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By H. B. Menardi

THE history, geology, ore deposits and current mining operations of the Huitzuco district have been described by C. W. Vaupell1 and the current mill operations by David Segura.2 This paper completes the story of Huitzuco with a description of the reduction of the flotation concentrates. The predominant ore mineral in the Huitzuco deposit is livingstonite, a rare, mercury-antimony sulphide (HgS.2Sb2S3). Other associated minerals include cinnabar, stibnite and elemental sulphur. The gangue is largely limestone and gypsum. Former operators mined a selected grade of ore, from which the mercury was recovered by an expensive, inefficient operation. A consid-erable tonnage of rejects and fills, carrying mercury and antimony, was left in the mine. In order to recover both mercury and antimony from these fills and also from newly developed ore, a combination method has been developed, by means of which the livingstonite is concentrated by flotation and the flotation concentrates subsequently reduced to metallic mercury and antimony. An essential part of the flotation treatment, as developed by Segura, is the use of copper sulphate as an activating agent. A typical analysis of concentrates now being produced at the property is as follows: Hg, 7.73 per cent; Sb, 26.40; Fe, 1.20; S, 29.68; CaO, 11.50; MgO, 7.25; Si02, 1.63; A1203, 0.65.

Jan 1, 1939

By A. K. Bhattacharya

Cylindrical bridge piers are widely used and equations exist that can predict the maximum depth of local scour around such piers. Scour around piers is an undesirable phenomenon, as it requires the foundation to be placed to a greater depth resulting in increased cost, making it worthwhile to investigate scour-reducing measures. A number of scour-reducing measures have been tried out for cylindrical bridge piers including placing a concrete collar around the pier, having a delta-wing projecting upstream in front of the pier, placing riprap around the pier, using a group of piers instead of a single pier, having a slot in the pier aligned in the longitudinal direction. The objective of this study is to investigate the effect of upstream protective piles on reduction of maximum local scour depth around a cylindrical bridge pier. The upstream piles are placed at different radial distances in front of the pier and the scour depths are observed. The proposed equation of Dey (1997) for determining the maximum depth of scour around a cylindrical bridge pier is used. The reduction of local scour around the pier is compared with local scour around an unprotected pier.

Jan 1, 2009

By A. Warczok, T. A. Utigard

"Slags from smelting of copper concentrates contains from 1 to 15% of copper. Copper is present in the form of copper or copper matte inclusions of size from 2 to 1000 micro, and as dissolved cuprous oxide. Removal of the copper requires the slag reduction, primarily reduction of magnetite and co-reduction of cuprous oxide. Thus, the kinetics of the slag reduction play an important role in copper recovery. Instantaneously, at the contact of carbon and a slag the gaseous film is formed. The magnetite and cuprous oxide reduction is going through a gaseous film, separating the slag and carbon of a coke or electrodes. The thickness of a gaseous film grows to a critical value and gas bubbles, containing CO and CO2, are created and rise up in the slag. Results of measurements of kinetic of the slag reduction with graphite showed high value of activation energy, close to the value of activation energy of Boudouard reaction. Strong temperature dependence of the reaction rate points out the thermal instability of the reacting system. It was found that the slowest process in the reduction stages determines the loop of CO and CO2 transfer and magnetite diffusion to the slag/gas film boundary. Strongly endothermic Boudouard reaction seems to cause thermal instability on the reaction surface. So, heat transfer to the reaction surface is very important. Due to low thermal conductivity of a slag the convection dominates in the heat transfer. So, any slag stirring accelerates the rate of reduction and coalescence of metallic copper or copper matte inclusions."

Jan 1, 2015

By Richard Elliott

Current methods for producing low-carbon manganese alloying materials for the steel industry are energy intensive and costly. To enable wider implementation of high Mn steel alloys, a novel solid-state Mn ore reduction strategy is therefore being investigated. This solid-state process, modelled on existing Direct Reduced Iron technology, employs a methane-containing atmosphere to reduce Mn ore pellets to a metal carbide. These pellets may then be smelted, yielding a Mn-rich master alloy. It is well established that CH4 is a suitable reductant for Mn ore powders; however, the reduction behaviour of industrially relevant Mn ore pellets by CH4 is poorly understood. The present work reports the results of an investigation undertaken to address this knowledge gap. The results of this study highlight the significantly different reduction behaviour exhibited by the Mn ore pellets relative to the ore powder under similar conditions and suggest that the diffusion of CH4 into the pellet interior is the limiting factor in achieving complete reduction.

