Abstract
Poor raw water quality has pushed the frontier of science and technology research in seeking greener water treatment techniques such as advanced oxidation processes. In wastewater treatment, advanced oxidation processes such as ferrate (VI) salts have been considered as an emerging green oxidant, cost-effective, and coagulant/flocculent in a single mixing and dosing unit. The aim of this study was to synthesize a benign green chemical, calcium ferrate (VI) through a facile wet oxidation method for the treatment of water and wastewater. In this study, a series of stable aqueous calcium ferrate (CaFeO4) were successfully synthesized in an alkaline aqueous medium following the wet oxidation method at various temperatures (i.e., 60, 70, 80, and 90 °C), where Fe3+ ions from ferric chloride were oxidized to Fe6+ by using a mixture of calcium hypochlorite and calcium hydroxide as oxidizing and alkaline reagents, respectively. The prepared materials of CaFeO4 were named 60-CaFeO4, 70-CaFeO4, and 80-CaFeO4, 90-CaFeO4, where the prefix values correspond to the temperature used during synthesis. The prepared CaFeO4 were systematically characterized using XRD, FT-IR, UV-Vis, TEM, SEM, Raman, and redox titration. FT-IR analysis confirmed the presence of the Fe-O stretching vibrations in all the freeze-dried CaFeO4 powders, signifying the successful preparation of the materials. Moreover, the XRD patterns and Raman analysis also confirmed the crystal structure of the as-prepared CaFeO4. All the materials exhibited nanoflake-like morphology, typical for CaFeO4. The physicochemical characteristics of raw water, such as turbidity, colour, COD, pH, electric conductivity, and TDS, were analysed before and after treatment with CaFeO4. The as-prepared 90-CaFeO4 showed superior performances compared with 60-CaFeO4, 70-CaFeO4, and 80-CaFeO4. A jar test was performed to evaluate the efficiency of the materials towards wastewater treatment through coagulation process. The COD (43.56 % - 71.56 %), turbidity (97 % - 99 %), and TDS (3.61 % - 14.76 %) of the raw water sample were reduced upon the treatment with the CaFeO4. After coagulation using CaFeO4, the pollutants levels were reduced, signifying the effectiveness of the as-prepared materials. All the prepared stable aqueous calcium ferrate (VI) presented excellent coagulation abilities, with a reduced settling time. All the calcium ferrates were successfully produced and were stable enough to be stored at room temperature for over six months without decomposing significantly. As a result, using CaFeO4 to treat wastewater is an excellent environmentally friendly method. Keywords: Calcium ferrate (VI), coagulant green chemical, wastewater treatment, wet oxidation method, jar test, water treatment.