Rare Precious Metals Research Articles

Efficient recovery of gold from solution with a thiocyanate-modified Zr-MOF: adsorption properties and DFT calculations.

The design and development of new large-capacity and selective materials for extracting rare precious metals via electronic waste is practically essential. In this paper, a new efficient UiO-66-NCS has been obtained as a consequence of the modification of the classical Zr-MOF (UiO-66-NH2), and its ability to recover gold has been investigated. These batch results adequately illustrated that UiO-66-NCS exhibited good adsorption capacity (675.5 mg g-1) and exceptional selectivity. In addition, UiO-66-NCS achieved faster adsorption equilibrium times of about 120 min. Adsorption kinetics and isotherms demonstrated that the pseudo-second-order adsorption scheme and a Langmuir-type procedure were shown by the adsorption of Au(III) on UiO-66-NCS. Characterized by pH effect experiments, TEM, XRD, and XPS, the adsorption of UiO-66-NCS with Au(III) relies on coordination, which further results in reduction, and the generated Au(0) is uniformly dispersed in the MOF. The adsorbent has considerable advantages for cyclic regeneration. Finally, DFT fitting results showed that the adsorption binding energy of UiO-66-NCS with [AuCl4]- was -8.63 kcal mol-1 for the adsorption process. UiO-66-NCS is likely to be an ideal substance for gold recovery.

Jiangxi Copper Group Remuneration Policy Study

China's copper industry is an important industry in the national economy, with 91% of 124 industries related to copper. Jiangxi Copper Group has the highest self-sufficiency rate of copper concentrate in China, and is the largest and most modern copper production and processing base in China, and an important production base for gold, silver, selenium, tellurium, rhenium and other rare precious metals, and sulfur chemical industry. 1997, Jiangxi Copper Corporation was listed on the Hong Kong stock market, and in 2008, the management bodies of Jiangxi Copper Group Company and Jiangxi Copper Corporation were merged into a single one, and the company was listed as a whole. In 2008, Jiangxi Copper Group Corporation and Jiangxi Copper Corporation realized the merger of their management bodies into one, realized the overall listing, and established a modern management system and operation mechanism with the division system as the basic framework. This paper analyzes the remuneration policy of Jiangxi Copper Group by studying the remuneration status of its executives and employees, and compares it with other companies in the same industry to put forward development suggestions.

A DFT study on flotation behavior of sphalerite with indium and iron impurities

Indium (In) is a rare precious metal with extremely low abundance in the Earth's crust, mostly occurring as impurities in sphalerite, and it is closely related to the high iron content in sphalerite. Flotation is generally used to recover such minerals. However, there are few for the flotation mechanism of sphalerite containing indium and iron impurities. In this paper, the adsorption of xanthate (C4H9OCSS−) and depressants (CN–, CaOH+, OH–) on the surface of sphalerite that contains indium and iron impurities is investigated by employing density functional theory (DFT), and compared with pure sphalerite. The findings demonstrate that the presence of indium ions results in stronger adsorption of H2O on sphalerite surface and sphalerite containing InFe exhibits higher hydrophilicity. C4H9OCSS− forms strong covalent InS and FeS bonds on InFe-containing sphalerite surface, transforming the adsorption of C4H9OCSS− on sphalerite surface from weak physical adsorption to strong chemisorption. This enhances the collecting power of C4H9OCSS− on sphalerite and improves the floatability of InFe-containing sphalerite. Studies on electronic interactions have revealed that in the interaction with C4H9OCSS−, the outer s and p orbitals of the indium atom are primarily involved, which is different from the pure sphalerite surface where only the s orbital of zinc is involved. The participation of the p orbitals significantly enhances the interaction of In with xanthate. Additionally, the Fe 3d orbitals can provide a pair of π electrons that can form π-backbonding with C4H9OCSS−. These two factors contribute to the increased adsorption capability of C4H9OCSS− on InFe sphalerite. The adsorption of CN–, CaOH+ and OH– on both In and Fe sites on the surface of InFe-containing sphalerite is stronger than that on the surface of pure sphalerite, with CN– adsorption being the strongest, indicating that CN–, CaOH+ and OH– have stronger depressing effects on InFe-containing sphalerite.

