Silica Scale Technology and Water Conservation. [Recirculating Evaporative Cooling]. PDF Download

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Book Description
Conservation of water at the Los Alamos Scientific Laboratory (LASL) has been accomplished by recirculating evaporative cooling waters. Because of high silica concentration (80 mg/l) in Los Alamos groundwater, the concentration of recirculating water must be carefully controlled to prevent scaling. The most troublesome scale at Los Alamos has been identified as colloidal silica bound in a crystalline matrix of calcium carbonate. Several approaches to controlling this scale are: (1) chemical treatment using a chelate, sequestrant, or threshold approach, (2) softening, or (3) pH control. Silica alone will form deposits when supersaturated. In LASL systems, where silica concentrations are 200 to 240 mg/l, no problems have been observed. However, there is evidence that deposits are forming at slightly higher concentrations. These amorphous silica deposits are not as hard and tenacious as the calcium carbonate--silica scale. Complete external treatment, which combines silica removal and water softening, may be an economically competitive process for scale control. The advantages of slightly reducing the quantity of makeup water and drastically reducing the amount of blowdown water have environmental and conservation implications that may encourage the selection of complete treatment.