Lead removal from solution by a porous ceramisite made from bentonite, metallic iron, and activated carbon

Abstract

There is increasing interest in using a porous ceramisite as the filter medium for removing heavy metals from wastewater in China given its low cost, easy preparation, large available quantities, high mechanical strength, and good performance to remove various pollutants. In this study, bentonite, metallic iron (Fe⁰), and activated carbon (AC) were used to prepare a Fe⁰/AC-ceramisite (diameter 2–4 mm) by sintering at 800 °C in a N₂ environment. The Fe⁰/AC-ceramisite achieved a high Pb²⁺ removal efficiency (>99%) at ceramisite dosages of 5–10 g L⁻¹, an initial solution pH of 3.0–5.7, and initial Pb²⁺ concentrations of 50–200 mg L⁻¹. Compared with three control ceramisites including B-ceramisite (made by bentonite only), AC-ceramisite (made by bentonite and AC), and Fe⁰-ceramisite (made by bentonite and Fe⁰), the enhanced Pb²⁺ removal by the Fe⁰/AC-ceramisite was mainly attributed to the iron–carbon micro-electrolysis induced by the addition of AC. A first-order kinetics model fit well for the Pb²⁺ removal by the Fe⁰/AC-ceramisite, and the Pb²⁺ uptake rate increased linearly with the increasing initial solution pH. Results from scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM/EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) indicated that the Pb²⁺ removal by the Fe⁰/AC-ceramisite involved multiple mechanisms including sorption, reduction (from Pb²⁺ to Pb⁰), and precipitation (in the forms of PbCO₃ and Pb₃(CO₃)₂(OH)₂).