Highly efficient and selective adsorption of palladium(II) from simulated nuclear waste solution using Amberlite XAD-7 resin impregnated with a phenanthroline-derived diamide

The increasing demand and limited natural resources for rare precious metal palladium render its separation and recovery from secondary sources such as acidic nuclear liquid waste greatly interesting. Herein, a novel Et-Tol-DAPhen extraction resin was prepared by impregnating Amberlite XAD-7 resin with a phenanthroline-derived diamide extractant N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen), and the adsorption behavior of this new extraction resin towards Pd2+ in HNO3 solution was investigated through the batch and column experiments. The Et-Tol-DAPhen extraction resin exhibited strong adsorbability, high adsorption capacity, excellent selectivity and good reusability for Pd2+ in highly acidic HNO3 solution. In addition, the pseudo-second-order and Langmuir models were applied to understand the adsorption process of Pd2+ on Et-Tol-DAPhen extraction resin, respectively. It demonstrated the characteristics of a uniform single-layer chemisorption. The maximum uptake capacity could reach as high as 74.6 mg g−1 for Pd2+ in 3.0 mol/L HNO3 solution which is much higher than most adsorbent materials of palladium reported before. Furthermore, Et-Tol-DAPhen extraction resin could selectively uptake Pd2+ from a simulated acidic nuclear waste solution containing 20 different kinds of ions with the separation factor SFPd/M values as high as 100 to 10,000. Moreover, although the adsorption efficiency had a slight decrease after 5 times of adsorption-desorption process, it still remained at a high level. This new extraction resin displayed a potential application prospect in the field of separation and recovery of Pd2+ from acidic nuclear liquid waste.

Study on extraction of Rh(III) by DABCO-based ionic liquid from hydrochloric acid medium

Rhodium, as a rare precious metal, has always been a challenge for the chemical industry to efficiently recover rhodium by extraction due to the complex existing situation in hydrochloric acid medium. Herein, a strongly hydrophobic DABCO-based ionic liquid (IL) [C8DABCO][NTf2] was designed and synthesized to construct a solvent-free extraction system of Rh(III) from high-concentration hydrochloric acid medium. At first, the effects of some important parameters on Rh(III) extraction were studied, such as equilibrium time, IL dosage, hydrochloric acid concentration, and initial Rh(III) concentration, the results showed that 81.54% Rh(III) can be extracted under the optimum extraction conditions. Based on the experimental run results, a quadratic model equation was established by using the response surface method (RSM), which can be used to calculate the amount that [C8DABCO][NTf2] will be offered at various HCl concentrations during the actual extraction of Rh(III). Then, using Job's method, the Ultraviolet visible spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FT-IR), Energy-dispersive X-ray spectroscopy (EDS), and Electrostatic potential (ESP) prove that the extraction mechanism is an anion exchange mechanism. Finally, in the mixed solution of multi-metals, the extraction efficiency of [C8DABCO][NTf2] for Rh(III) is not disturbed, and the extraction efficiency for other metals is less than 1%. And the single-stage stripping efficiency of Rh(III) was up to 88% through HCl stripping, which solved the problem of difficult stripping of Rh(III) solution and realized the recycling of IL. The study provides a reliable and efficient way for recovering Rh(III) from high-concentrations HCl solutions.

Microstructural evolution of a nickel-based single-crystal superalloy embrittled by molten Zn

The embrittlement treatment of Ni-based single-crystal superalloys in a Zn atmosphere causes the superalloys to break easily. This considerably increases the contact area in the dissolution process. Hence, this treatment has the potential for conveniently recovering rare precious metals from Ni-based superalloys. This study systematically examines the microstructures of Ni-based single-crystal superalloys after Zn embrittlement. Microstructural changes in the superalloy after reaction with Zn at 700, 900, 1100, and 1200 °C for 8 h were investigated and analyzed in detail via X-ray diffractometry, scanning electron microscopy, and electron probe microanalysis, using the phase and element composition as the evaluation indices. Results showed that the formation of the Ni5Zn21 intermetallic compound in the superalloys was the main reason. The formation of Ni5Zn21 disturbed the distribution balance and promoted the recombination of metallic elements, resulting in the embrittlement of the superalloys. The embrittlement mechanism involved a mutual diffusion reaction of Zn and Ni, but the degree of Zn diffusion was higher.

