RECOVERY OF THE CRITICAL MINERAL BARITE AND OTHER ENERGY-CRITICAL ELEMENTS THROUGH CO-PRECIPITATION FROM HIGH SALINITY WASTEWATERS

Produced waters from oil and gas operations, geothermal waters, and seawater are saline waters that hold potential critical mineral resources. Precipitation is one key process that can recover critical elements from such saline, aqueous sources. In this work, we examine the precipitation of barite, a critical mineral used in hydrocarbon production, and how this precipitation process may also recover other energy-critical elements through co-precipitation. We will explore the effect of salinity, ion competition, and saturation index of barite on the recovery of trace elements and of barite. To examine the co-precipitation of multiple competing critical elements As and Cr in solution, co-precipitation experiments were conducted using BaCl₂, Na₂HAsO₄, and Na₂CrO₄. Na₂SO₄ was added to induce precipitation. Experiments were conducted at BaSO₄ saturation indices of 2.19, 2.89, and 3.49. The saturation indices of BaCrO₄ were -1.6 and 1.89, while the saturation index of BaHAsO₄ was -0.8. We also conducted experiments with 1.0 M NaCl and without NaCl. Inductively coupled plasma atomic absorption spectroscopy (ICP-AES) was used to analyze solutions for Ba, As, and Cr. X-ray diffraction (XRD) was used to analyze the precipitated minerals. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS) and handheld X-ray fluorescence spectroscopy (XRF) were used for chemical analyses of individual particles and for the bulk solid phase.

For the recovery of barite, higher salinities increased barite recovery. At high salinity, we also observed increased barite mineralization with increasing barite saturation index. For trace elements, as saturation index of BaSO₄ increased, more Cr and As were removed from the solution into the solid phase. When more Cr was removed, more As was also removed from solution. Our results also indicate that the element that is less soluble with the host mineral outcompetes the more soluble phase. For example, with BaSO₄ as our host mineral, because K_sp(BaCrO₄) < K_sp(BaHAsO₄), more Cr was recovered than As into the mineral phase. X-ray diffraction indicated that mostly barite and sometimes hashemite (BaCrO₄) formed. Chemical analyses of precipitates indicated variable quantities of Cr and As with Ba in the mineral phase.