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Refereed/Peer-reviewed This paper examines the time-frequency spillovers and connectedness between the major precious metals futures markets (gold, palladium, platinum, and silver), the West Texas Intermediate (WTI) oil futures, the US stock market, the US 10-year Treasury Bond (T-Bond) market, and the US dollar index. Applying Barunik and Krehlik's (2018) novel framework, the results show that spillovers across markets strengthens in the short-term, suggesting that diversification opportunities are lower in the short-term than the long-term. Furthermore, we find that the net transmitter/receiver of spillover is dependent on the frequency being analyzed, thereby indicating asymmetric spillovers among markets. Moreover, gold and silver (platinum, T-Bonds, and US dollar index) are net transmitters (receivers) of spillover regardless of the time horizon. Palladium is the net transmitter of spillover to the other markets in the short-term period (1–8 days); in contrast, in the long-term period (8–256 days), the S&P 500 index is the net transmitter of spillover. Precious metals futures, crude oil, and T-Bond assets are diversifiers for the US stock market for short-term and the long-term investments. The US dollar index is a strong hedge regardless of the time horizon and a strong (weak) safe haven asset in the short (long) term. Precious metals are a safe haven in the short-term and long-term periods. Crude oil and T-Bonds are not a safe haven for US equity investors. Finally, our result support evidence of diversification benefits and better hedging effectiveness by adding precious metals, WTI, T-Bond, and USDX to S&P500 index, which is higher in the long-term than in the short-term. WTI offers the highest hedging effectiveness, regardless the time investment horizons.

The aim of the paper is to identify unobservable factors that may significantly determine the level of gold and silver returns and to assess the risk of investment in these metals. To measure risk, the value at risk and other, less popular measures are used: the ES, MS, Rachev ratio and GlueVaR risk measure. Normal and Student’s t‑distributions are used as theoretical distributions. The results of the study show that we can identify latent factors based on observable variables that have a significant impact on the level of gold and silver returns. In addition, it was observed that the risk measures would vary depending on the period of research. It was shown that the estimates of the risk measures using Student’s t‑distribution have a lower estimation error than those based on the normal distribution. Rynki alternatywne, do których zalicza się rynek towarowy, stanowią doskonałe miejsce na zabezpieczanie lokowanych środków inwestycyjnych w sytuacji pogarszającej się koniunktury na rynkach finansowych. Szczególne zainteresowanie kierowane jest w stronę inwestycji w metale szlachetne, takie jak złoto czy srebro. Oba metale mają szerokie zastosowanie w przemyśle, jednakże dodatkowo ich wartość ukryta powiązana jest ze stosunkiem człowieka do tego rodzaju kruszców. Od dawien dawna złoto i srebro kojarzone były z majątkiem i bogactwem. Przedmiotem pracy jest identyfikacja ukrytych czynników, mogących wpływać na zmienność stóp zwrotu złota i srebra oraz ocena ryzyka inwestycji w te metale szlachetne. Zidentyfikowano dwa istotne czynniki oraz dokonano porównania ocen ryzyka za pomocą miar kwantylowych. Wyniki wskazują na istotny wpływ zidentyfikowanych czynników na zmienność stóp zwrotu złota i srebra. Zaobserwowano także różnice w poziomie ryzyka inwestycji dla tych dwóch metali.

This paper examines the volatility transmission between crude oil and four precious metals (i.e., gold, silver, platinum, and palladium) and investigates whether oil can be considered as a hedge or safe-haven asset against four precious metals. Our empirical analysis reveals several important findings. First, we determine that the volatility transmission was time-varying and that influence from the Asian crisis, the bursting of the dot-com bubble, the 2008 global financial crisis, the recent oil-price crash, and COVID-19 alternated between negative and positive values over the entire studied period. We further conclude that Brent oil is a diversifier and a weak safe haven for precious metals; and thus, that a combined portfolio composed of Brent-oil and precious-metals futures yields better hedging effectiveness. These findings indicate that oil futures are a useful investment that reduces downside risks and strengthens diversification benefits in portfolio risk management. Refereed/Peer-reviewed

Purpose The purpose of this paper is to scrutinize three different points: How safe haven properties of precious metals (gold, silver, platinum and palladium) differentiate in two recent major crises such as the Global Financial Crisis (GFC) and the COVID-19 pandemic? How safe haven properties of precious metals change by the severity and the duration of shocks? and whether precious metals have hedge properties or not in normal conditions against different stock markets. Design/methodology/approach To analyze the time-varying behavior of precious metals with respect to stock market returns, the authors used the rolling window approach. After obtaining the time-varying beta series that way, the authors regressed the beta series on different severities of stock market shocks. Findings The findings show that the number of safe haven precious metals increases in the COVID-19 pandemic period compared to the GFC. Furthermore, the number of safe haven precious metals increases as the severity of shocks increases and the duration of them extended. Finally, in the absence of an extreme market condition, only gold has strong hedge asset properties. Originality/value To the best of the authors’ knowledge, this study is the first that examines the safe haven and hedge properties of all tradable precious metals against seven major stock markets. Besides this, it presents a comparative analysis for the safe haven properties of precious metals in terms of two major crises.

In this paper, the behavior of precious metals and oil is examined using a fractionally integrated and cointegrated modeling approach. Using daily data from January 2015 to December 2020 and using both endogenous and exogenous structural breaks, we examine the behavior of the related series before and during the COVID-19 pandemic with the aim of investigating whether the degree of persistence has changed since the onset of COVID-19. We found that precious metals and oil exhibit long memory and are mean reverting regardless of the sample considered as the fractional parameter d 0.5. Both cointegration techniques alongside the parameter stability tests lend support to the existence of a persistence and stable long-run relationships among the series irrespective of the sample period considered. Attendant policy recommendations for investors and policymakers are recommended.

We assess the hedging capabilities of four prominent precious metals namely gold, palladium, platinum and silver against market risks due to epidemics and pandemics. The research objective is informed by the COVID-19 pandemic which amplifies health risks with attendant concerns for financial markets. We utilize the health-related uncertainty index developed by Baker et al. (Equity market volatility: infectious disease tracker [INFECTDISEMVTRACK], 2020) which measures uncertainty in the financial markets due to infectious diseases including the COVID-19 pandemic and construct a predictive model that accommodates the salient features of both the predictand and predictor series. Our results support the safe haven property only for gold before and during the COVID-19 pandemic. We push the analysis further for in-sample and out-of-sample forecast evaluation and find that accounting for uncertainty due to infectious diseases improves the forecast of the four precious metals relative to the benchmark model (historical average). We highlight for investors that the gold market remains the safest market among the precious metals particularly during the COVID-19 pandemic.

