Beneficiation of an ilmenite waste stream containing undesirable levels of chromite

Please read the abstract in the section, 00front, of this document (Role and responsibility of the author)Dissertation (MEng)--University of Pretoria, 2008.Materials Science and Metallurgical Engineeringunrestricte

Wear mechanisms of carbon-base refractory materials in SiMn tap-holes : Part II : In situ observation of chemical reactions

The purpose of the study presented here is to determine to what extent chemical reactions between carbon-based refractory and slag or metal in the tap-hole of a SiMn furnace can contribute to wear of tap-hole refractory. The results of the study are reported in two parts. In Part I, thermodynamic calculations suggested that reaction between silicomanganese slag and carbon-based tap-hole refractory is possible, and experiments with nominally pure materials support this. However, practical refractory materials are by no means pure materials and contain secondary phases and porosity which can be expected to affect reaction with slag. In Part II, such reactions are examined experimentally, in cup and wettability tests, using commercially available carbon block and cold-ramming paste refractory materials and mainly industrial SiMn slag. Clear evidence was found of chemical reaction at approximately 1870 K (approximately 1600 C), forming SiC and, it appears, metal droplets. Both carbon block and ramming paste refractory reacted with slag, with preferential attack on and penetration into the binder phase rather than aggregate particles. The two types of carbon-based refractory materials showed similar extents of chemical reaction observed as wetting and penetration in the laboratory tests. The differences in refractory life observed practically in industrial furnaces should therefore be attributed to wear mechanisms other than pure chemical wear as studied in this work.National Research Foundation of South Africa (Grant TP2011070800005).http://link.springer.com/journal/116632016-04-30hb201

Thermal conductivity of solidified manganese-bearing slags : a preliminary investigation

The thermal conductivity of slag is an important parameter in the design of furnace-containment systems based on freeze-lining technology. Literature indicates that the crystal content of a slag has a significant influence on its thermal conductivity. Industrial, rich, manganese-bearing slag was cooled at different rates to create samples with different microstructures. The coefficients of thermal conductivity of these samples were measured in a nitrogen atmosphere from room temperature to 990°C at 100°C intervals. The laser-flash measurement technique was used for this purpose. Follow-up investigations included XRF and XRD and modelling in FACTSage.http://www.saimm.co.za/ai201

Wear mechanisms of carbon-based refractory materials in silicomanganese tap holes : Part I : Equilibrium calculations and slag and refractory characterization

Silicomanganese (SiMn) as an alloy supplies silicon and manganese to the steelmaking industry. It is produced through carbothermic reduction in a submerged arc furnace. The slag and metal are typically tapped through a single-level tap hole at 50 K (50 C) below the process temperature of 1873 K to 1923 K (1600 C to 1650 C). In one tapblock refractory design configuration, the tap hole is installed as a carbon tapblock and rebuilt during the life of the lining using carbon-based cold ramming paste. The carbon tapblock lasts for a number of years and ramming paste only for months. The purpose of the study presented here was to determine to what extent chemical reactions between carbon-based refractory and slag or metal in the tap hole of a SiMn furnace can contribute to wear of tap-hole refractory. The results of the study are reported in two parts. In Part I, the results of thermodynamic calculations of the potential for chemical reaction between carbon-based refractory material and slag or metal are reported. The results were tested experimentally using pure graphite and synthetic SiMn slag (produced from pure oxides). The paper also reports the composition, microstructure, and phases of industrial SiMn slag, and commercially available carbon block and cold ramming paste refractory materials. These compositions were used in predicted equilibria of refractory–slag reactions. Thermodynamic calculations suggest that reaction between SiMn slag and carbonbased tap-hole refractory is possible, and experiments with nominally pure materials support this. However, practical refractory materials are by no means pure materials, and contain secondary phases and porosity which can be expected to affect reaction with slag. Such reactions are examined in Part II.National Research Foundation of South Africa (Grant TP2011070800005).http://link.springer.com/journal/116632016-04-30hb201

