Chemistry of Silica in Cerro Prieto Brines
The precipitation of amorphous silica from synthetic geothermal, brines which resemble the flashed brine at Cerro Prieto has been studied. It was found that part of the dissolved silica quickly polymerizes to form suspended colloidal silica. The colloidal silica flocculates and settles slowly at unmodified brine pH values near 7.35. Raising the pH of the brine to about 7.8 by adding base and stirring for a few minutes causes rapid and complete flocculation and settling. these results have been confirmed in the field using actual Cerro Prieto brine. Both in the laboratory and in the field quaternary amines were found to be effective with some brine compositions but not with others. Polyacrylamides do not work at all. These results suggest the following simple preinjection brine treatment process: age the brine for 10-20 minutes in a covered holding tank, add 20-30 ppm lime (CaO), stir for 5 minutes, and separate the flocculated silica from the brine using a conventional clarifier. The brine coming out of such a process will be almost completely free of suspended solids. The pilot plant tests needed to reduce this conceptual process to practice are discussed. The rate of deposition of silica scale from synthetic brines was separately studied. It was found that a modest decrease in pH could significantly reduce the scaling rate at a reasonable cost. The equilibrium chemistry of Cerro Prieto brine was studied theoretically. These calculations indicate that increasing the brine pH to remove silica might cause some precipitation of carbonate minerals, but also that this problem could easily be eliminated at a reasonable cost if it did arise.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- Earth Sciences Division
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 1048253
- Report Number(s):
- LBL-10166; TRN: US201217%%20
- Country of Publication:
- United States
- Language:
- English
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