Ferrochrome Production Research Articles

Direct Production of Ferrochrome by Segregation Reduction of Chromite in the Presence of Calcium Chloride

A solid reduction process is described whereby chromite is reduced with the help of calcium chloride to produce ferrochrome alloy powders with high metal recovery. The process involves segregation reduction of chromite using graphite as the reductant and calcium chloride as the segregation catalyst. Experiments were performed in the temperature range of 1200–1400 °C to evaluate the influences of various design parameters using both a thermogravimetric analyzer and an electric tube furnace with continuous off-gas analysis. The reduced products were characterized by scanning electron microscopy, X-ray powder diffraction, synchrotron X-ray absorption spectroscopy, and were subjected to wet chemical analysis. It was concluded that the addition of calcium chloride not only accelerated the carbothermic reduction of chromite but also promoted the formation and growth of individual ferrochrome alloy particles. The alloy formation within chromite particles was minimized, enabling the effective separation of ferrochrome alloy particles from the unwanted gangue without the need for fine grinding. Majority of the calcium chloride remained in a recoverable form, with a small percentage (<10 wt %) consumed by reacting with the siliceous gangue forming wadalite. Pure ferrochrome alloy powders were successfully produced with high metal recovery using elutriating separation.

Influences of alkali fluxes on direct reduction of chromite for ferrochrome production

Influences of alkali fluxes on direct reduction of chromite for ferrochrome production

Energy-saving ferroalloy production

In the laboratory, ore–coal blends consisting of small components (ore, coal, and flux) are prepared. If the coal consumption in the reduction of metals is standardized, ferroalloys with moderate iron content may be obtained; the carbon content in the alloys may be adjusted within the range 0.80–1.5%. This fundamentally new technology for the production of ferrochrome and ferromanganese permits the replacement of electric power by fuel. That considerably reduces production costs, while improving alloy quality and reducing the environmental impact of the process.

Effect of Stoichiometric Reductants on the Process of Ferrochrome Production at 1200–1550°C

Ferrochrome alloys are mainly produced in submerged-arc furnaces. Reductants used in ferrochrome production include coke, anthracite, and char. However, it is still unclear what happens after charging carbon in stoichiometric amount or in amounts lower or higher than that. The phase formation and phase transformations of products at different reducing temperatures in the presence of stoichiometric amount of a reductant are studied. The experiments were conducted at 1200, 1300, and 1550°C. Anthracite and coke were used as reductants. The steps, extent, and mechanisms of reactions for coke and anthracite at the same temperature and soaking time are discussed. Reductants are characterized using different analytical techniques to identify the changes in the morphology of reductants and phases associated with changes in the temperature.

Aqueous solubility of Cr(VI) compounds in ferrochrome bag filter dust and the implications thereof

The production of ferrochrome (FeCr) is a reducing process. However, it is impossible to completely exclude oxygen from all of the high-temperature production process steps, which may lead to unintentional formation of small amounts of Cr(VI). The majority of Cr(VI) is associated with particles found in the off-gas of the high-temperature processes, which are cleaned by means of venturi scrubbers or bag filter dust (BFD) systems. BFD contains the highest concentration of Cr(VI) of all FeCr wastes. In this study, the solubility of Cr(VI) present in BFD was determined by evaluating four different BFD samples. The results indicate that the currently applied Cr(VI) treatment strategies of the FeCr producer (with process water pH ≤ 9) only effectively extract and treat the water-soluble Cr(VI) compounds, which merely represented approximately 31% of the total Cr(VI) present in the BFD samples evaluated. Extended extraction time, within the afore-mentioned pH range, proved futile in extracting sparingly-soluble and water-insoluble Cr(VI) species, which represented approximately 34% and 35% of the total Cr(VI), respectively. Due to the deficiencies of the current treatment strategies, it is highly likely that sparingly water-soluble Cr(VI) compounds will leach from waste storage facilities (e.g. slimes dams) over time. Therefore, it is critical that improved Cr(VI) treatment strategies be formulated, which should be an important future perspective for FeCr producers and researchers alike. Keywords: hexavalent chromium, Cr(VI), ferrochromium, ferrochrome, bag filter dust, smelter waste

