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By Peter V. Barr

Despite the advent of modem firing control systems reheating furnace operations frequently allow significant thermal excursions in the discharged slabs or billets after furnace delays. Although HSM furnaces are not immune to this and other related problems, mini-mill operations are most vulnerable due to their more frequent delays and (often) less sophisticated control systems. In order to reduce these problems control systems will commonly include a thermal model, operating either on-line (interacting directly with the controller logic) or in an advisory, off-line mode. Using a new 'fast' thermal model, the paper examines the thermal response of a typical mini-mill furnace during both delays and the subsequent recovery period. A variety of firing strategies are explored and compared on the basis of maintaining thermal excursions within allowable limits for rolling. Other factors, such as the potential for overheating of billets within the furnace during delays and the overall thermal state of the furnace, are also considered in some detail. Although common practice, the use of conventional thermocouple zone temperatures for furnace control during and after delays is shown to be a dubious proposition. Keywords: Reheat Furnace, Modeling, Process Control

Jan 1, 2003

By Ahmet Haxhiaj, Jaroslaw Drelich

"Both composition and porosity of pellets are the main parameters influencing the reductive melting process in water-jacket furnace during the roasting of sulfide lead concentrate. Roasting in a smelter located in Trepçë is done at about 9000C, for pellets which are composed of PbS, CaCO3, Fe2O3, and SiO2. In order to faciltiate the formation of slag in the reductive melting, the pellets must have the proper content of CaO, SiO2, and FeO, and porosity. The plant’s practice indicates that pellets with porosity of 18% do not melt adequately in the water-jacket furnace. The optimum porosity for the proper melting of pellets needs to be 32-40% and can be achieved when pellets are loaded with more than 10 wt.% CaO. Pellets with less than 10% CaO have a limited network of pores, such that reactive gases cannot reach the entire ore structure. Also, the composition of the pellets must satisfy the ratio of CaO : SiO2 : FeO = 1 : 1.2 : 1.8 to facilitate the formation of slag in the reductive melting process.IntroductionAgglomeration roasting of sulfide lead concentrate is an important phase in the production of lead by reductive melting [1-6]. The reductive melting process is a complex process with contradictory effects of several technological indexes which many times are hard to measure and determine. In this process, loading the water-jacket furnace with pellets of optimized composition and structure can reduce the consumption of coke, and achieve high level of lead recovery. Pellets (agglomerates) should be porous, but at the same time they should have necessary mechanical strength. ‘Self-melting’ ability of pellets is controlled by the types and quantities of fluxes blended into the pellet composition. Three major additives and their role are:"

Jan 1, 2011

By A. René Silva

The separation of Fe(III) from simulated Ni(II) solutions using different ion exchange resins was studied. The resins tested included cation exchangers with sulfonic and carboxylic groups and chelating resins with iminodiacetic, aminophosphonic, and mixed sulfonic and phosphonic groups. The dosage of resins was varied from 0.1 to 0.5 g/mL to study the impact of resin type and dosage on iron separation from simulated nickel leach solution containing 25 g/L Ni(II) and 25 g/L Fe(III) at pH 1.5. Also, the effects of different metal ion concentrations, Fe (III):Ni(II) ratios in solution, pH, and adsorption times were investigated. Experimental results demonstrate that all the chelating resins selected favored the adsorption of Fe(III) over Ni(II) with high Fe(III) loading. Soft cation exchange resins also favored the adsorption of Fe(III) over Ni(II), but no significant Fe(III) loading was observed. In contrast, strong cation exchange resins did not show adsorption preferences. The most efficient separation was observed using resin with aminophosphonic groups at resin dosage of 0.2 g/mL, having a Fe(III) adsorption over 94% and Ni(II) adsorption below 5%.

