Flash Smelting Research Articles

CFD–DEM modeling of particle segregation behavior in a simulated flash smelting furnace

Particle behavior plays a crucial role in flash smelting furnaces, but limited understanding is hindering further development of this modern pyrometallurgical process. This study presents a two-way coupled CFD–DEM approach to investigate particle distribution, collision, and segregation behaviors within a furnace. The simulation results are validated against experimental data, demonstrating good agreement. The effects of the particle mass–flow rate and size distribution are then analyzed. The results indicate that small particles are carried by airflows to the center of the particle-dense region, whereas large particles remain at the outer part, worsening segregation. Increasing the mass–flow rate significantly increases the particle number density and number of particle collisions but barely influences size-induced segregation. In contrast, enlarging the size of fed particles reduces particle number density and broadens dense distribution within a safe range. This ensures the necessary space and high mixing index of the particles, which benefits high-rate smelting processes.

Oxidation of nickel concentrates in simulated reaction shaft conditions of the flash smelter

The suspension oxidation of nickel sulfide concentrates in flash smelting conditions was studied using a laboratory-scale laminar flow furnace. The effects of temperature (800–1100 °C) and oxygen concentration (40–85 vol%) in the process gas were investigated. The surface morphology and mineralogical compositions of samples were examined using scanning electron microscopy equipped with energy-dispersive X-ray spectrometry. The sulfur removal from concentrates was determined using chemical analysis assuming iron as a non-volatile component. It was found that ignition of the nickel concentrates started at a temperature below 800 °C. The sulfur removal from the sieved concentrates increased with increasing temperature. The oxidation was initiated with preferential oxidation of iron in sulfides forming an iron oxide-rich scale on sulfidic core.

Industrial Deportment of Minor and Trace Elements in Direct Nickel Matte Smelting

A sampling campaign was carried out at an industrial nickel flash smelter with the aim of evaluating the trace element distributions along the smelting line from raw materials to high-grade nickel matte and discard slag. The industrial technology was direct-to-nickel matte smelting without conventional Peirce–Smith converters, thus having two different nickel mattes as smelting products and feeds in the refinery: the sulfidic low-iron nickel matte from smelting furnace and the low-sulfur electric furnace matte from slag cleaning. Major and trace element concentrations were obtained from the solidified samples by electron probe microanalysis and laser ablation–inductively coupled plasma–mass spectrometry. Due to the industrial sampling environment, i.e., the slow cooling rate of the samples, not all the trace element concentrations were able to be measured at the lowest detection limits of the techniques used in some of the phases formed after cooling. However, the obtained results and element distribution coefficients were in good agreement with equilibrium values published in the literature.

Distribution of Copper, Iron, and Sulfur in Copper Concentrate Particles during Oxidation under Simulated Flash Smelting Conditions

The distribution of copper, iron, and sulfur during the oxidation of La Caridad copper concentrate particles under simulated flash smelting conditions was studied in a laboratory reactor. Six wet-sieved size fractions and the unsieved copper concentrate were oxidized at 1123 K and 40% and 70% O2 by volume in the process gas during the experiments. Samples of partially oxidized particles were collected at 0.2, 0.8, and 0.9 m from the point of entry and analyzed in a QEMSCAN® unit to determine the elemental composition within the population of particles. The distribution of the major elements during oxidation was strongly dependent upon the size and chemical composition of the initial particles. Overall, the copper content tended to increase and sulfur content decreased along the reactor length within all sizes. In contrast, the distribution of iron did not follow a general trend, as it was found to increase, decrease, or remain unchanged depending on the particle size. This finding may represent a key feature to further investigate the reaction path followed by particles during flash smelting, especially those associated with particle fragmentation. In general, the larger the particle size was, the larger the change in the content of the major elements within the particle population. Based on the experimental results, particles within a size fraction of <45 µm tended to follow a reaction path consisting of rapid melting followed by the collision and coalescence of reacting droplets during flight. In contrast, particles within the fraction of 45–53 µm tended to react individually. The oxidation behavior of the unsieved concentrate particles showed a combination of both reaction paths.