Covalent organic polymers with azido group for efficient recovery of gold from gold-bearing waste

BackgroundGold is a rare precious metal. Efficient and selective adsorption of Au(III) is of great significance for gold recovery. MethodsA covalent organic polymer with azido group (N3-COP) was synthesized utilizing enaminone covalent organic polymer and Ts-N3 as raw materials. Significant FindingsThe adsorption capacity of N3-COP for gold ions was up to 1220 mg·g−1 under the condition that the adsorption process took place at room temperature and at a pH value of 4. The results of adsorption thermodynamic and adsorption kinetic experiments illustrated that the adsorption process of N3-COP for the trivalent gold ion is consistent with the Langmuir adsorption model and Quasi second-order adsorption model. Additionally, this adsorbent has high adsorption selectivity when it is used to adsorb trivalent gold ion from effluent containing gold (III), cadmium (II), nickel (II), cobalt (II), and copper (II) ions. This adsorbent also has good reusability for it maintains excellent adsorption performance after five consecutive adsorption operations.

Improving the Stability of Silicon Nanowires During Photoelectrochemical Hydrogen Generation with Zinc 1T‐Phase Molybdenum Disulfide

AbstractSemiconductor photoelectrodes directly convert sunlight into stored chemical energy. In photoelectrochemical (PEC) devices, this photoconversion process relies on the junction between the semiconductor and catalyst to drive charge separation and generate electron/hole charge carriers. The growth of native oxides (SiOx) on the surface of semiconductors during device operation induces charge carrier recombination and photodegradation, which limit the operation lifetime of PEC devices. Likewise, the commercialization of photoelectrochemical devices is hindered by the use of expensive, rare precious metal catalysts such as platinum to enhance hydrogen evolution kinetics. This work demonstrates how drop casting zinc 1T‐phase molybdenum disulfide (Zn 1T‐MoS2) onto silicon nanowires (SiNWs) generates an interface that overcomes these challenges. This Zn 1T‐MoS2/SiNWs junction drives hydrogen evolution under acidic conditions (0.5 M H2SO4) comparably to platinum‐modified SiNWs (Pt/SiNWs) with a positive overpotential of 164 mV at 10 mA cm−2 and low Tafel slope of 42 mV dec−1. Compared to the bare SiNWs, the Zn 1T‐MoS2/SiNWs junction retains roughly 66% more photocurrent density and reduces SiOx growth by 16% after 24 h of continuous electrolysis. By developing a deep understanding of the catalyst‐semiconductor interface, photoelectrochemical devices may be effectively designed to maintain their stability over a lifetime of operation.

Sequestering Rare Earth Elements and Precious Metals from Seawater Using a Highly Efficient Polymer Adsorbent Derived from Acrylic Fiber

An amidoxime and carboxylate containing polymer adsorbent derived from acrylic fiber has shown extremely high efficiencies for extracting critical materials and precious metals from seawater. Among 50 extractable elements, the lanthanides, cobalt, and palladium were ranked near the top with KD values in the order of 107, about an order of magnitude higher than that of uranium. The KD value of the lanthanides increased linearly with the atomic number indicating charge density is a factor controlling trivalent lanthanide extractability in seawater. The data given in this report provides crucial information regarding the strategies of ocean mining of critical materials and precious metals.

