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By G. Zhan, P. Mousset-Jones, G. Danko, J. J. K. Daemen, C. Mezei

Paper presented at the conference Risk assessment in the extractive industries, held in Exeter, 23-24 March 1994, and first published London: IMM, 1994, preprint volume. 18pp., 12 refs. (Originally entitled: Tunnel roof diagnosis using a robotic sensor test bed.) An integral roof diagnosis method is proposed to assist in assessment of risk regarding the stability of an excavation. A Robotic Sensor Test Bed (RSTB) is being developed for the characterisation of roof stability. The sensor test bed consists of a sonic/ultrasonic wave response sensor, a laser surface profiler and a surface temperature sensor. These sensors are mounted on an articulated robot manipulator for performing remote-controlled or fully automated diagnoses. A number of laboratory and field sonic/ultrasonic tests were conducted. A high-energy ultrasonic transducer and an impact device were used to resonate rock slabs. The fracture depths of the slabs were found to be inversely related to the measured resonance frequencies. The agreement between identified and actual dimensions was acceptable. Field tests also showed that loose rock on the surface can be clearly distinguished from solid formation by comparing their wave responses. The robotic laser profiler part of the RSTB was used to measure surface geometry. Different scanning methods are being developed to achieve the fastest and most precise measurements and to provide pertinent information about rock joints and major fractures

Dec 1, 1994

By C. Graeme-Barber, R. L. Bell, T. G. Langdon

An analysis is made of the formulas and ,methods used to estimate the contribution of grain boundary sliding to the overall strain of a polycrystal. The errors involved in the approximations and/or ,mistakes in earlier work are assessed quantitatively so as to make possible the critical use of previously published data. SINCE it has been found that, under conditions of very slow creep, the strain due to grain boundary sliding (?gb) may contribute as much as 80 pct of the total creep strain,1,2 it is obviously important to have reliable methods for estimating this grain boundary strain. In two recent papers Stevens3,4 has drawn attention to the pitfalls encountered in assessing ?gb. He criticizes 1) the assumptions made in the derivation of some of the formulas for ?gb, and 2) the indiscriminate averaging procedures used for obtaining the quantities substituted in these formulas. These and further criticisms of earlier work are mostly valid. Unfortunately the only formulas and procedures recommended are either impossible or very difficult to apply in practice. Furthermore no attempt is made to assess the errors involved by the earlier approximations or mistakes, and so it is not possible to make critical use of any of these early dab. The present article attempts to improve on these shortcomings by reference to empirical verification of easily applied formulas whose theoretical derivations involve some otherwise unjustifiable assumptions, and by a quantitative assessment of the errors in previous work. DEFINITIONS First it is necessary to define the terms and symbols to be used. The choice of symbols preferred here is a logical combination and extension of the v introduced by McLean5 and the u by Brunner and rant.' In Fig. 1 the two grains X and Y are displaced by the sliding vector AC. u is the component of sliding resolved along the stress axis, v is that measured perpendicular both to the stress axis and to the specimen surface, and w is that measured perpendicular to the stress axis but in the plane of the surface. Two angles define the orientation of the grain boundary: 8, between the stress axis and the surface trace of the boundary, and +, the internal angle on a longitudinal section cut perpendicular to the surface. In computing the strain resulting from the boundary displacement at all the in- dividual boundaries in a polycrystal the components u, v, or w are sometimes averaged along a longitudinal line (i.e., parallel to the stress axis), sometimes along a transverse line, and sometimes at randomly chosen boundaries. Averages obtained in these three ways are given subscripts 1, t, and r, respectively. Stevens rightly calls attention to the possibility of non-equiaxed grain shapes either at the start or at the end of deformation. In this article all values of numbers of grains per unit length will refer to measurements made before deformation. The subscripts 1 and t will be used for the number of grains per unit length obtained along longitudinal and transverse lines, r for that obtained by averaging along a number of randomly directed lines. FORMULAS FOR ?gb ?gt, as a Function of u. An obvious truth is that cgb can, in principle, be obtained by summation of all the v components at the boundaries intersected by a longitudinal line of known length I, viz.: where nl is the number of grains per unit length, parallel to the stress axis, in the unstrained specimen. There are assumptions in the analytic derivation of Eq. [I] due to Brunner and rant' but ~achinger' arrived at Eq. [la] by a rigorous method. Unfortunately the experimental procedure required by Eq. [ la] proves very difficult as boundary migration tends to obscure the points at which the longitudinal line meets the grain boundary and the errors on such measurements tend to be large, see Fig. 2. For example, on a specimen of Magnox AL 80 at a creep strain of 9.7 pct, 300 measurements of u obtained from the points of intersection of a longitudinal line with the grain boundaries gave ul = 8.95 ± 3.58 pm, or an error of ±40 pct, at the 95 pct confidence limit. These large errors due to migration may be avoided by measuring u from the separation of the segments

