Surface interaction sites of Ni adsorption on Montmorillonite

G. CURUTCHET; R.M. TORRES SANCHEZ; C. FERNANDEZ MORANTES

Kosice

Conferencia; 8th MID-EUROPEAN CLAY CONFERENCE; 2016

MID-EUROPEAN CLAY ASOCIATION

Clay minerals, due to its low cost, high cation exchange and ubiquitous presence in most soils, have been widely used as geological barrier to immobilize metal cations, arising from industrial or domestic waste. Particularly, for Ni2+ adsorption on raw Montmorillonite (Mt) the interlayer sites were assigned as the main surface adsorption sites involved in the Ca-Montmorillonite (from pH 5 and 6.4) [1] and two types of complexes were found for raw Mt: bidentate variable charge surface hydroxyl sites and bidentate permanent charge exchange sites [2].The aim of this study was to analyze the pH and solid/liquid relation influence in the Ni2+ adsorption on Mt and evaluate the surface sites involved trough analysis of inner and outer surface Mt. To attain this objective a raw Argentine Mt was utilized as adsorbent (isoelectric point at pH =2.7), with Ni Co= 50 ppm (from SO4Ni solution), pH analyzed were 2, 4 and 6, and solid/liquid relations = 1, 2 and 3 mg/ml. XRD analysis were utilized to determine the Ni entrance in the inner surface (interlayer) and zeta (ζ) potential measurements to evaluate the outer surface interactions.The Ni adsorption increased from 7 to 24 mg/g with pH increase from 2 to 6 and decreased to 57 and 38 % respect of maximum adsorption at pH 2 and pH 6, respectively with the increase of solid/liquid relations from 1 to 3. The Ni2+ interlayer entrance was favored at pH=2, by displacing the raw Na, with a 001 reflection peak area relation Ni/Na= 12.75, while for pH 6 the same relation decrease to 1.86. Similar shape and values of ζ potential curves were found for Mt and Ni2+ adsorbed on Mt at pH= 2 samples. Whilst the decrease on negative surface charge of Ni2+ adsorbed on Mt at pH= 6 respects to raw Mt sample was indicative of the Ni adsorption on the outer surface by interaction with the variable charge (or edge) surface hydroxyl sites.Those results indicated an important interaction of Ni2+, and replacement of Na+ raw cations, with the inner or permanent charge exchange sites at pH= 2, while a more important Ni2+ interaction with the outer or variable charge surface hydroxyl sites happened at pH = 6.