cooling sedimentation tank for cooling, and the cooling temperature is controlled at 0-20 °C, and the static clarification time is 2-10 days.

3. A method for resource recovery and utilization of rare earth industrial precipitation wastewater according to claim 1, characterized in that: The precipitant in step S3 is one or more of calcium oxide, calcium hydroxide, and calcium carbonate.

4. A method for resource recovery and utilization of rare earth industrial precipitation wastewater according to claim 1, characterized in that: The specific steps for precipitating and regenerating oxalic acid in step S3 are as follows: A precipitating agent is added to the wastewater after separating hydrochloric acid, and the addition amount of the precipitating agent is 1.1 times the stoichiometric ratio. The stirring time and the standing time are controlled to be 120 minutes respectively.