New Processes to Treat Anode Slime and Other Smelter Improvements

During efforts to solve common technical challenges to the comprehensive recovery of rare precious metals associated with copper smelting, Xiangguang Copper (XG) independently developed a new process to treat anode slime using technology that captures precious metal using bismuth. This paper focuses on the introduction and application of this technology for capturing precious metals with bismuth. It also discusses silver electrolysis at high current density and bismuth recovery from precious metals slag. The new process shows good adaptability of raw materials, elimination of lead pollution, low energy consumption, environmental protection and high comprehensive recovery rate of metals, which promotes the technological progress of comprehensive recovery and utilization of associated resources in copper smelting process.

High acidity- and radiation-resistant triazine-based POPs for recovery of Pd(II) from nuclear fission products

The recovery of platinum group metals (PGMS) from high-level radioactive liquid waste (HLLW) not only has a complementary role in alleviating the shortage of rare precious metals but also is helpful for the final disposal of radioactive waste. In this work, a new cationic covalent triazine framework (CTF) named as cationic pyridyl triazine polymeric network (CPTPN) is designed and synthesized by ZnCl2-catalyzed ionothermal method for recovering of Pd(II) from HLLW. The excremental results shows that palladium can be efficiently adsorbed by CPTPN from 3 M HNO3 solution via anion exchange with fast adsorption kinetics with adsorption equilibrium reached in 10 min. The adsorption isotherm for Pd(II) follows the Langmuir model, which reveals the maximum adsorption capacity (qm) of 339.8 mg g−1 and 389.7 mg g−1 at 3 M HNO3 for CPTPN-Cl and CPTPN-NO3 , respectively. Further studies show that the qm of CPTPN-NO3 in 6 M HNO3 can reach a higher level at 428.6 mg g−1, which is the highest record for Pd(II) recovery in 6 M HNO3. In addition to high thermal stability, CPTPN exhibits a good irradiation stability with excellent adsorption performance maintained after 1000 kGy of γ-irradiation. Furthermore, CPTPN has an excellent adsorption selectivity for Pd(II) in simulated HLLW. Although the selectivity of CPTPN-Cl for Pd(II) is found to be unsatisfactory due to the significant co-adsorption of Ag(I), this problem can be well solved by changing Cl− ions in CPTPN-Cl to NO3−. Both CPTPN-Cl and CPTPN-NO3 show excellent reusability in 5 adsorption–desorption cycles. Thus, CPTPN can be considered as a candidate adsorbent that can tolerate high irradiation and high acidity for selective recovery of Pd(II) from HLLW.

Harm and benefit of Khibiny mining waste

The article is focused on the assessment of the impact of mining waste on the environment. Mining waste (MW) is understood as mine (mining) dumps and dumps of processing plants (tailings dumps). The article also suggests considering MW as technogenic deposits of rare earth and precious metals, the development of which will allow solving many environmental, social and economic problems and using natural resources in a sustainable manner. The objects under study are located on the Kola Peninsula, within the Khibiny mountain range, and are the production assets of the Apatit Mining Complex. This enterprise develops the so-called deposits of the Khibiny Tundra, it also owns apatite-nepheline processing plants.

Enhanced adsorption and separation of gallium using silica-based P507-TBP/SiO2–P adsorbent from sulfuric acid solution

The designing of high adsorption capacity and selective porous materials to adsorb gallium (Ga) is essential for developing breakthrough Ga separation and purify methods based on resin adsorption to replace traditionally used extraction, chemical precipitation, and electrochemical method. Here, an advanced porous resin with the 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (P507) and tributyl phosphate (TBP) attached to the silica-based materials (SiO2–P) has been prepared, which are synthesized by vacuum impregnation followed by drying. At low concentration sulfuric acid solution (PH = 3.3), the synthetic adsorbent that simultaneously exhibits excellent Ga adsorption capacity and high separation ability (excellent adsorption capacity with 64.2 mg/g, and super-high separation ability with the Kd is over 1600). Adsorption and mechanism studies of Ga (III), using the above P507-TBP/SiO2–P resin, were carried out. IR, XPS, and BET, TG analysis were applied to confirm the resin were successful adsorb Ga (III) and the conversion of polymer to resin, respectively. More importantly, the P507-TBP/SiO2–P adsorbent can also be extended to the design of other silica-based materials for the challenging separate and purify other rare precious metals ions, indicating a very appealing application prospect.

