Coagulating and flocculating ferrihydrite: application of zinc acetate salt

Abstract

This paper outlines a method of extraction of iron from water in the form of iron oxyhydroxide natural nanoclusters at comparatively low concentrations and varied ranges of pH using zinc acetate salt. The zinc acetate salt dissociates into Zn²⁺ and acetate ions in water where Zn²⁺ interacts with iron clusters present in a solution of a given iron concentration and pH, while the acetate ion helps in charge-neutralization based coagulation and consequent precipitation of such nanoclusters. The Zn²⁺ ions may also lead to the growth of layered zinc hydroxide (LZH) nanosurfaces at pH ≥ 6 at sufficient loading. The advantage of this method is the active chemical interaction of Zn²⁺ with Fe clusters, followed by growth, which ensures that only some added Zn ions remain in the water while the rest precipitate out along with the residual iron oxyhydroxide, especially at higher pH. The solid that precipitated under various different conditions was successfully evaluated by XRD (formation of ferrihydrite-like nanoclusters (n-Fh)), FTIR (the presence of acetate in the solid n-Fh), TEM (the presence of zinc at higher pH), and EXAFS (local structural characterization). ICP analysis of the obtained solid and the corresponding filtrate revealed the removal efficiency of iron and zinc from the solution at various initial concentrations and pH values. This method of extracting soluble Fh-like nanoclusters by charge neutralization appears to be a suitable promising tool for water purification, because ferrihydrite is capable of isolating other adsorbed contaminants from water, along with itself.