Kazutoshi Haga

Selective sorption of palladium by thiocarbamoyl-substituted thiacalix[n]arene derivatives immobilized on amberlite resin: application to leach liquors of automotive catalysts

p-tert-Butylthiacalix[4/6]arenes (1 and 2) and their thiocarbamoyl derivatives (3 and 4) were immobilized on Amberlite XAD-7 (XAD). Pd(II) adsorption from single-metal solution, simulated mixed-metal solution, and automotive catalyst leach liquor in HCl media was performed in the batch mode. The Pd(II) sorption capacity of 3 and/or 4 immobilized on XAD (7 and 8) was 40.2 mg g−1 and 60.0 mg g−1, respectively. In contrast, 1 and/or 2 immobilized on XAD (5 and 4) had lower sorption capacities than 7 and 8, 10.1 mg g−1 and 13.4 mg g−1, respectively. Resins 7 and 8 selectively sorbed 99% of Pd(II) ions from automotive catalyst liquor comprising Rh, Pd, Pt, Zr, Ce, Ba, Al, La, and Y in 0.1 M HCl media. XAD and the extractant-impregnated XAD resins were characterized by FT-IR, XRD, SEM-EDAX, and WDXRF before and after Pd(II) sorption. The sorption data were fitted to Freundlich and Langmuir isotherms. Thermodynamic parameters such as ΔGo, ΔHo, and ΔSo were calculated to evaluate the nature of the sorption process. The Pd(II) sorption efficiency of 7 and 8 was also tested by column method. Desorption of Pd(II) ions from the loaded resins was performed using acidic thiourea, thereby enabling recycling of the resins. Thus, both resins 7 and 8 can be used for the effective separation of Pd(II) from secondary resources.

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

SCS pincer ligands 1–4 were synthesised, and their ability to extract Pd(II) from HCl and HNO3 media was studied. The Pd(II) extraction properties of 1–4 were compared with those of commercial extractants (DOS and LIX®84-I) in kerosene. 1 and 2 showed superior Pd(II) extractability (E% = 99.9) relative to DOS and LIX®84-I from 0.1–8.0 M HCl and to DOS from 0.1–8.0 M HNO3 and mixed HCl + HNO3 media. The Pd(II) extraction rate, acid durability, the most suitable organic/aqueous (O/A) phase ratio, and Pd(II) loading capacity of extractants 1, 2, and DOS were evaluated. 1 and 2 exhibited a greater Pd(II) extraction rate and Pd(II) loading capacity than DOS. 1 was very stable in acid media (HCl and HCl + HNO3), whereas 2 and DOS deteriorated in HCl + HNO3. Selective extraction of Pd(II) by 1 and 2 was achieved from a mixed solution containing Pd, Pt, Rh, rare metals, and base metal ions that simulated the leach liquors of automotive catalysts. The back extraction of Pd(II) and reusability of extractants 1 and 2 were studied. The Pd(II) extraction mechanism of 1–4 was investigated using FT-IR, UV-visible, and NMR spectroscopy.

Recovery of Valuable Metals from Waste Printed Circuit Boards by Using Iodine-Iodide Leaching and Precipitation

This study presents a viable approach for recovery of precious metals such as gold (Au), silver (Ag), palladium (Pd), and base metals, including copper (Cu), nickel (Ni), cobalt (Co), lead (Pb) and zinc (Zn) from waste printed circuit boards (WPCBs) via iodine-iodide leaching and precipitation. The behaviours of dissolution and precipitation of precious and base metals during iodine-iodide leaching and precipitation processes were discussed. Sodium hydroxide (NaOH) was used to remove base metal impurities exist in the pregnant leach solution under alkaline conditions. Precious metals remained in the resulting solution from NaOH precipitation were recovered by reduction using ascorbic acid (L-AA) solution. Results show that under optimum leaching conditions, almost all (> 99%) of Au was dissolved in an iodine-iodide solution when the dissolution efficiencies of other precious metals (Ag, Pd) and base metals, besides calcium (leaching of 25%) were less than 1 and 6%, respectively. The study revealed that more than 95% of Cu, Ni, Pb, Zn, Fe and Mn were initially removed from the pregnant leach solution at pH of 9.3 with addition of 0.1 M NaOH. Then 99.8% Au, 81.7% Ag and 74% Pd were precipitated from the obtained solution after NaOH precipitation while L-AA dose was 0.6 ml/ml at the condition. It can be concluded that the precious and base metals could be recovered selectively and economically from WPCBs via iodine-iodide leaching followed by precipitation using NaOH and L-AA.

