Electrochemical Alloy Formation for Mercury Decontamination of Aqueous Solutions

Roth, Vera

The effects of mercury pollution are a major concern worldwide. Mercury is a highly toxic, mobile and bioaccumulative heavy metal. It is widely dispersed in the environment in a variety of different forms, posing a significant threat to all living organisms. Current established methods for mercury decontamination of aqueous solutions, such as waters and waste streams, are far from ideal. It is often inefficient or even impossible to remove mercury from large volumes of solution at low mercury concentrations. In addition, current techniques are less effective at low pH and cannot operate in highly acidic conditions. For chemically complex streams containing number of different heavy metals, selective removal of mercury is often low; Therefore, developing new and improved methods for mercury removal is highly sought-after [1].

This presentation will introduce a new method for mercury decontamination that is currently under development. The method involves electrochemical reduction of mercury ions in solution followed by a formation of a stable amalgam on an electrode surface, mainly platinum. The formation of the amalgam, in the thermodynamically favored phase PtHg₄, has been extensively studied and characterized using electrochemical quartz crystal microbalance (EQCM), inductively coupled plasma mass spectroscopy (ICP-MS) and scanning electron microscope (SEM). This new decontamination method has the potential to offer numerous advantages over other established methods. It has e.g. been shown that the method has high efficiency, selectively removing >99% of mercury in aqueous solutions with initial concentrations ranging from 0.25 – 75000 ppb Hg²⁺. The process is reversible, unaffected by pH and the presence of most other compounds and impurities [2,3]. This presentation will focus on the reaction mechanism and energetics of the alloy formation, but it will also address practical issues and potential for large scale use.

1 Hua, K., Xu, X., Luo, Z., Fang, D., Bao, R., Yi, J. Effective Removal of Mercury Ions in Aqueous Solutions: A Review. Current Nanoscience, 16(3), 363–375 (2020).

2 Bengtsson, M. K. O., Tunsu, C. & Wickman, B. Decontamination of Mercury-Containing Aqueous Streams by Electrochemical Alloy Formation on Copper. Industrial & Engineering Chemistry Research 58, 9166-9172 (2019)

3 Tunsu, C. & Wickman, B. Effective removal of mercury from aqueous streams via electrochemical alloy formation on platinum. Nature Communications 9, 4876 (2018)