Aluminum salt precipitation for lithium extraction from real gas field produced water: The interference mechanism of coexisting components

Recovery of lithium from gas field produced water is an attractive strategy for utilizing unconventional lithium resources. However, the potential influence of complex coexisting components, including high concentrations of inorganic ions and organic compounds, on lithium precipitation behavior remain insufficiently understood. This study focused on elucidating the effects of complex coexisting components on lithium recovery by aluminum salt precipitation from real gas field produced water and evaluating an air flotation pretreatment strategy to mitigate their interference. Compared with the phosphate precipitation method, the aluminum salt precipitation method exhibits higher lithium recovery efficiency from gas field produced water containing a low lithium concentration of 50.6 mg/L. Under the optimal conditions, the highest lithium precipitation efficiency (the ratio of the amount of lithium precipitated to the total lithium content) reached 79.91%, with a lithium recovery rate (the ratio of the amount of lithium in the leach solution to the total lithium content) of 65.06% at same time. The common coexisting components in gas field produced water shared the influence on lithium precipitation with the order of Na + > organic compounds > Mg 2+ > Ca 2+ . Among them, the promoting effect of Na + was primarily associated with the salting-out effect, while the formation of NaCl crystals may provide additional contributions. Organic compounds exhibited significant inhibitory effects that may involve solution-phase complexation, surface coverage and active-site masking, and steric hindrance/aggregation interference. Using air flotation as the pretreatment could remove 55.32% of the chemical oxygen demand (COD), and 19.2% of total organic carbon (TOC), respectively, thereby improving the lithium precipitation efficiency and recovery rate to 84.38% and 70.13%, respectively. Characterization experiments confirmed that air flotation pretreatment significantly increased the relative content of the target precipitated phase of LiAl 2 (OH) 6 Cl‧nH 2 O, transforming the precipitates from a dense agglomerated structure to clearer irregular flake morphology. This study provides insights into the efficient recovery of lithium resources from real gas field produced water with complex coexisting components.