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By J B. McConnell

The Thompson smelter has three unique features which form the basis ~f its design: fluid bed roasters which treat nickel concentrate filter cake from the mill, as well as the flux, in order to achieve partial desulphurization; the use of electric furnaces for the smelting of the partially desulphurized, preheated roaster product; and the disposal of slag by water granulation and slag slurry pumping. The installation consists of three fluid bed roasters, each feeding an electric furnace. Nickel concentrate is received at the smelter via pipe line. It is thickened and filtered, and the filter cake, together with siliceous flux, is fed through rotary bin feeders and reciprocating double-gate seals into the fluid bed roasters. Air injected into the roasters through club-head tuyeres oxidizes part of the sulphur and associated iron in the concentrate. The heat of reaction dries and heats the charge. Roaster product is recovered from the gas stream in cyclones and from the roaster bed through automatic valves.

Jan 1, 1963

By F. R. Archibald

Introduction It is the purpose of this paper to review the subject of roasting as preparation of refractory gold ores and concentrates for cyanidation, with particular reference to operations at the mill of Beattie Gold Mines (Que.), Ltd., Duparquet, Quebec. Two earlier papers relating to the Beattie roasting operations are cited as background to the ? present discussion, and more general reference is made to other publications relating? to geology and metallurgy at Beattie. The Beattie roasting plant was built in 1937 as an addition to the existing flotation and cyanidation plant to permit complete processing of the ore at the mine property. Previously, the flotation concentrate had been cyanided, yielding 70 per cent of the gold values, followed by re-flotation of a concentrate from the cyanide residue. This re-floated residue was shipped to a smelter for recovery of gold values unavailable from direct cyanidation. The roasting plant itself is of interest through application in its design of multiple-hearth roasters and a Cottrell plant for separate recovery of dust and arsenic. In the laboratory and plant studies that accompanied development of the plant into a dependable and efficient working unit have been found principles and ideas applicable to other roasting 'problems. Before enlarging on these aspects relating particularly to the Beattie problems and plant, brief consideration is given to roasting in general.

Jan 1, 1949

By F. R. Archibald

MR. A. F. B. Norwood: Having been associated in the past few years with nine different plants roasting aurif erous concentrates in Australia, two of which were new installations for which design and construction were undertaken by the writer, I read Mr. Archibald's paper with very great interest, and I deem it a great privilege, as a member of a sister Institution, to be invited to contribute to the discussion on the paper. I wish to congratulate the author on a very informative and interesting paper, and, although situated many thousands of miles away, I feel I have gathered from it a very close idea of the operating conditions and of the work that has been carried on at the Beattie gold mine. Working along somewhat different lines, it is interesting to note that the conclusions drawn by the author run closely parallel to those accepted in Western Australia, viz., that the object of roasting is to obtain a porous calcine, and that this can best be achieved by roasting first at a temperature below 900 deg. F. to 1,000 deg. F., and then raising the temperature at the finish of the roast. Turning first to the laboratory work, the materials I have studied in Western Australia cover a range from those with little or no arsenic to concentrates carrying as high ?as 20 per cent, i.e., even higher than in the analysis quoted for the eoncentrates from Nepheline Products, Limited. In the ease of arsenic-free pyrite concentrates, the roast is ideally carried out at a temperature ranging from 900 deg. F. to 1,000 ferric oxide is one cause of the refractory gold remaining In deg. F. No improvement in extraction is obtained when the calcines are cyanided by raising the final temperature above this point; nevertheless, in technical practice it is desirable to finish the roast at 1,200 deg. F. in order to decompose basic ferric sulphate and thereby reduce the consumption of chemicals in the subsequent cyanidation step. However, if at any stage of the roast the temperature is raised above 1,200 deg. F., the extraction by cyanidation falls, and continues to do so the higher the maximum temperature that is reached. Line A in the accompanying graph typifies this effect.

