Removal of perchlorate from contaminated waters using surfactant-modified zeolite.

We investigated the potential of using surfactant (hexadecyltrimethylammonium)-modified zeolite (SMZ) as an inexpensive sorbent for removing perchlorate (ClO(4)(-)) from contaminated waters in the presence of competing anions. In batch systems, the presence of 10 mM OH(-) (i.e., pH 12), CO(3)(2-), Cl(-), or SO(4)(2-) had little effect on the sorption of ClO(4)(-) by SMZ, indicating that the sorption of ClO(4)(-) by SMZ was very selective. The presence of 10 mM NO(3)(-), however, reduced the sorption of ClO(4)(-) at low initial concentrations. The maximum sorption capacity for ClO(4)(-) by the SMZ remained relatively constant (40-47 mmol kg(-1)), in the absence or presence of the competing ions. In flow-through systems, ClO(4)(-) broke through the SMZ columns much later than other anions present in an artificial ground water. The affinity of the anions for SMZ followed the sequence of ClO(4)(-) > > NO(3)(-) > SO(4)(2-) > Cl(-). Perchlorate loading under dynamic flow-through conditions was 34 mmol kg(-1), somewhat less than the maximum loading of 40 to 47 mmol kg(-1) determined by the batch method. Less than 1% of previously sorbed ClO(4)(-) was leached out by ultra-pure water, by extraction fluid #1 of the standard toxicity characteristic leaching procedure (TCLP), or by a solution of 0.28 M Na(2)CO(3)/0.5 M NaOH. About 40% of the previously sorbed ClO(4)(-) was leached out from SMZ by a 0.5 M NO(3)(-) solution. The exchange of ClO(4)(-) with NO(3)(-) corroborated results of the batch tests where NO(3)(-) was shown to compete with ClO(4)(-) sorption.