Iron Silicate Slags Research Articles

Effect of As and MgO addition on arsenic vitrification in copper smelting slag

The arsenic (As) vitrification in copper smelting slag derived from the FeO−SiO2−Fe2O3−B2O3−CaO− Al2O3−(MgO) system was studied. The vitrification mechanism of As was systematically investigated by XRD, SEM, FTIR and XPS analysis. It is determined that As exhibits favorable compatibility with the iron-silicate slag. FTIR and XPS analysis indicates that As can partially substitute for silicon to form the Si—O—As structure, thereby enhancing the degree of polymerization of the melt. The [BO3]3− unit tends to decrease with the increase of the As content, while the opposite behavior is observed with the addition of MgO. Additionally, MgO increases the non-bridging oxygen (NBO) number of the melt. TCLP, SPLP and pH dependence tests show that the leaching toxicity of As increases with the increase of the As content but decreases with the addition of MgO. DSC analysis demonstrates that the incorporation of both As and MgO can improve the thermal stability of the As-containing glass.

Multiphase Equilibrium Relationships between Copper Matte and CaO-Al2O3-Bearing Iron Silicate Slags in Combined Smelting of WEEE and Copper Concentrates

Waste electrical and electronic equipment (WEEE) contains various valuable metals, making it a potential secondary resource for sustainable metal usage. Pyrometallurgical smelting is an efficient technique to recycle WEEE by extracting precious metals into copper matte and removing impurities into slags. The impact of WEEE impurities such as CaO and Al2O3 on the phase compositions of the smelting products attracts great attention for industrial metal recovery. This study clarified the impact of CaO and Al2O3 on the equilibrium phase compositions of copper matte and SiO2-saturated FeOx-SiO2-Al2O3-CaO slags. The high-temperature smelting experiments were taken at a controlled p(SO2) of 0.1 atm and 1300 °C, followed by quenching and electron probe microanalysis. The results showed that the copper and sulfur in the smelting system were highly deported into copper matte, and their distribution in matte was enhanced by increasing CaO and Al2O3 concentrations introduced by WEEE. The chemical copper dissolution in slags increased with increasing matte grade but decreased by adding CaO and Al2O3. The iron was preferentially concentrated in slags, and higher matte grades improved the iron distribution in slags. The current experimental results enrich fundamental thermodynamic data and help optimize WEEE smelting operations for efficient recovery of valuable metals.

Effect of MgO on phase equilibria of copper matte and SiO2-saturated iron silicate slag in smelting complicated copper resources

The effect of MgO on the phase equilibria between matte and tridymite-saturated FeOx−SiO2−MgO slag was investigatedusing high-temperature equilibration and microanalysis technique. The results showed that at 1300 °C and p(SO2) of 10 kPa, the presence of MgO reduced the FeO activity of the slag, leading to the decrease in the oxygen partial pressure (p(O2)) over the slag and the Cu solubility in the slag. Due to the lower FeO activity, FeS was oxidized from matte into slag, increasing the Cu concentration of the matte. In high-SiO2 concentrationslags, excessive MgO in the liquid slag recrystallized as solid olivine (Mg2SiO4−Fe2SiO4), increasing the slag viscosity and copper losses in the slag. The maximum MgO solubility in the FeOx−SiO2−MgO slag increased from 3 wt.% to 8 wt.% when the temperature raised from 1200 to 1300 °C under p(O2) of 10−6 kPa. At higher MgO content, the slag composition could be optimized by increasing temperature and adding SiO2 flux to maintain a fully molten slag or avoid high proportions of solids.

Ground granulated iron silicate slag as supplementary cementitious material: Effect of prolonged grinding and granulation temperature

The metallurgical and cement industries contribute significantly to anthropogenic carbon dioxide emissions. Utilizing oxidic by-products from the metallurgical industry as supplementary cementitious materials (SCMs) can improve resource efficiency and reduce emissions from cement production. Iron silicate copper slags have been studied as SCMs, but mainly in systems where Portland cement is used as an activator. There is limited research on the inherent reactivity of the slag under changing processing conditions. The present study offers insight into the effect of granulation temperature and grinding on the inherent reactivity of an industrially produced iron silicate copper slag. The results showed that granulation temperature had an insignificant effect on reactivity, while grinding generated substantial improvements. The latter effect was concluded to stem from the increased specific surface area, increased number of sites for nucleation and growth of hydrates, and changes in the inherent reactivity owing to structural changes induced by the grinding.

