Effects of Pig Manure Biochar on Adsorption of Tetracycline from Saline Soil at Different Depths

Abstract

The static adsorption experiment was used to study the adsorption performance of tetracycline (TC) on saline soil with different depths in cotton fields in southern Xinjiang. The effects of pig shit biochar (PSBC) prepared at 600℃ on the adsorption of saline soil were studied. The kinetic and thermodynamic adsorption processes were analyzed, and the effects of temperature, pH and ionic strength on the adsorption were clarified. FTIR and XRD were carried out on the saline soil system before and after adsorption in order to reveal the adsorption mechanism of TC on saline soil, which provide a certain basis for ecological risk assessment of TC. The results showed that the adsorption process of TC on the saline soil of cotton field accorded with the quasi-second-order kinetic model, and the adsorption process consisted of fast adsorption process and slow adsorption process, and the adsorption reached equilibrium within 6 hours; TC adsorption capacity decreased with the increase of soil depth, and the surface soil with high organic matter content and clay content had stronger adsorption capacity, but the addition of biochar changed the adsorption mechanism of the original saline soil system. Therefore, it results in a significant increase in adsorption capacity of deep soil and higher than that of surface soil. Adsorption isothermal process accords with Linear and Freundlich model, adding biochar can increase adsorption partition coefficient Kd and affinity of saline soil at different depths; When the temperature rises, the adsorption is favorable, and the adsorption capacity is the highest when the pH of the solution system is 7.The adsorption of TC by saline soil involves both physical and chemical processes, including π-π electron donor acceptor interaction, cation exchange, electrostatic interaction and pore filling effect.