Biosorption of hexavalent chromium and molybdenum ions using extremophilic cyanobacterial mats: efficiency, isothermal, and kinetic studies

Abstract

Two extremophilic cyanobacterial–bacterial consortiums naturally grow in extreme habitats of high temperature and hypersaline were used to remediate hexavalent chromium and molybdenum ions. Extremophilic cyanobacterial–bacterial biomasses were collected from Zeiton and Aghormi Lakes in the Western Desert, Egypt, and were applied as novel and promising natural adsorbents for hexavalent chromium and molybdenum. Some physical characterizations of biosorbent surfaces were described using scanning electron microscope, energy-dispersive X-ray spectroscopy, Fourier transformation infrared spectroscopy, and surface area measure. The maximum removal efficiencies of both biosorbents were 15.62–22.72 mg/g for Cr(VI) and 42.15–46.29 mg/g for Mo(VI) at optimum conditions of pH 5, adsorbent biomass of 2.5–3.0 g/L, and 150 min contact time. Langmuir and Freundlich adsorption models were better fit for Cr(VI), whereas Langmuir model was better fit than the Freundlich model for Mo(VI) biosorption. The kinetic results revealed that the adsorption reaction obeyed the pseudo-second-order model confirming a chemisorption interaction between microbial films and the adsorbed metals. Zeiton biomass exhibited a relatively higher affinity for removing Cr(VI) than Aghormi biomass but a lower affinity for Mo(VI) removal. The results showed that these extremophiles are novel and promising candidates for toxic metal remediation.