Magnesia refractory dryout : managing the risk of hydration

In 2002 the commissioning of an ilmenite smelter on the North Coast of South Africa was extended by three months due to the failure and subsequent replacement of the magnesia-based refractory lining. The lining failed due to the hydration of magnesia caused by an unexpected source of water. The incident resulted in significant financial losses and a prolonged insurance claim which was settled in 2009. As magnesia-based refractories are used extensively in both ferrous and non-ferrous applications, the authors of the paper want to share the experience gained from this incident with others. The paper reviews the literature available on furnace start-up practices and explains the hydration of magnesia using available sources. The incident is studied in more detail, both technically and economically, and the costs incurred are quantified in terms of the cost of the original lining. The paper concludes with lessons learned and recommendations made for future work. The intention of the paper is to stimulate open debate regarding best practices in preheating of furnaces lined primarily with magnesia.http://www.saimm.co.za

Chemical wear analysis of a tap-hole on a SiMn production furnace

In April 2013 a 48 MVA submerged arc furnace producing silicomanganese was excavated in South Africa. Since the high shell temperatures recorded in the tap-hole area resulted in the furnace being switched out for relining, the tap-hole area was excavated systematically. A refractory wear profile of the tap-hole area with affected hearth and sidewall refractory was obtained in elevation. The carbon ramming paste in front of, above, and below the tap-hole was worn, as was the SiC with which the tap-hole was built. A clay mushroom formed but was detached from the refractories. Thermodynamic and mass-transfer calculations were conducted to quantify the potential for wear by chemical reaction between refractory and slag and refractory and metal in the tap-hole area. It was found that chemical reaction between refractory and slag or metal could offer only a partial explanation for the wear observed; erosion is expected to contribute significantly to wear.http://www.saimm.co.za/journal-papersam2016Materials Science and Metallurgical Engineerin

Control of silica polymerisation during ferromanganese slag sulphuric acid digestion and water leaching

A major obstacle to the hydrometallurgical treatment of ferromanganese slags is the way in which silica polymerisation is controlled during sulphuric acid digestion and water leaching. In an acidic medium, silica enters in solution and forms silicic acid, which polymerises into silica gel and makes solid-liquid separation difficult. This article will show that the quick leach model, also called the water-starved system, limits silica solubilisation and its subsequent polymerisation during manganese extraction from ferromanganese slags by rejecting most of the ferromanganese slag silica content in the leach residue. It will further illustrate that the silica content in the residue is dependent on the acid concentration used during acid digestion. It will also show that dissolved silica in the pregnant leach solution is high when an unrestricted quantity of water is used and low when the water quantity is restricted during water leaching. Furthermore, a method for silica gel recovery from ferromanganese slag will be presented, as well as the silica gel analysis, in order to confirm the theory presented in this article. Manganese extraction of up to 90% is obtained and the leach residue presents good latent hydraulic properties, which can be used as an addition to Portland cement or a gypsum replacement. More than 95% of the initial silica content of the slag is rejected in the leach residue, and a residue silica content of more than 27% is obtained. Thus, silica solubilisation and polymerisation is controlled and solid-liquid separation accelerated.The BMBF (Federal Ministry of Education and Research, Germany) (DLR FKZ: 01DG12057) and the National Research Foundation (NRF), South Africa (UID 75971-2011).http://www.elsevier.com/locate/hydromet2017-12-31hb2017Materials Science and Metallurgical Engineerin

Chemical wear of carbon-based refractory materials in a silicomanganese furnace tap-hole

