Rare metal resources remain after their utilization, which are different from energy resources. We have a lot of industrial wastes, that is, urban mine in Japan. It is important to recycle valuable rare metals from the industrial wastes by applying suitable separation technologies. The contents of rare metals are usually higher than those of natural resources. They could be used without mining from the ground, though it is necessary to collect a certain amount. The importance of rare metal recycling is discussed here from the various aspects.
For the recycling of valuable metals contained in the printed circuit board wastes (PCBW), the effect of temperature on chlorination-volatilization behavior of metals under valuable chlorine resource was investigated. For the experimental sample powder of two types PCBW: crushed PCBW and roasted PCBW was used. The samples were heated at predefined temperatures ranging from 300°C to 900°C with chlorine, argon gas atmosphere or CaCl2 as a solid chlorine source. Chlorine/Argon gas flow into furnace was set at a rate of 100 mL/min. As a result, most of metals in crushed PCBW did not volatilize regardless the temperature, argon gas atmosphere and CaCl2 as chlorine source. In contrast, in the Cl2 gas atmosphere, a lot of metals in crushed and/or roasted PCBW volatilized by raising temperature. Compering the experimental samples, volatilization rate of crushed PCBW is higher than roasted PCBW. This is considered to be influenced by the chemical composition of metals in the samples. When using the crushed PCBW, most metals were volatilized over 90% at 900°C. In addition, in 70% of volatilized metals that were recovered, Cu, Au, Ni were concentrated. According to the results, valuable metals could be recovered by chlorination volatilization from PCBW.
This study focused on the development of hydrometallurgical process which allows the nickel (Ni) and cobalt (Co) recovery from a low grade laterite ore. The developed process consists of two main stages: leaching and precipitation. In the first stage, an appropriate leach liquor which contains a relatively high nickel and cobalt concentration is prepared by chemical leaching and pressure leaching followed by separation steps, respectively. The effects of sulfuric acid concentration, leaching temperature and time, internal pressure in an autoclave on the efficient leaching of Ni and Co from a laterite ore were presented. In the next stage, the Ni and Co ions present in the liquor are co-precipitated as sulfides by sulfuration with sodium hydrosulfide (pH 3.8). It was found that talc (Mg3Si4O10(OH)2), goethite (FeOOH) and quartz (SiO2) are main minerals of the laterite ore which contains 48.12% Fe, 1.8% Al, 0.95% Ni, 0.07% Co, 0.29% Cr and 0.15% Mg. The high efficiency of pressure leaching for Ni and Co from the low grade laterite ore was revealed by comparing the chemical leaching results. The vast majority of Co (>97%) and Ni (55%) from the purified liquor resulting after neutralization with calcium carbonate (CaCO3) was precipitated as mixed-sulfides by adjusting the NaHS/(Co + Ni) ratio to 3 by the addition of sulfuration agent (NaHS) at the solution pH of 3.8. Based on the experimental results, the efficient recovery of cobalt (Co) and nickel (Ni) from the low grade laterite ore can be achieved using the pressure leaching and neutralization treatment followed by sulfuration.