NRW hails mine water treatment breakthrough
Natural Resources Wales (NRW) has announced that it has achieved impressive results in two innovative trials which use electrochemical treatment to clean up polluted mine water.
Wales’s industrial past means that its environment feels the effect of long-abandoned metal mines, which once produced lead, zinc and copper; these mines are now the source of severe pollution whose toxic discharges can have a severe impact on the water quality of the surrounding area.
NRW is the body responsible for tackling metal mine pollution and it has been trialling cutting-edge technology in two trials at Cwm Rheidol and Frongoch, both locations where watercourses are heavily affected by mine run-off.
At Cwm Rheidol, the organisation has been trialling a sono-electrochemical technique provided by Swansea firm KP2M Limited, trading as Power & Water.
Now a popular tourist area, Cwm Rheidol was once home to mines producing lead and zinc, with production ending in the early 20th century. Two mine entrances still discharge highly acidic, orange water which contains high levels of zinc, lead and cadmium. Over the course of a year eight tonnes of metals are discharged into the Afon Rhiedol that impacts the river for 18km.
“The mine is situated in a narrow, steep sided valley which is unsuitable for traditional treatment processes which require a considerable area of land,” explains Peter Stanley, water and contaminated land technical specialist for NRW. “So, KP2M Limited trading as Power & Water, a Swansea company providing research led solutions to the water industry successfully tendered to run a trial using an innovative sono-electrochemical technique.
“Preliminary laboratory results were encouraging, and the small footprint of the equipment makes it particularly suitable to rugged upland locations where traditional passive pond systems simply will not fit.”
Further independent laboratory results followed which confirmed the treatment’s success with raw samples showing metal removal of 87% while filtered samples confirmed 99.5% removal of metals.
A full-scale system like the pilot trial, benefitting from added filtration to reduce fine particulate matter will be expected to achieve 98% or more reduction of metal loading.
Meanwhile, to the south east of Aberystwyth at Frongoch - another former lead and zinc mine which operated between the mid-18th century and 1905 – NRW have been trialling another electrochemical treatment approach.
Frongoch is the larger of the two sites and has already been the subject of extensive remedial work including intercepting and diverting streams, capping and landscaping much of the site to limit water seepage and reduce the volume of polluted water entering rivers downstream.
The work has dramatically reduced metals pollution, but concentrations in the run-off from the site are still high.
To combat this, trials are now underway with Elentec, a company located at Menai Bridge, who provide research-based water treatment solutions using an innovative approach involving an energy efficient portable containerised electrochemistry unit. The unit is ideal for upland terrain or adaptable for fly in fly out mine contracts abroad.
Peter Stanley continues: “Two highly polluted sources which contribute 3.8 tonnes per year of zinc, lead and cadmium to Frongoch stream are collected and fed through the electrode chambers.
“The polluting metals are then separated from the water through precipitation in a purpose built clarifying tank, allowing the treated water to be discharged.
“Again, preliminary results are encouraging enabling optimisation of the treatment process.”
NRW is also working with the Life Demine project at Swansea University to assess the use of renewable energy in the recovery of metals from precipitates.
“The success of the Cwm Rheidol and Frongoch trials have the potential to offer NRW and others interested in metal mine water remediation and the clean-up of metal mine process waters, new tools for successfully treating harmful discharges,” Stanley concludes. “And it’s not just the environment which will benefit from this technology, the Welsh economy could also receive a boost as the companies involved in this work share the technology with overseas markets.”
Overall, Wales is home to nine of the 10 worst metal mine polluted catchments in the UK and has more than 1300 abandoned metal mines, which impact on over 67 water bodies containing more than 600km of river.
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