Abstract
The recovery of gallic acid (GA) from GA processing wastewater was studied via solvent extraction. Tributyl phosphate (TBP)/4-methyl-2-pentanone (MIBK)/n-hexane, TBP/n-octanol/n-hexane and n-hexanol were used as the extractants. The effects of the component proportion in the mixed extraction solvent, stirring speed, extraction time, pH, phase ratio (extraction solvent/GA solution), temperature and salt on extraction rate were investigated. After univariate crossover experiments, the optimum conditions were obtained as a component proportion in the mixed extraction solvent of 1 : 2 : 1 at pH 1.5 with a phase ratio of 1 : 1, stirring speed of 150 rpm, extraction time of 60 s and temperature of 30 degrees C. The maximum extraction rates through the one-stage process were 88.2%, 82.5% and 76.7% for TBP/MIBK/n-hexane, TBP/n-octanol/n-hexane and n-hexanol, respectively. FT-IR spectroscopy was used to characterize the extracted organic phases. Afterwards, Box-Behnken design was used to optimize the three most influential parameters including pH, temperature and phase ratio whose values were optimized to 0.5, 30 degrees C and 1 : 1, respectively and subsequently, the extraction rate through the one-stage process using TBP/MIBK/n-hexane, TBP/n-octanol/n-hexane and n-hexanol further increased to 95.5%, 86.8% and 78.1%, respectively. TBP/MIBK/n-hexane was proved to be the most effective extractant in this study and more than 94.4% of GA was recovered through a four-stage stripping process. Finally, TBP/MIBK/n-hexane was used in actual GA processing wastewater with 92.5% of GA being extracted and more than 88.7% was recovered after the four-stage extraction and stripping process. The results can be referred to for the selection and design of processes to efficiently recover GA from GA processing wastewater.