CN108893607B - Method for recovering rare earth in ammonium-free rare earth mother liquor by removing impurities and precipitating step by step - Google Patents

Method for recovering rare earth in ammonium-free rare earth mother liquor by removing impurities and precipitating step by step Download PDF

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CN108893607B
CN108893607B CN201810998759.1A CN201810998759A CN108893607B CN 108893607 B CN108893607 B CN 108893607B CN 201810998759 A CN201810998759 A CN 201810998759A CN 108893607 B CN108893607 B CN 108893607B
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rare earth
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ammonium
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CN108893607A (en
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秦磊
王观石
彭陈亮
邓振乡
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Jiangxi University of Science and Technology
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
    • C22B3/44—Treatment or purification of solutions, e.g. obtained by leaching by chemical processes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B21/00—Obtaining aluminium
    • C22B21/0015—Obtaining aluminium by wet processes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B59/00—Obtaining rare earth metals
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Abstract

The invention relates to a method for recovering rare earth in ammonium-free rare earth mother liquor by step-by-step impurity removal and precipitation, which adopts ammonium-free precipitator calcium oxide (magnesium) to remove impurities and precipitate, the impurity removal and precipitation process is divided into two times, and a small amount of precipitator is added for the first time, so that a high-quality product is produced, namely a final product; adding excessive precipitant again for the second time to make the precipitate completely and carry a certain amount of alkaline impurities, which is called middling; and returning the middlings to the separation liquid in the last step for continuous sedimentation to form a loop only for returning and utilizing the precipitated products and the separation liquid. The invention solves the problem of ammonia nitrogen pollution of the rare earth mine, and simultaneously returns the intermediate solid to the previous operation section, thereby not only ensuring the full recovery of the rare earth, but also providing alkaline substances for the previous operation section, reducing the dosage of calcium oxide or magnesium oxide serving as a precipitator in the whole operation and saving the production cost.