By N. Anacleto, S. Ganguly

Reduction of Groote Eylandt (Australia) and Wessels (South Africa) manganese ores using CH4-H2-Ar gas mixture was investigated in a fixed bed laboratory reactor in the temperature range 1000?1200oC. The extent and kinetics of manganese ore reduction as a function of gas composition and temperature were determined by on-line off-gas analysis using mass-spectrometer and dew point sensor. Morphology of ores and its change in the course of reduction was examined by optical and scanning electron microscopy. Phases of raw materials and reduced samples were analysed by XRD and EPMA. Manganese oxides were reduced to carbide Mn7C3. High extent and rate of reduction by methane-containing gas in comparison with carbothermal reduction were attributed to high carbon activity in the reducing gas, which was in the range 15 - 50 (relative to graphite). The reduction rate of Wessels manganese ore increased with increasing temperature. Reduction rate and extent of Groote Eylandt manganese ore achieved maximum at 1050oC. The decrease in rate and extent of reduction of Groote Eylandt ore at higher temperatures, particularly at 1150-1200oC, was due to sintering and formation of semi-liquid silicate slag. The optimum conditions for the reduction of manganese ores were established as follows: a) temperature: 1150-1200oC for Wessels and 1050-1100oC for Groote Eylandt ores, b) methane concentration: 10-15 vol%, c) hydrogen concentration: above 30 vol%, (d) size: 1-3 mm. An addition of lime (10-15 wt% CaO) to the Groote Eylandt manganese ore increased melting temperature of slag and significantly increased the rate and extent of reduction at elevated temperatures.

Jan 1, 2004

By Y Peng, D Wannas

In the fine particle flotation technologies being developed today the fine hydrophilic (gangue) particles are usually well dispersed. These highly dispersed fine particles can be recovered into the flotation froth product by mechanical entrainment. Flocculation of hydrophilic particles caused by polymer depressants could potentially reduce the mechanical entrainment of these particles. This paper reports testwork completed on fine particles of several solids, iron oxide, hydroxylapatite, galena and sphalerite, as well as on a relatively coarse quartz sample (-75+38 ¦m). Dodecylamine was used as a collector for the quartz, and several dispersants and polymer depressants, including sodium silicate, sodium metaphosphate, zinc sulfate, potassium dichromate, corn starch, corn dextrin and carboxymethyl celluloses (with molecular weights of both 700 000 and 80 000) were used as flotation modifiers. The major part of the testwork involved flotation tests in a 200 ml flotation column. Both water and solid recoveries were recorded. The degree of flocculation and dispersion was determined by settling tests in 250 ml graduated cylinders. It was observed that flocculation of the fine hydrophilic particles significantly reduced their mechanical entrainment, while dispersion severely aggravated it. Thus, in the flotation separation of artificial mixtures of the -75+38 ¦m quartz and fine iron oxide or hydroxylapatite, polymer depressants that caused flocculation were found to perform better than the ones that did not cause flocculation.

Jan 1, 2005

By S. N. Sahu

Attempt was taken in this study to explore the misplacement phenomena in binary mixture in solid-liquid fluidisation system. The binary mixtures of hematite and quartz particles at different sizes were taken. The closed size range particles were taken to minimize the size and shape effect in fluidization. As both the minerals have appreciable density difference, the separation of both minerals with closed size range has an advantage. The experiments were conducted in different permutation and combination of different sizes of binary mixture to observe the fluidization phenomena. The samples were taken at different heights in fluidized zones and analyzed the distribution of particles of both minerals. The fluidization characteristics were evaluated with respect to operating and design parameters. It has been observed that when the terminal velocity of quartz and hematite particles is same or near to each other, then misplacement is significant. In general, the segregation index value is near to one, complete segregation takes place whereas this value is near to zero, complete mixing takes place. The experimental data were used to find out the segregation index for different size ratios of quartz and hematite particles and the values are within 0-1. When the size ratio is 1 or less, complete segregation takes place whereas this ratio is within 1.0-1.4, partial mixing takes place. Similarly, when the size ratio is within 1.4-2.0, complete mixing takes place whereas this ratio is within 2.0-4.6, then it moves towards complete segregation in inversion manner. Keywords: particulate fluidization, misplacement zone, bed expansion, terminal velocity, mixing characteristics, segregation index

