Removal of Heavy Metal Ions by Waste Biomass of Saccharomyces Cerevisiae

The kinetics, equilibriums, and thermodynamics of metal ion ( ${\text{Pb}}^{2+}$ , ${\text{Ag}}^{2+}$ , ${\text{Cu}}^{2+}$ , ${\text{Zn}}^{2+}$ , ${\text{Co}}^{2+}$ , ${\text{Sr}}^{2+}$ , and ${\text{Cs}}^{+}$ ) biosorption by the waste yeast cells of Saccharomyces cerevisiae from a local brewery were investigated. The results showed that the biosorption of these metal ions on the biomass was a very rapid process, following the pseudo-second-order equation gave the better fitting results in describing the kinetic data than the pseudo-first-order equation. The equilibrium data could be fitted well with the Langmuir model. The maximum sorption capacity obtained from the Langmuir model followed $\text{Pb}>\text{Ag}>\text{Cu}>\text{Zn}>\text{Co}>\text{Sr}>\text{Cs}$ (based on $\text{mmol}{\text{g}}^{-1}$ ). The biosorption process by the yeast was favorable for these metal ions removal according to the constant separation factor $\left(0<R_L<1\right)$ from the Langmuir model. The dried yeast cells showed high affinity for ${\text{Pb}}^{2+}$ uptake as soft ion and low affinity for ${\text{Cs}}^{+}$ as hard ion biosorption. The calculated values of the thermodynamic constants demonstrated that the biosorption process of ${\text{Ag}}^{+}$ , ${\text{Cu}}^{2+}$ , ${\text{Zn}}^{2+}$ , or ${\text{Co}}^{2+}$ was spontaneous and the entropy increased. pH increased during the metal biosorption by the yeast cells. ${\text{Pb}}^{2+}$ , ${\text{Ag}}^{2+}$ , ${\text{Cu}}^{2+}$ , ${\text{Zn}}^{2+}$ , or ${\text{Co}}^{2+}$ exhibited a certain degree of covalent binding with the waste yeast cells. ${\text{Cs}}^{+}$ , as a typical hard ion, showed ionic binding with the biomass.