Ignition and combustion of synthetic nickel mattes in simulated flash smelting conditions

The ignition and oxidation behavior of synthesized sulfur-lean nickel mattes was investigated using a laminar flow furnace simulating the conditions in the flash smelting reaction shaft to explore the ignition and oxidation processes of sulfur-lean electric furnace mattes obtained from slag cleaning. The experiments were conducted at 800–1100 °C with 40–85 vol% O2 in the reaction gas. Scanning electron microscopy equipped with energy-dispersive X-ray spectrometry was used to analyze the surface morphology and mineralogical compositions of the samples. Chemical analysis was employed to determine the sulfur remaining in the samples. The ignition temperature of the sulfur-lean nickel mattes was found to be below 800 °C. The highest sulfur removal from mattes was achieved under the most oxidizing conditions. The oxidation of the metallized nickel mattes started with preferential oxidation of iron and sulfur, forming sulfur dioxide and a porous iron oxide-rich rim. Particles were observed to melt completely and even to fragment due to fast combustion reactions and the formation of sulfur dioxide inside. The present results provide valuable insights into the mechanism of sulfur-lean nickel matte smelting in flash smelting furnaces.

Flue Dust Behaviour in FSF - Arsenic Condensation in Offgas Line Conditions

The suspension smelting oxidation step has favourable conditions to generate chemical flue dust from the low-boiling elements of the feed mixture due to the high particle temperatures in the reaction shaft where combusting sulphide mineral particles reach temperatures above the melting point of magnetite. Arsenic, antimony, lead, and zinc are common impurity elements of high volatility in copper concentrates. They tend to accumulate in the flue dust due to the high volatility and closed mode of the flue dust circulation practiced in most industrial smelting-converting processes. Then, the only outlets for the volatile impurities are the anodes and the discard slag. A separate flue dust treatment for impurity removal is an option but it creates an additional step for the smelting plant and cost in the processing. When the concentrate grades decrease, and their impurity levels rise this outlet for the trace elements may become necessary. The arsenic condensation mechanisms in dust-free conditions in the copper flash smelting process gas train have been recently studied in SO2-air-N2 gas mixtures. It seems that the formation mechanism of arsenic-containing dust deposits is kinetically constrained, and their chemistries are influenced by the condensation temperature and atmosphere.

Missing data filling in soft sensing using denoising diffusion probability model

With the aim of addressing the problem of degradation in soft measurement accuracy due to missing data in industrial processes, a filling method based on the denoising diffusion probability model (DDPM) is proposed here to improve the accuracy of soft measurement modeling. First, missing regions are detected with the help of an improved Isolation Forest algorithm to obtain information such as the locations and numbers of missing data regions. Next, a data generation model is constructed based on DDPM and new samples are obtained. By adjusting the threshold for normal operation of the system and the weight sampler, filler samples that are similar to the distribution of the original data can be filtered from the new samples to form a complete dataset. The feasibility of the proposed missing data filling method is explored through numerical simulations, and its superiority in terms of improving the prediction accuracy of soft measurements is verified in regard to the nickel flash smelting process.

CFD-DEM models for matte droplet settling in a flash smelting settler

The flash smelting process is widely used in copper production. In the process, sulfidic feed and flux are oxidized. The heat released in the reactions melts the feed which forms a slag layer through which matte droplets must settle. Understanding the different phenomena affecting the settling is important to minimize losses. Due to the high temperature, simulation methods were employed to study settling. In this work, coupled CFD-DEM was used to study the effect of coalescence and reactions with in-house built submodels and scaled-down geometries. Colliding droplets often coalesce into larger droplets while reactions decrease their size and make them denser. These increase the settling velocity which is further enhanced by the formation of a channeling flow. Channels make the droplet cluster denser causing more collisions. This method enables the phenomena to be studied at the individual droplets' details, although simulating a full-scale process is beyond the available computational resources.

