Voltammetry, mineral surface

Abstract This chapter first explains the natural flotability of some minerals in the aspect of the crystal structure and demonstates the collectorless flotaiton of some minerals and its dependence on the h and pH of pulp. And then the surface oxidation is analysed eletrochemically and the relations of E to the composition of the solutions are calculated in accordance with Nemst Equation. The E h-pH diagrams of several minerals are obtained. Thereafter, electrochemical determination such as linear potential sweep voltammetry (LPSV) and cyclic voltammetry (CV) and surface analysis of surface oxidation applied to the sulphide minerals are introduced. And recent researches have proved that elemental sulfur is the main hydrophobic entity which causes the collectorless flotability and also revealed the relation of the amount of sulfur formed on the mineral surfaces to the recoveries of minerals, which is always that the higher the concentration of surface sulphur, the quicker the collectorless flotation rate and thus the higher the recovery. 

Pyrrhotite is one of many sulphides which display collectorless flotation resulting from the formation of sulphur on the mineral surface (Hamilton and Woods, 1981 Heyes and Trahar, 1984 Hodgson and Agar, 1984). The anodic scan section of cyclic voltammetry for pyrrhotite electrode in pH = 2.2, 4.7, 7.0, 8.8, 11, 12.1, 12.7 buffer solutions respectively, is presented in Fig. 2.23. The cyclic voltammograms curve at pH = 8.8 is also presented in Fig. 2.23. It can be seen from Fig. 2.23 that anodic current peak emerges at about -0.1—0 V when pH < 11. As pH increases, the peak moves to the left. This peak may correspond to the following reactions ... 

Neubauer, U.. and Furrer, G. (1999). The use of voltammetry for sorption studies ofheavy metals on mineral surfaces in the presence of the siderophore desferrioxamine B. Anal. Chim. Acta 392(2-3), 159-173. 

Since the 1960s , various electrochemical methods such as linear potential sweep voltammetry, cyclic voltammetry etc. and various surface analysis apparatuses such as infrared spectra, X-ray photoelecfron spectroscopy etc. have been developed to investigate the electrochemical reaction mechanism involved in the flotation of sulphide minerals (Fuerstenau et al., 1968 Woods, 1976 Ahmed, 1978 Stm, 1990 Feng, 1989 Buckley, 1995 Arce and Gonzalez, 2002 Bulut and Atak, 2002 Costa et al., 2002). 

Many investigators have used different techniques to study the electrochemical behavior of different sulphide mineral electrodes in solutions of different compositions. Linear potential sweep voltammetry (LPSV), and cyclic voltammetry (CV) have been perhaps, used most extensively and applied successfully to the investigation of reactions of sulphide minerals with aqueous systems. These techniques have provided valuable information on the extent of oxidation as a function of potential for various solution conditions and have allowed the identity of the surface products to be deduced. 

Abrasive stripping voltammetry — Technique where traces of solid particles are abrasively transferred onto the surface of an -> electrode, followed by an electrochemical dissolution (anodic or cathodic dissolution) that is recorded as a current-voltage curve [i]. It allows qualitative and quantitative analysis of metals, alloys, minerals, etc. The technique is a variant of - voltammetry of immobilized particles [ii]. 

Buckley, Woods, and co-workers have applied XPS to the study of the adsorption of thiols, " building on previous investigations of the surface oxidation of sulfide minerals using this technique. In a recent study of the chalcocite/diethyl dithiophosphate system, coverages derived from XPS were compared with those derived by cathodic stripping voltammetry following immersion of chalcocite electrodes in dithiophos-... 

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