Selective separations are needed in a wide variety of industrial and commercial applications where discharge to publicly owned treatment works (POTW) requires certain metals concentrations to be sufficiently low to protect public health and the surrounding environment. Metals such as lead (Pb), copper (Cu), chromium (Cr), nickel (Ni), zinc (Zn), and cadmium (Cd) represent a non-exhaustive list of compounds requiring removal for discharge regulations. Typically, coagulants such as iron and aluminum combined with precipitation chemistry or ion exchange processes are used to meet these regulations.¹ However, these methods are not particularly selective and can produce sizable sludge waste that must be disposed of properly. Size-selective membranes are one alternative approach, but the pretreatment requirements for these membranes further complicates the water treatment process. Capacitive deionization (CDI) is an emerging water treatment option as well with notable advances in recent years, but it currently lacks the selectivity needed for many industrial streams.² Therefore, alternative methods are being sought to realize these separations.

The use of electrochemical processes offers a number of benefits such as a defined interface for interaction with the metal of interest, the ability to modulate the interface easily and quickly through changes in localized voltage, use of the electrical current to monitor system conditions, and the in situ generation of chemical species that can aid in the separation. Of particular interest in a wide variety of industrial applications is the removal or Cu from water being discharged to the POTW. Cu is found in waste streams emanating from electroplating, electronics, semiconductor, and battery manufacturing operations. While coagulation approaches mentioned above can often be used to meet effluent regulations, metal recovery through an electrochemical process can be highly effective and efficient, reaching current efficiencies in excess of 95% in many applications. The ability to plate Cu at a cathode under highly localized conditions affords the removal of Cu down to levels <100 ppb. Electrowinning has been used for over a century in the creation of purified metals such as Cu, so the concept is not entirely new, but the design of electrode materials and overall cell construction capable of removing Cu to such low concentrations in streams that have conductivities <1 mS/cm opens up new avenues for water treatment in industrial and commercial waste.

In this talk, electrochemical cell design and operation as well as feed water conditions will be reviewed towards the development of selective metal removal technologies. Copper removal will be highlighted as an example, but the concept will also be applied to other metals of interest, demonstrating the more ubiquitous nature of the approach.

References:

1. Azimi, A. Azari, M. Rezakazemi and M. Ansarpour, Removal of Heavy Metals from Industrial Wastewaters: A Review, ChemBioEng Reviews, 4, 37-59 (2017).
2. Gao, A. Omosebi, J. Landon, and K. Liu, Energy Environ. Sci., 8 (3), 897-909 (2015).
3. Boehme, C. Lippert, and J. Landon. “Faradaic Porosity Cell.” U.S. Patent 16/520,340 & PCT/US2019/043129, filed July 23, 2019.