Metal Foam Electrodes for the Removal of Mercury from Industrial Waters

Abstract

Mercury (Hg) is a dangerous pollutant that poses a large threat to the environment because of its high toxicity and tendencies to bioaccumulate. To decrease the release of Hg from industrial wastewater streams, several technologies can be used. One such technology is electrochemical alloy formation on platinum (Pt), where the Hg binds with the Pt forming a PtHg4 alloy. This thesis investigates different platinum covered stainless steel metal foam electrodes in a batch reactor. The Hg concentrations used are on the same order as those of a condensate stream from a typical municipal solid waste incineration plant. Hydrogen absorption and double layer capacitance measurements are used to obtain the electrochemical surface area (ESCA). The effects of the ESCA and geometrical surface area (GSA) on reaction speed are investigated, using a MATLAB model for the reaction. From this, it can be seen that the concentration of Hg is decreased to well below target values after a couple of hours. The effective surface area of each electrode is approximated to a value between the obtained GSA and ECSA. The effective surface area is bigger than the GSA because of the roughness of the surface, and smaller than the ECSA because not all the ECSA is accessible for the Hg ions. By comparing the Pt metal foam electrodes to a metal foam electrode without Pt, a similar decrease in concentration can be seen. This lifts a possibility that for the concentrations of Hg used in this thesis, only the effects of the first step of the PtHg4 alloy formation can be seen.