Sulfur Partial Pressure Research Articles

An unconventional approach for the efficient recovery of iron, cobalt, copper and silicon from copper slag

High-grade heavy metal elements in copper slag (CS) are worth recovering. Unfortunately, the high viscosity of leaching solution, low leaching efficiency, difficult filtration and low separation efficiency of valuable components exist in the traditional sulfuric acid leaching process. In this study, the above problems are solved by sulfuric acid pretreatment + curing + water leaching. Moreover, iron, cobalt and copper ions in solution are separated by stepwise precipitation. The final iron, cobalt, copper and silicon recoveries are 99.01 %, 98.45 %, 93.13 % and 99.52 %, respectively. Thermodynamic calculations show that H4SiO4 can be converted to insoluble SiO2 to improve filtration properties under curing conditions of sulfur dioxide partial pressures of 10−20∼0 atm, oxygen partial pressures of 10−20∼0 atm and 400–600k. Simulation studies of the phase equilibria of the components of the leach solution by Visual MINTEQ showed that the oxidation of Fe2+ to Fe3+ is necessary for the removal of Fe2+ from the solution by precipitation. This study provides a new idea for the efficient utilization of CS.

Sulfidation behavior of an AlCoCrNiSi high‐entropy alloy

AbstractHigh‐entropy alloys (HEAs) are promising new materials considered for application in high temperature environments. In this work, the sulfidation behavior of an Al–Co–Cr–Ni–Si HEA at different elevated temperatures and various sulfur vapor partial pressures is investigated. Thermogravimetric studies indicate that the sulfidation kinetics are in accordance with the parabolic rate law. The corrosion rate has a strong temperature dependence, whereas the influence of sulfur vapor pressure is practically nonexistent. Changes in temperature also do not seem to affect the sulfidation mechanism as evidenced by the Arrhenius correlation determined between the obtained parabolic rate constants and temperature. Combined SEM–EDS and XRD studies reveal the formation of a thick multilayer scale on the studied alloy, where the outermost relatively compact part is built of Co0.5NiS2 and CrAl2S4 while the inner, rather porous part also contains metallic inclusions, including Si near the scale/substrate interface.

Gasification Behavior of Plant-Based Biomass and Its Application to the Manufacturing Process of Titanium Sulfides under Sulfur Partial Pressure

Gasification Behavior of Plant-Based Biomass and Its Application to the Manufacturing Process of Titanium Sulfides under Sulfur Partial Pressure

Synthesis Process of Titanium Sulfides Suitable for the Manufacturing Process of Titanium via the Thermal Decomposition Process by Controlling Oxygen and Sulfur Partial Pressures in a Dilute Hydrogen Gas Flow

Synthesis Process of Titanium Sulfides Suitable for the Manufacturing Process of Titanium via the Thermal Decomposition Process by Controlling Oxygen and Sulfur Partial Pressures in a Dilute Hydrogen Gas Flow

Phase transformation and multiphase reaction properties of complex copper ore system under melting conditions

ABSTRACT Copper pyrometallurgical production relies heavily on copper sulphide concentrate as a raw material. The thermal behaviour of key components in complex copper sulphide during heating was investigated in this work. The findings reveal that under a nitrogen atmosphere, the thermal behaviour of natural chalcocite is split into three stages: crystal transformation, loss of water of crystallization, and disintegration of a minor number of components represented by carbonate minerals. In addition to the foregoing thermal behaviour of copper concentrate, S2 is disproportionated at high sulphur partial pressure to form Cu2O in the reaction system where Cu2S, CaO, and S2 coexist. As both are programmed in an oxygen atmosphere, their thermal behaviour is nearly identical. Cu and S combine with O to generate sulphate at temperatures between 400 and 700°C. This sulphate decomposes as an intermediate product as the temperature rises. The paths of primary constituents in the reaction system in the later stages of heating are as follows: S→SO2; Cu2S→CuSO4→CuO·CuSO4→Cu2O→Cu→Cu2O; FeS→Fe3O4→CuFeO2.

