A. López Valdivieso

Adsorption of isopropyl xanthate ions onto arsenopyrite and its effect on flotation

Abstract The adsorption of isopropyl xanthate ions, (CH 3 ) 2 CH–OCS 2 − , onto arsenopyrite (FeAsS) was studied through electrokinetics, voltammetry and rest potential measurements at pH 6. The electrokinetic behavior of droplets of isopropyl dixanthogen, (CH 3 ) 2 CH–OCS 2 –S 2 CO–CH(CH 3 ) 2 , in solutions of isopropyl xanthate ions was also determined at the same pH value. Adsorption occurred first as isopropyl dixanthogen through an anodic oxidation reaction of the xanthate ions on arsenopyrite, with no effect on the zeta potential of arsenopyrite. Then as isopropyl xanthate ions through hydrophobic bonding with the dixanthogen adsorbed at the arsenopyrite/aqueous solution interface, increasing negatively the zeta potential of arsenopyrite. The negative electric charge at the dixanthogen-arsenopyrite/aqueous solution interface limited the two adsorption steps. Microflotation studies showed that arsenopyrite floated highly owing to dixanthogen. This flotation was not affected by the polar group (OCS 2 − ) of the isopropyl xanthate ions at the dixanthogen-arsenopyrite/aqueous solution interface.

Dextrin as a Regulator for the Selective Flotation of Chalcopyrite, Galena and Pyrite

Abstract The adsorption of both dextrin and xanthate ions at the pyrite/aqueous solution and the galena/aqueous solution interfaces have been studied through batch adsorption tests. Batch flotation tests were also carried out on a chalcopyrite ore and a chalcopyrite-galena scavenger concentrate using dextrin. Dextrin adsorption isotherms on two types of surfaces of pyrite show that the greater the initial surface density of iron hydroxides, the higher the adsorption of dextrin is. These adsorption isotherms exhibit two plateaus suggesting that dextrin adsorbs on pyrite not only on ferric hydroxide sites, but also on ferrous hydroxide sites. Adsorption of xanthate ions gives rise to a partial desorption of dextrin lowering the surface hydrophilicity of pyrite. This desorption of dextrin is proposed to occur due to the dissolution of ferric hydroxide which is associated with the oxidation of xanthate ions to dixanthogen. It is shown that dextrin is an effective depressant for pyrite in flotation of copper in the chalcopyrite ore at pH 8, but the pulp needs to be aereated in order to promote the surface oxidation of pyrite and enhance the adsorption of dextrin. On galena, adsorption of xanthate ions also leads to the desorption of dextrin, but, dextrin can be an effective depressant only if the surface of galena is sufficiently oxidized to have dextrin left on the surface after xanthate adsorption. This surface oxidation of galena is more effective with pyrite than using air. Results are presented on the flotation of chalcopyrite from a chalcopyrite-galena bulk concentrate high in pyrite using dextrin as a depressant for galena and pyrite at pH 8.

Radiological Waste Processing for the Recovery of Silver through Cementation with Zinc Powder

Abstract The recovery of silver from silver-thiosulphate-fixer solutions of radiological wastes has been studied by cementation in batch-stirred reactors using zinc powder as the cementing agent. Silver is efficiently recovered from the solutions. The silver recovery rate and the total silver recovery increased with pH. Metallic silver was the product for cementation in deoxygenated solutions at all pH studied. With non-deoxygenated solutions and at low pH values, metallic silver cemented first, followed by silver sulfide. At high pH values, metallic silver was the cementation product. Electrochemical reactions are proposed for the cementation process in the presence and absence of oxygen.