The role of solution composition and ageing of arsenite treated with single and mixed mineral systems of kaolinite, montmorillonite and goethite injected with iron sulfide under sulfidic-anoxic conditions have been investigate. Variability in arsenite sorption exists over the range of pH investigated. This variability in sorption may be attributed to the presence of thiol (≡S-H) functional group contained in solution under sulfidic-anoxic condition. Arsenite sorption exhibits a non-promotive Cp effect (i.e. sorption decreases as Cp increases for all mineral systems. the nature of ionic species formed in solution is affected by changes in the mineral/ solution ratio. All mineral systems but kaolinite-goethite exhibits a step up arsenite sorption up to 288 hours residence time and flattens g out over the remaining residence time of the reactions.