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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