Review of investigations on the thermodynamics of reduction of copper from oxides and sulfides

The thermodynamics of reduction of copper from oxides and sulfides at T = 298–1273 K is considered. The absence of a correlation between the values of ΔG ⁰ of the reduction of copper from oxides and those of their formation is confirmed. The reducing ability of sulfide, elementary sulfur, and sulfite sulfur is investigated with respect to copper in oxides Cu(I) and Cu(II). The presence of an interrelation between the probability of reduction of metal and stability of the reducing agent is established. The possibility of reduction of copper from sulfides with the use of hydrogen and metals, as well as with the use of electron donor properties of sulfide sulfur, is investigated. The conditions for realization of reduction are found.     

Reduction of metals from sulfides

Existing notions on reduction of metals from oxides and sulfides are based on realization of dissociative processes associated with the formation of simple substances. Metal sulfides can be considered as compounds of oppositely charged species formed owing to totality of electrostatic and coordination binding in the Me^z+-S^2? system. Reduction of metals from such compounds with the use of donor properties of sulfide sulfur is an electrochemical process with the participation of the electrode pair Me^z+ and S^2? in the mode of internal electrolysis in the system, which provides utilization of elemental sulfur that is formed through chemical reactions. As an electrochemical medium, molten caustic soda is proposed. In its presence, elemental sulfur disproportionates with the preferential accumulation of sulfide and sulfate sulfur. The reaction causes irreversibility of the reduction process.     

Reactions of molten Fe,Co, Cu,and Pb sulfides with hydrogen

The kinetics and mechanism of reactions of molten Fe, Co, Cu, and Pb sulfides with hydrogen have been investigated between 1080° and 1340°C. While maintaining high flow rates of hydrogen and argon to ensure chemical control, the rate of reduction of these sulfides was found to be second order in sulfur concentration and half-order in hydrogen pressure. These dependences are similar to those reported earlier for molten nickel sulfide reduction by hydrogen. The kinetics and mechanistic proposal suggest a metal catalyzed step. If the activation energies for the rate determining step of S₂ reacting with hydrogen in the melt for the various sulfides are compared with the values for the hydrogen-liquid sulfur or hydrogen-gaseous sulfur reactions, the order of catalytic activity seems to follow generally the order of the pure metals themselves as found for other processes involving activation of molecular hydrogen.     

Recent Trends in the Search for New Extractants

Abstract

Since the introduction of solvent extraction as a separation method for metals, such solvating and acidic extractants have predominantly been used which are mono- or bifunctional compounds. They are able to form a five- or six-membered chelate ring, binding metal ions typically through one or two oxygen atoms, or through oxygen and nitrogen atoms. They can exhibit very useful selectivity, which is dependent on the localization of binding sites in various functional groups (acidic or neutral), chains or heterocyclic rings. However, a new approach in the search of new extractants is needed, if unusual selectivities are to be attained, e.g. within groups of chemically similar elements. Development of radius sensitive compounds represents one of the recent trends. The selectivity of macrocyclic ethers, mixed-heteroatom macrocyclic compounds and calixarenes is discussed in this review, with some emphasis laid on potential separation within groups of alkali and alkaline earth metals. Potential separation of lanthanides and actinides is also discussed, but less attention is paid to transition metals which can be separated by conventional extractants. Variables influencing the sensitivity are molecular configurations of the extractants nature of anions participating in the formation of extracted complexes, presence of mineral acids in the aqueous phase, nature of diluent and temperature. To separate elements with very similar ionic radii, extractants with less common, “soft” donor atoms can be applied. The separation of transplutonides (III) from lanthanides (III) is taken as an example, and the separation potential of acidic sulfur donor as well as neutral nitrogen donor extractants is discussed.     

Influence of chemically active elements on the hydrogen cracking of pipe steel

Vacuum treatment of pipe steel and the maintenance of superlow sulfur concentration (0.002%) are not enough to ensure high corrosion resistance. Hydrogen cracking of pipe steel may be prevented by if complex modifiers are used to maintain certain proportions of the active elements Al, Ca, rare-earth metals, and sulfur.     

