Studies on the Adsorption and Desorption Behaviour of Trace Metals in Soils

Khattak, Saber Gul Khan (1993) Studies on the Adsorption and Desorption Behaviour of Trace Metals in Soils. PhD thesis, University of Glasgow.

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Chapter 1 gives a general introduction to trace elements in soils. A brief discussion about their occurrence, forms in soils and state in which plants utilize them has been made. Physiological role and deficiency symptoms due to short supply have been identified. Much emphasis has been given to the adsorption and desorption behaviour and factors affecting adsorption and desorption of trace metals. Zinc, Copper and Nickel have been the focus of the Chapter. Chapter 2 lays emphasis on the methods and materials used for conducting the different experiments. Moreover a brief history and some physical and chemical properties of the five British soils have been mentioned in this chapter. Chapter 3 elucidates the development of different procedures for adsorption and desorption of zinc in soils. After a series of experiments an 18 hour shaking time for adsorption and desorption of zinc in soils was selected. The results obtained from these experiments suggest that prolonging the time of zinc contact with soils increases the adsorption of zinc, however it is more significant with lower concentrations than higher concentrations. Furthermore the soils high in clay content adsorbed more zinc compared to coarse soils. It is comparatively easier to desorb zinc from a soil at higher metal concentration than low concentration. Generally dilution by deionized water did not desorb a significant amount of adsorbed metal perhaps due to the inability of deionized water to break the strong bonds between metal and soil components Chapter 4 investigates adsorption and desorption behaviour of zinc, copper and nickel in 0.1 M NaNO3 background electrolyte. The results suggest that due to reducing the background interferences by using an electrolyte, lesser amount of zinc was adsorbed compared to deionized water used in chapters. Moreover it shows that zinc and nickel have almost similar behaviour towards adsorption in soils. Behaviour of copper indicates high affinity of adsorption by soils and is completely different from zinc and nickel. Clayey soil adsorbed higher amounts of metals than other soils. Although texture appeared to be dominant, other properties of soils in respect of adsorption behaviour could not be neglected, especially pH and organic matter. All the adsorption data regarding these metals fit well to both Langmuir and Freundlich equations. The desorption data suggest that copper formed strong bonds with soil components, perhaps with clay, and therefore very low percent of copper was desorbed with dilution by electrolyte. The other two metals were recovered up to 50% except in the clayey soil. Langmuir equation better fitted the desorption data of all metals compared to Freundlich equation. Chapter 5 illustrates that temperature has an effect on adsorption and desorption of zinc in soils. Adsorption of zinc increases with the increase of temperature and generally desorption decreases. However the desorption of zinc at higher temperatures sometimes showed no significant decrease in some soils. It suggests that higher temperature weakened the binding constants of zinc with those soils. The results also show the effect of dilution on the desorption of zinc at four different temperatures and suggest that activation energy increased with increased dilution. This is because to break the existing bonds of zinc with soil. It is necessary for desorption reactions to have a significant activation energy, while it is not necessary for adsorption reactions to have a significant activation energy. The low activation energy of all soils suggests that diffusion have played a major role in all reactions.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: I D Pulford
Keywords: Soil sciences, Biogeochemistry
Date of Award: 1993
Depositing User: Enlighten Team
Unique ID: glathesis:1993-75484
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 19:50
Last Modified: 19 Nov 2019 19:50

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