Batch and dynamic acid regeneration evaluation of granular activated carbons used in water cleaning treatment system. A comparative study between advanced analytical methods and a new infra-red thermographic method

Abstract

A new Infrared Thermography (IRT) technique was used for textural characterization of different granular activated carbons (GAC) samples. Virgin GAC was used in a water cleaning system. Upon GAC exhaustion, an HCl and HNO3 acid regeneration method was explored using different concentration and contact time. Thermographic parameters for evaluation were (1) average temperature of the sample and (2) surface thermal density which were both deduced after applying digital images processing from the obtained IRT thermograms by flooding water over the GAC sample. Linear correlations were found between IRT parameters with SBET and Vmic (obtained from N2 gas adsorption) for exhausted and regenerated samples, being for the temperature, 0.94 and 0.91 respectively and for the surface thermal density, 0.93 and 0.92 respectively. IRT measurement results have been correlated and assessed with TGA, XRF, gas adsorption (N2 at 77 K and CO2 at 273 K), SEM-EDX NMR, FTIR, TD-GC-MS, GC-MS, GAC stability and elemental analysis. Based on all these techniques, it was found that mainly metal ions were adsorbed on the GAC. Chemical regeneration using a 7.4 wt% HCl solution was the most successful approach in removing the adsorbed metal ions (Ca, Mn and Ba) in comparison with more diluted HCl solution and HNO3 solutions. Dynamic regeneration also demonstrated that HCl performs better with a breakthrough time of 249 min, much lower than HNO3 (337 min). The used experimental column and the industrial water filter behave quite similar. Finally, in order to confirm the performance of the regenerated sample, isothermal adsorption studies as a function of the total water hardness were done, which confirmed that the regenerated GAC sample using 7.4 wt% HCl offers the best results (58.3% removal) in comparison with HNO3.