Gabriella Tranell

Norwegian University of Science and Technology | NTNU · Department of Materials Science and Engineering

Monosilane (SiH 4 ) is a common precursor for the production of high-purity silicon for solar PV applications. As an alternative to carbothermic reduction of silica to produce metallurgical grade silicon with subsequent conversion to silane, an alternative route over magnesiothermic reduction of silica to Mg 2 Si has been explored in our earlier wo...

Recycling aluminium in a rotary furnace with salt-fluxes allows recovering valuable alloys from hard-to-recycle waste/side-streams such as packaging, dross and incinerator bottom ash. However, this recycling route generates large amounts of salt-slag/salt-cake hazardous wastes which can pose critical environmental risks if landfilled. To tackle thi...

This work is dedicated to developing a laboratory method for assessing emissions of polycyclic aromatic hydrocarbons (PAHs) from different carbon-based materials at elevated temperatures. The method will additionally contribute to enhancing the fundamental knowledge about the formation and decomposition of these compounds during various process con...

High-temperature wetting of natural, high-purity quartz (SiO2) and liquid magnesium (Mg) was investigated at temperatures between 973 and 1273 K. Sessile drop experiments using the capillary purification (CP) procedure were carried out under an Ar gas atmosphere (N6.0), eliminating the native oxide layer on the surface of Mg melt. The results showe...

Silicon alloys are produced by carbothermic reduction of quartz in a submerged arc furnace. This high-temperature pyrolytic process is a source of polycyclic aromatic hydrocarbons (PAHs), which are a group of aromatic organic molecules with known mutagenic and carcinogenic properties. In this study, the emission of oxy- and nitro-PAHs from a pilot-...

Organic coatings are a challenge for aluminium packaging recycling since they tend to increase the re-melting metal losses. A solution is de-coating the scrap via a thermal pre-treatment to burn-off the organics before re-melting. Due to logistic benefits, the scrap is often pressed into bales. This study evaluates the influence of compaction on th...

Two widely used atomic layer deposition precursors, Tetrakis (dimethylamido) titanium (TDMA-Ti) and titanium tetrachloride (TiCl 4), were investigated for use in the deposition of TiOx-based thin films as a passivating contact material for solar cells. This study revealed that both precursors are suited to similar deposition temperatures (150 • C)....

Salt fluxes with fluoride additions are necessary to recycle contaminated and oxidized aluminium scrap. Cryolite is a particularly effective fluoride in separating molten aluminium from the oxides, but its use needs to be minimized due to environmental concerns. This study aims to investigate the effect of various cryolite additions in the range of...

Aluminum (Al) white dross is classified as hazardous waste and originates from the primary production of Al as a result of molten metal oxidation at an industrial scale. As the produced dross reduces the annual metallic Al production by up to 10%, finding a way to reduce the dross formation has always been of interest. Several laboratory studies ha...

Fundamental studies have been carried out experimentally and theoretically on the magnesiothermic reduction of silica with different Mg/SiO2 molar ratios (1–4) in the temperature range of 1073 to 1373 K with different reaction times (10–240 min). Due to the kinetic barriers occurring in metallothermic reductions, the equilibrium relations calculate...

Coal tar pitch, a well-known source of polycyclic aromatic hydrocarbons (PAHs), is used as a binder of petroleum coke in prebaked anodes used for electrolysis of aluminum. Anodes are baked up to 1100 °C over a 20-day period, where flue gas containing PAHs and volatile organic compounds (VOCs) are treated using techniques such as regenerative therma...

This work is dedicated to developing a method of combined surface morphology- and crystallographic analysis for crystalline silicon. To demonstrate the applicability of the method, a series of chemical operations, such as polishing and texturing, were applied to multi-crystalline silicon samples. The samples were pre- and post-analysed with WLI and...

Salt fluxes with fluoride additions are necessary for the treatment and recycling of contaminated or oxidized aluminium scrap. This study aims to investigate the effect of cryolite additions on the thermal properties and the coalescence efficiency of a NaCl–KCl salt flux mixture. Thermodynamic calculations were carried out to examine the phase diag...

