COMPARATIVE STUDY USING RAW AND TREATED CASSAVA AND LEMON RESIDUES IN THE REMOVAL OF NICKEL (II)

Abstract

Increasing pollution of water bodies by heavy metals from different anthropogenic activities, mainly of industrial nature, generates a high level of danger due to accumulation. Within a given time, heavy metals reach high concentrations in living organisms, especially those around sites of discharge. The objective of this research was to evaluate the adsorption capacity of dried lemon (Citrus limon) and cassava (Manihot esculenta Crantz) peels, raw or treated with citric acid, to remove Ni (II) in synthetic aqueous solution with 100 mg L^-1 of metal. To assess adaptation and characterize these bio-adsorbents, biomasses were washed with distilled water. They were dried at 90 °C for 24 h and then ground in a mill. The modification of the cassava and lemon peels was carried out with 0.6 M citric acid; followed by adsorption and kinetic tests that were carried out in a discontinuous system. The biomaterials were characterized by chemical, elemental and Fourier transform infrared spectroscopy (FTIR) analysis. We found that both biomasses are composed mostly of carbon and cellulose. The FTIR showed the presence of carboxyl, amino, carbonyl and hydroxyl functional groups, which intervene in the adsorption process. Lemon and cassava peels showed 95.8% adsorption capacity of Ni (II) ions, and 75.69% removal of the contaminants. The best adsorbent particle sizes were 0.5 mm for lemon, and 1 mm for cassava peel, the two biomasses at pH 6. The best fit of the experimental data was Freundlich’s model and the pseudo-second-order model best described adsorption kinetics in the Ni (II) removal process. Treatment of the biomasses with citric acid did not render a significant improvement in metal removal. The best conditions for an efficient adsorption process were achieved using a specific particle size for lemon, 0.5 mm, and 1 mm for cassava residues.