Mercury elimination from synthetic petroleum produced water using green solvent via liquid-liquid extraction: Experimental, effective solubility behaviors and DFT investigation

This study focuses on the use of alternative vegetable oils (corn, linseed, and canola oil) as green extractants in the liquid-liquid extraction (LLE) of mercury elimination from synthetic produced water to meet Thailand’s standard discharge limits. Extraction parameters involve the type of vegetable oil used, pH of feed solution, time, and O/A ratio. Three parameters in the stripping process are optimized by applying response surface methodology (RSM). Models NRTL, UNIQUAC, and Van’t Hoff are employed in the mutual solubility of corn oil; the various strippants (NaOH, HCl, and thiourea) are investigated under different temperatures. Under optimal conditions, results demonstrate that percentages of extraction and stripping of mercury reach 99.4% and 95.4%, respectively. Corn oil proved to be the most efficient solvent for mercury extraction at pH ranges 2–8. Based on ANOVA, the stirring speed and A/O ratio had a significant influence on the stripping process. The mechanisms of extraction reaction were evaluated via density functional theory (DFT) along with Fourier-transform infrared spectroscopy (FTIR) and ultraviolet–visible spectroscopy (UV–vis). Extraction and stripping kinetics are found to be of first-order (k = 0.182 min−1) and second-order (k = 0.9244 L∙mg−1min−1), respectively. It is seen that our method has the ability to successfully remove mercury while still remaining below the standard discharge level. [Display omitted] •New alternative green solvents were firstly applied for mercury removal.•99.4% extraction and 95.4% stripping of Hg(II) were obtained using corn oil.•Hg(II) removal successfully achieved the wastewater discharge standard.•Solubility of corn oil in strippant as a function of temperature are studied.•Reaction mechanism are examined via spectroscopies and density functional theory.