Development of Experimental Techniques for the Phase Equilibrium Study in the Pb-Fe-O-S-Si System Involving Gas, Slag, Matte, Lead Metal and Tridymite Phases

Present society challenges, including metal scarcity, recycling, and environmental restrictions, resulted in the increased complexity and variability of metallurgical feed streams. Metallurgical processes involving complex lead and copper-containing slag and matte phases are now commonly used in response. Optimization of existing and development of new metallurgical processes require fundamental information on slag–matte phase equilibrium. Development of the experimental methodology for the characterization of slag–matte phase equilibrium is presented in the paper. Following a detailed analysis of the potential reaction pathways, experimental techniques have been developed that enable accurate measurement of slag–matte phase equilibrium in the Pb-Fe-O-S-Si system. The application of the techniques has been demonstrated for two important sets of conditions: (i) Condensed phase equilibrium for the slag–matte–metal–tridymite subsystem; and (ii) Gas–slag–matte–tridymite equilibrium at fixed oxygen and sulfur partial pressures. The experimental methodology involves high-temperature equilibration of synthetic samples, fast quenching, and microanalysis of the compositions of phases using electron probe X-ray microanalysis (EPMA). The experimental results are not affected by the changes in the bulk composition of samples during equilibration; this helps to overcome the significant barriers previously encountered in undertaking accurate measurement and characterization of these systems.

Low temperature synthesis of MoS2 and MoO3:MoS2 hybrid thin films via the use of an original hybrid sulfidation technique

In this study, an original hybrid technique based on rapid thermal annealing (RTA) and chemical vapor deposition (CVD) was used to synthesis MoS2 and MoO3:MoS2 hybrid thin films at low temperature on indium tin oxide (ITO). We show that using the annealing temperature, the annealing duration and the sulfur partial pressure as parameters, it is possible to switch from MoO3 (20–25 nm) to MoS2 directly without any intermediate compositions. The XPS analysis revealed a complete sulfidation at 380 °C without any deterioration of the ITO conductivity. Then, we synthesized thinner hybrid films (3nm) of MoO3:MoS2 in order to be used as anode buffer layer (ABL) in planar organic solar cells (PHJ-OPVs). We have demonstrated that the hybrid ABLs that appear best suited for use in PHJ-OPVs are those with high MoO3/MoS2 molecular ratio which have been treated around 210 °C. The introduction of the hybrid ABL with 5% of MoS2 in the PHJ-OPVs based Aluminum Phthalocyanine Chloride and Fullerene leads to a significant improvement of the OPV efficiency from 1.29% to 2.49%, this was explained by the complimentary advantages of MoO3 and MoS2.

Thermodynamic simulation of complex Pb−Bi concentrate oxidative bath smelting process

Abstract The element partitioning in a Pb−Bi concentrate oxygen-rich bath smelting process was studied using thermodynamic equilibrium simulation method. Effects of oxygen to feed ratio (OFR) and sulfur dioxide partial pressure (pSO2) on the partitionings of Bi, Pb, As, Sb, Cu and Ag were analyzed and compared with industrial data. The results suggested that the optimal OFR was between 6.3 and 6.8 kmol/t to maximize Bi, Pb, Cu and Ag partitioning in the metal phase. Further increase of OFR led to the drop of metal partitioning and increase of slag liquidus temperature. High pSO2 led to high deportment of Bi and Pb in the gas phase mainly in the form of sulfides, suggesting that a low pSO2 was conducive for reducing the dust ratio.

Reduction Process for Sulfur Chemical Looping Combustion with Fe <sub>2</sub>O <sub>3</sub> Oxygen Carriers

Chemical looping combustion (CLC) is a new energy-saving and energy-efficient combustion technology. In this study, the possible products of CLC were analyzed by determining the equilibrium constants of competitive reactions of sulfur and oxygen carriers (OCs) at different temperatures. The effects of reaction temperature, sulfur partial pressure, and sulfur dioxide partial pressure on the distribution of solid products were evaluated by computing the dominant region diagram. The gaseous and solid products produced by the reduction reaction of sulfur and OCs at different temperatures were simulated using Aspen Plus. The feasibility of sulfur chemical chain combustion was verified through experiments. Research findings indicated that almost all sulfur reacted with OCs to produce SO2 and metal oxide. In addition, a low sulfur equilibrium partial pressure was beneficial to the generation of metal oxide, whereas a high sulfur equilibrium partial pressure was beneficial to the generation of metal sulfide. Under the conditions of a S/Fe2O3 molar ratio of 1:6, a carrier gas flow rate of 300 ml/min, a sulfur gasification temperature of 500 ℃, and an OC reduction temperature of 900 ℃, sulfur CLC was the best. This study laid a foundation for the practical application of sulfur chemical chain combustion to produce high concentrations of SO2 gas and demonstrated the great development potential in the CLC acid-making industry.

