Selective Extraction of Precious Metal Ions with Novel Trident Molecules Containing Pyridyl Groups

Abstract

Trident molecules containing pyridyl groups have been prepared for use as novel extraction reagents to investigate their physicochemical properties for dissolution into the aqueous phase and their ability, together with their corresponding monomeric analogues, to extract precious metal ions. Differences in their behavior were related to the pK a values of the trident molecules and the position of the nitrogen atom in the pyridyl groups. The trident molecules exhibit the ability to selectively extract silver from mixtures of other precious metals. The extraction mechanism and the coordination site of the silver ion with a 2-pyridyl derivative were determined by slope analysis and peak shift of the 1 H-NMR spectra of the extraction reagent before and after silver loading. INTRODUCTIONThe solvent extraction technique has been extensively studied for the separation of precious metals from recycled e-wastes (1). Although processes for the separation of precious metal ions by the company such as INCO (Vale-Inco) have been well established (2,3), these methods are still ineffective and incomplete for mutual separation, especially for the selective recovery of valuable and functionally inert rhodium. The extraction mechanisms for precious metals are classified into two categories: anionic exchange and ion-pair extraction with coordination. Amine or pyridyltype ligands can facilitate the extraction by either mechanism due to their coordination and protonation properties (4-6). Many factors, such as donor properties based on HSAB theory (7), the chelate effect, interfacial activity, and the hydrophobic character of the extraction reagents, can affect the extraction behavior of precious metals.

Solvent Extraction Behavior of Silver with the Secondary Phenylamide Derivative of the Trident Molecule

“…That is, silver was loaded on the extractant without any peak shift. In our previous work, when host molecules such as calixarene derivatives were structurally fixed by silver loading, peak shifts of the aryl protons were observed due to the shielding effect of the for π-electrons of the benzene rings [17,18,28]. Silver was extracted inside the extractant molecule and sufficiently surrounded by functional groups.…”

“…Various types of extraction reagents based on macrocycles and pseudomacrocycles, such as calixarenes [5][6][7][8][9][10][11][12][13][14][15] and tripodal alkyltrimethylol compounds as "trident" molecule [16][17][18] have been prepared for metal separation by our group. A trident is a three-pronged spear as used for fishing for target Solvent Extraction Research and Development, Japan, Vol.…”

New Trident Molecule with Phosphoric Acid Functionality for Trivalent Rare Earth Extraction

“…They also provide three-dimensionally arranged coordination site for guest molecules or ions [25][26]. They were employed as extraction reagents and ion-selective electrodes [25][26][27][28][29][30][31][32][33], and we named as "trident" molecules [29]. Their coordination site can be narrower than that of calix [4]arene derivative when functional groups are introduced close to the carbon atom as a junction to tripodal branched groups.…”

Recovery of Palladium from Concentrated Nitrate Solutions with N,N 2-Dimethyl-N,N 2-Dioctyltetradecy lmalonamide as New Extractant

“…It has different important applications in industrial fields such as automobile catalytic converters [1][2][3][4] . In fact, palladium is a very rare metal in the earth's crust, the world wide reserves being localized in very few countries 1,5 .…”