Arsenic Condensation and Reaction Mechanisms in Flash Smelting Off-Gas Line Conditions

Arsenic is a common impurity element in sulfide concentrates. It tends to accumulate in the flue dust of smelting furnace due to the volatility and internal circulation of the flue dust practiced in the smelting-converting process chain. The only outlets for arsenic are anodes and discard slag. Arsenic condensation in dust-free conditions was studied below 800 °C where the gas atmosphere was controlled by SO2-air-N2 gas mixtures. Based on these experimental results, we confirm the kinetically constrained formation mechanism of the arsenic-containing dust, and its speciation into metallic, oxidic (III, V), and sulfidic species. The influences of temperature and atmosphere on the speciation of arsenic were compared with industrial data and discussed.Graphical Condensed arsenic‐bearing particles collected by electrophoretic forces on the surface of fused SiO2 in SO2‐O2 atmospheres: the crystal morphology shows euhedrally facetted As2O3 crystals and initially molten As‐OSalloy droplets together with poorly crystallized AsSx particles.

Control of Copper Content in Flash Smelting Slag and the Recovery of Valuable Metals from Slag—A Thermodynamic Consideration

To determine slag properties and the factors influencing these properties for optimization of operating conditions in the copper flash smelting process, the composition and microstructures of the quenched smelting and converting slags have been analyzed. Thermodynamic software FactSage 8.2 has been used to investigate the effects of matte grade, SO2 partial pressure, and the Fe/SiO2 ratio on the liquidus temperature and the copper content of the smelting slag. The possibility to recover valuable metals from the smelting and converting slags through pyrometallurgical reduction by carbon is also discussed. It was found that the flash smelting slag temperature is usually higher than its liquidus temperature and the copper (1.2% Cu) is mainly present in the slag as dissolved copper. In the copper flash smelting process, the copper content in the slag can be decreased by decreasing the Fe/SiO2 ratio and temperature. In pyrometallurgical slag reduction, most Cu, Mo, and Ni can be recovered as an alloy. The conditions of recovery such as the ratio of smelting slag to converting slag, temperature, and reduction extent have been discussed.

Tracking combustion behavior of copper monosulfide, ferrous sulfide, and chalcopyrite tablets by high-speed microscopic videography

A new suspended-combustion-test method involving high-speed digital microscopy and thermal measurements was developed to analyze small tablets of CuS, FeS, and CuFeS2 to elucidate their combustion behavior and phase changes in flash smelting. Moreover, the frequency of splash generation and homogeneous oxidation of the released gaseous sulfur from each sulfide were monitored. Microstructural analysis of quenched samples by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy revealed that the combustion intensity could be related to the formation of an oxide layer, which blocked the O2 supply to the sample interior. Moreover, the gas formed at various oxygen concentrations agitated the samples. In particular, the generated solid-oxide shell could move, the sulfide was exposed to the surface again, and the combustion reaction proceeded further. Insufficient agitation at lower O2 concentrations resulted in a thick and dense oxide layer, which blocked the O2 supply and caused extinction.

Kinetics of copper leaching from direct-to-blister copper flash smelting slag by sulfuric acid