Electrochemical water splitting for hydrogen production has sparked intensive interests because it provides a new approach for sustainable energy resources and the avoidance of environmental problems. The precious metal‐based single atomic catalysts (PMSACs) have been widely employed in water splitting catalysis by virtue of their maximum atom utilization and unique electronic structure, which can reduce metal amounts and remain high catalytic performance simultaneously. In this review, we will summarize recent research efforts toward developing SACs based on precious metals with excellent performance for electrochemical water splitting catalysis. First, the synthesis strategies for PMSACs will be classified and introduced including high‐temperature pyrolysis, electrochemical method, photochemical reduction, wet chemistry method, etc. Then, a short description of characterization techniques for SACs will be given, which mainly involves the aberration‐corrected scanning‐transmission electron microscopy (AC‐STEM) and X‐ray absorption spectroscopy (XAS). In particular, the relationship between the electronic structure of the precious metal atomic sites and performance for water splitting will be discussed according to the theoretical and experimental results. Finally, a brief perspective will be provided to highlight the challenges and opportunities for the development of novel PMSACs suitable for electrochemical water splitting applications.

Circular economy is considered a new chance to build a more sustainable world from both the social and the economic point of view. In this Essay, the possible contribution of inorganic chemistry towards a smooth transition to circularity in inorganic materials design and production is discussed by adopting an interdisciplinary approach.

This paper presents pioneering results on the evaluation of noble metal film hetero-structures to improve some functional characteristics of carbon-based implant materials: carbon-composite material (CCM) and carbon-fiber-reinforced polyetheretherketone (CFR-PEEK). Metal-organic chemical vapor deposition (MOCVD) was successfully applied to the deposition of Ir, Pt, and PtIr films on these carriers. A noble metal layer as thin as 1 µm provided clear X-ray imaging of 1–2.5 mm thick CFR-PEEK samples. The coated and pristine CCM and CFR-PEEK samples were further surface-modified with Au and Ag nanoparticles (NPs) through MOCVD and physical vapor deposition (PVD) processes, respectively. The composition and microstructural features, the NPs sizes, and surface concentrations were determined. In vitro biological studies included tests for cytotoxicity and antibacterial properties. A series of samples were selected for subcutaneous implantation in rats (up to 3 months) and histological studies. The bimetallic PtIr-based heterostructures showed no cytotoxicity in vitro, but were less biocompatible due to a dense two-layered fibrous capsule. AuNP heterostructures on CFR-PEEK promoted cell proliferation in vitro and exhibited a strong inhibition of bacterial growth (p < 0.05) and high in vitro biocompatibility, especially Au/Ir structures. AgNP heterostructures showed a more pronounced antibacterial effect, while their in vivo biocompatibility was better than that of the pristine CFR-PEEK, but worse than that of AuNP heterostructures.

In this study, we exploit the information contained in financial innovations in precious metals for hedging the risks associated with the Asia-Pacific equities during the current pandemic. We measure financial innovations as exchange traded funds (ETFs) for gold, silver, platinum and palladium which contrast with investment in the physical precious metals since the former tracks well the prices of the latter and as well provides cost-effective alternative to invest in the markets without storage costs. Based on the optimal portfolio weights and optimal hedge ratios, we find that gold offers the best hedge (followed by silver, platinum, and palladium) against the risk associated with the Asia-Pacific equities during the COVID-19 pandemic albeit with a lower hedging effectiveness during the pandemic. Overall, including gold ETFs in an Asia-Pacific equity portfolio would provide both a valuable portfolio combination that could improve the risk-adjusted performance of the market in addition to serving as an effective hedge for equity-related risks.

The effects of the amphoteric and basic oxides alumina and lime on the phase equilibria of copper matte and silica-saturated slags were investigated at 1300 °C and $$ P_{{{\text{SO}}_{ 2} }} $$ P SO 2 = 0.1 atm in a controlled CO-CO2-SO2-Ar gas atmosphere using a high-temperature isothermal equilibration technique followed by rapid quenching. The equilibrium phase compositions were obtained by Electron Probe X-ray Microanalysis. The relationship between the copper concentration in matte and the oxygen partial pressure, iron, and sulfur in matte was quantified. The pure iron-silicate slag exhibited the highest copper loss in slag, although the addition of alumina and lime decreased its value by approximately a quarter and a half, respectively, at a matte grade of 65 wt pct Cu. In contrast, copper and sulfur were highly distributed in the matte phase, and their deportment to the matte was favored by addition of alumina and lime.

Within the framework of metal separations and solvent extraction, chloride media are among the most studied systems. Bromide and iodide media have received much less attention, but can allow a diff...

This paper investigates the tail dependence dynamics and asymmetric risk spillovers between the futures of four important precious metals (gold, silver, platinum, and palladium) and seven leading currencies (EUR, GBP, JPY, CAD, AUD, CHF, and CNY) before and during the COVID-19 crisis using the time-varying-parameter copula and the conditional Value-at-Risk (CoVaR) method. The results show the symmetric dependence between currencies and precious metals before the COVID-19 crisis. In contrast, we show negative and positive tail asymmetric dependences during the pandemic crisis. The COVID-19 crisis significantly amplifies the magnitude of spillover effects among the studied markets where the AUD currency exhibits the largest transmission and reception of downside and upside spillover to/from most precious metals before and during the pandemic crisis. Currency investors and portfolio managers could use the obtained results to better hedge and manage their investment positions when markets are affected by health crises. info:eu-repo/semantics/publishedVersion

Gold is a scarce element in the Earth’s crust but indispensable in modern electronic devices. New, sustainable methods of gold recycling are essential to meet the growing eco-social demand of gold. Here, we describe a simple, inexpensive, and environmentally benign dissolution of gold under mild conditions. Gold dissolves quantitatively in ethanol using 2-mercaptobenzimidazole as a ligand in the presence of a catalytic amount of iodine. Mechanistically, the dissolution of gold begins when I$_2$ oxidizes Au$^0$ and forms a [Au$^I$I$_2$]$^−$ species, which undergoes subsequent ligand-exchange reactions and forms a stable bis-ligand Au$^I$ complex. H$_2$O$_2$ oxidizes free iodide and regenerated I$_2$ returns back to the catalytic cycle. Addition of a reductant to the reaction mixture precipitates gold quantitatively and partially regenerates the ligand. We anticipate our work will open a new pathway to more sustainable metal recycling with the utilization of just catalytic amounts of reagents and green solvents.

