Tetracycline adsorption by clay under the coexistence of three extracts from an invasive plant

The remediation of contaminated soil by invasive plant resources is a new research hotspot. Different proportions (0%, 1%, 2%, 5%, and 10%) of exudates (E) from the living roots (LR-E), dead roots (DR-E), and fallen leaves (FL-E) of the invasive plant Alternanthera philoxeroides were added to a tetracycline (TC) adsorption system to study the influence of extracts from invasive plant roots and litter (fallen leaves and dead roots) on the adsorption of TC by clays (bentonite [B] and kaolin [K]). Then, the batch method was used to study the isotherm adsorption characteristics of TC, and the effects of temperature, pH, and ionic strength on TC adsorption were compared. The following results were obtained: (1) The adsorption isotherms of TC on B and K under the coexistence of E were all consistent with the Henry model, and the adsorption amount of TC increased by 1.04–1.81 times after the addition of E. The addition of LR-E had a strong promoting effect on TC adsorption by the two clays. (2) The adsorption amount of TC on each tested clay with the coexistence of E was positively correlated with temperature within the range of 5°C–40°C. Thermodynamic analysis showed that TC adsorption was a spontaneous, endothermic, and entropy-adding reaction. (3) When the pH was changed from 2 to 10, the adsorption amount of TC on clay decreased. The range of this decrement narrowed with the increase in coexisting E. (4) When the ion concentration was changed from 0.01 to 0.5 mol/L, the adsorption amount of TC on B decreased with the increase in ionic strength, whereas that on K first increased and then decreased. In conclusion, invasive plant extracts can improve the adsorption of TC on clay, and the adsorption effect is superior when the temperature is high and the pH is low.