Removal of perchlorate (ClO4-) while using granular-activated carbon (GAC) that had been preloaded with cetylpyridinium chloride was appraised using Rapid Small-Scale Column tests (RSSCT) and pilot-scale demonstration. ClO4- competed with nitrate, sulfate, chloride, and other anions for ion exchange sites on the preloaded carbon. Tests used native groundwater from Fontana, CA, which contained nitrate of 32/mg/L as NO3-, 7/μg/L as ClO4 -, and 1.9/μg/L (as U) of uranyl carbonate species (predominantly UO2(CO3)34-) species. RSSCT with Fontana groundwater exhibited ClO4- breakthrough at 25,000 bed volumes. When the same groundwater was spiked to three times the native NO 3- concentration, ClO4- breakthrough occurred at 12,000 bed volumes. When the total dissolved solids (TDS) increased from the native 250/mg/L up to 660-810/mg/L TDS, by adding magnesium sulfate, sodium bicarbonate, or sodium chloride, the bed-life for removing ClO 4- increased by 10%-30%. This result was attributed to perchlorate's competition with native UO2(CO 34-, which limited the bed-life for ClO4- breakthrough. Specifically, at higher TDS the computed activity coefficient of UO2(CO3) 34- decreased relative to that of single-charged ClO 4-, and this effectively yielded more favorable ion-exchange competition by the ClO4-. Pilot-scale studies that used elevated nitrate levels in the water exhibited similar trends to the RSSCTs. These effects further emphasized the compounded competition that the uranyl carbonate posed on cetylpyridinium chloride-tailored GAC where this surfactant had been loaded in compact-micellar configuration. This represents an important consideration for a number of groundwater sources where uranium appears in trace concentrations.
All Science Journal Classification (ASJC) codes
- Environmental Chemistry
- Waste Management and Disposal