Approaching zero discharge: in plant evaluation of zinc thermal diffusion coating technology, phase I

There are different zinc coating technologies for corrosion protection of metal surfaces. The most widespread methods are hot dip galvanizing (zincing by dipping items into melted zinc) and electrolytic method by zinc deposition from the electrolytic solution (electroplating). The process of thermo-diffusion of a zinc coating is a newer process that forms a zinc alloy with the substrate. The US EPA conducted a detailed inspection of a manufacturing facility using the zinc thermal diffusion manufacturing process and evaluated the potential for emissions. The internal air at the plant was also monitored. The sampled air within the plant was well within the limitations set forth by OSHA Method ID-121 for zinc and zinc compounds. There are no water emissions from the plant and no drains in the plant. All sludge which contains the used zinc powder (waste) from the rinse and passivation tanks is recycled. There were minimal emissions from the pretreatment and degreasing operations which are seldom used because the process is friendly to ‘‘dirty parts,’’ i.e., parts with light oils and light rust and therefore pretreatment is not necessary for most of the parts entering the plant. It appears that the process does approach zero discharge. The corrosion resistance of the technology will be evaluated by EPA in a phase II study.