Antibiotic ciprofloxacin (CIP) is immobile in the subsurface but it has been frequently detected in the
aquatic system. Therefore it is important to investigate the factors impacting CIP's mobilization in
aquifer. Laboratory columns packed with sand were used to test colloid-facilitated CIP transport by
1) using kaolinite or montmorillonite to mobilize presorbed-CIP in a column or 2) co-transporting
with CIP by pre-mixing them before transport. The Langmuir model showed that CIP sorption by
montmorillonite (23 g kg−1) was 100 timesmore effective than sand or kaolinite. Even with strong
CIP complexation ability to Fe/Al coating on sand surface, montmorillonite promoted CIP transport,
but not kaolinite. All presorbed-CIP by sandwasmobilized bymontmorillonite after 3 pore volumes
through co-transporting of CIP with montmorillonite. The majority of CIP was fixed onto the
montmorillonite interlayer but still showed inhibition of bacteria growth. Our results suggested that
montmorillonite with high CIP sorption ability can act as a carrier to enhance CIP's mobility in
aquifer.