Selective Removal of Silica from Silica Containing Brines

Abstract

This invention relates to a method for selective removal of silica and silicon containing compounds from solutions that include silica and silicon containing compounds, including geothermal brines.

We claim: 
     
         1 . A method for selectively removing silica from a brine solution that comprises silica, the method comprising the steps of:
 providing a brine solution that comprises silica;   maintaining the pH of the brine solution at an adjusted pH of between about 4 and 7 and contacting said brine solution with activated alumina at the adjusted pH such that silica present in the brine solution selectively binds to the activated alumina; and   recovering an aqueous product stream from the contacting step, said aqueous product stream having a reduced silica concentration relative to the brine solution.   
     
     
         2 . The method of  claim 1 , further wherein the brine solution at the adjusted pH is contacted with the activated alumina in a column. 
     
     
         3 . The method of  claim 1 , further comprising maintaining the pH of the brine solution at between 4.8 and 5.3 during the contacting step. 
     
     
         4 . The method of  claim 1 , wherein the brine solution that comprises silica is a geothermal brine. 
     
     
         5 . A method for removing silica from an aqueous brine solution that comprises silica, the method comprising the steps of:
 providing an aqueous brine solution that comprises silica and an iron (II) salt;   oxidizing the iron (II) salt to iron (III) hydroxide;   maintaining the pH of the brine solution at between about 4.5 and 6;   contacting the silica and the iron (III) hydroxide for a time sufficient for the silica to attach to the iron (III) hydroxide and form a silica/iron precipitate;   separating the silica/iron precipitate from the aqueous brine solution; and   recovering an aqueous product stream from the separation step, said aqueous product stream having a reduced silica concentration relative to the aqueous brine solution.   
     
     
         6 . The method of  claim 5  wherein the aqueous brine solution is a geothermal brine. 
     
     
         7 . The method of  claim 5  wherein the iron (II) salt is iron (II) chloride. 
     
     
         8 . The method of  claim 5  further wherein the step of oxidizing the iron (II) salt comprises sparging the aqueous brine solution with air. 
     
     
         9 . The method of  claim 5  wherein the pH of the aqueous brine solution is maintained at a predetermined pH by the addition of base. 
     
     
         10 . The method of  claim 5  wherein the pH of the aqueous brine solution is maintained at a predetermined pH by the addition of base selected from calcium oxide or calcium hydroxide. 
     
     
         11 . The method of  claim 5  wherein the pH of the aqueous brine solution is maintained at between about 4.75 and 5.5. 
     
     
         12 . The method of  claim 5  wherein the pH of the aqueous brine solution is maintained at between about 4.9 and 5.3. 
     
     
         13 . The method of  claim 5  wherein the silica concentration of the aqueous product stream is less than 20 ppm. 
     
     
         14 . The method of  claim 5  further comprising the steps of:
 maintaining the pH of the aqueous product stream at between about 4 and 7; 
 supplying the aqueous product stream to a column charged with activated alumina at a pH of between about 4 and 7 such that silica present in the aqueous product stream selectively binds to the activated alumina; and 
 recovering a column product stream having a reduced silica concentration relative to the aqueous product stream. 
 
     
     
         15 . The method of  claim 5  further comprising supplying the aqueous product stream to means for recovering at least one metal selected from lithium, zinc and manganese from said aqueous brine solution. 
     
     
         16 . A method for removing silica from a brine solution comprising silica, the method comprising the steps of:
 providing a brine solution that comprises silica;   contacting the brine solution with an aqueous solution that comprises aluminum chloride to produce a second aqueous solution, said second aqueous solution comprising brine and aluminum chloride;   adjusting and maintaining the pH of the second aqueous solution such that the pH is between about 4.5 and 5.5 to form an aluminosilicate precipitate;   removing the aluminosilicate precipitate that forms from the second aqueous solution; and   recovering an aqueous product stream, said aqueous product stream having a reduced silica concentration relative to the brine solution.   
     
     
         17 . The method of  claim 16  wherein the brine solution is a geothermal brine. 
     
     
         18 . The method of  claim 16  further comprising adding an amorphous aluminosilicate solid to the second solution. 
     
     
         19 . The method of  claim 18  wherein at least 0.25% by weight of the aluminosilicate solid is added to the second solution. 
     
     
         20 . The method of  claim 16  wherein the pH of the second aqueous solution is maintained at between about 4.85 and 5.15.