Sep 1, 2012

By Kai Tang, Casper van der Eijk

Natural gas has been used as reductant in the production of iron for several decades. Recently, the use of natural gas as reductant for other metals has been drawing attention because of the low price of natural gas, as well as the reduction of CO2 emissions compared to the use of coke and coal. In this work, the reduction of a mixture of Ti- and Ni-oxides by natural gas has been studied. Within the Ni-Ti system, the intermetallic compound Ni3Ti is thermodynamically the most stable one. Therefore, powders of Ni-oxide and Ti-oxides were mixed in an atomic ratio of three to one and subsequently pelletized. Reduction was performed in a TGA furnace at constant temperature with varying reducing gas atmospheres. In a natural gas containing atmosphere, the Ni-oxide was easily reduced to metallic nickel while the Ti was reduced to Ti-oxycarbides or Ti-oxynitride when nitrogen was present. Depending on the process parameters, several percent of Ti was dissolved in the nickel-based solid phase.

Jan 1, 2014

By José R. de Tenorio

The aim of the present work was to investigate the reduction process of MnO~FeO-Si02 slags by carbon-saturated liquid iron. The effect of the initial Mn content in the bath was explored. The initial Mn content was in the range of 0 up to 40 wt. %. The MnO content in the slag was kept constant at 40 wt. %. Tests were performed in laboratory apparatus. Samples of slags and bath were taken. In the first 5 minutes, it was observed a very strong reduction of FeO. This first step promoted a MnO-Si02 enrichment of the slag and a formation of CO bubbles, which increases the slag level. The increase ofMn content decreases the MnO reduction rate.

Jan 1, 1996

By G. Castillo, J. Mortensen

"INTRODUCTION Molybdenite is typically produced as a co-product in the copper ore flotation process. At the Rio Tinto Kennecott Concentrator (RTKC) in Copperton, Utah, the molybdenite is initially floated with copper sulfides and other value minerals producing a Cu-Mo concentrate. This is then separated in the molybdenum plant by depressing copper sulfides and pyrite and floating only molybdenite. The molybdenum plant in RTKC comprises the rougher circuit and several stages of cleaning to achieve a certain grade requirement of Mo. The rougher circuit is where the first stage of separation occurs. Cu sulfides and pyrite are depressed in the rougher circuit by adding NaSH under nitrogen and in the cleaner circuit by adding NaSH under air. The depression of Cu sulfides (and pyrite) by NaSH is related to the redox activity1. It is important therefore to maintain a reducing potential in the circuit in order to achieve effective Cu-Mo separation. If the rougher circuit is under air, like RTKC’s molybdenum cleaner circuits, it is harder to maintain the target redox potential because NaSH oxidizes rapidly in the presence of air thereby increasing NaSH consumption significantly. CU-MO SEPARATION AND ROLE OF PULP POTENTIAL The collector adsorption on copper sulfide minerals is through an electrochemical mechanism2. The collector changes the surface chemistry of the Cu mineral allowing it to float. Molybdenite, or MoS2, on the other hand, floats readily in the presence of a frother as it is naturally hydrophobic. Usually, hydrocarbon oil extenders such as diesel or burner oil are added to enhance Mo recovery. In order to effectively separate Cu from Mo, the collector complex on the copper surface needs to be destabilized or desorbed using a reducing agent such as NaSH or Nokes. As long as the circuit is under highly reducing conditions, the collector remains detached from the sulfide mineral surface allowing Cu sulfide depression. Therefore, it is important to measure the oxidation-reduction potential (ORP) continually and maintain the reducing condition with addition of NaSH. For a given collector each mineral will have a characteristic potential or electrochemical window for flotation to occur3, therefore, it is necessary to reduce the potential outside of this window in order to effectively separate Cu and Fe sulfides from MoS2 minerals2. In RTKC plant, the target reducing condition is between -450 to -550 mV to effectively destabilize the collector and depress Cu and Fe minerals. Typically the dosage of NaSH used in the molybdenum plant could range from 6 to 30 gallons/min (gpm). The high dosage of NaSH could pose risk of H2S exposure. RTKC wanted to evaluate alternatives to NaSH in order to reduce its consumption and minimize risk of H2S gas generation."

