Mercury removal from aqueous solutions using silica, polyacrylamide and hybrid silica–polyacrylamide aerogels

Mercury(II) ions adsorption from aqueous solutions onto silica, polyacrylamide, and hybrid silica–polyacrylamide aerogels is studied. The aerogels structure was verified by FTIR spectroscopy and their texture by nitrogen adsorption. The adsorbents were tested under different experimental conditions where the effect of temperature, pH, contact time, initial mercury(II) concentration, and aerogels quantity were investigated. The mercury adsorption onto the three aerogels was shown to be very fast, with the fastest being performed at 45 °C onto the hybrid aerogels. pH 11 was revealed optimum indicating a superlative surface interaction between the adsorbent and the adsorbate. The adsorption kinetics follows a pseudo second-order pointing out the co-existence of chemisorption and physisorption with the intra-particle diffusion being the rate controlling step. The mercury(II) adsorption fits well with Langmuir adsorption isotherms where the polyacrylamide aerogels showed the highest adsorption capacity, followed by the hybrid aerogels. The regeneration of the aerogels at pH 2 and their reuse at pH 11 was conducted for three consecutive reuses where the adsorption capacity was successfully maintained. The hybrid aerogels were found to be the most economically interesting adsorbents due to their noticeable adsorptive capacity after regeneration coupled with their no-swelling behavior.