Sulfuric acid leaching of ocean manganese nodules using phenols as reducing agents

Pacific Ocean manganese nodule samples were leached with dilute sulfuric acid in the presence of phenol type aromatic reducing agents. Six phenols, including hydroxybenzene, o-dihydroxybenzene, m-dihydroxybenzene, p-dihydroxybenzene, o-trihydroxybenzene and m-trihydroxybenzene, were tested. The results indicated that all the tested phenols were effective reducing agents that significantly increased the extraction of Mn, Cu, Ni, Co from the nodules. At a dosage of 0.25 ∼ 0.4 grams of the reducing agents and 0.925 grams of H2SO4 per gram of nodules, over or nearly 95% of the Mn, Cu, Ni and Co could be extracted in 10 ∼ 20 minutes from an aqueous slurry containing about 20% manganese nodule, under ambient temperature and pressure. In the absence of the reducing agents, the extraction of Cu was about 65% and that of Mn, Ni and Co was below 20%. ESCA, TLC and UV/VIS spectroscopic analyses indicated that the Mn in the nodules was reduced in the presence of phenols in the acid medium, while the phenols could be oxidized to p-benzoquinone.