Efficiency evaluation of thermally and chemically regenerated activated carbons used in a water cleaning system by acoustic emission analysis

Abstract

Acoustic emission analysis (AEA) results for textural characterization of granular activated carbons (GAC) can be related with its porosity. GACs were evaluated using this AEA technique by band-pass filtering from 3.5 to 50 kHz of the sound produced by flooding GAC with water. Used acoustic parameters for evaluation were: area under the signal envelope curve, acoustic energy and power. An exhausted GAC used in a water filter system of engine-based power plant was subjected to thermal and chemical regeneration under different conditions. Acoustic measurement results have been correlated with TGA, XRF, gas adsorption (N2 at 77 K), GAC stability and elemental analysis for assessing the AEA. Based on all these techniques, it was found that mainly metal ions were adsorbed on the GAC. It was found that chemical regeneration using a 2.4 N HCl solution was the most successful approach in removing the adsorbed metal ions: Ca, Mn and Ba. Using this HCl solution did have the additional benefit in keeping the amount of elemental and fixed carbon almost intact compared to the more diluted HCl solution of 0.6 N and 1.2 N.