Conference on Environmental Science and Technology

This study determines the effect of Iron(II) on the granulation and removal of Nickel(II) using Fluidized-Bed Homogeneous Crystallization (FBHC), an innovative technology for metal recovery from wastewater. A face-centered Box Behnken Design was employed to evaluate the effects of three key variables: Carbonate-to-Nickel(II) molar ratio (1.5–2.0), pH (8.5–9.5), and Iron(II) concentration (0.36–1.07 mM). Nickel, a highly regulated heavy metal due to its toxicity and potential for bioaccumulation and biomagnification, was simulated in a synthetic wastewater system and operated for 168 hours per run, with a flow rate of 20 mL/min and a reflow rate of 60 mL/min. Atomic Absorption Spectroscopy (AAS) was used to quantify Nickel and Iron removal and granulation efficiencies. Results indicate that increasing Iron(II) concentration slightly enhances both Nickel removal efficiency (from 94% to 96%) and granulation efficiency (from 92% to 93%), likely due to Iron providing additional active sites that facilitate Nickel precipitation. Similarly, increasing the carbonate-to-Nickel molar ratio improves Nickel removal (93–96%) and granulation (92–94%) by increasing the availability of carbonate ions essential for crystallization. Furthermore, increasing pH levels increases the availability of carbonate and hydroxide species, leading to higher Nickel removal (90–98%) and granulation efficiencies (88–93%). X-ray Photoelectron Spectroscopy (XPS) analysis confirmed the oxidation states of the metals, with Nickel primarily existing as Ni(II) and Iron oxidized to Fe(III). Scanning Electron Microscopy (SEM) revealed that the presence of Iron disrupts the crystallinity of the precipitates.