Eishi Kusaka

Flotation separation of plastics using selective depressants

Abstract Four important plastics, namely polyvinyl chloride (PVC), polycarbonates (PC), poly acetal (POM) and polyphenylene ether (PPE) were successfully separated from their synthetic mixtures using common wetting agents like sodium ligninsulfonate, tannic acid, Aerosol OT and saponin. The efficient flotation separation amongst these naturally hydrophobic polymers could be attributed to the selective reduction in hydrophobicity (measured as the drop in contact angle) as a consequence of surfactant adsorption. The relative order of floatability measured with the help of column flotation experiments in the presence of various depressants selected for this study was found to be PPE > POM > PC > PVC, a trend consistent with the critical surface tension values determined for these solids except PPE. A flowsheet was developed on the basis of flotation results. It was possible to accomplish almost a perfect separation using the proposed flowsheet involving heavy media separation followed by flotation in two stages.

Effect of hydrolysed aluminum(III) and chromium(III) cations on the lipophilicity of talc

Abstract Liquid-liquid extraction and electrokinetic studies show that both the talc particles and the isooctane droplets are affected by the presence of hydrolysable metal species of Al(III) and Cr(III). The inherent lipophilicity of talc is unchanged by the hydroxo complexes of these metal species, while positive shifts in zeta potentials of talc and isooctane take place due partly to the strong adsorption of these hydroxo complexes. In the pH range where the hydroxide precipitates, the talc particles are rendered hydrophillic between the precipitation pH and the point-of-zero charge of the metal hydroxide. This hydrophile-lipophile transition of talc in the isooctane-water system relates to heterocoagulation among talc particles, isooctane droplets and hydroxide precipitates.

Role of surface free energy in a solid surface during collectorless liquid-liquid extraction

Abstract To determine the efficiency of liquid-liquid extraction for recovery of fine solid particles, the transfer of fine solid particles from a water phase to an oil/water interface, or to the oil phase, were investigated without using a collector. The tests were performed with solids of dissimilar hydrophobicity and n-heptane as the oil phase. High recovery levels of the solids having inherently hydrophobic surfaces were obtained. From contact-angle measurements and claculations of the surface free energies of the solids, the polar component of the surface free energy of the solid surface was found to govern the oil-solid adhesion. Moreover, the recovery levels of the collectorless liquid-liquid extraction method correlated with the work of adhesion, particularly, its polar component.

Effect of hydrolysed metal cations on the liquid–liquid extraction of silica fines with cetyltrimethylammonium chloride

Abstract Silica fines of 2 O systems indicate that decreases in percentage recoveries of the silica in the lower pH range are in line with increases in concentrations of the metal hydroxo complexes. Furthermore, the silica depression disappears when the pH approaches the point-of-zero charge of the hydroxide precipitate. In these pH ranges, the neutral to negative metal precipitates are also extracted into the oil–water interface during the liquid–liquid extraction. It seems that the lipophilic-to-hydrophobic transition, that is, depression by metal-salt addition of silica fines in cationic liquid–liquid extraction is controlled by the presence of metal-hydroxide species and their charges, attributable to the hydroxide coating on the silica surface.

The role of zeta potentials of oil droplets and quartz particles during collectorless liquid-liquid extraction

Abstract As a fundamental study on the recovery of fine particles of valuable minerals by liquid-liquid extraction, the concentration of fine quartz particles (0.24 μm average diameter) at the oil-water interface in the absence of a surfactant collector has been investigated. Isooctane and water were used as the two liquid phases. The recovery percentage of the quartz fines was determined as a function of the concentration of an added electrolyte (sodium, calcium and lanthanum chloride) and the pH value of the aqueous suspension. Based upon electrokinetic measurements, the liquid-liquid extraction results are interpreted in terms of colloid stability theory. Calculations of the total potential energy of interaction between isooctane and quartz indicate that height of the primary potential energy peak, which acts as an energy barrier in the quartz-isooctane coagulation process, correlates closely with the collectorless liquid-liquid extraction recovery of the quartz fines.