С начала возникновения мировой торговли драгоценные металлы играли центральную роль в международных расчетах. Национальные валюты, прямо или косвенно, были привязаны к ним. Во второй половине XX века казалось, что человечество избавилось от необходимости такой привязки. Нарастающие противоречия мировой торговли требуют пересмотра всей системы международных финансов и возврата к учету стоимости золота и других драгоценных металлов для формирования новой систему устойчивой международной торговли., Since the beginning of world trade, precious metals have played a central role in international settlements. National currencies, directly or indirectly, were tied to them. In the second half of the XX century, it seemed that humanity got rid of the need for such a binding. The growing contradictions in world trade require a revision of the entire system of international finance and a return to accounting for the value of gold and other precious metals to form a new system of sustainable international trade.

Авторы в статье указывают перечень судебных экспертиз, проводимых по таким предметам хищения, как золотые изделия и бижутерия. Приведенные в тексте экспертизы необходимы для отнесения рассматриваемых предметов хищения к драгоценным металлам и камням, а также для выяснения размера вреда, причиненного преступлением., The authors of the article indicate the list of forensic examinations conducted on such items of theft as gold products and jewelry. The examinations given in the text are necessary to classify the items of theft under consideration as precious metals and stones, as well as to determine the amount of damage caused by the crime.

Ho Chi Minh (HCM) City is the most important urban region of Vietnam, Southeast Asia. In recent times, the quantity of electronic waste (e-waste) has been growing by several thousand tonnes every year. In this research, some of the existing and developing technologies being employed for the recycling of e-waste have been reviewed. Accordingly, the paper has been divided into three sections namely, e-waste treatment technologies in Ho Chi Minh City, the effect of heavy metals on human health and the extraction of metals from e-waste using pyrolysis, hydrometallurgy, bioleaching, mechanical, and air classifier methods, respectively. The extraction of precious metals and heavy metals such as Cd, Cr, Pb, Hg, Cu, Se, and Zn from e-waste can be hazardous to human health. For example, lead causes hazards to the central and peripheral nervous systems, blood system and kidneys; copper causes liver damage; chronic exposure to cadmium ends up causing lung cancer and kidney damage, and mercury can cause brain damage. Thus, this study examines the key findings of many research and review articles published in the field of e-waste management and the health impacts of metal pollution., The authors would like to thank Van Lang University, Vietnam for funding this work. E.R. Rene expresses appreciation to IHE Delft Institute of Water Education (the Netherlands) for providing infrastructural facilities and staff time support to collaborate on this research.

Colloidal syntheses of nanoparticles (NPs) are one of the preferred approaches to prepare precious metal catalysts. Unfortunately, most colloidal syntheses developed require stabilizing agents to avoid NP agglomeration and/or control NP size and morphology. While these surfactants can bring positive features, they typically block catalytically active sites on the NP surface. As a consequence, these additives often need to be removed by energy and/or time consuming steps, at the risk of complicating the synthesis, introducing irreproducibility and negatively altering the structure and properties of the prepared catalysts. Fortunately, several surfactant-free colloidal syntheses have been reported and are being developed. This Mini Review addresses the challenges in defining a surfactant-free colloidal synthesis of NPs and survey established and emerging strategies to obtain surfactant-free colloidal precious metal NPs. A focus is given to approaches that show promising features to bridge the gap between fundamental and applied research towards industrial applications.

Polyextremophilic red algae, which belong to the class Cyanidiophyceae, are adapted to live in geothermal and volcanic sites. These sites often have very high concentrations of heavy and precious metals. In this study, we assessed the capacity of three strains of Galdieria (G. maxima, G. sulphuraria, and G. phlegrea) and one strain of Cyanidiumcaldarium to tolerate different concentrations of precious metals, such as palladium (Cl4K2Pd) and gold (AuCl4K) by monitoring algal growths in cultures exposed to metals, and we investigated the algae potential oxidative stress induced by the metals. This work provides further understanding of metals responses in the Cyanidiophyceae, as this taxonomic class is developed as a biological refinement tool.

It is frequently discussed in the literature that the correlation between low-correlation assets under ordinary market conditions may increase during crisis periods. To contribute to the ongoing debates, this paper empirically examines risk transmission between oil and precious metal markets induced by the COVID-19 pandemic using the DCC-GARCH model. The findings reveal evidence of a significant risk transmission between oil prices and precious metal prices, particularly during the onset of the COVID-19 pandemic. The findings point out that the negative relationship between oil and all precious metals returns in the pre-COVID-19 period has changed with the effect of the pandemic. In this process, it is revealed that the negative relationship between oil and gold has strengthened, but the negative relationship between oil and silver has weakened. In addition, the correlations between oil and platinum and palladium turn positive. The empirical findings imply that investors and portfolio managers seeking portfolio diversification and hedging opportunities in a high-risk environment such as the COVID-19 pandemic should consider gold and silver assets for investment.

Manufacturing of nickel by hydrometallurgical technology at Harjavalta plant (Finland) had been caring out since 1960 by Outokumpu. Later on, the technology was modernized and currently Harjavalta plant belongs to PJSC “MMC Nornickel”. The plant is specializing on processing of copper-nickel mattes, converter mattes and by-products, originated from “Kola MMC” and third-party enterprises. Currently, the technology for the materials processing includes oxidative autoclave leaching (POX), solvent extraction, nickel electrowinning as well as solutions purification and metal salts obtaining stages. Selective POX produces nickel solution and copper cake (Cu-cake), which is a valuable by-product of the plant. The article presents the results on investigating the possibility of Cu-cake processing using POX in sulfate media at different temperature regimes. Low-temperature POX (105 oC) allowed to extract more than 95% Cu into solution within 30-60 min, while the dominating compound of solid residue was elemental sulfur; mass output of the solid residue was 20-25%. High-temperature POX (190 oC) allowed to extract more than 98% Cu in 60-80 min; mass output of the solid residue was 2.5-5%, which significantly increased a concentration of precious metals. Mid-temperature POX (150 oC) is characterized by increased duration. Copper extraction level of 95-98% is achieved at least after 120-180 minutes of leaching. Mass output of the solid residue was 6-10%. A detailed analysis of Cu-cake and the resulting products is provided. The behavior of precious metals was considered.

https://revistas.unicartagena.edu.co/index.php/eltallerdelahistoria/article/view/2412 En este artículo se analizarán distintos aspectos del tráfico ultramarino del complejo portuario rioplatense, en primer lugar, la circulación de navíos, sus destinos y banderas. En segundo lugar, profundizaremos en la salida de cueros, su dinámica y destinos. En tercero y último, abordaremos la salida de metales preciosos. Para ello trabajamos con registros de navíos, notas y guías de aduana. El objetivo es profundizar en el análisis de la dinámica económica regional a partir de su comercio ultramarino.

