ARTICLE IN PRESS JID: JTICE [m5G;January 11, 2019;2:18] Journal of the Taiwan Institute of Chemical Engineers xxx (xxxx) xxx Contents lists available at ScienceDirect Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice Removal of iron as oxyhydroxide (FeOOH) from aqueous solution by fluidized-bed homogeneous crystallization Nicolaus N.N. Mahasti a , Yu-Jen Shih b , Yao-Hui Huang a,∗ a Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan b Institute of Environmental Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan a r t i c l e i n f o Article history: Received 1 November 2018 Revised 17 December 2018 Accepted 27 December 2018 Available online xxx Keywords: Fluidized-bed Homogeneous crystallization Iron oxyhydroxide Crystallization ratio Hydraulic condition a b s t r a c t In this study, iron is removed from aqueous solution using a fluidized-bed crystallizer. Homogeneous oxy- hydroxide pellets (FeOOH) were recovered at various value of pH, surface loading (L), and initial ferrous concentration to assess the treatability of iron-containing water. The optimal conditions for treating ini- tial ferrous concentrations of 100–300 mg/L were L = 0.6 kg/m 2 /h (with 29 m/h of upflow velocity), a bed expansion of 50% and pH = 6.5 yielding the total iron removal (TR) of more than 99% and a corresponding iron crystallization ratio (CR) of 85%. X-ray diffractometry (XRD) revealed that the pellets consisted of a mixture of goethite (α-FeOOH) and lepidocrocite (γ -FeOOH). Scanning electron microscopy (SEM) yielded images of pellets of up to 1 mm in diameter, which were assembled from FeOOH flakes with thicknessess of 0.2–0.4 μm. © 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. 1. Introduction Iron (Fe), as the fourth most abundant element on earth, con- stitutes 5.6% of the mass of the earth’s crust [1]. Fe exists in wa- ter as soluble ferrous ions (bivalent ions in the form of Fe(II) or Fe(OH) + ) or in a complex form (trivalent iron Fe(III) in equilibrium with Fe(OH) 3 precipitate) [2]. Iron is present in water in industrial effluent and domestic waste, and as a result of geogenic condition [1,2]. Iron is an essential element in hemoglobin, myoglobin, and various enzymes. However, an overdose of iron in the body can cause severe health problems such as hermosiderosis (liver dis- ease), heart diseases, nausea, gastrointestinal problems, and poten- tially abortive effects on pregnancy [3–5]. The WHO has set a max- imum Fe level in drinking water of 0.3 mg/L [6] and the FAO has set a maximum level in irrigation water of 5 mg/L to prevent soil acidification and loss of essential phosphorus and molybdenum [7]. Trickling filter and membrane filtration [8,9], ion exchange [10], electro-coagulation [11], and oxidation-filtration [12] are the common techniques for purifying the water that is contaminated with iron. Oxidation agents, such as chlorine, potassium perman- ganate, and ozone are used to convert ferrous ions to ferric ions, which can readily form the insoluble iron hydroxide complex Fe(OH) 3 . Precipitation and filtration using several filter media such as ceramics, electromedia, and ANTHRA/SAND TM (also known as iron-man sand) are commonly applied in water treatment plants ∗ Corresponding author. E-mail address: yhhuang@mail.ncku.edu.tw (Y.-H. Huang). because they are easy to implement, require simple equipment, and are fairly inexpensive [12]. However, the disposal of a large quantity of sludge is very costly [13], and the volume of sludge disposal must be decreased to reduce the total installation cost of a sludge treatment plant [14]. The precipitation of iron in the form of ferric oxyhydroxide from wastewater can create goethite (α-FeOOH) and lepidocrocite (γ -FeOOH) phases, which have great industrial and scientific im- portance because of their non-toxicity, chemical stability, and low production cost [15]. FeOOH has been used to remove heavy metal ions and organic pollutants from wastewater [16,17]; to fabri- cate composites of CBC (Carbonized Bacterial Cellulose) [18] or polyaniline [19], and as electromagnetic interference shielding [20]. The synthesis of goethite can be initiated by the precipitation of Fe(OH) 2 followed by rapid oxidation in a strongly alkaline solu- tion. Hydrogen peroxide and air bubbles are the common oxidants [21,22]. The oxidation of Fe(II) using H 2 O 2 has been described else- where as follows [23] 2Fe 2+ + 2H 2 O+H 2 O 2 → 2FeOOH(s) + 4H + (1) In the absence of any oxidant, the oxidation of Fe(II) highly depends on the oxygen partial pressure in corresponding to the amount of the oxygen dissolved in the solution [24]. 4Fe 2+ + O 2 + 2H 2 O → 4FeOH 2+ (oxidation) (2) FeOH 2+ + 2H 2 O ↔ Fe(OH) 3(s) + 2H + (precipitation/dissolution equilibrium) (3) https://doi.org/10.1016/j.jtice.2018.12.022 1876-1070/© 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Please cite this article as: N.N.N. Mahasti, Y.-J. Shih and Y.-H. Huang, Removal of iron as oxyhydroxide (FeOOH) from aqueous solution by fluidized-bed homogeneous crystallization, Journal of the Taiwan Institute of Chemical Engineers, https://doi.org/10.1016/j.jtice.2018. 12.022