Formation Of Iron Oxides In The Presence Of Dissolved Organic Matter And Removal Of Arsenic Contaminants

Oxidation of Fe???is an important way for the formation of iron oxides in nature,while there are often high concentrations of Fe???and DOM?dissolved organic matter?in the groundwater.Once groundwater is cycled to the earth's surface,Fe???will be oxidized.The effect of DOM on the formation of iron oxides by oxidation of Fe???is rarely studied.In this paper,the process of oxidation and hydrolysis of Fe???in the aqueous environment of the near neutral pH in the prensence of DOM is simulated.The types,morphology and crystal structure of iron oxides were studied by means of TEM,XRD and FT-IR,and the process of As???removal by Fe???oxidation flocculation in the presence of DOM was carried out.Both DOM with phenol and carboxylic acid can inhibit the oxidation and hydrolysis of Fe???.The inhibition of catechol to the oxidation and hydrolysis of Fe???is stronger than that of benzoic acid and phenol.The oxidation and hydrolysis of Fe???are mainly affected by C/Fe molar ratio and pH.With the increase of C/Fe molar ratio,the inhibition effect of catechol is enhanced.Under the condition of pH7.0-9.0,the dissolution of iron oxide and the re-precipitation of Fe???and Fe???occurs in the system.The leodpcrocite is the main form of iron oxide from pH 6.0 to9.0.Besides,goethite is formed at pH 6,and magnetite is formed at pH 8 and 9.The small particle ferrihydrite is dominant in the presence of catechol.The formation of ferrihydrite is inhibited with the increase of C/Fe molar ratio.Fe-OM complex compound prefers at C/Fe molar ratio of 5.0.In the system of catechol-As???,the decrease of As/Fe molar ratio and C/Fe molar ratio is beneficial to increase the removal efficiency of As_total[As?V?+As???].The removal efficiency of As_total[As?V?+As???]could reach 100%with a C/Fe molar ratio of 0.125.Compared with Fe???oxidative flocculation,Fe???-ferrihydrite shows higher effficiency and rate.