As a result of the innovative solutions found due to the joint efforts of Russian and Finnish researchers, the recovery of nonferrous and precious metals in Norilsk Nickel Harjavalta was significantly increased (%): the recovery of Ni was increased to 98.7; that of Cu, to 99.5; Pt, to 99.6; and Pd to 99.6. Simultaneously, a copper cake (one of the main commercial products) of an improved composition, namely, (%) 57–62 Cu

This paper aims at analyzing nonlinear dependence between fractionally integrated, chaotic precious metal and oil prices and volatilities. With this respect, the Markov regime-switching fractionally integrated asymmetric power versions of generalized autoregressive conditional volatility copula (MS-FIAPGARCH-copula) method are further extended to multi-layer perceptron (MLP)-based neural networks copula (MS-FIAPGARCH-MLP-copula). The models are utilized for modeling dependence between daily oil, copper, gold, platinum and silver prices, covering a period from 1 January 1990–25 March 2022. Kolmogorov and Shannon entropy and the largest Lyapunov exponents reveal uncertainty and chaos. Empirical findings show that: i. neural network-augmented nonlinear MS-FIAPGARCH-MLP-copula displayed significant gains in terms of forecasts; ii. asymmetric and nonlinear processes are modeled effectively with the proposed model, iii. important insights are derived with the proposed method, which highlight nonlinear tail dependence. Results suggest, given long memory and chaotic structures, that policy interventions must be kept at lowest levels.

The Kaldor furnace smelting process is currently the mainstream process for treating copper anode slime, but the existence of copper, tellurium and other impurities has adverse effects on the recovery of gold and silver during the Kaldor furnace smelting stage. Therefore, it is necessary to pretreat the copper anode slime to remove these impurities before Kaldor furnace reduction smelting. However, the current pretreatment process of copper anode slime generally has the problem of low removal efficiency of copper and tellurium, and little research on the occurrence state of main metals in copper anode slime. Therefore, this study quantitatively determined the phase composition of Cu, Te, Pb, Bi, As, Sb, Se, Ag and Au, and hydrogen peroxide was introduced to enhance the leaching of impurities. The leaching behavior of each metal in copper anode slime was investigated in detail. The results demonstrate that Cu and Te in the copper anode slime mainly exist in the form of CuO and CuSO4 and Te and AuTe2, respectively. More than 99% of the Cu and 97% of the Te were leached out using 250 g/L H2SO4 and 28.8 g/L H2O2 with a leaching pressure of 0.8 MPa at 150 °C for 2 h, while the leaching of Au and Ag was both < 0.03%. The removal of Cu and Te and the enrichment of precious metals were achieved. This study provides a rich theoretical reference for the optimization of the Kaldor furnace process.

This paper investigates the price stability properties of precious metals during the 1997 Asian Financial Crisis, 2007–2008 Global Financial Crisis, and 2010 Eurozone Crisis. To analyse the interaction between precious metal prices and the US stock market stock performances, we use the ICSS algorithm along with the GARCH model to evaluate how the number of rapid changes in volatility of precious metals has been reduced. The results suggest gold is the most stable of the precious metals. However, silver, platinum, and palladium showed positive price correlation when the US Dow Jones market was unstable. These results imply that: (1) the correlation among stocks market returns has little to no significant impact on the price movement of precious metals, but the US Dow Jones has some influence on precious metal markets except gold, which means investors can reap this benefit from diversification; (2) investors can systematically increase their portfolio returns by going short with the gold investments with low price co-movement and long on silver, platinum, and palladium with high co-movement with stock prices.

The paper examines the frequency-based interlinkages between stock indices and precious metals at extreme and median quantiles. It employs the quantile cross-spectral approach (Baruník and Kley, 2019) and the novel frequency quantile connectedness analysis (Chatziantoniou et al., 2021) to a sample of stocks and precious metals returns. The results show that the interdependence between equity indices and precious metals markets is contingent on the state of the market (bear, bull, or normal) and the horizon of frequency domains. Of all precious metals, the diversification benefits from gold, followed by silver, are consistently the highest for SP500 and STOXX50 and the least with palladium in most cases. The same holds when we investigate the diversification potential of precious metals for industrial sectors in the US and UK. A quantile frequency connectedness approach reveals that the diversification potential of precious metals diminishes in the long frequency horizon as coherence with stock indices becomes highly positive. The connectedness between stock indices and precious metals is high during market extremities but dampens as the market attains stability. At the same time, connectedness increases during periods of financial turmoil across all frequencies. We also document a change in the diversification role of precious metals during COVID-19. Refereed/Peer-reviewed

The successful study, understanding, optimization, and ultimately scaling up of electroactive and stable electrodes strongly rely on the careful design and preparation of electrocatalytic materials. In particular, precious metal nanoparticles are key electrocatalysts for a wide range of reactions. Colloidal syntheses offer several advantages to develop precious metal nanoparticles but unfortunately often require capping agents to stabilize the nanoparticles. These ligands or surfactants often block the surface active sites and need to be removed by time and/or energy demanding steps. These extra steps potentially (unnecessarily) complicate studies, might impair reproducibility and limit a direct transfer of fundamental breakthroughs to real-life applications. Fortunately, a range of surfactant-free syntheses have been reported and are well-suited to develop electrocatalysts with improved activity. Surfactant-free syntheses also bear promising features towards high-throughput screening of multi-metallic nanomaterials to explore new concepts in electrode design.

In this paper we investigate cross-commodity futures markets connectedness over different nearest-to-maturities. We thus implement time and time-frequency estimations for two constructed baskets of commodities, classified based on common delivery months. Using daily data spanning the period 1995-2020, we provide a set of stylized facts on the extent to which commodity markets are integrated or segmented. More specifically, our results show that the total connectedness is broadly insensitive to maturity. However, after 2008 financial crisis, the connectedness among commodity futures prices increases when the maturity increases. Furthermore, the overall connectedness amplifies during crises periods compared to tranquil periods. Moreover, certain pairwise markets are comparatively highly linked such as crude oil and heating oil, wheat and corn, corn and soybean, and soybean and soybean oil. The results also demonstrate that crude oil and heating oil are net transmitters all the time and across maturities, while natural gas, gold, and wheat are net receivers all the time and across maturities. More interestingly, the frequency decomposition reveals that most of periods of high total connectedness are driven mostly by high frequency components, which may indicate that commodity markets process information rapidly, except for the COVID-19 crisis period where total connectedness has been driven by lower frequency components.

