Removal and stabilization of arsenic(III/V) from water using Ca-based LDH derived from calcium oxide: Removal performance and mechanism
Yusuf Olalekan Zubair, Shigeshi Fuchida, Keishi Oyama, Chiharu Tokoro
Abstract
This study highlights the potential of using CaO as a precursor for synthesizing Ca-based layered double hydroxide (Ca-LDH) with excellent adsorption and stabilization performance for arsenic from water. The mechanism and performance of the Ca-LDH for As(III) and As(V) removal were evaluated using adsorption isotherms and kinetic studies. The adsorbent was characterized before and after As removal using X-ray diffractometry, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray Absorption Fine Structure, field emission scanning electron microscopy, and energy dispersive X-ray spectroscopy. The Ca-LDH exhibited maximum removal capacities of 4.50 and 2.39 mmol/g for As(III) and As(V), respectively. The removal process was complex and involved multiple mechanisms such as dissolution–precipitation, redox transformation, adsorption, and coagulation. The Ca-LDH underwent phase transformation in solutions containing As and generated secondary products like calcium carbonate, iron(oxy)hydroxide [FeO(OH)], and dissolved Ca 2 + , which played crucial roles in the removal and stabilization of As. As(III) was partially oxidized to As(V) and adsorbed on FeO(OH), while As(V) removal was mainly controlled by adsorption on FeO(OH), coprecipitation with and/or adsorption on calcium carbonate, and coagulation. The adsorption mechanisms involved the formation of bidentate complexes with FeO(OH) and/or Ca-bridged ternary complexes (FeO-Ca-As). The As-loaded solid products exhibited excellent stability and were categorized as non-hazardous waste. This work provides a cost-effectiveness and sustainability framework for the development of Ca-based LDH materials for the remediation of arsenic from water. • Layered double hydroxide was synthesized using CaO as source of Ca and precipitant. • Ca-LDH have remarkably high capacities in removing both As(III) and As(V). • Phase transformation of Ca-LDH facilitated As removal through complex mechanisms. • As-loaded products exhibited excellent stability under varied aqueous conditions.