Commercial Diatomite for Adsorption of Tetracycline Antibiotic from Aqueous Solution

Extensive use of antibiotics in human therapy and farming industry has resulted in their accumulation and potential hazards to the environment. In this study, diatomite, which is a siliceous rock with large surface area and high adsorptivity towards organic compounds, was used to adsorb the antibiotic tetracycline (TC) from aqueous media. The adsorption kinetics, isotherms, thermodynamics, and effects of the adsorbent amount and ionic strength were evaluated in batch adsorption experiments. The adsorption of TC onto diatomite followed the pseudo-second-order kinetics model, and the sorption equilibrium was reached in 120 min. The perfect adsorbent amount could be selected within the range of 1 similar to 20 g.L-1. The equilibrium data at different temperatures was satisfactorily fitted to the Langmuir isotherm equation with high R-2 above 0.999, and the maximum monolayer adsorption capacity of 303.03 mg.g(-1) was obtained at 318 K using 1 g.L-1 diatomite. Thermodynamic parameters showed that the adsorption reaction was spontaneous and endothermic. Moreover, the adsorption of TC was insignificantly affected by the ionic strength of 0.05-1% NaCl and CaCl2, indicating that diatomite has a potential practical application as adsorbent media for removing TC from real water.