Removal of antimonate and antimonite from water by schwertmannite granules

In order to overcome the drawbacks of small particle-sized adsorbents, schwertmannite powder was fabricated into granules in the present study. These granules were evaluated for Sb(III) and Sb(V) removal from water and intraparticle mass transfer resistance of Sb(III) and Sb(V) onto the porous adsorbent was modeled. Schwertmannite granules (SG) exhibited capacities of 32.9 mg/g for Sb(III) and 23.2 mg/g for Sb(V), respectively, which are superior to many reported granular adsorbents and even powder adsorbents. Mass transfer was separately modeled using the pore volume diffusion model and surface diffusion model. The film diffusion coefficients, kL, range from 1.09 × 10−5 to 3.08 × 10−5 cm/s. The pore diffusion coefficients, Dep, range from 6.20 × 10−5 to 10.85 × 10−5 cm2/s, and the surface diffusion coefficients, Ds, range from 1.12 × 10−9 to 3.57 × 10−9 cm2/s. The concentration decay data-sets were successfully fitted with these best obtained parameters. Sb(III) was effectively removed over a wide pH range, while the removal of Sb(V) was pH dependent and could be enhanced by lowering solution pH. Sb(III)-loaded SG was regenerated with 91.2% re-adsorption capacity retained after five cycles when using 0.6% NaOH as the stripping solution. The desorption of Sb(V) was not as successful as Sb(III). Before breakthrough (5 μg/L) occurred, 1,690 and 712 bed volumes (BVs) of Sb(III), and 769 and 347 BVs of Sb(V) were treated when operating at space velocity values of 2 and 6 h−1, respectively. Considering the low cost and the granular form of schwertmannite, the adsorbent is a promising modestly priced adsorbent and can be easily used in packed bed or filter units for practical application.