2.6. Chemical modifications of functional groups present
on the biomass surface
Portions of Spirulina biomass were chemically treated
in different ways to understand the role of functional
groups in proton exchange and in metal ion biosorption.
Chemical treatments applied to the biomass were done
according to the procedure given by Kapoor and
Viraraghavan (1997).
Biomass was suspended in anhydrous methanol and
concentrated hydrochloric acid to esterify carboxylic
groups, in formaldehyde and formic acid to perform
methylation of amine or hydroxyl groups and in triethyl
phosphite and nitromethane to esterify phosphate
groups. The aim of chemical modification was to block
a given functional group to prevent its participation in
biosorption and to check decrease of biosorption capacity.
This procedure enabled to evaluate a contribution of
each functional group in the overall biosorption process.
2.7. Heavy metal desorption experiments
Heavy metal-laden biomass was centrifuged and
washed three times with deionized water to remove
any residual solution. The biomass was then placed in
the test tube containing 1ml of desorbing agent. Two
different desorbents were used to strip the adsorbed
metal ion: 0.1M nitric acid and 0.1M disodium salt of
ethylenediaminetetraacetic acid (EDTA). The tubes
were incubated for 30min at 35C. Following each
desorption with either HNO3 or EDTA, the slurry was
filtered and heavy metal ions concentration in the filtrate
was determined. The amount of desorbed heavy metal
ion was calculated.