Abstract: A process is provided for reducing the silica content in silica-rich geothermal brine having dissolved heavy metals, particularly from brine which is flashed from a high natural pressure to a reduced pressure to convert some of the brine into steam, the flashing causing the brine to become supersaturated in silica. The process comprises combining a base material with the brine, in the brine flashing stage, to increase the brine pH from its natural range of about 5 to 5.5 to a range of between about 6.2 and about 6.6, with a pH of about 6.4 being preferred. The added base, which is preferably selected from ammonia, sodium or calcium hydroxide and sodium sulfide or polysulfide, reacts with heavy metals, notably iron, copper and lead in the brine to form a finely divided, insoluble compound or compounds which function as seed crystals onto which supersaturated amounts of silica are precipitated from the brine. The base may be added to the brine in an amount of between about 200 and about 400 ppm by weight.

Abstract: A process is provided for reducing the total concentration of heavy metals, notably lead, copper and zinc, naturally occurring in silica-rich sludge precipitated from geothermal brine in a brine handling system such as a geothermal brine electric generating plant. The process includes washing the sludge with hot water to displace any brine entrapped in the sludge, dewatering the washed sludge and leaching the silicious solids residue with hydrochloric acid having a concentration of between about 2 and about 9 weight percent and an acid-to-sludge weight ratio between about 0.10 and about 0.33. The acid-sludge mixture is heated to a temperature of at least about 50.degree. and the leaching time is at least about one hour. The leaching solution is separated from the leached sludge and the solids residue are washed with water. Preferably the water used in both washing steps is condensate of steam derived from the geothermal brine. Effluent from the process is preferably combined with the brine for reinjection.

Abstract: A process for regenerating media filters used to filter geothermal brine, especially flashed and clarified, silica-rich brine, comprises flowing steam through the filter in a backflush direction at a rate and for a time duration agitating the filter media and filtered-out material. The process includes, preferably after the steam flow is stopped, flowing brine, for example, filtered brine, through the filter in the backwash direction to flush out the material loosened and broken up by the steam scour and restratify the media bed components, and may include partially draining the filters prior to the steam scour. Preferably, the steam used for the steam scour is low pressure steam obtained from low pressure flashing of the brine being filtered. Steam flow rates are preferably between about 2 and about 10 SCFM per square foot of filter cross-sectional area in the region of the filter media; steam flow rate is preferably about 5 minutes after any steam quenching has ceased.

Abstract: A method is provided for combining a high pH steam condensate with a flow of a acidic geothermal brine from which the steam is extracted so as to inhibit the formation of suspended particulate matter, such as heavy metal sulfides, calcium carbonate and iron hydroxide, by the chemical reacting of such impurities as hydrogen sulfide and ammonia in the condensate with such impurities as heavy metals, iron and calcium in the brine. The method includes acidifying the steam condensate, preferably by hydrochloric acid, to reduce the pH to between about 7 and about 4.5 and then combining the acidified condensate with the brine. In a silica crystallizer stage in which flashed brine is contacted with a silica seed material to cause silica removal from the brine, the treated condensate is combined with the brine in a low pressure crystallizer upstream of brine clarification and reinjection stages.

Abstract: Ammonium hydroxide is added to a mixture of high-temperature, high-pressure geothermal steam and brine to raise the pH of the brine to between 6.0 and 7.0 and precipitate out a gelatinous sludge of aluminum and iron hydroxides. The hydroxide sludge is suspended in the brine and sweeps out enough dissolved silica so that the temperature and pressure of the brine can be reduced with little, if any, formation of silica scale. Various metals and ammonium hydroxide may then be recovered from the brine, the ammonium hydroxide being recycled in the process.