A new dolomite filtration method to remove heavy metals from produced water

Abstract:

The conventional and unconventional oil and gas industry produces huge quantities of water characterized by containing high concentrations of total dissolved solids (TDS) (mostly NaCl) and inorganic contaminants including heavy metals. Given the scarcity of freshwater resources, the idea has aroused of integrating produced water into industrial and agricultural uses. However, for produced water to be successfully integrated into industrial and agricultural uses, produced water needs to be treated not only for salinity (NaCl) but also for high concentrations of heavy metals. Currently, the use of conventional water treatment methods (e.g., membrane filtration) are not economically feasible methods to remove the high concentrations of heavy metals from produced water. Thus, we are researching the feasibility of using dolomite filtration as an economically feasible method to remove heavy metals from produced water. Sandstone filtration has been extensively used by oil and gas industry to remove a wide range of total dissolved solids from produced water, including heavy metals. However, our preliminary experimental results indicate that dolomite is more efficient than sandstone for removing heavy metals such as barium (Ba), strontium (Sr), and cadmium (Cd) from petroleum produced water. We found that dolomite from the Arbuckle Group has a distinctly high sorption capacity for heavy metals depending on the grain size. The smaller the grain size, the larger the surface area it covers which increases filtering efficiency. In our experiments, a dolomite filter (1.5 inch diameter and 6 inch length) made of compressed powdered dolomite (0.3-0.6 mm grain size) could remove 50% of Cd, 7% of Ba , and 5% of Sr from 1 L of synthetic produced water (76,856 mg-TDS/L) containing 94.67 mg-Cd/L, 97 mg-Ba/L, and 99 g-Sr/L. Injected rate of the synthetic produced water into the dolomite filter placed in a core-holder was of 0.1 ml/min. Injection flow rate was found to play an important role, filtration efficiency increases with decreasing the injection flow rate. Moreover, we found that the addition of polymers (guar gum) aids the filtration efficiency of the dolomite filters.