Jan 1, 1949

The roasting process of copper concentrates containing variable quantities of arsenic in a fluidized bed regime was analyzed, considering the technical literature published on the topic in the last quarter century. Although emphasis has been given to the analysis in the fluidized bed regime, other processes have also been considered, under a reducing, neutral or oxidizing atmosphere. The kinetic mechanisms of roasting, as well as the models that have been applied or those likely to be used to explain the kinetics of arsenic removal, are analyzed. Regarding the kinetic mechanisms, those that have been applied to copper concentrates with both high and low arsenic content are included. The roasting kinetic model includes the kinetic data analysis techniques, general models, equations and an estimation of the conversion degree through dynamic, differential and integral methods, as well as particular models for mineralogical components, such as smelter dust and copper concentrates with low and high arsenic content.

May 1, 2012

Roasting of molybdenite concentrate is an important stage in the production of commercial molybdenum trioxide. The oxidation kinetic and mechanism of molybdenum sulfide concentrates from two plants were investigated at temperatures from 444 °C to 640°C. The rate of reaction was determined for thin layer samples in a muffle furnace at controlled temperatures, oxygen excess and removal of sulfur dioxide. For both concentrates the rate of reaction is fairly slow at temperatures below 500°C and remains fairly constant from 540 to 600 °C. It was observed that the concentrate from the first plant presents a tendency for sintering or glazing at temperatures above 620°C, whereas the same phenomena was observed at 20 or 30 °C higher temperature for the second concentrate. A kinetic model of two reactions, involving the formation of Mo02 as intermediate oxide for the production of Mo03 is proposed and activation energies of 23.0 and 20.8 kJ/mol for the first and second reaction were calculated for temperatures between 520 °C to 600 °C. These low values of activation energies indicate that the overall rate of oxidation is controlled by mass transfer, particularly in a porous layer of oxides. Therefore, the renewal of the surface by mixing and motion of the concentrate layer is of great importance. Sublimation of Mo03 becomes significant for temperatures above 650 °C.

Jan 1, 2007

By Maija-Leena Metsärinta

The behaviour of copper and lead in zinc roasting has been studied in laboratory scale roasting experiments as well as in large scale trials in an industrial fluidized bed, with the background of Outokumpu Kokkola Zinc smelter. Commercial zinc concentrates with a low and high ( up to 3 wt % ) copper content and with a low and high (up to 3.5 wt % ) lead content were oxidized to various desulphurisation degrees in the fluidized bed to establish the reaction mechanisms and the paths for copper and lead oxidation in the roasting. Influences of the agglomerate size on the roasting kinetics and micro-scale phenomena were also determined. Optical microscopy was used on the calcine and the findings are presented as numerous photographs of the polished cross sections. SEMIEDS techniques were used for analyzing chemically the phases and particle morphologies present in the samples. Computational thermodynamics was applied to the complex phase equilibria occurring during roasting in the agglomerating calcine. A complete oxidation of zinc concentrate with a high copper and lead content requires a careful control of oxygen coefficient in the roasting in order to maintain a stable operation of the fluidized bed. Oxygen coefficient thus seems to have a significant impact on the hydrodynamic stability of the fluidized bed with fine raw materials.

Jan 1, 2003

By Maija-Leena Metsiirinta

The behaviour of copper and lead in zinc roasting has been studied in laboratory scale roasting experiments as well as in large scale trials in an industrial fluidized bed, with the background of Outokumpu Kokkola Zinc smelter. Commercial zinc concentrates with a low and high ( up to 3 wt % ) copper content and with a low and high ( up to 3.5 wt % ) lead content were oxidized to various desulphurisation degrees in the fluidized bed to establish the reaction mechanisms and the paths for copper and lead oxidation in the roasting. Influences of the agglomerate size on the roasting kinetics and micro- scale phenomena were also determined. Optical microscopy was used on the calcine and the findings are presented as numerous photographs of the polished cross sections. SEM/EDS techniques were used for analyzing chemically the phases and particle morphologies present in the samples. Computational thermodynamics was applied to the complex phase equilibria occurring during roasting in the agglomerating calcine. A complete oxidation of zinc concentrate with a high copper and lead content requires a careful control of oxygen coefficient in the roasting in order to maintain a stable operation of the fluidized bed. Oxygen coefficient thus seems to have a significant impact on the hydrodynamic stability of the fluidized bed with fine raw materials.