Focusing on the research work undertaken in the Kamitani Group

Chemical reactions are central to industrial processes and manufacturing. The ability to combine atoms into molecules and also break these molecules into various smaller components provides us with the building blocks for countless products and processes. However, not all reactions are efficient and they require energy to be completed. In many cases the amount of energy required to begin the reaction, the activation energy is too high and the rate of the reaction, how quickly it runs, is too slow. Thankfully, there is a solution. Catalysts are substances that can be added to reactions that can increase the rate of a reaction and/or lower the activation energy. They are also re-usable because they are not consumed during the reaction, meaning only a small amount of catalyst is needed to greatly improve a reaction. Chemical engineers have learned how to produce or improve catalysts and hence reactions that are required for industry. Unfortunately, the majority of catalysts come in the form of rare precious metals making them expensive and sometimes difficult to obtain for logistic and even political reasons. To get around this reliance on rare elements Masahiro Kamitani, Assistant Professor at Kitasato University in Japan founded a research group dedicated to the development and application of iron catalysts.

Effect of Carbazolyl Groups on Photophysical Properties of Cyanuric Chloride.

Long-lived room temperature organic phosphorescence is highly useful in biological imaging, electroluminescent devices, information security, and security protection on account of its unique photophysical process and long-lived luminescence. In recent years, pure organic phosphorescent materials that do not contain rare precious metals have received increasing attention. Carbazole and its derivatives have been used to develop room temperature organic phosphorescent materials. However, the effect of carbazolyl groups on the photophysical properties of pure organic phosphors has rarely been reported. In this work, three cyanuric chloride phosphors (CzDCIT, BiCzDT, and TCzT) modified with different numbers of carbazolyl groups were synthesized. Several characterization techniques were employed to reveal distinct crystal forms of CzDCIT, BiCzDT, and TCzT. The single crystal diffraction of CzDCIT and BiCzDT showed not only different crystal packing modes, but also the formation of internal H-aggregation. These three phosphor powders exhibited dual emissions of blue fluorescence and yellow phosphorescence at room temperature, with luminescence lifetimes of 0.16-0.34 s. Theoretical calculations indicated that different numbers of effective intersystem crossing channels between CzDCIT, BiCzDT, or TCzT were responsible for the luminescence lifetimes. After doping the phosphors into the polymer matrix, they exhibited good persistent phosphorescence and high recoverability in multiple compression-grinding cycles.

Orthorhombic WP co-catalyst coupled with electron transfer bridge UiO-66 for efficient visible-light-driven H2 evolution

The abundant transition metal phosphides co-catalysts on the earth can satisfy the sustainable and clean solar H2 production through photocatalytic water splitting, which is promising to replace the rare precious metals, such as Pt, Au, Pd, Ru and so on. In this paper, we use the temperature-programmed solid phase method to prepare WP nanoparticles. Based on the Density Functional Theory (DFT) calculations, we demonstrate that the WP nanoparticles possess outstanding electrical conductivity and excellent capability to transport electrons. WP nanoparticles are loaded onto the surface of UiO-66 via the ultrasound-assisted impregnation method to induce a highly efficient visible-light photocatalytic H2 production activity of 384 µmol in 5 h, which is 10.67 times than that of pure UiO-66. The catalytic performance is attributed to the excellent metallic conductivity and the favourable Fermi level position of WP nanoparticles. Further studies of PL, TRPL and Mott-Schottky curves, we can not only know that the modification of WP nanoparticles do improve the electron transfer ability, but also that the matched work functions between the EY and UiO-66 provides a feasible thermodynamic path for the transmission of electrons. Our work demonstrates that the earth-abundant transition metal phosphides material have the potential to construct cheaper and high catalytic performance photocatalysts.

