Abstract
To improve the removal performance of sludge biochar (BC) for heavy metal Cd2+ in wastewater, phosphate-modified sludge biochar (PBC) was prepared by impregnation-pyrolysis. Batch removal experiment was conducted to research the impact of initial solution pH, coexisting ions, contact time, reaction temperatures, and Cd2+ concentrations on the adsorption capacity of adsorbent. The outcome indicated that PBC exhibited excellent Cd2+ removal efficiency at pH 5-7. Compared to the original biochar, phosphate-modified biochar had a stronger resistance to ion interference. The models of pseudo-second-order and Langmuir well described the adsorption processes of Cd2+ on BC and PBC. The maximum adsorption capacities of PBC for Cd2+ were 163.93mg/g, significantly higher than that of BC (72.94mg/g). Adsorption mechanism analysis suggested that Cd2+ removal involved complexation, electrostatic attraction, cation-π interactions, and co-precipitation. According to the semi-quantitative analysis of the mechanism, the leading mechanism for Cd2+ removal by PBC was precipitation (79.94%), whereas the primary mechanisms for Cd2+ removal by BC were complexation (42.57%) and precipitation (48.85%). The strategy of converting highly mobile Cd2+ in aqueous solutions into insoluble cadmium phosphate precipitates using phosphate-modified sludge biochar can be an ideal approach for removing Cd2+ from wastewater.
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