Statistical optimization of extraction column parameters for the zinc (ll) solvent extraction by D2EHPA in a continuous mode

Abstract

The efficiency of zinc(II) extraction with di(2-ethylhexyl) phosphoric acid (D2EHPA) diluted in kerosene has been investigated in batch and continuous extraction columns, enabling a comparison between the performance of spray and packed column. The effect of pH of the aqueous phase, reaction time, and extractant volume ratio were considered as the operational variables in a lab-scale mixer-settler in batch mode. The optimum values for each variable were determined and used as the constant values in the pilot-scale continuous setup for optimization of the extraction process in the columns. A pilot-scale setup can provide more relatable results to industrial-scale production. The effect of dispersed phase flow rate, system temperature, nozzle diameter, and height of packing were investigated in continuous mode in spray and packed pilot-scale columns. To minimize the number of experiments, the response surface methodology (RSM) design of experiments (DOE) was adopted using five levels for each parameter. The effect of each variable and their binary and ternary interactions were analyzed by analysis of variance (ANOVA) with a confidence level of 95%. Maximum zinc extraction efficiency in the batch mode was 93.63%, which occurred at the pH of 2, a reaction time of 25 min, and an extractant volume ratio of 15% (V/V D2EHPA to kerosene). Maximum zinc extraction in the spray and packed columns were 76.13% and 84.06%, respectively. Despite the lower extraction efficiency in the continuous mode, a considerably lower required organic to aqueous ratio make these setups more favorable over traditional mixers.