Recent Advances in Amines as Separating Agents for Metal Ions

Abstract

In this article those aspects of the application of amines in metal ion separation during the last two decades which could be regarded as new facets or as clarifying earlier concepts have been briefly dealt with. This includes work with diammonium extractants and a comparison with their monocationic analogues and new approaches to explain the different secondary effects. In addition more emphasis has been placedon the neutral N-donor action ofamines and their application towards metal ion specificity. The importance of a thorough understanding of the basic properties of the amine and the metal ion were indicated for the development of new metal ion specificseparating agents.

The separation of nickel(II) from base metal ions using 1-octyl-2-(2′-pyridyl)imidazole as extractant in a highly acidic sulfate medium

“…Amines in their neutral form have not been extensively explored as separating agents for metal ions from a basic bonding viewpoint (du Preez, 2000). The application of the ammonia derivatives (R-NH 2 , where R is an alkyl or aryl group) is limited by their high protonation constants which prevent complexation even in weakly acidic solutions thereby resulting in the hydrolysis of metal ions.…”

An Exploratory Study of Tridentate Amine Extractants: Solvent Extraction and Coordination Chemistry of Base Metals with <i>Bis</i>((1<i>R</i>-benzimidazol-2-yl)methyl)amine

“…There has been an envisaged shift towards aminebased extractants, and this is motivated by the favourable properties that are offered by the nitrogenous ligands especially the aromatic amines as compared with oxygenbased extractants [3][4][5]. Some of these properties include the intermediate pK a values as well as  and  bonding capabilities resulting in extractions in the low pH range and in a possibility of separation through bonding preferences respectively.…”

“…Some of these properties include the intermediate pK a values as well as  and  bonding capabilities resulting in extractions in the low pH range and in a possibility of separation through bonding preferences respectively. The latter property has been dubbed "stereochemical tailor-making" by du Preez [5]. On the other hand, the strong aliphatic amine ligands with σ-donor only character show lack of relative preference for the metal ions but this can be improved if chelates are used, and also tend to form metal complexes at relatively high pH values which is undesirable [5].…”

“…The latter property has been dubbed "stereochemical tailor-making" by du Preez [5]. On the other hand, the strong aliphatic amine ligands with σ-donor only character show lack of relative preference for the metal ions but this can be improved if chelates are used, and also tend to form metal complexes at relatively high pH values which is undesirable [5]. The chelate effect has also been exploited effectively in a bidentate aromatic system (1-octyl-2,2'-pyridylimidazole) providing for effective separation of nickel from other base metals in strong acidic sulfate solutions with a possibility of back-extraction [3].…”

Studies on the separation of some transition metals using trialkylimidazole as selective extractant

“…Several extractants have been proposed for separation of Cu(II), Zn(II), and Cd(II) from aqueous solutions, e.g., carboxylic acids [10], derivatives of phosphinic acid [11], derivatives of acid amides, trioctylamine [11], alkylphenylamines [12], complex oximes [13], crown ethers [14][15][16] derivatives of ketones [17][18][19][20], derivatives of pyridine [21,22], as well as alkyl derivatives of imidazole [6,[23][24][25] and quaternary ammonium salt [26].…”