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TECHNICAL REPORTS

Waste Management

On the Adsorption of Tetracycline by Calcined Magnesium-Aluminum Hydrotalcites

^a State Key Lab. of Pollution Control and Resource Reuse, School of the Environment, Nanjing Univ., Nanjing 210093, China
^b Key Lab. of Yangtze River Water Environment of Ministry of Education, Tongji Univ., Shanghai 200092, China

^* Corresponding author (srzheng{at}nju.edu.cn); (yindq{at}mail.tongji.edu.cn).

Received for publication May 29, 2008. Exploiting effective sorbents for antibiotic adsorption is highly desirable for the elimination of ecological risks from antibiotic contamination. In this study, MgAl-CO₃^2– hydrotalcites with different Mg/Al molar ratios were prepared and tetracycline (TC) adsorption to the hydrotalcites and calcined hydrotalcites was investigated by batch experiments. Calcined hydrotalcites had higher adsorption capacities compared to MgAl-CO₃^2– hydrotalcites. At low TC equilibrium concentrations, calcined hydrotalcites with differing Mg/Al ratios showed approximately identical TC uptakes. However, at high tetracycline concentration, greater TC adsorption capacity was observed for calcined hydrotalcite having a high Mg/Al ratio (i.e., 4.4). X-ray diffraction (XRD) characterization showed the presence of Mg-Al oxide solid solution in TC -loaded calcined hydrotalcite, suggesting that suspension of the calcined product in water and adsorption of TC had led to only partial reconstruction of the layered structure. We hypothesize that TC was adsorbed on the MgO surface at high equilibrium concentrations. The behavior of TC adsorption on the calcined hydrotalcite was well described by a dual adsorption model. Kinetic analysis suggested that at low adsorption levels, TC adsorption by calcined hydrotalcite could be modeled by both a pseudo second-order kinetics model and a nucleation-growth model. The present work demonstrates that calcined hydrotalcites may be promising adsorbents for effective removal of TC from water resources.

Abbreviations: CHT(s), calcined hydrotalcite(s) • CHT-2.0, calcined MgAl-CO₃^2– hydrotalcite with Mg/Al molar ratio of 2.0 • CHT-2.9, calcined MgAl-CO₃^2– hydrotalcite with Mg/Al molar ratio of 2.9 • CHT-4.4, calcined MgAl-CO₃^2– hydrotalcite with Mg/Al molar ratio of 4.4 • HT(s), hydrotalcite(s) • HT-2.0, MgAl-CO₃^2– hydrotalcite with Mg/Al molar ratio of 2.0 • HT-2.9, MgAl-CO₃^2– hydrotalcite with Mg/Al molar ratio of 2.9 • HT-4.4, MgAl-CO₃^2– hydrotalcite with Mg/Al molar ratio of 4.4 • TC, Tetracycline • TG, Thermogravimetric • XRD, X-ray diffraction