Mechanism identification of temperature influence on mercury adsorption capacity of different halides modified bio-chars

Bio-chars as mercury sorbent were derived from cotton straw via pyrolysis carbonization, microwave/ steam activation and ammonium halides impregnation. Mercury adsorption capacity of various impregnated bio-chars was tested at different temperatures. Rising temperature improved the adsorption capacity of bio-chars modified with NH4Br and NH4I yet inhabited that of bio-char modified with NH4C1. Kinetic model analysis indicated that the changes of mercury adsorption capacity were related to the difference of enthalpy change for various bio-chars. In temperature programmed desorption technic (TPDT) analysis, high desorption energy (80.9-82.1 kJ mot(-1)) proved that mercury adsorption mainly depended on chemisorption for halide modified bio-chars. Modification effect of ammonium halides on mercury adsorption capacity followed the order: NH4I (7643.1 mu g g(-1))> NH4Br (842.0 mu g g-1) > NH4Cl (365.3 mu g g-1). X-ray photoelectron spectroscopy (XPS) analysis proved that C -X groups served as mercury adsorption sites and determined the mercury removal capacity of bio-chars. This study explained the mechanism of temperature effects and halides modification as well as proposed useful suggestion on mercury sorbent preparation and application. (C) 2017 Elsevier B.V. All rights reserved.