The aim of the study presented here was to investigate the potential for chemical wear of carbon-based refractory materials in a silicomanganese furnace tap-hole. In the study, three research questions were addressed: 1. Is chemical reaction between refractory and slag or refractory and metal a potential wear mechanism? 2. Is the choice in carbon-based refractory material important from a tap-hole refractory life perspective? 3. What are the implications for the life of the tap-hole in a SiMn furnace? To study the potential for chemical wear, thermodynamic calculations were conducted to determine the potential for the formation of SiC and SiMn at 1600°C through reduction of SiO2 and MnO and dissolution of C (and subsequent reaction with Si) in metal. The thermodynamic calculations were based on published [1] metal and slag composition and carbon. Cup test experiments based on synthetic slag and graphite proved SiC formation conclusively, but not SiMn formation. To study the effect of the choice in carbon-based refractory material, two types of refractory materials – carbon block and ramming paste – available commercially and industrial slag were sourced, prepared and characterised. Wettability studies proved the formation of SiC at 1588°C with slag being wetting towards refractory in an argon atmosphere and non-wetting in a CO-atmosphere. Under wetting conditions, the wetting angle of slag on carbon block was slightly higher (50°) at holding temperature compared to that of ramming paste (30°). Under non-wetting conditions the angles were 160° and 150° respectively. Cup test experiments based on industrial slag and carbon-based refractory material proved both SiC and SiMn formation at 1600°C conclusively and confirmed the wetting behaviour of slag towards refractory at larger scale. To study the implications for the life of the tap-hole in a SiMn furnace, the tap-hole of a 48 MVA SiMn furnace was excavated and profiled. The wear predicted by thermodynamic modelling was supported by mass flow calculations. It was concluded that chemical reaction between carbon-based refractory materials and slag and metal is one of the mechanisms responsible for wear in the tap-hole of a silicomanganese furnace.Thesis (PhD)--University of Pretoria, 2014.tm2015Materials Science and Metallurgical EngineeringPhDUnrestricte

Optimizing yield of metallic zinc tapped from a zinc smelter by studying factors causing zinc losses to dross

Zincor experienced significant losses of metallic zinc to dross during the melting of zinc cathode plates. In this study five factors affecting the formation of dross are identified from literature. Dross from both the plant and that produced in the laboratory is characterized using XRD. An empirical model, based on laboratory-scale investigations, was developed to quantify the effect these factors on their own or in combination with each other has on the amount of zinc loss to dross. The predictive capability of the model is evaluated based on the laboratory-scale investigations. Predictions are made on the effects that heat treating the cathode plates prior to melting, increasing the cathode plate thickness, washing and drying prior to melting, and loading the furnace in a controlled manner have on the amount of zinc loss to dross

Investigation into the dephosphorization of ferromanganese alloys for the production of advanced high-strength steel

Advanced high-strength steels (AHSS) are sophisticated materials being developed by the steel industry to mitigate challenges related to the performance of motor vehicles. To meet the requirements of AHSS, the ferromanganese alloys (FeMn) utilized in the production of the steel are required to contain acceptable levels of unwanted impurities, i.e. P, S, N, H, and C. The focus of the current study was to investigate dephosphorization of ferromanganese to produce a low-P alloy that could be effectively utilized in the production of AHSS. The study involved conducting laboratory-scale testwork to study the efficiency of CaO-based slag systems to dephosphorize FeMn alloys. The addition of Na2O, CaF2, and BaO to MnO-CaO-SiO2 slag was considered. The test work was carried out in a 25 kW induction furnace at temperatures of 1350°C, 1400°C, and 1450°C. The P partition coefficient (Lp) remained small at <1, which is an indication that dephosphorization had not been achieved. The baseline slag, comprising 40%CaO-40%SiO2-20%MnO, reported higher Lp values. Addition of Na2O and CaF2 did not show any further benefit. Substituting half of the CaO by BaO, resulted in similar Lp values to those of the baseline slag under conditions of 1350°C and 1450°C at 30 minutes. In summary, based on the Lp values obtained, the conditions investigated with the CaO-based slags appeared to have been unfavourable for dephosphorization of FeMn alloys, as most of this impurity element remained in the alloy.Mintekhttp://www.saimm.co.za/journal-papersam2022Materials Science and Metallurgical Engineerin