Investigation into the rejuvenation of spent electroless nickel baths by electrodialysis.

Electroless nickel plating generates substantially more waste than other metal-finishing processes due to the inherent limited bath life and the need for regular bath disposal. Electrodialysis can be used to regenerate electroless nickel baths, but poor membrane permselectivity, leading to high losses of valuable bath components, continues to be a weakness of the technology. This research has investigated improving electrodialysis permselectivity for removing contaminants (sodium, orthophosphite, and sulfate) in a spent electroless nickel bath while minimizing the losses of valuable bath ions (nickel, hypophosphite, and organic acids). Ion permselectivity was explored with respect to electrodialysis operating conditions, membrane type, and cell configuration. Excellent permselectivity for sodium over nickel was attained irrespective of operating condition, membrane, or cell configuration. Studies on the effects of four different operating conditions (current density, pH, flow rate, and temperature) on anion permselectivity revealed bath pH and current density to be critical operating parameters. The type of anion exchange membrane used had a crucial effect on selectivity; one membrane (Ionac MA-3475) was identified as having superior selectivity for bath contaminants particularly for sulfate. The improvements in electrodialysis permselectivity established by this research will decrease waste generation within the electroless nickel process and increase resource productivity by minimizing the loss of valuable plating chemicals.

An electrochemical system for removing and recovering elemental mercury from a gas stream.

The impending EPA regulations on the control of mercury emissions from the flue stacks of coal-burning electric utilities has resulted in the development of numerous advanced mercury control technologies such as sorbent injection and in-situ mercury oxidation. Although these technologies can effectively remove mercury from a flue stack they share, along with many other technologies, the common shortcoming of intermedia pollution transfer i.e. the traffic of mercury from the air phase to the solid phase and the subsequent generation of residue for landfill. This work addresses the need for an integrated system of mercury removal and recovery from flue stack gases and from the environment. The research explored the capture of elemental mercury from the gas phase at ambient temperature on an electrically conductive porous sorbent. The mercury loaded sorbent was regenerated at the anode in an electrochemical cell and the oxidized mercury recovered at the cathode as solid elemental mercury. Activated carbon cloth was selected as the most suitable sorbent as it had the highest mercury adsorption capacity of the sorbents tested and was electrically conductive. Direct and indirect electro-oxidation were shown to remove 95% and 100%, respectively, of the elemental mercury from the carbon cloth. After regeneration the carbon cloth was reused without any loss in mercury adsorption capacity. More than 99% of the mercury stripped from the cloth during regeneration was recovered at the cathode.