Ca-Mg-Doped Surface-Modified Nano-Sized Ferrihydrite Powder Synthesized by Surfactant Mediation-Precipitation Technique: A Novel Super Adsorbent for Cations

In this study, high surface area (312 m(2) g(-1)) nano-sized Ca-Mg-doped ferrihydrite was synthesized using surfactant mediation precipitation technique. The micrographs obtained by transmission electron microscopy confirmed the particle size to be in the range of 2-5 nm. The weak crystalline nature of powder was indicated by the selected area electron diffraction pattern. Here, we studied the adsorption of four cations [Pb(II), Cd(II), Cu(II) and Co(II)] onto self-prepared nano-sized powder under various experimental conditions. The contact time data followed pseudo-second-order kinetics model for all the four cations giving regression coefficient values >0.99. The isothermic data fitted well to both Langmuir and Freundlich models for Pb(II), Cd(II) and Cu(II) with corresponding Langmuir monolayer capacities of 312.5, 333.3 and 333.3 mg g(-1), respectively. For Co(II) isothermic data, only Freundlich model showed good fit and the experimentally obtained maximum loading capacity was 225 mg g(-1). Desorption studies confirmed that Pb(II)- or Cd(II)-loaded adsorbent can be regenerated/reused. Studies up to five cycles of adsorption-desorption confirmed increase in uptake capacity upon regeneration. Although Cu(II)- or Co(II)-loaded adsorbents could not be regenerated, toxicity characteristic leaching procedure tests confirmed that they were safe for disposal. This is the first study of its kind to report high-loading capacities for various cations and an increase in Pb(II) or Cd(II) uptake capacities after regeneration on an adsorbent. Therefore, the prepared sample can be regarded as a super adsorbent.