Jan 1, 2003

By Mahmut Altiner

In the present study, the use of horse residue as an alternative reducing agent in the roasting of a low-grade goethite ore containing 17.60% Fe was investigated. Additional roasting experiments were carried out with corn starch and without reducing agent for comparison. Each roasted product was characterized using X-ray diffraction (XRD) and magnetic hysteresis (MH) loops analyses. The optimum roasting conditions (roasting temperature [400, 500, and 600 °C], reducing agent/ore ratio [0.04, 0.08, and 0.12], and roasting time [10, 20, and 30 min]) were investigated based on the Taguchi approach. The magnetic susceptibilities of the roasted sample with the addition of reducing agents were higher compared to that of the roasted sample in the absence of reducing agent. Experimental findings indicate that the horse residue can be used as the reducing agent. Finally, an iron ore concentrate assaying a Fe grade of 62.12% with a recovery of 56.93% was prepared using wet magnetic separation at a magnetic intensity of 0.5 T from the ore roasted under the following roasting conditions: roasting temperature of 500 °C, reducing agent/ sample ratio of 0.08, and roasting time of 30 min.

Jun 3, 2020

By A. Roy, T. LeBel, P. Coursol, P. Lind

At the early stage of a mining project, small amounts of concentrates are available for testwork. For gold concentrate or ores containing significant arsenic levels, batch bench scale roasting is often unreliable, leading to highly variable gold recoveries to be used in the project’s financial justifications. With an appropriate bench scale unit using continuous feeding and residence time control for solid and gas phases, reliable numbers can be obtained at small scale with only a few hundred grams per test condition. This paper describes the development of a pilot fluid bed roasting unit by Kingston Process Metallurgy Inc. (KPM) to perform representative trials on gold concentrates containing arsenopyrite, arsenian pyrite and carbonaceous components. Calcines produced under different conditions were characterised by chemical analysis and electron microprobe; the calcine microstructure obtained is described. The most important parameter affecting gold recovery is oxygen content in the roasting atmosphere, with the lowest controlled oxygen level giving the highest gold recoveries. Higher local temperatures in the bed may cause the formation of molten glassy phases which can also reduce the gold recoveries significantly. The impact of roasting conditions in the two inch fluid bed is compared with commercial results obtained in full scale operation.

Jan 1, 2014

By Mark G. Aylmore, Eric J. Grimsey

Anenopyrite, both pure and in some cases associated with pyrite, was laboratory roasted either isothermally or at a constant heating rate, at temperatures mainly between 723 and 923 K and under environments of air, sulfur dioxide, oxygen and argon, as well as S02/02/H20/N2 mixtures. The mineralogy, arsenic contents and in some cases surface areas of the calcines were evaluated so as to provide an enhanced understanding particularly of the conditions under which the important transformations to pyrrhotite and magnetite occur. A thermodynamic analysis is also undertaken to rationalize the observations and provide some guidance for the operation of commercial roasters.

Jan 1, 1990

By F. J. Arriagada

Where gold is present in a finely disseminated form within sulfide particles, the porosity and surface area of the calcined material strongly influence leaching since they control the penetration of solution inside the gold-bearing grains. On the basis of a stability diagram for the Fe-O-S in the temperature range of 400 to 750aC, the expected sequence chemical transformations associated with the oxidation of pyrite is discus-sed. By using analytical techniques which include scanning electron microscopy, X-ray diffraction and BET gas adsorption, the chemical and structural changes experienced by auriferous pyrite-arsenopyrite concentrates and pure pyrite samples are studied under an oxidizing roasting atmosphere of com-position 80% N + 20% O2 in the temperature range of 450 to 750°C. The results indicate that as the roasting temperature increases, the surface area of the calcines decreases sharply after a maximum value attained at about 450-500°C. SEM micrographs show that the needle-shaped tips which characterize the surface of the oxide product become wider and the size of the pores between them is decreased when the roasting temperature is in-creased from 550 to 750°C. This effect suggests that the formation of a more "closed" hematite product at higher temperatures is due to sintering associated with a faster growth and crystallization of the oxide. A strong correlation is shown between increasing roasting temperature and increase in gold lost in cyanidation tailings, an effect which may be partly attributed to the loss in surface area of the calcines.

