Identification of pH-dependent removal mechanisms of lead and arsenic by basic oxygen furnace slag: Relative contribution of precipitation and adsorption

Abstract

Removal mechanisms, precipitation and adsorption, of lead (Pb) and arsenic (As) by basic oxygen furnace (BOF) slag were studied at pH 7epH 13 range. Specifically, the relative contribution of precipitation and adsorption on Pb and As removal was investigated. Pb was mainly removed by precipitation at the pH values tested, as evidenced by the presence of Pb-hydroxide precipitate confirmed by X-ray diffractometry. In contrast, As seemed to be removed mainly by adsorption at the pH range tested. But, precipitation of amorphous calcium (Ca) arsenate was observed at above pH 11. An experiment with Ca reduced BOF slag provides a line of evidence implying the involvement of Ca2+ in the adsorption of As, probably by bridging between slag surface and As oxyanions. X-ray photoelectron spectroscopy and thermogravimetric analysis also elucidated that calcium hydroxide and calcium carbonate were coated on the slag surface at pH 13, which probably blocked As adsorption. When tested following the toxicity characteristic leaching procedure, the precipitation seemed more stable than the adsorption. The removal mechanism and efficiency demonstrated in this study would contribute to the reuse of BOF slags for Pb and As removal. (C) 2020 Elsevier Ltd. All rights reserved.