Synthesis and crystallogenesis at low temperature of Fe(III)-smectites by evolution of coprecipitated gels: experiments in partially reducing conditions

Abstract

Abstract Syntheses of ferric smectites were performed at low temperature (75° C by aging coprecipitated gels of silica and Fe 2+ -sulphate under initially reducing then oxidizing conditions. Under strictly reducing conditions only nuclei of a trioctahedral ferrous stevensite were observed and crystal growth did not take place. When a spontaneous oxidization, in contact with air, was effected, the ferrous smectite nuclei transformed rapidly into a ferric, nontronite-like, smectite. Crystallogenesis of the ferric smectite was studied by XRD, IR, DTA, Mössbauer and EPR spectroscopies. The end-synthesis smectite contained only Fe 3+ ions, all located in the octahedral sheet. This clay was mixed with a cryptocrystalline iron oxide phase containing one-third of the iron atoms and undetectable by XRD.