Treatment of Columbia River water with aluminum sulfate and activated silica to coagulate undesirable solids has long been established as a satisfactory method for obtaining high quality process water to cool the Hanford reactors. The activated silica used in this process has been prepared by neutralization of less than 92 per cent of the initial alkalinity of a dilute solution of sodium silicate by mixing with dilute sulfuric acid. This mixture is then aged for a period of time equal to one-fourth to one-half of the gel time of the mixture. The concentration of the resulting activated silica solution is not permitted to exceed 1.6 per cent SiO₂ by weight. This activated silica preparation is presently carried out as a batch process with aging times on the order of one hour. A continuous silica activator recently made commercially available by the Omega Machine Company of Providence, Rhode Island, offers several potential advantages over other activated silica facility designs being considered. This continuous silica activator utilizes neutralization of up to 96 per cent of the initial alkalinity of the sodium silicate. The high percentage of neutralization results in gel times of approximately fifteen minutes for the concentrated solutions (up to 1.6 …