Sulfides in forgings of 40KhGM structural steel

Sulfides in large forgings of 40KhGM steel containing from 0.005 to 0.023% sulfur are studied by optical and scanning electron microscopy (on fracture surfaces and polished sections) and by transmission diffraction electron microscopy (on thin foils). Several types of sulfides are found to exist in the forgings, depending on the sulfur content. Globular sulfides exist at all sulfur contents. They are located inside grains in contact with aluminum, magnesium, and silicon oxides or titanium nitride and carbide particles, which serve as substrates during sulfide solidification. At a low sulfur content, faceted manganese sulfides form in the steel; they are not in contact with oxides and are located inside grains. At 0.013–0.023% sulfur, elongated eutectic sulfides, which are located near or at the boundaries of primary grains, appear. The data obtained suggest gaps between sulfides and the matrix, and these gaps can play the role of “hydrogen traps.”     

稀土金属脱除氧杂质的新技术及驱动机制研究进展

介绍了活泼金属除气法、等离子体熔炼法和固溶氢原子除气法等稀土金属脱除氧杂质的新方法,详细归纳了将氧杂质含量限制在5×10-5以下的工艺条件.重点介绍新方法中引入活泼金属、氢等离子体、活性固溶氢原子等各种外部驱动因素的设计思想,提出提纯新技术的同时探究了痕量杂质的迁移规律及去除机制,深化对杂质存在形式、行为规律及提纯机理的认识.采用FAST-2D与Stefan数值模拟技术、18O₂示踪同位素标记技术、CALPHAD相图数据库模拟计算技术对稀土金属高纯化的新工艺提供理论指导与评价,加深对提纯驱动机制的理解.      

稀土在铜银合金导线生产中的应用

介绍了稀土银铜合金导线的生产工艺，重点介绍了稀土的添加方法和分析了稀土的作用。在铜熔体中加入微量稀土元素，稀土能对铜银合金熔体中的氧、硫有较强的脱除能力，使铜熔体得到净化。同时，稀土的加入还能减少铸造过程中铜银合金线杆的表面裂纹缺陷和细化晶粒。从而，使铜银合金导线的各种性能得到很大程度的改善和提高，即稀土的加入使铜银合金线杆的延伸率、抗拉强度、导电率均得到提高。     

The possibility of oxidation reactions of the sulfides of heavy non-ferrous metals and iron by the chain mechanism

A thermodynamic evaluation of the oxidation of sulfides of heavy non-ferrous metals is carried out. It is shown that, according to the values of the decreasing Gibbs energy for these reactions, the sulfides are arranged in the following series: FeS, Ni₃S₂, CoS, NiS, ZnS, PbS, CdS, CuS, Cu₂ S. The thermodynamic probability that all stages of the chain mechanism of oxidation of sulfides will proceed with the isolation of gaseous oxygen and atomic sulfur is also evaluated.     

Rational design of novel carboxylic acid functionalized phosphonium based ionic liquids as high-performance extractants for rare earths

Developing the novel ionic liquids as the potential substitutes for conventional organic solvents in extraction of the rare-earth metals is highly desirable but challenges still remain. In this study, the well-designed carboxylic acid functionalized phosphonium based ionic liquids, (4-carboxyl)butyl-trioctyl-phosphonium chloride/nitrate, were synthesized and characterized. The as-prepared samples were tested as the undiluted hydrophobic acidic extractant for rare-earth metal ions, affording the maximal loading of 3 mol/mol towards Nd(III) in aqueous solution and the remarkable stripping performance. The results also reveal their excellent extractability and selectivity for Sc(III) in the mixtures of six rare-earth ions, as well as the outstanding separation properties between rare-earth and first row transition-metal ions (i.e., La/Ni, Sm/Co). Moreover, the extraction mechanism indicates that the extracted rare-earth complex via a proton exchange in the ionic liquid phase is structurally similar to the complexes obtained with neutral extractants. This work presents a prototype for the fabrication of the hydrophobic cation-functionalized ionic liquids for highly efficient rare-earth extraction and provides the future application in recycling of rare-earth metals from the spent magnets.     

