Evaluating the performance of cement-modified biochar adsorbent for Cu, Pb and Zn removal from urban stormwater

This research investigates the use of biochar modified with Ordinary Portland Cement (OPC) as an adsorbent for heavy metal removal and evaluates the impact of competing ions and nutrients on the adsorptive removal process. The cement-modified biochar composites, featuring functional groups from biochar and hydrated OPC, exhibited significantly enhanced adsorption capacities for Cu, Pb, and Zn, approximately 3.3, 2.4, and 6 times higher, respectively, compared to unmodified biochar upon introducing 1.5% (v/v) OPC. The Langmuir monolayer adsorption model accurately described the adsorption data, with heavy metals binding to functional groups like C=C and C=O, CO3-2, silanols (Si-OH), siloxanes and calcium silicate hydrate. The cement-modified biochar composite exhibited notable adsorption capacities for Cu, Pb, and Zn at 28.82mg/g, 38.76mg/g and 26.53mg/g, comparable to commercial activated carbons. There were negligible effects from NO3- on the removal of Cu, Pb and Zn, PO43- ions enhanced Pb removal, and NH4+ ions slightly reduced the removal of all three metals, while humic acid increased removal. The findings indicate that using OPC boosts heavy metal adsorption, and insights into the influence of competing ions and nutrients apprise strategies for using OPC-modified biochar in practical applications.