Coppermaking from sulfide concentrates entails two major steps: smelting and converting. In continuous direct-to-copper smelting process these two steps are combined into one. The principal advantages of this process are: isolation of SO2 emission to a single, continuous, SO2-rich gas stream, minimization of energy consumption and minimization of capital and operating costs. Disadvantages of the process are that about 25% of the Cu entering a direct-to-copper smelting furnace ends up dissolved in the slag (when compared with < 10% in traditional Peirce–Smith converting) and the cost of recovering this Cu is significant. Decopperization process is based on the reduction of cuprous oxide and other metals, mainly lead and iron, in the liquid state in an electric furnace in the presence of coke and technological additives. This paper presents the results of laboratory tests on flash smelting slag leaching with sulfuric acid solutions. Hydrometallurgical treatment of the slag could be an alternative route to the presently used way of processing. The influence of a number of leaching parameters such as sulfuric acid concentration, amount of H2O2 added, liquid to solid phase (l/s) parameter and process temperature on the copper leaching efficiency was investigated. Under optimized process conditions, 95.6% of the copper contained in the original sample of slag was transferred into a solution. The experimental results obtained in the study were supplemented with the analysis of the kinetics of the copper leaching process from the flash smelting slag. The commonly known from the literature diffusion model and chemical reaction model were used. The activation energy of copper leaching from flash smelting slag was estimated in the range from 12.77 to 17.34 kJ/mol.

Radiometric Temperature Measurement of Copper Concentrates in Flash Smelting Conditions Simulated at Laboratory Scale Coupled With a Macroscopic Chemical Reaction Model and Automated Mineralogical Characterization

Radiometric Temperature Measurement of Copper Concentrates in Flash Smelting Conditions Simulated at Laboratory Scale Coupled With a Macroscopic Chemical Reaction Model and Automated Mineralogical Characterization

Structure and adaptability of FexO-SiO2-MgO-15 wt% CaO-0.026 wt% NiO slag with the Fe/SiO2 mass ratio of 1.2 in flash matte smelting

The high-magnesium gangue severely affects the melting performance and fluidity of slag in nickel matte smelting. To detect the adaptability when the CaO-modified slag for treating high-magnesia nickel sulfide concentrate in flash smelting, the synergistic effect of MgO and other oxides on the microstructure and physicochemical properties of slag were analyzed through molecular dynamics simulation associated with the experimental analysis. The results indicate that the MgO content increases from 5 wt% to 11 wt%, part of the Fe2+ ions in silicate are gradually replaced by Mg2+, and some of them are transformed into Fe3+ in the external atmosphere. Accordingly, the generated Fe3+ may destroy the bridge oxygen between Si4+-O2--Si4+ and more complex silicate ions will be dissociated into SiO44+. As a consequence, the Q0 proportion in the modified high-magnesia smelting slag improved from 24.33% to 29.69%, and the n(BO/T) decreased from 1.45 to 1.29. However, when MgO content is high enough, SiO44+ tetrahedron ions may attract Fe2+ and Mg2+ to form (Fe, Mg)2SiO4 with a more robust interaction network structure, resulting in an adverse effect on melting temperature and ions diffusion coefficient. The modified nickel slags with 5–11 wt% MgO represent hospitable melting temperature less than 1320 °C, viscosity lower than 0.091 Pa s, and surface tension between 0.4811 N/m to 0.4838 N/m. In brief, the CaO-modified slag turned out to be conducive for treating high-magnesium nickel sulfide concentrates in flash matte smelting, especially for those containing MgO less than 7 wt%.

Mineralogical Properties of the Copper Slags from the SarCheshmeh Smelter Plant, Iran, in View of Value Recovery

