Nickel is widely used because of its excellent physical and chemical properties. Stainless steel and super alloys for turbine blades are representative nickel-based alloys. It is noteworthy that nickel has recently been adopted for use as a component of electronic devices such as capacitors and secondary batteries. Nickel is indispensable in our day-to-day life, and it is widely used in basic to advanced applications. A future shortage of nickel is anticipated because the demand for this metal in developing countries in places like BRICs and Southeast Asia is rapidly increasing along with their economic growth. There are two kinds of nickel ore: sulfide ore and oxide ore. Sulfide ore is mainly used because of its ease of concentration and smelting. Oxide ore, which is not as useful at this stage, should be considered as a potential new source of nickel for the future since it contains 70% of nickel resources. This paper reviews the current status of the resources and supply–demand of nickel as well as its metallurgical processing. An update and outlook on hydrometallurgical process technologies for nickel laterite ore, especially the HPAL process, which will be widely applied because of its high efficiency, are introduced.

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As an answer to the increasing demand for a stable supply of rare-earth element and yttrium (REY) , Kato et al. (2011) reported the discovery of "REY-rich mud" which has high REY concentration and is distributed widely on a deep seafloor in the Pacific Ocean. In addition to the high REY concentration, the REY-rich mud has great advantages as a mineral resource; (1) its exploration is easy to conduct due to its stratiform distribution as a deepsea sediment, (2) the concentration of radioactive elements such as U and Th which inhibit the development of mineral resource is very low, and (3) the most of REY can be easily extracted/recovered by using dilute acids for a few hours. In this study, we investigate the most appropriate recovery method of rare-earth element from the REY-rich mud by chemical leaching method toward its industrial development and usage in near future. The chemical leaching experiments were performed by five kinds of reagents (HCl, H₂SO₄, HNO₃, NaOH and (NH₄) ₂SO₄) under various leaching time, temperature and leachate concentration to aim the highest recovery ratio. The experiment showed that strong acids such as hydrochloride acid and sulfuric acid are appropriate leachate. Our results also showed that the recovery ratio is at the highest under the condition of the minimum required leachate concentration, minimum required leaching time and normal temperature. In our experiments, the recovery ratio except Ce from JMS-2 represents 88 % in case of hydrochloride acid (0.5 mol/L, 20min, 25 ℃, water-rock ratio 10:1) and 82 % in case of sulfuric acid (0.2 mol/L, 10min, 25℃, water-rock ratio 10:1) . The high recovery ratio of REY (80 - 90 %) even with dilute leachate under low temperature in a short leaching time is a strongly attractive characteristics of REY-rich mud as a new seafloor mineral resource.

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Distribution behavior of non-ferrous metals of Cu, Pb, Zn, Ni, Co, Na and Ca between matte and slag in industrial copper matte smelting of low grade secondary materials was studied by statistical analysis in order to obtain guiding principle of copper matte smelting for the recovery of rare metals such as nickel or cobalt. The distribution ratio of iron was used as a measure of oxygen partial pressure in this study. Because the distribution ratios of copper and lead were inversely proportional to that of iron, high grade copper matte is obtainable from the low grade secondary materials. This indicates that the concentration operation of rare metals in copper matte, i.e., efficient recovery of rare metals, is possible in the copper matte smelting of low grade secondary materials. In contrast, the distribution ratio of Na was proportional to that of iron despite the fact that the standard Gibbs free energy changes of reactions from sulfide to oxide of Cu and Na are very close each other; this suggests that unnecessary Na can be easily removed from the copper matte. Concentration variation of halogens and alkali metals in the charge strongly affected on the concentration of lead and calcium in matte, and copper and sulfur in slag; therefore, removal of halogens and alkali metals in the charge is effective to suppress unexpected variation of distribution ratio of non-ferrous metals between matte and slag.

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Partial polarization curves for Zn deposition, the crystal texture and orientation of deposited Zn were investigated to elucidate the synergistic effect of gelatin and antimony on the deposition behavior from the electrowinning solutions and on the crystal texture of Zn. Gelatin suppressed both the Zn deposition and hydrogen evolution, while antimony promoted both the Zn deposition and hydrogen evolution. Although the current efficiency for Zn deposition significantly decreased at low current densities below 200 A/m² in solution containing 50 μg/L of antimony, while the addition of gelatin significantly reduced the degree of decrease in current efficiency due to antimony. In a solution containing 50 μg/L of antimony, a lot of large holes resulting from the foam mark of hydrogen evolution were observed in deposited Zn, however the gelatin decreased the size and number of holes. The surface of Zn deposited from a solution containing both the gelatin and antimony became smooth layering the small platelet crystals. In a solution containing both the gelatin and antimony, 1 mg/L of gelatin formed the fieldoriented texture type of the Zn crystals with orientation of the <1120> direction, while 10 mg/L of gelatin formed an unoriented dispersed type of fine crystals from the bottom to the top of deposited Zn. The crystal texture of Zn deposited from the solution containing both the gelatin and antimony was obviously different from those in the solutions containing gelatin and antimony only, showing the synergistic effect of gelatin and antimony on the crystal texture of Zn.

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