Concentration hydrometallurgy

Ficeriova, J. Balaz, P. Boldizarova, E. Jelen, S. Thiosulfate leaching of gold from a mechanically activated Cu-Pb-Zn concentrate. Hydrometallurgy 2002, 67, 37-43. 

J. Milboume, M. Tomlinson, L. Gormely, Use of hydrometallurgy in direct processing ofbase metal/PGM concentrates, Hydrometallurgy 2003 - Fifth International Conference in Honor of Professor Ian Ritchie, Minerals, Metals and Materials Society (TMS), Vancouver, Canada, 2003, pp. 617-630. 

Hydrometallurgy. The treatment of ores, concentrates, and other metal-bearing materials by wet processes, usually involving the solution of some component, and its subsequent recovery from solution. 

The separation of solids from liquids forms an important part of almost all front-end and back-end operations in hydrometallurgy. This is due to several reasons, including removal of the gangue or unleached fraction from the leached liquor the need for clarified liquors for ion exchange, solvent extraction, precipitation or other appropriate processing and the post-precipitation or post-crystallization recovery of valuable solids. Solid-liquid separation is influenced by many factors such as the concentration of the suspended solids the particle size distribution the composition the strength and clarity of the leach liquor and the methods of precipitation used. Some important points of the common methods of solid-liquid separation have been dealt with in Chapter 2. 

Some of the types of equilibria involved in the unit operations separation and concentration are listed in the introduction, Section 9.17.1. Those which depend most on coordination chemistry, and for which details of metal complex formation are best understood, are associated with hydrometallurgy. Once the metal values have been transferred to an aqueous solution, the separation from other metals and concentration can be achieved by one of the following processes.3... 

Approximately 80% of Zn production involves hydrometallurgy, in which roasted sulfide concentrates are dissolved in sulfuric acid.181 Currently, the major separation steps involve the precipitation of other metals from the sulfate stream (Figure 7) 181>182 The precipitation of iron is achieved by raising the pH with calcine, the mixture of zinc/iron oxides from roasting, producing large volumes of iron oxy-hydroxide materials, the disposal of which presents major challenges.183-185... 

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. 

Liquid-liquid extraction of metals has been used for many years as a concentration technique in analytical chemistry consequently, it was logical to use the types of organic compounds employed in these systems for the development of industrial reagents for the same metals. However, because the overall requirements for these two end uses are different, modifications to the basic structure were necessary to take account of the particular requirements of hydrometallurgy, summarized by the following criteria ... 

Compared to 352 local female construction workers in which the spontaneous abortion rate was 8.5%, an increase in spontaneous abortions to 15.9% was observed among 356 women who worked in a nickel hydrometallurgy refining plant in the arctic region of Russia (Chashschin et al. 1994). Exposure concentrations were 0.08-0.196 mg nickel/m, primarily as nickel sulfate, and nickel concentrations in the urine were 3.2-22.6 pg/L. Nickel levels in the urine of persons not occupationally exposed are generally <0.1-13.3 pg/L (Sunderman 1993). The investigators noted that the nickel-exposed women manually lifted heavy nickel anodes and that they may have experienced heat stress. 

Hydrometallurgy Traditionally the winning of metals from their ores has been achieved by pyrometallurgy the reduction of relatively concentrated metallic ores at high temperatures. The reactions of the blast furoace form a typical example (see also page 377) ... 

The early development of ion exchange as a unit operation in hydrometallurgy was slow, mainly because of the lack of selectivity of the resins under operating conditions, and the limited capacities of the earlier commercial resins. Consequently, ion exchange found applications only in processes where the concentration of metal ions in solution was very low, and where the resin could be used to upgrade the solution prior to some final purification step. Recent developments, however, particularly the introduction of chelating resins, have considerably broadened the scope of resins in hydrometallurgy. 

SOLVENT extraction (liquid-liquid extraction) is the separation and/or concentration of the components of a solution by distribution between two immiscible liquid phases. A particularly valuable feature is its power to separate mixtures into components according to their chemical type. Solvent extraction is widely used in the chemical industry. Its applications range from hydrometallurgy, e.g., reprocessing of spent nuclear fuel, to fertilizer manufacture and from petrochemicals to pharmaceutical products. Important factors in industrial extraction are the selection of an appropriate solvent and the design of equipment most suited to the process requirements. 

Now it is difficult to conceive any field of human activity where PCMU are not used. Among them are health care and pharmacology (administering of desired metals into the organism, such as iron in the case of asiderotic anemia, as well as removal of harmful, particularly radioactive metals) atomic industry and hydrometallurgy (concentration and separation of rate metals and radioactive isotopes), chemistry and catalysis (preparation of highly effective immobilized catalysts) etc. 

Another unique feature of the interfacial reaction for metal complexes is the formation of the aggregate of the complex. As observed in many cases, the liquid/liquid interface can be saturated by any active surface molecules at the interfacial concentration of the order of 10 mol cm, which can be attained even at adiluted bulk concentration as in the case of highly hydrophobic solutes. Thus, the interface is prepared to become a two-dimensionally concentrated state for the solute. This situation very often results in the formation of the metal complex aggregates at the liquid/liquid interface. During the solvent extraction procedure for metal ions, the precipitate at the interface was observed, which was called crud or scum in the field of hydrometallurgy. This crud or scum must... 

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