MATERIALS 5R BY INDUSTRIAL SYMBIOSIS IN THE CEMENT INDUSTRY - UNDERSTANDING METABOLISM OF TOXIC METALS IN CO-PROCESSING

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Portland cement is traditionally manufactured by heating limestone and clay at high temperature in a kiln. On a global scale, cement production is responsible for about 7% of the CO2 emissions that we suspect of causing climate change and consumes more than 5,000,000,000 tonnes of raw materials. In recent years, there has been an increasing trend towards replacing both the fuels and minerals used in cement production with industrial wastes. This practice helps to conserve both fossil fuels and natural mineral resources. In general, wastes now fed to the cement kiln contain mainly combustible materials and the same harmless elements that are present in natural cement raw materials, so there is no undesirable effect on cement quality or the environment. However, it has been suggested that some wastes containing toxic metals could be used in cement kilns, and we need to know more about what happens to these potential pollutants during cement production and use, to decide whether such wastes can safely be added in the cement kiln. This collaboration between researchers in Environmental Engineering at University College London in the UK and Materials Scientists at the China Building Materials Academy and South China University of Technology therefore aims to conduct a scientific study of the fate and behaviour of toxic metals from untreated wastes, through the cement kiln, to hydrated cement pastes and the environment. We will use advanced techniques for chemical analysis and materials characterisation, including x-ray absorption spectroscopy with high energy x-rays from the UK's Diamond Light Source, and the Beijing Synchrotron, to see how the form of metals changes as they pass through the kiln and when water is added to the cement, and to understand how much metal-bearing waste can safely be added before undesirable effects occur. The new understanding gained in this work will support decision-making by industry and the government, about the use of waste in making cement.