In site of a cleaner solution

Polluted and brownfield land could be made ready for house-building in a matter of minutes according to researchers at the University of Greenwich.

With up to half a million homes due to be built on new land in the south-east over the next 30 years more might be diverted to brownfield land if decontamination were made cheaper and the long-term safety of the land could be ensured.

The Accelerated Carbonation Technology (ACT) system, developed by environmental researchers Dr Colin Hills and Dr Paula Carey of the university’s Centre for Contaminated Land Remediation, treats land contaminated by heavy metals such as lead and mercury left by industrial processes.

Some conventional methods can take days or even weeks to clean soil and may leave it in poor condition. This means it must be removed to landfill sites and replaced by new material, making the process more expensive.

The university’s system involves adding a granular binder such as Portland cement to contaminated soil and pumping carbon dioxide into the mixture.

‘The carbon dioxide reaction changes the contaminated soil so that the pollutants are immobilised in the carbonated product. The cement contains calcium silicate and this is very reactive with carbon dioxide in the presence of moisture, said Hills.

The process creates calcium carbonate as well as a polymerised silicate which then absorbs heavy metals, he said. ‘The carbonate acts like a cement and glues the particles together. This improves the properties of the soil. For instance, a clay soil would be made more granular, making it easier to build on and removing the need to replace it with fresh material.’

The development team hopes the technology can reduce the number of housing developments on greenfield sites in areas such as Kent and East Sussex, under John Prescott’s Communities Plan.

‘In experiments we have exposed cleaned soil to the elements as well as plant growth,’ said Hills. ‘The amount of leachate produced was superb compared to that produced by soil treated using traditional methods.’

The project is largely funded by Lafarge UK. The researchers said the system can be used to treat any type of soil, while machinery developed with Midlands engineering firm Forkers is capable of processing 100 tonnes of material per hour.

The method also has the potential to recycle large quantities of carbon dioxide including gas created during the cement making process, making the technology emissions neutral and so more attractive.

‘Anhydrous cements such as Portland take up half their own weight in carbon dioxide,’ said Hills. ‘Though cement making involves carbon dioxide release, this will reduce the net effect. The materials used are also sustainable.’

An industrial consortium has been formed to bring ACT to the market, and its developers are looking for a commercial partner.