Separation of Cr(VI) from aqueous solutions by adsorption on the microfungus Ustilago maydis

Cr(VI) adsorption from aqueous solutions on the microfungus Ustilago maydis modified with formaldehyde (UmF) was studied as a function of the initial pH, contact time, chromium concentration and temperature. The pH results showed that Cr(VI) adsorption on UmF is higher at acidic pH values and decreases as the pH increases to alkaline values. Cr(VI) adsorption also depends on the chromium concentration and temperature. The Cr(VI) adsorption data as a function of concentration obey the Freundlich and Langmuir isotherms at pH values of 2 and 6.5. The maximum sorption capacity of UmF for Cr(VI) at pH 2 was 2.53 × 10−3 mol/g (131.55 mg/g), which is significantly higher than that at pH 6.5 (0.33 × 10−3 mol/g or 17.60 mg/g). The negative value of ΔH° and the positive values of ΔG° indicate that the chromium adsorption process is exothermic and non-spontaneous. The pHpzc value was 5 for UmF and it played a role in the Cr(VI) adsorption.