| Various techniques have been developed to remove phosphate from water in response to phosphorus pollution in water. Adsorption has attracted increasing interest in phosphate removal from wastewater because of its high efficiency and easy handling.Hydrous manganese oxide, a type of amphoteric metal oxides of multiple crystal structure, high specific surface area and strong surface reactivity, is usually considered as an ideal adsorbent for ionic pollutants. Unfortunately, HMO is generally negatively charged at circumneutral pHs and cannot be used for effective removal of anionic pollutants like phosphate. We proposed a new strategy to enhance HMO-mediated phosphate removal by immobilizing nanosized HMO inside a polystyrene anion exchanger NS, and obtained a nanocomposite HMO@NS where HMO is present as nanoparticles of5.0～7.0nm in size. The point of zero charge (pHpzc) of HMO was shifted from6.2of the bulky HMO to-10.5after being nanosized and immobilized in NS. Consequently, the surface charge of nano-HMO is reversed to positive state at neutral pHs.HMO@NS displayed high removal capacity for phosphate at circumneutral pHs, even in the presence of sulfate, chloride and nitrate at greater levels. Based on the Donnan membrane effect, HMO@NS showed a fast adsorption kinetics with equilibrium time180min. Cyclic column adsorption indicated that the fresh HMO@NS could treat460BV of a synthetic influent containing2mg P(PO43-)/L initially to<0.5mg P(PO43-)/L, while only80BV was available for NS. After regeneration by NaOH-NaCl solution, the capacity of HMO@NS was lowered to-300BV constantly in the subsequent5runs. Cyclic runs on phosphate removal from a real biotreated effluent by using HMO@NS further validated constant efficiency and great potential in wastewater treatment. This study also provides a new strategy to tune the surface chemistry and expand the usability of other metal oxides in environmental remediation. |
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