Process for removal of silica from geothermal brine

In a method of recovering energy and minerals from a mixture of geothermal steam and brine produced at a high temperature and pressure from an underground formation, wherein said produced brine is to be reduced to a substantially lower temperature and pressure, said produced brine at said high temperature and pressure having a high total dissolved solids content including dissolved aluminum and ferrous ions and a high concentration of dissolved silica greater than the saturation level of silica in said brine when said brine is at said substantially lower temperature and pressure, said produced brine at said high temperature and pressure having a pH of about 5, the steps of:

• a. adding ammonium hydroxide to said produced mixture of steam and brine at said high temperature and pressure and reacting said ammonium hydroxide with said dissolved aluminum and ferrous ions to form soluble ammonium ions and a precipitated sludge of aluminum and ferrous hydroxides in said brine, said ammonium hydroxide being added in an amount sufficient to raise the pH of the brine to a level wherein a substantial portion of the dissolved silica will be swept out with said sludge such that the concentration of the remaining dissolved silica will be near the saturation level of silica in said brine when said brine is at said substantially lower temperature and pressure,
• b. separating and removing said steam from said brine,
• c. separating and removing said sludge from said brine,
• d. reducing the temperature and pressure of said produced brine to said substantially lower temperature and pressure after the formation of said precipitated sludge.