Impact of Phase Evolution in Platreef and UG-2 Concentrates on Matte Drainage in the Black Top of a Platinum Group Metal Smelter

ABSTRACT The melting behavior of Platreef and UG–2 platinum group metal (PGM) concentrates was studied under conditions typically found in the black top of PGM smelters. In order to understand how the phase changes influence the separation between matte and slag, the concentrates were characterized before and after firing at eight temperatures from 800°C to 1480°C. The PGM concentrates were isothermally heated in either silica (Platreef) or magnesia crucibles (UG–2), which in turn were sealed in steel capsules under argon atmosphere. This configuration prevented the escape of sulfur–containing gases during the experiments. Observed phase relations were compared against phase relations predicted by FactSage® under oxygen partial pressures in the range of 10–18 to 10–9 bar and sulfur partial pressures in the range of 10–9 to 10–3.5 bar. The results showed the effective separation of matte from the gangue minerals at sub–liquidus temperatures of the gangue (1480°C for UG–2 concentrate, 1400°C and 1480°C for Platreef concentrate). The PGM concentrates did not sinter at low temperatures (800–1100°C); however, from 1200°C the formation of a liquid phase promoted liquid phase sintering. The collection of matte in a button at the bottom of the crucible was facilitated by the formation of a continuous liquid phase in the sintered concentrate, through which the matte droplets could descend. This occurred after the main gangue phase, enstatite, melted incongruently.

The effect of sulfur dioxide partial pressure on gas-slag-matte-tridymite equilibria in the Cu-Fe-O-S-Si system at 1200°C

ABSTRACT The gas-slag-matte-tridymite equilibria in the Cu–Fe–O–S–Si system at 1200°C have been experimentally studied. An improved experimental technique was used, which includes high temperature equilibration of sulfide-oxide mixtures on silica substrates at p(SO2) = 0.6 atm, preservation of the equilibrium phases by rapid quenching, and direct compositional analysis of the phases using microanalysis techniques. The new data have enabled the effects of sulfur dioxide partial pressure between 0.1 and 0.6 atm on the equilibria to be accurately determined. Whilst, for a given matte grade, the dissolved copper in slag is not sensitive to sulfur dioxide partial pressure, the Fe/SiO2 in slag in equilibrium with tridymite was found to increase with increasing p(SO2). This latter observation has implications for fluxing practice in industrial copper smelting operations.

Non-uniform distribution of sulfur vapor and its influence on Cu2ZnSnS4 thin film solar cells

The morphological, compositional and structural properties of the Cu2ZnSnS4 (CZTS) thin films and the device parameters of solar cells are strongly influenced by the sulfur partial pressure during the sulfurization process. To investigate the distribution of sulfur vapors along the sulfurization chamber, the uniformity of the CZTS thin films and solar cells during sulfurization process, several same samples were sequentially placed in the chamber. The device performance of CZTS thin film solar cells shows a strong correlation with the positions in the sulfurization zone and the morphologies of the CZTS thin films. An optimal position was found in the sulfurization furnace where could improve the crystallinity of CZTS thin films, reduce the formation of secondary phases, and improve the efficiency of solar cells. The best solar cell in the optimal position shows an efficiency of 3.49%, which was restrained by the Sn loss. The possible reasons for the non-uniform distribution of sulfur vapor are analyzed.

Inflexible stoichiometry in bulk pyrite FeS2 as viewed by in situ and high-resolution X-ray diffraction.

Non-stoichiometry is considered to be one of the main problems limiting iron pyrite, FeS2, as a photovoltaic absorber material. Although some historical diffraction experiments have implied a large solubility range of FeS2-δ with δ up to 0.25, the current consensus based on calculated formation energies of intrinsic defects has lent support to line-compound behavior. Here it is shown that pyrite stoichiometry is relatively inflexible in both reductive conditions and in autogenous sulfur partial pressure, which produces samples with precise stoichiometry of FeS2 even at different Fe/S ratios. By properly standardizing in situ gas-flow X-ray diffraction measurements, no significant changes in the lattice parameter of FeS2 can be resolved, which portrays iron pyrite as prone to forming sulfur-deficient compounds, but not intrinsic defects in the manner of NiS2-δ.

