The Capacity And Mechanism Of The Removal Of Simple Chlorinated Organic Pollutants By Ferrate

Ferrate, also known as Ferrate(Ⅵ) or Fe(Ⅵ), is a new type of environmentally friendly water treatment agent with multiple functions, such as oxidation and adsorption. Recent studies of ferrate mainly focused on the respects of oxidation resistance, its stability and the ability to remove some pollutants. Ferrate shows a strong oxidative capability, with the ability to remove some organic pollutants including phenol and nitrobenzene. However, few studies have been reported about the removal of simple chlorinated organics by ferrate. Simple chlorinated organic compounds, such as 1,1-dichloroethylene(1,1-DCE), trichlorethylene(TCE), and tetrachlorethylene(PCE), are widely used in areas of industry, agriculture and daily life. They are common volatile chlorinated organic pollutants detected in groundwater with potentially carcinogenic, teratogenic, and mutagenic hazard.This paper focused on the removal efficiency of simple chlorinated organics by ferrate and associated mechanism. The removal efficiency of TCE by ferrate under different conditions was investigated, with the reaction conditions being optimized. Theremoval efficiency of different chlorinated organics by ferrate was significantly different. Reasons resulting in the difference were analyzed from two aspects, the oxidation reduction potential and the molecular orbital energy. By measuring and characterizing the reaction solution and precipitate produced, TCE was found to be primarily removed by ferrate through an oxidation process. Specific results are described in detail as follows:The reaction of ferrate with TCE was mainly affected by several factors including ferrate dosage, reaction p H, reaction time, etc.. With the increase of dosage, the overall removal efficiency of TCE increased, while the removal efficiency by unit mole ferrate decreased.. The best removal efficiency of TCE was achieved when the pH valuestabilized at about 7 during the reaction. The reaction of ferrate with TCE was very fast, reaching equilibrium in less than two minutes.With excessive ferrate, the removal efficiency of 1,1-DCT, TCE, and PCE were 99.39%, 95.15% and 2.32%, respectively. The reason of the inertia of PCE to ferrate was explored. It is found that the gap between EHOMO of PCE and ELUMO of potassium ferrate was greater than 6eV, without meeting the requirement of triggering a reaction between two substances according to the frontline molecular orbital theory. The EHOMO value of pollutants which can react with potassium ferrate was also calculated, ranging from-14.653 eV to-8.653 eV.The removal mechanism of TCE by ferrate potassium was studied using analytical instruments including GC-MS, infrared spectroscopy, X-ray diffraction, and ion chromatography, to analyze both the reaction solution and the compounds in produced precipitates after the reaction occurs. Results show that(1) in the reaction solution, the concentration of chloride ion increased, and no other chlorinated organic substances were produced, demonstrating that TCE was completely oxidized to carbon dioxide and chloride ions, and(2) in the precipitate, inorganic compounds such as potassium chloride, iron oxides and iron hydroxides are observed, with no organic compounds adsorbed onto their surface. As a result, it can be concluded that TCE is removed by ferrate mainly through oxidation reactions.