Polycyclic aromatic hydrocarbons (PAHsPolycyclic Aromatic Hydrocarbons (PAH)) are naturally present in raw materials used as a binder in prebaked anodesAnode for electrolysisElectrolysis of aluminumAluminum. Green anodesAnode are baked to about 1200 °C through a cycle of 14–17 days where organic hydrocarbon volatiles contribute to the carbonization...

Heavy metalHeavy metalsemissionsEmissions from the aluminiumAluminium industry are mainly carried from the plant through fugitiveFugitiveparticulate matterParticulate matter (PM) originating from the aluminium electrolysisAluminium electrolysis pot room. To evaluate the behaviour of metal-carrying PM, both airborne and settled PM from two different...

The current work aimed to demonstrate the application of a technique where white light interferometry (WLI) and Laue X-ray crystallography scanner character-isation were combined to study the chemical etching response of diamond cut multi-crystalline Si (mc-Si) wafers. Using this technique, the effect of different texturing additives (isopropyl alc...

Flue gas recirculation (FGR) for the silicon process may facilitate increasing the CO 2 concentration in the off-gas, which will be beneficial for potential future carbon capture. Lower oxygen concentration in the combustion gas will also reduce NO X emissions. An existing 400 kVA Submerged Arc Furnace (SAF) pilot setup was modified to be able to r...

Up to 10% of all metallic aluminum (Al) produced is lost due to dross generation during production. It also causes an environmental problem due to hazardous waste generation following treatment, as well as toxic gas generation when in contact with water/humidity. As a result, it is desirable to identify the parameters contributing to the generation...

In aluminum recycling, thermal de-coating pre-treatments remove moisture and organic contamination before re-melting. If the scrap is compacted into bales or briquettes before the thermal treatment and re-melting processes, less surface area is exposed to oxidation in contact with air. However, compaction may also limit the efficiency of the de-coa...

Airborne particulate matter (PM) is a concern for both occupational health and the environment, and, in the ferroalloy industry, the level of such particles in the air can be considerable. Small, low-cost sensors for measuring PM have generated interest in recent years, providing widespread monitoring of PM levels in the environment. However, such...

In this work, the kinetics of natural quartz reduction by Mg to produce either Si or Mg2Si was studied through quantitative phase analysis. Reduction reaction experiments were performed at various temperatures, reaction times and Mg to SiO2 mole ratios of 2 and 4. Rietveld refinement of X-ray diffraction patterns was used to obtain phase distributi...

In this study, one-step production of W2FeB2 and WFeB compounds from oxide raw materials was carried out through cost-effective and energy-efficient aluminothermic self-propagating high-temperature synthesis (SHS). Accordingly, the feasibility of SHS in the production of W2FeB2 and WFeB compounds was discussed. In addition, the selected SHS product...

Producing high-silicon alloys in submerged arc furnaces (SAF) involves the generation of an intermediate process gas, consisting of silicon monoxide (SiO) and carbon monoxide (CO). Combustion of process gas from the taphole can be an environmental challenge. SiO gas burns to fine SiO2 particles which can cause poor working conditions and fugitive p...

The Al2O3–CaO–SiO2 ternary is a basic oxide system relevant for the Pedersen alumina production process and for aluminothermic silicon production with low environmental impact using secondary aluminium and silica raw materials. Rheological property is one of the most important properties for the above applications. A phenomenological viscosity mode...

In industrial applications and laboratory studies, it has been shown that the use of water spray may significantly reduce the amount of fume generated from the oxidation process of liquid high carbon ferromanganese alloy. However, in our recent study, it was shown that the oxidation rate of liquid silicon alloy increases with increasing water conte...

TEM EDS–EELS and XPS have been performed on disc samples of Al alloys 5182 (AlMg4.5Mn0.4) and 6016 (AlSi1.2Mg0.4) heat treated in an oxidizing atmosphere of 76 pct synthetic air, 20 pct Ar, and 4 pct CO 2 . For both alloys, an amorphous C–C bonded layer on top of a nanocrystalline MgO layer was observed, which is believed to inhibit further oxidati...

