Removal of H2S by metal ferrites produced in the purification of metal-bearing waste water. Study of the reaction mechanism

Waste water polluted with heavy metals can be successfully purified by precipitation of the metals from an alkaline solution containing iron (II), giving rise to a ferrite sludge. The solid metal ferrites obtained in this manner can be used to remove hydrogen sulphide from a gas stream. Based on a Taguchi experimental design, ferrite solid particle and pore size, and the temperature resulting in maximum retention of H sub(2)S by the solid were optimised. Under the optimum conditions, predicted by the method, each gram of ferrite was able to retain 0.274 g H sub(2)S. In addition, a ferrite containing a known lead concentration, obtained by the precipitation method under optimal conditions of pH, temperature and Fe/Pb ratio, was used to study the exothermic H sub(2)S retention reaction. The chemical reaction occurring between the ferrite and the H sub(2)S was investigated by characterisation of the compounds before (Pb sub(0.04)Fe super(II) sub(0.96) Fe super(III) sub(2)O sub(4).nH sub(2)O solids composed of Pb sub(x)Fe sub(3-x)O sub(4), magnetite Fe sub(3)O sub(4) and hydrated lead oxide PbO sub(n).H sub(2)O) and after (PbS, PbSO sub(4), S, FeS sub(2) and alpha -FeO(OH)) the retention process.