BIOSORPTION OF Pb2+, Cd2+, & Ni2+ FROM WATERS BY ...

M Na-citrate. Finally, the concentration of the metal ions in the filtrate was
determined by FAAS.
2.6. Immobilization Studies
2.6.1. Immobilization of Biosorbents into Sodium-Silicate.
The method for biomass immobilization within the polysilicate matrix was
the same as that reported by Karunasagar (2005) and Torresdey (1999). Briefly, 3.0
mL of 5.0 % H2SO4 were mixed with sufficient volume of 6.0 % sodium silicate
(Na2SiO3) solution to raise the pH to 2.0. Here, the solution pH was checked with pH
paper in order not to damage the electrode system of a pH meter due to use of silicate
solution. Then, 200.0 mg of biomass were added to the silicate solution and stirred for
15 min. The pH was raised to 7.0 by a slow addition of 6.0 % sodium silicate.
Meanwhile, a polymer gel was formed and washed with ultra-pure water thoroughly
until the addition of barium chloride did not result in a cloudiness (BaSO4) due to the
presence of sulphate ion. The polymer gel with immobilized algae was dried
overnight at 40ºC and ground by mortar and pestle. A blank silicate containing no
algae was also prepared. Then, the particles were used in the sorption experiments.
The typical structure of silica gel surface is shown in Figure 2.1.
Figure 2.1. The structure of silica gel
27