This paper provides a listing of the ships and cargoes of goods that arrived in the northwest Spanish region of Galicia between 1743 and 1749. The main source is the correspondence between the French Consul in the Spanish seaport of Corunna and his superiors, kept in the Archives Nationales (Paris). Based on this information, global amounts of bullion arriving in the peninsula at the time are reassessed and presented alongside an interpretation of the mechanisms and key players which typified the “Galician phase” of precious metal imports from America to Spain. En este estudio se facilita la nómina de buques y cargamentos de caudales que arribaron a las costas gallegas entre 1743 y 1749 utilizando como fuente privilegiada la correspondencia del cónsul francés destinado en Galicia, y radicado en el puerto de A Coruña, que se conserva en los Archives Nationales (París). A partir de esta información, se realizan varias consideraciones sobre las series globales de llegadas de caudales americanos durante el periodo, así como sobre la interpretación de los mecanismos y personajes que participaron en esta «fase galaica» de los metales preciosos.

настоящей статье рассматриваются обязательства лица,имеющее намерение произвести вывоз с территории Республики Казахстансырьевых товаров, содержащих драгоценные металлы с территории РеспубликиКазахстан, в страны, входящие в Евразийский экономический союз., This article discusses the obligations of a person who intends to exportfrom the territory of the Republic of Kazakhstan of raw materials containing precious metals from the territory of the Republic of Kazakhstan to countries belonging to the Eurasian Economic Union.

Orientadores: Melissa Gurgel Adeodato Vieira, Meuris Gurgel Carlos da Silva Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química Resumo: Diante de um cenário de alta demanda, baixa disponibilidade e alto valor econômico dos metais preciosos, a recuperação destes compostos de efluentes é de grande interesse econômico e ambiental. O desenvolvimento de adsorventes alternativos é promissor para esta finalidade. Portanto, neste projeto foram desenvolvidos dois novos bioadsorventes, de baixa solubilidade em meio aquoso, para bioadsorção de íons metálicos nobres: partículas de sericina e alginato reticuladas quimicamente com proantocianidinas (SAPAS3) ou partículas de sericina e alginato reticuladas quimicamente com álcool polivinílico (SAPVA1). Dentre as proporções avaliadas, o processo de reticulação química da blenda de sericina (2,5% m/V) e alginato (2,0% m/V) com PAS (2,5% m/V) ou PVA (0,5% m/V) proporcionou a obtenção de partículas com baixa solubilidade em meio aquoso (3,56 ± 0,21% para as SAPAS3 e 3,74 ± 0,05% para a SAPVA1). Estas partículas apresentaram alta afinidade pelos íons metálicos nobres ouro (99,6 % para as SAPAS3 e 96,2 % para as SAPVA1), paládio (88,3% para SAPAS3 e 95,6% para SAPVA1) e platina (67,9 % para SAPAS3 e 70,6 % para SAPVA1) e baixa afinidade pelo íon metálico prata (6,6 % para SAPAS3 e 12,9 % para SAPVA1). A cinética, o equilíbrio e a fluidodinâmica de bioadsorção de ouro por SAPAS3 (sistema SAPAS3/Ouro) foi avaliada. O ajuste de modelos cinéticos mostrou que este processo segue uma cinética de pseudoprimeira ordem e é governado pela difusão externa. O estudo de equilíbrio mostrou que a capacidade máxima de adsorção de ouro foi de 1,0211 mmol/g a 30 oC. Os dados de equilíbrio foram bem descritos pelos modelos de Langmuir e Freundlich (10 oC) e pelo modelo de Dubinin-Raduskevich (25 e 30 oC). As grandezas termodinâmicas mostraram que houve um aumento da variação de entropia ('delta'S= +302,67 J/mol.K) e que o processo de bioadsorção de ouro em SAPAS3 é de natureza endotérmica ('delta'H= +78,20 kJ/mol) e espontânea ('delta'G = -7,28; -13,04 e -12,78 kJ/mol para as temperaturas de 10, 25 e 30 oC, respectivamente). Dentre os eluentes testados para dessorção de ouro, a solução de tiouréia (0,5M)/ácido clorídrico (2M) foi a que resultou em maior percentual de recuperação (84,389 ± 2,103 %). Com relação à capacidade útil e a porcentagem de remoção de ouro até o ponto de ruptura, observou-se que maiores valores para estes parâmetros (qu = 0,106 mmol/g e REMb (%) = 98,394 %) foram obtidos para a condição em que foi empregada a menor vazão e a menor concentração inicial de ouro (Q=0,40 mL/min e C=0,27 mmol/L). O modelo matemático de Yan e colaboradores foi o que melhor se ajustou aos dados experimentais de todas as curvas de ruptura. O teste de dessorção em sistema contínuo resultou em uma recuperação de ouro de 24,98 e 63,13 % após o primeiro e segundo ciclo de dessorção, respectivamente. Os espectros de FTIR sugeriram o envolvimento dos grupos funcionais hidroxila e amida I no processo de bioadsorção de ouro e o mecanismo proposto envolve as seguintes etapas: interação eletrostática de atração entre o íon AuCl4- e a superfície das SAPAS3 carregada positivamente e redução no estado de oxidação do íon de ouro de Au(III) para Au(0). A presença de ouro metálico na superfície das SAPAS3 após a bioadsorção foi confirmada pelas técnicas de difração de raios X e espectroscopia de fotoelétrons excitados por raios X Abstract: In a scenario of high demand, low availability and high economic value, the recovery of precious metals from wastewater is economically and environmentalally attractive. The development of novel alternative biosorbents is promising for this purpose. Therefore, two low water soluble biosorbents were successfully developed in this study for precious metal removal from aqueous media: sericin and alginate particles chemically crosslinked by proantocyanidins (SAPAS3) and sericin, alginate particles chemically crosslinked by polyvinyl alcohol (SAPVA1). Among the evaluated proportions, sericin (2.5% m / V) and alginate (2.0% m / V) blend chemically crosslinked with PAS (2.5% m / V) or PVA 5% m / V) provided particles with the lowest water solubility (3.56 ± 0.21% for SAPAS3 and 3.74 ± 0.05% for SAPVA1). These particles presented high affinity for gold (99.6% for SAPAS3 and 96.2% for SAPVA1), palladium (88.3% for SAPAS3 and 95.6% for SAPVA1) and platinum ions (67.9% % for SAPAS3 and 70.6% for SAPVA1) and low affinity for silver metal (6.6% for SAPAS3 and 12.9% for SAPVA1). Kinetics, equilibrium and fluid dynamics of gold biosorption by SAPAS3 (SAPAS3/Gold system) was evaluated. Kinetic models adjustment to experimental data showed that this process follows a pseudo first order kinetics and is governed by external diffusion. The equilibrium study showed that the maximum adsorption capacity for gold was 1.0211 mmol/g at 30 oC. Equilibrium data were well described by Langmuir and Freundlich models (10 oC) and by Dubinin-Raduskevich model (25 and 30 oC).The estimation of thermodynamic parameters showed that there was an increase in the entropy change ('delta'S = +302.67 J/mol.K) and that gold biosorption process is endothermic ('delta'H = +78.20 kJ/mol) and spontaneous ('delta'G = -7.28, -13.04 and -12.78 kJ/mol for 10, 25 and 30oC, respectively). Among all eluents tested, the solution of thiourea (0.5M)/hydrochloric acid (2M) resulted in higher gold recovery percentage (84.389 ± 2.103%). Regarding the useful capacity and the gold removal percentage until the breakthrough point, higher values for these parameters (qu = 0.106 mmol/g and REMb (%) = 98.394%) were obtained for the condition employing the lowest flow rate and the lowest gold inicial concentration (Q = 0.40 mL/min and C = 0.27 mmol/L). Yan model best described all breaktrough curves. The desorption of gold with thiourea (0.5M)/hydrochloric acid (2M) in continuous operation resulted in a recovery of 24.98 amd 63.13 % for the first and second desoption cycle, respectively. FTIR spectra suggested the involvement of hydroxyl and amide I functional groups in gold biosorption process and the proposed mechanism involves the following steps: electrostatic attraction interaction between the AuCl4- ion and the positively charged surface of SAPAS3 followed by gold reduction from Au(III) to Au(0). The presence of metallic gold on SAPAS3 surface after biosorption was confirmed by both the X-ray diffraction technique and X-ray photoelectron spectroscopy Mestrado Engenharia Química Mestra em Engenharia Química CNPQ 132470/2017-9 FAPESP 2017/18236-1

