Hydrometallurgy processing operations

In some respects, hydrometallurgy can be described as wet analytical chemistry carried out on a large scale. Many different dow sheets can be designed with various types of unit operations and most metals can be extracted from a complex ore and recovered at the desired level of purity. A viable hydrometaHurgical process, however, must achieve that goal at an economically acceptable cost. 

Hydrometallurgical Flow Sheets. The various hydrometallurgy operations can be combined in many ways to design processes appropriate for specific metals. 

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. 

At present, leaching is one of the most essential front-end operations in hydrometallurgy, but in future hydrometallurgical processes for secondary metal recovery, treatment of low grade and complex ores, and research and development into high-temperature and high-pressure processes will become increasingly important. 

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... 

Chalkley, M. E. Toirac, I. L. The acid pressure leach process for nickel and cobalt laterite. Part I review of operations at Moa. Hydrometallurgy and Refining of Nickel and Cohalt, Annual Hydrometallurgy Meeting of CIM, 27th, Sudbury, Ont., Aug. 17-20, 1997, 341-353. 

Ozberk, E. Jankola, W. A. Vecchiarelli, M. Krysa, B. D. Commercial operations of the Sherritt zinc pressure leach process. Hydrometallurgy 1995, 39, 49-52. 

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. 

The confidence acquired by this development has caused TR to review its conception of the scope of hydrometallurgy for lead processing. It is no longer the aim to promote the best hydrometallurgical process and evaluate it against conventional standards, but to design processes that take best account of the constraints within which users operate. The emergence of this confidence can be seen in the chapters that follow. 

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