Jan 1, 1968

By Shujian Jia, Mingming Song, Gaoyang Song, Bo Song, Yuhou Yang

An innovative method is investigated to separate inclusion particles from liquid metal by super gravity. To make clear the characteristics of the inclusion separation, Al melt containing MgAl2O4 particles with diameters less than 150 μm has been treated under various super-gravity fields. The thickness of particle-accumulated layer formed at the bottom of the sample and the area fraction, number density and size of inclusions were measured. It is found that the thickness of the particle-accumulated layer decreases and the area fraction of particles at this location increases with the increase of super-gravity field. With the gravity coefficient G=500, time t=2 min, and temperature T=1023 K, it is hardly to find any solid particles in the upper and middle areas of the sample and the separation efficiency is up to 90%.

Jan 1, 2015

By L. A. Matthews

The embrittlement of the Ti-6Al-4V alloy by hydrogen dosing at elevated temperature has been investigated. Metal coupons were subjected to isothermal treatments in a partial hydrogen atmosphere in the temperature range from 650ºC?950ºC and the degree of embrittlement after treatment was determined by drop-weight impact testing. Embrittlement was found to be inversely related to reaction temperature as a result of the combined effects of greater hydrogen absorption and titanium hydride precipitation at the lower isothermal temperatures. Keywords Titanium, hydrogen embrittlement, impact energy

Jan 1, 2011

By Michael E. Berndt

Asbestos first became an issue to Minnesota?s iron industry when it was revealed that mineral fibers similar to those in Reserve Mining?s tailings were being found in drinking water for several communities that used Lake Superior as their primary water source. This discovery turned what had largely been an environmental court battle into a case concerning public health. The courts listened to much conflicting and uncertain scientific testimony on the size and distribution of the mineral fibers and on the potential health effects imposed by them. In April 1974, the plant was ordered to shut down by a federal judge but the company quickly appealed the decision. The appeals court granted a stay and ultimately ruled that the plant?s closure could not be justified based on the unknown health effects of the mineral fibers since the consequences of such an action would have immediate and severe social and economic impacts. The plant was allowed to continue operation, but ordered to abate emissions to air around the plant and to switch to a land-based tailings disposal system. Much of the scientific uncertainty and public concern over mineral fibers in Minnesota?s taconite industry remain today. ©2007 Elsevier Inc. All rights reserved. Keywords: Minnesota; Iron ore; Taconite; Asbestos; Amphibole; Reserve Mining; Tailings; Mesabi Iron Range

Jan 1, 2007

By ANGELA NAIR AVELAR, Reiner Neumann, PAULO R. G. BRANDÃO

The understanding of the influence of the different types of apatite on the performance of mineral processing of igneous phosphate ores is still a challenge due to the difficulty to explain why some types of apatite floats in the froth flotation cell and others do not under the same conditions. Three types of apatite were identified by means of cathodoluminescence (CL) images in flotation concentrate and tailing samples from the Catalão mine: predominantly blue apatite, followed by green apatite and less frequently yellow apatite. The chemical composition of these types of apatite was determined by electron microprobe analysis (EPMA) and LA-ICP-MS. Blue and green apatite respond well to the process, thus remaining in the concentrate, while yellow apatite remained in the tailings. Yellow apatite is the one bearing the lowest P2O5 content and the largest anionic and cationic sites substitution, followed by green apatite, whereas blue apatite is the most homogeneous, with highest P and Ca grades and lowest substitution level. A negative correlation of the amount of phosphorus with fluorine was observed. Furthermore, impregnation of iron oxide-hydroxides in the yellow apatite was also observed. Therefore, the low flotation behaviour is due to low crystallinity coupled with impregnation onto its surface.