By James C. Barker

Recent investigations of a 55-km long trend of intrusive complexes on southern Prince of Wales Island have identified significant resources of Nb, Y, REE. U, Zr, and a host of potential by-product metals. The northwesterly trend comprises multi-phased sodic alkaline and peralkaline diorite, monzonite, syenite, and riebeckite granite. There are at least three significant deposit types recognized, two of which, 1) pegmatite dikes/vein-dikes that zone laterally from the intrusions and 2) concentrically zoned pegmatites, contain most of the lithophile metals. A third, epigenetic replacement-type mineralization, contains much of the U resource. Other deposit types with minor or unknown resource potential include diatremes, carbonatite, and placers. This report summarizes the deposit evaluations, characterizes the mineralization, and estimates the resources. To date a total of 40.7 million tons of mineralized material is estimated as indicated or inferred. Most of the Y203 plus REO is at a grade exceeding 0.5% and half of the Nb20S exceeds 0.125%. Tonnage estimates would likely be substantially lncreased with additional exploration. Mineralogy is generally fine-grained and complex, and consists of more than a dozen principal REE-Y-Nb-U-Th-Zr phases, the sum of which may compose up to half of the rock. Approximately half of the REE-Y content comprises the heavy yttrium subgroup which is uncommon compared to deposits elsewhere. Although the Alaskan deposits are likely subeconomic at today's metal prices and consumption levels. recent technological advances suggest future demand may increase.

Jan 1, 1988

By Kang-In Rhee

A series of processes to recover the gold from electronic scrap which contains initially about 200-600 ppm Au have been developed. First, mechanical beneficiation including shredding, crushing and screening was employed. Results showed that 99 percent of gold component leaves in the fraction of under 1 mm of crushed scrap and its concentration was enriched to about 800 ppm without incineration. The scrap was leached in 50% aqua regia solution and gold was dissolved completely at 60°C within 2 hours. Other valuable metals such as silver, copper, nickel and iron were also dissolved. This resulting solution was boiled to remove nitrous compounds in the leachate. Finally, a newly designed electrolyzer was tested to recover the gold metal. More than 99% of gold and silver were recovered within an hour in electrowinning process.

Jan 1, 1995

By Juan Daniel Martínez, Janaina Accordi Junkes, Dachamir Hotza, Tatiana Pineda

"The rice husk combustion in a bubbling and atmospheric fluidized bed reactor was investigated. The results showed the technical viability of producing both heat and amorphous silica from a renewable energy source. This paper presents the characterization of rice husk ash (RHA) obtained under varying fluidization velocities (0.13-0.15 m/s) and rice husk feed (4.5-7.2 kg/h). Characterization techniques include X-ray fluorescence, X-ray diffraction, particle size distribution and scanning electron microscopy. For the employed range of fluidization velocities of rice husk feed no noticeable influence on the chemical composition of produced RHA was observed. After combustion, RHA containing ~93% amorphous silica and <3% unburned char was obtained. RHA primary particles presented sizes from 90 to 100 µm and a tendency for agglomeration in aqueous media. Thus, the potential of this type of reactors with respect to speed, continuity and self-sufficiency energy of the process was shown.IntroductionDue to the increase of the agroindustrial production, the concern with processing by-products, such as rice husk (RH), is growing. For a better material and energy use, allowing a cleaner production and a more maintainable development, RH can be used as renewable fuel in the production plant, for instance, in steam generators. The adequate combustion of RH generates hot gases with low levels of pollutants, as carbon monoxide and particulate material.RH is the protecting coating formed during the growth of the rice grain, composed by four structural layers.1 The main components of the husk are cellulose and hemicelulose (50%) besides lignine (26%) and organic components (4%), as oils and proteins. The remaining amount includes inorganic materials (SiO2, Al2O3, K2O, Na2O, MgO, CaO, Fe2O3, MnO, P2O5).1The rice husk ash (RHA) is the product of the termochemical transformation of RH. The conditions of the different conversion processes (pyrolysis, gasification and/or combustion) determine the physical-chemical characteristics of the final product. RHA corresponds to 14 to 25% RH, depending on the variety of the rice, climate and soil of the producing area.2-4 The main component of RHA, which is generated at moderate combustion temperatures, is amorphous silica (SiO2) in the range from 80 to 97%.4,5"

Jan 1, 2008

By Xuan Cheng

The electrochemistry of sulfide mineral flotation is reviewed with particular emphasis on galvanic interaction among minerals and grinding media, and its relevance to flotation of complex sulfide ores is discussed. Surface alteration due to galvanic interactions among chalcopyrite, pyrrhotite and mild steel is analyzed in terms of voltammetric and chronoamperometric studies on individual minerals and through galvanic current measurements in 2- and 3- electrode combinations. The results are related to laboratory flotation behaviors of chalcopyrite-pyrrhotite mixtures simulating copper-nickel bearing Duluth gabbro.

