Silica phases precipitated, from soluble silicate

In laboratory studies, silica was adsorbed and precipitated by hydroxides of aluminum, iron, manganese, and magnesium, according to Harder (42). After precipitating 15 ppm Al(OH), from a 3 ppm SiO in solution, the residual silica was 0.8 ppm, whereas with 30 ppm aluminum hydroxide, no measurable silica remained. Willey has given an excellent review of the extensive literature on the interaction of silica and alumina in dilute solutions. The low levels of soluble silica reached (39) depended on the particular solid aluminum silicate phase that was formed or present. She studied the interaction at very low concentrations, generally less than 10 ppm, and found that only I ppm SiO is required to initiate the precipitation of 1 ppm of AljOs from solution, and if more than about I ppm AljO, is in solution the silica concentration becomes exceedingly low. 

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