Description

Method for recovering rare earth in ammonium-free rare earth mother liquor by removing impurities and precipitating step by step
Technical Field
The invention relates to a method for recovering rare earth from ammonium-free rare earth mother liquor by adopting a step-by-step impurity removal and step-by-step precipitation process, which is suitable for recovering rare earth mother liquor in an in-situ ore leaching process of an ionic rare earth mine and belongs to the field of hydrometallurgy.
Background
The ionic rare earth ore can not be obtained by physical ore dressing methods such as gravity separation, magnetic separation, electric separation and the like because of the special properties of the ionic rare earth ore, and can only be obtained by a chemical leaching method. The development of the mineral leaching agent goes through the process of developing sodium chloride into ammonium sulfate, but with the large use of the ammonium sulfate, the large surplus of the ammonium salt is found to cause eutrophication pollution of rare earth mines and surrounding water bodies. At present, new ammonium-free mineral leaching agents, such as magnesium sulfate, calcium sulfate and the like, are researched and used, a large amount of ammonium-free leaching mother liquor can be obtained, and a new ammonium-free impurity removal and precipitation process is urgently needed for treatment.
For the leaching mother liquor of the ionic rare earth, the conventional treatment method is an impurity removal precipitation method at present. The impurity-removing precipitant also goes through the process of developing ammonium bicarbonate from oxalic acid. However, with the stricter and stricter environmental requirements, the use of oxalic acid and ammonium bicarbonate is limited, and the research and development of novel ammonium-free impurity-removing precipitator and impurity-removing precipitation process are urgent.
At present, cations such as aluminum, rare earth, calcium, magnesium and the like exist in the ammonium-free rare earth mother liquor, and based on the difference of the solubility among aluminum hydroxide, rare earth hydroxide and calcium (magnesium) hydroxide, the aluminum hydroxide, rare earth hydroxide and calcium (magnesium) hydroxide are found to be precipitated sequentially along with the increase of alkalinity, so that the aim of separating the three cations can be achieved by controlling the pH value in the solution.
Disclosure of Invention
The invention aims to solve the problem of ammonia nitrogen pollution of rare earth mines and adopts calcium (magnesium) oxide without ammonium precipitant to remove impurities and precipitate. According to the existing research, when a saturated solution of calcium oxide (magnesium oxide) is used as a precipitator, aluminum hydroxide and rare earth hydroxide obtained by precipitation are flocculent, the solid settling time is long, solid-liquid separation is not easy to carry out, and the required solution is large in volume and is not suitable for industrial application. The invention takes calcium oxide (magnesium) solid as precipitant, which can provide alkalinity and can be used as seed crystal of aluminum hydroxide and rare earth hydroxide to facilitate crystallization. However, because the solubility of the calcium oxide (magnesium) solid is low, when the addition amount is too small, the product precipitation is incomplete, and the final recovery rate is influenced; after the excessive addition is carried out once, hydroxide precipitation of cations can be generated in the solution, and the product quality is influenced; when the control is accurately carried out at the critical point, the control difficulty is higher, and the reaction time is longer. The invention divides the impurity removal and precipitation process into two times, and a small amount of precipitator is added for the first time, so that a high-quality product is produced, which is called as a final product; and adding excessive precipitant again for the second time to ensure that the precipitate is completely precipitated and carries a certain amount of alkaline impurities, namely middling. And returning the middlings to the separation liquid in the last step for continuous sedimentation to form a loop only for returning and utilizing the precipitated products and the separation liquid.
The invention aims to provide a method for recovering rare earth in ammonium-free rare earth mother liquor by removing impurities and precipitating step by step, and the method solves the problem of ammonia nitrogen pollution of rare earth mines.
The technical scheme of the invention is as follows: a method for removing impurities and precipitating to recover rare earth in ammonium-free rare earth mother liquor step by step comprises the following steps:
step one, testing concentration:
testing the molar concentration C of aluminum ions in the mother liquor of the non-ammonium leachingAlAnd the molar concentration C of rare earth ionsRE；
Step two, calculating the theoretical dosage g/L:
according to chargeCalculating the dosage of calcium oxide or magnesium oxide required for precipitating aluminum ions according to formula (1) to obtain the theoretical dosage M of the precipitated aluminum ionsAl(ii) a Calculating the dosage of calcium oxide or magnesium oxide required for precipitating rare earth ions according to the formula (2) to obtain the theoretical dosage M of the precipitated rare earth ionsRE；
Figure BDA0001782463840000021
Figure BDA0001782463840000022
In formulas (1) and (2): mrIs the molar mass of magnesium oxide or calcium oxide;
step three, preliminary precipitation of aluminum:
adding M into the mother liquor of non-ammonium leaching1And 0.6M of a solid of magnesium oxide or calcium oxideAl≤M1≤1.0MAlStirring for more than 3h to obtain a solid-liquid mixture with the pH of 5.0-5.5, and performing solid-liquid separation to obtain a separation liquid containing rare earth, aluminum and calcium or magnesium ions and an aluminum hydroxide solid product;
step four, removing excessive aluminum:
adding M into the separated liquid obtained in the third step2And 0.3M of a solid of magnesium oxide or calcium oxideAl≤M2≤0.5MAlStirring for more than 2h to obtain a solid-liquid mixture with the pH of 6.0-6.5, performing solid-liquid separation to obtain a separation liquid containing rare earth and magnesium ions and a solid mixture of aluminum hydroxide and rare earth hydroxide, and returning the solid mixture of aluminum hydroxide and rare earth hydroxide to the third step to be mixed with the ammonium-free leaching mother liquor;
