Remediation recycles CO2

Polluted land and brownfield sites may be brought back to life more quickly following a new discovery by researchers from the School of Earth & Environmental Sciences at the University of Greenwich. Doctors Colin Hills and Cecilia MacLeod have developed a process to treat contaminated land and hazardous waste in minutes rather than the days and weeks required by some conventional methods.

First, a granular binder containing products which react with carbon is added to the contaminated soil, following which CO2 is pumped into the mixture. The three components rapidly combine to produce a cement that is very stable, and although a marginally more expensive process, the land can then be used for development more quickly, thereby reducing overall costs and the need to build on greenfield sites.

Dr Hills, a senior research fellow at the Medway University Campus, told IEM: 'People have been looking at carbonisation, based around hydrolic cements, as a means of solidification and stabilisation for 20 or 30 years. The difference is that the new binder systems consume larger amounts of CO2. As such, as a by-product of the process, there exists the potential to recycle large quantities of the gas rather than release it to atmosphere.'

Recent work
'I think it is important to stress that our more recent work has shown that we can make our binder system largely out of waste materials, i.e. with more environmentally sound materials than in our first experiments, as well as having the potential to bind larger quantities of CO2. For example, one of the binders can consume more than 50% of its dry starting weight in CO2. The CO2 is precipitated as a solid carbonate which encapsulates waste materials.

In addition, the pH environment is enhanced and insoluble pollutant-carbonate salts are formed. Thermodynamic modelling studies (which are underway) demonstrate the 'lower' energy state of a range of pollutant carbonate salts in support of this approach.

'Treated soils can be compacted using soil engineering techniques and be ready for development in minutes rather than days or weeks. Therefore, there exists the prospect of using waste materials in the binder together with large quantities of CO2 to treat contaminated land and hazardous wastes. This is the closed loop.'

The technology, which can be used on its own or to complement existing ground treatment techniques, is currently at development stage with a pilot project planned to treat 100m3 of soil at a site owned by one of the companies behind the industrial consortium bringing the technology to market. Commercial availability is expected within the next year.

The University of Greenwich is actively seeking industrial co-operation/support in order to commercialise its inventions. It has patented the process and has a wider research programme in operation. A recent further patent protects several other products and processes utilising carbonation technology.



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