Adsorption of Hydrogen and Hydroxyl Ions on Oxide Mineral

The adsorption amount of hydrogen and hydroxyl ions on alumina in water was determined by the acid titration method which was theoretically well explained in this study. It was found that there should be a value of pH, defined here as the equi-adsorption point, at which hydrogen and hydroxyl ions were equal in adsorption amount on alumina. The adsorption isotherms of hydrogen and hydroxyl ions on alumina were expressed in the form of Freundlich isotherm. The equi-adsoption point for alumina was pH 7.4, while the isoelectric point for the same material was pH 9.0 by the electrophoresis measurement. The heat of immersion of alumina was also measured in water at various pH values. The pH dependence of the heat of immersion related closely with the adsorption of hydrogen and hydroxyl ions. The pH value where there is the minimum value in the heat of immersion coincided with the equi-adsorption point. Thus, it was confirmed that the equi-adsorption point should not always be in agreement with the isoelectric point

Study on the Removal of Inorganic and Organic Mercury in Waste Water by the Flotation Method

The removal of inorganic and organic mercury in waste water by the flotation method was investigated as a part of the intensive studies of the water pollution control. The removal of inorganic mercury was examined by the following two methods : 1) Fe(OH)₃ co-precipitation-flotation method, 2) Fe(OH)₃ co-precipitation-Na₂S precipitation-flotation method. From the results obtained, it was recognized that inorganic mercury in waste water could be efficiently removed by the Fe(OH)₃ co-precipitation-flotation method with 80 mg/l cumulative addition of ferric ions in the pH about 9 after the third stage flotation using sodium oleate as a collector. By the first stage flotation, however, the removal of inorganic mercury in the waste water was inefficient. So, sodium sulphide was added to the waste water in order to precipitate completely the mercury. Thus, the precipitates of inorganic mercury produced with 40 mg/l ferric ions and 1 equivalent addition of sodium sulphide to the total amounts of mercury were completely removed at the pH 6.5―9.5 using sodium oleate in only the first stage flotation. The removal of organic mercury in waste water was performed by the following methods. A substance which contains organic mercury was decomposed into inorganic mercury with gaseous chlorine, followed by the Fe(OH)₃ co-precipitation-flotation method and the Fe(OH)₃ co-precipitation-Na₂S precipitation-flotation method. The decomposition of organic mercury into inorganic mercury was achieved readily by the oxidation reaction using Cl₂ gas. The optimum conditions of this reaction were found at pH below 1. The removal of excess chlorine in the flotation pulp is important for a successful flotation of the precipitates. The excess chlorine was eliminated by 8 g/l sodium thiosulphate or the aeration over 40 min. It was found that the mercury decomposed by Cl₂ gas was completely removed by the flotation method with an addition of 50―100 mg/l ferric ions and 1 equivalent of sodium sulphide to the total amounts of mercury at the pH 5.0―9.5. This new method being applied, the removal of inorganic and organic mercury in the waste water was successful in a short time by only one stage flotation using sodium oleate, and mercury in the tailing solution was not detected

Electrochemical Study on Flotation

For the purpose of studying the principle of mineral flotation, the mechanisms of both mercury-collector reaction and mercury-depressant reaction were investigated by means of electrochemistry ; furthermore the mechanism of reaction between sulphide minerals and notation reagents was discussed. From the electrochemical discussion on the mechanism of flotation reactions, it may be concluded that the floatability of the mineral in flotation using xanthate as a collector and NaCN, KCN, or Na2S as a depressant is governed by the reaction accompanying the electron transfer, namely, the redox reaction. And it is confirmed that the change in electrode potential relates closely with the contact angle or floatability and consequently it plays an important role in flotation

On the Equi-adsorption Point of Hydrogen and Hydroxyl Ions at the Alumina-Water Interface

The equi-adsorption point defined here as a pH value of the solution where hydrogen and hydroxyl ions are equal in adsorption density at oxide mineral-water interface is presented. The equi-adsorption point of alumina was found at pH 7.4 from the adsorption measurement, while the isoelectric point of the same material was at pH 9.0 in the electrophoresis study. It is shown that the equi-adsorption point is not always in agreement with the isoelectric point for oxide minerals. The equiadsorption point of alumina is also determined to be at pH 7.5 by considering the equilibrium solubility diagram which is obtained from thermodynamical information for several reactions in the alumina-water system. It is concluded that the adsorption of hydrogen and hydroxyl ions on oxide minerals is closely related to the chemical affinity between the constituent atoms of the mineral and the hydrogen or hydroxyl ion

Copper Silicate Mineral Flotation by Activation with Organic Copper-Avid Reagents

In order to collect the copper silicate, chrysocolla, a method in which the mineral is activated by a copper-avid organic reagent and then floated by using amyl xanthate was investigated. The copper-avid reagents used were salicylaldoxime. 8-hydroxyquinoline and α-benzoin oxime. The adsorption amounts of amyl xanthate on chrysocolla by the addition of each organic reagent in xanthate solutions were measured. The organic copperavid reagent coadsorbed with amyl xanthate onto the chrysocolla surface. Fundamental tests for the attachment of chrysocolla particles to the air bubble were carried out to clarify the effect of such factors as the pH of the solution, conditioning time, the addition of a copper-avid reagent and the xanthate addition on the floatability of chrysocolla particles. The pH region for the chrysocolla collection by activation with a copper-avid reagent and subsequent flotation using amyl xanthate is closely related to that for the formation of a copper-organic reagent complex, which can be obtained from thermodynamic data for the related stability constants. Flotation tests on the synthetic and natural ores were performed. As a result, it was confirmed that chrysocolla could be floated sufficiently and selectively by its activation with copperavid reagent like 8-hydroxyquinoline or salicylaldoxime, and also by its subsequent collection with amyl xanthate