A silica matrix biosorbent of cadmium

In the process of preparation of a non-toxic metal biosorbent by entrapment of yeast cells in silica matrix by sol–gel technique, the homogeneity of yeast cell dispersion and prevention of precipitation during tetraethoxysilane pre-polymerization were found to be the parameters substantially influencing the sorption capacity for Cd2+. Ultrasonic treatment of cell walls increased the sorption capacity by 25% as a result of the suppression of their agglomeration. Precipitation during tetraethoxysilane (TEOS) pre-polymerization was tracked by measurement of light absorbance at λ=600 nm. The biosorbent formed from pre-polymer with a light absorbance of 0.3 had 50% less sorption capacity than that with an absorbance of 0.05. Modification of the TEOS:methanol:water ratio in the range from 1:10:8 to 1:10:40 and specific surface between 210 and 390 m2 g−1 influenced the sorption capacity of biosorbents only within the limits of experimental error. The sorption capacity per unit weight of biosorbent was proportional to the yeast cell wall content. The content could be increased up to a cell walls:SiO2 ratio 1.5 (w/w). Biosorbent with higher cell wall content was fragile and friable. Biosorbents were shaped by crushing and regular particles were prepared by moulding into millimetre-scale cylindrical moulds. In this shaping process, the loss of biosorbent mixture was small and the process could easily be scaled up. Using a mathematical model of a packed-bed adsorber, taking into account axial dispersion and mass transfer resistance the break-through curve for crushed and moulded biosorbent was predicted with high fidelity.