Reusability of zero-valent iron particles for zinc ion separation

Abstract

Abstract Zero-valent iron (ZVI) is known to be effective in separating heavy metals from aqueous solution. However, used ZVI particles are usually discarded in heavy metal-containing sludge. Therefore, an appropriate technique for the reactivation of used ZVI for reuse is discussed in this work. A series of zinc desorption tests from zinc-adsorbed ZVI revealed that zinc desorption required both acidic conditions to dissolve zinc-containing iron hydroxide layers on ZVI and reductants to remove insoluble iron oxide layers from the ZVI surface. Organic acid reductants, such as citric acid, satisfy both these requirements. The ZVI particles that were reactivated by the desorption of zinc using 10.0-mM citric acid were applied repeatedly for zinc removal. Reusing the ZVI particles four times did not affect their zinc removal performance relative to that of virgin ZVI. Furthermore, the used 10.0-mM citric acid could be reused to desorb zinc from the used ZVI particles after separating the zinc and iron ions by hydroxide precipitation at pH 12 and re-acidifying the solution to pH 2.5 by the addition of sulfuric acid. Thus, both the ZVI particles and the 10.0-mM citric acid cleansing liquid were found to be reusable for zinc separation from aqueous solution.