In this work, biomass obtained from seeds (S-MO) and leaves (L-MO) of the Moringa oleifera plant were used as low-cost biosorbents to remove the Pb(II), Cd(II), Co(II), and Ni(II) from aqueous solutions. The biosorption of the heavy metal ions was done using the batch technique. The effects of contact time (30–1440 min), biosorbent dosage (10–50 g/L) (0.1–0.5 g), and initial concentration of metals (10–500 mg/L) on the sorption capacity of metal ions were investigated. The S-MO and L-MO samples’ characterization was performed using pH_pzc, X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). It was found that the pH_pzc was notably different between the seeds and leave-derived biosorbents. The removal process’s experimental kinetic data for both S-MO and L-MO were best described by the pseudo-second-order model for all metal ions, with R² above 0.997 in all cases. Langmuir and Freundlich’s models were also used to analyze the isotherms parameters. Based on the Langmuir model, the maximum sorption capacities (Qm) for L-MO were found as follows: L-MO-Pb > L-MO-Cd > L-MO-Co ≥ L-MO-Ni, and for S-MO, the values of Qm values presented the following order: S-MO-Pb > S-MO-Co > S-MO-Cd > S-MO-Ni.

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 ≤ 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 q_m = 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.

The use of Y zeolite and erionite to remove UO₂ ²⁺ ions from aqueous solutions has been investigated. The effect of temperature, the concentration of UO₂ ²⁺ uptake, the diffusion coefficients, and the ion-exchange isotherms were also studied. X-ray diffraction, thermal analyses, and transmission electron microsocopy were used to characterize the solids. The UO₂ ²⁺ content was determined by neutron activation analysis. The diffusion coefficients are not clearly affected by temperature or concentration. They definitely depend on the structure of each zeolite. The UO₂ ²⁺ exchange capacities were 0.2037 and 0.7345 meq UO₂ ²⁺/g for erionite and Y zeolite, respectively. It was found that UO₂ ²⁺ is exchanged with the cations of the large cavity in Y zeolite. In the case of erionite, UO₂ ²⁺ is exchanged with the cations localized in sites where the charge densities are very high.