The grinded material
was powdered in a mortar and passed through a screen in order to get two different particle sizes, 2 and
1 mm, for all powders. To estimate the biosorption capabilities of the tested materials, different heavy
metals were passed through the columns and the elution filtrate reloaded different times to increase
the retention of metals. The heavy metals used were prepared as synthetic samples at 10 mg/L of
Pb(NO3)2, Cd(NO3)2, and Cu(NO3)26H2O using primary standards. In preliminary experiments using
banana cortex, it was found that material with 1 mm of particle size showed higher retention capability
(up to12%) than the material with 2 mm of particle size. Considering these results, 1 mm particle size
material was used in further experiments with the other waste materials. It was found that for Pb and
Cu removal, lemon and orange cortex showed better biosorption capability when compared with banana
cortex (up to 15% less for Pb and 48% less for Cu). For Cd, banana cortex showed better biosorption capability
57% (67.2 mg/g of cortex) more than orange (28.8 mg/g of cortex), and 82% more than lemon
(12 mg/g of cortex). Reload of the columns with the filtrate after passing through the column improved
the removal capability of all the materials tested from 10% to 50% depending on the cortex and metal
tested.