Investigation for Removal of Organic Carbon from Carbonaceous Copper Sulphide Ore and Improving the Recovery of Copper Through Flotation

An investigation on improving copper and iron recovery by removal of organic carbon and carbonaceous gangue mineral through flotation was carried out. The ore contains chalcopyrite and bornite as valuable minerals, and dolomite and calcite as carbonaceous gangue minerals. The chemical composition of the ore indicates that grade of 2.08 and 5.37 mass% for copper and iron respectively, while carbon was 3.70 mass%. The total organic carbon in the feed was recorded as 2.02 mass%. The presence of these gangue minerals is detrimental to copper and iron recovery during flotation. Therefore a two stage flotation study was carried out to remove hydrophobic carbon and carbonaceous material from ore and to improve copper and iron recovery. The objective of the study was to find effective and selective flotation conditions which can eliminate gangue minerals from valuable minerals and improve quality (grade) and recovery of copper and iron. The obtained results could be used to develop a flotation circuit for recovering copper and iron from carbonaceous sulphide ores.

Copper Recovery from the Mine Tailings by Combination of Flotation with High-Pressure Oxidative Leaching and Solvent Extraction

The aim of this research was to develop a copper recovery process from mine tailings (0.34%Cu) using flotation followed by high-pressure oxidative leaching (HPOL) and solvent extraction. The results of HPOL using the concentrate of mine tailings obtained by flotation under the optimal conditions of the previous study shown that an efficient copper dissolution of 94.4% was achieved in an H2O media, while the copper concentration of PLS reached to be 2.9 g/L. The solvent extraction of PLS obtained from the optimal HPOL showed that 91.3% copper was recovered in stripped solution under the determined optimum conditions, in which the copper concentration achieved to be 44.8 g/L. Finally, a proposed copper recovery process from the concentrate of mine tailings was developed by combination of HPOL and solvent extraction, while a total copper recovery of 86% was achieved.

Development of copper recovery process from flotation tailings by a combined method of high‒pressure leaching‒solvent extraction

Sulfide copper mineral, typically Chalcopyrite (CuFeS2), is one of the most common minerals for producing metallic copper via the pyrometallurgical process. Generally, flotation tailings are produced as a byproduct of flotation and still consist of un‒recovered copper. In addition, it is expected that more tailings will be produced in the coming years due to the increased exploration of low‒grade copper ores. Therefore, this research aims to develop a copper recovery process from flotation tailings using high‒pressure leaching (HPL) followed by solvent extraction. Over 94.4% copper was dissolved from the sample (CuFeS2 as main copper mineral) by HPL in a H2O media in the presence of pyrite, whereas the iron was co‒dissolved with copper according to an equation given as CCu = 38.40 × CFe. To avoid co‒dissolved iron giving a negative effect on the subsequent process of electrowinning, solvent extraction was conducted on the pregnant leach solution for improving copper concentration. The result showed that 91.3% copper was recovered in a stripped solution and 98.6% iron was removed under the optimal extraction conditions. As a result, 86.2% of copper was recovered from the concentrate of flotation tailings by a proposed HPL‒solvent extraction process.

Mutual Separation of Palladium(II) and Platinum(IV) from Hydrochloric Acid Solutions Using m-Phenylene Diamine-Containing Agents

Platinum group metals (PGMs), especially Pd and Pt, are important industrial elements owing to their extensive use in electrical devices, dental materials, catalysts, and jewelry [1,2]. Given the scarcity of the PGMs primary resources, the recycling of these metals from secondary sources or post-consumer scrap is essential [3]. Solvent extraction is regarded as a typical and practical method to recover PGM ions [4-8]. For example, Pd(II) and Pt(IV) can be extracted from hydrochloric acid (HCl) solutions with di-n-octyl sulfide [9] and tri-n-butyl phosphate [10] extractant agents, respectively. However, the use of volatile organic solvents as extractant diluents negatively affects the recovery process owing to their toxicity and environmental load. Mutual separation of PGMs, which is required in the recovery process, is complicated because of the similar physical and chemical properties of the metal components. PGM ions are known to be recovered via coordination or ion-pair mechanisms [11]. Pd and Pt are typically recovered following a coordination mechanism with the trend Pd(II) >> Pt(IV) [12]. On the other hand, Pd and Pt chloro-complex anions (i.e., [PdCl4] 2and [PtCl6] ) were extracted to a similar extent via an ion-pair mechanism [11,13]. Therefore, mutual separation of Pd and Pt is generally performed by combining coordination and ion-pair recovery strategies, respectively. However, the utilization of different mechanisms within the recovery process requires several recovery agents specially designed for the corresponding recovery mechanism. In addition, the recovery of PGMs via a coordination mechanism is typically accompanied with base metals such as Cu, Fe, Al, and Zn [12]. In this study, we report on the selective precipitation and mutual separation of Pd and Pt using new precipitating agents (i.e., m-phenylene diamine-containing compounds). These precipitating agents were prepared by condensation of aniline or 4-phenoxyaniline with 3,5-bis(trifluoroacetamido)benzoyl chloride followed by deprotection with hydrazine. The precipitation behaviors of Pd and Pt with the as-prepared precipitating agents were examined by using Pdand Pt-containing HCl solutions with or without base metals. The precipitating agents prepared in this study enabled mutual separation of Pd and Pt from a HCl solution containing base metals via an ion-pair mechanism.