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

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.

Co-processing of wastes in the cement kiln is an internationally increasing trend, motivated both by the need to conserve raw materials and energy in cement production, but also by the difficulty and expense of waste management. There is frequently a contrast between ideologies regarding proposals for utilisation of wastes, where some oppose utilisation of waste in cement on principle; on the other hand, those who want to take advantage of practical benefits may be unwilling to engage with potential environmental risks. Scientifically defensible decisions about these matters require the availability of sound technical information, such as will be generated by this research. Apart from other academics conducting research in this area, the project findings will benefit:
1) the cement industry, waste generators, and niche waste-brokering businesses, by providing crucial missing information about the safety of the practice of co-processing metal-bearing wastes, which will reduce uncertainty associated with business risk, and enable rational decision-making about acceptance of metal-bearing wastes into the cement kiln;
2) regulators, who will have a sound basis for development of environmental policy and regulations in relation to the above sectors;
3) the public, who are concerned about the potential risks of human health impacts due to emissions of toxic metals from the cement kiln, or in cement-based products;
4) the environment, where eco- and agri-systems could be negatively impacted by toxic metal loadings from unsafe practice.

The project will have a dedicated website developed and maintained by the UCL CEGE Communications Officer, with a section aimed at lay people and a discussion forum. Youtube videos will be prepared for each of the main tasks. The results of this research will be disseminated by the research team through attendance at events including academic conferences, university open days and public engagement workshops, and through the university press office. 15 conference publications and 9 publications in high impact factor academic journals are planned.

The research programme includes a plan for exchange of researchers between the UK and Chinese teams for periods between 1 and 6 months, to enable the expertise of each to contribute to the design of experiments and evaluation of results, and enhance to opportunity for co-production of knowledge and novel advanced experimental techniques. The project as a whole, and particularly the researcher exchange scheme, will also provide valuable training for younger researchers, and an opportunity for them develop their own research networks.

Dissemination of project results will also be aided by the participation of advisors from industry (Environment Agency and Mineral Products Association [MPA] in the UK, and China Resources Cement R&D Co [Yuebao/Guangzhou Heidelberg Yuexiu Cement] and the Chinese Ceramic Society-Cement Branch [CCS] in China), who will keep in close contact with the project throughout and participate in meetings and Stakeholder Workshops in each country, with an emphasis on facilitating real-world applicability of the results. The CCS will hold the Chinese Stakeholder Workshop for the project, and they and the MPA can facilitate dissemination of the result to their members and global network of trade associations (e.g., CEMBUREAU).