Selective granulation of trivalent iron into ferric hydroxide from bi-metal containing wastewater using Fluidized-Bed Homogeneous Crystallization technology

Abstract

The traditional method that is used to treat the bi-metal-contained wastewater involves simultaneous chemical precipitation for the removal of both metals. However, recent trends in wastewater treatment emphasize the importance of recovery, recycling, and reuse. This study uses Fluidized-Bed Homogeneous Crystallization (FBHC) technology to selectively recover Fe(III) as granulated Fe(OH)3 from electroplating wastewater that contains iron and copper. For the treatment of a pure iron solution ([Fe(III)]0 = 650 mg/L), the optimal conditions include a pH value of 3.8, a reflux ratio (R) of 17.5, an up-flow velocity (U) of 35.9 m/h and a hydraulic retention time (HRT) of 17.9 min to give the maximum total removal efficiency (TR) for iron of more than 99.5%, and a crystallization ratio (CR) for iron of 93.6%. To treat real electroplating wastewater that contains iron and copper ([Fe(III)]0 = 1000 mg/L and [Cu(II)]0 = 500 mg/L), Fe(III) is effectively recovered as granules with a TR of 99% and a CR of 90%, and more than 90% of copper ions remain in the solution. SEM analysis observes that the product is an unseeded core-shell spherical particle. Additionally, XRD, FT-IR, and TGA results confirm that the product is an amorphous ferric hydroxide (Fe(OH)3) compound. A FBHC system has a high potential to separate iron and copper in a solution via a selective granulation process.