In the current work, the metallothermic reduction of natural quartz by magnesium has been studied at 1373 K under different reaction conditions, i.e. quartz type, quartz particle size, Mg:SiO 2 mole ratio and reaction time. The microstructure of reaction products was studied to illustrate the reaction progression through scanning and transmission e...

Oxidative ladle refining (OLR) is the most widely used refining process for removal of dissolved Ca and Al in the industrial production of metallurgical grade silicon (MG-Si). Refining occurs by purging the silicon alloy with an oxygen–air mixture at temperatures preferably between 1823 K and 1873 K, forming a SiO $$_{2}$$ 2 –CaO–Al $$_{2}$$ 2 O $$...

Oxidation of liquid aluminum (Al) during processing is a widely known problem, and magnesium (Mg), as a common alloying element, increases the oxidation rate of the alloy. It has been established that small additions of CO2 (≥ 4%) in an oxidizing atmosphere have a significant inhibiting effect on the rate of oxidation of Al alloys 5182 (AlMg4.5Mn0....

Scrap pre-treatments, such as compaction and thermal de-coating, are standard industrial practices for recycling aluminium post-consumer scrap. This study compares the recyclability of a coated and uncoated 8111 alloy under the application of compaction and/or thermal de-coating pre-treatments. Sheets of 600 μm thickness were shredded into chips an...

The SisAl process encompasses the production of silicon (Si) alloysSilicon alloy by reducing silica in slags aluminothermically, using secondarySecondary materials aluminum (Al) raw materials as reductants. Along with the Si alloy, a CaO–Al2O3–(low)SiO2 slag is produced. Alumina-rich slag can be a source for production of High-Purity Alumina (HPA)...

Silicon kerf residueSilicon kerf residue is generated during the wafering process of pure silicon in the photovoltaic value chain. The generated by-productUtilization of by-products has a high volume, and the particle size is typically below 1 μm. Although the fine particles are partly oxidized, the material may be beneficial in different metallurg...

Flue gas recirculationFlue gas recirculation (FGR) for the siliconSilicon process may facilitate increasing the CO2 concentration in the off-gas, which will be beneficial for potential future carbon capture. Lower oxygen concentration in the combustion gas will also reduce NOX emissions. An existing 400 kVA submerged arc furnace (SAF) pilot setup w...

Calcium aluminate slag produced by the aluminothermic reduction of silica is tested as a candidate raw material for the hydrometallurgical production of pure aluminium chloride hexahydrate (ACH) through leaching with hydrochloric acid. The crystallization of ACH follows by sparging the pregnant liquor with hydrochloric gas. Almost total extraction...

The recovery of major components of bauxite residue by carbothermic reduction at 1550–1750 °C and subsequent slag leaching in a Na 3 CO 3(aq) solution is studied. Iron recovers primarily to pig-iron and lime is added to tune the calcium aluminate slags towards the highly leachable mayenite phase. The concentration of aluminum in the leachate correl...

The increasing use of aluminimum in packaging applications results in many different aluminium-based products ending up in consumer mixed-waste bins. This waste is typically incinerated, generating an aluminium-containing bottom ash. The current work investigates the recyclability of the aluminium fraction in the bottom ash from waste incineration...

The sludge generated by wet scrubbing the off-gas from a silicomanganese plant in Norway represents a significant loss in silicon and manganese values. This work seeks to extract these values in the production of ferroalloys and slags that can be utilized by alternative industries. Carbothermic smelting the sludge together with iron or iron scraps...

Oxidative ladle refining (OLR) is the most used refining method in industrial production of metallurgical grade silicon. OLR is performed by purging the liquid alloy with oxygen-enhanced air at 1823 K to 1873 K, reacting with silicon and the primary slag forming impurities to a SiO $$_{2}$$ 2 -CaO-Al $$_{2}$$ 2 O $$_{3}$$ 3 slag. To further increas...

Thermal fume formation is a problem in manganese ferroalloy production and the metal production industry at large. A better understanding of the mechanisms of fume formation and the operational parameters affecting the fume formation rate may help in reducing and managing fuming. This paper aims to investigate the effects of oxygen content and gas...

