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This study is aimed at comparing the use of zinc oxide (ZnO), titanium dioxide (TiO2), and aluminium oxide (Al2O3) for removing lead ions from water through adsorption. The point of zero charge was obtained for ZnO, TiO2, and Al2O3 and was found to be 7.3, 7.1, and 9.0, respectively. The effect of pH, adsorbent dose, contact time, initial concentrations, and temperature was investigated in batch experiments. The optimal conditions obtained were 7, 2 g/L, 120 mins, 100 ppm, and 41°C, respectively, where the optimal removal efficiencies were 98.43%, 96.45%, and 85.50% for ZnO, TiO2, and Al2O3, respectively. In addition, analyses of adsorption kinetics, mechanisms, isotherms, and thermodynamics were performed. The adsorption kinetics of Pb(II) were compared to popular models, and it was found that the pseudo-second-order (PSO) model best fitted the Pb(II) uptake for all adsorbents at correlation coefficient ( R 2 ≥ 0.96 ). The adsorption isotherms of Pb(II) were also compared to popular models, and it was found that the Pb(II) uptake by TiO2 and ZnO was well-described by the Langmuir model ( R 2 ≥ 0.96 ) with maximum adsorption capacities of 55.04 and 58.88 mg/g, respectively. On the other hand, the behaviour of Al2O3 is described more accurately by the Dubinin-Radushkevich (D-R) model ( R 2 = 0.96 ), and the maximum adsorption capacity was 53.64 mg/g. The isotherm analysis proved that the limiting step of the adsorption process is the film diffusion mechanism. In addition, studying the heat of adsorption of Pb(II) implied that the adsorption is endothermic due to the positive values of enthalpy ( Δ H ° ≥ 30 ) for all adsorbents. The absorbents were characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) to study the morphology of surfaces and the chemical characterization of the adsorbents to ensure that adsorption is achieved. ZnO showed better performance for the uptake of lead followed by TiO2 then Al2O3.

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Indiscriminate dumping of solid wastes and the resulting groundwater contamination is a major issue, especially for developing countries. The main objective of this paper is to develop a groundwater mass transport model in order to study the effect of an open solid waste dumpsite on the water quality of water resources within the region around it. The harmful effects of indiscriminate solid wastes disposal by open dumping, which is still followed in many developing countries around the world, is highlighted. Abu Zaabal dumpsite; which is located in Qalyubiyah Governorate, Egypt; receives huge amounts of wastes daily causing leachate generation that percolates deep into the soil and polluting the shallow aquifer. The Groundwater Modeling System (GMS) software was used to model the groundwater flow and mass transport, using data collected from the site investigation and literature historical data available. Of the several contaminants measured in the site, six critical contaminants; namely Total Dissolved Solids (TDS), Lead, Boron, Nitrate, Manganese and Chemical Oxygen Demand (COD); were chosen to be modeled. The developed model was used to simulate the six contaminants using a transient-state model and concentration values for two different scenarios. Scenario-1 assumes that the dumpsite will be active until 2080, whereas Scenario-2 represents imminent closure of the dumpsite. The model results of each contaminant were calculated over 100-year interval, from 1980 until 2080, and the results of 2080 were presented. The results showed that the dumpsite had a major impact on the nearby water bodies, Abu Zaabal ponds and Belbais Drain. Moreover, the closure of the dumpsite showed that the maximum concentration of the majority of the considered contaminants was decreased by approximately 60–65%.

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