NL2035520B1

NL2035520B1 - A Method of Recovering Rare Earths from Rare Earth Bioleaching Solution by Solution Structure Transformation

Info

Publication number: NL2035520B1
Application number: NL2035520A
Authority: NL
Inventors: He Huajin; Cao Yuan; Qiu Guanzhou; Yu Hong; He Xiao; Shen Li; Meng Xiaoyu; Zhao Yu; Wang Yaowu; Zhao Hongbo; Xie Hanxiang
Original assignee: Univ Central South; Rising Nonferrous Metals Share Co Ltd; Pingyuan County Huaqi Rare Earths Ind Co Ltd
Priority date: 2022-11-02
Filing date: 2023-08-01
Publication date: 2024-06-06
Also published as: NL2035520A; CN115679131A; CN115679131B

Abstract

Disclosed is a method of recovering rare earths from rare earth bioleaching solution by solution structure transformation. The invented method comprises the following steps: 1) Obtain a bioleaching solution rich in rare earths; 2) Activate the chemical coordination bonds; 3) Break down and reconstitute the chemical coordination bonds; 4) Precipitate and recover the rare earths. The present invention precipitates and recovers the rare earths from their complexes in high efficiency, by exploiting the principles of chemical coordination bond activation, breaking down and reconstitution, and by solution structure transformation-rare earth precipitation. It not only solves the technical difficulty that the rare earth in the bioleaching solution cannot be directly precipitated, but also can remove partial impurity ions at the transformation stage, and thus improve the rare earth precipitation efficiency and product quality. This invention has several advantages, such as high precipitation efficiency, low cost, environment-friendly, easy operation, high overall utilization rate of resources, etc., and thus is of great potential for industrial application.

Description

A Method of Recovering Rare Earths from Rare Earth Bioleaching Solution by Solution

Structure Transformation

Field of Invention

The present invention is established for the field of mineral processing and hydrometallurgy, and specifically involves a method of recovering rare earths from rare earth bioleaching solution by solution structure transformation.

Prior Art

Rare earth elements (REE) are indispensable key raw materials in numerous high-tech areas such as power generation and storage, aerospace, defence military, electronic information, medical health and high-performance materials, etc. Rare earth elements are strategically key metal resources, considered as "mother of all new materials". The sources of rare earths mainly include mineral rare earth, ion type rare earth ore and solid wastes. The mineral rare earth source includes monazite, bastnaesite, xenotime and the like. The ion type rare earth ore is also known as the weathered crust elution-deposited rare earth ore. And the solid wastes include tailings, smelter slags, electronic wastes, spent catalysts and the like. In recent years, one serious challenge faced by the rare earth industry is to overcome the environmental pollution and ecological destruction problems in the development and utilization process of rare earths, and to achieve clean and efficient utilization of rare earths.

As the environmental protection standards rise higher and higher, numerous deficiencies of the conventional rare earth extraction techniques have been gradually exposed. For its advantages of low carbon, environment-friendly and low cost, etc., biohydrometallurgical {bioleaching or bioextraction) has been considered one of the most important directions for future clean and efficient extraction of rare earths, compared to chemical extraction techniques.

Bioleaching leaches out the rare earth elements mainly by the direction actions of microorganisms and the indirectly actions of microbial metabolites. And the rare earth elements are further recovered from the leaching solution, thereby achieving the clean and efficient utilization of rare earths. In contrast to chemical leaching, bioleaching typically operates at conditions of normal temperature and normal pressure. The required conditions of leaching process are mild, with low energy consumption, safe and environment friendly. The process can contributes to environmental pollutant degradation, soil amendment, and ecological remediation. During the processes of microorganism growth, metabolism and leaching, CO: can be efficiently absorbed and pinned down, contributing to "carbon peaking, carbon neutrality". Therefore, it is of great interest to develop biohydrometallurgical techniques for rare earths.