Jan 31, 2022

By John Wulff, J. H. Hollomon

Service failures in brass condenser tubes are often due to corrosion. One of the commonest types of corrosion reveals a surface structure of redeposited copper.' The study of the effect of alloy addition agents in preventing this kind of corrosion has received impetus from the extensive publication of Bengough and May.2 The mechanism of such inhibition gauged from immersion corrosion,2 cell corrosion,3 and electrolytic potential4 measurements is controversial. This controversy may be attributed in part to a lack of definite knowledge5 of the actual nature of the initial films formed in corrosion experiments. In our own corrosion work on copper and 70-30 brass this lack became apparent and necessitated an examination of surface films by X-ray and electron diffraction methods. The present paper is but an introduction to the subject of inhibition and reports the structure of films formed in active corrodents. Experimental Procedure The arsenical coppers and brasses used in this investigation were made by one of the writers* in the plant of the Revere Copper and Brass Co. at Rome, N. Y. Standard commercial melting practice was followed. O.F.H.C. copper and electrolytic zinc were used and all arsenic additions were made by additions of a master copper alloy. The final analyses are given in Table I. Likewise, the extrusion, cold-rolling, and intermediate anneals employed followed standard usage. Final heat-treatments were given to all materials to produce a similar grain size (0.035 to 0.045 mm. for brass and 0.015 to 0.025 for copper) for the alloys containing various percentages of arsenic. Samples 1/2 by M by 1/4 in. were cut from sheet material resurfaced and finished with 0000 metal-lographic papers. The surfaces were all degreased in alcohol and benzine before immersion. After immersion in the corrodent, they were washed gently in tap water, dipped first in alcohol and then in pure benzine and allowed to dry in the diffraction apparatus. The reflection electron diffraction apparatus used has been described by Burwell and Wu1ff.6 Fig. I is typical of the photo-grams obtained. The X-ray apparatus was

Jan 1, 1941

By John Wulff, J. H. Hollomon

Service failures in brass condenser tubes are often due to corrosion. One of the commonest types of corrosion reveals a surface structure of redeposited copper.' The study of the effect of alloy addition agents in preventing this kind of corrosion has received impetus from the extensive publication of Bengough and May.2 The mechanism of such inhibition gauged from immersion corrosion,2 cell corrosion,3 and electrolytic potential4 measurements is controversial. This controversy may be attributed in part to a lack of definite knowledge5 of the actual nature of the initial films formed in corrosion experiments. In our own corrosion work on copper and 70-30 brass this lack became apparent and necessitated an examination of surface films by X-ray and electron diffraction methods. The present paper is but an introduction to the subject of inhibition and reports the structure of films formed in active corrodents. Experimental Procedure The arsenical coppers and brasses used in this investigation were made by one of the writers* in the plant of the Revere Copper and Brass Co. at Rome, N. Y. Standard commercial melting practice was followed. O.F.H.C. copper and electrolytic zinc were used and all arsenic additions were made by additions of a master copper alloy. The final analyses are given in Table I. Likewise, the extrusion, cold-rolling, and intermediate anneals employed followed standard usage. Final heat-treatments were given to all materials to produce a similar grain size (0.035 to 0.045 mm. for brass and 0.015 to 0.025 for copper) for the alloys containing various percentages of arsenic. Samples 1/2 by M by 1/4 in. were cut from sheet material resurfaced and finished with 0000 metal-lographic papers. The surfaces were all degreased in alcohol and benzine before immersion. After immersion in the corrodent, they were washed gently in tap water, dipped first in alcohol and then in pure benzine and allowed to dry in the diffraction apparatus. The reflection electron diffraction apparatus used has been described by Burwell and Wu1ff.6 Fig. I is typical of the photo-grams obtained. The X-ray apparatus was

