Phil Renforth, a scientist at Cardiff University, is preparing to test the feasibility of using iron and steel slag deposits to remove carbon dioxide from the atmosphere.

During the process of steel-making, iron ore is mixed with limestone or dolomite and heated to extremely high temperatures. The end results are steel and slag, which is a waste mixture of calcium and magnesium silicates and oxides.

Earlier research by Dr Renforth has shown that carbon dioxide from the atmosphere is absorbed by material inside slag heaps. He now wants to try to improve the rate of this absorption which he believes could make significant reductions in atmospheric levels of carbon dioxide.

In the first stage of the three-year project, researchers will drill into old slag heaps to understand what chemical processes have been going on as rainwater has brought carbon dioxide into the heap.

In the second stage, they will create mini-heaps about the size of a skip and try to optimise their chemistry to sequester carbon from the atmosphere. These could then be used as models of larger devices that could reduce carbon levels in the atmosphere.

The current total global production of slag is estimated as being about 500 million tonnes a year. This rate should increase as developing nations produce more steel. By the end of the century, it is estimated that there could be as much as 200 billion tonnes of slag worldwide. The researchers believe that this has the potential to remove 50-100 billion tonnes of carbon from the atmosphere.