A Method for Synthesizing Iron Silicate Slags to Evaluate Their Performance as Supplementary Cementitious Materials

Utilizing iron silicate copper slag as supplementary cementitious material (SCM) is a means to improve resource efficiency and lower the carbon dioxide emissions from cement production. Despite multiple studies on the performance of these slags in SCM applications, the variations in cooling procedure, grinding, and methods for evaluating reactivity limit the ability to assess the influence of chemical composition on reactivity from the literature data. In this study, a methodology was developed to synthesize iron silicate slags, which were then evaluated for their inherent reactivity using the R3 calorimeter-based experiments. The results demonstrated that laboratory-scale granulation produced the same reactivity as industrially granulated slag. Furthermore, a synthesized triplicate sample showed high repeatability. Based on these two aspects, this method can be used to systematically study the influence of chemical composition on the inherent reactivity of iron silicate slags while producing results that are directly translatable to industrial slags.

Effect of Fe/SiO2 ratio and cooling regime on As stability in copper smelting slag

The present study investigated the effects of Fe/SiO2 ratio (0.8−1.6) and cooling methods (quenching and cooling with furnace) on the stability of As in typical copper smelting slag (FeO−SiO2−Fe2O3−CaO−MgO−Al2O3). It was determined that iron silicate slag can achieve As vitrification. In addition, the lower Fe/SiO2 contributed to the immobilization and reduced the leaching toxicity of As. FTIR analysis showed that the increase of Fe/SiO2 caused to the depolymerization of the glass structure and promoted the formation of [AlO6]9− octahedra. XPS spectra of O1s and Si2p showed that the amount of non-bridging oxygen (NBO) in the melt increases with increasing Fe/SiO2. In addition, Al2p and As3d spectra indicate that the covalency between the As−O and Al−O bonds decreased with increasing Fe/SiO2 to accommodate glass depolymerization. For the slow-cooled slag, As was mainly enriched in the iron olivine phase, with a small fraction in the silicate matrix. The increase of Fe/SiO2 promoted the precipitation of iron olivine phase and thus the leaching concentration of As increased with the increase of Fe/SiO2.

Direct-to-blister smelting of copper concentrate based on a calcium ferrite slag system

The direct-to-blister smelting process realizes single furnace smelting from chalcocite to blister copper. This process saves the matte transport process, avoids multiple feeding in the smelting process, and has the advantages of high productivity, a short production process, and less SO2 pollution. By comparing with the phase diagram of iron silicate slag system, it shows that calcium ferrite slag system is more suitable for direct-to-blister smelting under the condition of high oxygen potential. In this study, high-grade copper concentrate was used as the raw material and direct-to-blister smelting experiments were carried out at the laboratory scale. The variation of copper recovery with CaO/Fe ratio, smelting temperature and sedimentation time was studied. The phase composition of slag and the loss of copper in slag were analyzed by X-ray diffraction (XRD) and scanning electron microscopy with an energy spectrometer (SEM-EDS). The results showed that by adjusting process parameters, the copper recovery can reach 90.15 wt.% and the blister copper grade is more than 98.50 wt.%. It provides a theoretical basis for the industrial application of calcium ferrite slag in direct-to-blister smelting.

Novel fluxing strategy of copper matte smelting and trace metals in E-Waste recycling

The distribution behavior of trace metals between copper matte and spinel-saturated iron silicate slags was investigated at 1250 °C and pSO2 of 0.25 atm at low silica concentrations. The experiments were conducted in magnetite (Fe3O4) spinel crucibles in controlled CO-CO2-SO2-Ar gas mixtures using a high-temperature equilibration-quenching technique. The concentrations of trace elements in matte, spinel, and slag were quantified by electron probe X-ray microanalysis and laser ablation-inductively coupled plasma-mass spectrometry. The trace metals (Ag, Ni, Co, and Sn) in all phases and their distribution coefficients were calculated as a function of matte grade. Results show that silver and nickel can be effectively recovered into matte, whereas cobalt and tin are predominantly deported into slag and gas phases, respectively. These results augment the fundamental thermodynamic data of trace metal distributions in copper smelting processes at low-silica fluxing practices.

