a subsequent step of reducing sulphur in a solid product from step to a minus two ie sulphide valence state with a solution under predetermined contact conditions the process further includes a subsequent step of oxidising sulphur in a solid product from step with a solution under predetermined contact conditions and thereby releasing at least part of the remaining copper in the solid product into the solution as copper ions the process further includes recovering copper from one or more of the solutions from steps and application_number US 49405104 A description the reaction mechanism for bulk chalcopyrite leaching is shown schematically in fig1 and is described stoichiometrically in equations 1 to 4 below with reference to fig1 the initial reaction in the reaction mechanism is an oxidation reaction for sulphur in chalcopyrite equations 1 and 2 are the initial oxidation reaction in the following equations u201c n u201d is an integer greater than 1 12 n u2212 16 fe 3 3 n cufes 2 solid u2192 4 cufe 3 6 s n 2 u2212 solid 3 n u2212 4 cu 2 15 n u2212 20 fe 2 equation 1 3 n u2212 4 o 2 12 n u2212 16 h 3 n cufes 2 solid u2192 4 cufe 3 6 s n 2 u2212 solid 3 n u2212 4 cu 2 3 n u2212 4 fe 2 6 n u2212 8 h 2 o equation 2 the oxidation reaction is shown as cu 1 fe 2 s 1 5 u2212 2 u2192 s n 2 u2212 in fig1 equations 1 and 2 show the initial partial leaching of cu 2 and fe 2 and the formation of polysulfides s n 2 u2212 the oxidation states of cu and fe within chalcopyrite are cu 1.