RESUMEN
The X-ray absorption (XRA) method using digital image processing techniques is a reliable technique to determine the exhaustion degree of granular activated carbons (GACs). Using an innovative digital image processing technique, the identification of individual adsorbed molecules or ions in a GAC was possible. Adsorption isotherm models (Langmuir and Freundlich) were used to simulate the adsorption equilibrium data of Methylene Blue (MB), nickel, cobalt and iodine. Freundlich equation was found to have the highest value of R2 compared with Langmuir. The identification of distinctive patterns applying XRA for different adsorbed ions and molecules onto GAC was explored. It is demonstrated that unique XRA configurations for each adsorbed ion or molecule are found, as well as a proportional relationship between its incident energy (needed to achieve maximum photon attenuation) and the (effective) atomic number, the adsorbate mass and the molar or atomic mass of adsorbed molecule or ion. XRA method in combination with image histogram modifications was used to obtain a digital signature of adsorbed ions/molecules, giving distinct GSI values for each one in the used energy range. Probabilistic models prove that XRA results are within relationships between effective atomic number and photonic interaction probability, reinforcing the potentialities of XRA for monitoring (multi-)ion and/or molecule combinations on GAC using advanced digital image processing techniques. It was proved that the proposed approach could assess different adsorbed ions/molecules onto GACs in water purification systems.
RESUMEN
Analytical methods based on X-Ray radiation proved to be reliable and sensitive techniques to study activated carbons (ACs). An X-Ray absorption analysis based on digital radiographic images (XRA) is applied for the determination of the exhaustion degree of granular activated carbon (GAC) used in a water purification system for hemodialysis. XRA-method demonstrated the possibility to determine the exhaustion degree at different layers of the GAC filter. The results of the XRA-method were successfully correlated with X-Ray Fluorescence (XRF), TGA, Elemental analysis (EA), SEM, TD-GC/MS, ATR-FTIR, X Ray Diffraction (XRD) and Nuclear Magnetic Resonance relaxometry (NMR) analyses. It was demonstrated that the XRA-method is a fast and reliable analytical tool to give indirect information on the exhaustion degree of GAC at different layers. It is also demonstrated that XRA results can be correlated with the results of the other analytical techniques, rather dealing with the composition and morphology of GAC at different layers.