However, during the bioleaching process, the leaching of the rare earths is achieved by microorganisms and their various metabolites through the chemical reactions such as bonding/complexation. By leaching, the rare earth elements are transferred into the bioleaching solution, but they mainly exist in the form of various types of rare earth coordination compounds (complexes), with extremely complicated chemical status. Due to the large bonding energy of the coardination bond, these rare earth complexes are very stable. It is difficult to effectively precipitate and gather rare earths out of the bioleaching solution with conventional precipitants and precipitation methods, which is an important bottleneck and challenge limiting the industrial applications of rare earth biohydrometallurgical techniques.

Summary of the Invention

The present invention provides a method of efficiently recover rare earth elements from rare earth bioleaching solutions through solution structure transformation. This method ensures the precipitation rate of rare earths while also reduces the content of impurity elements, thereby obtaining a rare earth concentrate product of high quality.

The method, provided by this invention, of recovering rare earths from a rare earth bioleaching solution through solution structure transformation comprises the following steps: 1) obtaining a bioleaching solution rich in rare earths; 2) adding H* into the bioleaching solution rich in rare earths of Step 1), so that the pH value of the solution can be adjusted to the specified range, then stirring the bioleaching solution to facilitate the reactions of activating the chemical coordination bonds of the rare earth complexes in the bioleaching solution; 3) adding a solution of transformation agent into the bioleaching solution at the end of Step 2), when the pH value of the bioleaching solution reaches the specified range, stopping the addition of the transformation agent solution, stirring the bioleaching solution to facilitate the reactions, and the transformed bioleaching solution is obtained; 4) allowing the transformed bioleaching solution in Step 3) to stand to separate the solid and liquid phases, so that a clear filtrate solution is obtained; 5) adding a solution of precipitant into the clear filtrate solution obtained at the end of step 4) until the pH value rises to a set range, and then adding seed crystals into the filtrate solution and stirring it to facilitate the reactions, and after the reactions are finished, allowing the filtrate solution stand for aging to separate the solid and liquid phases, dehydrate the precipitates to dry them, and obtaining the rare earth product, the said solution of precipitant being prepared from precipitant and water.

Preferably, in Step 2), the agent adding H* is at least one of sulfuric acid, hydrochloric acid and nitric acid;

Preferably, in said Step 2), the said pH value is set to be 2 - 5. The said stirring of facilitating the reactions is carried out at 30 - 55°C and the reaction time period is 1.5 - 3.5 h.

Preferably, in Step 3), the solution transformation agent is a composition of a calcium- containing compound and an additive, wherein the calcium-containing compound is any one of a calcium-containing oxide, a calcium-containing hydroxide and a calcium-containing inorganic salt.

And the additive is at least one of polyacrylamide, starch, sesbania gum, polyaluminium chloride and polyaluminium sulphate. In the said solution transformation agent, the mass ratio of the calcium-containing compound to the additive is 5: 1 - 10:1.

Preferably, in said Step 3), the solution transformation agent is added in at a constant rate.

The pH value is raised to 3 - 6. The said stirring of facilitating the reactions is carried out at 20 - 50°C and the reaction time period is 2 - 4 h.

Preferably, in said Step 4), the standing time period is 3 - 4 h.

Preferably, in said Step 5),the molar concentration of the precipitant solution is 1 - 3 mol/l;

The pH value is raised to 7.5 - 10.5; The said stirring of facilitating the reactions is carried out at 20 - 50°C. The reaction time period is 2 - 3 h, and the standing time period for aging is 4 - 10 h.

Preferably, in said Step 5), the precipitant is any one of carbonate, bicarbonate, alkali metal oxide or alkali metal hydroxide.

Further preferably, in step 5), the said carbonate is sodium carbonate ; The said bicarbonate is ammonium bicarbonate or sodium bicarbonate ; The said alkali metal oxide is calcium oxide or sodium oxide ; The said alkali metal hydroxide is calcium hydroxide or sodium hydroxide.

Preferably, in said Step 5), the seed crystals are rare earth concentrate with uniform size, and they are added in an amount of 1% - 3% by weight of the rare earth precipitate.

The present invention works as follows:

The present invention first adds H* into the bioleaching solution rich in rare earth complexes.

