Fluosilicic acid extraction by high-molecular-weight amines

Abstract

The extractlon of fluoslilclc acid from dilute aqueous solutions by high-molecular-weight amines in kerosene has been studied. Extraction equlllbrium curves for various commercial amines are presented for room temperature, an amine concentration of 0.2 M, and aqueous acid concentrations up to 1 M. Formation of stable suspensions, coextraction of water, and aggregation of amine salts are discussed. Amine extraction of fluosilicic acid is compared with that of other mineral acids. The enthalpy, entropy, and equilibrium constant of the reversbble binding of NO to FeI'NTA in an aqueous solutionhave been determined to be AHo = -11.9 kcal/mol, AS = -11.1 eu, and K = 4.6 X lo5 M-' at 50 OC, respectively. The formation and dissociation rate constants of Fe"(NTAXN0) are k 1 7 X 10' M-l s-l a nd k -, 2 35 s-', respectively, at 25 OC. The rate of binding of NO to form the complex is much faster than the mass transfer rate at typical wet scrubber conditions.

Solvent extraction of hydrofluosilicic acid with alamine 336

“…Solvent extraction data have been presented (Tivnan and McCluskey, 1982) for HzSIF, with primary, secondary, tertiary and quaternary amines. They assumed the extracted species to be (R3NHt)2 SiFi-and presented equilibrium constants for this amine-salt formation.…”

“…Tivnan and McCluskey (1982) concluded that the extracted species was (R,NH'),SiFi-. Thus no limitations are imposed on the activity coefficients as defined in Equations (lo)-( 12).…”

“…This results in low individual values for both f l and f 2 at high ionic strengths. Tivnan and McCluskey (1982) reported their value as 5.6 < log K C 6.5 THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, VOLUME 64, JUNE 1986 This is at least one order of magnitude lower than K2, but no real comparison is possible because they did not describe how h and b were calculated, and no activity correlation was applied to the dissociation of H2SiF6. This model was thus adapted for H2SiF6 and the concentrations of the species in the aqueous phase could be calculated.…”

“…Because of the serious problems mentioned by Tivnan and McCluskey (1982) regarding third phase formation and phase separation it was decided to investigate the importance of the diluent further.…”

“…This model was thus adapted for H2SiF6 and the concentrations of the species in the aqueous phase could be calculated. Tivnan and McCluskey (1982) concluded that the extracted species was (R,NH'),SiFi-. From Figure 1 it is also clear that for aqueous concentrations between 0.…”