Recovery of platinum group metals from a spent automotive catalyst using polymer inclusion membranes containing an ionic liquid carrier

Novel dithioamide extractant for highly selective separation of Pd from acidic leach liquors of waste auto-catalysts

The development of novel efficient extractants for Pd recovery from high acidic chloride media leaching solutions has always been an important task. In this study, a novel pincer extractant N,N'-dibutyl-m-phenyldithioamide (DBTB-4) was successfully synthesized, and its structure was confirmed by FT-IR, 1H NMR, 13C NMR (DEPT 135), ESI-HRMS and EA. The possibility of Pd recovery from leaching liquors of waste auto-catalysts by DBTB-4 was evaluated. The Pd extraction mechanism by DBTB-4 from chloride media was studied. DBTB-4 has rapid extraction kinetics for Pd (<30 min), strong extractability and specific selectivity for Pd at acidity of ≤4 mol per L HCl. There are no precipitants or a third phase generation during Pd extraction using a mixture of kerosene and isooctanol with V kerosene/V isooctanol of 1 : 3 as diluent. DBTB-4 quantitatively extracts Pd with DBTB-4/Pd molar ratio of 1 : 1 through coordination with Pd via the two S atoms and the carbon in the phenyl between the two thioamide groups forming two five-membered chelate rings. The extracted complex can be written as (L-H)PdCl, where L stands for one molecular of DBTB-4. DBTB-4 can quantitatively and selectively extract Pd from leaching liquors of waste auto-catalysts leaving nearly all Pt, Rh and base metals in the raffinate.

Lightweight, Strong, and Transparent Wood Films Produced by Capillary Driven Self-Densification

Wood delignification and densification enable the production of high strength and/or transparent wood materials with exceptional properties. However, processing needs to be more sustainable and besides the chemical delignification treatments, energy intense hot-pressing calls for alternative approaches. Here, this study shows that additional softening of delignified wood via a mild swelling process using an ionic liquid-water mixture enables the densification of tube-line wood cells into layer-by-layer sheet structures without hot-pressing. The natural capillary force induces self-densification in a simple drying process resulting in a transparent wood film. The as-prepared films with ≈150 µm thickness possess an optical transmittance ≈70%, while maintaining optical haze >95%. Due to the densely packed sheet structure with a large interfacial area, the reassembled wood film is fivefold stronger and stiffer than the delignified wood in fiber direction. Owing to a low density, the specific tensile strength and elastic modulus are as high as 282 MPa cm3 g-1 and 31 GPa cm3 g-1. A facile and highly energy efficient wood nanotechnology approach are demonstrated toward more sustainable materials and processes by directly converting delignified wood into transparent wood omitting polymeric matrix infiltration or mechanical pressing.

Covalent Organic Framework Nanoarchitectonics: Recent Advances for Precious Metal Recovery

The recovery of precious metals (PMs) from secondary resources has garnered significant attention due to environmental and economic considerations. Covalent organic frameworks (COFs) have emerged as promising adsorbents for this purpose, owing to their tunable pore size, facile functionalization, exceptional chemical stability, and large specific surface area. This review provides an overview of the latest research progress in utilizing COFs to recover PMs. Firstly, the design and synthesis strategies of chemically stable COF-based materials, including pristine COFs, functionalized COFs, and COF-based composites, are delineated. Furthermore, the application of COFs in the recovery of gold, silver, and platinum group elements is delved into, emphasizing their high adsorption capacity and selectivity as well as recycling ability. Additionally, various interaction mechanisms between COFs and PM ions are analyzed. Finally, the current challenges faced by COFs in the field of PM recovery are discussed, and potential directions for future development are proposed, including enhancing the recyclability and reusability of COF materials and realizing the high recovery of PMs from actual acidic wastewater. With the targeted development of COF-based materials, the recovery of PMs can be realized more economically and efficiently in the future.

