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The Coal Authority’s latest collaboration wins awards

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World Coal,

The Coal Authority’s latest innovative collaboration has been recognised with two awards.

The work to treat soil heavily contaminated with arsenic at the Mersey Gateway toll bridge site in Cheshire, won Best Re-use of Materials and Best Infrastructure Project at Environment Analyst’s Brown-field Awards 2020.

As well as bringing sustainability benefits, by cutting carbon emissions and preventing landfill, it is estimated that safely reusing the hazardous material saved approximately £2 million.

It is now hoped the process could be repeated at other sites where disposal or off-site treatment is not practical or economically viable.

As part of its work to make a better future for people and the environment in mining areas, The Coal Authority operate 82 treatment schemes in the UK, cleaning 122 billion l/yr of mine water to prevent iron solids entering watercourses, aquifers and the sea.

This process removes thousands of tonnes of hydrous ferric oxide (HFO), also known as ochre, which has a high sorption capacity – a process by which one substance becomes attached to another – for metals and phosphate.

After laboratory and field trials demonstrated the suitability of ochre for remediation, an optimised mix was designed to meet the exacting standards of the project and gained approval from regulators.

More than 5000 t of dried ochre were collected from 4 Coal Authority mine water treatment sites across England, Wales and Scotland and delivered to the Mersey Gateway project.

Using magnesium oxide as a cementitious binder, 9000 m3 of contaminated soil were then stabilised on site and reused under an environmental permit.

Jon Aumonier, of the Coal Authority’s Innovation Team, said: “This optimised mix design has never been applied to the treatment of contaminated soils before and is unique to this project, which was one of the largest brownfield infrastructure projects completed in Europe in recent years.”

The work was carried out for Merseylink, the consortium behind the Mersey Gateway, with partners including CE Geochem, RSK Group, AECOM and RemedX UK.

As well as being ideal for immobilising contaminants – such as arsenic, lead and cadmium – on former industrial sites, ochre also acts as a replacement for ferric sulfate in waste water treatment and can even be used as an iron oxide pigment to create fine art paints.

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