Acid Extraction by Acid-Base-Coupled Extractants

The interphase distribution of weak acids in systems involving salts of quaternary ammonium bases with organic acids (binary extractants) has been analyzed. Significant differences in the extraction depending on the composition of the aqueous and organic phases for weak acids compared with that for strong acids in binary extractant systems have been shown. The difference in the extraction of weak acids with binary extractants compared with neutral extractants has been also revealed. The experimental data were interpreted by two variants of distribution processes, when two extracted species are formed (R4NX and HA) and for the case of forming extracted species with strong H-bonds (R4NX · HA). The least square regression method showed that the proposed mechanisms well describe the extraction of monocarboxylic acids with the binary extractant (the smallest sum of squares of relative deviations was 0.025) at their low initial concentrations (<0.05 mol · L−1). It was shown that the most effective extraction of monocarboxylic acids takes place from acidic solutions (at pH < 2) that indicates the possibility of their effective stripping from organic solutions with water.

The binary extraction is characterized by a number of properties being also typical for the coordinative extraction as well as by peculiarities in respect to the properties of union and cation exchanging extractants. Therefore it is suitable to consider it a new class of extraction processes. The extraction of acids, salts and metal hydroxides is described, examples are discussed, and extraction series are given. Due to the manifold possibilities of the variation of the binary extractant there are a number of variants to influence e. g. selectivity, and thus to control the processes of separation. The binary extraction thus leads to new efficient solutions of hydrometallurgical problems.

Effect of binary extractants and modifier–diluents systems on equilbria of propionic acid extraction

The distribution of platinum metals and gold in the systems with binary extractants (salts of amines, quaternary ammonium bases (QAB), and organic acids) in toluene has been studied. It was shown that anion exchange mechanism complicated by interactions of components in organic phase is realized during metal extraction from 1–3 M HCl solutions. When acidity of aqueous phase decreases distribution coefficients of noble metals are decreased according to binary extraction regularities of mineral acids in (he systems with salts of trioctylamine and QAB. In the systems with caprylate and alkylphenolate of dioctylamine in the region of high pH values of aqueous phase, palladium distribution coefficients are increased due to formation in the organic phase of complexes with direct coordination of amine molecules to atoms of palladium and their stability is, obviously, higher than that of dioctylamine salts with corresponding organic acids. From the investigated binary extractants, the salts of quaternary ammonium bases and strong organic acids (alkylphosphoric, alkylbenzolsulfonic acids) are of great interest for practice. It was shown during extraction of Pt (IV), Pd (II), Ir (IV) and Au (III) chlorocomplexes by 0.1 M solutions of trialkylbenzylammonium alkylsulphonate, metal distribution coefficients in the acidic region are changed from 5 to 150 while distribution coefficients for Rh(III) and Ir(III) did not exceed 0.1 and that creates possibilities for separation of platinum metals. Noble metals are lightly stripped from organic phase by water that it is impossible for initial systems with mineral salts of quaternary ammonium bases. The comparison of the systems with binary extractants and TBP has shown the advantage of binary extraction for obtaining more concentrated stripping solutions.

The equations describing the regularities of interphase distribution of platinum metals as their chloro complex acids in systems containing binary extractants have been derived. The dependencies of distribution coefficients of platinum metals on the composition of both phases, and their aqueous acidity have been determined when both binary extraction and a combination of anion-exchange and binary extraction occurred. The interrelation of the binary extraction constant of chloro complex acids of platinum metals with the extraction constant of hydrochloric acid and the anion-exchange constant is described. We studied platinum metal extraction by salts of organic acids and organic bases and showed that in the systems involving binary extractants, such as salts of quaternary ammonium bases, the distribution of platinum metals proceeds via either anion-exchange or binary mechanisms depending on the composition of the system. With increasing pH, the distribution coefficients of platinum metals decrease according to the regularities of binary extraction due to forming thermodynamicaHy stable binary extractants, R4NA When the anion-exchange extraction occurs, the distribution of complex acids of platinum metals in the systems containing binary extractants is affected by interactions of the extractants and the extracted compounds with the organic acids. Interactions between extractants in the chloride form and the molecules of organic acids have been shown to be largely responsible for the extraction characteristics. The binary extractant systems are preferred in the development of solvent extraction processes for the recovery and the stripping of platinum metals.

Extraction of mineral acids with methyltrioctylammonium dialkylphosphinate was studied, and the extraction ability of acids was shown to decrease in the series HNO3 ≫ HBr > HCl, which corresponds to anion-exchange series for the initial salts of quaternary ammonium bases (QAB). Extraction of lanthanum bromide with methyltrioctylammonium dialkylphosphinate was studied, the composition of extracted compounds was established, and extraction constants were calculated. The extraction ability of dinonylnaphthalenesulfonate was found to be considerably lower than that of QAB dialkylphosphinate because of a larger value of acid dissociation constant for dinonylnaphthalenesulfonic acid. It was shown that lanthanum in systems with binary extractants can be back extracted from organic phase with dilute solutions of mineral acids.