Jan 1, 1982

By F. R. Archibald

SINCE the opening of the Beattie mine, in 1933, the concentrate produced by flotation has been considered refractory. As the gold extraction by cyanidation was poor, the concentrate, during the first four and a half years of operation, was shipped to a smelter for further treatment. After the installation of the cyanide plant, in 1934, seventy per cent of the gold in the concentrate was recovered before shipment to the smelter. In 1937, a roasting plant was built so that treatment might be complete at the mine. Much experimental work had been done by a number of investigators prior to the installation of the roasters, but none of them had seriously attempted to identify the causes of, or the elements responsible for, the refractory behaviour of the concentrate. Intensive investigation in this direction commenced in the Beattie lab-oratory in July, 1938, has led not only to the identification of several causes contributory to the refractory behaviour, but also to revisions in procedure and principles with respect to roasting Beattie concentrate in particular and arsenical concentrates in general. The accuracy of the identification of these causes and the soundness of the principles is borne out by interpretation of roasting plant records, by improvements and simplification since applied. to plant operation, and also by laboratory and test-plant results on arsenical concentrate produced by another mine. It is the purpose here to present an account and interpretation of the laboratory investigation, together with a correlation of laboratory and plant results. Incomplete extraction of the gold by cyanidation after roasting is due primarily to the nature of the material roasted, and secondarily to the manner in which it has been roasted. There is a possibility that better extraction may be obtained by improvements in both particulars.

Jan 1, 1939

By G. Lindkvist

Roasting of concentrates with high impurity levels is normally done in multiple- hearth furnaces where the concentrates are heated with oilfired burners in order to remove As, Sb and Bi before the final sulfide oxidation. Although it is a countercurrent heat exchange process it uses a lot of oil. In order to develop an energy saving, and from a working environmental point of view a less harmful process than the multiplehearth process, pilot-plant tests have been done in a two-stage fluidized bed for partial roasting. The test materials have been As-rich concentrates with 8-25 % As some 5b and Bi. The Cu-content was 0-28 %. The tests have been successful with <0.3 % As,in the calcine and with an elimination of 5b between 80 and 90 %. In order to achieve the proper conditions for good impurity removal, 1.e. right temperature,residence time and sulphur potential, the tests were performed in a special designed roaster. The roaster consists of two beds with the facilities for recirculation of calcine, preheating of the blast, and possibility to use oxygen enrichment. The construction makes it easy to control the reactions that generate the heat in the bed and reduce the amount of dust that passes through the cyclones. As two roasting steps are used, the possibility to obtain optimal conditions for impurity removal is improved and the calcine can either be smelted to a normal matte, or after being dead-roasted in the second stage, be leached in the normal way for gold extraction. The calcine was smelted with slag. The matte and the slag obtained had low quantities of impurities in the matte and a favourable distribution of impurities to the slag.

