The acidic waste from galvanising has traditionally gone to landfill, but a research team in New Zealand has identified a solution close to commercialisation.
The history of galvanising began about 300 years ago, when an alchemist immersed clean iron into molten zinc and discovered a shimmering silver coating had developed in the iron.
What initially started out as testing and cleaning in parts of the globe, over time evolved into a construction industry standard process – applying zinc to steel and iron to prevent rust.
By 1742, a chemist named Melouin presented the French Royal Academy with a research paper detailing how a zinc coating could be obtained on iron by dipping it in molten zinc, according to the Galvanizers Association.
The discovery drew significant interest and by 1836 in Sorel, France, the term “galvanising” was coined after it was patented.
While historical accounts remain sketchy, the more-than-100-year lifespan of zinc-coated products means that many of these materials will now be reaching their end of life.
The galvanising industry produces very acidic waste containing iron and zinc due to the cleaning of steel prior to zinc coating. According to Blue Environment’s Hazardous Waste in Australia report, Victoria produced the largest quantities of acid wastes in 2014-15 at 59 per cent, followed by Queensland with 35 per cent. The report shows one of the main sources of this waste are galvanisers. Australians generated 51,002 tonnes of acids in 2014-15.
But researchers from the University of Canterbury in New Zealand have found a solution to protect the environment from the subsequent toxic acid waste.
Associate Professor of Engineering Dr Aaron Marshall and Chemical and Process Engineering Master’s student Jonathan Ring developed an almost zero-waste solution to treat the acid. Currently the galvanising process consists of neutralising the acid with carbonates (limestone) or alkaline chemicals, before being shipped off to landfill as sludge.
The inventive process, which recently won funding in the university’s annual Innovation Jumpstart contest, enables 100 kilograms of zinc and 150 kilograms of iron per tonne of waste acid to be removed and recycled, instead of landfilled. Due to intellectual property, the researchers are not able to reveal the exact process of how it works.
Aaron says that sending zinc to landfills is highly problematic.
“The problem with sending zinc to a landfill is that zinc is considered a toxic metal, which means steps need to be taken to prevent it leaching out,” he says.
“The other problem is that we’re going to run out of zinc eventually. At the current zinc usage rate, there’s only about 100 more years left of zinc, so if we keep throwing all the waste zinc away, it’s going to lead to some major environmental problems.
“Currently many places need to regalvanise steel. Before they do this, they dissolve off the old galvanising coating with the acid. This basically means they end up sending a lot of zinc to landfill.
“As the world’s zinc resources are depleting quite rapidly, using our process to recover this zinc from the waste will mean that the zinc resources will last a longer time.”
The research separated the zinc and iron from the acid and tested the leftover solution’s ability to be discharged safely within the environment.
Additional testing was conducted to further treat the salty leftover solution. Aaron says the ultimate goal is to produce a solution which will leave no waste within the galvanising process.
The new process will be used in the early stages of galvanising, with the outcome still delivering protective zinc coating to steel and iron.
Although the technology has several stages, companies can still benefit by stopping at stage one.
“Stage one of our process makes enough change to their system that’s economic or has environmental benefits, and as we add each stage, the overall process becomes cleaner and cleaner, but more technically challenging,” Aaron says.
Once fully commercialised, the solution will be able to annually recover up to $350,000 worth of discarded zinc from New Zealand’s galvanising industry and could lower disposal costs.
However it’s still early days for commercialisation and more research is needed before production can commence.
Key issues the technology is facing include selecting the right process equipment and testing the process at a galvanising plant to ensure that the equipment is fit for purpose.
Aaron says that the barriers to entry are breaking into an old and established industry, but fortunately as the disposal costs are high in many countries, companies have a real driver for implementing new waste processing technology.
As most galvanising factories have limited budgets to try new technology, the research team have taken this into consideration and avoided expensive and complex technology to ensure it is commercially viable.
“We’ve costed it and we think it’ll be beneficial, and the payback will be sufficient for the galvanising process,” he says.
For next steps, Aaron says that securing more funds will be vital.
Looking towards the future, a pilot plant is expected to be at a New Zealand galvanising factory by this year, but no deadline has been set yet.