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Hydroxyapatite (HAp) has been investigated for the removal of heavy metals in environmental application. However, little is known about the influences of surface modifications of the HAp. In this paper nano-HAp-polyvinyl alcohol (PVAL) gel was synthesized under pH control and the formed gel was used for removing nickel ions. The influence of nickel ions on the surface of HAp was studied. Reaction mechanisms were followed by ICP-MS and discussed via continuous variations method (CVM), mole ratio method (MRM) and slope-ratio method (SRM). The formed gel with nickel ions was characterized by various methods including UV, FTIR, XRD, and SEM. The ICP-MS was used to analyze the supernatant solution to confirm the presence of Ca and/or Ni ions. The nickel ions were found to reduce the degree of crystallinity of the synthesized HAp phase. The present results indicate that nickel ions were completely adsorbed on the HAp structure with its anion. The validation of the nature of HAp gel as chelating agent, or complex formation as well as physical sorption was discussed.