Jan 1, 1983

By J. Etcheverry, E. Seguel, R. Díaz, F. Parada, R. Parra, E. Balladares

A thermodynamic and kinetic model is proposed to explain the formation of bornite, chalcopyrite and magnetite during partial roasting of enargite-containing copper concentrates. The proposed mechanism involves solid-solid-gas and solid-gas reactions between chalcocite, pyrrhotite, gaseous sulfur and oxygen. The formation of bornite could be explained by a two-step reaction: the first one involving the formation of chalcopyrite by a reaction between Cu2S, FeS and gaseous sulfur, followed by a second step in which the newly formed chalcopyrite reacts with additional chalcocite to form bornite. Although thermodynamically the direct formation of bornite is more favorable than that of chalcopyrite, the lower diffusion kinetics of bornite formation could explain the preferential formation of chalcopyrite. If the reaction occurs with stoichiometric chalcocite and pyrrhotite in the presence of gaseous sulfur to form chalcopyrite, no bornite is formed, while for the stoichiometric reaction between chalcopyrite and chalcocite in the absence of sulfur, only bornite is formed. For the formation of magnetite and chalcopyrite the mechanism could involve the partial reaction of chalcocite and pyrrhotite in the presence of oxygen. The proposed model is thermodynamically consistent with the experimental results obtained in laboratory and pilot plant. INTRODUCTION The processing of high-arsenic copper concentrates with over 0.7 wt.-% arsenic by conventional smelting-converting normally require an additional arsenic removal step to reduce arsenic content to levels below 0.2–0.3%. One of these high-arsenic copper concentrates is the one produced by the Ministro Hales Division (DMH) of CODELCO, which has the typical chemical composition shown in Table 1. Enargite (Cu3AsS4), chalcocite (Cu2S) and pyrite (FeS2) are the main mineralogical species present in these concentrates, with over 75 wt.-%, as shown in Table 2. Partial or “neutral” roasting of these concentrates under controlled temperature and partial oxygen pressure conditions at 923–993K (650–720ºC) can remove up to 95% of the arsenic as As2S3 (As4S6), which has a high vapor pressure under these conditions, leaving a calcine with low residual arsenic. In copper concentrates, arsenic is present generally as enargite and arsenopyrite. This compounds as well as others such as pyrite and covelite, decompose readily above 770 K (500ºC), releasing, in addition to gaseous arsenic trisulfide, gaseous sulfur which by oxidizing to SO2 generates most of the heat required by the process.

Jan 1, 2019

By CYRIL W., William Campbell, Henry M. Howe

THIS paper gives the results of an investigation of the behavior of the argentiferous cobalt-nickel arsenides of Temiskaming, Ontario, in roasting, made in the metallurgical laboratories of the School of Mines, of Columbia University in the City of New York. The ore was kindly given by the owners of the La Rose and Trethewey properties at Cobalt, Ontario, and Mr. E. J. Hall, Tutor in Assaying in Columbia University, has helped us much. I. OBJECT OF THE INVESTIGATION. The object of the investigation was to learn:- 1. The temperature at which the arsenic is most rapidly expelled; 2. The thoroughness with which it is expelled by prolonged roasting at this temperature; 3. The effect of adding charcoal (a) near the end of the roast and (b) at the beginning of the roast. II. NATURE OF THE ORE. The important ores mined in the Temiskaming deposits are native silver-with small amounts of dyscrasite (Ag6 Sb), argentite (Ag2S), pyrargyrite (Ag3SbS3)-smaltite (CoAs2), chloanthite (NiAs2) and niccolite (NiAs). Mispickel (FeAsS) and cobaltite (CoAsS) also occur in smaller quantities. The average composition of the ore shipped from this district for the first six months of 1905 -was: silver, from 4.1 to 4.8 per cent.; cobalt, from 6.9 to 8.2 per cent ; nickel, from 3 to 4.7 per cent ; and arsenic, from 30.9 to 34.6 per cent. The ore which we treated consists chiefly of smaltite ; In our laboratory-work

Jan 1, 1907

By Roorda H. J, R. R. Saddington, Curlook W

THE copper-nickel sulfide ore deposits of the International Nickel Company of Canada, Limited contain the minerals pyrrhotite, pentlandite, and chalcopyrite. In the extraction of the nickel, copper, and iron, much of the processing involves oxidation of the metals as well as sulfur. Roasting plays a predominant role at several stages in the operations which prepare the constituent metals for refining. Copper, nickel and iron concentrates of various grades, ranging from low-grade nickeliferous pyrrhotite to high-grade nickel sulfide, must be partially or completely oxidized. Figure 1 shows the main points at which roasting is conducted at INCO. Roasting experience at INCO dates back to the time when lump ore was partially roasted in heaps. It has progressed through single hearth roasters, sinter machines, multiple-hearth roasters, flash roasters, and more recently has centered on the development and utilization of fluid bed roasters. The primitive, slow, and inefficient method of heap

