Valorising desalination brine for green cement production: toward mitigating global CO2 emissions.

Worldwide, 141.5 million cubic meters of brine are produced by desalination plants per day which is usually rejected and discharged into the ocean without further treatment. Even though some research has been done on brine valorisation, the economic and environmental benefits are rarely understood from a global perspective. This work investigates using desalination brine and low-carbon electricity from renewables as the feedstock in a hybrid process integrating membrane concentration, Chlor-Alkali and mineralisation to produce green MgO cement and other valuable by-products. Under the best practical performance of each individual unit operation, our present-day analysis shows that mitigating CO2 by brine utilisation has higher economic competitiveness ($48 to $61.8 per metric tonne of CO2) compared to other CO2 abatement technologies that are currently available. In addition, the capacity of the proposed process, which is attached to the world's largest seawater desalination plant, can potentially mitigate 5.45 million tons of CO2 per year. Based on this analysis, it is forecast that, when extrapolated globally with required process tuning based on the regional brine variability, the cement production from the brine utilization process has a theoretical maximum capacity to fulfill up to 14-43 % of conventional cement production in 2050. To meet the 2050 net-zero emission goal, utilising rejected desalination brine with green electricity could potentially fulfil up to 47.7 % of the global carbon capture sequestration task and mitigate 33.3 % to 51.3 % of CO2 from the cement industry, which represents 2.6 % to 4 % of global CO2 emissions. This work offers a novel circular economy pathway that transforms desalination brine-a major water industry by-product-into a high-value, low-carbon construction material. The proposed process advances sustainable water management by linking brine treatment with CO₂ mitigation and cement decarbonization.