Process for leaching rare earth elements

Abstract

Described herein is a process for stepwise leaching of all rare earth elements capable of forming peroxide and superoxide compounds, in particular cerium, lanthanum, neodymium, europium, from minerals containing these elements, namely from bastnaesites, orthites, chevkinites, and britholites.

1 . A process for stepwise leaching of all rare earth elements capable of forming peroxide and superoxide compounds, in particular cerium, lanthanum, neodymium, europium, from minerals containing these elements, namely from bastnaesites, orthites, chevkinites, britholites, which have previously been comminuted to at least the particle size of 75 micrometers, comprising the following steps:
 an initial stage comprising the following steps: a first step of preparing the reaction mixture consisting of a leaching agent, a solvent and mineral raw materials containing rare earth elements; a second step of leaching REE by heating the obtained reaction mixture to a working temperature of 80-100° C. and maintaining it at the given temperature with simultaneous stirring and a pH between 1 and 3; and a third step of subsequently filtering the suspension thus obtained to form the liquid solution of REE compounds and a solid residue;   one or more intermediate stages;   a final stage comprising the following steps: a first step of treating the solution obtained as a result of the previous process steps with air until the divalent iron contained in the solution is completely transformed into trivalent iron; a second step of treating the solution obtained in the previous step with sodium hydroxide at room temperature until a pH between 9 and 12 is reached; a third step of filtering the solution obtained in the previous step and drying the sediment obtained thereby at 90-100° C. for about 4 hours; a fourth step of processing the sediment dried in the previous step with oxalic acid at room temperature, thereby forming a solution; a fifth step of final filtration of the solution obtained in the previous step, thereby forming a solid REE concentrate in pure form, wherein iron trichloride is used as leaching agent and water is used as solvent, and wherein the ratio solid:liquid in the reaction mixture is 1:5, the duration of holding the reaction mixture at the working temperature is at least about 1 hour and all intermediate stages of the process are repetitions of its initial stage, the total number of intermediate stages typically being 2 to 3, the solid residue formed as a result of each respective preceding process stage being used as a starting raw material in each respective subsequent intermediate stage, wherein a reduction-oxidation process takes place parallel to the hydrolysis of iron trichloride, which results in the formation of water-soluble peroxide and/or ozonide compounds of the rare earth elements and iron(II) chloride, so that both the iron and the REE compounds remain in the solution and do not enter in the sediment.   
     
     
         2 . The process according to  claim 1 , wherein the minerals used are constituents of a stockpile material from residues of a previous leaching. 
     
     
         3 . The process according to  claim 1 , wherein the consumption of leaching agent during carrying out the initial stage and each intermediate stage is constant and is from 3 to 20%, preferably 5%, relative to the initial mass of the mineral raw materials. 
     
     
         4 . The process according to  claim 1 , wherein the amount of oxalic acid used in the fourth step of the final stage is equimolar relative to the trivalent iron contained in the dried sediment treated with the oxalic acid. 
     
     
         5 . The process according to  claim 2 , wherein the consumption of leaching agent during carrying out the initial stage and each intermediate stage is constant and is from 3 to 20%, preferably 5%, relative to the initial mass of the mineral raw materials. 
     
     
         6 . The process according to  claim 2 , wherein the amount of oxalic acid used in the fourth step of the final stage is equimolar relative to the trivalent iron contained in the dried sediment treated with the oxalic acid. 
     
     
         7 . The process according to  claim 3 , wherein the amount of oxalic acid used in the fourth step of the final stage is equimolar relative to the trivalent iron contained in the dried sediment treated with the oxalic acid.