It is concluded that silica coagulation with simple aluminum-based agents is effective, simple, and compatible with other industrial processes.
Some process optimization was performed for coagulant concentration and operational pH. In Phase IV, sodium aluminate emerged as an effective coagulant for silica, and the most attractive of more » those tested to date because of its availability, ease of use, and low requirement for additional chemicals. Lime-soda water softening and the precipitation of magnesium hydroxide were shown to be too limited in terms of effectiveness, speed, and energy consumption to be considered further for the present application. In Phase III, more detailed study of process conditions for aluminum chloride coagulation was undertaken. Some analysis was made of the molecular nature of the precipitated floc, which may aid in process improvements. In fact, the less exotic coagulants proved to be more efficacious for reasons not yet fully determined. In Phase II, it was decided that treatment of source or make up water was more appropriate, and that higher dosing with coagulants delivered promising results. A second example is a system with requirements to: Reduce Ni from 25 to < 2.38 mg / I Reduce Cr from 210 to < 1.71 mg / I Flow rate of 100 GPM. This does not include labor, sludge transportation or disposal costs. In Phase I, a screening of many typical as well as novel coagulants was carried out using concentrated cooling tower water, with and without flocculation aids, at concentrations typical for water purification with limited results. The estimated yearly operating cost saving using Electrocoagulation in place of chemical coagulation is 43,500.00 per year. The formation of silica scale is a problem for thermoelectric power generating facilities, and this study investigated the potential for removal of silica by means of chemical coagulation from source water before it is subjected to mineral concentration in cooling towers.
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