Enhanced adsorptive performance of tetracycline antibiotics on lanthanum modified diatomite

A natural mineral diatomite was modified with lanthanum species using an ion exchange process to improve its adsorption performance for tetracycline removal. The prepared lanthanum-modified diatomite was characterized by scanning electron microscopy, X-ray diffractometry and Fourier transform infrared spectroscopy. The results showed that lanthanum was successfully immobilized onto diatomite, with a content of lanthanum element of about 1.5% (atomic ratio). The prepared adsorbent was evaluated for the adsorptive removal of tetracycline, and the adsorption isotherm, kinetics and mechanism were investigated. The adsorbent exhibited higher adsorption capacity than other adsorbents reported in literature, reaching 1056.9 mmol/kg. Langmuir model better fitted the experimental data than did other models. The removal of tetracycline was favorable at near neutral pH conditions. The tetracycline adsorption well followed pseudo-second-order kinetics model, and most of tetracycline was adsorbed within the initial 15 min. The increase in ionic strength reduced the tetracycline adsorptive removal, indicating that tetracycline adsorption on La-modified diatomite may be attributed to the formation of out-sphere surface complexes.