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Preliminary exposure of a perchlorate solution of palladium(II) tetraaqua complex to a dc magnetic field (0.1! 0.95 T) affects the rate of a series of hydrogenation and oxidation reactions catalyzed by this species.

A possible mechanism of anaerobic dissolution of powdered palladium and gold is suggested.At present, the main technique used to recover gold and silver from ores is their treatment with aqueous solutions of sodium cyanide in the presence of atmospheric oxygen. The world's output of gold recovered by this method in the early 1990s was as large as 70% [1]. This hydrometallurgical technique has been well developed and described in detail in the literature [13 6].It is believed that silver and gold (M) dissolve in cyanide solutions in the presence of an oxidizing agent, atmospheric oxygen, in accordance with Elsner's equationAt the same time, the classical electrochemical mechanism of gold dissolution includes an anodic (2) and a cathodic (3) processes at the surface of a metallic particle and is described by the overall Bodlander equation (4):It follows from Eqs. (1) 3 (4) that presence of oxygen in the reaction system is a necessary condition for dissolution of gold in cyanide solutions.However, an important factor to be taken into account in studying the dissolution of gold is that its properties depend on particle size. A compact metal is chemically a very inert material, but, as its particles become smaller, not only the physical properties of the metal, but also its chemical activity start to change [7]. Metallic gold may be present in ores both in the form of rather large metallic particles and as colloiddispersed particles, part of which have a size close to that of gold nanoclusters. Accordingly, it may be assumed that the conventional chemistry can somewhat change for gold particles of this kind.Previously, the dissolution kinetics of powdered palladium and gold has been studied in relation to the concentration of sodium cyanide and composition of the gas atmosphere (oxygen, oxygen3argon, oxygen3hydrogen) [8].As established in [8], the dissolution rate of powdered gold and palladium is first-order with respect to the concentration of a metal and cyanide ions, but zero-order with respect to the concentration of oxygen (partial pressure in the gas mixture). As the concentration of the cyanide ion increases, the dissolution rate of the metals grows and so does the amount of absorbed oxygen per mole of the metal. The dissolution rate of the metals also grows with temperature. However, the rate of oxygen uptake changes only slightly and even falls at comparatively high temperatures (40 3 60oC). In this case, the amount of deceases oxygen consumed for complete dissolution increases dramatically.This communication reports on a study proceeding with these investigations in order to refine the possible pathways of dissolution of noble metals. On the whole, the experimental data obtained suggest that another oxidizing agent, water, is present in the system together with oxygen.

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