Bioelectrochemical recovery of Cu, Pb, Cd, and Zn from dilute solutions

Abstract

In a microbial bioelectrochemical system (BES) living microorganisms catalyze the anodic oxidation of organic matter at a low anode potential. We used a BES with a biological anode to power the cathodic recovery of Cu, Pb, Cd, and Zn from a simulated municipal solid waste incineration ash leachate. By varying the control of the BES, the four metals could sequentially be recovered from a mixed solution by reduction on a titanium cathode. First, the cell voltage was controlled at zero, which allowed recovery of Cu from the solution without an electrical energy input. Second, the cathode potential was controlled at -0.51 V to recover Pb, which required an applied voltage of about 0.34 V. Third, the cathode potential was controlled at -0.66 V to recover Cd, which required an applied voltage of 0.51 V. Finally, Zn was the only metal remaining in solution and was recovered by controlling the anode at +0.2 V to maximize the generated current. The study is the first to demonstrate that a BES can be used for cathodic recovery of metals from a mixed solution, which potentially could be used not only for ash leachates but also for e.g. metallurgical wastewaters and landfill leachates.

Bioelectrochemical metal recovery with microbial fuel cells

“…They showed the possibility to remove copper from wastewater and production of pure plated copper, in combination with electricity production (Figure 1.2). The novelty of the application of BES for the recovery of metal waste was that this provides an energy-efficient alternative to conventional electrowinning processes, because the electron donor (wastewater) provides (part of) the energy to drive the reduction reaction [27][28][29][30][31][32] .…”

“…The voltage and the power are also relevant to understand how efficient the process is from an energetic point of view. Copper and Chromium are the most studied metals in BESs, but other metals can be used such as silver, gold and mercury [27][28][29][30][31][37][38][39] . Wang et al (2008) published one of the first papers on MFC technology in which Cr (VI) in wastewaters was reduced to a less toxic aqueous species.…”

“…These competing reactions result in lower removal efficiencies for MECs compared to MFC processes. Modin et al (2012) 28 showed that for lead and cadmium, the recovery has lower energy demand than electrowinning processes. Cobalt reduction 42 can be achieved at much lower power consumption and higher removal efficiencies compared to the other metals nickel, lead, and cadmium.…”

“…A maximum current density of 3.2 A/m 2 was achieved in a setup with a flat plate graphite electrodes and a Bipolar Membrane (BPM). Since then ,other studies have reported MFCs in which copper was reduced at the cathode, reaching current densities ranging from 0.9 -7 A/m 2 with, for example, an increased surface area of the anode compared to the cathode 28,50 .…”

“…Several metals have been demonstrated as electron acceptors in BES cathodes such as silver 65,66 , iron 17,67,68 , nickel 41 , zinc 28 and copper 27,28,37,39,50,59,69 . A common feature in all these studies is that the electron donor in the anodic compartment is an organic substrate.…”