Use of electrochemical iron generation for removing heavy metals from contaminated groundwater

Abstract

This paper utilizes data from two pilot studies conducted at Superfund Sites to discuss the electrochemical iron addition process developed by Andco Environmental Processes, Inc. Electrical current and steel electrodes were used to put ferrous and hydroxyl ions into solution. Once added, the chemistry was properly manipulated to provide coprecipitation and adsorption conditions capable of simultaneously removing a wide variety of heavy metals. The goals of the two projects were distinctly different. At the first site, conversion of ferrous ions to the ferric state resulted in thorough reduction of hexavalent chromium to trivalent chromium. Observations and results from this study are used to discuss system design, sludge production, and operating costs. At the second location, high concentrations of many metals required removal. The presence of arsenic necessitated chemically induced oxidation. Hydrogen peroxide was introduced to convert Fe+2 to Fe+3 and arsenite to arsenate. By efficiently shifting the equilibrium state and adjusting pH to create conditions for maximum anion adsorption, an arsenic removal efficiency of over 99.8 percent was obtained. Proper process application resulted in simultaneous removal of aluminum, arsenic, cadmium, chromium, lead, mercury, nickel, selenium, thallium, and zinc. Also, when necessary treatment conditions were provided and maintained, metals removal by three major mechanisms resulted in iron matrices that passed regulatory levels listed in conjunction with the Toxicity Characteristic Leaching Procedures (TCLP).