Effective Transport Recovery of Palladium(II) from Hydrochloric Acid Solutions Using Polymer Inclusion Membrane with Tetrabutylammonium Bromide

This article reports on the extraction of palladium(II) from hydrochloric acid (HCl) solutions using polymer inclusion membranes (PIMs) containing tetrabutylammonium bromide (TBAB) as the ion carrier. The membranes were based on cellulose triacetate (CTA) as the polymer support. The main aim of this study is to determine the possibility of TBAB's application as the effective ion carrier/extractant of Pd(II) from hydrochloric acid solutions. At first, the effect of the hydrochloric acid concentration in the aqueous phase on palladium(II) extraction was investigated. Next, cellulose triacetate membranes with TBAB as the carrier were prepared and applied for the recovery of Pd(II) from HCl solutions. As a result of the investigations, the optimal composition of the receiving phase was determined to be 0.5 M thiourea in 0.1 M hydrochloric acid. The effect of the acid concentration in the source phase was investigated. The results show a linear decrease in the permeability coefficient and initial flux of palladium(II) with an increase in the hydrochloric acid concentration in the source phase. The separation of Pd(II) from Pt(IV) from the hydrochloric acid solution was also studied. The transport rate of Pd(II) was higher than Pt(IV). The separation coefficient SPd/Pt was 1.3. The results show that transport through PIMs with TBAB can be used as an effective method to recover Pd(II) from hydrochloric acid, especially at a low concentration of this acid.

Functionalized agriculture-derived biomass-based adsorbent for the continuous recovery of gold from a simulated mobile phone leachate

Electronic waste has become a global concern, as it has been steadily increasing over the years. The lack of regulation and appropriate processing facilities has rendered these wastes an environmental hazard. However, they represent excellent alternative sources of precious metals, which are highly in demand in various industries. Adsorption has been a popular method for metal removal/recovery because of several advantages, such as ease of use and low cost. In this regard, it is crucial to develop an inexpensive and functionalized adsorbent to selectively adsorb precious metals. Thus, silica, which is derived from rice husk and is abundantly present in Indonesia, was functionalized using an ionic liquid (SiRH_Im) and used for Au(III) adsorption from a simulated mobile phone leach liquor. SiRH_Im exhibited a high adsorption capacity (232.5 mg g-1). The Au(III) adsorption kinetic suitably fitted with the pseudo-second-order kinetic model. The Au(III) adsorption followed a chemisorption route that suited the monolayer model. Thomas' and Yoon-Nelson's models were well suited for the continuous Au(III) behavior. Selective recovery of Au(III) from SiRH_Im was achieved via sequential desorption. SiRH_Im also showed excellent reusability, as indicated by a negligible decrease in adsorptive performance over three cycles. The functionalization of silica derived from rice husk using an ionic liquid led to the successful creation of a solid adsorbent with a high adsorption capacity toward precious metals present in a simulated leach solution. Our results highlight the benefit of the functionalization of biomass through the immobilization of an ionic liquid toward the enhancement of its adsorption capability.

Sustainable and Selective Modern Methods of Noble Metal Recycling

Noble metals exhibit broad arrange of applications in industry and several aspects of human life which are becoming more and more prevalent in modern times. Due to their limited sources and constantly and consistently expanding demand, recycling of secondary and waste materials must accompany the traditional mineral extractions. This Minireview covers the most recent solvometallurgical developments in regeneration of Pd, Pt, Rh, Ru, Ir, Os, Ag and Au with emphasis on sustainability and selectivity. Processing-by selective oxidative dissolution, reductive precipitation, solvent extraction, co-precipitation, membrane transfer and trapping to solid media-of eligible multi-metal substrates for recycling from waste printed circuit boards to end-of-life automotive catalysts are discussed. Outlook for possible future direction for noble metal recycling is proposed with emphasis on sustainable approaches.

Removal of Copper (II), Zinc (II), Cobalt (II), and Nickel (II) Ions by PIMs Doped 2-Alkylimidazoles

Polymer inclusion membranes (PIMs) are an attractive approach to the separation of metals from an aqueous solution. This study is concerned with the use of 2-alkylimidazoles (alkyl = methyl, ethyl, propyl, butyl) as ion carriers in PIMs. It investigates the separation of copper (II), zinc (II), cobalt (II), and nickel (II) from aqueous solutions with the use of polymer inclusion membranes. PIMs are formed by casting a solution containing a carrier (extractant), a plasticizer (o-NPPE), and a base polymer such as cellulose triacetate (CTA) to form a thin, flexible, and stable film. The topics discussed include transport parameters, such as the type of carrier, initial fluxes, separation coefficients of copper in relation to other metals, as well as transport recovery of metal ions. The membrane was characterized using AFM and SEM to obtain information on its composition.