[Removal of tetracycline by a kind of nano-sized amorphous carbon]

The experiments were conducted to investigate the adsorption behavior of tetracycline on a kind of nano-sized amorphous carbon, which was synthetized in a molten salt electrochemical system, comprising a eutectic mixture of Li-Na-K carbonates. The results showed that, the carbon powder had a good adsorption performance. At 298K, the maximum adsorption capacity of tetracycline was 127.76 mg x g(-1). The adsorption data could be well fitted by the pseudo-second-order model and the Freundlich isotherm. Also, the thermodynamic tests for the adsorption were conducted. The adsorption was endothermic and spontaneous reaction with chemical bond as the dominant. The adsorption was pH dependent. The adsorption capacity reached the maximum when solution pH was 4 in the range from 2 to 11. The existence of cations had little effects on the adsorption. The adsorption capacity increased with the concentration of cations to a certain extent. Ion exchange may be one of the adsorption mechanisms, as well as, electric attraction and hydrogen bond. Moreover, desorption experiments were carried out in 0.25 mol x L(-1) CaCl2 or NaCl solution respectively. Desorption efficiency ranged from 7.42% to 25%, which was at a relatively low level. The result indicated that the chemical adsorption process was strong.