Sphalerite dissolution kinetics in acidic environment

Abstract

Sphalerite dissolution kinetics were studied by means of long-term (>500 h) flow-through experiments in the pH range of 1–4.2, at 25, 50 and 70 °C and at three different dissolved O 2 concentrations, from 0.2 to 8.7 mg L −1 to obtain a dissolution rate law useful to predict sphalerite long-term dissolution behavior in environments affected by acid drainage. The main factor affecting the rate of sphalerite dissolution is pH, whose increase results in a decrease in the dissolution rate, whereas rate is independent of dissolved O 2 concentration over the range of 0.2–8.7 mg L −1. In the range of conditions studied, the apparent activation energy was found to be 14.3 ± 1.9 kJ mol −1. A rate law accounting for the effects of pH and temperature on the sphalerite dissolution over this range of conditions is expressed as: R sphalerite = 10 - 6.49 ± 0.02 e - 14.3 ± 1.9 RT a H + 0.54 ± 0.02 where R sphalerite is the sphalerite dissolution rate (mol m −2 s −1), R is the gas constant (kJ mol −1 K −1), T is the temperature (K), and a H + is the activity of H + ion in the solution. X-ray photoelectron spectroscopy (XPS) analyses of the reacted samples furnish evidence of the formation of a surface layer enriched in S on the sphalerite surface during dissolution. The formation of this layer does not exert any passivating effect on sphalerite long-term dissolution.