The uptake of Ni(2+) by amorphous and crystalline gehlenite (Ca(2)Al(2)SiO(7)) was investigated. The Ca(2)Al(2)SiO(7) samples were prepared by solid-state reaction of mixtures of kaolinite, calcite, and aluminum hydroxide mechanochemically treated the mixture for 0-24h and fired at 600-900degreesC for 24 h. The mechanochemically treated samples crystallized to form gehlenite at greater than or equal to850degreesC, below which temperature they were amorphous. Ni(2+) uptake experiments were performed by a batch method at 25 degreesC using a solid/solution ratio of 0.002 g ml(-1) and a Ni(2+) concentration of 10(-4); to 5 x 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 CaAl(2)Si(2)O(8), zeolites, gylorite, and activated carbon. (C) 2004 Elsevier B.V. All rights reserved.