The mechanisms of arsenic removal from soil by electrokinetic process coupled with iron permeable reaction barrier

Abstract

An innovative remediation system of electrokinetic process coupled with permeable reaction barrier (PRB) was proposed for arsenic removal in soil matrix. Batch tests with PRB media of Fe(0) and FeOOH under potential gradient of 2 V cm(-1) for 5d duration were conducted to evaluate the removal mechanisms of arsenic. Arsenic enhancement of 1.6-2.2 times was achieved when a PRB system was installed in an electrokinetic system. A best performance was found in system with FeOOH layer located in the middle of elctrokinetic cell. This was largely because of higher surface area of FeOOH and the moving of HAsO(4)(2-) to the anode side by electromigration effect was inhibited by the electroosmosis flow. The surface characteristics of PRB media, which were qualified by SEM coupled with energy dispersive spectroscopy (EDS), were clearly confirmed that arsenic was found on the passive layer surface. Results indicated that the removal of As in EK/PRB systems was much more contributed by surface adsorption/precipitation on PRB media than by EK process. Furthermore among the electrical removal mechanisms, electromigration was predominant than electrosmotic flow. Surface adsorption and precipitation were respectively the principal removal mechanism under acid environment, e.g. near anode side, and under basic environment, e.g. near cathode side. The results reported in the present work will be beneficial to optimizing design of batch EK/PRB system and enlarging to the field scale system.