Sphalerite dissolution kinetics in acidic environment

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 O2 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 O2 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:imagewhere Rsphalerite 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 aH+ 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.