Investigation of nitric acid treatment of activated carbon for enhanced aqueous mercury removal

In the present work, Hg(II) adsorption of a commercial activated carbon with and without nitric acid treatment was compared in a batch system. Iodine adsorption test and nitrogen adsorption and desorption experiments were carried out to investigate the changes in porous characteristics during acid treatment. Although the results for iodine adsorption of two samples were approximately similar, the increase in porous characteristics during acid treatment was determined by micropore volume and total pore volume of treated and untreated samples. To evaluate the effects of acid treatment on the surface functional groups, FTIR analysis for both types of activated carbons was performed, and showed oxidized surface for treated sample. Furthermore, composition of the gaseous by-product resulted from this treatment has been qualitatively analyzed using a FTIR device. Consequently, NO, NO2, N2O4, N2O, CO, and CO2 were detected. Kinetic and equilibrium adsorption studies were performed considering effective parameters, including contact time, initial pH, and initial concentration. It can be seen that nitric acid treatment of activated carbon has enhanced Hg(II) adsorption capacity. Moreover, kinetic studies showed faster adsorption rate for treated activated carbon through changes in external surface rather than internal.