Aluminum chloride induced ferrate activation for p-arsanilic acid removal: The significant synergism mechanism and enhanced role of reactive Fe(IV)/ Fe(V)

The practical applications of potassium ferrate (K 2 FeO 4 ) are limited due to self -decomposition at nearly neutral pH and low removal efficiency for electron deficient pollutants. That is, K 2 FeO 4 was often insufficient to produce sufficient oxidative material, so the lack of oxidative reactivity remained a pressing problem. This study proposed an effective induction of K 2 FeO 4 activation by aluminum chloride (AlCl 3 ) in a novel highly concentrated simultaneous oxidation and coagulation (HOC) system of K 2 FeO 4 /AlCl 3 . It innovatively focused on the interaction between K 2 FeO 4 and AlCl 3 for the removal of p-arsanilic acid (ASA) in a HOC system. The HOC system exhibited higher ASA removal (62.6%) in a shorter period of time compared to K 2 FeO 4 oxidation (28.0%) and pre -oxidation -coagulation (POC) system (51.6%) with the addition of 1.5 mgAl/L of AlCl 3 at pH 7. AlCl 3 could induce the self -decomposition of K 2 FeO 4 , and more importantly, it could facilitated the conversion of Fe(VI) into the more reactive Fe(V)/Fe(IV) species for ASA removal. Moreover, AlCl 3 hydrolysis promoted the in -situ H 2 O 2 generation from K 2 FeO 4 decomposition, enhancing Fenton -like reaction and increasing center dot OH and center dot O 2 - for ASA removal. K 2 FeO 4 greatly influenced AlCl 3 hydrolysis and promoted rapid transformation of small polyaluminum Al a and medium polyaluminum Al b to colloidal high polyaluminum Al c . The content of Fe elements in the flocs produced by the HOC-ASA floc system was 19.27%, which was much higher than the 4.58% of the POC-ASA system, which enhanced the interfacial reaction and electron transfer and facilitated the removal of ASA.