EVALUATION OF THE INTERACTIONS BETWEEN HUMIC ACID AND CLAY SAMPLES ENRICHED WITH NICKEL IONS

Purpose: The objective of this work was to evaluate the interaction of humic acid (HA) and two different natural clays - kaolinite (KaO) and/or bentonite (Bent), enriched with nickel species. Methods: 0,5 g of each clay: kaolinite or bentonite enriched with nickel were added in 50 mL of 0.5 M  KCl solution with 0,05 g of HA during 5 hours. Aliquots were removed at intervals:  0 (without clays), 5, 10, 20, 40, 90 minutes; 2, 4 and 5 hours; and the HA concentration were analyzed by UV-vis spectroscopy after previous calibration. After 5 hours, by decantation, the clay fractions were separated from the supernatant. The materials were dried at 60 °C for 28 hours, and designated as KaONi1000HA and BentNi1000HA. For a determination of the HA concentration, a new kinetics considering the possible nickel leaching were evaluated using a nickel-adsorbed kaolinite 1000 mg/L. Results: In UV-vis spectroscopy a higher absorbance was observed due to transfer of nickel for aqueous medium evidencing their leaching from Ka. For KAONi1000HA the nickel present on the surface was removed, evidencing the low cation exchange capacity of the material. For BentNi1000HA occurs the maximum interaction between clay/HA due to transfer of charges between bentonite and HA and the high expansibility of the clay in aqueous solution is revealed. The X-ray powder diffraction (XRPD) and infrared absorption spectroscopy were employed to evidence the interaction between clays and HA. The kinetic study shown that bentonite presents higher affinity with HA than kaolinite.