Biosorption of some elements by algae from a cutinite-rich coal and its effect on organic geochemical composition: A case study from Abu Thora, Sinai, Egypt

Abstract

A Carboniferous-age unique cutinite-rich coal seam at Wadi Abu Thora in Sinai, Egypt, was subjected to biosorption extraction of uranium (U) and thorium (Th) by five native algal species. These algal species were used in the biosorption process with the coal acting as a cultivation substrate. The concentration of U and Th was measured before and after the biosorption process. The five algal species used included Sarconema filofirms, Ulva Lactuca, Sargassum detofiulum, Caulerpa prolifera, and Cystoseira osmundacea, in addition to the yeast Saccharomyces cerevisiae. Two species, namely Caulerpa prolifera and Cystoseira osmundacea, were able to grow and adhere well to the coal particles as indicated by the microscopic examination in fluorescence mode. The above two species showed a capability to biosorb U and Th completely followed by Sarconema filofirms (56.7%, 18.7 ppm), Ulva Lactuca (49.4%, 16.3 ppm), and Sargassum detofiulum (40.3%, 13.3 ppm). These three species were successful in the uptake of U, alongside Saccharomyces cerevisiae, which showed a greater capability (58.2% or 19.2 ppm U). Biosorption by Caulerpa prolifera and Cystoseira osmundacea algae is an effective procedure to extract U and Th from this coal. Coal macerals played an important role in U precipitation, reflecting the structure of the compound that contains the U. Extraction of U and Th by biosorption resulted in changes in the cutinite-rich coal sample. Geochemical evaluation of the treated samples reflects a change in their chemical structure with the partial or complete removal of carboxyl/carbonyl-only groups in addition to the n-alkane chains. Pyrolysis data indicated shorter n-alkane-alkene compounds and smaller ratios. Data show that algae play a role in the biotransformation of absorbed organic matter composition by type and quantity. Finally, these compositional changes may produce more mature organic matter from the parent sample.