Process for extracting tantalum and niobium from an aqueous acidic solution

Abstract

A process and an installation wherein a ternary system including an aqueous acidic solution, an organic solvent not miscible with water and a thermosensitive hydrotropic agent is used to selectively extract tantalum and optionally niobium by cycling extraction between low-temperature single-phase and high temperature two phase regions in the ternary phase prism far from the critical point.

1 - 16 . (canceled) 
     
     
         17 . A process for extracting, from an aqueous acidic solution, tantalum, in the form of a cationic salt, said process comprising at least the steps of:
 (i) providing, at a first temperature T1, a ternary mixture comprising: a) an aqueous acidic solution containing a mixture of metallic elements including at least tantalum to be extracted, b) an organic solvent not miscible with water, c) a quantity Q1 of a thermosensitive hydrotropic agent comprising a hydrophilic part and a hydrophobic part, T1 being comprised between 15° C. and 35° C. and being inferior to the critical temperature of said ternary mixture, (ii) heating said ternary mixture at a second temperature T2 at which said mixture presents a biphasic structure consisting of an aqueous phase and an organic phase at least partially loaded in at least tantalum, wherein T2 is comprised between 40° C. and 75° C., is superior to the critical temperature of said ternary mixture and is distinct by 15° C. to 50° C. from T1,   (iii) separating, from the biphasic structure obtained in step (ii), said organic phase and said aqueous phase,   (iv) extracting at least tantalum from said organic phase,   wherein:   said ternary mixture of step (i) is in a phase boundary pre-Ouzo zone, said pre-Ouzo zone being characterized as an ultra-flexible surfactant-free micro-emulsion comprising dynamic aggregates of about 20 to 300 molecules bound together,   said hydrophilic part of said hydrotropic agent comprises at least one ethoxy group,   the molarity of said aqueous acidic solution is at least 2M.   
     
     
         18 . The process according to  claim 17 , wherein the concentration of said tantalum in said aqueous acidic solution is comprised between 0.1 g/L and 10 g/L. 
     
     
         19 . The process according to  claim 17 , wherein the molarity of the aqueous acidic solution ranges from 2 M to 12 M. 
     
     
         20 . The process according to  claim 17 , wherein said acidic aqueous solution comprises a strong acid chosen among sulphuric acid and nitric acid. 
     
     
         21 . The process according to  claim 17 , wherein the molarity of said aqueous acidic solution is at least 5M and the process is for selectively extracting tantalum and niobium from said aqueous acidic solution. 
     
     
         22 . The process according to  claim 17 , wherein the amount of said acidic aqueous solution in the ternary mixture of step (i) ranges from 10 to 90 weight % relative to the total weight of the ternary mixture. 
     
     
         23 . The process according to  claim 17 , wherein said organic solvent is chosen among 1-octanol, 2-octanol, methyl isobutyl ketone, cyclohexanone, and tributylphosphate. 
     
     
         24 . The process according to  claim 17 , wherein the amount of said organic solvent in the ternary mixture of step (i) ranges from 5 to 70 weight % relative to the total weight of the ternary mixture. 
     
     
         25 . The process according to  claim 17 , wherein said hydrotropic agent is 1-propoxy-2-propanol or dipropylene glycol n-propyl ether. 
     
     
         26 . The process according to  claim 17 , wherein the amount of said quantity Q1 of the hydrotropic agent in the ternary mixture of step (i) ranges from 10 to 55 weight % relative to the total weight of the ternary mixture. 
     
     
         27 . The process according to  claim 17 , wherein T1 ranges from 20° C. to 30° C. 
     
     
         28 . The process according to  claim 17 , wherein T2 ranges from about 45° C. to 70° C. 
     
     
         29 . The process according to  claim 17 , wherein steps (i) to (iii) are reiterated at least once before step (iv) is carried out and after bringing said ternary mixture back to temperature T1. 
     
     
         30 . The process according to  claim 29 , wherein said process comprises, after step (iii) and before each reiteration of steps (i) to (iii), at least the following sub-steps:
 (1a) cooling the aqueous phase recovered at step (iii) to temperature T1,   (2a) mixing said aqueous phase with said organic solvent and said hydrotropic agent to obtain said ternary mixture, and   (3a) adjusting the amount of said hydrotropic agent in said ternary mixture to said quantity Q1.   
     
     
         31 . The process according to  claim 29 , wherein said process comprises, after step (iii) and before each reiteration of steps (i) to (iii), at least the following sub-steps:
 (1b) cooling the organic phase recovered at step (iii) to temperature T1,   (2b) mixing said organic phase with a new aqueous acidic solution containing a mixture of metallic elements including at least tantalum to be extracted and said hydrotropic agent to obtain said ternary mixture, and   (3b) adjusting the amount of said hydrotropic agent in said ternary mixture to said quantity Q1.   
     
     
         32 . An installation for carrying out the process as defined in  claim 17 , wherein said installation comprises at least:
 a mixing chamber for preparing a ternary mixture comprising a) an aqueous acidic solution containing a mixture of metallic elements including at least tantalum to be extracted, b) an organic solvent not miscible with water, c) a quantity Q1 of a hydrotropic agent comprising a hydrophilic part and a hydrophobic part, said hydrophilic part comprising at least one ethoxy group,   a heating device for heating said ternary mixture,   a cooling device,   means for conveying said aqueous acidic solution, said organic solvent, said thermosensitive hydrotropic agent and said mixture, and   means for controlling at least the flow and the temperature of said solutions and mixture.