Abstract
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 ([Formula: see text]). 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 ([Formula: see text]) 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 ([Formula: see text]), 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 ([Formula: see text]) 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.
Highlights
Contamination of aquatic environments by heavy metals is one of the most major environmental challenges because of their flexibility, aggregation, persistence, and nonbiodegradable nature
After applying the optimal values of the studied adsorption parameters for the adsorbents, the adsorption kinetics were investigated using different models, such as pseudo-first order (PFO), pseudo-second order (PSO), and Elovich equation, where PSO best fit the adsorption of lead for all of the adsorbents
The intraparticle adsorption model showed that the adsorption of lead was a multistep controlled mechanism, while Boyd’s kinetic model showed that the film diffusion mechanism is the limiting step of the adsorption process for all the considered adsorbents
Summary
Contamination of aquatic environments by heavy metals is one of the most major environmental challenges because of their flexibility, aggregation, persistence, and nonbiodegradable nature. Some of the toxic heavy metals, in particular lead, can have severe and poisonous effects on human beings and marine organisms even at trace levels [1, 2]. This problem is exacerbated in developing countries, where polluting industries are rapidly developed for various applications, such as mining operations, tanneries, batteries, fertilizer, pesticides, paper industries, and coke factories [3]. Lead is discharged into aquatic ecosystems from various industrial activities, such as storage batteries, ceramic glass industries, mining, plating, coating, and automotive industries. Lead poisoning causes serious harm to the kidneys, Adsorption Science & Technology damages the central nervous system and liver, and can result in cancer and brain damage, in addition to abnormalities in living creatures’ organs [9, 10]
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