Jan 1, 1941

By C. Pelley, S. Kelebek, T. Katsabanis, B. Nanthakumar

"As part of a larger investigation on generation of fines from mining activities and their effect on downstream operations, ore samples from Onaping area stockpiles of Falconbridge Ltd were studied. Batch flotation tests were conducted on the stockpile samples and fresh ore samples to explore the effect of stockpiling on grade-recovery performance. Head grade and particle size distribution of the samples from stockpiles were adjusted so that the samples compared are similar to each other. In additional tests, fresh ore samples were blended with stockpile samples at various percentages, representing 27.4, 50.2 and 81.5% of stockpile samples.The samples from stockpiles produced inferior nickel grade-recovery curves compared to fresh ore. The poorer grade-recovery performance was attributable to two factors. First, a significant dilution effect was observed due to the nearly complete flotation of pyrrhotite. Secondly, while pyrrhotite from stockpiled ore became highly floatable, the same stockpiling conditions caused nickel losses that were attributable to non-floatability of some pentlandite.In the case of blending, there was generally insignificant difference in the nickel grade-recovery between fresh and blended samples when the blending cases involved 27.4 and 50.2% stockpile samples. However, an increase in pyrrhotite recovery was observed for both blending cases. At 81.5% blending case, degraded grade-recovery was significant primarily due to the nearly complete flotation of pyrrhotite. There was a small, but noticeable amount of nickel loss for this case. However, for lower ratios of blending this loss was negligible.The increase in pyrrhotite recovery was partly attributed to its activation by Cu and Ni ions. Formation of a significant amount of elemental sulphur was also apparent from analysis of stockpiled samples. It can be concluded that pyrrhotite is mildly oxidized under stockpiling conditions while part of the pentlandite undergoes a more severe oxidation."

Jan 1, 2006

Poorly designed sampling protocols generally result in high project risk by artificially increasing grade variability (ie the nugget effect). Sample collection, preparation and assay protocols that suit the ore type, together with QA/QC systems, will reduce this risk. All reporting codes (eg JORC, 2004) require the Competent Person to consider the quality and implication of sampling and assaying programs. High sampling errors beget higher project uncertainty; despite this fact, sampling does not receive the attention it deserves. The case studies presented show that many sampling issues frequently go unrecognised or unaddressed, resulting in poor project decisions during exploration through to feasibility and production. The overall conclusion is that correct sampling is critical to mining project success and that there is often a need for its optimisation.

Jan 1, 2007

By Abrahamsson S, Niklasson B

In a follow-up of 12 production blasts in a quarry at the Mrica project on Java, tightly spaced porous bands were found to govern fragmentation to the extent that the average fragment size k5o was nearly independent of the specific charge within the range 0.30-0.56 kghn3. This fording resulted in a reduction of the running costs for drilling and blasting by 20-40%. Our work has given considerable practical benefits and insights into the blasting process, even if the results were of no direct use to check out fragmentation predictions based on models, which was one of our main Goals.

Jan 1, 1990

By Jose Antonio Ardito

El objetivo de este trabajo técnico es mostrar las fuentes de desinformación que impiden el desarrollo de esos proyectos mineros y limitan una concertación viable y el diálogo con diversos stakeholders al no tener un consenso o entendimiento básico sobre temas importantes como son: 1) uso del agua y minería en cabeceras de cuenca, 2) uso de tierras por la actividad minera, 3) contaminación, 4) pasivos ambientales, 5) minería ilegal y 6) conflictividad social. Estas limitaciones en uso y manejo de la información así como la atmósfera social confrontacional persisten aun cuando se trabaje comprometidos con el desarrollo sostenible en un marco de responsabilidad social empresarial.

