p-Arsanilic acid degradation and arsenic immobilization by a disilicate-assisted iron/aluminum electrolysis process

p-Arsanilic acid (p-ASA) is widely used as feed additives in animal production, and its transformation in environment media may cause arsenic contamination of soils and waters. It is essential to find a technology to effectively treat p-ASA, and meanwhile greatly decrease the mobility of the arsenic. Herein, we propose a disilicate-assisted Fe/Al electrolysis (D-FeAl-E) process for the degradation of p-ASA and the subsequent immobilization of inorganic arsenic. The results showed that, in the first stage of D-FeAl-E, namely the iron anode electrolysis process with disilicate, p-ASA was degraded by 92% under a near-neutral condition. The efficient degradation of p-ASA could be attributed to the disilicate-coordinated electrolytic ferrous ions, which activated dioxygen to produce more reactive oxygen species (e.g., center dot O-2(-), H2O2 and center dot OH in this study) to attack p-ASA molecules. Following the first stage, the produced inorganic arsenic and other intermediates can be further removed in the second stage of D-FeAl-E process (the Al anode electrolysis), via the coagulation effect initiated by the electrogenerated hydroxylated aluminum species. Electrogenerated Al(III) ions hydrolyzed into positively charged monomeric/oligomeric Al species, which could result in the dissociation of disilicate-Fe(III) complexes, and the formation of hydroxides and oxo-bridging polynuclear entities for arsenic immobilization. Leaching stability tests suggested that the D-FeAl-E process was superior to the conventional electrocoagulation method with respect to the stability of the generated arsenic-containing solid sludge. The D-FeAl-E process is free of the use of chemical oxidants and coagulants, but it provides both oxidation and coagulation effects for the abatement of p-ASA during the two-stage electrolytic process. Therefore, it is expected to be engineered as efficient and compact electrochemical technology capable of providing both oxidation and coagulation effect for decontamination.