Cwm Rheidol Mine closed before World War I
A filter made from compost, woodchip and whelk shells is to be used to stop polluted water from an old zinc works from entering a mid Wales river.
Water from Cwm Rheidol Mine near Aberystwyth is currently flowing into the nearby River Rheidol.
But scientists at Newcastle University have developed a filter, which will form part of a pilot project.
Some of the most polluted metal mine sites in Wales are in Ceredigion, according to the Environment Agency.
But the agency said if the university's new filter system worked it could solve pollution problems not just in Ceredigion, but at mines around the world.
A pilot treatment plant is to be built near Cwm Rheidol Mine to see if it works.
A pipeline has been built to carry the water to a new treatment works
There has been mining in Cwm Rheidol since the Bronze Age, but it eventually came to an end just before World War I.
A filter system was developed in latter years, but the Environment Agency said it did not work and polluted water from Cwm Rheidol Mine was still ending up in the River Rheidol.
Paul Edwards of Environment Agency Wales said: "The water purification project started in 2006 when we had funding from the Welsh Assembly Government.
"Newcastle University has been working on a way of purifying the water and has come up with a mixture of compost, woodchips, digested sludge and whelk shells, which reduce acidity in the water.
"In the meantime, we have been working on ways of stopping water getting into the mine.
"We plan to put the university's mixture in a tank and pass the water from the mine through it to see if it works.
"If it does it could have implications for disused mines throughout the world.
"We plan to build a pilot treatment plant during this financial year."
The River Rheidol has a relatively high concentration of zinc, which puts it in danger of not reaching a "good ecological status" target by 2015.
But Mr Edwards said concentration levels of zinc in the Rheidol were not dangerous and fish and other wildlife seemed unaffected.
About £230,000 has been spent on the project in Ceredigion so far, with funding coming from the Welsh Assembly Government and the European Union's Objective 1 scheme.