This paper examined the competitive removal of metal ions from quaternary aqueous solutions containing Ni²⁺, Mn²⁺, Cr⁶⁺, and Cd²⁺ using adsorption on both acid-modified and unmodified activated carbon. Activated carbon (AC) was oxidized with nitric acid, both in granular (AGC) and powder (APC) forms, and tested for the competitive adsorption of Ni²⁺, Mn²⁺, Cr^6+, and Cd²⁺ from an aqueous solution. Surface oxidation led to a reduction in BET surface area and HK pore width and an increase in the intensities of hydroxyl and carboxyl functional groups for both AGC and APC compared to unmodified activated carbon, AC, as indicated with BET and FTIR analyses. The adsorption capacity of all four metal ions on AC was in the order Ni²⁺ > Cd²⁺ > Cr⁶⁺ > Mn²⁺, while it was altered for the two oxidized AGC and APC carbons to be Cr⁶⁺ > Ni²⁺ > Cd²⁺ > Mn²⁺. Acid treatment resulted in high selectivity for Cr⁶⁺ over all other available ions with a 100% removal efficiency, while it decreased for Ni²⁺, Cd^2+, and Mn²⁺ compared to AC. This improvement in Cr⁶⁺ adsorption is due to its higher ionic potential and smaller size, which results in a faster diffusion and stronger adsorption to the acidic groups located at the pore edges. Therefore, it will repel and hinder other ions from accessing the activated carbon pores. Modeling of the adsorption isotherms with DKR was better than both Freundlich and Langmuir for the competitive ions. DKR showed strong attraction for both Ni²⁺ and Cd²⁺ by ion exchange on the AC surface, as indicated by their apparent adsorption energy (E) values. Cr⁶⁺ adsorption was found to be by physical adsorption on AC and by ion exchange on both AGC and APC. Mn²⁺ ions had a very weak attraction to all types of tested activated carbons in the presence of other ions.

In this study, the effects of several synthesis parameters including aging time, micropore-structure-directing agents, and hydrothermal treatment temperature profile were systematically examined with respect to their impact on the crystallinity of macroscopic zeolite Y spheres formed in the presence of organic anion-exchange resin templates. Spherical resins were utilized as hard templates to shape the zeolite Y particles. Zeolite Y precursors were initially deposited into the pores of the resin template and subsequently crystallized over time through precise control over these synthesis parameters. The resulting zeolite Y spheres were characterized using an array of characterization techniques, including XRD, SEM, TEM, BET, FTIR, and XRF. We identify the optimal conditions for maximizing the crystallinity of the macroscopic zeolite Y particles using resin templates as macroscopic shaping agents. This functional material has the potential to be used as both catalyst and adsorbent in several applications.

The objective of this research was to understand the dehydration mechanism of technical dihydrate and the variation of the physical properties of β‐hemihydrate after the first hydration‐dehydration process. In this study, the recycling mechanism of different hemihydrate types as raw material was investigated. The influence of the first hydration‐dehydration process on the hydration rate, microstructure, and mechanical properties of recycled hemihydrate were characterized by differential calorimetric analysis (DCA), calcium ion‐selective electrode (Ca²⁺‐ISE), conductivity, particle size distribution (PSD), scanning electron microscopy (SEM), and X‐ray diffraction (XRD). The results showed that the formed hemihydrate after the first hydration‐dehydration process differs in its properties than the unrecycled hemihydrate in some characteristics such as the morphological structure, number of surface, and side defects due to the grinding process after the first hydration step. In addition to the grinding step, the calcination process was responsible for increasing the number of defects on the crystal surface, which leads to a change in setting time and the microstructure of the recycled hemihydrate. Therefore, after the 1st reaction cycle of β‐HH, the compressive strength decreases due to a decrease in the hemihydrate crystal size, an increase in the surface area, and an increase in the amount of water required to perform the hydration reaction. The obtained hemihydrate after the first hydration‐dehydration process was in β form due to the applied calcination process after the first cycle.