Jan 1, 1993

By U .. C. Rojas, J .. C. Gomez

"Fire Refined Copper (EI Teniente Three Stars) has been produced at Caletones Smelter of Codelco Chile since almost the beginning of its operations.Due to changing features of the copper market, together with the targets on technical efficiency and productivity, it has become more and more relevant for copper industry to reach both, good final product quality and a proper environmental control.At present, copper refining process at Caletones Smelter takes place in two cylindrical tilting furnaces, where solid fluxes are injected through horizontal tuyeres into the molten bath. (Fig. N2 1)Solid reagents are pneumatically conveyed and injected into the liquid copper bath attaining excellent solid - liquid contact, so the impurities removal efficiencies are found to be high. Same injection tuyeres are used to introduce both oxidising agent (normal air) and reducing agent (reformed gas) into the molten bath. Air or nitrogen is used as conveying gas for solid reagents, depending on the process stage.This pap~r gives a fundamental description of the process and industrial results related to the injection of blend of sodium and calcium carbonates to remove arsenic and antimony, silica and granulated reverberatory slag to remove lead and a mixture of calcium carbonate and mineral coal to reduce the selenium content of the fire refined copper."

Jan 1, 1996

By Alicia E. Ares

316 L Stainless Steel samples were solidified directionally under conditions which produced the columnar to equiaxed transition. The position of the transition was located in each sample and the distance from the bottom of the ingot was measured. During solidification the distribution of temperatures were measured by means of thermocouples located strategically. From the measured temperatures the following parameters were derived; the local temperature gradient, the cooling rate and the velocities of the liquid and solidus fronts. Comparing the location of the transition and the values of these parameters it was found that the temperature gradient reaches negative values of as low as -13.44 "C/cm, and velocities of the fronts of around 0.1 cm/s. Also, a supercooling of 5.81°C were measured which was associated with the supercooling for the nucleation and growth of the equiaxed grains ahead of the columnar front. In addition the primary and secondary dendritic spacing was measured in both regions. The spacing was compared with the predictions from available models. The results are presented and discussed in the frame of the results obtained for other alloys

Jan 1, 2002

By T. T. Chen

Canadian Electrolytic Zinc has developed the "cement-stabilization of jarosite residue" Garofix) process to stabilize zinc plant jarosite residues for disposal. The cement-jarosite mixtures cure quickly, have good mechanical strength and low hydraulic permeability; they possess good neutralizing capability and chemical stability. In the jarofix process, Portland cement partly decomposes jarosite to form (SO4MOH)12.nH2O, ferric hydroxide and an alkali sulphate. Approximately 40% of the jarosite reacts in mixtures containing 30% cement. The jarofix product also contains various Ca-Al-Fesilicate-sulphate-hydrate phases and gypsum, which bond the individual particles together imparting mechanical strength and reducing the permeability. Most of the reactions take place in the first few hours of curing. Ammonium jarosite is slightly more reactive than sodium jarosite but releases NH3 gas; water-soluble Zn in the jarosite residue is stabilized in the cement reaction products.

Jan 1, 1996

By E. A. van Dijk

Dusts from steel-making processes contain substantial amounts of zinc. Such dusts are also a hazardous waste and dumping them becomes unacceptable from environmental point of view. Therefore processes that can recover zinc and possibly other metals from steel-making dusts are being investigated. The aim of this paper is a contribution to the more fundamental kinetic aspects of zinc reduction from silica free calcium ferrite slags. The effects of alumina, lime and magnesium oxide contents of the slag, the COICO, ratio and the effect of initial Fe2O3/CaO ratio were studied experimentally at 1400°C The results indicated that the reduction of zinc from molten slag was possibly a first order reaction. As expected higher COICO, ratios increased both the extent and the rate of reduction. It was also observed that a higher iron content of slag improved the reduction of zinc from calcium ferrite slags. This fact seems to support the proposed mechanism that zinc is partly reduced by ferrous iron to zinc vapour and that ferric iron is reduced by carbon monoxide. The reduction rate of zinc in these slags was decreased by increasing alumina content of the slag. Alumina decreased the calculated optical basicity of the slag showing the fact that reduction of zinc oxide was more favorable in more basic slags. Probably the formation of complex ions by alumina and zinc oxide such as ZnAl2O32+ lowers the activity of Zn2+ ions in the slag and hence render them more difficult to reduce.

