Acid pressure oxidation of pyrite: reaction kinetics

The pressure oxidation (H 2SO 4-O 2) kinetics of narrow-sized pyrite particulates were experimentally determined in the temperature range 140–180°C and pressure range 5–20 atm. The oxidation kinetics were found to follow a shrinking core model, with the surface chemical reaction as the rate-controlling step. The reaction proceeds to completion only at temperatures exceeding 160°C, but at temperatures below 160°C the formation of liquid elemental sulphur blocks the grain surface and eventually terminates the reaction before completion. The activation energy was found to be 46.2 kJ mol −1 between 140 and 160°C, and 110.5 kJ mol −1 between 160 and 180°C. The reaction order with respect to oxygen pressure was found to depend on temperature and pressure. First order dependency was found at 140–160°C/5–20 atm and at 160–180°C/5–10 atm. The order becomes 0.5 at elevated temperatures and pressures (160–180°C/10–20 atm). Finally, appropriate rate equations were developed for the two temperature ranges.