Metals leached

Other Reductions. Ductile, pure zirconium has been made by a two-stage sodium reduction of zirconium tetrachloride (68) in which the tetrachloride and sodium are continuously fed into a stirred reactor to form zirconium dichloride [13762-26-0], heating with additional sodium yields zirconium metal. Leaching with water removes the sodium chloride from the zirconium. Bomb reduction of pure zirconium tetrafluoride with calcium also produces pure metal (69). 

Particular attention was given to the question of whether the catalysis with these systems is homogeneous or heterogeneous. It was found that the nature of the functional groups bound to the polymer backbone affects the rate and the extent of metal leaching, which also... 

The procedures which allow for the immobilization of a metal complex on or in a solid are numerous and well described they result from more than thirty years of continuous and imaginative efforts. More difficult, and consequently less successful, work has been described regarding the syntheses of efficient catalysts from these precursors. An immobilized complex must show high activity and selectivity for the target reaction, must be easily recovered intact, and must be stable towards metal leaching under the reaction conditions. These two latter requirements are particularly important where asymmetric catalysis is the goal, because the metal and the ligands... 

Puvvada, G. V. K. Murthy, D. S. R. Selective precious metals leaching from a chalcopyrite concentrate using chloride/hypochlorite media. Hydrometallurgy 2000, 58, 185-191. 

The metal leached from the support is re-adsorbed to a guard bed of ion exchange material. This shows that the concept of noncovalent anchoring is very attractive, especially if the homogeneous catalyst needs no further modification. 

Since in some of the preliminary experiments no rhodium losses could be detected, it is assumed that in an optimised continuous process the metal leaching will be in the range of the biphasic Ruhrchemie/Rhone-Poulenc process operating around 1 ppb. This would result in a loss of rhodium of 0.1 kg per year which is approximately 0.7 % in the case of the biphasic ionic liquid process and 0.2 % in the case of the SILP process. The inventory of the ionic liquid is slightly lower in the case of the liquid-liquid... 

Amphiphilic resin supported ruthenium(II) complexes similar to those displayed in structure 1 were employed as recyclable catalysts for dimethylformamide production from supercritical C02 itself [96]. Tertiary phosphines were attached to crosslinked polystyrene-poly(ethyleneglycol) graft copolymers (PS-PEG resin) with amino groups to form an immobilized chelating phosphine. In this case recycling was not particularly effective as catalytic activity declined with each subsequent cycle, probably due to oxidation of the phosphines and metal leaching. 

The heterogenization of organometallic catalysts on inorganic or organic solids has been extensively studied with traditional organic solvents. Mass transfer limitations and metal leaching have been identified as major obstacles for the practical use of this approach. Both factors might be reduced if an SCF is used as the mobile phase, albeit systematic studies are currently not yet available. 

Degradation of the ligand or the linker to the support must be avoided, as this results in metal leaching and catalyst deactivation. For example, phosphorus ligands are sensitive to oxidizing impurities in the feed (peroxides). 

Price, W.A., Morin, K.A., Hutt, N.M. 1997. Guidelines for the prediction of acid rock drainage and metal leaching for mines in British Columbia Part II. Recommended procedures for static and kinetic testing. In Proceedings of the 4th International Conference on Acid Rock Drainage. Vancouver, I, 15-30. 

KEYWORDS open pit lakes, metal leaching, mine waste, rehabilitation... 

The critical metal leaching rate depends on critical dissolved metal concentrations, which can be derived in different ways, for instance as a critical limit for soil solution (see above). 

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