Electrochemical investigations of Pt−Hg and Cu−Hg alloys for mercury decontamination purposes
Examensarbete för kandidatexamen
Mercury is a heavy metal of large environmental concern due to its potential to spread and bioaccumulate and to its high toxicity for all living organisms. To date, there is no method capable of efficient and sustainable removal of mercury from aqueous solutions under a wide range of conditions. The focus of this thesis is to investigate several aspects of mercury removal by electrochemical alloy formation between mercury and platinum or copper. Mercury ions in the solution are reduced by the application of an electric potential, and form an alloy with a solid platinum or copper electrode. Using an electrochemical quartz crystal microbalance, the temperature dependence of the alloy formation between mercury and platinum is studied in the range 20−60 C, and the apparent activation energy of the reaction is determined to be 0.29 eV. Another purpose of the thesis is to relate the structure of the electrode at various length-scales to the rate of mercury removal. The electrochemical surface area is determined by underpotential deposition of hydrogen and by measurements of the electrical double-layer capacitance, and the electrode structure is studied using a scanning electron microscope. Mercury removal rates are determined through batch experiments with subsequent inductively coupled plasma mass spectrometry analysis. It can be concluded that a surface area with feature size of the order of 1 mm, e.g. a metal foam, generates an enhanced rate of mercury removal. On the other hand, a nanoporous material with feature size of the order of 100 nm, such as platinum black, does not contribute to an increased mercury removal rate. Two case studies investigating the applicability of the technology are also performed within the thesis; removal of mercury from concentrated sulphuric acid produced by Boliden in the commercial smelting plant in Kokkola and from scrubber liquids from a combined heat and power plant. Mercury is successfully removed from the scrubber liquids using platinum coated titanium fibre electrodes, and from the sulphuric acid using platinum coated stainless steel electrodes. In the case of the sulphuric acid, it is also demonstrated that the process can be scaled up 400 times without loss of efficiency.
mercury , heavy metal , electrochemistry , alloy , decontamination , water treatment