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By John C. Calhoun, Raymond G. Loper

Theoretical calculations for the decline of pressure and the variation of instantaneous producing gas-oil ratio with increased cumulative production have been made for reservoir systems under various producing drawdown values and for various spacings. These variables have been included by a modification of previously Published techniques. This consists essentially of utilizing a radial system flowing gas and oil in a succession of steady state calculations. The results of the calculations do not show any variation in the predicted behavior of the internal gas drive reservoir when either the drawdown or the spacing are changed. The prediction of performance on an internal gas drive reservoir has been presented by various authors. ',"' These predictions are in the form of a pressure decline and an instantaneous producing gas-oil ratio as a function of cumulative oil withdrawal. In making these predictions a basic assumption has been that the saturation of the reservoir is uniform throughout at any time, or that the pressure differential imposed on the reservoir system is zero. Because of these assumptions the validity of such predictions has been questioned. Their application to actual systems, where saturations are not uniform and where producing differentials exist, has been a hazardous procedure. The authors cited have used different methods of approach to the derivation of equations for making their predictions and for arriving at a solution of both equations, but basically the same relationships are utilized in each case. In all instances the instantaneous producing gas-oil ratio is calculated from the equation: In utilizing this equation an average reservoir pressure and an average reservoir saturation must be known, the former to define ß, v, s, and uo/ug and the latter to define kg/ko. Predictions can be made, therefore, only for the conditions of a uniform reservoir saturation and a uniform reservoir pressure. This restriction of requiring a uniform oil saturation can be resolved by applying two-phase steady state flow for the radial system to the reservoir's history. Radial steady state flow is defined when the ratio of phases flowing,

Jan 1, 1949

By S. E. Craig

Jen Inc., operator of the Cord mine, in the Big Indian district of San Juan County, Utah, has a contract with a milling company that provides a small bonus for proper grading and preparation of uranium ores shipped. To obtain maximum returns on this contract very close grading is required with settlements made on individual lots, which vary from 250 to 300 tons. Another feature of the contract, and one that is rather unique in this country, is that the ore is sold over truck scales at the mine. Grade is determined at the buyer's sample plant. It is necessary to take a moisture sample of each truckload shipped for ac- curate weighing and this is done by the representative of the buyer, using facilities supplied by Jen Inc. The sample is hardly more than a grab sample and includes only the finer and smaller pieces of the ore shipped.

Jan 10, 1958

By H. S. Cannon, F. N. Rhines

The application of a static load to a copper powder compact during sintering at an elevated temperature accelerates the rate of sintering in such a way that a given load induces the same proportional increase in rate for all times of sintering. It is shown that sintering under a load is like creep under a fixed load in that the stress required to accomplish a given degree of densification is proportional to the logarithm of the sintering time. VIRTUALLY all of the theories of sintering that have been put forward within recent years have contained the assumption that the chief driving force of the process is the surface tension resident in the exposed surfaces and internal pores of the compact, or powder mass. An externally applied load might be expected to provide a somewhat equivalent driving force for sintering. It is known that the application of a compressive load, during sintering, hastens densification, but it is by no means clear whether sintering under the influence of surface tension alone and sintering under an applied load are fundamentally similar processes. The present study was undertaken in an effort to obtain an answer to this question and with the hope that the answer may contribute to an understanding of the mechanism of sintering. It has been found that there is a close relationship between sintering and creep processes. Copper powder compacts were sintered in hydrogen at 1000 °C under dead loads of 0 to 165 psi and the progress of sintering was observed by means of density measurements. Using a commercial reduced oxide copper powder, see Table I, cylindrical compacts Yz in. x x in. high were made at a pressure of 12,500 psi. For sintering, these were placed in a cylindrical graphite container into which they fitted snugly. A compressive axial load was applied to the compact through a graphite rod of similar diameter, which rested upon the upper end face of the compact; iron weights, in suitable amount, were placed upon the graphite rod to provide the load. This assembly was encased in a vertical silica tube within a resistance-type furnace capable of maintaining a substantially constant temperature within the working zone. After various predetermined times at temperature, the samples were removed from the furnace and their density was measured by conventional means. The heating-up and cooling-down times have been included in the computed sintering time, using the assumption that the sintering rate doubles for each increase of 10 °C in temperature. The experimental results are presented in Table 11. Upon metallographic examination of the specimens, it was found that there was no apparent change in the shape of the pores as a result of loading, i.e, no flattening, Fig. 1. Substantial contraction away from the container walls was observed in all samples sintered with loads of 10.5 psi and less.

Jan 1, 1952

By C. M. St. John

INTRODUCTION The stress redistribution accompanying the excavation of a deep tunnel may induce failure of the rock. The role of the support system is to control the extent of the failed region and hence to limit closure of the tunnel within an allowable amount. In such circumstances, the design of the support system is generally based on the Ground Reaction Curve (GRC). The GRC is the relationship between the support pressure and the induced displacement at the tunnel wall for a circular tunnel under hydrostatic loading. In the calculation of the GRC (see Brown et al. (1983) for an exhaustive list of reference), the rock is generally treated as an elastoplastic material characterized by cohesive-frictional yield strength and by dilatancy during plastic deformation. A recent analytical development (Detournay, 1983) has allowed the generalization of the GRC concept for some cases of non-hydrostatic in-situ stress fields (Detournay and Fairhurst, 1982). As an application of that development, this paper describes design charts that provide powerful means of performing parametric analysis for tunnels subject to non-hydrostatic loading. BACKGROUND The in-situ stress in a plane perpendicular to the tunnel axis can be decomposed into mean and deviatoric components, Po and So (see Fig. 1). Since it is assumed that the rock is characterized by a Mohr-Coulomb yield strength, the deviatoric invariant So must be less than the limiting value Sl0 given by

Jan 1, 1984

By William K. Callaway

Cominco American has operated the Magmont Mine for 16 years as a traditional open stope room and pillar mine. Diminishing ore reserves and the discovery of high grade ore zones over 90' in thickness caused consideration to be given to hydraulic sandfilling as a method of ground support to increase pillar extraction and mine life. This paper will review the results of sandfill testing. Plans for underground experiments, and operational plans for the future will also be discussed.

