Process for reducing the concentration of heavy metals in geothermal brine sludge

摘要

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 DEG 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.