A correction to this paper has been published: https://doi.org/10.1007/s11085-021-10031-0

Oxidation of aluminum alloys during production is a well-known problem and contributes to significant metal losses. As small additions of CO2 in the oxidizing atmosphere has proven to inhibit the oxidation rate for high-Mg(≥5wt%) aluminum alloys, the present study has aimed at evaluating its effect on alloys with varying Mg concentration in combina...

One of the problems when recycling aluminium is its oxidation and consequent metal loss. This is especially critical for the thin sheet/foil materials used for food packaging applications. Compacting the scrap into briquettes may partly reduce such losses in addition to facilitate transport and storage. Shredded aluminium materials of different thi...

Aluminium (Al) white dross is defined as a heterogeneous mixture consisting of unreacted metallic Al, nitrides and oxides in the form of large flakes, lumps, small particles, dust and films. The dross is formed during skimming of Al melts when in direct contact with oxidising atmospheres before casting. To get a better understanding of dross charac...

Al 4 C 3 particles form during the primary production of aluminum via molten salt electrolysis due to the carbon solubility and direct contact between bath, metal, and carbon anodes. Additional Al 4 C 3 may form during melt processing through direct contact between the melt and carbonaceous materials. As a result of their small size and similar den...

The management of airborne particulate matter (PM) emissions from silicon and ferrosilicon production is, in many ways, similar to the management of airborne PM emissions from other pyrometallurgical industries. Certain challenges are, however, highly branch specific. For example, the simultaneous production of silica dust and NOX gas in the submer...

The quality requirements of aluminum products are steadily increasing, and the presence of non-metallic inclusions have a large impact on the quality of aluminum products. Sedimentation is a widely applied technique to remove inclusions and the settling characteristic of particles is one of the most important parameters determining the removal effi...

As a result of increasing demands for aluminium in numerous sectors such as construction, automotive and transportation, its rate of consumption has sharply risen in recent decades. Aluminium is also used in containers for food- and drinks packaging due to its good formability, low density and corrosion resistance. The use of aluminium in everyday...

The oxidation of silicon (Si) has been extensively investigated over the past 50 years. Yet, an understanding of the mechanism and rate of liquid Si oxidation in atmospheres containing water vapor, is lacking. The effect of water vapor on the oxidation process is of particular importance in the industrial, metallurgical production and processing of...

The presence of non-metallic inclusions in aluminium has become a more critical issue with increasing demands on surface quality and low final wall thicknesses of products. Aluminium carbide particles form during the primary aluminium production due to the contact between aluminium and carbon/carbonaceous species in the electrolysis cell . These pa...

AlMg alloys are known to suffer from problematic oxidation that can result in significant dross formation and loss of Mg from the melt. Historically, beryllium has been used to minimize the oxidation as it forms a protective BeO layer at the oxide-metal interface that inhibits further oxidation of the Mg. Alternative protection agents to beryllium...

Aluminum is widely used in daily household consumable goods such as food and drink packaging materials, storage containers, etc. The disposal of such goods into household waste means that this waste stream contains a significant amount of aluminum . Domestic waste is commonly sent to incinerator plants where the organics are combusted while the met...

DeMaskUs er et tverrfaglig forskningsprosjekt som startet i Juni 2015 og avsluttes i 2019. Prosjektet har vært finansiert av Norges Forskningsråd gjennom programmet NANO2021, Ferrolegeringsindustriens forskningsforening (FFF) og silisiumkarbidprodusentene Washington Mills AS og Saint-Gobain. Forskningsgruppa har bestått av prosessmetallurger fra SI...

Al-Mg alloys are known to suffer from problematic oxidation during melting, refining and casting. The use of a CO2/air cover gas is known to minimize this oxidation; however, a mechanistic understanding of the beneficial inhibiting effect is lacking. A series of thermogravimetric experiments were conducted under a variety of different CO2-containin...

Carbothermic reduction of neodymium (III) oxide (Nd2O3) was performed by arc melting and in a graphite resistance furnace, using copper as a solvent metal. Successful carbothermic reduction was evident by formation of copper-neodymium intermetallics, where predominant phases were found to be Cu6Nd and Cu5Nd. The reduction reaction is proposed to be...

