Removal of Valuable Divalent Cations from Produced Water

A process is proposed to extract valuable constituents, namely strontium, calcium, and magnesium, from Permian Basin produced water. The sale of these products can be used to offset additional water treatment costs. In addition, the removal of these divalent constituents purifies the water which can potentially be reused, benefitting surrounding water-scarce communities.The proposed design includes three steps to recover strontium (with barium impurity), calcium, and magnesium. These steps are sulfation, softening, and hydrolysis, respectively. Solid reactants are added to the produced water using precipitation methods to extract strontium sulfate, calcium hydroxide, and magnesium carbonate products. Crystallizers promote precipitation of the products, decanter centrifuges separate the water from the wet solids, and dryers prepare the dry solids for shipping. Laboratory testing of the process on Permian Basin produced water samples achieved 99.9% removal of magnesium ions, indicating that nearly all were precipitated from solution. Calcium removal was similarly effective, with 98.5% of calcium ions precipitating out.