Heterogeneous Ni- and Cd-Bearing Ferrihydrite Precipitation and Recrystallization on Quartz under Acidic pH Condition

Abstract

Ferrihydrite, as one of the most common naturally occurring iron oxides, can sequester toxic metals through coprecipitation. In this study, using grazing-incidence small angle X-ray scattering (GISAXS), the heterogeneous precipitation of pure, Ni-, and Cd- bearing ferrihydrite on quartz were quantified in 0.1 mM Fe3+ solutions in the absence and presence of 1 mM Ni2+ or Cd2+ (pH = 3.8 ± 0.1). Under acidic condition, the limited hydrolysis of metal ions resulted in their small amounts of incorporation in ferrihydrite lattices (< 0.1%), several orders of magnitude lower than those reported at neutral and alkaline pH conditions. The presence of Ni2+ or Cd2+ did not significantly affect the surface charges of either ferrihydrite pre-nucleation clusters (PNCs) or quartz surfaces. Therefore, with similar electrostatic interactions between PNCs and quartz, similar initial heterogeneous precipitation rates of pure, Ni-, and Cd- bearing ferrihydrite on quartz were observed. Later on, continuous heterogeneous nucle...