Removal of silica from Raft River geothermal water

Lack of sufficient quantities of clean surface or near-surface water at Raft River for cooling purposes dictates that cooled geothermal fluid, effluent from the Raft River 5 MW(e) Pilot Power Plant, must also be used as condenser coolant. Prior testing revealed that a water-treatment system would be required to reduce silica and calcium concentrations of the cooling fluid. The water-treatment system specified was to use dolomitic lime for both pH adjustment and source of magnesium. The dolomitic lime treatment was investigated and found to be inadequate. Subsequent testing was done to find chemical systems that would adequately reduce silica concentrations. Three magnesium and two iron compounds were found which reduced silica to acceptable concentration levels. They are magnesium bicarbonate, magnesium chloride, magnesium sulfate, iron sulfate, and iron chloride. Magnesium oxide, using a two-stage countercurrent process, will also reduce silica to adequate levels