Enhanced removal of Mn2+ from seawater by marine sediments and clay minerals in the presence of bacteria

Abstract

One of four different sediment samples from the Pacific ocean bound Mn2+ in a form which certain marine bacteria could then oxidize, provided that the sediment had been activated by pretreatment with ferric chloride in the laboratory. Cell extracts of one of the bacteria could oxidize Mn2+ sorbed by the same sediment even without pretreatment of iron. Leaching this sediment with concentrated HCl did not destroy its ability to sorb Mn2+ in biooxidizable form, indicating that neither carbonate nor ferromanganese was the active component in the sediment. However, acid treatment altered the sediment in such a way that intact cells of Oceanospirillum BIII 45 oxidized Mn2+ bound by it only without prior ferric chloride pretreatment, while four other test cultures still required ferric chloride pretreatment to oxidize the bound Mn2+. Azide inhibited oxidation of Mn2+ bound by iron-pretreated active sediment using intact cells and of Mn2+ bound by unpretreated active sediment using cell extract. Clay minerals of the montmorillonite and kaolinite types but not of the illite type, all of nonmarine origin, also sorbed Mn2+ in a form oxidizable by Oceanospirillum BIII 45. Ferric chloride pretreatment of these clays was needed when intact cells but not cell extract of the test cultures were used. The active components in the marine sediments may thus have been montmorillonite or kaolinite or both.