Calcium Removal From Produced Water Brine Via Soda Ash Softening

Produced water (PW) from oil and gas operations poses a major disposal challenge in the Permian Basin due to high volumes and limited infrastructure. However, PW contains valuable elements, including calcium, which presents an opportunity for resource recovery. This study focuses on extracting calcium from PW brine by precipitating calcium carbonate (CaCO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>), a compound with strong regional demand in construction, oil production, and emerging direct air capture technologies. After evaluating several treatment pathways, soda ash softening – adding sodium carbonate (Na<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>CO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>) to induce CaCO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> precipitation – was selected based on solubility modeling and bench-scale testing. PHREEQC modeling guided experimental design, identifying optimal carbonate-to-calcium molar ratios. Jar tests were conducted on real PW samples across a range of Na<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>CO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> dosages, with resulting CaCO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> purities ranging from 80% to 88% as measured by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). These purities meet market requirements for cement and drilling applications and suggest potential for further refinement in high-purity markets. The process is compatible with standard industrial equipment and integrates well with existing oilfield operations. Overall, soda ash softening demonstrates strong potential as a technically feasible and scalable method for reducing PW disposal volumes while recovering a useful product.