Selective recovery of platinum from spent autocatalyst solution by thiourea modified magnetic biocarbons

Optimization of Pt(II) and Pt(IV) Adsorption from a Water Solution on Biochar Originating from Honeycomb Biomass

Novel CO2- and H3PO4-modified biochars were successfully synthesized from raw honeycomb biomass. They were characterized via several instrumental techniques. The optimal Pt(II) and Pt(IV) adsorption onto the studied biochars was reached for the initial pH of 1.5 and a contact time of 5 min (Pt(II)) and 24-48 h (Pt(IV)). The highest static adsorption capacities for Pt(II) and Pt(IV) were obtained for the H3PO4-modified biochar: 47 mg g-1 and 35 mg g-1, respectively. The Freundlich model described the Pt(II) adsorption isotherms onto both materials and the Pt(IV) adsorption isotherm onto the CO2-activated material, and the Langmuir model was the best fitted to the Pt(IV) adsorption isotherm onto the H3PO4-activated biochar. The best medium for the quantitative desorption of the Pt form from the H3PO4-modified biochar was 1 mol L-1 thiourea in 1 mol L-1 HCl. The adsorption mechanism of both the studied ions onto the synthesized H3PO4-modified biochar was complex and should be further investigated. The H3PO4-modified biochar was successfully applied for the first time for Pt(IV) removal from a spent automotive catalyst leaching solution.

Stimuli-Responsive Ion Adsorbents for Sustainable Separation Applications

Stimuli-responsive ion absorbents (SRIAs) with reversible ion adsorption and desorption properties have recently attracted immense attention due to their outstanding functionalities for sustainable separation applications. Over the past decade, a series of SRIAs that respond to single or multiple external stimuli (e.g., pH, gas, temperature, light, magnetic, and voltage) have been reported to achieve excellent ion adsorption capacity and selectivity while simultaneously allowing for their reusability. In contrast to traditional adsorbents that are mainly regenerated through chemical additives, SRIAs allow for reduced chemical and even chemical-free regeneration capacities, thereby enabling environmentally friendly and energy-efficient separation technologies. In this review, we systematically summarize the materials and strategies reported to date for synthesizing single-, dual-, and multiresponsive ion adsorbents. Following a discourse on the fundamental mechanisms that govern their adsorption and desorption under various external stimuli, we provide a concise discussion of the regeneration capacity and application of these responsive ion adsorbents for sustainable water desalination, toxic ion removal, and valuable ion extract and recovery. Finally, we discuss the challenges in developing and deploying these promising multifunctional responsive ion adsorbents together with strategies to overcome these limitations and provide prospects for their future.

Targeting of platinum capture under 1+1 aqua regia using robust and recyclable polymeric polyamine resin: Adsorption performance and mechanism

The targeted capture of platinum from complex and harsh acidic digests such as those platinum-containing secondary resources is essential from the perspectives of green development. Here, a polyamine chelating resin (CMPs-PEI) with excellent selectivity and acid resistance was prepared by a nucleophilic substitution reaction using chloromethylated polystyrene as the parent and polyethyleneimine as the modifier. The experimental results revealed that the adsorbent showed excellent adsorption effect on platinum under different acidities, and its maximum adsorption capacity was up to 337 mg/g at pH 2. More impressively, a rather high capacity of 162.41 mg/g was achieved in 1 + 1 aqua regia (pH -0.7), which was much higher than other adsorbent materials under the same conditions. In addition, the recovery of platinum by CMPs-PEI in practical platinum-containing iron concentrate abatement solution was 100 %. Mechanistic studies showed that the protonated amine groups on CMPs-PEI bound PtCl₆^2- and partially reduced PtCl₄^2- by electrostatic attraction. Meanwhile, the excellent regeneration performance of CMPs-PEI indicated that it showed great potential for green and economic recovery of precious metal ions.

CO2-assisted 'Weathering' of Steel Slag-Derived Calcium Silicate Hydrate: A Generalized Strategy for Recycling Noble Metals and Constructing SiO2-Based Nanocomposites

The spent adsorbent loaded by toxic metals is a solid hazardous waste which could cause significant secondary pollution due to potential possible additional release of metal ions. Therefore, the main subject is direct reutilization of spent adsorbents which can further economically and realistically offer new features, like recycling metal adsorbed, or formation of functional SiO₂-based nanocomposites. The nanoporous structure and negative surface charges enable steel slag-derived amorphous calcium silicate hydrate (CSH) to retain effectively the incoming metal ions (e. g. Au³⁺, Ag⁺, Pd²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ce³⁺, Y³⁺, and Gd³⁺) by chemisorption. Sparked by natural carbonation 'weathering', which ultimately sequestrates atmospheric CO₂ by alkaline silicate minerals to leach calcium from mineral matrix, the decalcification reactions of metal-bearing CSH results in successful recovery of noble metals (Ag, Au, Pd) upon NaOH etching the resultant SiO₂ support. Further, SiO₂-based heterostructures, containing nanocrystalline metals (e. g. Au⁰, Ag⁰, Pd⁰, Fe⁰, Co⁰, Ni⁰, Cu⁰, and Zn⁰) or rare-earth oxides (e. g. CeO₂, Y₂O₃, and Gd₂O₃), are formed after reduction in H₂/Ar (5 vol% H₂) flow, which is also very important for the multipurpose immobilization of diverse hybrid materials on SiO₂ surface (e. g. Cu⁰-Ag⁰@SiO₂, Cu⁰-CeO₂@SiO₂, and Cu⁰-Ag⁰-CeO₂@SiO₂).

Recovery of Platinum Group Metals from Leach Solutions of Spent Catalytic Converters Using Custom-Made Resins

Platinum group metals (PGMs) play a key role in modern society as they find application in clean technologies and other high-tech equipment. Spent catalytic converters as a secondary resource contain higher PGM concentrations and the recovery of these metals via leaching is continuously being improved but efforts are also directed at the purification of individual metal ions. The study presents the recovery of PGMs, namely, rhodium (Rh), platinum (Pt) and palladium (Pd) as well as base metals, namely, zinc (Zn), nickel (Ni), iron (Fe), manganese (Mn) and chromium (Cr) using leachates from spent diesel and petrol catalytic converters. The largest amount of Pt was leached from the diesel catalytic converter while the petrol gave the highest amount of Pd when leached with aqua regia. Merrifield beads (M) were functionalized with triethylenetetramine (TETA), ethane-1,2-dithiol (SS) and bis((1H-benzimidazol-2-yl)methyl)sulfide (NSN) to form M-TETA, M-SS and M-NSN, respectively, for recovery of PGMs and base metals from the leach solutions. The adsorption and loading capacities of the PGMs and base metals were investigated using column studies at 1 M HCl concentration. The loading capacity was observed in the increasing order of Pd to be 64.93 mmol/g (M-SS), 177.07 mmol/g (M-NSN), and 192.0 mmol/g (M-TETA), respectively, from a petrol catalytic converter. The M-NSN beads also had a much higher loading capacity for Fe (489.55 mmol/g) compared to other base metals. The finding showed that functionalized Merrifield resins were effective for the simultaneous recovery of PGMs and base metals from spent catalytic converters.