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Alkalinity is a critical parameter for describing the composition, pH buffer capacity, and precipitation potential of petroleum produced water (PW). Besides salinity, alkalinity and metal concentrations are generally greater in PW than in freshwater (FW) and seawater. This study presents batch reaction experimental and simulation results showing that the removal of Ba, Sr, and Cd from PW by dolomite is mostly due to sorption reactions, with sorption reactions and thus removal levels being higher for Cd than for Ba and Sr. In contrast, we found that the removal of Pb and As from PW by dolomite is largely due to precipitation and coprecipitation reactions of carbonate minerals on dolomite. Analyses of changes in the morphology as well as in the elemental and mineral composition of dolomite surface, along with pH, alkalinity, and Ba, Sr, Cd, Pb, and As removal measurements using synthetic PW and FW containing high concentrations (∼100 mg/L) of single and mixture toxic metals and metalloids (Ba, Sr, Cd, Pb, and As) at different initial alkalinity and pH conditions, indicate that in addition to salinity, alkalinity and pH generated from the dissolution of dolomite controls the removal of Ba, Sr, Cd, Pb, and As from PW by dolomite. However, we found that their impact is different for each metal in PW and FW. Ba, Sr, and Cd removal by dolomite is 10, 2, and 4 times smaller in PW than in freshwater (FW), respectively. Whereas As removal is practically the same regardless of salinity. Moreover, this study reveals the need of thermodynamic data of complex carbonate minerals formed from the precipitation of Ba, Sr, Cd, Pb, and As to capture the effect of alkalinity on their removal from PW by dolomite. 

Predicting the transport of toxic metals in dolomite saline aquifers where petroleum produced water (PW) is commonly injected is important to prevent underground sources of drinking water contamination. This study presents new experimental results on the degree and impact of precipitation and sorption reactions on the transport of high concentrations of toxic metals (80-100 mg-Ba/L, 80-100 mg-Sr/L, 70-100 mg-Cd/L, 2-100 mg-Pb/L, and 80-100 mg-As/L) in dolomite injected with PW of variable alkalinity (0–200 mg/L), total dissolved solids (1700–77,000 mg/L), and pH (2–7). Changes in the elemental and mineral composition of dolomite surface were measured by BSEs SEM, SEM-EDS, and high-resolution XRD analyses. The results reveal a key role of alkalinity generated from the dissolution of dolomite. We show that a short initial stage where the removal of toxic metals is driven by the initial pH and alkalinity of PW is followed by a prolonged stage where the removal of toxic metals by sorption and precipitation reactions is driven by the alkalinity and pH that results from the kinetic dissolution of dolomite. Precipitated/coprecipitated metals were carbonate minerals reflecting the metal composition of PW. Attained removal levels of tested toxic metals from 1 L of PW using a dolomite core made of 200 g were >90% for Pb, >50% for As, >30% for Cd, and >5% for Ba and Sr. Apparently, the in-situ generation of alkalinity (carbonate ions) and sorption reactions of metals on dolomite catalyzes the precipitation of toxic metals as carbonate minerals. This catalytic effect of dolomite is different with PW and fresh water (FW) of low salinity (NaCl). Precipitation reactions are more prominent with FW than with PW, whereas sorption reactions are more prominent with PW than with FW.