X-ray Absorption (XRA): A New Technique for the Characterization of Granular Activated Carbons

Abstract

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.

Chemical Regeneration of Activated Carbon Used in A Water Treatment System for Medical Services

“…GAC samples from the first 20 cm of the adsorber (GAC-Top) were selected for the regeneration, considering the large amount of adsorbed inorganics found at the upper layers in the adsorber compared with a virgin GAC sample [3]. Samples were collected using the procedure described in [3,15,16]. The GAC-Top sample was selected using GAC samples between 0 cm and the first 20 cm of the GAC bed (see Figure S1).…”

“…XRA method [3,[15][16][17] uses digital image processing on digital X-Ray radiography. X-ray radiography experiments were conducted using a TOSHIBA Mamorez-mgu 100d X-ray equipment used for mammography studies in manual mode, according to [16].…”

“…X-ray radiography experiments were conducted using a TOSHIBA Mamorez-mgu 100d X-ray equipment used for mammography studies in manual mode, according to [16]. The mathematical analysis of the digital X-Ray radiographic images and obtaining the image's histograms and frequency spectra were performed using dedicated software developed in MATLAB® specifically for this application [3,[15][16][17].…”

“…XRA takes advantage of the different attenuation levels of X-ray radiation by materials with different densities [3,[15][16][17]. Figure 2 depicts the original X-ray radiographic images(a), the image histograms(b) and the frequency spectra(c) of the exhausted GAC before and after the regeneration using HCl 20%(v/v) and 2 h contact time and CH 3 COOH 15%(v/v) and 4 h contact time as well as the virgin GAC sample.…”

“…The performance of both acids for regeneration has been compared using different analytical techniques such as TGA and ICP-AES, SEM and RSSCT (for obtaining breakthrough curves), as well as a new X-ray absorption method (XRA) [3,[15][16][17].…”