Submitted to: Journal of Chemical Technology & Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 10, 1997
Publication Date: N/A
Interpretive Summary: Low-value, agricultural by-products such as rice straw, soybean hull, sugarcane bagasse, and shells of peanut, pecan, and walnut were made into granular activated carbons (GACs). The softer materials required a binder, cane molasses, to make GACs. Both carbon dioxide and steam activations, as well as oxidation using gas or liquid, were used in making the GACs. These carbons were tested for their ability to adsorb organic and metal pollutants from water. Many of the by-products produced GACs having excellent physical properties for commercial usage. The carbons made from pecan and walnut shells had greater adsorption of several organic priority pollutants than the commercial GACs tested. Exceptional metal adsorbing properties were found with activated carbons made from soybean hull, peanut shell, rice straw, and sugarcane bagasse. Oxidation using an oxygen-nitrogen gas improved metal adsorption for these GACs. The metals tested were lead, cadmium, nickel, copper, and zinc. GACs made from soybean hulls adsorbed three to four times the amount of copper that commercial GACs were able to adsorb. The GACs made from the agricultural by-products have excellent potential for use in removing organic and metal pollutants from water.
Technical Abstract: Surplus, low value agricultural by-products can be used as feedstocks for producing granular activated carbons (GACs) which are used in environmental remediation. This study characterized and evaluated GACs, made from these feedstocks, as effective removers of organics and metals from water. The by-products included soft lignocellulosics such as rice straw, soybean hull, sugarcane bagasse, peanut shell, and harder materials such as pecan and walnut shells. The softer materials were combined with a binder, molasses, to produce briquettes and pellets. The precursors were CO2 or steam activated, and subsequent treatments included oxidation to enhance metals adsorption. Many of the GACs had acceptable physical GAC attributes, such as durability, for commercial usage. GACs made from pecan and walnut shells adsorbed higher levels of benzene, toluene, methanol, acetonitrile, acetone, and 1,4-dioxane from an aqueous mixture than commercial GACs. Neither CO2 nor steam activation was particularly advantageous in enhancing metal adsorption. Oxidation using O2-N2 gas increased metal adsorption while (NH4)S2O8 solution did not. In a Cu solution, oxidized GACs made from soybean hull had three to four times the Cu(II) adsorption capacity of metal adsorbing, commercial GACs. Using a mixture, oxidized GACs made from soybean hull, sugarcane bagasse, peanut shell, and rice straw adsorbed higher amounts of Pb(II), Cu(II), Ni(II), Cd(II), and Zn(II) than any commercial GACs. Commercial GACs adsorbed only Pb(II), Cu(II), and Cd(II). The GACs made from the agricultural by-pr s have considerable potential for adsorption of organics and metals of environmental concern.