Hazardous elements speciation in sandy, alkaline coal mine overburden by using different sequential extraction procedures

Abstract

This paper deals with the problem of hazardous elements (HE) speciation in sandy, alkaline coal mine overburden destined for restoration. Two sequential extraction procedures [five stages Tesier's (T) and seven stages Zeien and Brümmner's method (ZB)] were employed that focused on potentially bioavailable HE fractions previously found in plants growing during this soil restoration process. The results showed that the selection of the extraction procedure in HE speciation is essential, due to the different potential threats of HE fractions obtained for plants. The biggest residual fraction obtained by both extractions suggest geogenic origin of Cu, Zn, Ni, Cr and Pb. Tesier's extraction procedure works reasonably well for low concentration of water soluble and exchangeable HEs, whilst giving higher values for their organically bound forms. Zeien and Brümmner's method, however, was found to be more appropriate for evaluation of the mobility of HE as Mn and Fe oxide fractions. The principal component analysis test estimated three main groups where the relationship between soil properties (pH, clay and silt), total content of element and available fractions (Zn, Ni, Cr, Pb-T and Ni-ZB) was defined as a PC 1 group. Other PC 2 and PC 3 from the PCA analysis include Corg and CEC, and available Cu-T and Cr, Pb-ZB, respectively. The PC 3 factor linked fine sand and available Zn-ZB. Pearson's correlation coefficients showed a high correlation between available HE and high pH(KCl) obtained by T-extraction, and Ni by Zn-extraction. Also, clay, silt and fine sand were highly correlated with the Ni-ZB available forms.