Home – Home – Jornals – Chemistry for Sustainable Development 2005 number 4

The kinetics of leaching pyrrhotine solutions in sulphuric solutions containing small amount of nitrous acid was investigated. It was shown that pyrrhotine treatment under the given oxidative conditions proceeds through the stages of intensive initial and subsequent slow dissolution. The first stage is likely to correspond to the dissolution of the oxidized layer on sulphide surface and to intensive non-oxidative leaching with the formation of hydrogen sulphide. A decrease in the process rate at the second stage is due to the transition to the oxidative regime of leaching and the formation of a film of difficultly soluble compounds (oxidized iron with oxygen, elemental sulphur) on the reaction surface. The activating action of nitrous acid is likely to be exhibited at the second stage when FeSO₄ solutions are oxidized with molecular oxygen. It was shown experimentally that even small concentration of HNO₂ (0.001 M) at low temperature (293 K) causes a substantial increase in the intensity of regeneration of the active agent of chemical weathering of hypergenesis zone, namely, Fe³⁺ ions. In this connection, the system H₂O + O₂ + HNO₂ + H₂SO₄ can play a substantial part in oxidative processes in sulphide tailings. Pyrite remained almost completely non-solved in this oxidative system within the experiment duration.