Ni²⁺ uptake by amorphous and crystalline Ca₂Al ₂SiO₇ synthesized by solid-state reaction of kaolinite

The uptake of Ni²⁺ by amorphous and crystalline gehlenite (Ca₂Al₂SiO₇) was investigated. The Ca ₂Al₂SiO₇ samples were prepared by solid-state reaction of mixtures of kaolinite, calcite, and aluminum hydroxide mechanochemically treated the mixture for 0-24 h and fired at 600-900°C for 24 h. The mechanochemically treated samples crystallized to form gehlenite at ≥850°C, below which temperature they were amorphous. Ni²⁺ uptake experiments were performed by a batch method at 25°C using a solid/solution ratio of 0.002 g ml^-1 and a Ni²⁺ concentration of 10^-4 to 5 × 10^-2 M. The uptake capability increased with increasing pH > 6 and decreasing initial Ni ²⁺ concentration. The amorphous sample showed a higher Ni ²⁺ uptake than the crystalline sample, and its uptake was also higher than values reported in the literature for amorphous CaAl₂Si ₂O₈, zeolites, gylorite, and activated carbon.