Simultaneous Removal of Cd(Ii) and As(V) by Ferrihydrite-Biochar Composite: Enhanced Effects of As(V) on Cd(Ii) Adsorption

Abstract

The coexistence of cadmium and arsenate pollution has long been an environmental problem. Biochar, a porous carbonaceous material with tunable functionality, has been used for the remediating contaminated soils. However, it is still challenging for the dynamic quantification and mechanistic understanding of the simultaneous sequestration of multi-metals in biochar-engineered environment, especially in the presence of anions. In this study, ferrihydrite, a ubiquitous and porous iron oxide with nano-sizes, was coprecipitated with biochar (2Fh-BCM) to investigate how 2Fh-BCM presence affects the fate of heavy metals, especially coexisting Cd(II) and As(V). The maximum adsorption capacities of 2Fh-BCM for Cd(II) and As(V) when treated with solutions containing cadmium and arsenate were reached 82.03 μmol/g and 531.53 μmol/g, respectively, much higher than those of the pure biochar (26.90 μmol/g for Cd(II), and 40.24 μmol/g for As(V)) and ferrihydrite (42.26 μmol/g for Cd(II), and 248.25 μmol/g for As(V). Cd(II) adsorption increased in the presence of As(V),but not the vice versa. Further microscopic and mechanistic results showed that Cd(II) complexed with both biochar and ferrihydrite, while As(V) was mainly complexed by ferrihydrite. The different distribution patterns revealed by this study help to a deeper understanding of the behaviors of cations and anions in the natural environment.

Keywords: ferrihydrite, Biochar, Cadmium, arsenate, simultaneous sequestration, binding mechanisms