Dissolution kinetics of stilbite at various temperatures under alkaline conditions

Abstract

Experiments measuring the dissolution rates of stilbite (NaCa2 [Al5Si13O36].14H2O) in pH-buffered solutions were performed in batch reactors at 4, 25, 40 and 60°C. The pH conditions of the buffer solutions ranged from 8.5 to 12.5. The dissolution rates calculated from silicon concentration of the reacting fluid increased with increasing temperature (4-60°C) and pH. The dissolution rates ranged from 3.45 × 10-15 (mol cm-2s-1) at pH 10.7 and 4°C to 1.93 × 10-9 (mol cm-2s-1) at pH 12 and 60°C and were pH dependent. The rate law was established as R = k (aOH-)n, where k is the rate constant, a is the activity of the OH- species and n the reaction order. The n values obtained were, 0.32 at 4°C, 0.35 at 25°C, 0.38 at 40°C and 0.38 at 60°C. Activation energy determined using Arrhenius plot was 48.45 kJ/mol at pH 9 and 30.88 kJ/mol at pH 12.