Fig. 2. The reactive extraction of HGA with Ph3PO and the
formation Ph3PO-HGA complex.
Column design
Solvent to feed ratio (S/F) and the number of theoretical units (NTU)
are important parameters to design a liquid-liquid counter-current
extraction column. Basically, the S/F and NTU are calculated to reveal
the applicability of column design [37].
\({(S/F)}_{\min}\)=\(\frac{X_{\text{\ in}}-\ X_{\text{out}}\ }{{K_{D}\text{\ X}}_{\text{\ in}}-\ Y_{\text{in}}}\)(7)
EX = KD \(\frac{S}{F}\) (8)
NTU =\(\frac{ln[\ \left(\frac{X_{\text{in}}-Y_{\text{in}}/(K_{D}}{X_{\text{out}}-Y_{\text{in}}/(K_{D}}\right)(1-\ 1/E_{X})+\ \frac{1}{E_{X}}\ ]}{{\ln E}_{X}}\)(9)
where xin and xout are the HGA
concentration in the feed and raffinate phases, Yin is
HGA concentration in the extract phase. As a known rule,
(S/F)act is calculated by multiplying
(S/F)min by 1.5. The NTU are calculated from the Eq. (9)
above by using a Modifier Kremser equation [30, 37]. Here,
Ex is the separation factor. In this study, the column
design parameters, (S/F)act and NTU, were calculated
based on the maximum Ph3PO concentrations used in the
solvents, the results of which are given in Table 4. As seen, around 2
to 4 NTU are needed to meet the targeted extraction efficiencies.