CN110344086B

CN110344086B - Method for separating and recovering electrolyte components from fluoride system rare earth electrolysis molten salt slag

Info

Publication number: CN110344086B
Application number: CN201910771676.3A
Authority: CN
Inventors: 赖耀斌; 洪侃; 梁鑫; 李忠岐; 徐建兵
Original assignee: GANZHOU NONFERROUS METALLURGICAL RESEARCH INSTITUTE
Current assignee: GANZHOU NONFERROUS METALLURGICAL RESEARCH INSTITUTE
Priority date: 2019-08-21
Filing date: 2019-08-21
Publication date: 2021-03-30
Anticipated expiration: 2039-08-21
Also published as: CN110344086A

Abstract

The invention discloses a method for separating and recovering electrolyte components from rare earth electrolysis molten salt slag of a villiaumite system. The fluoride electrolyte is directly recovered by a vacuum distillation method, the whole recovery process does not generate secondary pollution, and the separated fluoride electrolyte is directly returned to the rare earth electrolysis process, so that the high-efficiency comprehensive recovery and utilization of rare earth, lithium, fluorine and graphite resources in the rare earth electrolysis molten salt slag which is difficult to treat is further realized.

Description

Method for separating and recovering electrolyte components from fluoride system rare earth electrolysis molten salt slag

Technical Field

The invention relates to the field of metallurgy and environmental protection, in particular to a method for separating and recovering electrolyte components from rare earth electrolysis molten salt slag of a villiaumite system.

Background

The existing preparation methods of rare earth metal (alloy) mainly comprise a molten salt electrolysis method, a calcium thermal reduction method, an intermediate alloy method, a direct reduction-distillation method of rare earth oxide and the like. Among them, the molten salt electrolysis method is widely applied to large-scale industrial production because of its advantages of simple operation, low production cost, uniform product components, good quality, easily controllable process, easy realization of continuity, etc. However, during the process of producing rare earth metals and rare earth alloys by the fused salt electrolysis of the rare earth fluoride-lithium fluoride-rare earth oxide system, a large amount of rare earth electrolysis fused salt slag is generated. The generation of the fused rare earth electrolysis fused salt slag causes the yield of the rare earth in the whole rare earth fused salt electrolysis process to be only about 91-93 percent, and the vast majority of the lost rare earth is in the rare earth electrolysis fused salt slag. The rare earth electrolytic molten salt slag not only contains rare earth and lithium, but also contains a large amount of graphite powder, calcium fluoride, aluminum oxide, ferric oxide and other non-metallic impurities. In addition, the impurity content and rare earth grade of the rare earth electrolytic molten salt slag generated in the process of producing different rare earth and alloy are different, the difference is large, and the rare earth electrolytic molten salt slag belongs to rare earth secondary resources which are difficult to treat and recycle. At present, the annual output of rare earth metals produced by adopting an electrolysis process in China is about 35000-45000 tons, and the produced rare earth electrolysis molten salt slag is about 2200 tons every year. If the valuable components in the electrolytic slag can be fully recovered, great economic benefits can be generated.

The main ideas for treating the rare earth electrolytic molten salt slag at present are as follows: the rare earth fluoride is converted into rare earth oxide by adopting an efficient fluorine fixing agent, so that the separation of the rare earth and fluorine is realized, and on the basis, impurity suppression leaching is considered to produce qualified rare earth oxide. By taking the method as a research idea, a process route such as sodium carbonate roasting, sodium hydroxide roasting, calcium hydroxide roasting, negative pressure heating alkali decomposition method, sodium silicate roasting and the like is formed. However, the processes only pay attention to the recovery of rare earth, but do not comprehensively recover the graphite, fluorine and lithium resources in the rare earth electrolytic molten salt slag, and the process methods have the problems of long process route, large secondary pollution, low comprehensive utilization rate of resources, high cost and the like.

Disclosure of Invention

Aiming at various problems of the existing treatment process of the rare earth electrolysis molten salt slag of the fluorine salt system, the invention aims to provide a method for separating and recovering electrolyte components from the rare earth electrolysis molten salt slag of the fluorine salt system, fluoride electrolyte is directly recovered by a vacuum distillation method, secondary pollution is not generated in the whole recovery process, the separated fluoride electrolyte directly returns to the rare earth electrolysis process, and the high-efficiency comprehensive recovery and utilization of rare earth, lithium, fluorine and graphite resources in the rare earth electrolysis molten salt slag which is difficult to treat is further realized.

