Zinc Removal from Waters by Hybrid Sorbent with Humic Acid

Humic biogenic organics can promote the detoxification of aquatic ecosystems from heavy metal ions. However, humic acids have not been widely used in adsorptive remediation of natural waters because of high solubility. In the present article, we proposed hybrid adsorbent based on silica gel sequentially modified with a quaternary ammonium salt, tetradecylammonium nitrate, and humic acids and tested it for the removal of Zn(II) from the tap water. The maximum adsorption capacity of humic acids on the modified silica gel can reach 7.1 and 11.4 mg/g at pH 7 and 3.0, respectively. The immobilized humic acids are resistant to dissolution at pHs of 5-7 and different KCl concentrations. Elution of humic acids from sorbent at pH 5-7 is below 15%. Functional groups of immobilized humic acids can bind Zn(II) ions. By using the hybrid adsorbent, the removal of Zn(II) from aqueous solution reaches 94-97% at pH 5.0-6.0. We registered the H-type adsorption isotherm at a low initial concentration of Zn
²⁺
ions. The uptake of Zn(II) was relatively fast, and the equilibrium was reached for 20-25 min. The hybrid sorbent can be used to concentrate metal ions from natural waters and in water purification technologies.