Состояние хромовой промышленности России

The paper analyzes the state of the sources of raw materials and production of chrome alloys in the Russian Federation. It is mentioned that the increase of chrome ore reserves in the last decade is insufficient, and principal reserves are located in the regions hard to develop. Issues of the production of charge chrome, changing standards towards decrease of chromium in the ferrochrome, and implementation of direct current furnaces for processing poor ores, dressing rejects and industrial wastes are becoming important because of low ore quality in the deposits currently being mined. Unlike the production of other ferroalloys where the tendency to development of small specialized plants is observed, production of ferrochrome is characterized by consolidation and establishment of holdings that incorporate not only mining and processing, but also preparative industries like sintering plants as well as mining and preparation of non-ore materials, viz. limestone and quartzite.

Smelting of high-carbon ferrochrome from chromium agglomerate produced with alumina-silica flux

In a test melts, high-carbon ferrochrome is produced from chrome sinter and chrome-ore fines in an arc electrofurnace. Two types of sinter with the best performance—the best sintering rate, strength, and product yield—are studied. It is demonstrated by experimental melts that high-carbon ferrochrome can be produced from proposed agglomerates. An estimation of smelting parameters for production of high-carbon ferrochrome is made.

Design of a ferrochrome – slag mechanical separator case study

This research focused on the design of a ferrochrome – slag mechanical separator for a company in Harare, Zimbabwe. The company’s current production is 420 tonnes of alloy per month. The aim of project is to raise the production from 420 to 500 tonnes of ferrochrome production per month by introducing a mechanical separator at metal recovery plant that produces 80 tonnes. The difference in specific gravities of ferrochrome and slag is the key principle applied in achieving separation of the two products. The densities of ferrochrome and slag are 6800 kg/ m 3 and 2800kg/ m 3 respectively hence gravity separation method in water medium can be done.

The Effect of Carbonaceous Reductant Selection on Chromite Pre-reduction

Ferrochrome (FeCr) production is an energy-intensive process. Currently, the pelletized chromite pre-reduction process, also referred to as solid-state reduction of chromite, is most likely the FeCr production process with the lowest specific electricity consumption, i.e., MWh/t FeCr produced. In this study, the effects of carbonaceous reductant selection on chromite pre-reduction and cured pellet strength were investigated. Multiple linear regression analysis was employed to evaluate the effect of reductant characteristics on the aforementioned two parameters. This yielded mathematical solutions that can be used by FeCr producers to select reductants more optimally in future. Additionally, the results indicated that hydrogen (H)- (24 pct) and volatile content (45.8 pct) were the most significant contributors for predicting variance in pre-reduction and compressive strength, respectively. The role of H within this context is postulated to be linked to the ability of a reductant to release H that can induce reduction. Therefore, contrary to the current operational selection criteria, the authors believe that thermally untreated reductants (e.g., anthracite, as opposed to coke or char), with volatile contents close to the currently applied specification (to ensure pellet strength), would be optimal, since it would maximize H content that would enhance pre-reduction.

Process innovations and sustainability in Finnish metallurgical industries

ABSTRACTSustainability is a central issue in metallurgical processes due to their energy intensiveness and environmental impacts. The role of metallurgical industry in Finland is significant accounting for 12% of the value of exports. Meanwhile it is also responsible for 7% of CO2 emissions. Sustainability has been in focus during the latest decennia. Foremost progresses in iron and steelmaking for energy saving and reduction of emissions are surveyed in this contribution. Ferroalloys smelting is a highly energy intensive process. Utilization of local low-grade chromite ore led to major technological advances including innovative agglomeration technique, closed smelting furnace with pre-heating and off-gas recovery contributing to high energy efficiency and low carbon footprint in ferrochrome production. In non-ferrous metallurgy developments in flash smelting for copper rose from a need of substantial reduction of energy consumption and SO2 emissions. The focus was then set on energy efficient technologies with low carbon footprint, sulphur fixation and fugitive emissions. Oxygen in smelting, continuous converting, direct to blister and direct nickel matte smelting are the main achievements. The impact of novel technologies to global sulphur emissions and local environmental issues in the smelters has been considerable.

