Selective removal of silica from silica containing brines
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.
1. 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, said oxidizing step comprises sparging the aqueous brine solution with air;
maintaining the pH of the aqueous brine solution at between about 4.5 and 5.5;
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;
recovering an aqueous product stream from the separation step, said aqueous product stream having a reduced silica concentration relative to the aqueous brine solution;
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 silica concentration of less than about 15 ppm.
2. The method of claim 1 wherein the aqueous brine solution is a geothermal brine.
3. The method of claim 1 wherein the iron (II) salt is iron (II) chloride.
4. The method of claim 1 wherein the pH of the aqueous brine solution is maintained at a predetermined pH by the addition of base.
5. The method of claim 1 wherein the pH of the aqueous brine solution is maintained at a predeteimined pH by the addition of base selected from calcium oxide or calcium hydroxide.
6. The method of claim 1 wherein the pH of the aqueous brine solution is maintained at between about 4.75 and 5.5.
7. The method of claim 1 wherein the pH of the aqueous brine solution is maintained at between about 4.9 and 5.3.
8. The method of claim 1 wherein the silica concentration of the aqueous product stream is less than 20 ppm.
9. The method of claim 1 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.
10. The method of claim 1 wherein the column product stream has a silica concentration of less than about 10 ppm.
11. The method of claim 1 wherein the column product stream has a silica concentration of less than about 5 ppm.
12. The method of claim 1 wherein the said oxidizing step comprises sparging the aqueous brine solution with air for a period of at least 10 minutes.
13. The method of claim 1 wherein the said oxidizing step comprises sparging the aqueous brine solution with air for a period of at least 30 minutes.
14. The method of claim 1 wherein the molar ratio of iron (III) to silica is at least about 1:1.
15. The method of claim 1 wherein the molar ratio of iron (III) to silica is at least about 4:1.
16. The method of claim 1 wherein the molar ratio of iron (III) to silica is at least about 7:1.
17. The method of claim 1 further comprising adding flocculent to the aqueous brine solution.
18. The method of claim 1 further comprising regenerating the column charged with activated alumina.
19. The method of claim 1 further comprising a step of monitoring the column product stream to determine loading of the column charged with activated alumina.
20. The method of claim 1 further comprising supplying the aqueous product stream to at least two columns 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.