Through the competing coordination actions between H* and H20 with the rare earth complexes, the coordination bonds of rare earth complexes are activated at a suitable temperature. And then, a transformation agent more reactive with the complex anion and with a higher complexation stability constant is added into the bioleaching solution, leading to the breaking down and reconstitution of the coordination bonds. The rare earth complexes are therefore converted to free rare earths or to be with broken valence bond structure. Through such structural reconstitution of coordination bonds, the bioleaching solution transformation is achieved; The solid and liquid phases of the transformed bioleaching solution are separated. The filtrate is transferred to a precipitation tank. And then a precipitant is added to the filtrate, while a small amount of seed crystals are added into the filtrate to suppress primary nucleation and reduce solution supersaturation. In this way, the crystallization process is regulated to obtain rare earth precipitation product with large particle size and uniform distribution. After the precipitation is finished, the solid and liquid phases are separated, and the solid items are dried by dehydration to obtain high quality rare earth product, and the remained liquid can be used for the regeneration and recycling of leaching agent.

Beneficial Advantages of the Present Invention: 1) The present invention utilizes the principles of activation, breaking down and reconstitution of the coordination bonds to precipitate and recover rare earths out of the bioleaching solution through solution transformation-rare earth precipitation. The present invention is highly efficient, with low cost, and capable of producing a crystalline rare earth precipitate that can be easily obtained by solid-liquid separation; 2) The present invention can remove partial impurity ions at the solution transformation stage, which is advantageous for improving rare earth precipitation efficiency and product quality; 3) In the process of the present invention, after the precipitation and recovery of rare earths is completed, the bioleaching agent can be regenerated and recycled.

This can improve the overall utilization rate of resources and economic benefits. 4) Multiple precipitants are optional in the precipitation stage in the present invention, which breaks through the limitation in the conventional methods that only the precipitants with same cationic as in the leaching agent can be used. By controlling the precipitation conditions and the addition of seed crystals, the high quality rare earth product can be produced; 5) The present invention also has advantages such as green environmental friendliness, high product quality, easy operation, high comprehensive utilization of resources, and good industrial application prospects. The present invention has several advantages, such as environment-friendly, high product quality, easy operation, high overall utilization rate of resources, etc., and thus is of great potential for industrial application.

Detailed Description of the Invention

In order to make the technical solution of the present invention easy to understand, the present invention will now be further described with reference to application cases. It should be noted that the specific application cases described herein are merely illustrative of the present invention and are not intended to limit the present invention.

The leaching solutions obtained in the below application cases and comparative cases are produced mainly by leaching rare earth minerals or secondary resources containing rare earths with the method disclosed in Chinese Patent CN 113293287 A.

Application Case 1

A bioleaching solution rich in rare earths was obtained ; A small amount of sulfuric acid was added to this bioleaching solution, and the pH value of this bioleaching solution was adjusted to 2.0. The this bioleaching solution was stirred to facilitate the reactions at 35°C for 2.5 h, and then a solution of transformation agent was prepared by mixing calcium carbonate and polyacrylamide in ratio of 5:1 by mass, and added into the bioleaching solution until the pH value of the latter solution rose to 3.0. The bioleaching solution was stirred to facilitate the reactions at 35°C for 3.5 h, and the solution was stood for 4 h to separate the solid and liquid phases. The clear filtrate liquid was transferred to a precipitation tank. A bicarbonate solution with a concentration of 1.8 mol/l was prepared and added into the clear filtrate liquid at a constant rate. When the pH value of the filtrate rose to 8.5, the addition of bicarbonate solution was stopped. The filtrate solution was stirred to facilitate the reactions at 40°C. Seeds of 2% rare earth concentrate were added, and the reactions proceeded for 3 h. The filtrate solution was then stood for aging for 6 h. By then,

the solid and liquid phases were separated. By filtering, the rare earth precipitates were obtained.

And by further dehydrating the rare earth precipitates, the rare earth product was obtained. The remainder solution can be used in the regeneration and recycling of the leaching agent. The final precipitation rate (recovery rate) of the rare earth was 98.5%, and a high quality rare earth 5 carbonate concentrate product was obtained.

The concentrations of rare earth elements and aluminium in the bioleaching solution before and after precipitation of this Application Case are shown in Table 1.

