Trace element removal

Honeyman and Santschi 1989). Therefore, flocculation of colloids to form settling particles in estuaries is an important mechanism for trace element removal (Sholkovitz 1977). This is particularly true of Fe, which is a ubiquitous colloidal species and is removed at low salinities. Additional removal may occur by adsorption onto floes, as demonstrated by mixing of organic-rich waters with seawater in the laboratory (Sholkovitz 1977). 

Aluminum silicates clays, oxides - Ion exchange binding of phosphates and metal ions unless present in large concentrations, overall effect on trace element removal is small. 

NORTON ET AL. Coal Cleaning Effect on Trace Element Removal... 

Trace Element Removal During Physical Cleaning. Comnercial coal cleaning processes employ physical means for beneficiation and are aimed at removing ash forming minerals and sulfur, although removal of the mineral matter also results in reduced levels of some trace elements. Trace element extraction efficiencies for various physical cleaning processes have been reported. 

In our own work, the effectiveness was examined of trace element removal by two chemical coal cleaning methods being studied for possible large-scale application. One method involved treatment with aqueous Na,C03 solutions, and the other involved treatment with molten NaOH/KOH mixtures. In each case, acid washes were used as subsequent cleaning steps to decrease the ash content, followed by water washes in the final step. Although the primary objective of these treatments was to remove sulfur and ash-forming minerals, the extraction of trace elements from these coals was examined as an additional benefit of chemical coal cleaning. 

Based on literature data, physical cleaning methods generally seem to be less effective at trace element removal then chemical methods. 

No data are available on reproducibility with respect to trace element removal during chemical cleaning. 

Ford, C.T. Care, R.R. Bosshart, R.E. "Preliminary Evaluation of the Effect of Coal Cleaning on Trace Element Removal" Report 3, Trace Element Program, Bituminous Coal Research, Inc., 1976. 

Acid-treated coal, trace element removal, 65... 

Such research into inorganic medicinal chemistry will attract increasing attention, but research into trace element removal using chelation therapy will not decrease. Indeed, reliable experimental data and a sound theoretical understanding of how administered agents modify metal ion distributions in vivo will become more important than ever. 

Figure 8.7. Fraction of trace element removed from solution as a function of the fraction of major element precipitated in a mixed flow reactor.

Prior to the agricultural and industrial revolutions, the main fertilisers applied to the land were animal products which had been derived from it, such as blood and bone meal, farmyard manure and human faeces although seaweed was also applied in coastal areas. A large fraction of the trace elements removed from the soil was therefore returned and the rate of depletion was therefore relatively slow. The system of agricultural production was therefore, to a large extent, self-regenerating, in that both major and minor nutrients were returned to the land in balanced proportions. Although the problem of dispersion of non-essential elements did not exist, soil fertility was sustained by this system at a low level by modem standards. 

At present, therefore, depletion of essential trace elements as a result of crop removal is high and only a small fraction of the trace elements removed... 

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