Environmental application of MgMn-layered double oxide for simultaneous efficient removal of tetracycline and Cd pollution: Performance and mechanism

The MgMn-layered double oxide (MgMn-LDO), which was fabricated by calcining MgMn-layered double hydroxide (MgMn-LDH), was used to remove tetracycline (TC) and cadmium (Cd) pollution. In MgMn-LDO activated peroxymonosulfate (PMS) system, 97.1% of TC was degraded within 20 min. The high oxidizing sites exposed on MgMn-LDO surface played a main role on activating PMS to generate OH, SO4-, O2- and 1O2 (the key species) for TC degradation. MgMn-LDO could keep excellent degradation performance in a wide range of pH (from 4 to 10). The degradation degree of TC in distilled water is basically the same as that in Pearl River water, and even above 80% of TC could be degraded in human urine. The good reusability and high structure stability of MgMn-LDO were further verified. Meanwhile, Cd immobilization on MgMn-LDO reached equilibrium within 10 min, and its maximum fixed quantity was 8.234 mmol g-1 (922.208 mg g-1). The outstanding Cd fixed ability resulted from the formation of CdCO3 and Cd (OH)2. In combined system, the existence of TC promoted the immobilization of Cd on MgMn-LDO. Low concentration of Cd (0.0125 mM) had synergism effect on TC degradation, while high concentration of Cd (0.025 and 0.05 mM) had inhibiting action. Finally, a column filled with MgMn-LDO was designed for repairing TC and Cd pollution hierarchically. This study provided an effective strategy to clean up the organic-heavy metal combined pollution.