Solvent extraction amine salts

For solvent extraction of pentavalent vanadium as a decavanadate anion, the leach solution is acidified to ca pH 3 by addition of sulfuric acid. Vanadium is extracted in about four countercurrent mixer—settler stages by a 3—5 wt % solution of a tertiary alkyl amine in kerosene. The organic solvent is stripped by a soda-ash or ammonium hydroxide solution, and addition of ammoniacal salts to the rich vanadium strip Hquor yields ammonium metavanadate. A small part of the metavanadate is marketed in that form and some is decomposed at a carefully controlled low temperature to make air-dried or fine granular pentoxide, but most is converted to fused pentoxide by thermal decomposition at ca 450°C, melting at 900°C, then chilling and flaking. 

For direct precipitation of vanadium from the salt-roast leach Hquor, acidulation to ca pH 1 without the addition of ammonia salts yields an impure vanadic acid when ammonium salts are added, ammonium polyvanadate precipitates. The impure vanadic acid ordinarily is redissolved in sodium carbonate solution, and ammonium metavanadate precipitates upon addition of ammonium salts. Fusion of the directly precipitated ammonium salts can yield high purity V20 for the chemical industry. Amine solvent extraction is sometimes used to recover 1—3 g/L of residual V20 from the directly precipitated tail Hquors. 

Dissociation extraction is the process of using chemical reac tion to force a solute to transfer from one liquid phase to another. One example is the use of a sodium hydroxide solution to extract phenolics, acids, or mercaptans from a hydrocarbon stream. The opposite transfer can be forced by adding an acid to a sodium phenate stream to spring the phenolic back to a free phenol that can be extrac ted into an organic solvent. Similarly, primary, secondary, and tertiary amines can be protonated with a strong acid to transfer the amine into a water solution, for example, as an amine hydrochloride salt. Conversely, a strong base can be added to convert the amine salt back to free base, which can be extracted into a solvent. This procedure is quite common in pharmaceutical production. 

Example 1 Amine salts—It is first changed to the water-soluble free base, extracted with an appropriate organic solvent and treated with an excess volume of standard acid subsequently, the solvent was evaporated, and the remaining acid determined with a standard base. 

The object of equilibration is to provide a solvent that will effectively extract the required species, either because of the form of the active constituent of the solvent or by maintaining the necessary extraction pH. As an example of the former condition, consider the extraction of uranium using a tertiary aliphatic amine as extractant. Extraction of metal species by such amines is considered to occur by liquid ion exchange (see Chapters 3 and 4). For a tertiary amine to act in this manner, it must be first converted to an amine salt ... 

Having formed the amine salt, the solvent can be used for the extraction of uranium. This is shown as an ion exchange process in Eq. (7.3) ... 

Vanadium usually is recovered from its ores by one of two processes, (1) leaching raw mineral with hot dilute sulfuric acid, and (2) roasting ore with common salt to convert vanadium into water soluble sodium vanadates. In the sulfuric acid leaching process, vanadium is extracted from acid leach liquors by solvent extraction with an aliphatic amine or an alkyl phosphoric acid in kerosene. The organic solvent extract then is treated with an aqueous solution of ammonia in the presence of ammonium chloride to convert vanadium into ammonium metavanadate. Alternatively, the organic extract is treated with dilute sulfuric acid or an aqueous solution of soda ash under controlled conditions of pH. Vanadium is precipitated from this solution as a red cake of sodium polyvanadate. 

Solvent extraction of base metals by amine salts 802... 

The use of amine salts in the commercial solvent extraction of the platinum-group metals from chloride solutions is described in Section 63.3.2.5. 

The existence of the PGM and gold in the form of complex anions in chloride media has been used to advantage in the design of several solvent-extraction processes. Thus, metal-chloro complexes of the type MCI/- can be extracted by, for example, salts of secondary amines ... 

The extraction of the PGM by amine salts was first reported some 30 years ago,235 shortly after which a process for the recovery of the PGM by solvent extraction was patented in the Soviet Union.236 The results of pilot-plant operations for the recovery of PGM from copper and nickel refinery slimes have also been described,237-23S and it is probable that such processes are currently in full-scale commercial use. Further extensive studies by Soviet workers have been described in a recent review.239 It has been shown that, in addition to the anion-exchange mechanism, e.g. 

If the crude solid product contains the required product in the form of a salt (e.g. the alkali metal salt of a phenol) and is therefore water soluble, acidification of the aqueous solution (or basification in the case, for example, of amine salts) liberates the free acidic compound (or base) which may be recovered by filtration or solvent extraction as appropriate. 

A second purification strategy involves the substitution of the amine moiety on the a-aminoadipyl side chain at C-7. Two substituted derivatives, iV-2,4-dichlorobenzoyl CPC and tetrabromocarboxybenzoyl CPC, can be crystallized from the acidic aqueous solution. Alternatively, salts can be formed between the, /V-substituted derivatives and an organic base, such as dicyclohexylamine or dimethylbenzylamine, resulting in cephalosporin salts that are solvent extractable. Bristol-Myers Squibb uses a solvent-extractable process resulting in the isochlorobutylformate (ICBF) ester of CPC, termed cephalosporin D. Several extraction steps are usually necessary to achieve the desired final purity. iV-Substituted CPC salts containing small amounts of contaminants can be effectively converted to 7-ACA. 

Sayari et al [202,203] extended the LCT technique to the synthesis of mesostructured zirconium oxide. The use of long chain quaternary ammonium salts or primary amines as templates led to the formation of hexagonal and lamellar Zr02 phases, respectively. Zr(S04)2 was used as zirconium source, which provided a highly acidic medium, pH < 1.5. Consistent with the synthesis conditions and EDX analysis data a S X I mechanism where the surfactant-inorganic interaction is mediated by sulfate anions was proposed. Unfortunately, both structures collapsed upon removal of the surfactant either by high temperature calcination or by solvent extraction [203]. However, the hexagonal form was successfully... 

Separation by solvent extraction Uranium can be extracted from aqueous solutions using extraction agents into the solvent phase, from which it can be stripped. The extraction agents used are phosphorus compounds such as di-(2-ethylhexyl)-phosphate, tri-n-butyl-phosphate and tri-n-octylphosphine oxide as well as primary, secondary and tertiary amines in salt form or as quaternary ammonium salts. The extraction agents are diluted with inert hydrocarbons, preferably kerosene, to concentrations of 4 to 10% by volume. The solubility of the amine salts, particularly the hydrogen sulfates, chlorides and nitrates is increased by adding long chain alcohols (e.g. isodecanol). 

---