A pilot scale, silicomanganese alloy production campaign was performed in a 440 kVA, single phase electric furnace in order to establish an overview of the minor- and trace element contents in process input raw materials and their distribution in the resulting primary and secondary products. Samples of the in-going raw materials (manganese ore, cok...

The addition of beryllium to Al-Mg alloys is known to cause a dramatic decrease in oxidation; however, the mechanism behind this protective effect is not yet fully understood. To aid in finding an alternative to the toxic Be, a fundamental study of Be additions has been carried out. Industrial samples containing 2 ppm Be and a model alloy with 100...

The addition of beryllium to high magnesium aluminum alloys has long been known to cause a significant decrease in the rate of alloy oxidation. A clear understanding of the fundamental mechanism behind this effect is still lacking. Previous work by the authors has shown that the first formed oxide layer and the oxide metal interface is of key impor...

Thermally generated fumes from the production of manganese ferroalloys are mostly composed of metallic oxides generated due to reaction between high-temperature molten metal and ambient oxygen in the air. In the current study, the fume characteristics (particle morphology, compositions and particle size distribution) from the exposure of a SiMn all...

This research is aimed to improve our knowledge on the dust formation and clustering in the ferroalloy industry. Specifically, this paper focuses on the evaporation of manganese metal, and how different parameters influence the evaporation rate. Experiments were done with pure manganese metal heated to between 1400 and 1700 °C in a pure argon atmos...

Apatite, Ca 5 (PO 4 ) 3 F, concentrate from LKAB in Kiruna, Sweden, has been characterized and pyrometallurgically treated using (i) silicon metal and fluxes to extract phosphorus and transition metals at 1600 °C (Part I publication), and (ii) carbon to extract phosphorus without fluxing at temperatures exceeding 1800 °C (Part II publication), with...

Apatite, Ca5(PO4)3F, is a useful raw material for the production of both elemental phosphorus and phosphoric acid, and the mine tailings present at Luossavaara-Kiirunavaara AB (LKAB) in Kiruna, Sweden, represent a significant potential European source of apatite if upgraded to a concentrate. In the present study, pilot apatite concentrate made from...

In this work, an n-type high performance multicrystalline silicon (nHPMC) ingot (τ >1.2 ms) was cast at NTNU. A new method to manufacture nHPMC solar cells with hetero junction solar cell architecture is presented. Texturing of the wafers is performed through silver assisted chemical etching followed by an alkaline solution treatment process. The s...

Equilibrium distribution and transport kinetics of boron between ferrosilicon and calcium silicate slag were investigated through experimental study. A 50 pct CaO-50 pct SiO2 slag (by weight) was held for different durations at 1873 K (1600 °C) in a graphite tube furnace together with boron-doped ferrosilicon alloys in the range 50 to 85 wt pct Fe....

The oxidation of molten aluminum has been thoroughly studied, and it is established empirically that beryllium has an inhibiting effect on the oxidation behavior. The aim of this work was to increase the fundamental understanding of this inhibiting effect. Two 5XXX aluminum alloys (4.7% Mg), one with 2 ppm of beryllium and one without beryllium, we...

Hydrometallurgical treatment of silicon is an effective process for the removal of metallic impurities for producing solar grade silicon feedstock. In the present research, the removal of impurities from silicon is studied through the addition of Mg into a commercial silicon, its solidification, and acid leaching. The effect of concentration of HCl...

During the tapping and casting of manganese ferroalloys, fumes are generated and released to the working environment. The fumes are mostly composed of metallic oxides generated due to reaction between high temperature molten metal and ambient oxygen in the air. From an environment perspective, it is important to limit these emissions. However, to d...

The mass transfer of Al and Ca between silicon and synthetic SiO 2-CaO-Al 2O 3 slags of varying composition has been investigated, using different experimental set-ups. Samples were kept at 1600 °C, varying the holding times in an individual crucible kinetic series set-up or sampled at given sample intervals in a larger crucible set-up. Solute conc...