In this paper, a new core-shell nanostructured magnetic bio-based composite was prepared by immobilizing persimmon tannin (PT) onto Fe3O4@SiO2 microspheres, and the as designed Fe3O4@SiO2@PT was utilized for adsorptive recovery of Au(III) and Pd(II). The preparation, morphology, composition and magnetic property of Fe3O4@SiO2@PT were characterized. Adsorption parameters of Fe3O4@SiO2@PT towards Au(III) and Pd(II) including initial pH, reaction time, initial concentration of metal ions, effect of acidity and interference of coexisting metal ions were investigated. It is sufficiently confirmed that silica was coated on Fe3O4 and persimmon tannin was immobilized on aminated Fe3O4@SiO2. The thickness of silica and loaded persimmon tannin are around 18 nm and 14 nm, respectively. With only 1.00 wt% of persimmon tannin, however, the maximum adsorption capacities of Fe3O4@SiO2@PT for Au(III) and Pd(II) were as high as 917.43 and 196.46 mg·g−1, respectively. In addition, after adsorption of Au(III) and Pd(II), the magnetization saturation values (Ms) of Fe3O4@SiO2@PT were high enough to guarantee efficient magnetic seperation. Metallic gold could be facilely recovered from wastewaters containing Au(III)., This research was funded by Hubei Collaborative Innovation Center for the Characteristic Resources Exploitation of Dabie Mountains (2015TD01), the Fundamental Research Funds for the Central University (52902-0900202542) and Scientific Research Project of Hubei Provincial Department of Education (D20174302).

The rapid development of light-emitting-diode (LED) technology is attributed to its superiority over light sources of earlier generations. Although LED lamps, compared to compact fluorescent lamps, are considered less harmful to the environment, there is still no efficient solution to deal with them at the end of their lifecycle. The first part of the study provides a detailed characterisation of LED lamps, focusing on their most interesting component: the LED module. LED packages attached to the module are highly enriched with Ga, In, Pd, Ag, Au, Sr, Y, Ce, Eu, Gd, and Lu, with the content of each element varying greatly depending on the LED technology. In the second part of this research, two new approaches for liberation and concentration of valuable components from LED modules are presented and compared: a chemical route and a thermal route. The chemical treatment leads to a highly selective separation of LED chips and encapsulation. Enrichment factors up to about 125 are achieved, and a concentrate is obtained containing approximately 14 wt% of the aforementioned valuable components. However, the process requires aromatic solvents, which are viewed as toxic. The thermal treatment results in separation of the aluminium heat sink from all other components of the LED module. Enrichment is approximately ten times lower, but the approach is technically feasible.

In this study the relation between stock markets and precious metals during first wave of Covid-19 pandemic are investigated. We use a wavelet-based quantile procedure to investigate correlation between major stock markets of emerging countries (BRIC) and the United States. Our procedure reveals that precious metals offer market diversification opportunities during the period under consideration. In particular, it is found the gold, silver, platinum, and palladium, all serve as safe-haven assets during periods of market distress across short, medium and long investment horizons.

金沢大学理工研究域物質化学系, End-of-life electrical and electronic equipment is the potential secondary resource for economically-viable precious metals (PMs), e.g., gold (Au), palladium (Pd), or platinum (Pt). The hydrometallurgical processes produce acidic leachates during the recovery of PMs from waste sources, while the selective recovery of Au, Pd, or Pt from such a matrix is challenging either due to the chemical similarities of elements or complexities in the sources and matrices. A total of nine solid-phase extraction (SPE) systems, all claimed to designed for separation of PMs from complex matrices, was evaluated at varying solution pH (≤2 to 10) based on the selectivity towards Au, Pd, or Pt. The observation was used to develop a technique for selective Au, Pd, or Pt separation from acidic waste solutions using a macrocycle-equipped SPE. The feed solution flow-rates, eluent-type or compositions has been optimized to achieve maximum separation efficiency of the target analytes. The relative affinity of the macrocycles in solid-phase towards the ions (Pd > Au > Pt) is the core phenomenon of the proposed technique, and the host-guest type interaction is expected to be more stable than the resin-based separation processes. Furthermore, application of the macrocycle-equipped SPE system is advantageous regarding economics as it minimizes the impact of coexisting ions in the matrix and provides unaltered separation performance for several loading-elution cycles. © 2018 Elsevier B.V., Embargo Period 12 months

The current state of the mineral resource base of gold, silver, platinum and palladium for different geological and industrial types of deposits has been shown. For each of the given metals reserves, probable reserves and allocated fund of deposits in Russia have been given. For all bank precious metals volumes of the market offers have been given. Special attention has been paid to the use of the metals both in the world and in Russia. In the practice of market relations, the demand for precious metals can be divided into two types: fabrication (industrial) and hoarding (investment). Precious metals are used in jewelry, electronic, glass, nuclear, pharmaceutical, chemical, petrochemical and other industries. They find their application in medicine and biomedicine, automotive, microelectronics, aerospace instrument making, the manufacturing of lasers and nuclear tests. It has been noted that in our country a great disadvantage is the weak industrial use of precious metals.

