M. Tanaka et al., ROLE OF THE EXTRACTION EQUILIBRIUM-CONSTANT IN THE COUNTERCURRENT MULTISTAGE SOLVENT EXTRACTION-STRIPPING PROCESS FOR METAL-IONS, Industrial & engineering chemistry research, 37(5), 1998, pp. 1943-1949
Computer simulation of a steady-state countercurrent multistage metal
solvent extraction-stripping process (ESP) using cation-exchange reage
nts shows that there is a value of extraction equilibrium constant, K,
yielding the maximum metal recovery when the other operational parame
ters are constant. Qualitatively, this is because the larger K makes s
tripping more difficult. Steady-state local linearization reveals the
symbolic relation behind the numerical results. The coefficient of d(l
n K) in the differential equilibrium relation extended to the counterc
urrent multistage process is the weighted average of the partial deriv
ative, in each stage, of the equilibrium organic-metal molarity with r
espect to In K under constant equilibrium aqueous-metal molarity, wher
e the weight is related to the partial derivative of the equilibrium o
rganic-metal molarity with respect to the equilibrium aqueous-metal mo
larity under constant K. The balance of these coefficient values for t
he extraction and stripping sections of ESP determines the trend of th
e recovery with varying K: at the maximum recovery, these values are e
qual to each other. The stagewise plot of the partial derivative of th
e equilibrium organic-metal molarity with respect to In K under consta
nt equilibrium aqueous-metal molarity versus organic-metal loading rat
io clarifies the relation between the trend of the recovery with varyi
ng K and the organic-metal loading.