Assessing South American Guadua chacoensis bamboo biochar and Fe3O4 nanoparticle dispersed analogues for aqueous arsenic(V) remediation

Abstract

Discarded bamboo culms of Guadua chacoensis were used for biochar remediation of aqueous As(V). Raw biochar (BC), activated biochar (BCA), raw Fe₃O₄ nanoparticle-covered biochar (BC-Fe), and activated biochar covered with Fe₃O₄ nanoparticles (BCA-Fe) were prepared, characterized and tested for As(V) aqueous adsorption. The goal is to develop an economic, viable, and sustainable adsorbent to provide safe arsenic-free water. Adsorbents were characterized using scanning electron microscopy (SEM) and energy dispersive analysis by X-ray (SEM-EDX), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (TEM-EDS), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), Brunauer-Emmett-Teller surface area measurements (S_BET), point of zero charge determinations (PZC), and elemental analysis. Activation with KOH increased the O/C ratio and the surface area of BC from 6.7 m²/g to 1239.7 m²/g (BCA). As(V) sorption equilibrium was achieved within <2 h for all four adsorbents and kinetics followed the pseudo-second-order model. At a 10 mg/L initial As(V) concentration, BC-Fe achieved a 100% removal (5 mg/g) over a pH 5 to 9 window. Sorption was endothermic on all four adsorbents and the capacities rose with the increasing temperature. Langmuir capacities at 40 °C for BC, BCA, BC-Fe, and BCA-Fe were 256, 217, 457, and 868 mg/g, respectively, and capacities were compared with other sorbents. Breakthrough fixed-bed column sorption was carried out for BC and BC-Fe producing 6.6 mg/g and 13.9 mg/g bed capacities, respectively. Potassium phosphate was a better As stripping agent than sodium bicarbonate. Performance of the adsorbents in an As(V)-spiked natural water and a naturally As(V)-contaminated domestic water were assessed. Robust arsenate sequestration occurred generating As-safe water (As <0.01 mg/L), despite the presence of competing ions. Stoichiometric precipitation of iron-arsenate complexes triggered by iron dissolution was also established.

Keywords: Arsenic(V); Bamboo biochar; Fe(3)O(4) nanoparticle-covered; Multiphase adsorbent; Water remediation.