Clay minerals widely occur as a product of the water-rock interaction in hydrothermal, diagenetic and weathering systems at the surficial part of the earth. They show highly diverse and systematic variations in mineralogical properties related to their localities and occurrences. The mineralogical properties of the clay minerals such as mineral chemistry, mixed-layer structure, polytype, particle size, etc., have been investigated to understand the environmental conditions of mineral formation. Recent studies on the chemical compositions and the particle size of clay minerals show that they can be linked to the physicochemical conditions and/or hydrogeological conditions of water-rock interactions performed in the surficial geologic systems. The chlorite geothermometer which links the chlorite compositions to temperature conditions of formation, is highly applicable as a physicochemical index of the water-rock interaction at hydrothermal systems. The particle size properties of clay minerals can be related to their crystal-growth mechanisms and to the hydrogeological conditions of mineral formations, in the water-rock interaction including kinetic reaction. These suggest that the chemical composition and the particle size property of clay minerals are usable as a mineralogical indicator also in exploration of natural resources hosted in the surficial parts of the earth.

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Geochemical characteristics and the increase in the total reactive surface area of the sulphide-bearing rock due to weathering processes at dumping area, are expected to enhance the oxidation of sulphides, leading to the generation of acid mine drainage (AMD) . The study of the changes of geochemical characteristics of sulphidebearing rocks showed that the oxidation process in waste rock dump in 10 years was more advanced than that of 2 years. As the results of mineralogical investigation, the weathering is easy to accelerate around the surface of dumping area due to climatic conditions and acidification by oxidation of sulphides. Moreover, the study showed that the formation of clay minerals after the weathering processes took place at the dumping area, suggested that the generation of AMD would be minimized because the interior of the waste rock dump provided a barrier to oxygen and water. However, during the formation of clay minerals, the oxidation of pyrite will still occur, therefore, some additional countermeasures should be taken into consideration at the same time such as the dumping method of waste rock and application of low-permeable layer.

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The lithium ion secondary batteries (LIBs) contain valuable metallic components and although spent LIBs are not generally classified as dangerous waste, recovery of these metals is necessary from an economic point of view. In this work, separation of main metals such as copper, aluminum, manganese, cobalt, nickel and lithium contained in spent LIBs has been investigated using a hydrometallurgical treatment based on solvent extraction. The results obtained in this study are summarized as follows: Aluminum could be selectively separated from manganese, cobalt, nickel and lithium with solvent extraction using PC-88A at pH 2.0−2.5 after the selective extraction of copper with Acorga M5640 at pH 1.0−2.0. The extractant combination, D2EHPA+TOA, was efficient and selective for the extraction of manganese at pH 2.5−3.5 while leaving cobalt, nickel and lithium in the raffinate. Cyanex 272 was favorable to the separation of cobalt and nickel at pH 4.5−5.0 and nickel could be selectively separated from lithium using Cyanex 272 at pH 5.5−6.0. A separation process of copper, aluminum, manganese, cobalt, nickel and lithium from the spent LIBs using hydrometallurgical treatment based on solvent extraction was proposed.

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Metallic manganese has been obtained by an electrowinning process. Since the current efficiency of manganese electrowinning is low, it need to be improved. In this study, we focused on the separation of a cathode and anode cell to improve current efficiency by during the oxidation of manganese ions at the anode electrode. A copper sheet, a platinum coil, and an Ag/AgCl electrode were used as the cathode, anode, and reference electrode, respectively. The cathode and anode cells were separated by an ion-exchange membrane. The optimum manganese ion concentration was 0.7 mol dm^-3, and the optimum initial pH was 7; where1.0 mol dm^-3 of ammonium sulfate was added as a pH buffer and complexing agent into 0.7 mol dm^-3 of a manganese solution. Electrowinning on a manganese electrode was easier than on a copper electrode. Agitation of the solution did not influence the current efficiency in this study. However, an increase in the bath temperature decreased the current efficiency. The maximum current efficiency was 82.6%, and the purity of manganese was 99.97%. The concentration of cobalt ion contamination influenced the manganese electrowinning, and stable manganese electrowinning requires that the cobalt concentration in the electrolyte be less than 10 mg dm^-3.

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In order to observe the impurity behavior during a hydrometallurgical copper recycling process using ammoniacal solution and cuprous ions, copper was recovered from wasted printed circuit boards, where the solution was recycled after adjustment of the solution volume and composition by addition of copper-free solution and oxygen gas. It was confirmed that zinc, nickel and manganese accumulate in the solution, although the accumulation showed no significant impact on the copper purity. It was also found that the accumulation of zinc in the solution increases the risk of copper oxide or hydroxide precipitation during the process, because of the consumption of ammonia. The lead content in the copper deposit was around 20ppmw, 4 times higher than that of LME grade A standard, regardless of the number of the solution recycle. Thus, lead removal using a column filled with an adsorbent was further investigated, and sintered calcium phosphate (hydroxyapatite) was found to be a potential candidate as the lead adsorbent for this process.

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