Browsing by Author "Basilio, Cesar Indiongco"

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    Fundamental studies of thionocarbamate interactions with sulfide minerals
    Basilio, Cesar Indiongco (Virginia Polytechnic Institute and State University, 1989)
    The interactions of O-isopropyl-N-ethylthionocarbamate (IPETC) and O-isobutyl-N-ethoxycarbonylthionocarbamate (IBECTC) with Cu₂S, CuFeS₂ and FeS₂ have been characterized using thermodynamic calculations, electrochemistry, microflotation tests, contact angle measurements, FTIR, and UV spectroscopy. Pearson’s theory of hard and soft acids and bases (HSAB) has also been applied to these flotation systems, through the use of Drago’s acid-base concept and flow microcalorimetry. The results of the thermodynamic calculations and electrochemical measurements suggest that IPETC and IBECTC adsorption on copper and chalcocite are dependent on potential. This has been verified by contact angle and in-situ spectroelectrochemical measurements. Microflotation tests with these thionocarbamates show that the floatability of Cu₂S and CuFeS₂ is dependent on pH. The floatability of FeS₂ only becomes significant at acidic conditions and high collector additions. Spectroscopic measurements also show that thionocarbamate adsorption is dependent on pH and is most favored on Cu₂S followed by CuFeS₂ and FeS₂. FTIR results indicate that IPETC is adsorbed on Cu°, Cu₂S, and CuFeS₂ through a coordination of the sulfur atom with the surface Cu. IBECTC adsorption on these substrates involves the coordination of Cu with both sulfur and oxygen atoms to form a six-membered chelate ring. Adsorption of these collectors cannot remove or prevent the formation of sulfoxy oxidation products on the FeS₂ surface, unlike the case with the xanthate-pyrite system. This may explain the improved selectivity of IPETC and IBECTC over xanthates. Infrared reflection-absorption spectroscopic studies show that KEX is preferentially adsorbed on Cu° over IPETC and IBECTC. Between IPETC and IBECTC, the latter is more favorably adsorbed than the former. Kinetic studies using UV spectroscopy show that the rate of thionocarbamate adsorption is highest on Cu₂S followed by CuFeS₂ and FeS₂. IBECTC adsorption on each sulfide mineral is relatively faster than IPETC, indicating the higher collecting power of IBECTC. The HSAB concept suggests that the interaction of thionocarbamates (soft bases) with sulfide minerals that are classified as soft acids should be favored. The C/E ratios of Cu₂S and FeS₂ were determined to be 0.86 and 0.52, respectively. This indicates that FeS₂ is a harder acid than Cu₂S, thus providing an explanation for the observed selectivity of both IPETC and IBECTC against FeS₂.
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    Thermodynamics and electrochemistry of the chalcocite-potassium ethyl xanthate system
    Basilio, Cesar Indiongco (Virginia Polytechnic Institute and State University, 1985)
    Comprehensive thermodynamic calculations have been carried out on the chalcocite-KEX-water system based on complete mass balance equations which include both soluble and insoluble species. The calculations have yielded i) Eh-pH stability diagrams for different KEX additions, ii) equilibrium concentrations and amounts of all the dissolved and insoluble species including those of CuX and CuX₂, iii) two- and three-dimensional plots showing the effect of Eh and pH on the formation of selected species, and iv) minimum xanthate additions required to form CuX and CuX₂. These information can be used as a guide in predicting the optimum conditions for flotation and leaching of chalcocite. The upper limiting potentials predicted from the thermodynamic calculations are in excellent agreement with those determined from the microflotation tests. The lower flotation edges, on the other hand, are found to be dependent on the sequence of reagent additions. When xanthate is added after the addition of a reducing or oxidizing agent to control the potential, they are in reasonable agreement with predicted values. When the collector is added prior to the potential control, however, the lower flotation edges are significantly higher than the predictions. The flotation experiments carried out at several different concentrations show that the minimum amount of the collector is required between 0 to 200 mv, as predicted by the thermodynamic calculations. Voltammetry experiments carried out in the absence of a collector at pH 9.2 and 6.8 suggest that the anodic oxidation of chalcocite results in the formation of Cu₂O, Cu(OH)₂ and SO. At potentials below -400 mv, Cu₂S is reduced to CuO and HS⁻. When xanthate is added, several adsorption peaks are observed. There are indications that the peaks appearing between -200 and -100 mv may involve the reaction between xanthate and CuO. However, at potentials above -40 mv, xanthate may adsorb directly on chalcocite without involving CuO.