Jan 1, 1999

By James A. Voigt

The efficient separation of metal species from aqueous streams by precipitation techniques requires &apos;a fundamental understanding of the various processes that occur during precipitation. These processes include particle nucleation, particle growth by solute deposition, agglomerate formation, and agglomerate break-up. The application of the population balance approach has been used to develop a kinetic model that accounts for these competing kinetic processes. The usefulness of the model is illustrated through its application to the precipitation of yttrium hydroxynitrate, YHN. The kinetic parameters calculated from the model equations and system-specific solution chemistry are used to describe several aspects of the effect of pH on the precipitation of the YHN. Implications with respect to the simultaneous precipitation of more than one cation type are also discussed through use of example systems: The effects of solution chemistry, precipitator design, and solvent choice are considered.

Jan 1, 1996

By Varuzan Kevorkijan

A new method for faster production of functionally graded metal-ceramic laminates is based on reactive pressureless counterflow infiltration/penetration of a ceramic substrate with two different metallic infiltrants. The porous or dense ceramic preform is pressurelessly infiltrated or penetrated from one side by the first metallic infiltrant to the desired cross section of the preform, producing the top layer made up of the solidified infiltrant and the underlayer consisting of reactive infiltrated preform. The partly infiltrated perform is then completely infiltrated starting from the other side by the second metallic infiltrant, in this way fabricating the internal layer, consisting of the ceramic perform infiltrated with the second infiltrant and the bottom layer formed by the solidified second infiltrant. Systems already investigated include carbide, nitride and boride ceramic performs infiltrated with aluminum and magnesium alloys.

Jan 1, 2003

By N. V. Gorelikova

A new type of zirconium mineralization has been recognized in the Devonian volcanic rocks from an orogenic depression in the Central Kazakhstan. The most characteristic features of this deposit are the fine-grained nature of the zirconium mineralization, an unusual texture of the zirconium ores, and a close association of zirconium with phosphorus in the ores. Zircon grains form fine globular aggregates with the features of hexagonal crystal habit. In addition to crystalline zircon, the ores contain metacolloidal zircon, similar to hydrozircon. The morphological and textural features of the zirconium ores suggest that the deposition of ore deposits took place at a low temperature from colloidal solutions. It is believed that this deposit should be considered to be a new type of zirconium mineralization that is related to low-temperature hydrothermal processes.

Jan 1, 1995

By C. A. Pickles

Microwave processing is a relatively new technology that has been successfully applied in a number of industries. However, in the field of metal extraction, there is a paucity of success, despite considerable hype in the early years. Increased reaction rates, lowered reaction temperatures and higher energy efficiencies were some of the advantages claimed. Even with over almost two decades of research and some pilot plant studies, microwave metal extraction remains essentially a laboratory technique. In this paper, the research performed over the last few decades will be reviewed and some reasons for the lack of success in developing microwave metal extraction processes will be discussed. Based on the knowledge gained from these experiences, a more informed view of microwave heating can lead to the realization that there is still some untapped potential for this heating technique in metal extraction processes.

By Metehan Erdogan, Mustafa Serdal Aras, Sedef Cift Karagul, Ishak Karakaya, Esra Karakaya, Merve Kolay Ersoy

Pickling is the treatment of metal surfaces by removing oxide layer, rust, scale, inorganic contaminants or other impurities from ferrous metals, copper or precious metals. A strong inorganic acid such as hydrochloric acid is used for plain carbon or low alloy steel pickling. When the concentration of copper in the pickling solution exceeds about 100 mg/L, reversion may take place and randomly plating of copper onto the steel strips which causes visual incompatibility occur. Furthermore, efficiency of pickling decreases with the increase of copper content. The reversion may be delayed to higher Cu concentrations by adding fresh acid to the line. Increased acid consumption only delays the time to discard the solution but increases the cost and hazardous nature effect on the environment. An experimental electrochemical procedure has been conducted to remove copper from pickling solution to reduce the concentration below 100 mg/L. Within this scope, effects of applied current density, copper concentration and electrolysis duration on copper deposition were studied. Current density was determined as the most effective parameter to remove copper from the regenerated pickling solutions of steel plants.

