Characterization of Mn-nodules in shimajiri mahji soil from Okinawa, Japan / Alexandre Pereira de Bakker.

Tese (Ph.D.)- -Kagoshima University, Japan, 2004.

The present study-work was carried out to characterize and evaluate the mineralogy, micro-morphology, and the elemental composition of manganese nodules and their surrounding soil occurring in Shimajiri Mahji soil derived from Ryukyu limestone. Furthermore, results generated from this study were undoubted develop a hypothesis on the source of genesis of the manganese nodules occurring in Shimajiri Mahji soil. The following are summarized as the major results obtained in this study. 1) The Mn-nodules and their surrounding soil and/or sub-soil samples were collected at different sites in Okinawa, Miyako and Kume Islands and were undergone the successive selective dissolution procedure (SSDP) followed by the by the treatments of sodium hydroxide (NaOH), hydroxylamine hydrochloride (HAHC) at 25°C, 60°C, and dithionite-citrate-bicarbonate (DCB) in combination with X-ray diffraction (XRD), and scanning electron microscopic techniques to fulfill the above objectives. 2) In the Mn-nodules, the presence of manganese oxide minerals were bimessite and lithiophorite, and goethite and gibbsite as iron oxide and aIuminum mineraIs respectively, while kaolinite, illite, vermiculite-chlorite intergraded mineral were also investigated as layer silicate mineraIs. 3) These layer silicate mineraI compositions showed a similarity in the clay fraction of Mn-nodules as well as surrounding soils, envisaging an inter-relationship between both materiaIs. 4) In one of the samples, the presence for iron oxide minerais hematite and lepidocrocite were observed in the Fe-concretion, while the presence for layer silicate minerais smectite and chlorite in the surrounding soils. 5) Detailed micro-morphology of mineraIs showed globular aggregates for bimessite, while lithiophorite displayed pseudo-hexagonal platelets. In addition, micro-morphology of iron, aIuminum oxide and layer silicate mineraIs showed their occurrence and crystaI arrangements. 6) ElementaI composition analyzed by acid digestion system (HCIO4, HNO3 and HF) using inductive coupled plasma atomic emission spectroscopy (ICP-AES) showed that the following elements Zn, P, Ni, Co, Mn, Fe, V, Cu, Ca, Ba, and Na had their concentration higher in Mn-nodules than surrounding soil, while elements such as Cr, Mg, AI, and K did not show such tendency. 7) The presence of both Mn and Ba especially were observed higher in the nodules. 8) Elemental composition in soil Mn-nodules of this study envisaged similar to that of marine Mn-nodules formed under marine remains and the sea water. 9) When comparing the mineralogy and elemental composition of Mn-nodules with surrounding soils, it was suggested that, at first, the nodules might be developed from the Ryukyu limestone covered with Shimajiri Mahji soil or marine remains accumulated at sea bottom. Moreover, it was suggested to be a possibility of developing Mn-nodules at sea bottom resembling the formation of marine Mn-nodules and at the land environment after the upheaval.