Role of a silicate phase in the reduction of iron and chromium and their oxidation with carbide formation during the manufacture of carbon ferrochrome

The reactions of reduction of chromium and iron from chromospinelide and the reactions of carbide formation from the reduced metals are separated in space in experiments performed on ore grains with an artificially applied silicate shell. It is found that the silicate layer that isolates spinelide fro direct contact with carbon takes part in the reactions of both reduction and carbide formation. Free carbon extracts oxygen anions from the layer at the contact surface with the formation of CO, and the forming anion vacancies transfer “excess” electrons to the iron and chromium cations in the spinelide lattice and reduce them. Free and carbide-fixed carbon extracts iron and chromium cations from the silicate layer, and carbides form on the surface. The cation vacancies and electron holes (high-charge cations) that form in the silicate phase under these conditions are involved in the oxidation of the metal reduced in spinelide and cause its dissolution in the silicate phase and the precipitation of lower carbides on the surface of the silicate phase. The structure that is characterized of carbon ferrochrome forms on the surface of the silicate phase. Carbide formation is slower than reduction because of higher energy consumed for the formation of high-charge cations and the transfer of cations from the spinelide volume to the outer surface of the silicate phase. In the absence of a silicate layer, a carbide shell blocks the contact of carbon with oxides, which leads to the stop of reduction and, then, carbide formation. In the presence of a silicate (slag) shell around a spinelide grain, the following two concentration galvanic cells operate in parallel: an oxygen (reduction) cell and a metal (oxidation) cell. The parallel operation of the two galvanic cells with a common electrolyte (silicate phase) results in a decrease in the electric potentials between spinelide inside the silicate phase and carbon and carbides on its surface, and each of the processes is significantly facilitated and accelerated. In other words, the production of carbon ferrochrome is accelerated.

Optimization of Process Parameter for Smelting and Reduction of Ferrochrome

The increasing costs of electric energy and continuous depletion of quality raw material such as Chromite ore and coke for production of high grade Ferro-chrome imposed a big challenge for the Ferro- alloys industries. In order to sustain in the globalized market, an attempt have been made in the present investigation for production of high grade Ferro-chrome utilizing lean grade raw materials. Chromite ore having different Cr/Fe ratio were smelted in a 100 KVA submerge arc furnace (SAF) with low grade nut coke. The Cr/Fe ratio of the Chromite ore pellets were optimized with respect to the slag basicity and power consumption to yield high grade Ferro-chrome. The basicity of the slag and Cr/Fe ratio of the ore were optimized to produce high grade Ferro-chrome (Cr > 60%) with low power consumption. It was observed that high grade Ferro-chrome can be produced utilizing low grade Chromite ore having Cr/Fe ratio 2.4 at the slag basicity of 1.

Ball milling of high carbon ferro chrome slag to liberate the alloy for gravity concentration

High carbon ferrochrome slag is a byproduct of High Carbon Ferrochrome (HCFeCr) production in submerged arc furnaces. The slag is conventionally tapped from the furnaces and granulated before being dumped as waste. The major uses of the slag have been in road and civil engineering construction and in production of refractories. HCFeCr slags however, contain appreciable amounts of residual ferrochrome alloy which can be liberated and recovered profitably using cheap and environmentally friendly gravity concentration methods. In this work the milling behavior of a high-carbon ferrochrome slag is investigated. Milling experiments for a typical HCFeCr slag were conducted using a 0.303 by 0.282m laboratory ball mill to establish liberation as a function of particle size and to determine the associated key breakage parameters like the breakage function (Bij) and selection function (Si). The breakage parameters were obtained using the monosize fraction method by milling the following size fractions −13.2+9.5mm, −9.5+5.6mm, −5.6+4mm, −4+2.8mm, −2.8+1.18mm and −1.18+0.15mm. The effects of powder filling and mill speed were also tested experimentally. An increase in the milling speed from 75% Ncrit to 85% Ncrit caused an increase in the selection functions of different fractions however a further increase to 90% Ncrit resulted in a drastic reduction in the rate of milling across all size fractions. Increasing the powder filling from 40% to 60% caused a marked increase in the selection functions for the particles in the size fraction −5.6+4mm and smaller and a decrease in the selection functions for the particles in the size fraction −9.5+5.6mm and larger. A further increase in the powder filling to 80% caused a marked fall in the selection functions for all size fractions to values lower than those obtained at 40% powder filling. The results from the size by assay test-work showed that the sizes of particles that contain the highest amount of the ferrochrome alloy and the least amount of silica are in the range −1.18+0.6mm. The milling process has to maximize the generation of particles in this specific size range in order to achieve the best alloy recoveries in the downstream concentration unit.

