Polycation-exchanged clays as sorbents for organic pollutants: Influence of layer charge on pollutant sorption capacity

The uptake curves for the adsorption of a polycation ([CH2CH(OH)CH2N(CH3)(2)](n)(n+)(Cl)(n)(n-)) onto a low iron Texas bentonite, WL, have been determined and compared with those onto two source smectites, Swy-1 and SAz-1. The polycation exhibited a marked affinity for all the smectite surfaces but polycation uptake was maximized on the fine fractions of Na+-WL. Variable temperature X-ray diffraction of the clay polycation complexes showed that the polycation was segregated into different interlayers at loadings below 30% of the CEC. The adsorption of benzene onto TMA(+)-exchanged SWy-1, SAz-1, and WL showed that, despite having a comparable layer charge to SWy-1, WL was as poor a sorbent for benzene as SAz-1, which has a much higher layer charge. The adsorption of p-nitrophenol (PNP) from aqueous solution onto the TMA(+)-exchanged sorbents exhibited the same trends, although a smaller amount was adsorbed due to the greater size of PNP. The amount of PNP adsorbed by polycation-treated SWy-1 depended upon the polycation loading, and PNP uptake maximized at loadings of 28 and 46 mg (g clay)(-1). At higher loadings (80, 102, and 147 mg (g clay)(-1)) the uptake curves became linear and the PNP uptake decreased with increased polycation loading. No polycation-treated clay was as effective as TMA(+)-exchanged SWy-1 for the removal of PNP from water. (C) 1998 Academic Press.