Remediation of arsenic-contaminated water by green zero-valent iron nanoparticles

The optimal conditions for the green synthesis of nano zero-valent iron (G-NZVI) using mango peel extract were investigated using a Box-Behnken design approach. Three factors were considered, namely the ratio of iron solution to mango peel extract ratio (1:1-1:3), feeding rate of mango peel extract (1-5 mL min^-1), and agitation speed (300-350 rpm). The results showed that the optimal conditions for the synthesis of G-NZVI for arsenate removal were a 1:1 ratio of iron solution to mango peel extract, a mango peel extract feeding rate of 5 mL min^-1, and an agitation speed of 300 rpm. Under these conditions, nearly 100% arsenate removal was achieved. X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), and scanning electron microscopy (SEM) with energy-dispersive X-ray analysis (EDX) methods were used to characterize the properties of the G-NZVI. Finally, the arsenate removal efficiency of the G-NZVI was compared against that of commercial nano zero-valent iron (C-NZVI). The results revealed that the G-NZVI was roughly five times more efficient at arsenate removal than the C-NZVI. The influence of background species such as chloride (Cl^-), phosphate (PO₄^3-), calcium (Ca²⁺), and sulfate (SO₄^2-) was studied to evaluate their effects on arsenate removal. As a result, Cl^- and Ca²⁺ were shown to play a role in promoting arsenate removal, whereas SO₄^2- and PO₄^3- were observed to play an inhibiting role.