Computational Screening for Developing Optimal Intermetallic Transition Metal Pt-Based ORR Catalysts at the Predictive Volcano Peak

Practical development of cost-effective and environmentally sustainable oxygen reduction reaction (ORR) catalysts has not yet been fully realized despite years of effort. Specifically, state-of-the-art ORR catalysts typically require high Pt-loading while still suffering significant overpotential losses and only providing moderate current density. In this work, we present results from new DFT calculations screening a wide range of Pt3(MN)1 ternary catalysts to see the range of values for oxygen adsorption energy (the known ORR volcano plot descriptor) such systems can achieve. Our results identify many promising materials based purely on performance via this descriptor; unfortunately, many of these promising candidates still require a very high loading of rare precious transition metals in the guest (MN) composition role. We have further used our results to generate a predictive fitted model for the ORR descriptor value itself based on the normalized valence and mass of a given fcc(111) Pt3(MN)1 surface c...

Novel in situ synthesized carbide reinforced Ni base composite for structural castings with high creep resistance

Ni base superalloys for structural castings of aero engines demand higher service temperatures and lower costs while retaining their processing characteristics. To achieve these properties, alloying with the rare precious metals inevitably leads to a decrease in the castability and a marked increase in the raw material cost. In this work, we develop a novel Ni base composite (MC/IN718C) with a high creep resistance, excellent microstructure stability and excellent castability by optimizing the chemistry and microstructure of the commercial IN718C superalloy. In this work, both tensile strengths at room temperature and at 704 °C were obviously improved, while the steady-state creep rate of the MC/IN718C composite at 704 °C was reduced by one order of magnitude. The rupture life of MC/IN718C at 704 °C/620 MPa was enhanced by one order of magnitude compared to the IN718C alloy due to the load bearing effect of the MC carbide, the elimination of the metastable strengthening precipitation phase γ″ and a decrease in the harmful Laves and δ phases. MC/IN718C Ni base composite presents a new strategy for the design and preparation of high-temperature materials potentially for critical structural castings.

Cobalt-nitrogen-doped graphdiyne as an efficient bifunctional catalyst for oxygen reduction and hydrogen evolution reactions

For replacing the use of rare precious metals, finding an electrocatalyst with low-cost, stable and excellent activity for both the oxygen reduction reactions (ORR) and hydrogen evolution reactions (HER) is desirable and challenging. Herein, a novel electrocatalyst of cobalt (Co) and nitrogen (N) doped graphdiyne (Co-N-GDY) was designed and synthesized using a facile method with just a small amount of Co precursor to reach up to 1.3 wt % based on XPS data. Among them, the 1% Co-N-GDY, synthesized with 1 wt % of Co in the preparation stage, was demonstrated as the most effective ORR and HER catalyst. Due to the synergistic effect of Co, N, GDY and strong interaction between Co and GDY, the Co-N-GDY exhibited excellent ORR and HER catalytic performance. As for ORR, the activity of 1% Co-N-GDY is comparable to that of commercial Pt/C. Especially the half-wave potential of 1% Co-N-GDY is superior to most previously reported Co-based carbon materials. In HER, the 1% Co-N-GDY shows a low onset overpotential of 97 mV and a small Tafel slope of 132 mV per decade, which exhibits comparable or even better performance than many reported non-precious metals catalysts.

One Pot Assembly of Vertical Embedded MoS2/Graphene Heterostructure and Its High Performance for Hydrogen Evolution Reaction

Two-dimensional molybdenum disulfide has great potential to replace rare precious metals for hydrogen evolution reaction. Herein, we report a one pot assembly strategy for in situ growing vertical embedded MoS2 nanocrystals on graphene surface. The resultant sandwiched architecture could not only expose more active sites within MoS2 edge but also reduce stacking tendency of the layer-structured graphene support, leading to a significant improvement in HER performance. The materials showed an overpotential of 142 mV at 10 mA·cm–2 and a Tafel slope of 68 mV·dec–1, which are among the best results ever obtained by the similar materials. Moreover, this method is facile, environmentally friendly, and suitable for mass production, making it attractive for practical applications.