Sulfidation of 2D transition metals (Mo, W, Re, Nb, Ta): thermodynamics, processing, and characterization

Sulfidation of selected transition metal thin films (Mo, W, Re, Nb, Ta) was combined with thermodynamic calculations to study the synthesis of transition metal dichalcogenides (TMDCs) and understand variations among the metals as well as processing atmosphere. Metal seed layers were prepared by DC magnetron sputtering and sulfidized using sulfur vapor and H2S. Surface chemistry, structure, and morphology of the films were investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy (AFM), respectively. XPS analysis revealed that after treatment with sulfur vapor (p (S2) = 1–10 Torr), Mo, W, and Re films were transformed into MoS2, WS2, and ReS2, respectively. However, Nb and Ta films changed little, and Nb2O5 and Ta2O5 remained the predominant components. Alternatively, conversion of Nb and Ta films to NbS2 and TaS2 was feasible under H2S. Raman spectroscopy also revealed improved crystallinity for Mo, W, and Re sulfidized under H2S. Isobaric and isothermal stability diagrams were calculated to identify feasible processing conditions (sulfur partial pressure and temperatures) for the sulfidation of all of the metals, and our findings were in good agreement with the XPS and Raman results. It was found that for Mo, W, and Re a p (S2) = 10−5 bar is sufficient for the metals to be converted to sulfide phases at 750 °C. On the other hand, due to very high stability of Nb2O5 and Ta2O5, even at very low p (O2), a sulfur partial pressure of 103–104 bar is required to make NbS2 and TaS2, respectively. Nevertheless, thermodynamic calculations confirmed that Nb and Ta could be transformed to NbS2 and TaS2 under 760 Torr H2S. AFM analysis revealed very smooth films for MoS2, WS2, and NbS2 films, but dewetting of TaS2, and ribbons for ReS2. These results provide guidance for designing new processes for synthesizing 2D TMDCs.

Evolution of Cu2ZnSnS4 during Non-Equilibrium Annealing with Quasi-in Situ Monitoring of Sulfur Partial Pressure

Chalcogen-based materials like Cu2ZnSnS4 (CZTS) have attracted extensive attention for applications such as photovoltaics and water splitting. However, an inability to monitor the sulfur partial pressure (PS2) during the non-equilibrium annealing process at high temperatures complicates the synthesis of CZTS with controlled optoelectronic properties. Here we demonstrate that PS2 can be monitored by investigating the Sn–S phase transformation. We showed that PS2 drops considerably over the annealing time, causing gradual alterations in CZTS: (i) a change in defect type and (ii) evolution of ZnS and SnxSy phases. With additional ordering treatment, we observed that the low room-temperature photoluminescence energy usually seen in CZTS can result from insufficient PS2 during annealing. It is proven that remarkable Voc beyond 700 mV for solar cells with nonoptimal CdS buffer can be repeatedly achieved when CZTS is prepared under a sufficiently high PS2. An ordering treatment before CdS deposition can further ...

Hot Corrosion Mechanism of Steels Exposed to Heavy Metal Chlorides and Sulphates in SO2 Environment

Copper flash smelting produces flue dust containing SO2-rich exhaust gas, causing corrosion problems in the heat recovery boiler of the gas train. In order to understand the corrosion behaviour of boiler steels, conditions of the boiler were simulated in the laboratory. Corrosion damage occurred as chlorine reacted with steel surfaces forming chlorides which deplete the steels from their alloying metals. At the scale/dust deposit interface, where the highest sulphur partial pressures prevail, a sulphate layer covered the mixed oxide and chloride scale. Molten sulphate deposit reduced the metal loss of AISI 304 steel by preventing chromium chloride diffusion away from the steel surface. The Cr2O3 scales were quite stable under molten sulphates. The dust deposit melted partially due to the presence of ZnCl2 in the deposit which initiated corrosion damage by producing a molten salt layer on the steel surfaces bringing it in contact with aggressive compounds in the copper smelter flue dust.

Preparation of high-quality Cu2ZnSnS4 thin films for solar cells via the improvement of sulfur partial pressure using a static annealing sulfurization approach

Cu2ZnSnS4 (CZTS) thin films were prepared by spin-coating deposition of sol–gel precursor followed by sulfurization in sulfur atmosphere. A comparative study on the properties of the CZTS thin films sulfurized by using dynamic annealing and static annealing approaches was carried out. A higher sulfur partial pressure processed from static annealing was demonstrated. Static annealing contributed to the reduction of Sn loss. The CZTS thin films sulfurized by static annealing showed larger grains, better crystallinity and thinner MoS2 layer, but more ZnS on surface and minor Cu2−xS, SnS2 and SnS at the back surface. Diffusion of Zn into MoS2 layer was found to be associated with those minor secondary phases at the back surface. Solar cells incorporating the CZTS thin films sulfurized by static annealing exhibited a better cell performance with the device efficiency as high as 6.15%, which was further improved to 6.68% by using hydrochloric acid solution to etch ZnS at the surface and inhibiting the decomposition reaction of CZTS at the back surface based on the use of a thin ZnO nanolayer barrier.

