Dissolution Kinetics of Silicate Minerals in Aqueous Catechol Solutions

Summary Fine particle samples of silicate minerals and of gibbsite were shaken with solutions of pyrocatechol, 4‐nitro‐pyrocatechol or 3,4‐dihydroxybenzoic acid at pH 9·3–9·7 and 25°C. In 63 days, from 1·4 per cent (illite) to 17·9 per cent (nepheline) of the silica present was dissolved. Except for kaolinite in solutions of the two substituted catechols, the aluminosilicates dissolved incongruently, leaving residues enriched with aluminium. When accumulated amounts of elements (Si, Al, Na, K) dissolved from nepheline were plotted against time on log‐log paper straight lines were obtained. For quartz, kaolinite, and in some cases gibbsite similar plots could be approximated by two straight‐line segments. The plots for microcline and oligoclase may be described by a combination of three‐line segments. Several possible reaction mechanisms are discussed but a mechanism which explains the similar rate profiles has not yet been formulated.