In order to achieve the technical purpose, the invention provides a method for separating and recovering electrolyte components from fluoride salt system rare earth electrolysis molten salt slag.

Preferably, the fluoride system rare earth electrolysis molten salt slag is rare earth fluoride-lithium fluoride-rare earth oxide system molten salt electrolysis molten salt slag generated in the process of producing rare earth metals and rare earth alloys.

Preferably, the rare earth electrolysis molten salt slag is crushed to have a particle size of 50-500 meshes, preferably 50-100 meshes.

Preferably, the vacuum distillation conditions are as follows: the distillation temperature is 700-1600 ℃, and the preferred distillation temperature is 1000-1100 ℃; the distillation time is 1-12h, preferably 3-8 h; the degree of vacuum is 1-100Pa, preferably 1-10 Pa.

Preferably, the residual distillation slag of the rare earth electrolysis molten salt slag after vacuum distillation comprises the following treatment processes: and (3) dissolving the distillation slag by hydrochloric acid to obtain rare earth leachate and graphite slag, further removing impurities from the rare earth leachate, precipitating and firing to obtain a rare earth oxide product, and further removing impurities from the graphite slag by acid dissolution to obtain graphite powder.

Compared with the prior art, the invention has the advantages that:

the process recovers fluorine, rare earth and lithium resources in the rare earth electrolytic molten salt slag in the forms of rare earth fluoride and lithium fluoride through vacuum distillation (in the prior art, the rare earth fluoride in the slag is firstly converted into rare earth oxide, and then the rare earth is recovered in the form of rare earth oxide), realizes high-value utilization of the rare earth, fluorine and lithium resources in the rare earth electrolytic molten salt slag, avoids secondary pollution of fluorine in the slag to the environment in the recovery process (a large amount of fluorine-containing waste residues and wastewater can be generated in the prior art), and has the advantages of short process flow (the processes of batching, alkali-transfer roasting and crushing are omitted), simplicity in operation, low acid and alkali consumption, environmental friendliness, low production cost, high comprehensive utilization rate of resources, high comprehensive recovery value and the like.

The method for treating the rare earth electrolytic molten salt slag can realize the clean separation of fluoride electrolyte from rare earth oxide, graphite and other impurities, break through the traditional thought that the rare earth electrolytic molten salt slag only recovers the rare earth, and further realize the efficient comprehensive recovery and utilization of the rare earth, lithium, fluorine and graphite resources in the rare earth electrolytic molten salt slag on the basis of realizing the recovery purpose of the fluoride electrolyte. The method has the advantages of green and environment-friendly process, short process flow, low cost, high comprehensive utilization rate of resources and high comprehensive recovery value, and is very suitable for large-scale industrial popularization and application.

Drawings

FIG. 1 is a flow chart of the separation and recovery process of rare earth electrolysis molten salt slag.

FIG. 2 is an XRD comparative analysis chart before and after vacuum distillation of rare earth electrolytic molten salt slag.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

The invention will now be further described with reference to the following examples, which are intended to illustrate the invention but not to limit it further.

The rare earth electrolytic molten salt slag used in the embodiment of the invention comprises the following main components in percentage by weight: REO-38.76%, Li₂O-5.73％，F-20.40％，C-30.12％，Fe₂O₃-4.21％，SiO₂-0.7％，Al₂O₃-1.61％，CaO-2.49％。

Fluoride electrolyte was recovered by vacuum distillation, and fluoride recovery was used as an evaluation criterion for separation effect.

The recovery rate is fluoride volatilization amount/total fluoride electrolyte amount in the electrolytic slag multiplied by 100 percent

Example 1

The rare earth electrolytic molten salt slag is put into a vacuum distillation tank, the influence of the vacuum degree in the furnace on the recovery rate of fluoride electrolyte is examined under the conditions that the vacuum distillation temperature is 1100 ℃, the material granularity is 50 meshes, and the distillation time is 4 hours, and the results are shown in table 1.

TABLE 1 influence of vacuum degree on fluoride electrolyte recovery

Example 2

The rare earth electrolytic molten salt slag is put into a vacuum distillation tank, the influence of the distillation temperature on the recovery rate of fluoride electrolyte is examined under the conditions that the vacuum degree is 5Pa, the material granularity is 50 meshes and the distillation time is 4 hours, and the results are shown in Table 2.