Jan 1, 2016

By Patricia Martínez Nicolás

Nickel and ferronickel are some of the major components in the production of special alloys; however, the energy consumption for their production greatly increases their price. A cheaper option could be to use NiO and a reducing agent. This work presents experimental and theoretical analysis to estimate the effect of slag basicity and amount of reducing agents on the NiO reduction from the slag which interacted with molten steel at 1600 °C in an EAF. The slag system contained CaO, SiO2, CaF2 and NiO together with a reducing agent, ferrosilicon or carbon. The NiO content in the slag was 25 mass%. The amounts of the reducing agents (Si and C) were 1 to 4 times the stoichiometric mass to reduce NiO. The CaO/SiO2 ratio was 1.5 and 2.5. The kinetics of the process was very fast since after few minutes the maximum nickel yield was obtained. The slag basicity had a negligible effect on the reduction of NiO.

Jan 1, 2006

By N. A. Ziegler

THE chief difficulty in determining oxygen in steels is its tendency to form a variety of compounds. Almost every element, found as an ingredient in steels, maybe expected to be present as an oxide. Some of these oxides have widely differing properties, and consequently behave differently when attempts are made to reduce them by the vacuum fusion method. As I pointed out in a paper published in the Transactions of the A.S.S.T., Vol. 20, No. 1, many experimenters are spending considerable time and effort in attempting to deter¬mine the degree of completeness of the above reactions, and hold different opinions on the matter. In studying this subject the following table, taken from Hodgman and Lange's "Handbook of Chemistry and Physics" may be used as a guide.

Jan 1, 1933

By Henderson J

Iron ore samples selected from the Deepdale, Iron Prince and Mt. Newman ore bodies have been pelletised on a pilot scale plant and subsequently reduced under laboratory conditions by hydrogen or carbon monoxide. Pellets approximately 1 cm in diameter have been reduced by hydrogen over the temperature range 5000- 900¦C and the results examined by thermogravimetric, microscopic, electron probe and x-ray techniques. After an initial time delay it was found that up to 95% reduction the rate of reduction could be described by a transport con- trolled porous model, in which the effective diffusivities of hydrogen in theòpr¦duct layer and the reaction zone are filar. Independent measurements of effective diffusivity supported the values obtained from the reduction data. ve 95% reduction the rate decreased markedly due to the formation_of retained wustite or fayalite. Comparison with reduction by carbon monoxide over the temperature range 7500 - 900¦C showed that the rate eduction by carbon monoxide was approximately five times slower than the rate by hydrogen. The rate of reduction was found to be a function of the properties of the pellets, which may account for the ely conflicting results that have been obtained in previous investigation on porous pellets.

Jan 1, 1970

Hydrogen and carbon monoxide reduction data were obtained on pelletized materials of the type currently being prepared commercially in Australia.Pellets, approximately 1 cm diameter, made from Deepdale, Iron Prince, and Mt. Newman iron ore were reduced by hydrogen over the temperature range 500°-900°C and the reduced pellets were examined by thermogravimetric, microscopic, electron probe, and x-ray techniques. After an initial time delay it was found that up to 95 per cent reduction the data could be described by a porous model where gaseous diffusion through the solid is rate controlling. Independent measurements of effective diffusivity supported the values obtained from the reduction data. Above 95 per cent reduction the rate decreased markedly due to the formation of retained wustite or fayalite.Comparison with reduction by carbon monoxide over the temperature range 750°-900°C showed that the rate of reduction was approximately five times slower than for reduction by hydrogen.The rate of reduction was found to be a function of the initial properties of the pellets which may account for the widely conflicting results that have been obtained with previous investigations on porous pellets.