Long-Term Leaching Effects on CaO-Modified Iron Silicate Slag

Granulated iron silicate slag, a by-product of pyrometallurgical copper extraction, has excellent properties for construction applications. Slag modification with CaO enhances the application properties regarding pozzolanic reactivity, potentially extending slag use in the future. The slags’ short-term leaching behavior has already been investigated with promising results, while the long-term leaching effects are less studied. Therefore, this study aims to determine the long-term leaching effects on CaO-modified iron silicate slags. The CaO-modifications were conducted during full-scale slag treatment operation. The slags were characterized and leached, and the remaining slags were investigated regarding the formation of secondary phases. The long-term leaching of main and trace elements was determined over 30 days using a dynamic leaching method corresponding to an extended time period. The leaching tests showed increased leaching of the main slag elements (Si, Ca). Zn and Cu showed peak leaching after four days of leaching, and the leaching of As and Sb decreased with the increasing CaO content in the samples. After dynamic leaching, secondary phases formed on the Cu-containing inclusions on the sample surfaces. Independent of the CaO content, the leaching of Cu was increased when subjected to external acidic and oxidating conditions using static pH titration at pH 5 in dilute nitric acid.

Investigation on the Matte/Slag/Spinel/Gas Equilibria in the Cu-Fe-O-S-SiO2-(CaO, Al2O3) system at 1250 °C and pSO2 of 0.25 atm

ABSTRACT The equilibrium-phase relations between copper mattes and spinel-saturated iron silicate slags were investigated at 1250°C and pSO2 of 0.25 atm. The experiments were conducted in synthesized spinel crucibles (Fe3O4) in controlled CO-CO2-SO2-Ar gas mixtures using a high-temperature isothermal equilibration/quenching technique. The equilibrium-phase compositions were characterized using an electron probe X-ray microanalyzer. The compositions of matte and slag were displayed as a function of matte grade or oxygen partial pressure. The present results obtained at spinel saturation in the matte-slag equilibrium system were compared with observations in the literature. This study improves the experimental thermodynamic data on the matte-slag-spinel-gas equilibria systems.

An experimental study on the phase equilibria of FeOx-saturated iron silicate slags and metallic copper alloys at 1200–1300 °C

The equilibrium phase relations between metallic copper alloys and magnetite/wüstite-saturated iron silicate slags were investigated at 1200–1300 °C and PO2 of 10−10 to 10−6.5 atm. The experiments involved high-temperature equilibration of samples in a controlled CO–CO2 atmosphere, followed by rapid drop quenching and direct measurement of the phase composition using the electron probe microanalysis technique. The equilibrium compositions for the metal and slag phase at different temperatures were displayed as a function of PO2. The present experimental results were compared with data from the literature as well as the thermodynamic assessment using MTDATA thermodynamic software. The present results contribute to the improvement of copper matte and black copper converting and slag cleaning processes.

Characterisation and leaching behaviour of granulated iron silicate slag constituents

ABSTRACT Due to increased copper production and the associated environmental consequences, copper production processes need to be improved, considering the impact of their byproducts, among others slag. This study investigated the leaching of individual constituents of iron silicate slag from a copper smelter. This was done by characterising granulated samples of its constituents – glass, matte, speiss – to determine their leaching contribution. It was observed that leaching in distilled and deionised water without pH regulation achieved various natural pH for the constituents. At natural pH, glass (Cu, Zn) and speiss (Ni, Sb) contributed to leaching. Static pH titrations showed the increased leaching of Zn, Cu, Ni, As, and Sb with decreasing pH. The results showed that, an iron silicate slag consisting of glass, matte and speiss, contributes to leaching as follows: matte – Cu and Ni, speiss – Cu, Ni, As, and Sb. Zn leaching is similar among the constituents.

