Seafloor hydrothermal deposits, which were formed by deposition of precipitates from hydrothermal fluids vented from seafloor, are one of unconventional mineral resources beneath deep seafloors in the Exclusive Economic Zone of Japan. The authors have proposed a concept for Mineral Processing of Seafloor, where useful minerals are separated on deep seafloor and then lifted while remaining gangue is disposed on seafloor in appropriate ways. In this paper the authors studied the new ball milling system which was adapted under seafloor mineral processing. A simulator for ball mill grinding using simple discrete element method was built for this analysis. In this simulation two conditions in ball milling were examined: the method of grinding by enclosing the inside of a ball mill with air and with sea water. Especially we discussed the implementability of the ball mill grinding fulfilled with water because of the ease of installation in the real operation. Consequently, it was suggested that the grinding phenomenon can be performed effectively by the increase in the existence ratio of iron ball in the first quadrant in the mill. In the case where the mill is filled up with the water, it can be expected that crushing efficiency increases by carrying out ball milling at high rotational rate and with the mixture of the small ball size.
Biomethylation of arsenic is usually considered as a detoxification of arsenic because toxicity of most organic methylated arsenic is much less than that of inorganic arsenic. We investigated the feasibility of a novel bioremediation using an arsenic methylating bacterium. An arsenic methylating bacterium Cellulomonas sp. strain K63, isolated from soil in Miyazaki, was evaluated for growth characteristics and arsenic metabolism. The growth of strain K63 was inhibited in 200 mg As/L arsenic medium. Strain K63 metabolized arsenite (<50.0 mg As/L) to nonvolatile species such as monomethylarsonic acid, dimethylarsinic acid, trimethylarsenic oxide and arsenobetaine effectively. The percent of organic methylated arsenic excreted into the medium by strain K63 showed 90.1% of total arsenic compounds when strain K63 was cultured aerobically in the medium containing 5.0 mg As/L of arsenite for five days.
Catalysts are widely used in petroleum refining and chemical industries. Hydrodesulphurization (HDS) catalysts account for about one third of the total worldwide catalyst consumption. Spent HDS catalysts contain rare metals such as molybdenum, vanadium, nickel and cobalt on an alumina carrier. Among secondary resources, spent HDS catalysts are regarded the most important catalysts for recycling these metals due to not only their large amounts and economic values, but also the environmental concerns if disposed of. In most cases, spent catalysts are treated with hydrometallurgical leaching processes such as caustic leaching and acid leaching with roasting as a pre-treatment step. In the alkaline leaching processes such as sodium carbonate roasting followed by water leaching, most of the molybdenum and vanadium are selectively leached and most of nickel and cobalt are left in the residue after the alkaline leaching of spent HDS catalysts. Therefore, it is important to recover nickel and cobalt from the residue. The main form of nickel and cobalt in the residue is spinel, therefore, it is difficult to extract nickel and cobalt from the residue using mineral acids. In the present study, the effect of grinding, acid concentration, leaching temperature and stirring speed on the leaching efficiency of nickel and cobalt from the residue after sodium carbonate roasting followed by water leaching of spent HDS catalysts with sulfuric acid was investigated. The grinding, sulfuric acid concentration and leaching temperature significantly affected the leaching efficiency of nickel, cobalt and aluminum. However, the extraction of nickel and cobalt was ca. 80% and ca. 60%, respectively. The spinel was not affected by only mechanical grinding, therefore, it was considered that the extraction of nickel and cobalt was relatively low.
The crushing and physical separation technologies as the pre-treatment of hydrometallurgical process were carried out for recovering valuable metals such as Ni, Co and rare earth from nickel-hydrogen battery. Two types of nickel-hydrogen batteries which use a paste type electrode and sintered type electrode were roasted in the temperature range of 273–873 K and crushed by a single-axis cutter mill, a hammer crusher and a two-axis shear force crusher. Then the crushed products were classified with screens to give size distributions of the valuable metals. Magnetic separation was carried out for the crushed products of nickel-hydrogen battery using a paste type electrode. The optimum crushing conditions are different from the type of electrode. For the sintered type electrode, the crusher having an impact force is effective. For the paste type nickel foaming electrode, the crusher having a cutting and shear force is suitable. Classification after roasting in the proper conditions such as temperature and atmosphere followed by a magnetic separation is possible to separate Fe and NiO. The nickel content more than 80 wt% is possible.