Pathway of Sucrose Oxidation in Manganese (Pyrolusite) Nodule

Abstract

Polymetallic sea nodules are the potential resources of copper, cobalt, manganese, and nickel. The exploration and exploitation of manganese nodules are necessary to meet the future demands of Mn in the world. This work describes the valuable extraction of Mn through an innovative approach of using sucrose as a reductant. The metal extraction from the nodule leaching was studied in ambient temperature (27 degrees C) and at an elevated temperature 90 degrees C with and without agitation. In both cases, 99.9% of Mn was extracted while the extraction time appears to be significantly low (2 h) at 90 degrees C but it requires a longer time of 24 h at 27 degrees C. The optimum sucrose concentration selected was 7% (w/w) of nodule for maximum metal extraction. With use of 10% (v/v) H2SO4, 7% (w/w) sucrose at 90 degrees C, and solid to liquid (S/L) ratio of 1:10 the achieved metal recovery figures were the following: Mn >99%, Ni 98%, Cu 87%, Co 83% in 2 h. The oxidation pathway of sucrose is outlined in this study with the aid of mass spectrometry during reductive leaching of ocean bed nodule. Sucrose in acidic environment generates 1- or 6-monoacid of sucrose with ions of m/z (mass-to-charge ratio) 355 and 127, 5-hydroxymethylfurfural (5HMF). A dehydrated glucose complex (m/z 325) was generated at elevated temperature. These released organics act as reductant for the leaching of Mn2+ from MnO2. Glucaric acid (m/z 211) is generated as the end product of the sucrose oxidation in the solution.