The kinetics of chlorite dissolution

Abstract

A model for the dissolution of chlorite has been developed based on fast ligand assisted proton attack of the alumina tetrahedra within the alumina-silica lattice followed by slower dissolution of the remnant silica lattice. While the rate determining step is within the silica dissolution regime, the rate is a function of the H + and Al 3+ concentrations and the dominant aqueous Al species. Individual rates may be described by a generic rate equation applicable across the spectrum of Al species: r n = k n K n β Al p L q ( 3 p - zq ) a H + 3 p a Al 3 + p 1 + K n β Al p L q ( 3 p - zq ) a H + 3 p a Al 3 + p τ n , where r n is the rate subscripted for the nth Al species, k is the rate constant of the rate controlling step, K is the surface exchange constant, β is the solution stability constant subscripted for the Al species, a is the species activity subscripted for species and raised to the power of the stoichiometry, p and q are stoichiometric coefficients, z is the ligand charge and τ is the fractional coefficient for the precursor of the rate defining step. The observed rate is the sum of the individual rates. When the observed rate is in a domain of dominance for a single aluminium species and in the absence of strong complexing agents such as oxalate, the observed rate is proportional to a H + 3 / a Al 3 + τ n . The model is supported by experimental data for the dissolution of chlorite over a pH range of 3–10 and temperature range 25–95 °C. The results have hydrometallurgical application.