Mar 1, 2018

By A. O. Apata, F. V. Adams

The use of rice husk ash as aggregate for foundry sand mould production has been studied. 5 –25wt% rice husk ash was added to the sand mixture. The chemical, physical and mechanical properties measured include: chemical analysis of the rice husk ash, particle size, density, permeability, compatibility mouldability, moisture content, green compression and shear strength, dry compression and shear strength. The result revealed that, addition of rice husk ash to River Niger Silica sand, increased the mouldability, compatibility, grain fineness number, both green and dry strength, slightly decreased the density, permeability and moisture content. The result shows that better properties is achievable by the addition of rice husk ash to River Niger silica sand and can be used to enhance the mould properties of foundry sand.

Mar 1, 2017

By Marcelo Mourao, Adolfo Pillihuaman, Alberto Nogueira, Cyro Takano

"The self-reduction is an alternative and promising process for production of pig iron because offers decisive benefits such as enhancing the reaction kinetic with decrease in fuel consumption and C02 emissions. The self-reduction mixture of iron ore fines, carbonaceous reducer and additives for slag forming components, without agglomeration, was tested in a laboratory rotary kiln. The additives for slag were defined for presenting two different estimated liquidus temperatures (1623 Kand 1773 K) to verify the effect of these temperatures on the iron-carbon nuggets coalescence process. These mixtures were tested at 1673 and 1773 Kin an experimental rotary kiln. After reduction-melting and coalescence processes the samples were disaggregated and the iron nuggets were classified by size. It was considered that nuggets larger than 7,93mm would be a good reference for coalescence index. Low liquidus temperature slag presented 37% of this larger fraction against only 13.5% for high liquidus temperature one. The low liquidus temperature slag would facilitate contact between the particles of iron-carbon in a rotary kiln, enhancing the coalescence.IntroductionThe slag composition usually depends on the reducer ash composition, the ore gangue, the binder composition and any fluxing material [l], and the mechanism of carbon transportation in slag that contains iron oxide reducible by carbon can be explained by the oxide reduction and the metal carburization. During carbon transportation, the carburized particle is transported to slag-metal interphases by the gravity effect, being assimilated by the metallic phase [2]. When the slag's iron oxide comes in contact with the solid carbon, it is immediately reduced, forming Fe particles and CO bubbles as it is shown in the figure l(a). The Fe particles are carburized by carbon particles; they are liquefied simultaneously in the carbon-slag interphase. The Fe-C liquid particles are transported from the slag-carbon interphase to iron-slag interphase as a result of slag flow, based on the surface tension difference (Marangoni effect), figure l(b). The Fe-C liquid particles coalesce on the iron surface and the carbon is immediately diffused in the iron as it is shown in figure l(c). The reduced iron is carburized continuously by repeated sequences [3]."

Jan 1, 2013

By Ljiljana Solujic

The need for the removal of mercury from the precious metals extraction circuits may be influenced by process, environmental, as well as by occupational hazard reasons. In these circuits mercury is mainly present as cyanide complexes. The effectiveness of any stabilization method will be influenced by the high thermodynamic stability mercury-cyano species exhibit in an aqueous solution. In this study, we have investigated the utility of the trisodium salt of trimmercapto-s-triazine (TMT) for precipitation of mercury from the corresponding cyano-complexes. The influence of pH molar ratio of TMT to Hg, coagulant and flocculant additions, excess of free cyanide, as well as the presence of other metal-cyano species on the effectiveness of mercury precipitation were investigated in detail. Also, a "teal world" precious metals mill effluent initially containing ~7 ug/mL (ppm) of Hg was treated and A was found that greater than 99.8% of the mercury was removed from the solution as am insoluble Hg/TMT complex.

Jan 1, 1996

By Ayşe Ece Yıldızçelik, Mehmet Buğdaycı, Onuralp Yücel

ZrB2 and TiB2 are significant metal borides. They are being used in various industrial areas from space technology to nuclear industry owing to their physical properties such as high melting point, high thermal/electrical conductivity and low density. Present study was conducted in two main stages: self-propagating high-temperature synthesis (SHS) reactions and leaching. ZrO2, TiO2, B2O3 were used as starting material and Mg was used as a reductant to produce ZrB2-TiB2 powders via SHS. Therefore, it was aimed to determine production parameters, leaching conditions and comprehensive examination of final product features. The samples were characterized by using chemical analysis (AAS), XRD, XRF and SEM/EDS techniques.

Jan 1, 2015