Leaching of metal

Microbial leaching of metals from ores is a promising adjunct to more aggressive metal recovery technologies (77), but is generally achieved by oxidative processes that generate very acidic waters. It seems unlikely that similar approaches will be of much value in removing contaminant metals and metalloids from soils. 

Acid rain adversely affects trees as well (Figure A). It appears that the damage is largely due to the leaching of metal cations from the soil. In particular, H+ ions in acid rain can react with insoluble aluminum compounds in the soil, bringing Al3+ ions into solution. The following reaction is typical ... 

Humans may also be indirectly affected through exposure to increased levels of toxic metals in drinking water and food. Increased levels of toxic metal are a consequence of direct deposition of pollutants into water sources, increased leaching of metal from soils and lake sediments, and increased corrosion of water pipes. 

Suzuki, I. Microbial leaching of metals from sulfide minerals. Biotechnol. Adv. 2001, 19, 119-132. 

Leaching of metal into the product/contamination of the products. 

Trace elements on the surfaces of fly ash particles that are accessible to humans through air, soil, water, can affect health in several ways. The pathways by which metals from CCP may cause harm include (1) soil deposition and resulting plant uptake of metals and subsequent movement into the food chain (2) direct ingestion of soil by animals or humans (3) leaching of metals from CCP to water systems and uptake by plants, animals, or humans and (4) inhalation of dust (from soil) or respirable ash particles (Ryan Bryndzia 1997). 

Olefin Catalyst Temp [°C] Press. [atm] Yielda nli- ratio Leaching of metal Ref. 

Seven factors were studied to assess their importance on the acid microwave-assisted leaching of metallic elements... 

The Sumitomo Metal Mining Co. in Japan uses a carboxylic acid extractant to recover nickel and cobalt from a solution obtained from the pressure leaching of metal sulfide concentrates with sulfuric acid.44 Iron, copper, zinc and manganese are removed from the leach liquor by conventional precipitation methods prior to the extraction of nickel and cobalt into a 40-60% solution... 

The use of hydroxyapatites as a catalyst support has the following advantages (1) well-defined monomeric active species can be immobilized on the surface based on multiple functionalities, for example, cation exchange ability, adsorption capacity and nonstoichiometry (2) their hydrophilic character allows smooth reactions under aqueous conditions and (3) due to their robust structure, no leaching of metals occurs. 

Speciation in solution is considered a major factor in the mobilisation and leaching of metal cations (DeKoninck, 1980 Bloomfield, 1981 Stevenson and Fitch, 1986). Complexation increases the total soluble concentration of a metal and hence increases its potential to be leached. Organic ligands (e.g. humate, ful-vate, citrate, polyphenols) are the major complexers involved in this mechanism, but they are effective only if the soluble organic complex does not become saturated and precipitate (DeKoninck, 1980). 

The commercial importance of this metal was first recognized in 1950s when its high strength/density ratios were found attractive in aerospace applications. The corrosion resistance in a variety of conditions led to its use in wet chlorine gas coolers for chlor-alkali cells, chlorine and chlorine dioxide bleaching equipment in pulp/paper mills, and reactor interiors for pressure acid leaching of metallic ores. The metal and its alloys were used in seawater power plant condensers, with over 400 million feet installed in application.65,66 The most commonly used alloys and their composition are given in Table 4.48. 

Burgstaller, W. Schinner, F. (1993). Leaching of metals with fungi. Journal of Biotechnology, 27, 91-116. 

Leaching of metals from soil Leaching of metals from plant... 

Ultrasound energy has also been used to accelerate the leaching of metal proteins (particularly metallothionein-isoforms and superoxide dismutase from liver samples) [103]. One of the main problems encountered in analysing these samples (namely, the need to preserve the species stability during leaching) is circumvented by USAL. 

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