Characterisation and leaching behavior of CaO-modified iron-silicate slag produced in laboratory and industrial scales

ABSTRACT Water-granulated CaO-modified iron-silicate slags have shown beneficial properties for cement applications. To further evaluate potential applications, the leaching properties must be understood. Therefore, this study aims to characterise and assess the metal leaching of iron-silicate slags (2.6% CaO) modified with lime (CaO, up to 20 wt.%) produced on both laboratory and industrial scales. The granulated samples showed amorphous contents for the studied CaO range. Generally, the metal content of the samples decreased with the increasing CaO content. Batch leaching tests were conducted on the slags, and the metal leaching and CaO content of the slag were strongly correlated. The leaching of Zn and Cu decreased with the increasing CaO content in the slag. Overall, the slags with 12–13% CaO exhibited minimal leaching of Zn, Cu, Ni, and Sb. These findings indicate that CaO influences the properties of the slag and can suppress metal leaching from water-granulated iron-silicate slags.

Handling trace elements in WEEE recycling through copper smelting-an experimental and thermodynamic study

Recycling of waste electrical and electronic equipment (WEEE) is attracting increasing attention, due to the presence of valuable metals and the risk of environmental emissions associated with WEEE disposal. In this study, the distributions of trace elements (Ag, Ni, Co, and Sn) between copper alloy and magnetite/wüstite-saturated iron silicate slags were investigated at 1200–1300 °C and PO2 of 10-10-10-6.5 atm, simulating the conditions of WEEE reprocessing through secondary copper smelting and converting. The high-temperature isothermal equilibration experiments were conducted in synthesized magnetite/wüstite crucibles under controlled CO-CO2 atmospheres followed by quenching in an ice-water mixture. The phase compositions and concentrations of the trace elements in copper alloy, magnetite/wüstite, and slag were determined by Electron Probe X-ray Microanalysis and Laser Ablation-High-Resolution Inductively Coupled Plasma-Mass Spectrometry. The distribution coefficients of all investigated trace elements between copper alloy and slag increased with decreasing oxygen partial pressure and increasing temperature. Ag distributed strongly into the copper alloy at all conditions, whereas Co mainly deported into the slag phase. Ni and Sn were concentrated in the alloy at lower PO2 and in the slag at higher PO2. Varying concentrations of Ni, Co, and Sn were also dissolved into the solid magnetite/wüstite phase.

Settling of Copper Phases in Lime Modified Iron Silicate Slag

Copper in discarded slag decreases the profits and copper recovery during the pyrometallurgical extraction processes. The copper losses to slag can be reduced by using a settling furnace, in which mechanically entrained copper droplets separate from the slag under the action of gravity. The settling rate of entrained droplets can be increased by modifying the slag composition and, thus, the slag properties, which are known to influence the settling rate. The knowledge of industrial CaO slag modification in a reduced iron silicate slag with a Fe/SiO2 ratio close to unity is limited. An industrial trial was thus conducted in an electric settling furnace, where the slag had been pretreated in a fuming furnace, to investigate the effect of CaO slag modification on the final slag copper content. Slag samples were collected from the ingoing and outgoing slag and from within the furnace of batches modified with CaO up to about 16 wt %. The trial was evaluated by comparing the final slag copper content and the copper recovery in the settling furnace. The results indicate that the settling becomes more efficient with the CaO modification as the final slag copper content decreased with increasing CaO content.

Influence of Process Parameters on Copper Content in Reduced Iron Silicate Slag in a Settling Furnace

During the pyrometallurgical extraction of copper, a significant fraction of this metal is lost with discard slag, which decreases profits and overall copper recovery. These copper losses can be reduced by using a settling furnace, in which suspended droplets containing copper separate from slag under the influence of gravity. An industrial trial was conducted in a settling furnace to increase the knowledge of the effect of temperature and settling time on the copper content of slag, and thus enhance the settling process to increase copper recovery. Slag samples were collected from four sample points: the ingoing and outgoing slag stream, within the furnace during settling, and the granulated slag. The chemical composition of the slag samples was analyzed and compared between batches with different temperatures and settling times. The appearance of copper and its associated phases were analyzed using a scanning electron microscope with an energy-dispersive X-ray spectroscopy detector (SEM-EDS). The results indicated that the outgoing slag copper content increased with an increase in temperature, and it was also concluded to be influenced by the attachment of copper to spinels and gas bubbles. The results indicate that regulating the settling furnace temperature to a lower interval could increase copper recovery.

