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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 (pH_PZC) 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 &#8804; Si/Al &#8804; 7.9 were found to be as follows: Contact time of 60&#8722;360 min, pH: 6&#8722;8, and adsorbent dose of 6 mg g^&#8722;1; whereas for acid-modified clinoptilolite-rich tuffs with 9.01 &#8804; Si/Al &#8804; 9.52, these conditions were as follows: Contact time of 1440 min, pH: 8&#8722;10, and adsorbent dose of 10 mg g^&#8722;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 <i>q_m</i> = 48.54, 37.04, and 14.99 mg g^&#8722;1, respectively, while the kinetic data and isotherm for samples with 9.01 &#8804; Si/Al &#8804; 9.52 were found to fit the pseudo-first order and Freundlich model.