the known concentration of Fe(VI) in phosphate buffer (pH~10) prepared by 0.005 M Na2HPO4 +. 0.001 Na3PO4 and observed the absorbance at different time ...
대한환경공학회 2006 추계학술연구발표회 논문집, 강릉대학교, 2006. 11. 2～11. 3
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Ferrate(VI): A Green Chemical for the Simultaneous Oxidation of Cyanide and Removal of Cu(II) from Aqueous/Waste Waters Hyoung-Uk Kim1, Diwakar Tiwari1, Seung-Mok Lee* , Jae-Kyu Yang** *
Department of Environmental Engineering. Kwandong University, Kangnung ** Department of Environmental Engineering Kwangwoon University, Seoul
1. Introduction: Cyanide in any form i.e., free cyanide, cyanide gas or metal complexed cyanide poses serious 1threat to the environment as well to the human being because of its acute and/or chronic toxicity. 5) The treatment processes involved for the several industrial operations particularly in mining operations, electroplating processes, coal gasification and other industries attracting public and 6-7) As regulatory attention since they contain significantly the cyanide or associated compounds. 5 reported the commonly used physical and chemical treatments viz., ion-exchange, adsorption or foam floatation only can separate the cyanide from one matrix to another. Moreover, the oxidation of cyanide by HClO/chlorine often generates harmful intermediates along with the aromatic organic chlorides (AOX), which are unacceptable if discharged directly into the environment. Thus, these methods are found to be limited towards the environmental point of view. Therefore, it become worth considering to innovate or to modify the existing technologies for the treatment of cyanide containing effluent/waste waters by using some alternative chemicals that could have acceptable efficiency/selectivity and also behave more environmentally friendly. In this context the role of ferrate(VI), the higher oxidation state of iron showed promising behavior as possess relatively high 0 3+ 0 22oxidative capacity (redox potentials of Fe(VI)/Fe(III) couple (E (FeO4 /Fe ) and E (FeO4 /Fe(OH)3 are 2.20 and 0.72 V, respectively at pH 1 and 14) and the byproducts obtained followed by the reduction of Fe(VI) i.e., Fe(III) are not harmful for human being or environment. Moreover, the reduced Fe(VI) into Fe(III) is fond to be a good coagulant and flocculating agent. Hence, the application of Fe(VI) in the waste water treatment plays multifunctional role as not only to oxidize the oxidizable impurities from the waste solution but also at the same time can remove the 8) associated impurities i.e., heavy metals through coagulation/flocculation. Although, couple of 9) 10) conditions by studies were reported for the oxidation of cyanide in oxygenated and in anaerobic Fe(VI). However, the role of Fe(VI) in the mixed systems i.e., cyanide and metals is yet to be investigated. Hence, with an increased interest, in a quest for cleaner and environmentally friendly treatment processes, the present investigation deals for the simultaneous oxidation of cyanide and removal of copper from the aqueous/waste solutions.
2. Experimental: 2.1 Materials: Copper (CuSO4.5H2O) and potassium cyanide, GR Reagent were obtained from Duksan Pure Chem. Co. Ltd., Korea and all other chemicals were used of GR/AR grade. Cyanide containing wastewater was obtained from the electroplating industry (Kyung-In Plating Co, Ansan, Korea) and the initial concentrations of the cyanide along with the other heavy metals are given in table 1. The potassium ferrate was prepared indigenously in the laboratory by the method described 11) 12 The purity of the compound was checked by the reported method and it was found to be earlier. 98% plus.
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Table 1: Wastewater analyzed for cyanide and heavy metal concentration. Concentration (mmol/L) * Cyanide 2.04 ** Nickel 2.18 ** Copper 0.51 * ** Analyzed by cyanide probe; Analyzed by AAS 2.2 UV-Visible Measurements: The UV-Visible Spectrophotometer, OPTIZEN 2120UV, Megasys Co. Ltd, Korea was used to obtain the absorbance of the solutions. First we performed the experiments with blank i.e., taking the known concentration of Fe(VI) in phosphate buffer (pH~10) prepared by 0.005 M Na2HPO4 + 0.001 Na3PO4 and observed the absorbance at different time intervals. Further, the similar experiments were done in presence of cyanide concentrations and observed the absorbance at different time intervals. The necessary self-decomposition correction for Fe(VI) was corrected with the blank. 2.3 Measurements with Cyanide Probe: To determine the cyanide concentration, a cyanide probe (Orion Cyanide Electrode 9606, Ionplus annexed with Orion pH meter 720A, USA) was used. The cyanide electrode was calibrated by using the standard cyanide solutions at pH~10. Further, the calibrated cyanide probe was used for the direct cyanide determination. In case of Cu-CN system, the cyanide concentration was obtained by the standard EDTA method i.e., first to decomplex the Cu-CN complex by EDTA at pH~4 (adjusted by addition of drops of glacial acetic acid and kept the solution for 5 mins at temperature 0 50 C) and then raised the pH 13 (by addition of conc. NaOH). At this pH, determined the free cyanide concentration by using the previously calibrated cyanide probe. 2.4 Wastewater Treatment: The wastewater obtained from the electroplating industry was filtered first to remove any suspended impurities and the pH of this solution was measured as ~13.0. The initial concentration of cyanide and heavy metals was determined respectively by using the cyanide probe and the Atomic Absorption Spectroscopy (Varian Spectra AA-300). Further, in 100 mL of waste solution, various doses of Fe(VI) was added in order to obtain the CN to Fe(VI) molar ratios: 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5 and 1:10. Stirred the solution for ca 2 hrs and filtered with syringe filter (membrane filter 0.2 µm). The filtrate was subjected for the determination of final CN and other heavy metal concentration.
3. Results and Discussion: 3.1 Cyanide Oxidation with Fe(VI): 3.1.1 UV-VIS Measurements The UV-Visible data were obtained for analyzing the oxidation of cyanide at different time intervals. The basic oxidation-reduction reaction involved may be represented below: …(1) Fe(VI) + CN → Fe(III) + CNO i.e., in presence of Fe(VI) the cyanide is supposed to reduced into cyanate which is 1,000 times less toxic and is often accepted for the end disposal. Earlier studies were also enabled that in the oxygenated environment, Fe(VI) oxidized cyanide and cyanate and nitrite were the products formed 9) while oxidation. The cyanide concentration varied from 0.3 to 15.0 mmol/L were taken in phosphate buffer pH~10 with the initial concentration of Fe(VI) 1.0 mmol/L and the absorbance data were recorded at different time intervals. The change in Fe(VI) concentration with time were shown graphically in Figure 1, which clearly showed that within few seconds of contact, a sharp decrease followed by
