Micro-pixe study on sorption behaviors of cobalt by lichen biomass

Sorption behavior of Cobalt (Co) by lichen biomass has been studied in the foliose lichen Permotrema tinctorum in solution between pH 3 and 5. Disc of P. tinctorum, weighing approximate to9 mg was incubated in 25 ml 0.1 M NaCl solutions containing 1 mM Co for up to 96 h. Concentrations of Co in the solutions were measured at 24, 48, 72 and 96 h by ICP-AES. Spatial distribution of Co, K, P and Fe in the cross-section of P. tinctorum was examined by in-air mu-PIXE (particle induced X-ray emission) technique developed in the TIARA facility of JAERI. Sorption of Co by P. tinctorum reached equilibrium within 24 h. Co uptake was averaged to be 27 dry wt.%, and was independent of solution pHs between 3 and 5. Two-dimensional distribution of Co indicates that the sorbed Co was localized, and the density of Co in the lichen was ordered lower surface > upper surface, medullary layer > algal layer. Highest density in the two-dimensional distribution of Co is obtained in the lower surface suggesting that Co was sorbed by melanin-like pigment contained in the lower surface. Two-dimensional distribution of Co did not correspond to Fe indicating that Co was not adsorbed on the Fe-containing minerals trapped on P. tinctorum. It is concluded that mu-PIXE analysis is a useful technique to detect the distribution of low concentration of elements in lichen biomass. (C) 2003 Elsevier B.V. All rights reserved.