Preparation and ion exchange properties of egg-shell glass beads with different surface morphologies

A subcritical water treatment method was developed for preparing porous-surfaced glass beads with an egg-shell structure in a batch reactor. Based on the "corrosion-ion-migration-recondensation" strategy, ordinary soda-lime glass beads with a diameter of about 100 m were made first to react with subcritical water to effect controlled quantity of silicate dissolution of glass by adjusting treatment time and temperature. The dissolved silicate was then made to recondense on the glass core to form different porous shell morphologies: pores, flakes and fibers. Among these, glass beads coated with fibers with surface area of 154.5 m2/g, pore volume of 0.27 cm3/g and pore size of 7.1 nm were obtained at 573 K after 2 h of treatment. The prepared porous-surfaced glass beads were then used as adsorbent for heavy metal ions, showing various ion exchange properties. Glass beads covered with fibers displayed fast kinetics and high sorption capacity because of their egg-shell structure and high surface area. More than 90% of copper ions were adsorbed within 100 min from a solution with an initial concentration of 110 mg/L at 313 K. Ion sorption capacities were 149.33, 81.33 and 42.96 mg/g respectively for Ag+, Cu2+ and Ni2+ at 313 K. A green and low-cost method was thus developed to produce egg-shell-structured porous glass with high sorption capacity.