The management of airborne emissions from silicon and ferrosilicon production is, in many ways, similar to the management of airborne emissions from other metallurgical industries, but certain challenges are highly branch-specific, for example the dust types generated and the management of NOX emissions by furnace design and operation. A major diff...

During the casting of ferromanganese alloys, a considerable amount of dark fumes, consisting primarily of manganese oxides, are generated when the Mn vapour oxidises in the atmosphere. Previous studies indicate that these fumes can be reduced by increasing the humidity above the melt. However, the reduction mechanism is not fully understood. In an...

Oxidative refining of silicon after tapping from the furnace is performed to remove calcium and aluminum impurities. Depending on the slag composition, the refining limit is determined by the thermodynamic equilibrium between silicon and slag. Silica-rich CaO-Al2O3-SiO2 slags were equilibrated with silicon at 1823 K (1550 °C) in the present study....

The three-dimensional structure of silica diatom frustules offers a great potential as nanoporous material for several nanotechnological applications, but the starting point for these applications is the ability to obtain clean frustules with sufficient mechanical strength and intact structure. Here, frustules from the diatoms Coscinodiscus central...

NdFeB magnet scrap is an alternative source of neodymium that could have a significantly lower impact on the environment than current mining and extraction processes. Neodymium can be readily oxidized in the presence of oxygen, which makes it easy to recover neodymium in oxide form. Thermochemical data and phase diagrams for neodymium oxide contain...

As part of the research activities related to emissions and energy recovery in SFI Metal Production, a thorough review of published and unpublished work on emissions from, and emission measurements in, the production of MG-Si and FeSi alloys, has been carried out. This work has been submitted as a review article (DOI:10.1007/s11837-016-2149-x) for...

A mathematical model for industrial refining of silicon alloys has been developed for the so-called oxidative ladle refining process. It is a lumped (zero-dimensional) model, based on the mass balances of metal, slag, and gas in the ladle, developed to operate with relatively short computational times for the sake of industrial relevance. The model...

Dust, or airborne particulate matter, from metal smelting can be either mechanically or thermally generated and it negatively affects the indoor air quality as well as the fugitive emissions from the plant. The thermally generated dust is often referred to as fume and it is typically generated whenever liquid metal comes into contact with air. For...

Rare Earth Elements (REEs) have unique properties that have led to a rapid increase of consumption in modern technological products. This has in turn led to a greater awareness of the limited and highly localized nature of mineral reserves, and the dilute nature of the undeveloped resources including those from secondary sources.

Dust, or airborne particulate matter, from metal smelting can be either mechanically or thermally generated and it negatively affects the indoor air quality as well as the fugitive emissions from the plant. The thermally generated dust is often referred to as fume and it is typically generated whenever liquid metal comes into contact with air. For...

Rare Earth Elements (REEs) have unique properties that have led to a rapid increase of consumption in modern technological products. This has in turn led to a greater awareness of the limited and highly localized nature of mineral reserves, and the dilute nature of the undeveloped resources including those from secondary sources. Recycling of REEs...

Dust, or airborne particulate matter, from metal smelting can be either mechanically or thermally generated and it negatively affects the indoor air quality as well as the fugitive emissions from the plant. The thermally generated dust is often referred to as fume and it is typically generated whenever liquid metal comes into contact with air. For...

EPD Congress is an annual collection that addresses extraction and processing metallurgy. The papers in this book are drawn from symposia held at the 2015 Annual Meeting of The Minerals, Metals & Materials Society. The 2015 edition includes papers from the following symposia: • Materials Processing Fundamentals • Solar Cell Silicon • High-Temperatu...

The removal of boron from silicon by top blowing of humidified hydrogen has been studied in the present work through experimental work, thermodynamic calculations, computational fluid dynamic modeling, and quantum chemistry calculations. The effect of process parameters; temperature, lance diameter, lance distance from the melt surface, gas flow ra...

The ecological success of diatoms is emphasized by regular blooms of many different species in all aquatic systems, but the reason behind their success is not fully understood. A special feature of the diatom cell is the frustule, a nano-patterned cell encasement made of amorphous biosilica. The optical properties of a cleaned single valve (one hal...