Sep 1, 2017

By C. E. Birchenall

DaVIES and Richardson1 have measured composition changes for Mn1-Owith variation in the equilibrium partial pressure of oxygen at 1500°, 1575°, and 1650°C, where 6 is the deviation from the simple stoichiometric ratio. No trend in this relationship with temperature was observed, so these remarks apply to the whole temperature range. The experimental values and their spread are shown by the bounded straight-line segments in the figure. Davies and Richardson assume that the stoichiometric oxide shows Frenkel disorder, given by the equation Mn2+Mn2+ + Mn" [1] where Mn2+ is a normal lattice ion which moves into an interstitial site (Mni2+) leaving a vacancy (Mn,"). The superscript dashes indicate that there is an excess charge on the anions surrounding the vacancy. Schottky disorder, in which a perfect crystal acquires equal numbers of cation and anion (Ov") vacancies according to leads to equations of exactly the same form in the analysis below. In view of the neutron diffraction results of Roth,2 which shows extensive Frenkel disorder in Fe1-o, Eq. [I] seems more appropriate. The deviations from stoichiometric composition, MnO, result from the addition of oxygen according to In effect Davies and Richardson ignore the variation of Mn3+in constructing equilibrium constants. This approximation might not appear to be very serious if the excess positive charges are really free posi- tive holes (P+) and if the intrinsic conductivity is high as a result of the reaction where e- is a conducting electron. However, the calculations of Buessem and Butler3 indicate that the partition functions of the free charges make a large contribution to the equilibrium constant, and this approximation would not be a desirable one. Furthermore, Morin4 shows that the positive holes are probably localized in MnO and therefore are described better by the mass action principle than by a degenerate gas model. Davies and Richardson's considerations require that activity corrections be applied beyond a 6 value of about 0.005. It is proposed to show here that the dissociation pressure curve can be calculated reasonably well over the whole composition range studied without activity corrections by choosing appropriate equilibrium constants for reactions 1 and 2. As stoichiometric composition The mass action constant, Ks, for reaction [I.] and the equilibrium constant, K,, for reaction [2] are given by where the concentrations which do not change significantly have been absorbed into the constants. The brackets denote concentrations. The deviation from stoichometric composition is given by gardless of [Mni2 ]. Substituting Eq. [7] in [6]

Jan 1, 1961

By James R. Wickens, David La Rosa, Robert E. McIvor, Adrian Dance

"The comminution circuit at Barrick Cortez Gold Mine uses an open circuit primary jaw crusher followed by a standard SABC grinding circuit. The grinding circuit incorporates a 26’Ø x 11’ SAG mill, an Omnicone 1560 pebble crusher and a 16’Ø x 28½’ ball mill. Both mills are driven by 4500 HP motors.In 2007, several comminution circuit studies were performed to assess circuit performance and map a course for improvement. This paper discusses the results of those studies including an analysis of mine-to-mill opportunities, grinding work index efficiency, and ball mill functional performance. Subsequently, improvements to the circuit were made to enhance operating efficiency. Specifically, improvements to the pebble crusher liner configuration, advanced process control system (expert system) and ball mill classification and ball charge are discussed. In addition, other current and future improvement opportunities are discussed.INTRODUCTIONThe Barrick Cortez property is expanding to include the new Cortez Hills open pit and underground mines. Ore from these new mines will be processed in the existing Pipeline mill facility. In conjunction with ore characterization work, performance of the comminution circuit needed to be quantified. Thus, in 2007, the comminution circuit was surveyed and opportunities for improvement identified.Figure 1 below shows the Pipeline mill flowsheet. It is a standard SABC grinding circuit using an open circuit primary jaw crusher followed by a 26’Ø x 11’ (7.92m Ø x 3.35m) SAG mill, in closed circuit with a Omnicone 1,560 pebble crusher, and a 16’Ø x 28½’ (4.88m Ø x 8.69m) ball mill. Both mills are driven by 4,500 HP (3,357 kW) motors. The SAG discharge screen aperture is 5/16” (8 mm) x 1-1/16” (27 mm) slots. Ball mill circuit classification is done with Krebs D20B cyclones."