Exergy and its efficiency calculations of shaft furnace for sinter pellet production

In ferrochrome production, chromite ore fines are first agglomerated as green pellets and then fired in a shaft furnace (SF) to produce sintered pellets. These sintered pellets are then charged to a submerged electric arc furnace (SAF) for the production of ferrochrome alloy. The SAF off gases are utilised in the SF to heat green pellets resulting in sintered pellets. The specific energy consumption of sinter pellet production was observed to be 1.9–2 GJ per tonne of pellet. The exergy efficiency of the existing process and a variation of it was evaluated in this work. Presently, 47% excess air is used for the combustion of SAF off gases and carbon present in green pellets and the only valuable product in the existing process is the sinter pellets. We have considered the case with only 20% excess air and the valuable products are sinter pellets and power generation.

Production of high-carbon ferrochrome from dry-quenched semicoke

The quenching of semicoke by saturated steam (heating-gas temperature 550°C) is described. The working-moisture content Wr in the semicoke is 3.0–6.7% for the new quenching method. As a reducing agent, semicoke has good characteristics: relatively low ash content (Ad = 7.1%), low sulfur content (Sd = 0.13%) and phosphorus content (Pd = 0.029%), and high reactivity (\({K_{C{O_2}}}\) = 4.0 cm3/g s) and electrical resistivity (ρ > 1.9 × 106 Ω cm). In tests, dry-quenched semicoke performs well in the production of high-carbon ferrochrome: decreased power consumption; increased furnace productivity; decreased consumption of chromium ore; and decreased sulfur content in the ferrochrome when Karaganda coal is completely reduced by the semicoke. The optimal semicoke content in the batch is up to 50 kg.

Characterization of particle exposure in ferrochromium and stainless steel production

ABSTRACT This study describes workers’ exposure to fine and ultrafine particles in the production chain of ferrochromium and stainless steel during sintering, ferrochromium smelting, stainless steel melting, and hot and cold rolling operations. Workers’ personal exposure to inhalable dust was assessed using IOM sampler with a cellulose acetate filter (AAWP, diameter 25 mm; Millipore, Bedford, MA). Filter sampling methods were used to measure particle mass concentrations in fixed locations. Particle number concentrations and size distributions were examined using an SMPS+C sequential mobile particle sizer and counter (series 5.400, Grimm Aerosol Technik, Ainring, Germany), and a hand-held condensation particle counter (CPC, model 3007, TSI Incorporated, MN). The structure and elemental composition of particles were analyzed using TEM-EDXA (TEM: JEM-1220, JEOL, Tokyo, Japan; EDXA: Noran System Six, Thermo Fisher Scientific Inc., Madison,WI). Workers’ personal exposure to inhalable dust averaged 1.87, 1.40, 2.34, 0.30, and 0.17 mg m−3 in sintering plant, ferrochromium smelter, stainless steel melting shop, hot rolling mill, and the cold rolling mill, respectively. Particle number concentrations measured using SMPS+C varied from 58 × 103 to 662 × 103 cm−3 in the production areas, whereas concentrations measured using SMPS+C and CPC3007 in control rooms ranged from 24 × 103 to 243 × 103 cm−3 and 5.1 × 103 to 97 × 103 cm−3, respectively. The elemental composition and the structure of particles in different production phases varied. In the cold-rolling mill non-process particles were abundant. In other sites, chromium and iron originating from ore and recycled steel scrap were the most common elements in the particles studied. Particle mass concentrations were at the same level as that reported earlier. However, particle number measurements showed a high amount of ultrafine particles, especially in sintering, alloy smelting and melting, and tapping operations. Particle number concentration and size distribution measurements provide important information regarding exposure to ultrafine particles, which cannot be seen in particle mass measurements.