The utilisation of sunlight as an abundant and renewable resource has motivated the development of sustainable photocatalysts that can collectively harvest visible light. However, the bottleneck in utilising the low energy photons has led to the discovery of plasmonic photocatalysts. The presence of noble metal on the plasmonic photocatalyst enables the harvesting of visible light through the unique characteristic features of the noble metal nanomaterials. Moreover, the formation of interfaces between noble metal particles and semiconductor materials further results in the formation of a Schottky junction. Thereby, the plasmonic characteristics have opened up a new direction in promoting an alternative path that can be of value to the society through sustainable development derived through energy available for all for diverse applications. We have comprehensively prepared this review to specifically focus on fundamental insights into plasmonic photocatalysts, various synthesis routes, together with their strengths and weaknesses, and the interaction of the plasmonic photocatalyst with pollutants as well as the role of active radical generation and identification. The review ends with a pinnacle insight into future perspectives regarding realistic applications of plasmonic photocatalysts. © 2018 Leong et al.

Lack of intrinsic value, hybrid nature of commodities and recent financialization of commodity markets make of understanding precious metals price moves complicated. Predicting future development of precious metals market can be more feasible if we discover what drives these markets and describe nature of the drivers. The aim of the paper is to explain metal price movements by assessing an impact of multiple economic and financial factors. Based on the literature review we study 8 possible macroeconomic and financial drivers. The data are collected from Bloomberg. We use mixed-data-sampling methodology that enables me to study drivers of various frequencies (daily and monthly) simultaneously in a single model. Results show that the interest rate, the exchange rate, stock levels, stock index returns and crude oil returns are generally significant to drive precious metal markets. The stock index has the most significant impact on the metals returns that is negative. Furthermore, the results divide precious metals into two groups with gold and silver on the one hand and platinum and palladium on the other. The first group is worse explained by considered drivers. Moreover, the interest rate does not have any impact on the price development of gold and silver and crude oil returns influence the pair negatively, contrary to the second pair of platinum and palladium.

The subject of investigations were rodingites, whose outcrops were recently found inTaukha terrane of the Sikhote-Alin. The contents of the rock-forming oxides in rodingites were determined using the methods of chemical analysis as well as the gravimetry (SiO2, H2O, and Loi) and atomic-emission spectrometry with the induction-bound plasma at the iCAP 6500Duo spectrometer (Thermo Scientific Corporation, USA) (other oxides). The contents of the secondary elements were determined with the method of mass-spectrometry with the induction-bound plasma at the Agielent 7500 с spectrometer (Agielent Technologies, USA). Analyses of minerals were done using the JXA8100 microanalyser with three wave spectrometers and the INCAx-sight power-dispersion spectrometer. The contents of precious metals were determined with the atomic-absorption method. The paper presents the results of investigations of the geological conditions of occurrence, petrochemistry, geochemistry, and mineralogy of rodingites and the Au-Pd-Pt mineralization in them. The rock-forming minerals of rodingites of the Sikhote-Alin’ are pyroxene, garnet, vesuvian, epidote, prehnite, amphibole, chlorite, plagioclase, potassium-feldspar, apatite, zircon, titanite, and others. In rodingites of the Sikhote-Alin’ there were found the relatively high contents of Au, Ag, Pt, and Pd and the typical of such rocks “copper gold” and native forms and intermetallic compounds of diverse metals. The investigations carried out allowed the substantiation of the conclusion about the genetic relation of rodingites with the Paleocene ultrabasic-intermediate and alkaline-subalkaline complex of the Sikhote-Alin’. The rodingites were formed by metasomatic way on the basic and ultrabasic rocks of the vent and intrusive phases. They have preserved some geochemical characteristics of protoliths, in which they clearly differ from skarns with the boron, polymetal, and iron mineralization of the Dalnegorsky and Olginsky ore districts and from the contact-metamorphosed Triassic metal-bearing sediments of the Sikhote-Alin’. The Paleocene magmatic complex of the Sikhote-Alin’ is of a special interest because with it the precious-metal mineralization is genetically related that is localized not only in rodingites but also in other rocks of the Paleocene explosive structures and in the alluvium of the springs draining them.

In this paper we model the dynamics of 100 years long monthly price series of eight non-ferrous and precious metals. Applying the state space framework we impose and identify two common factors related to non-ferrous and precious metals, respectively, which exhibit quite distinct autoregressive dynamics. The preferred two common factor specifications outperform single common factor approaches which are usually used in the current literature. Furthermore, we provide interpretation for the extracted common factors by investigating their exposure to the major macroeconomic fundamentals.

This paper investigates the relationship between white precious metals and gold, oil and global equity by means of spillovers and volatility transmission. Relying on the recently introduced ETFs, this study is the first to analyse return spillovers derived from an E-GARCH model and to take into account frequency dynamics to understand changes in connectedness across periods of time. Results uncover numerous channels of return transmission across the selected ETF markets over the last 10 years and highlight the role of gold ETFs as the most influential market in the sample. Furthermore, our work provides insights into the characteristics of white precious metal markets using a hidden semi-Markov model. Finally, we argue that even though silver and platinum have gained more importance as investment assets over the last few years, palladium still very much remains an industrial metal.

The basalt-hosted Semenov-2 hydrothermal field on the Mid-Atlantic Ridge is host to a rather unique Cu-Zn– rich massive sulfide deposit, which is characterized by high Au (up to 188 ppm, average 61 ppm, median 45 ppm) and Ag (up to 1,878 ppm, average 490 ppm, median 250 ppm) contents. The largest proportion of visible gold is associated with abundant opal-A, which precipitated after a first generation of Cu, Fe, and Zn sulfides and before a second generation of Fe and Cu sulfides. Only rare native gold grains were found in earlier sulfides. Fluid inclusions in opal-A associated with native gold indicate precipitation at 300° ± 40°C from fluids of salinity higher than that of seawater (3.5–6.8 wt % NaCl equiv). According to laser ablation-inductively coupled plasma-mass spectrometry analyses, invisible gold is concentrated in secondary covellite (23–227 ppm) rather than in the primary sulfides ( 1,000 ppm) than all other sulfides (1 are more consistent with a mafic signature. Thermodynamic modeling of hydrothermal fluids produced by reactions between various proportions of seawater and basalt or peridotite at 350°C shows that mineral assemblages broadly similar to those of the Semenov-2 deposit can precipitate from fluids produced in a mafic environment, but that Au and Ag minerals are not predicted to precipitate from such fluids over a wide temperature range. These results suggest that an additional contribution to the hydrothermal system is required in order to achieve saturation in precious metals. A magmatic input is suggested by the occurrence of plagiogranites and tonalites dredged on sea floor in the Semenov area, which could be a potential source of Au-rich magmatic fluids, and by mineralogical and geochemical similarities with magma-related, low- to intermediate-sulfidation epithermal systems, namely high Au and Ag grades, high Au/(Cu + Zn + Pb) and Au/Ag ratios, and presence of Ag, Bi, and Te minerals. The likely crucial role of silicic melts in producing high Au and Ag grades suggests that exploration for precious metal-rich, volcanic-hosted massive sulfide deposits should be primarily directed to sites in which evolved igneous rocks occur on sea floor. Both in modern and ancient mafic-hosted deposits, zones characterized by abundant deposition of silica could be good clues to the presence of significant gold.

