Ammonia-assisted carbonation of NaCl-rich produced-water brine: CO2 uptake, sodium conversion, and recoverable salt formation

Saline brines generated during oilfield-produced-water treatment are difficult to manage and remain underused as resource-recovery feedstocks. This study evaluated ammonia-assisted Solvay-type carbonation of a field-derived NaCl-rich produced-water brine using a laboratory bubble-column reactor. Controlled synthetic-solution experiments were used to examine how ammoniation and NaCl concentration affected liquid-phase total carbon (TC), while produced-water experiments quantified apparent dissolved-sodium conversion and recovered-solid characteristics. Among the tested produced-water conditions, the highest apparent Na + conversion was 47% at a nominal NH 3 concentration of 6.5 M. In synthetic solutions, ammoniation increased liquid-phase TC accumulation, whereas increasing NaCl concentration reduced the TC response, consistent with ionic-strength and salting-out effects. XRD identified NH 4 HCO 3 as the dominant crystalline phase in the recovered solid, with overlapping reflections permitting only qualitative assignment of possible minor Na-bearing bicarbonate/carbonate and residual chloride contributions. FTIR supported bicarbonate/carbonate functionality, and SEM–EDS showed a heterogeneous C-, O-, and N-rich solid with spatially variable Na and Cl. The results demonstrate the feasibility of ammonia-assisted carbonation for apparent sodium conversion in a real produced-water brine, while showing that product selectivity, ammonia partitioning and recovery, and complete Na/C/N mass balances are central to further process development.