Jan 1, 1961

By E. Peters

Roasting processes are divided into several elementary mechanisms, any of which could be significant or pre-dominant in a particular roast. The elementary processes considered in-elude beat transfer, gas-solid inter-actions with accompanying mass transfer between the bed and furnace atmosphere, vapor phase transport processes in solid-solid interactions, and solid phase diffusion processes. Examples are chosen of processes in which one of these mechanisms pre-dominates and some recently obtained data is presented to support the existence and significance of these mechanisms. Proposals are also made for future research in these areas, and for utilizing the information in the improvement of roaster capacities’ OASTING of ores as a preparative treatment for smelting or leaching has been practiced for so long that its origin has been lost in antiquity, but little has been under-stood of its basic nature until fair-ly recent times. The nominal chemistry of roasting processes is now understood; that is, the initial chemical com-pounds present in the ores or con-

Jan 1, 1961

By Emmanuel N. Zevgolis

In the present work, a reduction roasting experimental study of Greek nickeliferous laterite samples with a gaseous reducing mixture ? CO:N2- is presented. The effect of parameters such as temperature, ore grain size, and composition of the reducing mixture were examined. It is deduced that the reducibility of intermediate type laterite sample, where iron appears mainly in the form of goethite (a-FeOOH), is considerably higher than that of limonitic type laterite samples, where hematite (a-Fe2O3) is the predominant iron mineral phase. The degree of reduction of the limonitic type laterite samples does not exceed 50%, while it reaches 95% in the case of the intermediate-type laterite sample under the same experimental conditions. Increasing the temperature in the range 750-900°C does not considerably favor the reduction of the limonitic type laterites, whereas decrease of ore grain size of the limonitic-type ore samples and more intense reducing conditions increase the reduction. The considerably higher specific surface area values of the intermediate laterite samples, diminishes the effect of the ore grain size and this can be regarded as the critical parameter leading to the higher reducibility of this ore.

Jan 1, 2009

By Just J, Nguyen G, Dunn J. G, Graham J

A sample of pyritic gold concentrate was investigated by wet chemical and electron optical techniques. Sub-samples were roasted in a laboratory scale fluidized bed roaster in the temperature range 400-700¦C. The calcine was characterised, and cyanide-leached using a standard bottle rolling test. Gold extraction efficiencies varied with roasting temperature. At temperatures of 400 and 450¦C gold ex- tractions of less than 40% were achieved, but between 500-700¦C the extraction had increased to 93--98Z. The surface area of the calcine varied with roasting temperature, reaching a maximum at 500¦C. There was no correlation between the surface area of the calcine and the efficiency of gold extraction.

Jan 1, 1987

By A. R. Barnes, N. Stubina

Increasingly, gold producers are forced to treat ever more refractory ores. While ores containing pyrite, arsenopyrite and carbonaceous material have been subjected to complete pressure oxidation (PDX) as the standard process for such ores, recent improvements in fluid bed roasting technologies have led to a resurgence of interest in roasting as a viable alternative. The lower capital and operating costs of roaster installations add further impetus to this trend. The Extractive Metallurgy Group at Xstrata Process Support operates four fluid bed reactors of various sizes which have been utilised on a large number of projects to treat highly refractory ores. Preliminary mineralogical modelling of both the physical and chemical aspects of the roasting process and subsequent testing under carefully controlled conditions has allowed clients to obtain gold recoveries approaching or matching those achievable by PDX. The flexibility of the units to operate in various modes- " bubbling bed", circulating bed, two stage, sub-stoichiometric and combinations of these, and the range of sample sizes accommodated, from a few kilograms to a few tons, has enabled XPS to accommodate clients with a wide variety of gold bearing refractory ores from all over the world. This paper outlines the key challenges of fluid bed roasting of refractory gold ores, describes the methodology used to design the testwork program and provides some results from select test campaigns.

Jan 1, 2011