The rapidly increasing demand for technologies aiming to resolve challenges of separations and environmental protection causes a sharp increase in the demand for ion exchange (IX) and chelating polymers. These unique materials can offer target-selective adsorption properties vital for the removal or recovery of harmful and precious materials, where trace concentrations thereof make other techniques insufficient. Hence, recent achievements in syntheses of IX and chelating resins designed and developed in our research group are discussed within this mini-review. The aim of the present work is to reveal that, due to the diversified and unique physiochemical characteristics of the proposed materials, they are not limited to traditional separation techniques and could be used in multifunctional areas of applications, including catalysis, heat management, and biomedicine.

International audience; This paper examines and compares financial market reaction and recovery of four broad classes of financial assets – equity indexes, precious metals, 10-year benchmark bonds and cryptocurrencies, to the COVID-19 pandemic. The data set comprises daily observations of close prices in the selected markets from 17-04-2018 to 20-06-2021. Using the Yang and Zhao (2020) and Koenker and Xiao (2004) quantile unit-root tests for return persistence, we find heterogeneity in reactions and recovery patterns not only across asset classes, but also within them. Specifically, we find strong potential for mean reversion in equity markets even at high levels of shocks. While gold offers limited mean reversion, platinum shows very strong resistance to the COVID. Government bonds show small declines in value to the COVID in addition to high persistence. Cryptocurrencies, as a group, turn out to be the riskiest in the long-term, with more than a 50% decline in value coupled with high degrees of persistence. Our results raise questions as to the safe haven characteristics of the newly-popular Bitcoin. Our findings are useful for policy makers and investors through a better understanding of differences in the potential for mean reversion provided by different asset classes.

To study the mass transfer of metal compounds, a model of filtration combustion of metal-containing combustible mixtures is developed. Using cadmium-containing mixture as an example, the main characteristics of filtration combustion are determined when the gas pressure at the reactor inlet is constant. It is shown that under the conditions of a filtration combustion wave, a metal can evaporate into the gas phase and be transferred with gas through the reactor. Due to the evaporation and condensation of cadmium, it is transported and accumulated before the combustion front. The possibility of controlling the mass transfer of metal compounds under the conditions of a filtration combustion wave with the aim of concentrating them is shown. It is revealed that a 4-fold increase in the pressure difference at the open boundaries of the reactor can lead to a decrease in the maximum metal concentration by about 1.5 times. An increase in the concentration of metals due to mass transfer will subsequently make it economically feasible to extract them by traditional methods.

Hasta hace aproximadamente una década, las nanopartículas y nanominerales eran unos auténticos desconocidos en el ámbito de los yacimientos minerales. Sin embargo, el progresivo desarrollo de técnicas analíticas más potentes ha permitido caracterizar partículas cada vez de menor tamaño, lo cual ha llevado aparejado una verdadera explosión de la nanociencia y sus posibles aplicaciones directas en los procesos tecnológicos o nanotecnología.

Electroplating and metalworking industries produce enormous amounts of waste containing heavy metals in their effluents, leading to potential threats to biotic and abiotic life. According to regulation, heavy metal contamination must be kept within the regulated standard of a few parts per million, which has led to a recent pique in interest in the utilization of nanofiltration technology for metal recovery. The effect of feed pH, pressure, metal concentration, and oxidation of metal on the rejection of heavy metal ions using three commercial nanofiltration membranes (NF, NF90, and NF270) were explored. To begin, studies of electrolyte salts, contact angle, and water permeability were employed to characterize the nanofiltration membranes. A dead-end module was used to test the permeation and retention capacities of the nanofiltration membranes. The results showed an increase in salt rejection for all metals examined irrespective of the membrane, at a pH below the isoelectric point. For divalent cations, the NF90 membrane achieved recovery capacities of 97% and 85% at 200 ppm and 20 ppm respectively, as compared to the recovery observed for Ni2+, Cu2+, and Pd2+ ions by NF and NF270. At a pH 2, 20 ppm and 5 bar, the NF90 membrane had the highest percent recovery, but at a pH 3, the recovery was at 95%. Mono and divalent stable Ag+ and Ni2+ ions showed a comparatively high percent recovery as compared to Pd2+ and Cu2+, which have high molecular weight and charge effect. In the presence of chelating agents, the membrane surface area is increased, resulting in high divalent ion recovery capacities due to favourable interaction with the polyamide functional group of the membranes. This study establishes the significance of oxidation in high removal efficiency cation in varying experimental conditions.

Milliflow devices operating under slug flow (Taylor-flow) conditions provide an efficient mass transfer, a highly uniform droplet morphology and a narrow residence time distribution i.e. characteristics which are excellent for the performance of reactions under kinetic control. Milliflow devices have also been proposed in combination with ionic liquids, due to their ability to intensify the solvent use of these rather expensive and viscous liquids. In present research, the solvent extraction separation of a mixture of Au(III), Pd(II), Cu(II) and Fe(III) was studied using the chloride and bromide forms of the undiluted quaternary ammonium ionic liquid Aliquat 336 in a slug flow reactor channel with an internal diameter of 1.0 mm. The extraction of Au(III) and Pd(II) was found to be faster than that of Cu(II) and Fe(III), allowing the precious/base metal separation to be improved by modification of the contact time between both phases. An apparent correlation between the observed extraction rates and the equilibrium distribution ratio D was found. The most significant separation improvement was achieved at those conditions where the equilibrium separation was best i.e. low halide and metal concentrations and low organic-to-aqueous flow rate ratios. At a residence time of 25 s, quantitative Au(III) and Pd(II) recovery was achieved and decontamination factors increased by a factor up to 2, which corresponds to an increase in product purity of up to 14%. Upon substituting the chloride system for a bromide extraction medium, similar observations were made, except for a reversed Cu(II)/Fe(III) selectivity. Experiments were also conducted on the separation of Pt(IV), Pd(II) and Rh(III), where a reduced Rh(III) extraction rate was observed, allowing to suppress its co-extraction by up to 20%. A hydrodynamic analysis of the obtained flow regime of the ionic liquids revealed a stable and uniform slug flow characterized by a decreasing plug length and width with increasing flow rates. A comparison of the applied and observed phase ratio revealed a stagnant ionic liquid excess (i.e. hold-up) inside the reactor of up to 40% which effectively reduced the reactor diameter and consequently plug residence time.