Combinatorial Reactive Sputtering of In2S3 as an Alternative Contact Layer for Thin Film Solar Cells

High-throughput computational and experimental techniques have been used in the past to accelerate the discovery of new promising solar cell materials. An important part of the development of novel thin film solar cell technologies, that is still considered a bottleneck for both theory and experiment, is the search for alternative interfacial contact (buffer) layers. The research and development of contact materials is difficult due to the inherent complexity that arises from its interactions at the interface with the absorber. A promising alternative to the commonly used CdS buffer layer in thin film solar cells that contain absorbers with lower electron affinity can be found in β-In2S3. However, the synthesis conditions for the sputter deposition of this material are not well-established. Here, In2S3 is investigated as a solar cell contact material utilizing a high-throughput combinatorial screening of the temperature-flux parameter space, followed by a number of spatially resolved characterization techniques. It is demonstrated that, by tuning the sulfur partial pressure, phase pure β-In2S3 could be deposited using a broad range of substrate temperatures between 500 °C and ambient temperature. Combinatorial photovoltaic device libraries with Al/ZnO/In2S3/Cu2ZnSnS4/Mo/SiO2 structure were built at optimal processing conditions to investigate the feasibility of the sputtered In2S3 buffer layers and of an accelerated optimization of the device structure. The performance of the resulting In2S3/Cu2ZnSnS4 photovoltaic devices is on par with CdS/Cu2ZnSnS4 reference solar cells with similar values for short circuit currents and open circuit voltages, despite the overall quite low efficiency of the devices (∼2%). Overall, these results demonstrate how a high-throughput experimental approach can be used to accelerate the development of contact materials and facilitate the optimization of thin film solar cell devices.

Study of Bunsen reaction in agitated reactor operating in counter current mode for iodine-sulphur thermo-chemical process

The iodine-sulphur (IS) thermo-chemical process is being studied as a potential process for production of hydrogen by water splitting. It consists of three chemical reactions: 1) Bunsen reaction, which is the acid production step, 2) sulphuric acid decomposition to produce oxygen; 3) hydrogen iodide decomposition to produce hydrogen. In this work, a detailed parametric study of the Bunsen reaction is presented, which was carried out in agitated reactor (ABR) in counter current mode of operation. Experiments have been carried out in the reactor at different temperatures by varying the sulphur dioxide (SO2) flow rate and partial pressure of SO2. Bunsen reaction rate and SO2 conversion are calculated experimentally from feed rate and scrubbing rate of SO2. It has been observed that the reaction rate and SO2 conversion increase with increase in SO2 flow, increase in SO2 partial pressure and decrease in temperature. 'Tanks-in-series' model, one of the non-ideal reactor models, has been proposed to describe the ABR reaction system. The model has been validated with experimental results. This approach can be useful for the design and scaling up of the agitated reactor.

Efficiency enhancement by adding SnS powder during selenization for Cu2ZnSn(S,Se)4 thin film solar cells

A two-step process with post-annealing of stacked precursors has been widely used for Cu2ZnSn(S,Se)4 (CZTSSe) absorbers. However, no simple approach is currently available for simultaneously tuning the S/(S+Se) ratio and avoiding tin loss issue in CZTSSe films, which are critical factors to achieve high efficiency. In this work, we demonstrate by simply adding SnS powder during selenization, we can eliminate the tin loss and also control the S/(S+Se) ratio. Furthermore, we can suppress the formation of Mo(S,Se)2 during selenization. Based on thermodynamic calculations, we propose SnS powder reacts with selenium to form SnSe and releases sulfur vapor during selenization. The Sn-contained vapor avoids tin evaporation from CZTSSe. By varying the amount of SnS powder, the partial pressure ratio of sulfur to selenium can be tuned; therefore, the film composition and band bap of CZTSSe can be changed. The presence of sulfur partial pressure also dramatically decreases the formation of Mo(S,Se)2 during selenization. The efficiency is substantially boosted from 3.97% to 7.35% by adding SnS powder during selenization. Our approach realizes one-step sulfo-selenization, providing a general tuning knob for compositional control of CZTSSe absorbers, which shines light on various process developments of CZTSSe absorbers by post-annealing vacuum- or solution-fabricated precursors.