Table 1 Concentrations of rare earth element and aluminium in bioleaching solution before and after the precipitation of Application Case 1 ‘Elements Y La Ce Pr Nd Sm Eu Gd

Concentration before precipitation (mg/) 111 196 50.5 496 1748 39.2 3.7 36.7

Concentration after orecipiation (mg/) 18 33 054 083 0.29 34 032 035 “Elements TD Dy Ho _ Er Tm Yb Lu Al

Concentration before orecipitation (mg/) 5.2 243 43 10.6 0.76 6.5 0.74 320.2

Concentration after orecipitation (mg) 0.57 0.76 043 0.03 0.11 1.2 0.16 218.8

Comparative Case 1

A bioleaching solution rich in rare earths was obtained. A conventional precipitation method was performed, in which an ammonium bicarbonate solution of 1.8 mol/l was added into this bioleaching solution at constant rate, until the pH value of the bioleaching solution rose to 8.5.

The reactions proceeded at 40°C for 3 h. The bioleaching solution was stood for aging for 6 h.

The final precipitation rate (recovery rate) of the rare earth was only 1.2%.

Application Case 2

A bioleaching solution rich in rare earths was obtained. A small amount of nitric acid was added to this bioleaching solution, and the pH value of this bioleaching solution was adjusted to 2.5. This bioleaching solution was stirred to facilitate the reactions at 30°C for 3.5 h. And then calcium oxide and sesbania gum were mixed homogeneously in a ratio of 8:1 by mass as the solution of transformation agent, which was added to the bioleaching solution until the pH value of the latter solution rose to 3.0.The solution was then stirred to facilitate the reactions at 45°C for 2.5 h, and then was stood for 3 h to separate the solid and liquid phases. The clear filtrate liquid was transferred to a precipitation tank. A calcium oxide solution (as OH) with a concentration of 1.0 mol/l was prepared and added into the clear filtrate solution at a constant rate. When the pH value of the filtrate solution rose to 9.5, the addition of the calcium oxide solution was stopped.

The filtrate solution was stirred to facilitate the reactions at 35°C. Seeds of 1.5% rare earth concentrate were added, and the reactions proceeded for 2 h. The filtrate solution was then stood for aging for 6 h. By then, the solid and liquid phases were separated. By filtering, the rare earth precipitates were obtained. And by further dehydrating the rare earth precipitates, the rare earth product was obtained. The remainder solution can be used in the regeneration and recycling of the leaching agent. The final precipitation rate (recovery rate) of the rare earth was 99.1%, and a high-quality rare earth oxide product was obtained.

Comparative Case 2

A bioleaching solution rich in rare earths was obtained. A conventional precipitation method was performed, in which a 1.0 mol/l calcium oxide solution (as OH) was added to the bioleaching solution at a constant rate until the pH value of the bioleaching solution rose to 9.5. The reactions proceeded at 35°C for 3 h. The bioleaching solution was then stood for aging for 6 h. The final precipitation rate of the rare earth was only 2.8%.

Application Case 3

A bioleaching solution rich in rare earths was obtained. A small amount of hydrochloric acid was added to this bioleaching solution, and the pH value of this bioleaching solution was adjusted to 3.0. The bioleaching solution was stirred to facilitate the reactions at 50°C for 1.5 h. Then calcium oxide and polyaluminium chloride were mixed homogeneously in a ratio of 10:1 by mass as the solution of transformation agent, which was added to the bioleaching solution until the pH value of the latter solution pH rose to 3.5. The bioleaching solution was then stirred to facilitate the reactions at 45°C for 2.5 h, and then was stood for 3 h to separate the solid and liquid phases.

The clear filtrate liquid was transferred to a precipitation tank. A solution of sodium hydroxide with a concentration of 2.5 mol/l was prepared and added to the clear filtrate liquid at a constant rate.

When the pH value of the filtrate rose to 7.5, the addition of sodium hydroxide solution was stopped. The filtrate solution was then stirred to facilitate the reactions at 30°C. Seeds of 2% of rare earth concentrate were added and the reactions proceeded for 2 h. The filtrate solution was then stood for aging for 4.5 h. By then, the solid and liquid phases were separated. By filtering, the rare earth precipitates were obtained. And by further dehydrating the rare earth precipitates, the rare earth product was obtained. The remainder solution can be used in the regeneration and recycling of the leaching agent. The final precipitation rate (recovery rate) of the rare earth was 97.1%, and a high-quality rare earth oxide product was obtained.

