Negative emissions using Mg sourced from desalination brine or natural evaporite deposits

Abstract

We establish a profitable negative emissions technology that converts desalination brine or salt deposits into saleable products while concurrently mineralizing atmospheric CO2 as Mg-carbonates. The process produces water, gypsum, salt, potash, aggregate, and hydrochloric acid with the ratios of products dependent on the brine or evaporite deposit composition. In addition to the negative emissions realized through direct removal of CO2 from the atmosphere, the co-products drive out existing production methods resulting in CO2 emissions reduction. Notably, the process uses no chemicals or fossil fuels and can be powered completely by electricity. This not only increases the net CO2 removal it also leverages the decreasing cost of renewables and batteries to increase operating profit. We outline how extant equipment and technologies can be used to implement this process. The net energy usage and CO2 removal of the process are calculated, accounting for differences with current production methods for the co-products. At large enough implementation, some products will saturate their respective markets, converting the excess product into a waste stream. As such, performance indices for the process (e.g., GJ/t-CO2, USD/t-CO2) depend on the extent of implementation. We limit our investigation to prior to such market saturation effects. Assuming the global average CO2 intensity of electricity generation, the process provides 4.1 t-CO2 of emissions reduction for every tonne of negative CO¬ emissions. Per tonne of total CO2 reduction (mitigated+removed), the process operates at an energy consumption of 2.1 GJ/t-CO2, falling to 1.1 GJ/t-CO2 if the system is powered by renewable energy. Via Monte Carlo analysis using global price distributions, we find that even without including a price on CO2 the process operates, on average, at a profit of 196 USD/t-CO2 (total reduction). Applying the process to evaporite deposits of Bischofite or Carnallite provides a profit of 47 USD/t-CO2 and 103 USD/t-CO2 (total reduction), respectively.