Removal of H2S by Metal Ferrites Produced in the Purification of Metal-Bearing Waste Water. Study of the Reaction Mechanism

Abstract

Waste water polluted with heavy metals can besuccessfully purified by precipitation of the metals from analkaline solution containing iron (II), giving rise to aferrite sludge. The solid metal ferrites obtained in thismanner can be used to remove hydrogen sulphide from a gasstream. Based on a Taguchi experimental design, ferrite solidparticle and pore size, and the temperature resulting inmaximum retention of H2S by the solid were optimised.Under the optimum conditions, predicted by the method, eachgram of ferrite was able to retain 0.274 g H2S.In addition, a ferrite containing a known lead concentration,obtained by the precipitation method under optimal conditionsof pH, temperature and Fe/Pb ratio, was used to study theexothermic H2S retention reaction. The chemical reactionoccurring between the ferrite and the H2S wasinvestigated by characterisation of the compounds before(Pb0.04FeII 0.96 FeIII 2O4·nH2O solids composed ofPbxFe3-xO4, magnetite Fe3O4 andhydrated lead oxide PbOn·H2O) and after (PbS, PbSO4, S, FeS2 and α-FeO(OH)) the retention process.