Jan 1, 2009

By Vagner Silva Guilherme

Na busca de novas tecnologias para o processo de sinterização de minério de ferro, a recirculação dos gases de saída do processo podem proporcionar algumas vantagens em relação ao processo convencional. Para tal estudo, foi utilizado um modelo multi-fásico de sinterização para a avaliação da recirculação dos gases de saída do processo. Foram analisados cinco casos de recirculação dos gases de saída, do processo de sinterização, visando, sempre uma operação estável do processo. Os resultados de simulação indicam alargamento da frente de combustão com a recirculação dos gases de saída e a possibilidade da redução do consumo do combustível sólido. Como resultado, houve aumento da fração de cálcio-silicatos, proporcionando melhoria da redutibilidade do sínter, além da redução da emissão de CO2 e PCDD/Fs na máquina de sínter.

Aug 1, 2018

By S. Boone, J. N. Shirlaw

INTRODUCTION Soft, near normally consolidated clays generally provide ideal conditions for tunneling using Earth Pressure Balance (EPB) shields. It is easy to turn the clay into a low permeability, viscous spoil that can be pressurized to maintain the required face pres-sure. Despite this, there are records of relatively large, and often quite variable, surface settlements over EPB driven tunnels in soft clay. To understand this variation it is necessary to identify the various factors that contribute to settlement. Tunnels in soft clay are ideal for study these effects in the field, as an unsupported void will close almost immediately, due to the low shear strength of the soil. In the short term, deformation in a soft clay will occur at constant volume, so short term surface settlements can be related to movements at tunnel level. In this paper, data will be used from EPB driven tunnels in Singapore marine clay. In all of the cases discussed the lining consisted of precast concreted segmental rings erected in the tail of the shield. The marine clay in Singapore has been studied, among others, by Tanaka et al.(2001). The clay typically has a plasticity index of 40 to 60, and the undrained shear strength (SU ) can be derived from: SU = 0.22 svo' where svo' is the current vertical effective stress. Figure 1 shows a summary of undrained strength/depth plots used for design on two sections of Singapore’s North East Line. The stability of a tunnel in clay can be assessed by comparing the stability number (N) of the tunnel with the stability number at total collapse (NTC). The stability number can be calculated from the equation: N = (?Z + q – Pt)/SU where: ? = the average unit weight of the ground above the springline of the tunnel Z = the depth to the springline of the tunnel from the ground surface q = the surcharge Pt = the support pressure within the tunnel The stability number at total collapse depends on the size, geometry and depth of the tunnel, and typically ranges between 5 and 9. Charts for assessing the number at total collapse are provided in Kimura and Mair (1981), based on the testing of model tunnels in a geotechnical centrifuge. For tunnels in the Singapore marine clay, the stability number of an unsupported tunnel would be over nine if the tunnel ois more than 8m deep. As a result, a support pressure

Jan 1, 2007

By J. D. Noll

Elemental carbon (EC) is used as a surrogate for regulating the exposure to diesel particulate matter (DPM) of underground metal/non-metal miners. EC was chosen as a surrogate because EC is selective to DPM and is a major component of DPM. Using EC as a surrogate also gives one the advantages of no sampling artifacts and being able to sample at all locations in the mine. Currently, EC represents DPM well in underground mines. Some control technologies have been shown to possibly alter the relationship between DPM and EC and characteristics of DPM. Therefore, future work will investigate the relationship between DPM and EC as new control technologies are implemented.

Jan 1, 2002

By J. D. Noll

Elemental carbon (EC) is used as a surrogate for regulating the exposure to diesel particulate matter (DPM) of underground metal/non-metal miners. EC was chosen as a surrogate because EC is selective to DPM and is a major component of DPM. Using EC as a surrogate also gives one the advantages of no sampling artifacts and being able to sample at all locations in the mine. Currently, EC represents DPM well in underground mines. Some control technologies have been shown to possibly alter the relationship between DPM and EC and characteristics of DPM. Therefore, future work will investigate the relationship between DPM and EC as new control technologies are implemented.