Evaluation of the Furnace Method for the Production of Low Carbon Ferrochrome

ABSTRACTThe furnace method was evaluated as a potential improvement on the mixing method for the production of low carbon ferrochrome. The furnace method can provide significant savings in the operating cost, primarily due to a saving of 29%–47% in the energy consumption. Hexavalent chromium formation is also expected to be lower due to the difference in furnace design and operating conditions. Thermochemical modeling showed a lime-fluxed slag with a basicity of between 1.8 and 1.9 to be the most desirable slag. A magnesia refractory lining is the most suitable material for this process. Smelting tests largely confirmed the modelling results.

A Short Review on Utilization of Ferrochromium Slag

ABSTRACTThe ferrochromium slag is an important by-product of ferrochromium industries. Recycling and efficient utilization of the large volumes of slag generated by ferrochrome production process is a huge challenge for ferrochrome producers. This article reviews ferrochromium slag utilization with reference to refractory, ceramics and construction and other applications. In addition to this the development of crystal phases and the environmental aspects of ferrochromium slag in relation to its utilization are discussed. The crystalline phases evolve during solidification impart unique properties like strength, stability and refractoriness which open its opportunities as an alternative raw material for ceramic, refractory, civil construction. Chemical composition of ferrochromium slag can be altered suitably for application in high temperature refractory ceramic application. The use of ferrochromium slag in building and road making material will relieve some of the burden from natural resources.

Utilisation of pre-oxidised ore in the pelletised chromite pre-reduction process

Ferrochromium is a vital alloy mostly used for the production of stainless steel. It is produced from chromite ore, the only economically exploitable natural chromium resource, through carbothermic smelting in submerged arc or direct current furnaces. The pelletised chromite pre-reduction process is currently the industrially applied ferrochromium production process with the lowest specific electricity consumption. Results obtained from this study proved that the pre-oxidation of chromite ore prior to milling, agglomeration and pre-reduction significantly enhances the level of chromite pre-reduction achieved in the pelletised chromite pre-reduction process. The optimum pre-oxidation temperature was established as the temperature where a balance was achieved between maximising iron (Fe) migration to the surface of ore particles that were pre-oxidised, while avoiding the formation of free eskolaite (Cr2O3). For the case study metallurgical grade chromite ore considered, the optimum pre-oxidation temperature was found to be 1000°C. Utilising such pre-oxidised ore could theoretically lead to an improvement of approximately 8.5% in the specific electricity consumption and a 14% decrease in the lumpy carbonaceous material required during submerged arc furnace smelting of pelletised chromite pre-reduced feed.

Smelting characteristics of fluxed chromite sinter and its performance assessment in electric arc furnace to produce high carbon ferrochrome

More than 80% of the high grade chromite ores are fragile and tend to form fines during their handling. In order to utilise these chromite ore fine, in ferrochrome production, agglomeration is necessary. In the present study, the direct sintering of chromite ore fines in the presence of coke breeze has been carried out, which does neither require further grinding of ore fines ( − 10 mm) nor binder. It uses suitable fluxes and coke breeze as heat source to raise temperature up to 1600°C and produces a semifused mass (20% molten phases) with good strength. The developed sinter showed very good strength properties suitable for cold handling. Since it contains higher amount of fluxes than conventional pellet, the study on its smelting characteristics is necessary to assess its suitability in Fe–Cr production. In the present paper, smelting reduction characteristics and assessment of its performance with respect to the lump ore in a 50 kVA electric arc furnace have been studied in 10 kg scale. Different smelting parameters such as coke and flux requirement, energy consumption, etc. has been optimised through both thermodynamically and experimentally to get maximum extent of reduction, metallic yield and chromium recovery. Coke (21%), quartzite (7.52%) and bauxite (10%) addition with 45 kWh of heat input was found to be optimum to achieve 76% metallic yield and 91%, chromium recovery. In the comparative study in identical condition, the chromite sinter showed much better metallic yield (76%) and higher chromium content (54.6%) in the produced ferrochrome than the lump ore (70 and 51. 9% respectively) of the same grade.