Mechanism of tetracycline sorption on rectorite

The use of antibiotics and hormones in human and veterinary has resulted in frequent detection of these pharmaceuticals in groundwater and wastewater. Thus, it is of great interest to study the interaction between common pharmaceuticals and clay minerals. In this research, we investigated the sorption and intercalation of tetracycline (TC) from water onto rectorite, a regular interstratified clay mineral made of 1:1 ratio of illite and montmorillonite, under different pH and initial concentration conditions. The TC sorption capacity on rectorite reached to 140 mg g−1 at pH 4–5 and decreased to 54 mg g−1 at pH 11. The intercalation of TC into the interlayer space of the montmorillonite component resulted in an increase in d-spacing. Under acidic condition, the intercalated TC produced an interlayer gallery height of 10 Å, compared to 17 Å at pH 11, although the amount of TC intercalated is much less than that under acidic condition. Thermogravimetric analyses showed a peak decomposition temperature (Tpeak) of 230 °C for crystalline TC, which increased to 410–420 °C after intercalated in rectorite. Both XRD patterns and FTIR spectra showed different interlayer configurations of TC at low and higher amounts of intercalation. The results indicate that rectorite could be a good candidate as sorbent to remove TC from water.