Reaction condition effects on nickel sorption mechanisms in illite-water suspensions

ABSTRACT to this solution, the edge-situated interlattice sites be-come occupied by ions other than K, presumably leadingNickel sorption in illite suspensions was studied as a function of to partial opening of the interlattice space (Bolt et al.,pH (4.5–8.0), reaction time (3 h, 24 h, and 1 wk) and ionic strength (I 5 0.1 and 0.003 M) using x-ray absorption spectroscopy (XAS) to 1979). characterize the Ni sorption complexes formed. The formation of The different sites available for metal uptake by illite Ni-Al layered double hydroxide (LDH) phases was observed at pH may lead to different Ni retention mechanisms occurring values.6.25, with increasing formation of these phases with time, in Ni–illite systems. The planar sites constitute perma-and a faster formation rate with increasing pH. Comparison among nent negative charge. Metal interactions with these sites samples with the same Ni loading, but different reaction times and are electrostatic in nature and lead to the formation of pH values, showed larger second neighbor scattering for the samples outer-sphere metal complexes; that is, the metal ionsreacted at higher pH, which had a faster Ni sorption rate. Most likely do not lose their primary hydration spheres upon inter-this was due to a greater importance of Ni-Al LDH precipitation action with the clay mineral surface (Sposito, 1989;relative to other (mononuclear) Ni sorption mechanisms at higher Sparks, 1995). At the illite edge sites, both the formationpH, and/or a higher Al content in the Ni-Al LDH phase formed at lower pH (slower Ni sorption rate). Lowering the ionic strength re- of outer-sphere complexes and chemisorption may oc