Mineral carbonation is one of the ways to reduce carbon dioxide gas in the atmosphere, which has attracted industrial and academic interest for its permanent storage of CO2 with no leakage of threat. This paper focuses on development of new energy-saving and economic alkali sources for seawater decalcification by mineral carbonation process, with which not only carbon dioxide could be sequestrated, but also the calcium ions in the seawater could be removed. Magnesium hydroxide was firstly tested as the alkali source in a simple Ca2+,Mg2+/Cl--H2O system, showing the ability of assisting in the decalcification according to the monitor of calcium ions concentration in solution and the analytical results of the sediments using XRD and SEM. This innovative approach permits the use of moderate temperature and pressure conditions in the process of seawater decalcification with mineral carbonation and the production of pure CaCO3 with a potential sale value. Then it is inspired that the brine pretreatment waste of soda ash plant, mainly containing Mg(OH)(2) and CaCO3, may act as the alkali source. Therefore, the seawater decalcification processes using the brine pretreatment waste of soda ash plant as alkali source by CO2 were carried out. (C) 2016 Published by Elsevier B.V.