The Reactivity of Soil Organic Fractions towards Cadmium, Copper, Calcium and Zinc
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Date
2006-08-25
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Abstract
Humic substances are extremely important soil components because they constitute a stable fraction of carbon and improve their water holding capacity. They also play an important role in the behaviour of trace metals in natural environments, due to the formation of complexes which modify can mobility of these ions.
In this project, the physico-chemical characteristics and metal binding for six (6) different soil types from Bibiani mines have been investigated. The physical properties viz: pH, conductivity,particle size distribution, moisture content, exchangeable acidity were determined on the raw
Samples and potassium, phosphorus, iron, calcium, cadmium, lead and zinc were determined from the digest. The total nitrogen and organic matter were also determined. Although the characterization could not reveal details of chemical processes taking place in the sample, some characteristics that revealed differences between the samples were identified. The mine tailings ^exhibited some characteristics similar to samples Bibiani forest (cocoa plantation) eg: Organic ter (New Tailings - 0.53%; Old Tailings - 0.64%; Cocoa Plantation - 0.58%); and Carbon-
Nitrogen ratio (New Tailings -12; Old Tailings -10.30; Cocoa Plantation -11,20) were similar.
Humnic substances were extracted from the soil samples using various standard procedures. The amount of humic acids extracted ranged from 0.493g to 0.092g, whilst the volumes of orange fulvic acid were 215mL for Russel Pit and 212mL for the Old Tailings.
A study of complexation of humic acids by trace metals (Cd, Zn, Ca, and Cu) revealed that
metal-humic substances association depends on the metal, the nature of the humic substance and
concentration. Ca was complexed to a higher extent than Cu, followed by Cd and Zn. The Complexation strength was in the order FA < HA. A comparison of the calculated stability
constants suggests that the strength of metal complexation by humic substances from Old
Tailings was higher than that of humic substances from Russel Pit. For the Old Tailings, the order of decreasing complexation stability constants of the humic and fulvic acids is Ca ^ > Cu+
Cd 2+ > Zn 2+ and Ca 2+ > Cu 2+ > Zn 2+ > Cd 2+ respectively. For Russel Pit the order is ric Acid: Ca 2+ > Cu 2+ > Cd 2+ > Zn 2+ Humics Acid: Ca 2+ > Cd 2+ > Cu 2+ > Zn 2+
Description
A Thesis submitted to the Department Of Chemistry Faculty of Physical Sciences College of Science Kwame Nkrumah University of Science and Technology, Kumasi
in partial fulfilment of the requirements for the Degree of Master of Science (Environmental Chemistry), 2006