Abstract
The removal of Pb(II) from aqueous solutions by acid-modified clinoptilolite-rich tuff was investigated in this work. Clinoptilolite-rich tuff samples were treated using H2SO4 at different concentrations. Prior to and following acid treatment, the samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Fourier-transform infrared spectroscopy (FTIR). The pH of the point of zero charge (pHPZC) was also determined as part of this characterization. Batch studies were studied to investigate Pb(II) removal as a function of contact time, initial Pb(II) concentration, adsorbent dosage, and solution pH. The results of the XRD and SEM techniques showed that clinoptilolite is the main mineral of the non- and acid-treated natural zeolite samples. However, EDS analysis indicated that the Si/Al ratio increases as the exchangeable ions decrease with increasing acid concentrations. The optimum conditions for Pb(II) removal for samples with 4.37 ≤ Si/Al ≤ 7.9 were found to be as follows: Contact time of 60–360 min, pH: 6–8, and adsorbent dose of 6 mg g−1; whereas for acid-modified clinoptilolite-rich tuffs with 9.01 ≤ Si/Al ≤ 9.52, these conditions were as follows: Contact time of 1440 min, pH: 8–10, and adsorbent dose of 10 mg g−1. The experimental data were analyzed by kinetic and isotherms models. The results showed that the sorption of Pb(II) on samples with Si/Al ratios of 4.37, 5.31, and 7.91 were in agreement with the pseudo-second order and Langmuir isotherm with qm = 48.54, 37.04, and 14.99 mg g−1, respectively, while the kinetic data and isotherm for samples with 9.01 ≤ Si/Al ≤ 9.52 were found to fit the pseudo-first order and Freundlich model.
Highlights
Zeolites are hydrous and crystalline alumino-silicates minerals with a regular and microporous structure [1]
It can be observed that all samples contained clinoptilolite as the principal mineral which is defined by its main characteristic peaks at 2θ = 9.85◦, 11.19◦, 22.21◦, 22.34◦, 25.96◦, and 28.09◦ according to JCPDS card 25-1349 [34]
These results suggest that the treatment of natural zeolite with H2 SO4 caused some structural changes and loss of crystallinity in the clinoptilolite phase
Summary
Zeolites are hydrous and crystalline alumino-silicates minerals with a regular and microporous structure (pore size from 3.0 to 10 Å) [1]. Natural zeolites exhibit interesting structural properties such as a large specific surface, flexibility, and well-defined micropores in molecular dimensions, as well as high chemical and physical stability (e.g., thermal and mechanical) [5], and sorption characteristics obtained by combined ion-exchange and molecular-sieve properties [6]. These outstanding properties allow these materials to offer promising applications in many sustainable processes such as wastewater treatment [7] and petroleum refining [8] as well in agriculture and construction [9]. The lead (Pb2+ ) is a toxic metallic specie which is necessary to eliminate from the environment [17]
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