Amino‐acid extraction using D2EHPA: New description of equilibrium behavior

Aggregation vs. breakup of the organic phase complex

“…We now propose that complex MR 2 HR ð Þ 2qÀm P (denoted as C P ) formed on the interface further reacts (aggregates) with itself in the bulk of the organic phase to form larger complex MR 2 2q À m À 1 ð Þ HR ð Þ 2 P (denoted as D P ) and releases some carrier, which can extract additional metal ions through interfacial reaction, thereby allowing for more efficient utilization of carrier. This reaction mechanism is similar to the mechanism proposed earlier by us (Tulasi and Kumar, 1999) to explain the equilibrium extraction behaviour of amino acids using D2EHPA. Thus,…”

“…Following the procedure of Tulasi and Kumar (1999), the value of K b can be obtained by plotting ], which cannot be measured directly, were obtained by Tulasi and Kumar using mass balance equations in conjunction with the detailed experimental data on initial and equilibrium concentrations of solute, initial concentration of extractant, and equilibrium concentration of hydrogen ions. Unfortunately, such detailed data for extraction of metal ions at high loading ratio are not available in the literature; the literature reported data are mostly in the form of C predicted vs. C experimental (Mansur et al, 2002), or K a vs. L plots (Huang and Juang, 1986).…”

“…A least square fit runs into difficulty because K a approaches infinity for a finite value of L (equal to 1 / q) for each case. Availability of detailed experimental data for the experiments reported in the literature would have been useful in determining the K b independently, as was the case with the D2EHPA mediated extraction of amino acids (Tulasi and Kumar, 1999). A method for calculating equilibrium extraction for the present mechanism for given values of K i , K b , q, m[B ] i , initial concentration of metal in aqueous phase, and pH at equilibrium is provided in Appendix.…”

Intensified solvent extraction of L-tryptophan in small channels using D2EHPA

“…Only the cationic form of the amino acids, depending on the pH of the aqueous solution, can be extracted using D2EHPA. Since previous equilibrium studies have been conducted for pH < 3.0 [24,25,55], the pH value in the current work is set to 1 with nitric acid. The dissociation constants for the above equations are given below:…”