QUATERNARY AMMONIUM SURFACTANT EFFECTS ON SORPTION OF TRACE-METALS ONTO QUARTZ AND ALUMINOSILICATES

This study was conducted to investigate the potential impact of quater nary ammonium compounds (QACs) on trace metal ion desorption from soil constituents. Three soil constituents (quartz, kaolinite, and montmor illonite), two trace metal cations [Co(II) and Sr(II)], and three alky ltrimethylammoniumchloride surfactants (C8TMAC, C12TMAC, and C16TMAC) were chosen for this investigation. For the quartz system, Co(II) show ed no desorption while Sr(II) showed a slight pH-dependent desorption. For kaolinite or montmorillonite systems, desorption of Co(II) and Sr (II) by QACs occurred only for the fraction of the trace metal cations sorbed on permanent-charge sites. In the case of montmorillonite, Sr( II) was significantly desorbed at all pH values. This was thought to b e a result of the nearly exclusive sorption of Sr(II) to the permanent -charge sites in this system. In all other clay systems studied [Sr(II ), Co(II) on kaolinite; Co(II) on montmorillonite], desorption only oc curred at lower pH from permanent-charge sites. No desorption occurred at higher pH values where sorption to surface hydroxyl sites was indi cated. In general, QAC-induced desorption of trace metal cations was f ound to be significant only when QAC sorption equaled or exceeded the cation-exchange capacity. Surfactant chain length was found to have li ttle effect on the overall pH-dependent desorption trends. As expected , higher surfactant concentration was required to cause trace metal io n desorption as the surfactant chain length decreased.