The concentrations of rare earth elements and aluminium in the bioleaching solution before and after precipitation of this Application Case are shown in Table 2.

Table 2 Concentrations of rare earth element and aluminium in bioleaching solution before and after the precipitation of Application Case 3 “Elements NY La Ce Pr Nd Sm Eu Gd

Concentration before precipitation (mg/l) 102 206 459 59.5 175 41 35 407

Concentration after precipitation (mg/l) 0.88 5.3 034 0.23 229 14 0.02 0.15 “Elements Tb Dy Ho Er Tm Yb Lu Al

Concentration before precipitation (mg/l) 8.2 183 23 92 055 55 1.14 3336

Concentration after precipitation (mg/l) 0.07 0.55 0.13 0.03 0 1.2 0.02 292.8

Comparative Case 3

A bioleaching solution rich in rare earths was obtained. A conventional precipitation method was performed, in which a 2.5 mol/l sodium hydroxide solution was added to the bioleaching solution at a constant rate until the pH of the bioleaching solution rose to 7.5. The reactions proceeded at 30°Cfor 3 h. The bioleaching solution was stood for aging for 6 h. The final precipitation rate of the rare earth was only 1.6%.

Application Case 4

A bioleaching solution rich in rare earths was obtained. A small amount of sulfuric acid was added to this bioleaching solution, and the pH value of this bioleaching solution was adjusted 4.0.

The bioleaching solution was stirred to facilitate the reactions at 55°C for 1.5 h. Then, calcium oxide and polymerized aluminium sulphate were mixed homogeneously in a ratio of 6:1 by mass as the solution of transformation agent, which was added to the bioleaching solution until the pH value of the latter solution rose to 5.0. The bioleaching solution was then stirred to facilitate the reactions at 45°C for 2.5 h, and then was stood for 3 h to separate the solid and liquid phases.

The clear filtrate liquid was transferred to a precipitation tank. A sodium bicarbonate solution with a concentration of 2.0 mol/l was prepared and added to the clear filtrate liquid at a constant rate until the pH value of the filtrate rose to 8.5. The filtrate solution was then stirred to facilitate the reactions at 25°C. Seeds of 1% of rare earth concentrate were added and the reactions proceeded for 2 h, and then the filtrate solution was stood for aging for 5.5 h. By then, the solid and liquid phases were separated. By filtering, the rare earth precipitates were obtained. And by further dehydrating the rare earth precipitates, the rare earth product was obtained. The remainder solution can be used in the regeneration and recycling of the leaching agent. The final precipitation rate (recovery rate) of the rare earth was 99.1%, and a high quality rare earth carbonate product was obtained.

Comparative Case 4

A bioleaching solution rich in rare earths was obtained. A conventional precipitation method was performed, in which a 2.0 mol/l sodium bicarbonate solution was added to the bioleaching solution at a constant rate until the pH value of the bioleaching solution rose to 8.5. The reactions proceeded at 25°C for 3 h. The bioleaching solution was stood for aging for 6 h. The final precipitation rate of the rare earth was only 1.8%.

Application Case 5

A bioleaching solution rich in rare earths was obtained. A small amount of hydrochloric acid was added to this bioleaching solution. And the pH value of this bioleaching solution was adjusted to 5.0. This bioleaching solution was stirred to facilitated the reactions at 35°C for 3.0 h. Then, calcium hydroxide and starch were mixed homogeneously in a ratio of 7:1 by mass as the solution of transformation agent, which was added to the bioleaching solution until pH value of the latter solution rose to 8.0. The bioleaching solution was then stirred to facilitate the reactions at 20°C for 2.5 h, and was further stood for 3 h to separate the solid and liquid phases. The clear filtrate liquid was transferred to a precipitate tank. A sodium carbonate solution with a concentration of 1.0 mol/l was prepared and added to the clear filtrate liquid at a constant rate until the pH value of the filtrate rose to 10.0. The filtrate solution was stirred to facilitate the reactions at 45°C. Seeds of 1.5% of rare earth concentrate were added and the reactions proceeded for 2 h, and then the filtrate solution was stood for aging for 5.5 h. By then, the solid and liquid phases were separated.

