FIELD TRIALS of a new remediation process that 'carbonates' contaminated soils are nearly finished on the site of an old fireworks factory in Dartford, Kent.
The method, developed by cement manufacturer Blue Circle Industries and the Centre for Contaminated Land Remediation at the University of Greenwich, is claimed to be more effective than other Portland Cement solutions in reducing metal leaching.
The process uses 'accelerated carbon technology' to fix contamination in soils by mixing them with carbon dioxide and a special cement. The EnvirOceM cement reacts with the carbon dioxide rather than any water in the soil, chemically and physically 'locking in' pollutants.
Excavated material is placed in a crusher/shredder before being blended with the cement binder in another crusher/shredder.
The material is then put into a rotating carbonation chamber and mixed with vaporised carbon dioxide.
The reaction occurs in minutes and there is no curing time, which means treated material can be reused immediately. The process can be tailored to specific sites and is flexible enough to provide focused treatment of hot -pots.
The method also embraces the concept of sustainability, by using waste carbon dioxide from other manufacturing processes and by reducing the amount of imported backfill needed. Blue Circle says it can be more cost-effective than dig and dump. Emissions, noise and nuisance are reduced as a result of fewer lorry movements.
The firm holds the licence agreement for the process which is patented in the UK, US and Canada. A European patent has been applied for and applications will soon be submitted in Singapore, Malaysia and the Philippines.
At Dartford, BOC Gases will supply the estimated 10t needed to treat the site. Civil and geotechnical contractor P Forker Group began carrying out the work in September and is due to finish early in the new year.