Abstract
Lead is one of the most toxic heavy metals that can create a severe risk to water ecosystem health. Zero-valent iron is an effective material for Pb2+ removal treatments. In particular, nanoscopic zero-valent iron (nZVI) particles are characterized by high reaction rates; nevertheless, their utilization in water and groundwater remediation techniques requires further investigations. Indeed, it is necessary to define effective methods able to avoid the drawbacks due to the aggregation tendency of nanoparticles and their potential uncontrolled transport in groundwater. In this work, nZVI was supported on magnesium oxide grains (MgO_nZVI) to synthesize an alternative material for lead removal from aqueous solutions. Many experiments were conducted under several operating conditions in order to analyze the effectiveness of the produced material in Pb2+ abatement. The performance of MgO_nZVI was also compared with those detected using commercial microscopic Fe0 (mZVI) as a reactive material. The experimental findings showed a much greater reactivity of the supported nanoscopic iron particles. By means of a kinetic analysis of batch tests results, it was verified that, both for MgO_nZVI and mZVI, the lead abatement follows a pseudo-second-order kinetic law. The reaction rates were affected by the initial pH of the treatment solution and by the ratio between the Fe0 amount and initial lead concentration. The efficiency of MgO_nZVI in a continuous test was steadily around 97.5% for about 1000 exchanged pore volumes (PV) of reactive material, while by using mZVI, the lead removal was approximately 88% for about 600 PV. X-ray diffraction (XRD) and energy-dispersive spectroscopy EDS analyses suggested the formation of typical iron corrosion products and the presence of metallic lead Pb0 and Pb2+ compounds on exhausted materials.
Highlights
The contamination of water bodies and groundwater by toxic heavy metals represents an extremely serious environmental and health issue
The X-ray diffraction (XRD) analysis of the synthesized particles confirmed the presence of nanoscopic iron included in the grains of magnesium oxide (MgO)
In a reaction time of about 1 h, with the higher initial concentrations, yields greater than 90% were achieved. These results proved the high ability of the reactive material to remove lead ions
Summary
The contamination of water bodies and groundwater by toxic heavy metals represents an extremely serious environmental and health issue. Pb2+ ions are commonly found in aquatic systems due to their extensive use in many industrial activities, such as battery manufacturing, mining, refining, painting, metal plating and cleaning, agricultural treatments, and so forth [1,2]. This element is characterized by a high toxicity and can accumulate in human organs, causing severe health harms [3]. The Pb2+ removal treatments from contaminated water and wastewaters include chemical precipitation, ion exchange, membrane filtration, adsorption, electrodialysis, and so forth [3] Among these different techniques, the use of zero-valent iron (ZVI) has recently gained great attention. ZVI-based processes work through many mechanisms including adsorption, reduction, and precipitation/immobilization
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