Leaching extraction

Leaching. Extracting a soluble metallic compound from an ore by selectively dissolving it in a suitable solvent. The solvent is usually recovered by precipitation of the metal or by other methods. 

Auslauge-. lixiviating, leaching, extraction, -be halter, m. lixiviating tank, -hiilse,/. extraction thimble, -hasten, m. lixiviating vat, leaching vat. 

Unlike the amine extractants, this compound does not protonate easily and provides excellent selectivity over those metals and metalloids that exist as chloroanions in this medium. Extraction of the latter species becomes significant only above 8 mol dm chloride, as protonation becomes significant. This extractant [Acorga CLX 50], which contains 50% of the active ingredient, has been proposed for an integrated leach, extraction, electrowinning circuit (Cuprex process) [19]. 

Mineral exploration stream sediment geochemical survey data for the Otago region includes more than 2000 standard stream sediment samples from 19 surveys, more than 800 BLEG (bulk leach extractible gold) samples from 14 surveys and a few pan concentrate samples (MR reports). The stream sediment samples were typically analysed for Au and As, and... 

Sahuquillo, A., Rigol, A. and Rauret, G. (2003) Overview of the use of leaching/extraction tests for risk assessment of trace metals in contaminated soils and sediments, Trends in Analytical Chemistry 22,... 

Particularly lengthy are the preparations associated with leaching procedures, as after the leaching itself has been completed (a leaching extraction alone may last from 18 to 48 hours) and before the leachate extracts can be analyzed, the laboratory must perform an organic extraction, similar to one described in Example 4.3, or a metal digestion. The total process takes at least 3-4 days. 

Van der Sloot, H.A., Heasman, L. and Quevauviller, Ph. (1997) Harmonization of Leaching/ Extraction Tests. Elsevier Studies in Environmental Science 70, Amsterdam, 281 pp. 

Numerous extraction methods and techniques have been developed and reported, especially if one takes into account the variety of modifications. The most common and simple general classification of these methods is similar to that introduced in chromatography and based on the kind of phase to which the analyte is transferred. One can distinguish the extractions as liquid, solid, gas, and supercritical fluid phase extractions. More precise description specifies the two phases between which the analyte is distributed (e.g., liquid-liquid or solid-liquid [leaching] extractions). The latter methods are all called solvent extraction. 

In both solution and suspension formulations, the propellant can potentially leach extractables (nitrosamines, elastomers) from the gaskets in the containers, which may result in instability. 

In a very rough approach, the amorphous phase Si/Al ratios y have been chosen so that the zeolitic fraction (1-z) is equal to the XRD crystallinity of the solids. It appears, from these calculations, that y varies from 0 to about 2 for (HT) and (HTA1) solids, (Table I) which is in qualitative agreement with STEM results (31). Concerning the (HTA2) solids, y can reach very large values, (>20), which is consistent with the fact that the severe acid leaching extracts most of the extra-framework species. With these values for y, only approximate NH /Al ratios can be calculated (Table I). 

Regarding procedures for characterization of waste, harmonization on various objectives and leaching/extraction test methods is undertaken by European Standardization Network CEN, Technical Committee (TC) 292, and a distinction is made between three types of leaching tests which will be applied in different circumstances (Van der Sloot et al. 1997, Van der Sloot 1998, 2002) ... 

Van der Sloot HA, Heasman L and Quevauviller Ph (1997) Harmonization of leaching/extraction tests. In Studies in Environmental Science 70. 281 p. Elsevier Publishers, Amsterdam. 

Toxicity. Toxicity is estabhshed through the Toxicity Characteristic Leaching Procedure (TCLP), which measures the tendency of certain toxic materials to be leached (extracted) from the waste material under circumstances assumed to reproduce conditions of a landfill. The TCLP list includes a relatively small number of industrially important toxic chemicals and is based on the concentration above which a waste is considered hazardous. Failure to pass the TCLP results in classification of a material as a toxic waste. 

Sn GC-MIP-OES sediments Bu-Sn and Ph-Sn compounds -acid leaching/extraction into organics/complexation with dithiocarbamates [526]... 

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