Jan 1, 1971

By Girley Ferreira Rodrigues, Crocce Denise Romano Espinosa, Victor Bridi Telles, Eduardo Junca, Jorge Alberto Soares Tenorio

"Steel sector is responsible for the generation of solid waste, liquid and gaseous effluents. The Solid waste are mainly composed of slag, dust, sludge and scrap. The industry generates approximately 650kg of solid waste per tonne of steel. Approximately 10% of this waste is in the form of dust and mud. The basic oxygen furnace dust is a waste generate by steel sector. Each tonne of produced steel generates 10 to 20 kg dust. Thus, the aim of this paper is study the reduction of pellets made with BOF dust using hydrogen and study kinetic during the reduction. The tests were performed in a netzsch thermobalance to obtain the data of lost mass. This loss mass is coming from iron oxides present in the BOF dust.IntroductionThe generation of solid waste is a problem for many companies in the steel sector. The main solid wastes generated are slag, dust, sludge and scrap [1]. Beyond solid waste liquid and gaseous effluents are also generated.The basic oxygen furnace is responsible for 60% of all steel produced. This sector is the second largest generator of solid waste from an integrated steel mill, contributing with 27% of solid waste generated in a plant ( 5-7 million tons of waste generated annually worldwide) [2,3,4]."

Jan 1, 2013

By Alain Denis, Marcelo Curtes Martins, Jeferson Rocio de Oliveira

In this work we present a study of optimization of a new inhibitor for turbulence pickling line. The efficiency of inhibition was measured and the weight of loss was evaluated in four different materials to optimize the dosage of the inhibitor. In seven months we had 8.7% of reduction in pickling losses.

Oct 1, 2019

By R. B. Inturi, R. G. Reddy

Solid-state reduction of roast Movat chromite ore with carbon was carried out as a function of the C/FeO ratio at temperatures ranging from 800°C to 900°C. The reduction was studied using thermogravimetric analysis (TGA). A two¬stage mechanism consisting of the reduction of FeO with carbon monoxide and the regeneration of CO by the oxida¬tion of carbon with CO2 was proposed. The rate-controlling step is the carbon oxidation reaction. A kinetic equation, that of random nucleation, was proposed. The activation energy for the reduction was determined to be 55,800 J/mole and is compared to those activation energies determined for other chromite ores.

Jan 1, 2000

By R. G. Reddy

Solid state reduction of roast movat chromite ore with carbon was carried out as a function of C/FeO ratio and temperature in the range 800°C to 900°C by thermogravimetry analysis (TGA). A two stage mechanism, (1) the reduction of FeO present in Roast Movat with carbon monoxide; and (2) the regeneration of CO by the oxidation of carbon with CO2 was proposed. The rate controlling step is the carbon oxidation reaction. A kinetic equation, that of random nucleation, was proposed. The activation energy for the reduction was determined to be 55800 J/mole and is compared to those activation energies determined for other chromite ores.

Jan 1, 1998

By W. W. Loo

A REVIEW of the literature on the reduction of cassiterite showed. that scarcely any progressive changes were made in the methods of reducing cassiterite until within the last two decades, and that during that period many improvements in the metallurgy of tin have taken place. Since 1914 the world's consumption of tin has increased considerably, resulting in the exploitation of primary tin deposits such as the Bolivian lode, which has become an important source of tin. On account of the low tin content of Bolivian ore, and the presence of objectionable impurities of the reduced tin, the smelting of this ore and the refining of the tin has changed considerably from the methods formerly used. A comparative study of the methods of smelting cassiterite concentrates suggested that an investigation be planned so as. to determine what factors effect the extraction of tin from its ores by reduction with carbon. The first part of the experimental work was the determination of whether roasted cassiterite concentrates can be reduced by carbon without the use of flux, and the reduced pellets of tin be collected into a single mass separate from the dry gangue residue The second part of the experimental work was a comparison of the effect of variations of the different factors on the smelting of roasted cassiterite concentrates: first, the effect of varying the composition of the slag; second, the effect of varying the amount of reducing agent; third, the effect of varying the relative amount of the resulting slag; and fourth, the effect of different kinds of reducing agents:

Jan 1, 1928

By Paulo Rodrigues dos Santos Junior, Luciano Passos de Jesus, Vagno Dordenoni Beltrame, Vinicius Antonio Ramos Pin

Faced with an increasingly demanding and selective market, a thorough analysis of each step of the processes is required in order to achieve high levels of performance. In addition to a major factor of importance in the rolling process, due to its high price, the rolls represent one of the main items in the cost of hot coils production. Using the 6 sigma methodology, there were opportunities for improvement in the grinding process, fatigue analysis, improvement in NDT in rolls, as well as means to guarantee operational stability, which allowed the reduction of roll’s consumption and consequently the cost of production.

Oct 11, 2019