The organic solvent is a liquid organic compound capable of dissolving a water-insoluble compound. In the solvent extraction method which is one of metal refining techniques, the large amount of organic solvent plays an important role not only to solubilize the extractant but also to affect the extraction behavior of metal complexes formed in the organic phase. However, most organic solvents have high volatility and toxicity, and their use is limited owing to health damage and environmental burden. In this study, we synthesized activated carbon impregnated extractant without organic solvent and aimed to separate Co and Ni. Specifically, activated carbon was impregnated with 2-isonitrosopropiophenone as extractant, and the effect on Ni and Co separation characteristics was investigated. As a result, the activated carbon was able to selectively adsorb Co over Ni compared to toluene diluent and that this activated carbon had high adsorption capacity for Co and leakage of extractant lower.

Silicon wafer cutting waste is produced from the slicing process of silicon wafer which consists of silicon carbide (SiC) and silicon (Si) powders. This study aimed at the separation of SiC and Si in silicon wafer cutting waste by means of liquid-liquid extraction method for recovery. Isooctane and water served as the two liquids. Sodium oleate (NaOL) served as the collector. Firstly, the extracted fraction of SiC and Si powders from water phase to isooctane phase was investigated separately. Secondary, the separation of SiC and Si in silicon wafer cutting waste was conducted. The results indicated that the extracted fraction of SiC reached nearly 100% at a pH of 5 when more than 1 kg/ton of NaOL was added, whereas that of Si was at most 25%. Optimal separation of SiC and Si in silicon wafer cutting waste was achieved at a pH of 5 with the addition of 0.5 kg/ton NaOL. The grade of SiC recovered from isooctane phase was 88.3% with a recovery of 90.2%; the grade of Si recovered from water phase was 87.6% with a recovery of 85.9%.

Silica scale formation is one of the potential problems for the practical operation of geothermal plants. In this study, we examined optimal pH (3, 6 and 9) and temperature (298–353 K) conditions for the treatment process of waste geothermal fluids using a silica polymerization kinetics calculation. The kinetic model of Fleming was applied to nuclear growth and rate-limiting steps. The polymerization rate at pH 9 was about 3 times higher than that at pH 6 during the nucleus growth process, whereas these speeds did not change due to the difference in temperature. The pseudo-equilibrium concentration at pH 6 followed Van’t Hoff theory, but that at pH 9 was higher at 298 K than that at 313 K. Our results, therefore, suggest neutral pH conditions are the most suitable to suppress the silica scale, and then the optimal temperature for the treatment could be estimated from the initial silica concentration according to this kinetic model.