Gallochalcogenides of the rare-earth metals

A discussion of published data on the structure of gallochalcogenides of the rare-earth metals is followed by an account of an experimental study of the electrical properties of neodymium galloselenide. The electrical resistance and thermo-emf were measured over a range from room temperature to 1100°K. It is shown that neodymium galloselenide is a semiconductor in which the width of the forbidden band and ionization energy of the impurity level are 1.78 and 0.77 eV, respectively. The semiconductor nature of the conductivity of NdGaSe₃ is explained on the basis of the electronic structure of isolated atoms and their ionization potentials. An assumption is made regarding the nature of the chemical bond in chalcogenides of rare-earth metals.Presented at the Fifth All-Union Inter-Institute Seminar of the Physical Properties and Electron Structure of the Transition Metals and Their High-Melting Compounds and Alloys, Kiev, April 5–9, 1966.Translated from Poroshkovaya Metallurgiya, No. 1(49), pp. 99–104, January, 1967.     

Effect of the sintering temperature and time on the structure and phase composition of temperature stable hard magnetic materials of the REM–Fe–Co–B system

The structure, the phase composition, and the distribution of alloying elements in the structure of temperature stable hard magnetic materials of the REM–Fe–Co–B system (REM = rare-earth metals), which are prepared under different manufacturing conditions, namely, at different sintering temperatures and times, have been studied. The phase composition, the local chemical composition of phases, the volume fraction of pores, and the manufacturing conditions that allow one to prepare the structure ensuring high magnetic properties have been determined.     

Removing oxide and sulfide inclusions from molten steel by filtration

On the basis of thermodynamic calculations indicating that rare-earth sulfide inclusions may form in molten nonalloyed structural steel, the influence of filtration on the content of sulfur, oxygen, and nonmetallic inclusions in the steel is investigated. It is found that filtration removes the oxide phase and oxygen from 30Л steel. There is no change in the content of sulfide inclusions and sulfur. Filtration of steel preliminarily treated with 0.05–0.30% rare-earth metals removes 10–60% of the sulfur. Metallographic data show that the content of both oxide and sulfide inclusions is reduced here. Gray impressions of filter templates show that the sulfur-bearing phase is removed by an adhesive mechanism: this phase adheres to the filter surface, forming continuous borders around it.     

Phase equilibria in the metal-sulfur-oxygen system and selective reduction of metal oxides and sulfides: Part I. The carbothermic reduction and calcination of complex mineral sulfides

The difference in the standard Gibbs free energy for the formation of any two oxides or sulfides is the chemical potential for selective reduction of metals from complex minerals. The magnitude of the Gibbs free energy difference is shown by plotting the univariant relationships for relevant sulfides and oxides. In this investigation, three examples of mineral sulfides are considered, and the experimental results are compared with the predicted thermodynamic calculations. These examples include the reduction conditions for nickel and iron sulfides and pentlandite (Fe,Ni)₉S₈ and chalcopyrite (CuFeS₂) minerals. The reduction behavior of mineral sulfides, such as those of nickel, cobalt, iron, and copper, is illustrated by referring to both the sulfide and alloy phase equilibria. In particular, the solution thermodynamic properties of the metallic phase equilibria are featured for determining the physical chemistry of preferential or selective reduction of the metal oxides and sulfides. The mechanism for the reduction of the aforementioned sulfide minerals is explained with the aid of the governing phase equilibria for the calcination process. The results from the carbothermic reduction of sulfide minerals are also compared. The important roles of lime and calcium sulfate in controlling the emission of sulfurous gases during the reduction reaction are explained. A qualitative analysis of reduction reactions of nickel and iron sulfides is reviewed to provide a comparison of the mechanism for complex nickel-bearing minerals. The importance of these results in producing alloy and pure metallic phases is also examined.     

Removal of a sulfur impurity from complex nickel melts in vacuum

Various methods of removing sulfur from a complex nickel melt are considered. They are based on the use of slags based on CaO or metallic calcium and the introduction of a rare-earth metal (La, Y) during melting in a vacuum induction furnace. Some properties of alloys (high-temperature strength, long-term strength, ductility) are improved after decreasing the sulfur content.     

Intermetallic compounds of rare-earth metals with aluminum and some of their properties

Conclusions The article reviews literature data on the systems of the rare-earth metals with aluminum, taking into account new results obtained by using high-purity rare-earth elements. The intermetallic compounds in these systems are classified. A table is included, summarizing the crystallographic, as well as some physical and chemical properties of all known intermetallic compounds in these systems.Translated from Poroshkovaya Metallurgiya, No. 8(44), pp. 76–85, August, 1966.     

