Metal sorption isotherms of agricultural calcareous soils from Malta

Abstract

The scope of this dissertation was to analyse how a better understanding of metal sorption isotherms in agricultural calcareous soils in the local scenario can help boost and maintain soil fertility. The question this study sought to answer is whether there is a relation between the extent of solutes adsorped when comparing diverse metals at different concentrations and whether the level of metal adsorption differs from one soil sample and another. It also required a detailed analysis on the differences in the predicted and obtained results for the sorption affinity of the samples tested. This was carried out by investigating the amount of metals studied (Copper (Cu), Lead (Pb) and Zinc (Zn)) that were attached to different types of soil as a function of solute concentration and analysing the extent of adsorption of each specific metal in the soil samples tested. Solutions of each individual metals at concentrations of 0, 10, 50, 100, 250, 500 and 1 OOOµM were analysed. These were derived using the MP-AES. From the values obtained, the adsorption affinity of each individual metal was established. From the results obtained, it was found that all samples tested demonstrated a high affinity in adsorption for all the three metal cations observed. Pb had a relatively slightly higher but similar affinity when compared with Cu. Zn, on the other hand, had a slightly lower adsorption capability at higher concentrations. From the texture analysis data, a high adsorption affinity was expected in the soil having more clay. However the adsorption affinity values were similar in the two soil types used. This outcome could be the effect of a high soil organic matter (SOM) content. All these results will help give a more profound understanding of the local soil properties and will help move towards more ecologically aware agricultural practices, particularly when considering the amounts of metal applied with fertiliser in the fields.