Measurement and Chemical Modeling of the Solubility of Na2SiO3·9H2O and Na2SiO3 in Concentrated NaOH Solution from 288 to 353 K

Abstract

In order to comprehensively use magnesium and silicon resources existing in serpentine ore, an efficient process for decomposing serpentine by the use of concentrated NaOH solution is proposed at elevated temperature. In this new process, magnesium is obtained as residues with the form of Mg(OH)2 after filtration, while silicon is dissolved in an alkaline solution and then separated by a crystallization operation with the common ion effect of NaOH at relatively low temperature. Solubilities of sodium metasilicate nonahydrate (Na2SiO3·9H2O) and anhydrous sodium metasilicate (Na2SiO3) in NaOH solutions were measured. The experiments were carried out at the temperature range from 288.2 to 313.2 K and 343.2 to 353.2 K for these two solids, respectively. Over the investigated concentration range from 0.0 to 11.2 mol·kg–1, the addition of NaOH caused the solubility of both Na2SiO3·9H2O and Na2SiO3 to decrease due to common ion effect. It was also found that increasing the temperature favored the solubility of sodium metasilicate nonahydrate but depressed the solubility of anhydrous sodium metasilicate in NaOH solutions. A chemical model has been established with newly obtained interaction parameters of the Bromley–Zemaitis model by regressing the experimental solubility of Na2SiO3·9H2O in NaOH solutions from 288.2 to 313.2 K along with the experimental solubility data of Na2SiO3 in NaOH solutions at 353.2 K.