Behavior of dissolved silica in parent solution at the formation of calcium carbonate.

Abstract

The authors have studied experimentally on the coprecipitation of dissolved silica with calcium carbonate (calcite or aragonite) and on the influence of silica dissolved in a parent calcium bicarbonate solution on the crystal form of calcium carbonate precipitated from the parent solution. The coprecipitation of dissolved silica with calcium carbonate is affected significantly by the crystal form of precipitated calcium carbonate and by the presence of sodium chloride in a parent solution. That is, dissolved silica is more easily coprecipitated with aragonite than with calcite. The presence of dissolved silica in a parent solution favors the formation of calcite and inhibits that of aragonite. The amounts of silica coprecipitated with calcite and also with aragonite increase with increasing concentration of sodium chloride, that is, with increasing value of ionic strength in the parent solution. This trend is observed at the coprecipitation of undissociated chemical species with calcium carbonate.