Annually, hundreds of thousands of tons of slags are involved in the reverberator and flash smelting as well as converting operations of Cu-Fe sulfide concentrates to produce matte in the Sar Cheshmeh copper smelter plant, Iran, disposed in the landfill and cooled in air. Due to their relatively high average copper content (about 1.5 wt%), a mineral processing plant based on the flotation process has recently been established to produce thousands of tons of Cu-sulfide concentrate after slag crushing and fine grinding operation. In order to make the flotation process more efficient, more knowledge is required on the form and origin of the copper losses in the slag. To achieve this, mineralogical studies of the slags using optical microscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) methods have been carried out. Mineralogical analyses showed the main part of copper losses into the semi- to fully-crystallized magnetite-rich reverberator and flash slags characterized by crystal–glass matrix ratio ≤ 1 is moderate to coarse particles of Cu-Fe sulfides, i.e., chalcopyrite (CuFeS2) and bornite (Cu5FeS4), that are mainly chemically entrapped. In contrast, the mechanically entrapped fine- to coarse-grain (from 20 up to 200 µm) spherical-shaped of high-grade matte particles with chalcocite (Cu2S) composition containing droplets or veinlets of metallic copper (Cu0) are the dominant forms of copper losses into the converter slags characterized by crystal–glass matrix ratio &gt; 1. From the value recovery point of view, our result show that the fully crystallized slags containing moderate- to coarse-grain copper-bearing particles will result in efficient recovery of a significant amount of entrained copper due to better milling response compared to semi-crystallized ones due to locking the fine- to moderate-grain copper particles in the silicate glassy matrix. Laboratory-scale grinding experiments showed that normal (≤74 μm) to fine (≤44 μm) grinding of high- Cu grade slags lead to a significant increase in the liberation degree of copper particles. in contrast, the increase in fine particle fractions (&lt;37 μm) due to re-grinding or ultra-fine grinding of the originally low-Cu grade slags does not lead to the liberation of copper particles, but it will reduce the efficiency of the flotation process. This study suggests that the highest rate of copper recovery of the slag by the flotation process will be obtained at particle size 80% passing 44 µm which has also reached the optimal liberation degree of copper-bearing particles.

Improving the flotation recovery of Cu from flash smelting slags by utilizing cellulose-based frother formulationss

• First published study using polymer-surfactant mixes as frothers in Cu slag flotation. • Using the PS-mix improved overall Cu recovery compared to commercial frother. • PS-mix significantly increased productivity, i.e. similar froth product in less time. • PS-mix demonstrated superior tolerance in performance when reducing xanthate dosage. Froth flotation is an operation currently used for the recovery of Cu from pyrometallurgical smelting slags due its simple operation and relatively low operational costs. While it has been utilized for many decades, it may be necessary to develop strategies that improve Cu recovery from slags, as the unprecedented increase in Cu demand has made industrial waste and side streams economically relevant sources of metals. This study presents a novel chemistry-based approach for the flotation of Cu from smelting slags by utilizing an amphiphilic cellulose-surfactant mixture as a flotation frother, hereby referred to as CellFroth. The present work pursues two main objectives: i) to improve the performance of flotation for the treatment of smelting slags and ii) to accomplish a first proof of concept for frothers produced from renewable sources in the context of industrial waste treatment. The flotation performance of CellFroth was compared with a commercially available additive (i.e., DowFroth250) and hydroxypropyl methyl cellulose (HPMC). The results showed significant advantages in performance for CellFroth. At the highest collector concentration, Cu recovery was higher with CellFroth compared to DowFroth 250 and pure HPMC (73%; 62% and 65% respectively). A 75% reduction in xanthate concentrations had negligible effects on Cu recovery for CellFroth (70%), while recoveries decreased drastically with DowFroth250 (47%) and pure HPMC (50 %). Finally, CellFroth consistently reached comparable concentrate productivity (grade and recovery) as DF250 within significantly shorter flotation times. The use of CellFroth thus offers the possibility of increasing the Cu recovery from flash smelting slags, while reducing the environmental impact of the process by using a frother produced from sustainable sources and simultaneously reducing xanthate consumption.

Flash Smelting Settler Design Modifications to Reduce Copper Losses Using Numerical Methods

A mathematical modeling approach was used to test different design modifications in a flash smelting settler to reduce the copper losses in slag, which is economically disadvantageous for copper processing using the pyrometallurgical route. The main purpose of this study was to find ways to reduce copper losses in slag by improving the settling and coalescence of copper matte droplets, in particular, the smallest droplet sizes of ≤100 µm. These improvements inside the flash smelting (FS) settler were targeted through different settler design modifications. Three different design schemes were tested using the commercial computational fluid dynamics (CFD) software, Ansys Fluent. These settler design modification schemes included the impact of various baffle types, positioning, the height inside the settler, and settler bottom inclinations. Simulations were carried out with and without coalescence and the results were compared with normal settler design. The results revealed that the settling phenomenon and coalescence efficiency were improved significantly with these design modifications. It was concluded that a single baffle design was optimal for reducing copper losses and increasing coalescence efficiency instead of using multiple baffle arrangements. The top-mounted baffle outperformed the bottom-mounted baffle and inclined settler design.