step five, primarily precipitating rare earth:
adding M into the separated liquid obtained in the fourth step3And 0.6M of a solid of magnesium oxide or calcium oxideRE≤M3≤0.9MREStirring for more than 3h to obtain a solid-liquid mixture with the pH of 7.3-8.3, and performing solid-liquid separation to obtain a separation solution containing a small amount of rare earth ions and a large amount of calcium or magnesium ions and a target product, namely a rare earth hydroxide solid product;
step six, excessive precipitation of rare earth:
adding M into the separated liquid obtained in the step five4And 0.2M of a solid of magnesium oxide or calcium oxideRE≤M4≤0.5MREStirring for more than 2h to obtain a solid-liquid mixture with the pH of 9.0-10.0, performing solid-liquid separation to obtain a separation liquid containing calcium or magnesium ions and a solid mixture of calcium hydroxide or magnesium hydroxide and rare earth hydroxide, and returning the solid mixture of calcium hydroxide or magnesium hydroxide and rare earth hydroxide to the fifth step to be mixed with the separation liquid obtained in the fourth step;
seventhly, recycling separation liquid:
and returning the separation liquid obtained in the sixth step to a liquid preparation pool, and using dilute sulfuric acid to adjust the slurry to the pH value of 5-6 for continuous use as an ore leaching agent.
According to the invention, an ammonium-free precipitator is adopted in the process of recovering rare earth elements from the mother liquor, so that the problem of ammonia nitrogen pollution caused by ammonium salt precipitation adopted in the existing industry is avoided; aluminum is removed step by step and rare earth is precipitated step by step, and calcium oxide and magnesium oxide can be used as seed crystals, so that the precipitated crystal form is more perfect and is easier to filter; but also can ensure that the purity of the obtained aluminum hydroxide and rare earth hydroxide products is higher; the intermediate solid product is returned to the solution in the previous operation section, so that the sufficient recovery of aluminum and rare earth can be ensured, the alkaline substance can be provided for the previous operation section, the dosage of calcium oxide or magnesium oxide serving as a precipitator in the whole operation is reduced, and the production cost is saved.
Detailed Description
The invention carries out experiments (unpublished experiments) in a certain rare earth mining area, and prepares a representative black-searching ionic rare earth mining sample by mixing the mining samples from different places on site. Magnesium sulfate with the mass concentration of 4% is adopted for leaching the ore sample to obtain ammonium-free leaching mother liquor, and the mother liquor is subjected to a fractional impurity removal and precipitation test. The specific implementation steps are as follows:
step one, testing concentration:
testing the molar concentration C of aluminum ions in the mother liquor of the non-ammonium leachingAlIs 2.5 mmol/L and the rare earth ion molar concentration CRE17.8 mmol/L;
step two, calculating theoretical dosage:
calculating the theoretical amount M of magnesium oxide required for precipitating aluminum ions according to the formula (1)Al0.15 g/L, the amount M of magnesium oxide required to precipitate the rare earth ions was calculated according to formula (2)RE1.068 g/L;
Figure BDA0001782463840000031
Figure BDA0001782463840000032
in formulas (1) and (2): mrIs the molar mass of magnesium oxide of 40 g/mol;
step three, preliminary precipitation of aluminum:
adding M into the mother liquor of non-ammonium leaching1Stirring 0.11 g/L of magnesium oxide for 4h to obtain a solid-liquid mixture with pH of 5.22, and performing solid-liquid separation to obtain a separation liquid containing rare earth, aluminum and magnesium ions, wherein the solid is an aluminum hydroxide product;
step four, removing excessive aluminum:
adding M into the separated liquid obtained in the third step2Stirring the solid magnesium oxide solid of 0.06 g/L for 3h to obtain a solid-liquid mixture with the pH value of 6.12, performing solid-liquid separation to obtain a separation liquid containing rare earth and magnesium ions, wherein the solid is a mixture of aluminum hydroxide and rare earth hydroxide, and returning the solid mixture of the aluminum hydroxide and the rare earth hydroxide to the third step to be mixed with the ammonium-free leaching mother liquor;
step five, primarily precipitating rare earth:
adding M into the separated liquid obtained in the fourth step3Stirring 0.65 g/L of magnesium oxide for 4h to obtain a solid-liquid mixture with the pH of 7.55, and carrying out solid-liquid separation to obtain a separation liquid containing a small amount of rare earth ions and a large amount of magnesium ions, wherein the solid is a rare earth hydroxide product;
step six, excessive precipitation of rare earth:
adding M into the separated liquid obtained in the fifth step4Magnesium oxide of 0.38 g/L was stirred for 3 hours to give a solid-liquid mixture having a pH of 9.10, and the solid-liquid separation was carried outSeparating to obtain a separation liquid containing magnesium ions, wherein the solid is a mixture of magnesium hydroxide and rare earth hydroxide; returning the solid mixture of magnesium hydroxide and rare earth hydroxide to the step five, and mixing the solid mixture with the separation liquid obtained in the step four;
step seven, recycling the separation liquid:
and returning the separation liquid obtained in the sixth step to a liquid preparation pool, and using dilute sulfuric acid to adjust the slurry to the pH value of 5-6 for continuous use as an ore leaching agent.
The test effect is as follows:
after a fractional impurity removal and precipitation test, respectively roasting the aluminum product and the rare earth product to obtain Al2O3Grade 96.18% and Al2O3The recovery rate is 98.54 percent, the REO grade of impurities is 1.11 percent, and the REO recovery rate is 0.10 percent; the REO grade is 93.26 percent, the REO recovery rate is 99.79 percent, and the impurity Al is obtained2O3Grade 0.06%, Al2O3The recovery rate of the rare earth product is 1.46 percent. Meets the national standard requirements of rare earth products.

