Dioxin removal from solution by clays and hydroxy aluminum polymers.

Abstract

Novel solution removal techniques for hydrophobic pollutants were investigated. In particular, the research focused upon combining clays with hydroxy aluminum polymers to develop Polychlorinated Dibenzo-p-dioxin (PCDD) and Polychlorinated Biphenyl (PCB) separation strategies. Montmorillonite clay treated with hydroxy aluminum polymer produced a composite pseudo-zeolitic structure with the hydroxy aluminum polymer intercalating montmorillonite layers and coating the external clay surface. In aqueous phase partitioning experiments, the hydroxy aluminum montmorillonite composite achieved octachlorodibenzo-p-dioxin (OCDD) partitioning coefficients of approximately 100,000 ml/g, which was a forty-fold increase over untreated montmorillonite. Experiments performed with hydroxy aluminum-treated kaolinite and precipitated hydroxy aluminum polymer (gelatinous aluminum trihydroxide) demonstrated OCDD sorption occurred due to OCDD interaction with hydroxy aluminum polymers. Selected PCDD and PCB congener partitioning studies confirmed hydroxy aluminum polymers had high binding affinity for a wide range of low solubility organic pollutants. Experimental studies indicated some PCDDs and PCBs appeared soluble in an aqueous solution while actually being in a supersaturated state. Soluble salt addition to PCB and PCDD solutions precipitated supersaturated molecules, but did not precipitate truly soluble molecules. Thus, salt addition was a viable technique to determine if PCBs and PCDDs were truly soluble. Hydroxy aluminum polymers in solution were found to actually increase PCB and PCDD solubility. This increase occurred because hydroxy aluminum polymers bind PCBs and PCDDs very strongly. Hydroxy aluminum polymers applied to montmorillonite-PCDD solutions produced an OCDD 'in situ' treatment that had very high PCDD removal efficiencies because montmorillonite captured hydroxy aluminum polymer very effectively from solution. Finally, PCDD binding to hydroxy aluminum polymers probably occurred through a hydrophobically driven mechanism.