REMOVAL OF A MIXTURE OF TOXIC METALS FROM PETROLEUM PRODUCED WATER BY DOLOMITE

Produced water (PW) is wastewater from oil and gas production characterized by high salinity and toxic metals content. These huge quantities of PW need to be managed to prevent an environmental crisis. Thus, and to reinforce the freshwater resources, PW is proposed to be integrated into industrial and agricultural uses. To this purpose, PW needs to be treated not only for salinity but also for high concentrations of toxic heavy metals, alkali earth metals, and metalloids. However, most of the conventional water treatment methods are expensive techniques for removing these toxic metals from PW. Previous studies have suggested the possibility of using dolomite filters made of compressed powdered dolomite to remove these mixture metals from petroleum PW at an economic cost. However, those studies were conducted using a single type of heavy metal. The aim of this study is to elucidate the feasibility of using dolomite filtration and guar gum to remove a mixture of toxic metals from high salinity PW. To this aim, we conducted core flooding experiments as well as reactive transport simulations. Because of the common occurrence of Sr, Ba, and Cd in PW from Oklahoma, the focus of this study is on PW containing Sr, Ba, and Cd, and on dolomite from the Arbuckle Group. We found that salinity has a negative impact on the removal of Sr and Ba, but not on Cd removal from PW. In addition, guar-gum complexes inhibit Sr, Ba, and Cd sorption reactions on dolomite. Sorption reactions of Sr, Ba and Cd on dolomite are kinetically controlled reactions that are not limited by the availability of pore surface area, but by the retention time of PW in the dolomite filter. An increase of metals removal by increasing the filter volume suggests that the complete removal of Sr, Ba, and Cd can be obtained by optimizing a relationship between the injection rate and size of the dolomite filter. Our findings have large implications toward the establishment of a new economic treatment method of PW for contaminant metals and the elucidation of the fate of toxic metals present in PW disposed into deep dolomite saline aquifers.