Development of nZVI-Pumice/Zeolite Composites for Effective Removal of Arsenic (III) from Aqueous Solution

Nano zero valent iron (nZVI) composites were developed with iron loading ratios of 10% and 20% (w/w) using base materials, pumice, and zeolite. The four composites (PnZVI 10, PnZVI 20, ZnZVI 10, and ZnZVI 20) developed were then used to analyzing their efficiency for the removal of arsenite (III) [As(III)] from aqueous solution using a series of batch and column experiments. Scanning electron microscopy (SEM) images of the composites revealed that spherical iron nanoparticles were uniformly dispersed over the base materials. The removal efficiency was investigated for varying initial concentrations (25–200 mg/L) of As(III), pH (3–11), and adsorbent dose (0.5–5 g/L). All four composites showed a fairly high removal capability of As(III) over a wide pH range, in particular, between 5 and 9. The observed data were then evaluated against various adsorption kinetics equations, and the pseudo second order model fitted the data well, with the rate constants being in the range of 0.51–1.38 g/(mg·h). The Freundlich isotherm model emerged as the best to describe As(III) adsorption on the heterogeneous surface of composites, demonstrating the maximum adsorption capacity for PnZVI 20 = 24.96 mg/g. A plexiglass column setup with 20 cm height and 4.5 cm inner diameter was then used to study the in situ removal of As(III). A constant flux of 30 mL/h with 5 mg/L of As(III) concentration was applied at the bottom boundary of the column for 30 days. It was observed that approximately 99% of As(III) was removed during the process and 0.95 mg/g of As(III) was found to be adsorbed on the adsorbent at the end of the experiment. The high removal efficiency over a wide pH range in combination with its low cost and better hydraulic and mechanical properties demonstrated it to be a promising adsorbent for field application.