Comparative Study on Palladium(II) Extraction Using Thioamide-Modified Acyclic and Cyclic Extractants

Abstract

For extraction from a single Pd(II) solution, 1,1′bis[(dimethylthiocarbamoyl)oxy]-2,2′-thiobis [4-t-butylbenzene] (1) in a CHCl 3 diluent was found to exhibit a higher extractability for Pd(II) ions (E% = 99.9%) in Cl − media (0.1 M) over 30 min as well as a higher extraction efficiency compared to 2,2′-thiobis[4-tbutylphenol] (2) as a starting material of 1 and macrocyclic compounds such as tetrakis[(dimethylthiocarbamoyl)oxy]thiacalix-[4]arene (3) and p-tert-butylthiacalix[4]arene (4). Also, various parameters, such as the shaking time, diluents used, concentrations of Pd(II) and 1, effects of HCl, and effects of H + and Cl − ions, were studied. Extractant 1 could also be used for the selective extraction of Pd(II) ions (E% > 99%) from the leach liquors of automotive catalysts that also contained the ions of Rh, Pd, Pt, Zr, Ce, Ba, Al, La, and Y in Cl − media and was found to be a more efficient extractant than 2 for Pd(II) recovery. In addition, the Pd(II) ions could be stripped from 1 using 0.1 M thiourea in 1.0 M HCl, thus enabling the reuse of 1. Extractant 1 was actually found to exhibit a high E% for Pd (>96%) after five extraction cycles, indicating good stability in acidic media and potential usefulness for the rapid and selective recovery of Pd(II) from catalyst solutions in platinum group metal refineries.

Recycling of Palladium from Spent Catalysts Using Solvent Extraction—Some Critical Points

“…Several thiocarbamate derivatives have recently been tested by Yamada and collaborators for the recovery of Pd(II) [54,55]. The structures of the most promising compounds found in these studies are depicted in Figure 5.…”

Synthesis of pincer-type extractants for selective extraction of palladium from PGMs: An improved liquid-liquid extraction approach to current refining processes

“…Many synthesised and commercial extractants 23–36 exhibit slow extraction rates and extract other PGMs and base metals in minor amounts in addition to Pd ions, which affects the selectivity of extraction. In these cases, extraction removes only Pd(II) into the organic diluent, chlorinated diluent, or mixture of diluents 18–22, 28–33 , and oxidation in acidic media causes Pd(II) extraction to be highly dependent on the acidity and type of leach liquors. Pd(II) extraction efficiency is good in weakly acidic media, but decreases dramatically in strong acid media 22, 31, 33–35 .…”

“…In these cases, extraction removes only Pd(II) into the organic diluent, chlorinated diluent, or mixture of diluents 18–22, 28–33 , and oxidation in acidic media causes Pd(II) extraction to be highly dependent on the acidity and type of leach liquors. Pd(II) extraction efficiency is good in weakly acidic media, but decreases dramatically in strong acid media 22, 31, 33–35 . Synthesis of new, robust extractants faces several major issues including use of expensive reagents, multiple synthetic steps 22, 31 , advanced purification methods, durability, and difficulties in back extraction and reusability.…”

Calix[4]arene‐Based n‐Dialkylamino Extractants for Selective Platinum Group Metal Separation from Automotive Catalysts

“…However, no effective extractants have yet been developed for the complete recovery of PGMs from secondary resources . PGM extractants with higher selectivity and extraction rates and superior durability are required . It was therefore considered important to develop new extractants possessing high separation efficiency for PGMs and high stability in acidic media.…”

“…[4][5][6] PGM extractants with higher selectivity and extraction rates and superior durability are required. [7][8][9][10][11][12][13] It was therefore considered important to develop new extractants possessing high separation efficiency for PGMs and high stability in acidic media.…”