Adsorption uptake of Philippine natural zeolite for Zn²⁺ ions in aqueous solution

The Philippine natural zeolite (PNZ) was characterized and subjected to Zn²⁺ adsorption tests in aqueous solutions to determine its adsorption uptake and to understand its adsorption behaviour. The PNZ was characterized using XRD, SEM, BET-analysis and TG-DTA. XRD showed significant peaks indexed to natural mordenite-type zeolite along with other natural zeolites and minerals. SEM micrographs revealed a rough and corrugated surface morphology of the sample. BET physisorption analysis showed a surface area of 222.63 m²/g. From the analytical tests report given by the supplier, the Si/Al ratio (SAR) was computed to be equal to 4.29 based on the silica and alumina content of the PNZ. Adsorption kinetic and thermodynamic studies were done to determine the adsorption mechanism and adsorption capacity of PNZ for Zn²⁺ ions in aqueous solution. From the adsorption kinetic curve, the PNZ attained chemical equilibrium after 50 min. Pseudo-second-order kinetic model was the most applicable kinetic model providing the highest correlation with the data. Langmuir model better described the adsorption isotherm of the PNZ than Freundlich model. The theoretical maximum cation exchange capacity of PNZ was computed as 27.17 mg Zn²⁺/g according to the Langmuir model. (paper)