Claims (1)

1. A method for removing impurities, precipitating and recovering rare earth in ammonium-free rare earth mother liquor step by step is characterized by comprising the following steps:
step one, testing concentration:
testing the molar concentration C of aluminum ions in the mother liquor of the non-ammonium leachingAlIs 2.5 mmol/L and the rare earth ion molar concentration CRE17.8 mmol/L;
step two, calculating theoretical dosage:
calculating the theoretical amount M of magnesium oxide required for precipitating aluminum ions according to the formula (1)Al0.15 g/L, the amount M of magnesium oxide required to precipitate the rare earth ions was calculated according to formula (2)RE1.068 g/L;
Figure FDA0002370781620000011
Figure FDA0002370781620000012
formula (1),(2) The method comprises the following steps: mrIs the molar mass of magnesium oxide of 40 g/mol;
step three, preliminary precipitation of aluminum:
adding M into the mother liquor of non-ammonium leaching1Stirring 0.11 g/L of magnesium oxide for 4h to obtain a solid-liquid mixture with pH of 5.22, and performing solid-liquid separation to obtain a separation liquid containing rare earth, aluminum and magnesium ions, wherein the solid is an aluminum hydroxide product;
step four, removing excessive aluminum:
adding M into the separated liquid obtained in the third step2Stirring the solid magnesium oxide solid of 0.06 g/L for 3h to obtain a solid-liquid mixture with the pH value of 6.12, performing solid-liquid separation to obtain a separation liquid containing rare earth and magnesium ions, wherein the solid is a mixture of aluminum hydroxide and rare earth hydroxide, and returning the solid mixture of the aluminum hydroxide and the rare earth hydroxide to the third step to be mixed with the ammonium-free leaching mother liquor;
step five, primarily precipitating rare earth:
adding M into the separated liquid obtained in the fourth step3Stirring 0.65 g/L of magnesium oxide for 4h to obtain a solid-liquid mixture with the pH of 7.55, and carrying out solid-liquid separation to obtain a separation liquid containing a small amount of rare earth ions and a large amount of magnesium ions, wherein the solid is a rare earth hydroxide product;
step six, excessive precipitation of rare earth:
adding M into the separated liquid obtained in the fifth step4Stirring 0.38 g/L of magnesium oxide for 3h to obtain a solid-liquid mixture with the pH value of 9.10, carrying out solid-liquid separation to obtain a separation liquid containing magnesium ions, wherein the solid is a mixture of magnesium hydroxide and rare earth hydroxide;
step seven, recycling the separation liquid:
returning the separation liquid obtained in the step six to a liquid preparation pool, and using dilute sulfuric acid to adjust the slurry to the pH value of 5-6 for continuous use as an ore leaching agent;
the REO recovery rate is 99.79 percent.
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