Keeran R. Srinivasan

Use of inorgano-organo-clays in the removal of priority pollutants from industrial wastewaters; adsorption of benzo(a)pyrene and chlorophenols from aqueous solutions

Benzo(a)pyrene (B(a)P), and chlorophenols were sorbed from their respective aqueous solutions onto inorgano-organo-clays (IOCs). Cetyl pyridinium hydroxy-Al montmorillonite (CPC-hydroxy-Al montmorillonite), an IOC, containing only 11–12% surface organic carbon by weight, bound pentachlorophenol strongly, with an observed monolayer capacity of 0.08 mmole/g. The comparable value for granulated activated carbon (GAC) was found to be 0.12 mmole/g. On the other hand, cetyl pyridinium cation-exchanged montmorillonite (CPC-montmorillonite), containing 19.2% surface organic carbon by weight, did not bind pentachlorophenol as efficiently as did IOCs. For benzo(a)pyrene, CPC-hydroxy-Al montmorillonite was found to be a better adsorbent than GAC and CPC-montmorillonite. The significant difference in the sorption potential of the two types of surfactant-laden clays for pentachlorophenol and benzo(a)pyrene was probably due to the surface orientation of the adsorbed organic carbon. For 3,5-dichlorophenol, however, both types of organo-clays exhibited weak binding, which was probably due to the greater aqueous solubility of the dichlorophenol.

USE OF INORGANO-ORGANO-CLAYS IN THE REMOVAL OF PRIORITY POLLUTANTS FROM INDUSTRIAL WASTEWATERS: STRUCTURAL ASPECTS

Novel modified clay adsorbents were prepared by blocking cation-exchange sites of an expandable clay, such as montmorillonite, with polymeric or polyvalent inorganic ions and by using cationic surfactants as sources of surface organic carbon. Electrokinetic measurements demonstrated that the adsorbed polycations were essentially nonexchangeable. Adsorption and desorption experiments revealed that about 90% of the cationic surfactant was apparently irreversibly bound to the surface. Flocculation and peptization studies were performed to establish that the adsorbed surfactant moiety was oriented with its hydrocarbon tail towards the surface. Such a configuration of simultaneously adsorbed polycations and cationic surfactants was designated as an inorgano-organo-clay (IOC). As shown in an accompanying paper, these IOCs bind priority pollutants as strongly as granulated activated carbon.

Dioxon sorption by hydroxy-aluminum-treated clays

The treatment of smectites with a hydroxy-Al polymer produced chemically modified clays that had much greater affinities for chlorinated dioxins and biphenyls than untreated clays. For hydroxy-Al-treated kaolinite, the high affinity for chlorinated dioxins is thought to have arisen from an interaction between the hydroxy-Al polymer bound to the clay and the chlorinated dioxin in solution. Thus, the adsorption of dioxins from aqueous solution by hydroxy-Al-treated clays is similar to the adsorption of reactants from the gas phase by metals supported on mineral oxides during catalysis. In both systems, the essentially inert mineral oxide support effectively disperses the active adsorptive agent. At the concentrations of octachlorodioxin used in this study (≤5 ppb), hydroxy-Al-montmorillonite had a distribution coefficient of 90,000 (ml/g), corresponding to about 95% removal efficiency of the dioxin from solution per batch. For hexachlorohiphenyl, the distribution coefficient was 30,000 (ml/g), and the removal efficiency was 85%.

Use of modified clays for the removal and disposal of chlorinated dioxins and other priority pollutants from industrial wastewaters

Abstract The dynamics of adsorption and elution of octachlorodibenzodioxin (OCDD) on modified clay adsorbents has been studied. In batch type experiments, a rapid approach to sorption equilibrium (within hours) as well as a Freudlich type sorption isotherm were noted. In packed bed sorption experiments using a step input of adsorbate concentration, no breakthrough was observed under a variety of volumetric flow rates suggesting multilayer adsorption of dioxins on modified clay sorbents. Elution of sorbed dioxin with carrier solvent tetrahydrofuran (THF) exhibited two peaks indicating heterogeneity of modified clay sorbents. Finally, successive sorption/elution/sorption experiments reveal that modified clay sorbents can be regenerated and reused.