Jan 1, 2002

By R. G. Hudson, H. W. Paxton

The activities of iron and chromium in their binary system have been measured by the Knudsen orifice technique. The system is close to ideal at 1200- 1250 C with slight positive deviations. The effect of this on the liquidus and solidus is discussed and these are calculated for two limiting assumptions. The vapor pressure of pure iron, pure chromium, and one alloy is compared with that obtained by the Langmuir free-evaporation technique. The results agree, indicating a vaporization coefficient close to 1. HERE are no reported data on the thermody-A namic activity of iron and chromium in the solid portions of the phase diagram. It is generally assumed'.' that the liquid solutions of iron and chromium obey Raoult's law. Chen and Chipman" have inferred that the liquid solution obeys Raoult's law. The minimum' in the solidus-liquidus curves for the iron-chromium system shows that there are deviations from ideality in either the solid or liquid or both. Because of the importance of developing reliable techniques for obtaining activity data in alloy systems at high temperatures and of the data so obtained, an investigation of the activity of iron and chromium in the binary at 1200-1250 C was undertaken using the Knudsen cell. Experimental The apparatus and experimental procedures used in this investigation were described in a previous paper." The various materials used for the construction of the Knudsen cell are listed in Table I. The metal used for the determination of the vapor pressure of chromium was 99.9 pet pure, obtained from A. D. Mackay, Inc. The iron was obtained as electrolytic grade from Fisher Scientific Company. The Fe-Cr alloys used are shown in Table 11. The largest error and controlling factor in the accuracy in the experiments reported here are introduced because of temperature uncertainty, which is estimated to be ±3 deg C. This introduces an uncertainty of 26 pet in the measured pressure. Experimental Results and Calculations The vapor pressures of pure iron and pure chromium were calculated from the measurements by the Knudsen equation3 on the assumption that only Cr or Fe atoms were present in the gas phase. For metal vapors, at the high temperatures and low pressures involved in these measurements this should be a reasonable assumption. Whitman" corrections for the cells were made. The data and results of pressure calculations are presented in Table I, and are plotted in Fig. 1. In addition the heat of vaporization at the absolute zero, ?E°°, has been calculated for chromium. These calculations are summarized in Table 111. The data used in these calculations are as follows kelley13 (F° - E°°/T ) Speiser, et al H (F° - E°°/T ) 010 where F" — standard free energy at temperature T It was necessary to calculate the total pressure above the alloys from the total weight loss W of the cell during a run, because of the fact that all attempts to collect and analyze the chromium and iron vapor effusing from the cell in the apparatus available failed. The failure resulted from the re-

Jan 1, 1959

By N. Nehoroshev, P. Solozhenkin, N. Voyloshnikova, A. Pshennikov

"Molecular modeling of clusters of major bismuth minerals, Bi2S3, was carried out whereby molecular models of minerals and reagents clusters were created. Their HOMO and LUMO energy levels were calculated and using known modelling equations, the absolute hardness ?, eV and electronegativity were calculated. The charges of separate atoms of clusters and the change of properties of the minerals were determined which allowed predictions of the flotation properties of raw ores containing rare bismuth minerals. Modeled complexes containing the clusters of minerals and various collectors were constructed, consisting of atoms and bonds within clusters of minerals. Major physical and chemical parameters were determined for the complexes created, including the total and electronic energy. Based on the energy calculations, predictions of the collector efficiency were proposed. The efficiency of collector was established for various thiolic reagents, the compounds of phosphorus (III) and mixtures of reagents. Theoretical results were checked and confirmed against laboratory ore flotation tests. A gold-bismuth-magnetite ore type was studied where gold, bismuth and iron (magnetite) are of industrial interest. The ore contains 2.8 g/t Au, 1.0 g/t Ag, 0.26% Bi, 45% Fe and 1.25% As. Sulphide mineralization can be mainly found in the form of pyrrhotite, pyrite and arsenopyrite. Bismuth can be mainly found in the form of bismuthite and native bismuth. Gold is fine. A flow sheet for Zhelezny Kryazh ore treatment was proposed. This flow sheet consists of grinding to 95-98% -74 µm, sulfide flotation with two cleaner with xanthate addition, cyanidation of flotation concentrate and flotation tailings included treatment with with CaO (6 kg, 6 hours), cyanidation (8 hours) and CIL (8+24 hours). Saleable products are gold doré, bismuth and iron concentrate."

Jan 1, 2014