Pulp Oxidative Potential Control

Hayes and Ralston showed that the control of pulp oxidative potentials allows flotation selectivity, and is therefore a worthwhile approach in the flotation of complex sulfide ores, in addition to pH strategies. Direct electrochemical interactions between physically separated sulfide minerals, in which one affects the other's flotation behaviour directly through an anode-cathode relationship, have so far not been convincingly demonstrated on plant scale.

Galvanic and electrochemical interaction between sulfide minerals, and general chemical reactivity, is to a large degree dependent on the presence of oxygen in solution. The control of oxygen levels is thus generally the objective and result of pulp oxidative potential control. Since industrial flotation relies heavily on the use of ambient air, it has been proposed to regulate the oxygen concentrations entering flotation by admixture of nitrogen, or by partial re-circulation of process air released from the froth surface. The former approach is expensive whereas the latter depends on cells specifically designed to collect and re-circulate air leaving the top surface of the froth. Cylindrical cells seem to be most effective in this respect. The gas composition of bubbles generated by pressure differentials in flotation cells is dependent on a suite of factors, including the magnitude of the pressure drop, dissolved substances, and nature of the nucleating surfaces. Benefits in flotation results were shown when regulating certain reagent additions on the basis of pulp oxidative potential, e.g. sulfuric acid, rather than pH. However, benefits might well be mostly due to froth structure improvements.

Trahar has shown that interactions between sulfide minerals were much decreased if they are ground separately, and only combined in the flotation cell. In this case, no mineral interaction between chal-copyrite, galena and sphalerite could be statistically proven. This demonstrates that galvanic interaction between sulfide minerals is only practically noticeable when mechanical contact exists. Grano et al. have also found that flotation selectivity between sulfide minerals is most sensitive to milling and preconditioning parameters, more so than to oxidative potentials during flotation itself, and mostly due to the presence of mild steel particles originating from equipment wear. For this reason, amongst others, research into comminution techniques which maximize mineral separation, whilst minimizing smearing, over-grinding, and steel consumption, must be a priority in the minerals industry. The effect of mild steel particles generated during ore comminution is mainly due to oxygen consumption, corrosion inhibitors being essentially ineffective. Full oxidation of these particles during conditioning removes their deleterious effect. Even for real ores containing significant quantities of more than one sulfide mineral, reasonable correlations exist between the behaviour of minerals in the ore and single minerals, as found by Grano et al. This indicates the limited extent of electrochemical mineral interactions in general practice.

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Solar Panel Basics

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