The changing dynamics of the gas-dust flow in the flash smelter due to addition of a spoiler. Part 2. Pilot tests

The use of man-made deposits and fine ore concentrates in the flash smelter process, as well as the poorer quality of the raw materials observed (due to a higher share of particles smaller than 10 &mu;m) lead to a higher amount of entrained dust and causes accretion in the slag end, uptake shaft and waste heat boiler. A higher dust entrainment is associated with a higher recycle, lower energy capacity of the raw materials and poorer recovery of non-ferrous metals. Numeric modelling of the heat and mass exchange processes in the gas environment of the settler and uptake shaft helped determine how different sizes and locations of the spoiler can change the gas flow parameters of the flash smelter. The modelling study showed that a 500 mm wide (the width of the settler) and 270 mm high spoiler mounted on the fire side of the settler at least 2,000 mm away from the entry to the uptake shaft could help reduce the amount of entrained dust by as much as 20% (relative) depending on the size and density of gas-dust particles. On the basis of the above calculations, a series of pilot tests was conducted on Line 1 of Nadezhda Metallurgical Plant in July 2019. Using various analysis techniques (such as thermal imaging of the surface in the spoiler area, the gas temperature, the gas flow rate, as well as methods used in analytical chemistry, scanning electron microscopy and X-ray spectral microanalysis), the authors of this paper examined the effect produced by the mounted spoiler on the gas flow. The authors would like to thank the leadership and the operations personnel of Nadezhda Metallurgical Plant for their support and great contribution to the pilot tests performed.

Comprehensive use of raw materials through optimization of the concentration and metallurgical complex of Norilsk division

Using a concentration process introduced in 2016, Talnakh Concentrator produces copper and nickel-pyrrhotite concentrates by processing high-grade and cupriferous ores. Dump tailings comprise rock tailings separated at the early process stage and low-nickel pyrrhotite product obtained at the final concentration stage. The predominant mineral found in the ores processed by Talnakh Concentrator includes pyrrhotite, which in most cases contains nickel. Low-nickel pyrrhotite product contains pyrrhotite that bears maximum Ni 0.4% in the form of impurity. Another feature characterizing the pyrrhotites found in Norilsk is the presence of isomorphic inclusions of platinum group metals. Aimed at a more comprehensive use of raw materials, in 2018 Talnakh Concentrator introduced a process for repreparation of low-nickel pyrrhotite concentrate. A low-grade flotation concentrate is obtained with Ni 0.8&divide;1.2%, which is then sent to the hydrometallurgical circuit of Nadezhda Metallurgical Plant named after B.I. Kolesnikov (NMP). Being a sulphide, pyrrhotite enhances the autogenic performance of matte smelting process. The nickel concentrate produced by Norilsk Concentrator from disseminated and cupriferous ores is a low-energy material containing 15&ndash;17% of sulphur. So the heat generated during its oxidation flash smelting is insufficient to maintain the heat balance of the furnace. The nickel concentrate produced by Norilsk Concentrator is processed mixed with Ni-containing burden, which lowers the total heat balance of the flash smelting furnaces at NMP. In 2021, a process was introduced when a part of the tailings from the low-nickel pyrrhotite concentrate line of Talnakh Concentrator is used to recover high-pyrrhotite concentrate to be added to the nickel concentrate produced by Norilsk Concentrator in order to improve th e latter&rsquo;s energy performance.

Arsenic Condensation and Reaction Mechanisms in Flash Smelting Off-Gas Line Conditions

Arsenic Condensation and Reaction Mechanisms in Flash Smelting Off-Gas Line Conditions