Recovery of gold with ion exchange resin from leaching solution by acidothioureation

Abstract Elemental gold present in ores is easily dissolved by leaching with a solution of sulfuric acid and thiourea in the presence of ferric ions as oxidizing agent. The authors previously found that lixiviation was dependent on concentrations of thiourea, ferric ions and sulfuric acid, and also temperature and leaching time. In the present study, a series of adsorption tests using strong acidic cation exchange resins was carried out on a pregnant solution containing thiourea complexes of gold, iron, copper and zinc, and then elution tests were conducted, using different types of eluates. It was found that Amberlite 200, among the ion exchangers used, was effective for the recovery of Au(CS(NH2)2)2+. Using Amberlite 200C, gold could be separated from other metal thiourea complexes through adsorption and elution processes.

The role of hydrolyzed metal cations in the liquid-liquid extraction of ultrafine silica with dodecyl sulfate☆

Abstract As part of a fundamental study on the recovery of fine particles, ultrafine silica was liquid-liquid extracted with the anionic collector sodium dodecyl sulfate (SDS). Isooctane and water were used as the two liquid phases. The pH dependence of the recovery level of the silica was determined in the absence and presence of metal salts, such as Fe(III), Al(III) and La(III), for physicochemical interpretation on the role of the hydrolyzed metal species during the anionic liquid-liquid extraction of the silica fines. The results showed that the silica could not be recovered without the metal salts, while the addition of the metal salt led to a significant increase in recovery in a certain pH range. Comparison of these results and the distribution diagrams of the metal species indicated that the increase in recovery is in line with the formation of metal hydroxides, hydroxo complexes and precipitates. Also, the minimum extraction edges of the silica in terms of pH were correlated to the residual concentration of the respective metal species in the water phase; the hydroxo complexes that form prior to the precipitation pH were the species responsible for the silica activation as well.

Collectorless liquid-liquid extraction of fine mineral particles using various organic liquids as the oil phase

Abstract As part of the fundamental studies on the recovery of fine mineral particles by liquid-liquid extraction, the transfer of fine quartz and galena particles from a water phase to an oil phase or to the oil-water interface was investigated in the absence of a surfactant collector. Various organic liquids of paraffin, aromatic hydrocarbous, ether, ketone, and higher alcohols were test oils. High recoveries of the galena particles were obtained using comparatively low polar liquids, while the recovery of quartz was impossible using any organic liquids. Calculations of the wetting property, the work of adhersion, of these solid surfaces with the liquids, based upon contact-angle measurements and the liquid surface free energy, indicated that the wetting on the quartz surface with water was most likely to occur, while the wettabilities of the two solids with the organic liquids were comparable. In addition, a thermodynamic criterion of collectorless liquid-liquid extraction were discussed in terms of the surface free energy change in the oil-water-solid, three-phase system during the oil-to-solid adhesion in water.

Collectorless liquid-liquid extraction of silica fines in trivalent metal salts solutions

Abstract The recovery level of silica fines by liquid-liquid extraction without the use of a collector has been investigated as a function of the aqueous pH in the absence and presence of trivalent metal ions such as aluminum (III) and chromium (III) ions. The results of the extraction are correlated with the corresponding electrokinetic measurements. In the system including no metal ions, the recovery of silica fines is possible around pH 3.3. This pH value exists between the two isoelectric points of silica and isooctane, where the two carry different charges. Heterocoagulation theory is closely related to the recovery peak in this pH range. When a metal nitrate salt is added in the system, several peaks appear in the pH-recovery curve. The electrokinetic measurements show that at these pH values the zeta potential of silica and isooctane are considerably decreased due partly to the presence of metal hydroxide species, complexes or precipitates, so that no electrostatic repulsion between fines and oil droplets could take place; the fines can concentrate at the oil-water interface through attraction due to dispersive forces.

Flotation for Removing Impurities from Synthesized Diamond.

This study deals with flotation as a method for removing impurities, such as ceramic brick and unreacted graphite, from synthesized diamond. Firstly, a series of flotation tests was conducted on raw synthesized diamond in order to determine the optimum conditions for removing ceramic brick. When kerosene was used as a collector, it was found that the grade of diamond recovered in the froth was high within a pH range of 2 to 4. The recovery and grade of diamond concentrate were about 90% and 95%, respectively. Secondly, to assess the effectiveness of separating unreacted graphite from raw synthesized diamond, a series of tests was carried out using hydrocarbons of C6 to C8, such as cyclohexane, xylene, benzene and n-decane. It was recognized that any hydrocarbon reagent was effective in separating unreacted graphite from raw synthesized diamond in an alkaline region of around pH 11.