Valorization of Pecan Shell Waste into Magnetic Fe3O4@Biocarbon for Arsenic Removal from Water: Optimization Using Fuzzy Decision Networks and RSM

This study converted pecan shell waste into magnetic Fe3O4@biocarbon for arsenic (V) removal from aqueous medium. A preliminary test was conducted on a binary system of arsenic (V) and lead. A dual-optimization approach was applied using a fuzzy decision network for material synthesis and response surface methodology (RSM) for adsorption performance. The fuzzy model predicted FS2 as an optimal design (particles between 0.38–0.7 mm in size, Fe ratio of 1:1) with high accuracy (R2 > 0.95). In the RSM, removal efficiency and adsorption capacity were estimated to find out the influential parameters, which turned out to be adsorbent dose and As(V) concentration. It was predicted that removal capacity would remove 90.99% As(V) at the dose of 0.95 mg L−1 As(V), pH 3.4 and 1.8 g L−1 dose. However, it was also revealed that the qe model provided a higher confidence (final conditions: 9.95 mg L−1 As(V), pH 3.0 and 0.5 g L−1 dose; qe = 3.96 mg g−1). Evaluation of Fe3O4@biocarbon was conducted at 0.217 mg L−1 As and 34.3 mg L−1 Pb. This suggests removal of lead in addition to arsenic, indicating that the method can be used in multicomponent metal removal. FTIR and XPS analysis showed that removal of As(V) took place through surface complexation with Fe-O and oxygen-containing functional groups.