TABLE 2 influence of distillation temperature on fluoride electrolyte recovery

Example 3

The rare earth electrolytic molten salt slag is put into a vacuum distillation tank, the influence of the distillation time on the recovery rate of fluoride electrolyte is examined under the conditions that the vacuum distillation temperature is 1100 ℃, the material granularity is 50 meshes and the vacuum degree is 5Pa, and the results are shown in Table 3.

TABLE 3 influence of distillation time on fluoride electrolyte recovery

Example 4

The rare earth electrolytic molten salt slag is put into a vacuum distillation tank, the influence of the material granularity on the recovery rate of fluoride electrolyte is examined under the conditions that the vacuum distillation temperature is 1100 ℃, the distillation time is 6 hours and the vacuum degree is 5Pa, and the results are shown in Table 4.

TABLE 4 influence of material particle size on fluoride electrolyte recovery

Example 5

Vacuum distillation:

and (3) putting the rare earth electrolytic molten salt slag into a vacuum distillation tank, performing tests under the conditions that the vacuum distillation temperature is 1100 ℃, the distillation time is 6 hours, the material granularity is 100 meshes, and the vacuum degree is 5Pa, wherein the recovery rate of the fluoride electrolyte reaches 95.3%, and the obtained fluoride electrolyte is directly returned to the rare earth electrolysis process for use. XRD comparative analysis of the electrolytic slag and the distilled product is shown in FIG. 2. As can be seen from FIG. 2, the electrolytic slag is mainly NdF₃、PrOF、NdF₂、NdOF、Nd₂Ce₂O₃F₃LiF and C, and after primary vacuum distillation of vacuum distillation, the condensate is mainly NdF₃、LiF、PrF₃No other impurities are found, and NdF in the distillate₃、LiF、PrF₃The diffraction peak of (D) is sharper, indicating NdF₃、LiF、PrF₃Is enriched.

And (3) treating distillation residues:

carrying out hydrochloric acid preferential dissolution on the distillation residues, leaching the rare earth with a leaching rate of 99.3% under the conditions that the acid leaching temperature is 80 ℃, the acid leaching time is 1h, and the acid leaching end point pH is 4.0, precipitating the rare earth under the conditions that the adding amount of oxalic acid is 1.2 times of the mass of the rare earth, the precipitation temperature is 80 ℃, and the precipitation end point pH is 2.0, filtering and drying the obtained rare earth oxalate, and firing for 2h at 850 ℃ to obtain rare earth oxide. And (3) removing impurities from graphite slag obtained by preferential dissolution of hydrochloric acid under the conditions that the pH value of an acid solution is 0.5 and the acid dissolution time is 2h, and filtering, washing and drying insoluble solids to obtain graphite powder. The total rare earth yield of the whole process is up to 98.21%, the lithium recovery rate is up to 95%, the fluorine recovery rate is more than or equal to 95%, and the graphite recovery rate is more than or equal to 98%.

Claims

1. A method for separating and recovering electrolyte components from fluoride system rare earth electrolysis molten salt slag is characterized in that: crushing the rare earth electrolytic molten salt slag, performing vacuum distillation on the crushed rare earth electrolytic molten salt slag, collecting fluoride electrolyte after the vacuum distillation is finished, and directly returning to the rare earth electrolysis process;

the fluoride system rare earth electrolysis molten salt slag is rare earth fluoride-lithium fluoride-rare earth oxide system molten salt electrolysis molten salt slag generated in the process of producing rare earth metal and rare earth alloy through molten salt electrolysis;

crushing the rare earth electrolysis molten salt slag until the particle size is 50-100 meshes;

the vacuum distillation conditions are as follows: the distillation temperature is 1000-1100 ℃; the distillation time is 3-8 h; the vacuum degree is 1-10 Pa.

2. The method for separating and recovering electrolyte components from the fluoride salt system rare earth electrolysis molten salt slag according to claim 1, characterized in that: the residual distilled slag after the rare earth electrolytic molten salt slag is subjected to vacuum distillation comprises the following treatment processes: and (3) dissolving the distillation slag by hydrochloric acid to obtain rare earth leachate and graphite slag, further removing impurities from the rare earth leachate, precipitating and firing to obtain a rare earth oxide product, and further removing impurities from the graphite slag by acid dissolution to obtain graphite powder.