Processes composition, leaching

A review of processes for leaching of base metals from their ores has appeared recently.2 Recent developments involving the generation and composition of sulfate-, chloride-, or ammonia-based streams which are used to feed solvent extraction processes are considered briefly below. 

The natural radioactivity of soils depends particularly on the origin and composition of the parent rock, on the degree of weathering, and on the prevalent types of the soil formation process (particularly leaching). For example, the soils obtained by weathering of acid rocks contain higher amounts of radioactive elements as compared to those produced from basic rocks. Heavy soils contain higher amounts of radioactive elements than sandy soils. The distribution of radioactive isotopes in the soil profile is usually fairly uniform, and only in certain soils is it possible to observe an increased accumulation in illuvial horizons. 

The process of leaching when applied to the measurement of pore-water compositions is essentially very simple. A leaching solution, normally deionized water, is applied to the sample in such a manner that it accesses the pore space within the rock material, mixing with the pore-water or dissolving residual solutes of the pore-water if the sample has been dried first. The leaching solution is then separated from the rock matrix and analysed for the chemical components extracted from the pore-water. 

Reaction 3 also occurs on cooling since the concentration of SO is very low at roaster temperatures of 950°C and approaches zero at 1000°C. Another important reaction that occurs during roasting is the formation of zinc ferrite, Zn0-Fe2 03 above 650°C (see Ferrites). Zinc ores contain 5—12% iron. Zinc ferrite forms soHd solutions with other spinels, such as Fe0-Fe203, and therefore the zinc—iron compositions formed are of indefinite stoichiometry. Ferritic zinc is difficult to solubilize in hydrometaHurgical leaching but several recovery processes are discussed below. 

Process and Operating Conditions The major parameters that must be fixed or identified are the solvent to be used, the temperature, the terminal stream compositions and quantities, leaching cycle (batch or continuous), contact method, and specific extractor choice. 

Terminal Stream Compositions and Quantities These are basically linked to an arbitrary given the produc tion capacity of the leaching plant (rate of extrac t production or rate of raw-material purification by extrac tion). When options are permitted, the degree of solute remov and the concentration of the extrac t stream chosen are those that maximize process economy while sustaining conformance to regulatory standards. 

Ground-water composition and Pu transport processes, leaching... 

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. 

Extraction or rather leaching of colourants is the first and a very important step in the analytical procedure for the analysis of natural dyes. The chemical composition of extracts from historical materials depends on many factors, such as the source of natural dyes, the technological procedure of their production, storage conditions over the centuries, ageing processes and extraction conditions. The choice of the extraction method depends on the properties of the components and the matrix from which they are isolated, as well as on the mechanism of dyeing with the particular dyestuff. In this regard, they are usually divided into three groups direct, vat and mordant dyestuffs. 

In situ encapsulation processes, 16 445 In situ leaching, 16 153 In situ metal—matrix composite processing, 16 173-175... 

Dwyer et al. (43) have also reported that dealumination of Y zeolites by a steam/acid leaching process produces a more uniform composition than dealumination by EDTA. The later method caused a depletion of Al in the outermost surface layer, producing a compositional gradient in the zeolite crystals. The conclusions reached by J. Dwyer in his studies of aluminum-deficient zeolites using the FABMS method are summarized in Table IV. 

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