Uptake of heavy metals in batch systems by a recycled iron-bearing material

Abstract

An iron-bearing material deriving from surface finishing operations in the manufacturing of cast-iron components demonstrates potential for removal of heavy metals from aqueous waste streams. Batch isotherm and rate experiments were conducted for uptake of cadmium, zinc, and lead. In the pH range of 4–7, the iron sorbent had the highest capacity, on a mass-per-mass basis, for lead followed by zinc and cadmium. As anticipated, solution pH has a notable impact on metal removal, while ionic background and initial metal concentration exhibited a lesser impact on adsorptive behavior. Metal surface complexation with a developing oxide layer is postulated as the principal mechanism of heavy metal removal. Batch adsorption kinetics are quite rapid, with 90% or more of metal uptake occurring within the first 5–10 h of reaction for powdered fines. Larger, granular-sized particles exhibited a longer, slower approach toward the equilibrium position. Surface complexation as well as semi-empirical equilibrium and rate models provided a useful description of experimental phenomena in that conditional trends were reflected in the estimated values of the model coefficients. Given the availability and comparable metal uptake capacity of the recycled iron sorbent to natural metal oxides and some commercial adsorbents, use of the iron-bearing material offers potential environmental and economic benefit for certain industrial pretreatment applications.