A novel, integrated treatment systems for coal wastewaters

Abstract

The aims of this study are to develop, characterize and optimize a novel treatment scheme that would be effective simultaneously against the toxic organics and heavy metals present in coal conversion wastewaters. Hec-CBDA-DT, a modified hectorite containing a mixed bilayer of a cationic (CBDA) and a diamine (DT) type surfactants, was shown to adsorb simultaneously heavy metals such as Cu[sup 2+] and Cd[sup 2+] and toxic organics such as chlorophenols. The pH dependence of the adsorption of chlorophenols on Hec-CBDA-DT suggested hydrophobic partitioning, counterion adsorption and hydrogen-bond interaction of the phenolate ions with the surface diamine groups as the possible mechanisms of sorption. Adsorption of Cu[sup 2+] by Hec-CBDA-DT was shown to be only slightly affected by a large excess of counterions, thus indicating that Cu[sup 2+] adsorbed specifically to the surface. A second type of modified clay, Hec-CBDA-Palmitic Acid (Hec-CBDA-PA) adsorbed both Cu[sup 2+] and Cd[sup 2+] strongly. However, the pH optima for adsorption were 6.0 and 8.0 respectively in the case of Cu[sup 2+] and Cd[sup 2+]. It is inferred that the mechanisms of adsorption of these two metal ions to Hec-CBDA-PA are different, specific and counterion binding respectively in the case of Cu and Cd ions.