On the Kinetic Behavior of Recycling Precious Metals (Au, Ag, Pt, and Pd) Through Copper Smelting Process

The recycling and recovery of precious metals from secondary materials, such as waste-printed circuit boards, are an important area of circular economy research due to the limited existing resources and increasing amount of e-waste produced by the rapid development of technology. In this study, the kinetic behavior of precious metals Au, Ag, Pt, and Pd between copper matte and iron-silicate slag was investigated at a typical flash smelting temperature of 1300 °C in both air and argon atmospheres. SEM–EDS, EPMA, and LA-ICP-MS-advanced analysis methods were used for sample characterization. The results indicate that precious metals favor the matte phase over slag, and the deportment to matte occurred swiftly within a short time after the system had reached the experimental temperature. With increasing contact times, the precious metals were distributed increasingly into the sulfide matte. The distribution coefficients, based on experimentally measured element concentrations, followed the order of palladium > platinum > gold > silver in both air and argon, and the matte acted as an efficient collector of these precious metals. The obtained results can be applied to industrial copper matte smelting processes, and they also help in upgrading CFD models to simulate the flash smelting process more precisely.Graphical

Solubility of Palladium in Alumina-Iron Silicate Melts

Dissolution and solubility of palladium in iron silicate melts saturated with alumina–iron spinel at 1300°C has been measured using an equilibration-drop quenching technique combined with electron probe microanalysis and laser ablation–inductive coupled plasma–mass spectrometry analysis from polished sections. Composition of the resulting Fe-Pd alloy allowed estimation of the activity of palladium at different oxygen partial pressures, and, thus, the solubilities of palladium in the studied slags in conditions typical of copper and nickel smelting as well as slag cleaning at pO2=10-5 to 10-10 atm. The mechanism of palladium dissolution in the studied iron silicate slags was oxidation by formation of the monovalent oxide species PdO0.5 over the entire oxygen activity range of this study. Testing the applicability of the various palladium isotopes for quantitative analyses of Pd in these types of matrices resulted in a good fit of measured concentrations of 104Pd and 105Pd with interference-corrected 106Pd and 108Pd.

Distributions of As, Pb, Sn and Zn as minor elements between iron silicate slag and copper in equilibrium with tridymite in the Cu–Fe–O–Si system

Abstract The distributions of arsenic, lead, tin and zinc between iron silicate slag and copper in equilibrium with tridymite in the Cu–Fe–O–Si system have been experimentally determined at selected oxygen partial pressures (P(O2)) at temperatures of 1 523 K and 1 573 K. The experimental technique involved high temperature equilibration in a sealed silica ampoule to minimize the vaporization of minor elements, rapid quenching of the condensed phases, and the direct composition measurements of the condensed phases using microanalysis techniques. The effective P(O2)s of the samples were determined based on the measured Cu2O concentrations in slag. The new experimental data resolve discrepancies found in previous studies and have been used in the development of a new thermodynamic database of the Cu–Fe–O–Si system containing minor elements.

Rheology of an alkali-activated Fe-rich slag suspension: Identifying the impact of the activator chemistry and slag particle interactions

Iron-silicate slags, originating from metallurgical industry, are upon alkali-activation precursors for synthesis of inorganic polymer binders, which can be used in construction. The slag's rheology is important for certain construction applications, which is for alkali-activated Fe-rich slag suspensions (AAS) still largely unmapped. To identify the contribution of the activator and of an early formed binder to the rheology, the activator SiO2/Na2O molar ratio and H2O content was modified. The flow behaviour of AAS was compared with an activator alone, and a quartz suspension to reveal the effect of the slag particles on the rheology and its degree of activation. Raising SiO2/Na2O molar ratio resulted in a higher yield stress and elasticity, explained by the increase of silicate complexes, while decreasing SiO2/Na2O molar ratio resulted in more monomers. AAS exhibited a yield stress fluid-like behaviour conform to the Herschel-Bulkley model and driven by the strong physical interaction between the slag particles.