By filtering, the rare earth precipitates were obtained. And by further dehydrating the rare earth precipitates, the rare earth product was obtained. The remainder solution can be used in the regeneration and recycling of the leaching agent. The final precipitation rate of rare earth was 99.1%, and a high quality rare earth carbonate product was obtained.

The concentrations of rare earth elements and aluminium in the bioleaching solution before and after precipitation of this Application Case are shown in Table 3.

Table 3 Concentrations of rare earth element and aluminium in bioleaching solution before and after the precipitation of Application Case 5 ‘Elements Y La Ce Pr Nd Sm Eu Gd

Concentration before precipitation (mg/l) 122 190 60 445 1825 424 22 41

Concentration after precipitation (mg/l) 1.02 23 04 015 1.89 0.94 0 0.22 “Elements Tb Dy Ho Er Tm Yb Lu Al

Concentration before precipitation (mg/l) 6.5 243 6.2 89 102 82 0.55 306

Concentration after precipitation (mg/l 0 065 0.22 0 0.06 0.82 0 275

Comparative Case 5

A bioleaching solution rich in rare earths was obtained. A conventional precipitation method was performed, in which a 1.0 mol/l sodium carbonate solution was added to the bioleaching solution at a constant rate. When the pH value of the bioleaching solution rose to 10.0, the addition of sodium carbonate solution was stopped. The reactions proceeded at 45°C for 3h and then the bioleaching solution was stood for aging for 6 h. The final precipitation rate of the rare earth was only 1.6%.

Application Case 6

A bioleaching solution rich in rare earths was obtained. A small amount of nitric acid to this bioleaching solution, The pH value of this bioleaching solution was adjusted to 2.5. The bioleaching solution was stirred to facilitate the reactions at 30°C for 3.0 h. And then calcium carbonate and polymerized aluminium sulphate was mixed homogeneously in a ratio of 5:1 by mass as the solution of transformation agent, which was added to the bioleaching solution until the pH value of the latter solution rose to 5.0. Then, the bioleaching solution was further stirred to facilitate the reactions at 45°C for 2.5 h. Next, the bioleaching solution was further stood for 3 h to separate the solid and liquid phases. The clear filtrate liquid was transferred to a precipitation tank. A ammonium bicarbonate solution with a concentration of 1.5 mol/l was prepared and added into the clear filtrate liquid at a constant rate, until the pH value of the filtrate rose to 9.0. The filtrate solution was then stirred to facilitate the reactions at 50°C. Seeds of 1.0% of rare earth concentrate were added and the reactions proceeded for 2 h. The filtrate solution was then stood for aging for 8 h. By then, the solid and liquid phases were separated. By filtering, the rare earth precipitates were obtained. And by further dehydrating the rare earth precipitates, the rare earth product was obtained. The remainder solution can be used in the regeneration and recycling of the leaching agent. The final precipitation rate of rare earth was 98.9%, and a high quality rare earth carbonate product was obtained.

Comparative Case 6

A bioleaching solution rich in rare earths was obtained. A conventional precipitation method was performed, in which a 1.5 mol/l ammonium bicarbonate solution was added to the bioleaching solution at a constant rate. When the pH value of the bioleaching solution rose to 9.0, the addition of ammonium bicarbonate solution was stopped. The reactions proceeded at 50°C for 2 h and then the bioleaching solution was stood for aging for 8 h. The final precipitation of the rare earth was only 5.6%.

Application Case 7

A bioleaching solution rich in rare earths was obtained. A small amount of sulfuric acid to the bioleaching solution and the pH value of the bioleaching solution was adjusted to 2.5. The bioleaching solution was stirred at 35°C for 3.0 h ‚and then calcium carbonate and sesbania gum were mixed homogeneously in a ratio of 6:1 by mass as the solution of transformation agent, which was added to the bioleaching solution until the pH value of the latter solution rose to 3.5.

