Buoyant ALG/HA/HGMs composite adsorbents for highly efficient removal of copper from aqueous solution and contaminated kaolin soil

•Two novel buoyant ALG/HA/HGMs composite adsorbents were prepared and characterized.•The buoyant adsorbents could efficiently remove copper from aqueous solution and kaolin.•The buoyant adsorbent of AHG(acid) could reduce pH value of kaolin soil.•The buoyant adsorbent of AHG(base) could increase pH value of kaolin soil.•AHG(acid) showed excellent reusability in removal of copper from contaminated kaolin.

Two buoyant ALG/HA/HGMs composite adsorbents, AHG(acid) and AHG(base), were prepared by encapsulating hollow glass microspheres and humate within alginate gel beads in this study. Both AHG(acid) and AHG(base) were characterized and their adsorption properties for removal of copper(II) ions from aqueous solution and kaolin soil were investigated. In aqueous solution, the maximum adsorption capacities of copper on AHG(acid) and AHG(base) were 34.8 and 40.4 mg g−1, respectively, and the adsorption kinetics for AHG(acid) and AHG(base) followed the mechanism of the pseudo-second order kinetic model, and their equilibrium data were well fitted with the Langmuir isothermal model. The removal of copper from contaminated kaolin by AHG(acid) and AHG(base) was conducted by soil washing with deionized water containing buoyant adsorbents. As AHG(acid) could release hydrogen ions and reduce the pH value of the system consisting of adsorbent, water and kaolin, while AHG(base) could release hydroxide ions and increase the pH value of the system, the removal efficiency of copper from kaolin soil by AHG(acid) was much higher than that by AHG(base). Under soil washing conditions of the dosage of AHG(acid) of 3%, water/soil ratio of 3/1, and washing time of 48 h, the removal efficiency of copper from kaolin by AHG(acid) was 72.8%, and after 5 times reuse of AHG(acid) it was kept at 70%, while the pH value of kaolin soil was maintained in the pH range of 4.60-4.80. The results indicate that AHG(acid) has a potential application prospect in removing heavy metals from soil compared with AHG(base).