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The effects were studied of mechanochemical treatment of Ni oxide ore garnierite, (Ni,Mg)3Si2O5(OH)4, from Montagnat, Gebe and Monted, on the extraction of Ni during subsequent sulphuric acid leaching. High-intensity grinding in a planetary ball mill for 60 minutes resulted in an increase in the extraction rate from 10% to more than 90% in 0.05 mol/l of sulphuric acid at room temperature, due to decomposition of crystals to the amorphous phase. The effects of additives such as sulphur and oxidants during mechanochemical treatment were also studied. Addition of sulphur had almost no effect on total Ni extraction but increased the selectivity for Ni. Addition of sodium pyrosulphate, Na2S2O7, resulted in more than half the Ni being extracted using water, and may be a suitable pretreatment for laterite ore., The effects were studied of mechanochemical treatment of Ni oxide ore garnierite, (Ni,Mg)3Si2O5(OH)4, from Montagnat, Gebe and Monted, on the extraction of Ni during subsequent sulphuric acid leaching. High-intensity grinding in a planetary ball mill for 60 minutes resulted in an increase in the extraction rate from 10% to more than 90% in 0.05 mol/l of sulphuric acid at room temperature, due to decomposition of crystals to the amorphous phase. The effects of additives such as sulphur and oxidants during mechanochemical treatment were also studied. Addition of sulphur had almost no effect on total Ni extraction but increased the selectivity for Ni. Addition of sodium pyrosulphate, Na2S2O7, resulted in more than half the Ni being extracted using water, and may be a suitable pretreatment for laterite ore.

The effects were studied of electrolyte fluid motion on the surface morphology of deposited Cu, impurity concentrations (As, Bi and Sb) and cathode potential. Laboratory-scale experiments were conducted at high current density with and without forced convection of the electrolytes. Mathematical modelling was employed to elucidate the electrolytic phenomena, taking into account ionic mass transfer in the electrolyte and charge transfer on the electrode surface. The results showed that the cathode overpotential increased with increasing current density and decreased with increasing fluid velocity of the electrolyte, and the surface roughness and impurity concentrations of the cathode decreased with increasing fluid velocity. At high current densities without forced convection, cathode overpotential increased rapidly within seconds of the start of electrolysis as a result of concentration polarisation and then gradually decreased due to an increase in surface roughness., The effects were studied of electrolyte fluid motion on the surface morphology of deposited Cu, impurity concentrations (As, Bi and Sb) and cathode potential. Laboratory-scale experiments were conducted at high current density with and without forced convection of the electrolytes. Mathematical modelling was employed to elucidate the electrolytic phenomena, taking into account ionic mass transfer in the electrolyte and charge transfer on the electrode surface. The results showed that the cathode overpotential increased with increasing current density and decreased with increasing fluid velocity of the electrolyte, and the surface roughness and impurity concentrations of the cathode decreased with increasing fluid velocity. At high current densities without forced convection, cathode overpotential increased rapidly within seconds of the start of electrolysis as a result of concentration polarisation and then gradually decreased due to an increase in surface roughness.

Following on from research showing that electrolyte motion smooths the deposited copper and significantly suppresses anode passivation, its effects on the behaviour of arsenic, antimony and bismuth at the cathode were investigated under conditions of high current density. The impurities were present in both electrolyte and anode. In the absence of forced convection, their concentrations in the deposited copper increased with current density, but this increase was suppressed at greater fluid velocities. It was found that consumption of the copper ions near the cathode caused concentration polarisation, resulting in electrochemical deposition of the impurities; fluid motion suppressed the polarisation and thus provided an effective means for electrorefining copper at high current densities., Following on from research showing that electrolyte motion smooths the deposited copper and significantly suppresses anode passivation, its effects on the behaviour of arsenic, antimony and bismuth at the cathode were investigated under conditions of high current density. The impurities were present in both electrolyte and anode. In the absence of forced convection, their concentrations in the deposited copper increased with current density, but this increase was suppressed at greater fluid velocities. It was found that consumption of the copper ions near the cathode caused concentration polarisation, resulting in electrochemical deposition of the impurities; fluid motion suppressed the polarisation and thus provided an effective means for electrorefining copper at high current densities.

The development of a new pyrometallurgical process for the treatment of zinc leach residue is needed in Japan to overcome the strict environmental regulations. A fundamental study of a pyrometallurgical treatment process for zinc residue has been carried out. The melting point of the residue was measured by a hot thermocouple technique and the effects of CaO and SiO2 additions were investigated. Both were shown to decrease the melting point. The distribution ratios of Fe, Zn, Pb, Si, S, As, Cu, Cd and Ag in gas, slag and metal phases were also studied. The results show that high temperature melting treatment is very effective for the recovery of valuable metals and for transforming slags into harmless substances. However, for residues with a large amount of As, As was found to stay in the metal obtained and the treatment of this metal still remains a problem., The development of a new pyrometallurgical process for the treatment of zinc leach residue is needed in Japan to overcome the strict environmental regulations. A fundamental study of a pyrometallurgical treatment process for zinc residue has been carried out. The melting point of the residue was measured by a hot thermocouple technique and the effects of CaO and SiO2 additions were investigated. Both were shown to decrease the melting point. The distribution ratios of Fe, Zn, Pb, Si, S, As, Cu, Cd and Ag in gas, slag and metal phases were also studied. The results show that high temperature melting treatment is very effective for the recovery of valuable metals and for transforming slags into harmless substances. However, for residues with a large amount of As, As was found to stay in the metal obtained and the treatment of this metal still remains a problem.