The bioleaching solution was stirred to facilitate the reactions at 25°C for 2.5 h. The bioleaching solution was then stood for 3 h to separate the solid and liquid phases. The clear filtrate liquid was transferred to a precipitation tank. A sodium carbonate solution with a concentration of 3.0 mol/l was prepared and added to the clear filtrate liquid at a constant rate until the pH value of the filtrate rose to 10.5. The filtrate solution was then stirred to facilitate the reactions at 20°C. Seeds of 1.0% rare earth concentrate, was added to the filtrate solution, and the reactions proceeded for 4 h. The filtrate solution was then stood for aging for 10 h. By then, the solid and liquid phases were separated. By filtering, the rare earth precipitates were obtained. And by further dehydrating the rare earth precipitates, the rare earth product was obtained. The remainder solution can be used in the regeneration and recycling of the leaching agent. The final precipitation rate (recovery rate) of the rare earth was 99.1%, and a high-quality rare earth carbonate product was obtained.

Comparative Case 7

A bioleaching solution rich in rare earths was obtained. A conventional precipitation method was performed, in which a 3.0 mol/l sodium carbonate solution was added to the bioleaching solution at a constant rate. When the pH value of the bioleaching solution rose to 10.5, the addition of sodium carbonate solution was stopped. The reactions proceeded at 20°C for 3 h and then the bioleaching solution was stood for aging for 10 h. The final precipitation rate of the rare earth was only 3.7%.

Application Case 8

A bioleaching solution rich in rare earths was obtained, and a small amount of sulfuric acid was added to this bioleaching solution, so that the pH value of this bioleaching solution was adjusted to 2.5. The bioleaching solution was stirred to facilitate the reactions at 30°C for 3.0 h.

Then, calcium carbonate and polyaluminium chloride were mixed in a mass ratio of 8:1 as the solution of transformation agent, and added to the bioleaching solution until the pH value of the latter solution rose to 4.5. The bioleaching solution was further stirred to facilitate the reactions at 50°C for 2 h, so that the solid and liquid phases were separated. Next, the bioleaching solution was stood for 2 h. The obtained clear filtrate solution was transferred to a precipitation tank. A solution of sadium bicarbonate with a concentration of 1.5 mol/l was prepared and added to the clear filtrate solution at a constant rate until the pH value of the filtrate solution rose to 8.5. The filtrate solution was stirred to facilitate the reactions at 20°C. Seed crystals of 1.0% rare earth concentrate were added to the filtrate solution. The reactions proceeded for 2.5 hours, and then the filtrate solution was stood for 10 hours for the solid and liquid phases to separate. The rare earth precipitates were obtained by filtering, which were further dehydrated and dried to obtain the rare earth product. The remainder solution can be used in the regeneration and recycling of the leaching agent. The final recovery rate of the rare earth was 98.4%, and a high-quality rare earth carbonate product was obtained.

The concentrations of rare earth elements and aluminium in the bioleaching solution before and after precipitation of this Application Case are shown in Table 4.

Table 4 Concentrations of rare earth element and aluminium in bioleaching solution before and after the precipitation of Application Case 8 “Elements ~~ Y La Ce Pr Nd Sm Eu Gd

Concentration before precipitation (mg/l) 99 201 58 44 1901 374 1.9 36.7

Concentration after precipitation (mg/l) 20 35 094 023 208 044 0 0.4 “Elements TD Dy Ho Er Tm Yb Lu Al

Concentration before precipitation (mg/l) 4.9 28 8.8 101 092 59 064 3459

Concentration after precipitation (mg/l) 0.06 0.21 0.34 0.09 0 042 0.04 2952

Comparative Case 8

A bioleaching solution rich in rare earths was obtained. A conventional precipitation method was performed, in which an sodium bicarbonate solution of 1.5 mol/l was added into this bioleaching solution at a constant rate, until the pH value of the bioleaching solution rose to 8.5.

The reactions proceeded at 20°C for 2.5 h. The bioleaching solution was stood for aging for 10 h.

The final precipitation rate of the rare earth was only 1.2%.