Influence of Microalloying on the Strength and Corrosion of Low-Carbon Stainless Steel

Attention focuses on how nitrogen and rare-earth metals modify the mechanical properties and corrosion characteristics of unstabilized low-carbon Fe–Cr–Ni stainless steel, additionally alloyed with silicon and molybdenum. The influence of the selected microalloying method on the mechanical properties of unstabilized low-carbon chromonickel stainless steel and its resistance to local corrosion is studied experimentally. Nitrogen-bearing 03X17H9AC2, 03X17H9AM3, and 03X18H15AM3 stainless steel microalloyed with rare-earth metals is investigated.     

惰性气体蒸发-冷凝法制备尺寸可控的纯稀土纳米粉末

利用惰性气体蒸发-冷凝法制备了系列纯稀土金属的纳米粉末颗粒.通过分析稀土金属的蒸气压随温度的变化特征,指出了适合用惰性气体蒸发-冷凝法制备纳米粉末的稀土金属的种类.以Sm、Nd、Gd纯稀土金属为例,用透射电镜观测了稀土金属纳米颗粒的形貌及晶体结构,并测算了平均粒径及粒径分布.     

Hot workability of nickel-containing alloys after reheating using sulfur-containing fuel

The effects of fuel sulfur on the hot workability of several nickel-containing alloys have been explored in static exposures and in hot rolling trials following reheating in S-bearing. combustion atmospheres. Using thermochemical calculations, it is shown that the locus of oxidation and sulfidation potentials of such gases over practical air-fuel ratios can be made to coincide for a variety of hydrocarbon fuels, and propane doped with H₂S has been used as a fuel to simulate environments resulting from firing distillate and residual oils. Nickel-base alloys containing chromium are not affected by the presence of sulfur species, and workability is independent of reheating conditions at fuel sulfur levels of up to 2 wt pct. Stainless steels may form solid subscale sulfides under air deficient heating, but there is no effect under lean firing conditions; billet workability is not influenced by sulfur. Nickel and nickel-copper alloys form liquid sulfides during air deficient heating, and very poor workability results. Sulfur is also picked up from the gas, and other properties may be affected. The thermochemical predictions for the occurrence of these liquid sulfides agree well with observations. An attempt has been made to identify safe reheating conditions (temperature and air-fuel ratio) for sensitive alloys on the basis of equilibrium combustion gas computations.     

The Site Preferences of Transition Elements and Their Synergistic Effects on the Bonding Strengthening and Structural Stability of γ′-Ni3Al Precipitates in Ni-Based Superalloys: A First-Principles Investigation

Advanced mechanical properties of Ni-based superalloys strongly depend on the site preferences of alloying X elements in γ′-Ni₃Al-X precipitates, which are associated with the partial bonding characteristics between Ni, Al, and X atoms. Therefore, in the current work, the site occupancy tendencies of transition X metals were revealed via first-principles ab initio calculations at 0 K. Bonding features of Ni-Al, Ni-X, and Al-X pairs were simulated by using the charge density difference (CDD), electron localization function (ELF), and density of states (DOS) methods, respectively. According to simulations, higher atomic size X elements preferably occupy Al sites of γ′-Ni₃Al-X intermetallics and lead to strong covalent-like directional bondings between themselves and their nearest neighbor (NN) Ni atoms along 〈110〉 directions. However, if these larger X metals substituted for Ni sites, the bonding properties would differ by plane due to the nature of the L1₂-type crystal structure of γ′-Ni₃Al-X precipitates. Considering all transition elements, refractory metals (i.e., X = Re, W, Mo, Ta, or Nb) appear as the most effective strength inducers, improving the structural stability of γ′ phase, even if Ni site substitution of X = Re atoms would start to increase structural instability. On the other hand, relatively small alloying X elements having electron configuration similarities with Ni (i.e., X = Co, Cu, Rh, Pd, Ag, Ir, Pt, or Au) are more likely to worsen bonding strengthening. Instead, these transition X metals creating metallic bondings with NN Ni atoms would contribute to ductility and malleability of Ni-based superalloys. Furthermore, depending on the relative atomic size of γ′-former and refractory elements, the phase and site preferences of refractory atoms would alter in multicomponent systems. As a result of the attractive or weak repulsive forces between Re-Re, Re-Mo, and Re-W pairs, the structural stability of the constituent phases would deteriorate and harmful topologically close-packed (TCP) phases would precipitate.