Acceleration of CO2 mineralisation of alkaline brines with nickel nanoparticles catalysts in continuous tubular reactor

CO2 mineralisation is an effective process to sequester this greenhouse gas into solid carbonates permanently. A source of alkaline earth metals for CO2 mineralisation that has significant sequestration capacity based on worldwide availability, but seldom studied, are desalination brines. In this work, we investigate the brine carbonation process with a continuous plug-flow tubular reactor. This reaction system is particularly suitable for industrial applications as it can be easily scaled-up, and enables better process control, optimization and integration. Catalytically active nickel nanoparticles (NiNPs) are applied to improve the mineralisation process, by accelerating the rate-limiting step of carbonic acid formation. To counter CO2 acidification effect, the brine was contacted with blast furnace (BF) slags to transfer alkalinity, with sodium hydroxide being used as an additional alkali to achieve the required pH. The effects of reaction temperature, composition of alkaline brine solution and residence time in the tubular reactor, on the calcium conversion efficiency (CCE) and the mineral composition of the precipitates were investigated. The extent of brine carbonation, and hence carbonate precipitation in the outlet solution was measured by ICP-OES, and by imaging of the void fraction in the outlet stream. The mineralogy and morphology of precipitates were analysed by XRD, FTIR and SEM. It was found that CCE is increased by about 10% at 50 degrees C with 30-ppm NiNPs addition, which also favoured the formation of calcite polymorph. Under other process conditions, such as in the presence of other salts (Mg2+, Na+), aragonite and vaterite polymorphs were also obtained.