Effect of inorganic salt impurities on seeded precipitation of silica hydrate from sodium silicate solution
(School of Metallurgy and Environment, Central South University, Changsha 410083, China)
Abstract: To clarify the precipitation of silica hydrate from the real desilication solutions of aluminosilicate solid wastes by adding seeds and improve integrated waste utilization, the seeded precipitation was studied using synthesized sodium silicate solution containing different inorganic salt impurities. The results show that sodium chloride, sodium sulfate, sodium carbonate, or calcium chloride can change the siloxy group structure. The number of high-polymeric siloxy groups decreases with increasing sodium chloride or sodium sulfate concentration, which is detrimental to seeded precipitation. Calcium chloride favors the polymerization of silicate ions, and even the chain groups precipitate with the precipitation of high-polymeric sheet and cage-like siloxy groups. The introduced sodium cations in sodium carbonate render a more open network structure of high-polymeric siloxy groups, although the carbonate ions favor the polymerization of siloxy groups. No matter how the four impurities affect the siloxy group structure, the precipitates are always amorphous opal-A silica hydrate.
Key words: aluminosilicate; sodium silicate solution; siloxy group; impurity; silica hydrate