Industry First Zero Liquid Discharge and Zero Mineral Discharge Process for a Produced Water

Abstract The zero liquid discharge approach, by recovering water and dissolved valuable salts, is the most attractive clean technology for valorizing brines from low salinity brines like seawater, using desalination reverse osmosis (SWD-RO) plants. In the case of current technology, a key aspect is calcium removal/recovery to avoid scaling problems in the successive advanced separation units for recovering other valuable salts. Most of the current technology relies on discarding salt and recovering some salts based on the available technology. Here, we are proposing a systematic process by which all the salts of sodium, calcium, magnesium, strontium, and lithium can be recovered in their highest purity (>99%) from the produced water brines from the oil wells with very high salinity (TDS > 250,000 ppm). The hard brine (>250,000 ppm total dissolved solids) considered here from an oil producer well, the concentration of divalent ions such as Ca2+, and Mg2+ is very high. The brine considered in this study is supersaturated in divalent ions such as calcium and magnesium, with 5.0%-7.5% and 0.3%-0.47%, respectively. Brine also has a sodium concentration of 1.2%, a strontium concentration of 0.5%-0.75%, and a lithium concentration of around 26-162 ppm. We are proposing a process that combines a chemical reaction pathway to recover Ca2+, Mg2+ in carbonate form, Sr2+ in sulfate form, and Na+ using vacuum-driven evaporative crystallization and Li+ using a direct lithium extraction process. In this study, we established a laboratory-based chemical reaction pathway to recover > 99% purity salts in the sequence of CaCO3, SrSO4, and MgCO3, using various reactants and optimizing operating conditions by controlling pH and temperature to yield the highest purity salts. We performed a systematic analytical characterization of the recovered solids and filtrate and fine-tuned a process to maintain the quality of the salts we recovered from this process. After these sequential reactions, the mother liquor is then processed in a vacuum-driven crystallization apparatus by evaporating 75-80% of the brine to recover NaCl in the highest purity form > 99%. The concentrated mother liquor after the evaporation step has a Li+ concentration of higher than >150 ppm that can be a feed to the direct lithium extraction process. A hybrid method of zero liquid discharge and zero mineral discharge is proposed based on laboratory evaluation and pilot plant study. It has been observed that high-purity salts of calcium, magnesium, strontium, sodium, and lithium can be recovered from the produced water brine using a sequential chemical reaction pathway followed by vacuum-driven crystallization and direct lithium extraction process.