(149d) Mine Tailings for CO2 Mineralization - Towards Efficient Processes and Usable Products

The long-time storage of CO2 in form of minerals can serve as one option to decrease the CO2 content in our atmosphere in the next decades. Mine tailings currently considered a useless waste, are containing ions like Calcium or Magnesium in significant amounts. Binding CO2 to these ions via a complex process of dissolution, reaction and filtration will lead to low-soluble carbonates which can be safely and efficiently stored for a long time. The considered process chain for this carbonization has to be of low cost and more importantly, of low CO2 footprint itself. As mine tailings are very different when coming from different sources the complex chain needs to be flexible to be adopted to the initial material conditions as well as to the conditions at the processing site. It is then obvious that all the possible variations of input, process and output conditions call for a multi-objective optimization strategy to find the best approach for a given situation. We have started investigations on specific mine tailings in a collaboration with an US-based research group. We apply a dissolution process with mild organic acids like citric or oxalic acid and combine this with a pH swing process in a medium pressure CO2 reaction vessel. We focus on Calcium and Magnesium carbonate formation as the mineral output. In this contribution we show precipitation results of our miniplant experiments in a 1.5L reactor under varying conditions of educt concentration and composition, pH value, CO2 pressure and temperature. Product analysis is carried out to obtain partice size distributions, crystal structure data and remnant ion concentrations. The ongoing investigations shed light on important aspects of process sensitivity towards the aformentioned goals of economic efficiency as well as energy requirements which are strongly connected to the CO2 footprint of the process itself. Under current conditions such a CO2 mineralization process is in particular not yet economically feasible but if the CO2 release into the atmosphere will be limited by govermental regulations like CO2 emission certificates and the energy supply from renewable sources increases and becomes cheaper, a point can be reached where the process will provide a viable options for the long-time CO2 storage with the desired climate saving impact.