Improvement of the Successive Selective Dissolution Procedure for the Separation of Birnessite, Lithiophorite, and Goethite in Soil Manganese Nodules

摘要

A successive selective dissolution procedure was improved to distinguish two Mn oxide minerals namely, birnessite (Bs) and lithiophorite (Lp) from Fe oxide minerals in soil Mn nodules. Soil Mn nodules collected from Typic Hapludalfs in Okinawa Island, Japan, were dissolved using successive NaOH, hydroxylamine hydrochloride (HAHC), and dithionite-citrate-bicarbonate (DCB) reagents at various temperatures. A test sample was prepared by mixing synthetic Bs, Lp (USNM#8811), natural gibbsite (Gb) and goethite (Ge), and soil clay containing kaolinite, illite, and vermiculite-chlorite intergrade mineral and used as a comparative standard. The NaOH treatment was able to dissolve kaolinite and Gb, concentrated the Bs, Lp, and Ge in the comparative sample. The HAHC treatment at 25°C effectively dissolved Bs but Lp and Ge remained undissolved. A subsequent extraction with HAHC at 60°C dissolved Lp without disturbing Ge. Finally, the DCB treatment was able to dissolve Ge. Thus, extraction with HAHC at 25 and 60°C were useful in distinguishing Bs and Lp respectively from Fe oxides minerals. The proposed method can also be applied to distinguish Mn, Fe, and Al oxide minerals in Fe-Mn nodules of natural soil.