Kaolin waste, generated in abundance by companies from Pará state, has caused to the
environmental problems. In order to give input on the reuse of this waste was evaluated
retention of nitrate ions on kaolin waste natural and modified with urea and studied the
equilibrium of adsorption processes at solid-solution interfaces. The materials were
characterized by X-ray diffraction and X-ray fluorescence (XRF and XRD, respectiely), IR
spectroscopy (FTIR spectrum), scanning electron microscopy and estimated data of surface
charge. Adsorption experiments of nitrate ions in the waste natural kaolin (CRJN) and
modified with urea (CRJU) were performed without pH adjustment. H +
concentrations were
measured by direct potentiometry before and after the process of adsorption and equilibrium
concentrations of nitrate were measured by ion chromatography. The results indicated: high purity kaolin waste; formation of kaolinite-urea complex confirmed by XRD reflection at 2
8,28o
e d = 1.068 nm and the FTIR spectrum with the appearance of a broad band of low
intensity, containing two discrete shoulder around 3500-3380 cm-1, corresponding to
asymmetric and symmetric vibrations of the group-NH2 of urea-kaolinite, superimposed to the
vibration of water. surface charges data, suggesting that the materials have a higher capacity
to adsorb cations than anions, but depending on the concentration of H +
and OH-
on
adsorbent, the hydroxyl surface can be protonated yielding positive charges that are reflected
in the adsorption of anions, obtaining significant adsorbed nitrate, both in CRJN as CRJU
(0,27-0,73 and from 0,18-0,70 3.5 mg g-1, respectively), the separation coefficient (RL) of
from 0,28 to 0,828 change in free energy ΔG ° = -2,094 to + 0,445 kJ mol-1 for CRJN and
ΔG° = -1,036 to + 1,32 kJ mol-1 for CRJN molecule. The data from RL indicated that the
adsorption processes are less favorable in most points of the adsorption processes and based
on the results of the free energy change (ΔG º) was showed low spontaneity to no spontaneity
and adsorption processes are physical.
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