Study Of Adsorption Of Tetracycline And Copper In Soils And Impact Of Factors On Their Adsorption

There has been an increase concentration of tetracycline (TTC; H2L) and Cu in soil and they are posing more and more environmental risk as the result of development of agriculture and acceleration of industrialization and urbanization. On this background, adsorption of TTC and Cu in soils and soil minerals and impact of factors on their adsorption were studied by batch experiments. The main results are summarized as following:1) Cu adsorption in the Red soil (RS), Wushan soil (WS) and kaolinite increased with the increasing solution Cu concentration. Adsorption quantity of Cu in the WS was higher than that in the RS. TTC strongly adsorbed in the RS, WS, attapulgite and kaolinite. Adsorption quantity of TTC in the RS was higher than that in the WS and the same as attapulgite rather than that on the kaolinite. Freundlich equations fit the adsorption isotherms of Cu and TTC in the soils and minerals well.2) When the equilibrium solution pH was below 5.0, 6.0 and 6.3 for the RS, WS and kaolinite, respectively, TTC enhanced Cu adsorption which could be due to the stronger affinity of TTC-Cu complex (CuH2L2+and CuHL+) to the adsorption sites than Cu2+ itself, or due to more Cu adsorbed via the TTC bridge. While the solution pH was above 7.0, 7.4 and 7.4 for the RS, WS, montmorillonite and kaolinite, respectively, TTC suppressed Cu adsorption, which is ascribed that Cu reacted with dissolved TTC to form no charged complexes (CuL) that had lower affinity to the negative charged soil or minerals surface in comparison with Cu2+ itself.3) When the solution pH was below 4.7 for the RS and 3.4 for the WS, Cu suppressed the adsorption of TTC in the soils, which is ascribed that TTC exists as cationic, zwitterionic and positive charged complexes of TTC and Cu species at low pH, and Cu decreased the adsorption of TTC due to competition for the adsorption sites; while the solution pH was above 4.7 for the RS and 3.4 for the WS, the adsorption quantity of TTC increased, which is ascribed that at high pH, the complexes of TTC and Cu have fewer negative charges, and have higher affinity to the negative charged soil surfaces than TTC itself. In addition, the adsorption of TTC can take place on the sites where Cu was adsorbed, and act as a bridge between soil particles and TTC.4) Twenty hour was enough for adsorption equilibrium of TTC in the RS and the WS. The presence of phosphate and sulphate decreased the adsorption of TTC in the soils by competition of the adsorption sites of soil with TTC. Phosphate adsorbed in soils stronger than sulphate, and decreased the adsorption of TTC in the soils more significantly.5) The presence of 2,4-D increased Cu adsorption quantity in the colloids of RS and WS. The higher the solution 2,4-D concentration, the more the Cu adsorbed in the soil colloids.