Application of binary extraction in hydrometallurgy

Design and optimization for the separation of cyclohexane-isopropanol-water using mixed extractants with thermal integration based on molecular mechanism

Extraction chromatography of common anions in liquid-liquid anion exchange systems. Part. III. Monobasic aliphatic organic acids and their sodium salts as eluants

Characterization of iron plaque stability on roots of wetland plants is of value in consideration of several wetland issues. Active and dormant roots of common reed [ Phragmites australis (Cav.) Trin. ex Steudel] sampled from a constructed wetland were treated sequentially with 0.5 M MgCl 2 (salt extraction), HCl solution at pH 3, 2, 1.6, 0.6, 0.3, and 0 (acid extraction), and 0.385 M Na 2 S 2 O 4 (reductant extraction). Iron was measured with an orthophenanthrolene method. Results indicated that dormant roots contained 6, 890, 180, and 140 µg Fe g ‐1 fresh root weight in salt extractable, acid extractable, reductant extractable, and residual fractions, respectively, and active roots had a higher proportion of acid extractable Fe and lower proportions of reductant extractable and residual Fe than dormant roots. Following acid extraction, substantial Fe 2+ was detected. Ferric iron reduction after extraction was also found. The models of Fe extraction dynamics at different pH levels were fit to standard equations. According to the comparison of the constants in these models, the Fe release rate and potential for extraction in the acid solutions tended to increase as the pH decreased, but the effect on Fe extraction became saturated when pH approached zero. The oxidation state of Fe in root plaque was examined with Mossbauer spectroscopy after the roots were dried at 80°C in a regular oven and were powdered. The results indicated that the Fe(II) proportion is 33% in powdered dormant roots, and 27% in active roots. Based on these results, we suggest that the previously accepted concept of plaque composed entirely of Fe 3+ needs to be further examined.

Experimental design for extraction and quantification of phenolic compounds and organic acids in white “Vinho Verde” grapes

The air-brake as related to progress in locomotion

The aim of this work was to test if the use of an organic acid as an extractant of phosphorus from sediment could be developed as a new method of measuring bioavailable phosphorus. Based upon work done previously, the organic acid, glycolic acid, was chosen. This acid is one of a number known to be implicated in phosphorus solubilization by biological action, and was chosen because of its lack of interference (except at relatively high concentrations) with the molybdenum blue colorimetric method of determining phosphate in solution.It has been shown that glycolic acid extracts increasing amounts of phosphate from sediment with increasing acid concentration up to a maximum extraction at a concentration of the acid of 1.25 M. It has also been shown that when compared to various inorganic acid extractions of the sediment, glycolic acid extracts appreciably less phosphate, and appears to extract different forms of phosphorus to those removed by the inorganic acids; it also correlates relatively poorly with these inorganic acid extractions in terms of phosphorus extracted.The glycolic acid extraction method has been shown to correlate badly with the very commonly used inorganic extraction method of assessing bioavailable phosphorus, viz. the NH4F / HC1 extraction method. However, an unexpected result was obtained, when it was found that 1.00 M sodium glycolate both extracts more phosphorus from sediment than does the NH4F / HCl extractant, and correlates very well with this method of assessing bioavailable phosphorus. The sodium glycolate method correlates relatively poorly and very badly with the glycolic acid and inorganic acid extraction methods respectively, in terms of phosphorus extraction.Sediment sample pre-treatment has been shown to be of great importance in determining phosphorus extraction, almost regardless of the extractant and method of extraction used.

The extraction of HNO3, HClO4, H2SO4 and H3PO4 by 20% (v/v) TBP (0.73 M) in n‐octane was measured under identical conditions up to and beyond the critical point of third phase formation (Limiting Organic Concentration, or LOC condition). The data, together with those obtained previously for HCl, allowed us to establish the following lyotropic series of effectiveness with respect to third phase formation in the extraction of acids by TBP: HClO4>H2SO4>HCl>H3PO4>HNO3. This series correlates with the amount of water present into the organic phase at the point of phase splitting. This result reinforces the validity of the reverse micellar model developed previously for the extraction of metal salts by TBP. The measurements of LOC values as a function of temperature revealed major differences among the acid‐TBP systems investigated. For HClO4, the strong increase of the LOC value with increasing temperatures is accompanied by a large favorable entropy change. The opposite is true for HCl, while H2SO4 and H3PO4 represent intermediate cases. Measurements of the LOC values for the extraction of HClO4 by TBP dissolved in a series of diluents confirmed that topological parameters, such as the Connectivity Index, CI, are useful for predicting the critical condition for phase splitting in different diluents. Based on the linear correlation between LOC values for HClO4 and CI values of diluents, the effective Connectivity Index of the French nuclear reprocessing diluent, HTP, a complex mixture of highly branched alkanes, was determined.

General dependences of interphase distribution of weak acids in systems containing binary extractants were studied. Substantial differences in the extraction dependences of the composition of the organic and aqueous phases were shown for weak acids compared to systems that contain strong acids and binary extractants, as well as weak acids and neutral extractants. The influence of hydrogen bonding between two extracted compounds was observed when low-molecular monocarboxylic acids were extracted with agents based on quaternary ammonium bases and organic hydroxy acids.