This work is focused on the removal of Ni(II) from aqueous solutions by sorption onto newly developed magnetite-loaded calcium alginate particles. The uptake of Ni(II) by these magnetite particles, with their mean geometrical diameter 84 and 508 pm, is best described by the Freundlich isotherm and the constants K-F and 1/n were found to be 3.491 mg g(-1), 0.731 and 0.793 mg g(-1) and 0.907, respectively. The mean sorption energy, as determined by Dubinin-Radushkevich isotherm for 508- and 84-mu m sized particles was evaluated to be 8.9 and 8.0 kJ mol(-1), respectively, thus, suggesting the ion-exchange mechanism for uptake process. Of the various kinetic models proposed, the kinetic Ni(II)-uptake data were best interpreted by "Simple Elovich" and "Power function" as suggested by their higher regression values. The almost linear nature of plots of log(% sorption) versus log(time) was indicative of intraparticle diffusion. The values of intraparticle diffusion coefficients K-jd were found to be 63.49 x 10(-2) and 94.35 x 10(-2) mg l(-1) min(0.5). The intraparticle diffusion was also confirmed by Bangham equation. Finally, various thermodynamic parameters were evaluated. The negative Delta G degrees indicated spontaneous nature of uptake process while positive Delta H degrees value suggested exothermic nature of the sorption process. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 475-483, 2009