ACT now

Field trials of a process that 'carbonates' contaminated soil - Accelerated Carbonation Technology, or ACT - got underway this month on the site of an old Astra fireworks factory in Dartford, Kent. A new business within Cement company Blue Circle, Blue Circle Land Remediation Systems, is working with the Centre of Contaminated Land Remediation at the University of Greenwich in developing the process.

Active until 1989, the site suffers copper and zinc contamination at around 96,000ppm and 80,000ppm respectively, with ‘hot spots’ as high as 260,000ppm and 200,000 (explosions on the site, according to local papers, literally shook the town).

Locked up

ACT is the term for the reaction of special cements with gaseous CO2. Once the contaminated soil has been sufficiently broken up, it is blended with a cement binder and then fed into an enclosed rotating carbonation chamber. Gaseous CO2 is then pumped into the chamber for anything up to 20 minutes, depending on the consistency and make-up of the soil. The cement, rather being hydrated – the normal result from mixing cement with water – is carbonated, encapsulating the contaminants and so drastically reducing any leaching of metals. CO2 is permanently locked up, amounting to 20-40% of cement by weight.

Leaching tests are available to NRA, DIN or the more aggressive US TCLP standard (notably, 30% of USEPA “Superfund” sites have been treated with stabilisation/solidification techniques). Blue Circle has exclusive license agreements for the process, which is already patented in the UK, USA and Canada; a European patent has been applied for. Whereas the field trial and subsequent performance monitoring is expected to end early next year, the technique is expected to be commercially available by Christmas.

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