Clinoptilolite, a (K-2, Na-2, Ca)(3)Al(6)Si(30)O(72)(.)24H(2)O (generally, Si/Al, 4.2-5.25) zeolite, particle size (a) 0.3-1.4, (b) <0.088 mm, was used to adsorb neodymium from 0.5 mM Nd3+ in 0.1M NaNO3 for 1-10 h. As particle size was reduced, the rate of ion exchange rose. With (a), equilibrium was achieved in 8 h; monolayer capacity was estd. at 56.8, and with (b), at 690 mumols Nd/g. As pH was varied from 2 to 11, adsorptions on (a) and (b) rose slowly at pH 1-6, then jumped high and leveled off at pH 6.5. Several adsorption reactions were given, involving ion exchange, hydrolysis and surface complexation on the zeolite's Na and Worms. As the NaNO3 concn. (and ionic strength) was raised from 0.1 to 2M, Nd adsorbate decreased. The affinity for Nd was affected by zeolite's particle size and solution's pH and ionic strength.