Relation of Solubility of Chrysotile with pH of Solution under Hydrotheral Conditions

Abstract

Solubility of chrysotile in the solution of various pH was measured under pressure. In the phase diagram of the MgO-SiO2-H2O system already determined by Bowen and Tuttle, the solubilities of silica and magnesia have been neglected up to date. However, small amount of silica (about 1×10-3wt. %) was detected in pure water at 420°C, and solid phase of brucite equivalent to the amount of silica dissolved in chrysotile composition was precipitated.In hydrochloric acid solution, the chrysotile was easily decomposed to magnesium chloride and silica. In the presence of the large amount of chrysotile, however, the solution became weakly acidic by the reaction of brucite in chrysotile with the acid. In this case, the ratio of magnesium to silica in the solution of near pH=6 coincided with that ratio in chrysotile, then one suitable reaction conditon for synthesis of chrysotile would be suggested.In sodium hydroxide solution, solubility of silica from chrysotile was about one twentieth compared to that from α-quartz. From the relation of this solubility with the pH of the solution, the predominant species of silicate ion group in the solution was estimated to be (Si5O12)4- which nearly coincided with (Si3O7)- estimated by Laudise in a solution of Na2O-SiO2-H2O system.