Adsorption of water‐soluble polychlorinated biphenyl aroclor 1242 and used capacitor fluid by soil materials and coal chars

Abstract

Adsorption of the water‐soluble PCBs Aroclor 1242 and a used capacitor fluid (impregnated with Aroclor 1242) by five earth materials and their low‐temperature ashes were studied under constant‐temperature laboratory conditions. The five earth materials studied were medium‐temperature coal char (MTC), high‐temperature coal char (HTC), Catlin soil (CS), montmorillonite clay (MC), and Ottawa silica sand (OS). Adsorption followed the series MTC > HTC > CS > MC > OS.

There were no significant differences between adsorption of the Aroclor 1242 and the used capacitor fluid by any of the five earth materials. A simple linear relation described the adsorption of PCBs from aqueous solution by the earth materials and yielded an adsorption constant (K) unique to each adsorbent.

Very highly significant (.001 level) linear correlations were found for K as a function of total organic carbon (TOC.), the coefficient of determination, r ² equals 0.87; K as a function of the surface area measured with carbon dioxide (CO₂‐SA), r ² = 0.82; and K as a function of TOC and CO₂‐SA, r ² = 0.95. Poor correlations were found for K as a function of the surface area measured with nitrogen (N₂‐SA) and K as a function of the surface area measured with ethylene glycol. PCB molecules did not penetrate into and were not adsorbed by the interlayer surfaces of montmorillonite. TOC and CO₂‐SA were the most important properties of earth materials controlling PCB adsorption; TOC was the dominant property by a factor greater than three.

PCB analysis by capillary column gas‐liquid chromatography (GLC) techniques indicated preferential adsorption of higher‐chlorinated isomers over lower‐chlorinated isomers; however, preferential adsorption also depended on the position of chlorine substitution on the biphenyl ring. Preferential adsorption of the particular isomers 2‐monochloro‐, 4‐monochloro‐, and 3,4'‐dichlorobiphenyl were found. Preferential adsorption of GLC peaks 4, 31, and 33, identified only as a di‐, tri‐, and tetra‐chlorobiphenyl, respectively, were also noted.

Key words:

• Montmorillonite
• low‐temperature ashes
• Freundlich isotherm
• adsorption constant
• partition coefficient
• surface area
• total organic carbon