Process for the utilization of vanadium bound in chromium ore as vanadium(V) oxide by electrolysis

Abstract

Process for recovering the vanadium present in the chromium ore chromite, as vanadium pentoxide, as a by-product from the vanadium-containing sodium chromate solution produced in the process of preparing sodium chromate and sodium dichromate from said ore, by precipitation of calcium vanadate from the sodium chromate solution, treatment of the precipitate with water and sodium carbonate, sodium bicarbonate, carbon dioxide or sodium carbonate and carbon dioxide, to precipitate calcium carbonate and electrolysis of the solution remaining after separation of the calcium carbonate precipitate, to produce vanadium pentoxide.

We claim:  
     
         1 . Process for recovering the vanadium present in the chromium ore chromite, as vanadium pentoxide, as a by-product from the vanadium-containing sodium chromate solution produced in the process of preparing sodium chromate and sodium dichromate from said ore, which comprises: 
 1. precipitating calcium vanadate from the sodium chromate solution by adding calcium oxide or calcium hydroxide or calcium dichromate or calcium chromate at a pH of 12-13, said pH being established by addition of sodium hydroxide to the sodium chromate solution to give a low-vanadium sodium chromate solution,    2. separating the calcium vanadate precipitate from the solution to form a low vanadium content sodium chromate solution,    3. treating the calcium vanadate precipitate with from 1.5 to 10 times its amount of water, based on the dry weight of the residue precipitate), and (a) at least an amount of sodium carbonate which is stoichiometrically equivalent to the calcium content of the precipitate or an excess of sodium carbonate and an amount of carbon dioxide or sodium bicarbonate sufficient to establish a pH to 8.5-12.3, preferably 9-11, or (b) with a molar amount of sodium bicarbonate which is at least 1.0 times the molar amount of calcium in the precipitate, stoichiometry based on the CO 2  content, or an up to 3-fold molar excess of sodium bicarbonate, or (c) with carbon dioxide in an at least stoichiometric amount based on the calcium content and sodium hydroxide in an amount sufficient to establish a pH of at least 8, to form a calcium carbonate precipitate,    4. separating the calcium carbonate precipitate from the solution,    5. electrolysis of the aqueous solution obtained after step 2 or 4 at 20-50° C. by introducing the solution into the anode chamber of an electrolysis cell which is divided by a diaphragm into an anode chamber and a cathode chamber; the cathode chamber being supplied with an alkalizable aqueous solution, and generating and maintaining a pH of from 1 to 4 within the anode chamber,    6. withdrawing the solution from the anode chamber heating it to a temperature above 80° C. to precipitate vanadium pentoxide and,    7. separating the vanadium pentoxide precipitated in step 6 from the solution and washing the separated vanadium pentoxide with water.    
     
     
         2 . Process according to  claim 1 , wherein any excess carbonate or bicarbonate which has been used in step 3 is recovered as sodium bicarbonate after step 4 and before step 5 by passing carbon dioxide into the solution at a pH of from 7 to 5 and cooling the solution to from about −10 to 20° C. and separating the precipitated sodium bicarbonate from the solution.  
     
     
         3 . Process according to  claim 1 , the alkalizable aqueous solution introduced into the cathode chamber in step 5 is an aqueous solution of sodium chromate, or sodium dichromate, or a mixturethereof.  
     
     
         4 . Process according to  claim 1 , wherein the remaining after separation of the vanadium pentoxide in step 7 is used as pH-regulating agent and as partial replacement for sodium dichromate solution in the furnace clinker dissolution process of the process for producing sodium chromate.  
     
     
         5 . Process according to  claim 1 , wherein the solution in the cathode chamber in step 5 is withdrawn and is returned to the process for producing sodium chromate.  
     
     
         6 . Process according to  claim 1 , wherein the separation step 2 is carried out by filtration or centrifugation.  
     
     
         7 . Process according to  claim 1 , wherein the precipitate separated from the solution in step 2 is washed with water or with water which has been made alkaline by means of sodium hydroxide.  
     
     
         8 . Process according to  claim 1 , wherein, in step 3, the calcium vanadate precipitate is treated with from 2 to 4 times its amount of water.  
     
     
         9 . Process according to  claim 1 , wherein variant c) of step 3 is carried out at a temperature of 50-110° C.  
     
     
         10 . Process according to  claim 1 , wherein the treatment with the 1.3- to 2-fold amount of sodium hydrogen carbonate in variant (a) in step 3 and the treatment in variant (c) are carried out for a time of from about 0.1 to 5 hours.  
     
     
         11 . Process according to  claim 9 , wherein variant c) of step 3 is carried out for a time of from about 0.1 to 5 hours.