Unripe calamansi peels were prepared and used as a bioadsorbent in the removal of congo red from an aqueous solution using batch adsorption studies. The efficiency of adsorption was evaluated by varying adsorbent dose and contact time. The removal of congo red increased at higher adsorbent dose and longer contact time. The overall rate of adsorption processes appeared to be in accordance with the pseudo-second order reaction mechanism. Higher initial adsorption rate, extent of surface coverage, and activation energy were favored at a lower adsorbent dose, while the intraparticle diffusion was relatively faster at a higher adsorbent dose. The intraparticle diffusion, Elovich, and MacArthur-Wilson models were adequate in describing the chaotic behavior of the kinetic processes involved in the removal of congo red dye onto unripe calamansi peels.

Batch adsorption of toxic Cr(VI) ion from an aqueous solution using lumbang (Aleurites moluccana) activated carbon-chitosan composite crosslinked with epichlorohydrin as an adsorbent was investigated. The adsorption experiments were performed at varying pH, agitation time, initial Cr(VI) ion concentration, temperature, and adsorbent dose. At an initial concentration of 60 ppm Cr(VI), the maximum adsorption was observed at pH 3, adsorbent dose of 3 g/L, contact time of 75 min, and temperature of 30 o C. Analysis of the experimental data using different kinetic models revealed that the biosorption phenomenon behaved under a pseudo second-order rate mechanism.

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Removal of Pb(II) using lumbang activated carbon carboxymethylcellulose composite crosslinked with epichlorohydrin was investigated. Batch adsorption studies were performed to evaluate the effects of pH, contact time, temperature, adsorbent dose, and metal concentration. To characterize the adsorbent, proximate analysis, bulk density, DSC, FT-IR, and SEM analysis were performed. Results of FT-IR revealed that crosslinking did not alter the structure of carboxymethylcellulose due to the presence of the -COO functional groups, while the presence of the C-O signal indicates that the adsorbent was successfully crosslinked by epichlorohydrin. Furthermore, SEM results showed highly porous nature of the prepared adsorbent. The optimized parameters of the adsorbent were pH 3, contact time of 15 min. 30 o C temperature, adsorbent dose of 4 g/L at 5 ppm Pb (II) solution. With these optimized parameters, 73% removal of Pb (II) was attained in aqueous solutions, while 37% removal was observed in the wastewater sample. Moreover, the adsorption process was best described by Dubinin-Radushkevich isotherm and obeyed the pseudo-second order kinetic model.

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