The result obtained from the study of extraction of UO22+ from 0.01 M, 0.1 M and 1 M SO42- ion concentration respectively in the aqueous phase into 0.05 M solution of organic solvent (chloroform of 1-phenyl-3-methyl-4-trichloroacetylpyrazolone-5) showed that UO22+ was not extracted between the pH range of 0 - 2. This was attributed to the formation of unextractable sulphate-uranyl complex.

UO22+ + SO42- → (UO2)SO4 ……………………………………………….…… (1)

UO22+ + SO42- → No reaction …………………………………………………….. (2)

However, extraction of UO22+ occurred between pH 2 - 3.5. Figures 1 and 2 show the variation of Log D with pH and the percentage extraction for the extraction of UO22+ from buffered solutions containing 0.01 M SO42- ion concentration. A slope of 1 was obtained indicating that 1 proton was displaced during the reaction process while the percentage extraction obtained was 88.70 %.

The extraction process of UO22+ from aqueous media containing HTCP (or) which is the ligand can be represented by the following equations:

UO22+ (aq) + HTCP (or) ↔ UO2(HTCP)(or) + H+ (aq) …………………………………………. (3)

The metal: ligand interaction is in the 1:1 mole ratio.

The extraction constant (Kex) is given by the equation

The distribution ratio D is given by

Substituting equation 5 into equation 4, gives equation 6.

Log D = log Kex + log [HTCP] + pH ……….…………………………………………………….. (6)

Extraction of UO22+ occurred between pH 2 - 3.5. Figures 3 and 4 show the variation of Log D with pH and the percentage extraction for the extraction of UO22+ from buffered solutions containing 0.1 M SO42- ion concentration. A slope of 1 was also obtained indicating that 1 proton was displaced during the reaction process while the percentage extraction obtained was 76.84 %.

Figures 5 and 6 also gave a result similar to those of Figures 2 and 4, but a lower percentage extraction of 55.49 % for UO22+ from buffered solutions containing 1 M SO42- ion concentration.

Figures 2, 4 and 6 showed that optimal percentage extraction decreased from 88.70 % to 76.84 % to 55.49 % as the SO42- ion concentration in the buffered phase increased from 0.01 M to 0.1 M and 1 M respectively. The results thus indicated that the extraction of UO22+ is more favorable between pH 2 and 3.5, although maximum extraction of UO22+ ion decreased with increase in SO42- ion concentration in the buffered phase. Similar results have been reported by Okafor and Uzoukwu (1990) in their extraction study on the extraction of Fe(II) with chloroform of 1-Phenyl-3-methyl-4-trichloroacetylpyrazolone-5 from aqueous solutions of different acids and complexing agents. Furthermore, the result showed that a slope of 1 was obtained for all the three SO42- ion concentrations, indicating that the interaction between UO22+ and the ligand (HTCP) resulted in the release of one mole of H+. The result further indicates that distribution (D) depends on the pH of the solution (aqueous phase) and the concentration of the ligand in the organic phase.

Method of slope analysis of the extraction of UO22+ is as discussed by previous authors Godwin and Uzoukwu, (2012) and Uzoukwu, (1998). The slope gives the number of molecules, n, of the ligand (HTCP) that reacted with the molecules of the metal (UO22+) ion during the extraction process and can be represented by the following equations:

From equation 8, n is equal to 1, which confirmed that in each case, 1 mole of proton was displaced. Plot of variation of log D with log [HTCP] for the extraction of UO22+ into chloroform solutions containing 0.01 M SO42- buffer media at a pH value of 3 is presented in Figure 7.

A slope of Zero was obtained. This was taken as an indication that the interaction involved 1 mole of the metal at the pH value studied after solving equation 7. Earlier results showed that 1 mole of proton was released during the interaction. The results also showed that at all levels of interaction studied, the interaction involved 1 mole of the ligand and 1 mole of the metal. The degree of extraction as a function of UO22+ ion concentration is represented in Figure 8 at a pH value of 3.00 containing 0.01 M SO42- ion in chloroform.

A slope of zero was obtained. This again is an indication that the interaction involved 1 mole of the metal at the pH value studied after solving equation 9 in which n-1 is equal to 1. Consequently, a is equal to 1 indicating that 1 mole of metal UO22+ ion was involved in the interaction statistically (Godwin and Uzoukwu, 2012, Uzoukwu, 1998, Uzoukwu, 1998). Hence the metal ligand ratio is 1:1 and the complex formed under this condition is similar to (UO2)TCP.