Development of effective porous geopolymer adsorbent with high strength for copper(II) ion removal

Due to the serious consequences of the accumulation of heavy metals in organisms throughout the aqueous phase, the treatment of heavy metal pollution has received extensive attention. Porous geopolymer adsorbent (PGA) has been proposed as a promising remover of heavy metal ions due to its production convenience, low cost, and large surface area. However, it is easy to be broken under water impact. Besides, compared to some other adsorbents, the heavy metal ions capacity of PGA needs to be enhanced. In this paper, PGA with 1000 kg/m3 density was directly prepared based on solid waste including fly ash and slag at room temperature. Nano-silica (NS) was added to improve material strength. The compressive strength of PGA with 2 % NS addition increases up to 63.5 % compared with the material without NS addition, and the removal rate of Cu2+ goes to 78.4 % under this condition. Although the filling effect caused by NS addition is not beneficial for the adsorption ability improvement, the molecular dynamics simulation results confirm that the physical adsorption ability upward is mainly caused by the more Natrium-Aluminate-Silicate-Hydrate formation due to the decreasing Ca/Si ratio. Compared with Calcium-Aluminate-Silicate-Hydrate, Natrium-Aluminate-Silicate-Hydrate has a higher physical adsorption ability due to the evenly distributed electropositive region known from the density functional theory analysis, which contributes to PGA adsorption capacity from the outside environment.