Research Article Removal of High-Concentration Sulfate from Seawater by Ettringite Precipitation Jian Hou , 1 Fahd Alghunaimi, 2 Ming Han, 2 and Norah Aljuryyed 2 1 Beijing Research Center, Aramco Asia, Beijing 100102, China 2 EXPEC Advanced Research Center, Saudi Aramco, Dhahran 31311, Saudi Arabia Correspondence should be addressed to Jian Hou; jian.hou@aramcoasia.com Received 29 April 2022; Revised 27 August 2022; Accepted 29 August 2022; Published 19 September 2022 Academic Editor: Ahmad M. Mohammad Copyright © 2022 Jian Hou et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Due to the worldwide scarcity of fresh water, seawater becomes an alternative base fluid in hydraulic fracturing for oil and gas production. However, the injection of seawater that contains high concentration of sulfate will induce the scale formation and thus reduce hydrocarbon production. One of the most effective ways to solve this problem is to remove sulfate ions from seawater before fracturing application. e objective of this study is to develop an effective and environment-friendly approach to remove sulfate ions from seawater based on coprecipitation of SO 4 2− with NaAlO 2 and CaO as ettringite (Ca 6 Al 2 (SO 4 ) 3 (OH) 12 ·26H 2 O). Residual sulfate concentration in treated seawater was determined when NaAlO 2 and CaO dosed at different molar ratios to sulfate. Results showed the efficiency of sulfate removal was more than 90% (4290 ppm to ∼400 ppm) when Al : Ca : S  2 : 6 : 1. It was found the sulfate precipitation completed in 15 mins with stirring under an alkaline condition (pH ≈ 12) and was not affected by temperature (15 ° C to 45 ° C). Increasing the Na + concentration from 0 to 25,000 ppm in waters resulted in the increment of residual sulfate concentration from 250 to ∼600 ppm, decreasing the removal efficiency. Besides, the analysis of Ca 2+ and Mg 2+ in treated seawater showed the Ca 2+ concentrations were on the similar level as that before the treatment and Mg 2+ was removed in the precipitation process, which is beneficial to the application of the treated seawater. e morphology and element analysis of the collected precipitates showed that the ettringites were in a layered shape with composition between Ca 6 Al 2 (SO 4 ) 3 (OH) 12 and Ca 4 Al 2 (SO 4 )(OH) 12 at the optimized chemical dosage; therefore, the developed ettringite precipitation method could effectively remove sulfate from seawater without toxic chemicals involved, which benefits seawater hydraulic fracturing in an economic way, and this contributes to water sustainability. 1. Introduction Hydraulic fracturing technique has been extensively used in the oil and gas industry to produce oil from reservoirs, but it is currently challenged by the limited availability of fresh water for preparing fracturing fluids [1]. Seawater is con- sidered to be an alternative water source for hydraulic fracturing. However, one of the primary challenges is the tendency of scale formation due to the incompatibility between seawater and formation water [2–4]. As the sea- water usually contains a high concentration of sulfate ions (>4,000 ppm) and the formation water contains very high concentrations of calcium, barium, and/or strontium ions, CaSO 4 , BaSO 4 , and/or SrSO 4 precipitates can be formed when these two fluids encounter in the reservoir [5]. e formed sulfate precipitates could lead to severe formation damages, overall reduction in hydrocarbon production ca- pacity, and some other adverse effects [6, 7]. erefore, the sulfate concentration in seawater should be reduced by >90% for a successful seawater hydraulic fracturing, espe- cially when normal scale mitigation strategies perform poorly in high-temperature reservoirs [8, 9]. Currently, the most effective and popular method ap- plied to remove sulfate from seawater for hydraulic frac- turing is nanofiltration [10, 11]. is technology is based on the rejection of sulfate ions when water passing through a membrane with nanometer-sized pores under high pressure (usually 2–15 bar). It has been reported to reduce sulfate Hindawi Journal of Chemistry Volume 2022, Article ID 8723962, 11 pages https://doi.org/10.1155/2022/8723962