Claims

CONCLUSIONS

1. A method for recovering rare earth metals from a biological leachate solution of rare earth metals by solution-structure conversion, the method comprising the steps of: 1) obtaining a biological leachate solution rich in rare earth metals; 2) adding H* to the biological leachate solution rich in rare earth metals of step 1) so that the pH value of the solution can be brought into the specified range, then stirring the biological leachate solution to facilitate the reactions of activating chemical coordination bonds of the rare earth metal complexes in the biological leachate solution; 3) adding a solution of a conversion agent to the biological leachate solution at the end of step 2) when the pH value of the biological leachate solution reaches the specified range, stopping the addition of the solution of the conversion agent, stirring the biological leachate solution to facilitate the reactions whereby the converted biological leachate solution is obtained; 4) allowing the transformed biological leaching solution from step 3) to stand to separate the solid and liquid phases so as to obtain a clear filtrate solution; 5) adding a precipitant solution to the clear filtrate solution obtained at the end of step 4) until the pH value rises to a fixed range, and then adding seed crystals to the filtrate solution and stirring to facilitate the reactions, and after the reactions, allowing the filtrate solution to stand to age to separate the solid and liquid phases, removing water from the precipitate to dry, and obtaining the rare earth metal product, wherein said precipitant solution is prepared from precipitant and water.

2. The method for recovering rare earth metals from a biological rare earth leaching solution by solution-structure conversion according to claim 1, wherein the means for adding H* in step 2) is at least one of sulfuric acid, hydrochloric acid and nitric acid.

3. The method for recovering rare earth metals from a biological leaching solution of rare earth metals by solution-structure conversion according to claim 1, wherein said pH value is adjusted to 2 - 5 and the stirring to facilitate the reactions is carried out at 30 - 55 °C and the reaction time is 1.5 - 3.5 hours.

4. The method for recovering rare earth metals from a biological rare earth leaching solution by solution-structure conversion according to claim 1, wherein the solution of the conversion agent in step 3) is a composition of a calcium-containing compound and an additive, wherein the calcium-containing compound is one of a calcium oxide, a calcium hydroxide and an inorganic calcium salt, and the additive is at least one of polyacrylamide, starch, sesbania gum, polyaluminum chloride and polyaluminum sulfate, wherein the mass ratio of the calcium-containing compound to the additive in the solution is 5:1-10:1.

5. The method for recovering rare earth metals from a biological leaching solution of rare earth metals by solution-structure conversion according to claim 1, wherein the solvent in step 3} is added at a constant rate and the pH value is increased to 3 - 6, the stirring to facilitate the reactions is carried out at 20 - 50°C, and the reaction time is 2 - 4 hours.

6. The method for recovering rare earth metals from a biological rare earth leaching solution by solution-structure conversion according to claim 1, wherein the standing time in step 4) is 3 - 4 hours.

7. The method for recovering rare earth metals from a biological leaching solution of rare earth metals by solution-structure conversion according to claim 1, wherein the molar concentration of the precipitant solution in step 5) is 1 - 3 mol/L and the pH value is increased to 7.5 - 10.5, the stirring to facilitate the reactions is carried out at 20 - 50 °C, the reaction time is 2 - 3 hours, and the aging time is 4 - 10 hours.

8. The method for recovering rare earth metals from a biological rare earth leaching solution by solution-structure conversion according to claim 1, wherein the precipitant in step 5) is one of carbonate, bicarbonate, alkali metal oxide or alkali hydroxide.

9. The method for recovering rare earth metals from a biological rare earth leaching solution by solution-structure conversion according to claim 8, wherein the carbonate in step 5) is sodium carbonate; the bicarbonate is ammonium bicarbonate or sodium bicarbonate; the alkali metal oxide is calcium oxide or sodium oxide; and the alkali metal hydroxide is calcium hydroxide or sodium hydroxide.

10. The method for recovering rare earth metals from a biological rare earth leaching solution by solution-structure conversion according to claim 1, wherein the seed crystals in step 5) are rare earth metal concentrates of uniform size added in an amount of 1% - 3% of the weight of the rare earth metal precipitate.