Solvent extraction acid-base

The liquid-liquid (solvent) extraction is based on the extraction of various ions into either an organic or aqueous phase according to the complex ion structure. The structure of the complex ions generally depends on the solution parameters and, first and foremost, on the acidity of the aqueous solution. At... 

A gas liquid chromatographic (GLC) method was described for determining residues of Bayer 73 (2-aminoethanol salt of niclosamide) in fish muscle, aquatic invertebrates, mud, and water by analyzing for 2-chloro-4-nitroaniline, a hydrolysis product of Bayer 73 [83]. Residues were extracted with acetone-formic acid (98 + 2), and partitioned from water samples with chloroform. After sample cleanup by solvent and acid base partitioning, the concentrated extract was hydrolyzed with 2N NaOH and H202 for 10 min at 95°C. The 2-chloro-4-nitroaniline was then partitioned hexane ethyl ether (7 + 3) and determined by electron capture GLC. Average recoveries were 88% for fish, 82% for invertebrates, 82% for mud, and 98% for water at 3 or more fortification levels. 

Solvent extraction of base metals by carboxylic acids 789... 

Reverse osmosis also serves some of the waste management and resource recovery needs in the metals and metal finishing industry. Effluent streams from mining and plating operations containing heavy metals, acids, and other chemicals can be treated with reverse osmosis to recover both the metal as its salt, and purified water for reuse. For metal ion recovery from dilute solutions, however, reverse osmosis faces competition from conventional solvent extraction, membrane-based solvent extraction, and its variant, coupled transport (see Section V.F.3). 

Solvent extraction methods estimate a high proportion of FFAs. However, when the acids are quantified by titration, some of these methods can overestimate the FFA level because of the inclusion of lactic acid, acidic phospholipids and other acidic interfering compounds in the extract (Chil-liard et al., 1983 Selselet-Attou et al., 1984). Solvent extraction methods based on mixtures of isopropanol, heptane and sulphuric acid (Dole and Meinertz, 1960 Landaas and Solberg, 1974 Deeth et al., 1975 Mouillet et al., 1981 Mahieu, 1983) have found widespread use in several countries and are used in routine analysis of large numbers of samples in automated versions (Lindqvist et al., 1975 Suhren et al., 1977 Brathen, 1984 Anderson et al., 1991). 

The process for treating the baghouse dusts consists of leaching the dusts with a sulphuric acid solution, generating a lead and silver residue as a by-product, which is returned to the lead smelter, and a zinc sulphate solution, that is purified to remove Pb, Fe, Cd and As. Zinc extraction is carried out by a solvent extraction process based on Lurgi technology. The zinc-rich solution obtained in the solvent extraction plant is sent to the electrolytic zinc plant for zinc recovery and an ammonium sulphate and chloride salt is obtained fix>m the raffinate for agricultural applications. The plant has a capacity of 5,000 totmes Zn/year. 

Dilute sodium hydroxide solution (and also sodium carbonate solution and sodium bicarbonate solution) can be employed for the removal of an organic acid from its solution in an organic solvent, or for the removal of acidic impurities present in a water-insoluble solid or liquid. The extraction is based upon the fact that the sodium salt of the acid is soluble in water or in dilute alkali, but is insoluble in the organic solvent. Similarly, a sparingly soluble phenol, e.g., p-naphthol, CioH,.OH, may be removed from its solution in an organic solvent by treatment with sodium hydroxide solution. 

In a simple liquid-liquid extraction the solute is partitioned between two immiscible phases. In most cases one of the phases is aqueous, and the other phase is an organic solvent such as diethyl ether or chloroform. Because the phases are immiscible, they form two layers, with the denser phase on the bottom. The solute is initially present in one phase, but after extraction it is present in both phases. The efficiency of a liquid-liquid extraction is determined by the equilibrium constant for the solute s partitioning between the two phases. Extraction efficiency is also influenced by any secondary reactions involving the solute. Examples of secondary reactions include acid-base and complexation equilibria. 

The concentration of o-phthalic acid in an organic solvent, such as n-butanol, may be determined by an acid-base titration using aqueous NaOH as the titrant. As the titrant is added, the o-phthalic acid is extracted into the aqueous... 

Anhydrous Acetic Acid. In the manufacture of acetic acid by direct oxidation of a petroleum-based feedstock, solvent extraction has been used to separate acetic acid [64-19-7] from the aqueous reaction Hquor containing significant quantities of formic and propionic acids. Isoamyl acetate [123-92-2] is used as solvent to extract nearly all the acetic acid, and some water, from the aqueous feed (236). The extract is then dehydrated by azeotropic distillation using isoamyl acetate as water entrainer (see DISTILLATION, AZEOTROPIC AND EXTRACTIVE). It is claimed that the extraction step in this process affords substantial savings in plant capital investment and operating cost (see Acetic acid and derivatives). A detailed description of various extraction processes is available (237). 

Solvent extraction—purification of wet-process phosphoric acid is based on preferential extraction of H PO by an organic solvent vs the cationic impurities present in the acid. Because selectivity of acid over anionic impurities is usually not sufficient, precipitation or evaporation steps are included in the purification process for removal. Cmde wet-process acid is typically concentrated and clarified prior to extraction to remove post-precipitated sludge and improve partition of the acid into the solvent. Concentration also partially eliminates fluoride by evaporation of HF and/or SiF. Chemical precipitation of sulfate (as Ba or Ca salts), fluorosiUcates (as Na salt), and arsenic (as sulfides) may also be used as a prepurification step preceding solvent extraction. 

The nature of the donor atoms in the chelating agent. Ligands which contain donor atoms of the soft-base type form their most stable complexes with the relatively small group of Class B metal ions (i.e. soft acids) and are thus more selective reagents. This is illustrated by the reagent diphenylthiocarbazone (dithizone) used for the solvent extraction of metal ions such as Pd2+, Ag+, Hg2+, Cu2+, Bi3+, Pb2+, and Zn2 +. ... 

Theory. Conventional anion and cation exchange resins appear to be of limited use for concentrating trace metals from saline solutions such as sea water. The introduction of chelating resins, particularly those based on iminodiacetic acid, makes it possible to concentrate trace metals from brine solutions and separate them from the major components of the solution. Thus the elements cadmium, copper, cobalt, nickel and zinc are selectively retained by the resin Chelex-100 and can be recovered subsequently for determination by atomic absorption spectrophotometry.45 To enhance the sensitivity of the AAS procedure the eluate is evaporated to dryness and the residue dissolved in 90 per cent aqueous acetone. The use of the chelating resin offers the advantage over concentration by solvent extraction that, in principle, there is no limit to the volume of sample which can be used. 

There are a large number of literature references that refer the use of SPE cartridges for the extraction of pesticides from water. There are several comprehensive reviews of the use of SPE, including that by Soriano et al. who discussed the advantages and limitations of a number of sorbents for the analysis of carbamates. Hennion reviewed the properties and uses of carbon based materials for extraction of a wide multiclass range of pesticides. Thorstensen et al. described the use of a high-capacity cross-linked polystyrene-based polymer for the SPE of phenoxy acids and bentazone, and Tanabe et al reported the use of a styrene-divinylbenzene copolymer for the determination of 90 pesticides and related compounds in river water. SPE cartridges are also widely used for the cleanup of solvent extracts, as described below. 

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