Low-temperature fused salt electrolysis of quartz

Abstract

A process for preparing silicon comprising the following steps a) fused salt electrolysis of an SiO 2 -containing starting material together with antimony, mercury and sulfur to obtain a decomposed material; b) washing to remove elemental sulfur; c) acid treatment to eliminate foreign ions; d) reduction treatment to reduce mercury and/or antimony salts; e) density separation to separate the silicon from the residual components.

1 . A process for preparing silicon comprising the following steps
 a) fused salt electrolysis of an SiO 2 -containing starting material together with antimony, mercury and sulfur to obtain a decomposed material;   b) washing to remove elemental sulfur;   c) acid treatment to eliminate foreign ions;   d) reduction treatment to reduce mercury and/or antimony salts;   e) density separation to separate the silicon from the residual components.   
   
   
       2 . The process according to  claim 1 , wherein the molar fractions of step a) are selected as follows:
 SiO 2 :S=from 1:4 to 1:6   SiO 2 :Sb=from 1:0.4 to 1:0.6 and/or   SiO 2 :Hg=from 1:1 to 1:1.3.   
   
   
       3 . The process according to  claim 1 , wherein the fused salt electrolysis of step a) is performed at a field strength in the range of from 0.1 to 0.5 V/m. 
   
   
       4 . The process according to  claim 1 , wherein the washing step b) is performed by washing with at least one compound selected from the group consisting of: carbon disulfide, guanidine, thiazole, thiophene, dioxan and mixtures thereof. 
   
   
       5 . The process according to  claim 1 , wherein the acid treatment is performed with a mixture of nitric acid and an acid selected from the group consisting of: sulfuric acid, hydrochloric acid, phosphoric acid, perchloric acid, chloric acid, chlorous acid, hydrobromic acid, bromic acid, and methane acid. 
   
   
       6 . The process according to  claim 1 , wherein the reduction is performed with an aqueous sodium dithionite solution. 
   
   
       7 . The process according to  claim 1 , wherein the density separation is performed by a density centrifugation in trichlorosilane. 
   
   
       8 . The process according to  claim 1 , wherein the fused salt electrolysis is performed in a vessel made from iron. 
   
   
       9 . The process according to  claim 1 , wherein the soluble material is crushed after step a) and/or after step d). 
   
   
       10 . The process according to  claim 1 , wherein a water washing is performed after step c) and/or step d). 
   
   
       11 . The process according to  claim 1 , wherein separated amounts of acids, solvents, sulfur, mercury, mercury compounds, antimony and/or antimony compounds are processed and reused.