Removal of Cr(VI) From Aqueous Solutions By Self-Flocculating Yeast

In this study, the ability of self-flocculating yeast to remove Cr(VI) from aqueous solutions was investigated. Effect of pH, contact time and temperature on the biosorption was examined, and it was found that pH was a significant factor, affecting not only the removal ability of Cr(VI) by the self-flocculating yeast but also the contact time required for the biosorption to reach equilibrium, while the biosorption was not significantly affected by temperature at the range from 30 to 40 °C suitable for the self-flocculating yeast to perform. The fitness of the experimental data with the Freundlich and Langmuir isotherms was further evaluated, and good correlation was observed, indicating both monolayer biosorption and the presence of heterogeneous surfaces. Since no Cr(VI) was directly detected in the solution when the self-flocculating yeast after adsorption was treated by HNO₃ under high temperature, the removal mechanism of Cr(VI) was deduced to be its reduction under acidic conditions on the surfaces of the self-flocculating yeast cells. The first order dependence of the biosorption rate on each of Cr(VI) and biomass concentrations was experimentally validated, and a pseudo second-order kinetic model was established for the biosorption process.