Adsorption Mechanism and Performance of Tetracycline on Different Biochar-Based Amphoteric Clays

Abstract

Bentonite (50BS-B and 100BS-B) modified with different proportions (50%, 100%) of dodecyl dimethyl betaine (BS-12) was prepared by wet method and then was loaded into the pores of xerophyte and hydrophyte biochar (XAp-C and WAp-C) respectively to form XAp-C/50BS-B (50%BS-12 modified bentonite supported by xerophyte alternanthera philoxeroides biochar, the same below), XAp-C/100BS-B, WAp-C/50BS-B and WAp-C/100BS-B. Batch method was used to study the isothermal adsorption and thermodynamic characteristics of tetracycline on biochar-based amphoteric bentonites, and the adsorption differences under different pH, ionic strength and temperature were compared. Results indicated the following. (1) The adsorption of tetracycline by the tested materials showed the trend of WAp-C/100BS-B > XAp-C/100BS-B > WAp-C/50BS-B > XAp-C/50BS-B > XAp-C/BS-B > WAp-C/BS-B > XAp-C > WAp-C. The adsorption isotherms of tetracycline by all tested materials were suitable to be described by Langmuir model. Compared with bentonite modified by single BS, the adsorption capacity of tetracycline for biochar-loaded amphoteric bentonite was greatly improved, and the adsorption effect of XAp-C-loaded amphoteric bentonite was better than WAp-C-loaded amphoteric bentonite when the amphoteric modification degree was same. (2) The optimal pH value of tested materials was three. The adsorption capacity of tested materials for tetracycline in the range of 0.01-0.5 mol·L-1  showed the trend of first increasing and then decreasing except XAp-C and WAp-C, and the best ionic strength was 0.1 mol·L-1 . (3) The adsorption process of tetracycline by tested materials was positively correlated with increasing temperature. The adsorption process of tetracycline by tested materials was spontaneous and endothermic entropy increasing.

Keywords: biochar, BS-12, bentonite, tetracycline, adsorption capacity