Abstract

The cement industry produces Portland Cement (PC) at a rate of 3 billion tonnes/year, contributing by over 5% to anthropogenic CO2 emissions. The production of PC is an energy intensive and environmentally polluting process and sustainability initiatives in its production have been put forward. Among these initiatives is the development of alternative low carbon cements such as reactive magnesia (MgO). MgO has been developed with a range of sustainability advantages over PC. However, a major concern is that the production of MgO is more energy intensive than PC per tonne of material produced. One way of overcoming this is to explore other production routes that have the potential of being more environmentally sustainable. Magnesia cement is currently produced by the calcination of magnesite and from processing seawater and brine. Potential production routes for MgO include its production from magnesium silicate minerals and from magnesium chloride (MgCl2) solutions – a main component of waste brine – which are both targeted for their CO2 sequestration potential. The first part of this research project investigates the environmental sustainability of current and potential production routes of MgO as compared to PC. The second part focuses on optimising an experimental procedure for the production of hydrated magnesium carbonates (HMCs) by examining the effect of different parameters such as reaction temperature, solution concentration and CO2 flow rate on the formed precipitates; which are then calcined to produce MgO. The environmental sustainability evaluation shows that the production of MgO from magnesite and from seawater consumes more energy than the production of PC form calcite however; the former production method has a lower carbon footprint than PC due to its CO2 sequestration potential. Moreover, the production of MgO from magnesium silicates and MgCl2 solutions also consume more energy than that of PC however depending on the selected production route several will result in carbon negative MgO production. The optimum experimental conditions for the production of MgO from magnesium chloride solutions based tested parameters, on crystal morphology of the precipitated samples, degree of reaction and CO2 content of the HMCs is reacting 0.5M MgCl2 solution at room temperature, titrated at a rate of 2.6 ml/min with a solution of ammonium hydroxide and sparged with CO2 at a flow rate of 500 ml/min. The reactivity of the MgO produced by calcining the HMCs produced using this method was comparable to that of commercially available MgO samples.