Jan 1, 1984

By Robert E. Delavault, Harry V. Warren

Geochemistry in all its branches is playing G an increasingly important part in the business of mine finding. Although geochemical studies were commenced more than 50 years ago, interest in this subject did not become widespread until the late 1930's when in Scandinavia and the U.S.S.R. a whole series of investigations were initiated. Unfortunately for those in North America, the results of these investigations have only recently become available. In Canada and the U.S. geochemistry as a serious mine finding tool dates back only to the period following World War II. This article deals primarily with soils, which have found widespread acceptance as a useful tool in geochemical prospecting. Actually soils vary greatly in texture, structure, profile, and mineral background. Soil sampling poses no hardship for normal intellects, but it does assume an elementary knowledge of soil science and of the chemical problems involved in determining the absolute and relative amounts of a particular element in any particular soil.

Oct 1, 1956

VITRIOL is likewise a mineral substance from whose exhalation, according to the opinion of some, are generated and produced the elemental materials or substances which produce metals, particularly gold. It is not a fumosity from metal nor is it a thing from which metal is extracted in any manner, although it shows in certain ways that it is not entirely without metal since it produces a certain trace of it. It is a thing that has a great resemblance to alum; it has a biting substance, is sharp to the taste and pungent to the tongue, and has an astringent nature. It dissolves in water and every damp place in a short time. They say that the reason for this lies, as with every other mineral, in its poorly joined watery substances. Nor does this mean that it does not contain much earthiness; on the contrary it seems to me that there are in it five. [2.9v] different participating qualities, that is, the property of sulphur, the action of alum, the corrosion of niter or of salt, and from the metals, the properties of copper and of iron. Its ore is mined in the valleys of mountains in wild but not too rugged places. It is more a gray earth or soft dead rock than a hard stone. It always has in it some yellow and green spots or near it is some sulphur mineral, either large or small.. When it is beneath the earth it exhales a sharp and very strong foul odor of scorching similar to that of sulphur. And the waters that rise where it is are all foul, earthy, and thick, some boiling with great fumes and others without great fumes, so that they surely appear to be infernal products in many places where there is a large quantity of it. After you have excavated and sorted well the quantity you wish, the ore must be put in a heap in open airy places before the vitriol can be extracted from this soil or ore, however you wish to call it. And it is left thus exposed to the weathering of the rains, the cold, and the sun for five or six months. It must be turned several times in order to bring to the surface that which was underneath; and always when this is done it is broken small with the eye of a mattock so that it is better heated and baked throughout. When it has been brought to this point it is covered over by a shed built above it or it is carried under a hut that has already been made. Here it is left to stand for another six or eight months before it is worked.

Jan 1, 1942

By A. L. Labbe

IT Is well known that the Cottrell process is more easily applied to certain kinds of smoke than to others. The successful Cottrell installations are those treating smokes that carry dust of a mechanical nature; also smoke carrying fume dust that contains an excess of sulfuric acid over that required to combine with the oxides in the dust. But up to the present time the process has not reached a satisfactory economical basis of operation, in the treatment of smoke' containing basic dust. It is not impossible to make a smoke containing basic dust suitable for the process by. humidifying or acidifying. A number of Cottrell plants use these two methods of conditioning smoke previous to Cottrell treatment, which are quite successful, but the use of either results in expensive operation and a substantial loss in metals.. For these reasons, I would say that the baghouse process has not been replaced by the Cottrell process in the treatment of smelter basic smoke. Basic smoke must be given a. preliminary conditioning treatment because the dust is not a conductor of electricity; the water or acid treatment imparts some conductivity to the dust.. The rate at which dust is recovered depends on the proportional amount of power transmitted to the, treater and on the rate at which the smoke passes through; therefore to maintain a maximum constant amount of power across the electrodes of the treater, the same degree of conductivity should prevail, at all times between the surface of the electrodes. For all practical purposes, in the application of this process to lead and copper-smelter smoke, we can consider that the conductivity of the gases is a .constant. The variations in temperature of the smoke have a much greater effect on the solids than on the gases; the only instance where the temperature of the gases plays an important part in the process is at plants using humidifying: The temperature does not affect the conductivity of mechanical dust because such dust has natural conductive properties. However, in the case of smoke carrying acid-fume dust, where the conductivity is imparted to the dust particles by coming into contact with the acid fumes, the temperature is of importance.

Jan 8, 1925

By Cadwallader Jr. Evans

THE Hudson Coal Co. is an anthracite concern with 22 mines, employing, when operating full, something around 18,000 men. We have, there-fore, necessity for a large number of subordinate officials and for a considerable number of major officials, and we carry on two separate courses of training in our endeavor to develop these two groups. The one in which college professors will be most interested is that which we call our two-year course. A man to be eligible for it must have completed a college course at one of several institutions from which we regularly seek our men, but he need not necessarily be a graduate of the course in mining, although we have been giving prefer-ence to graduates of schools of mines. Each year we take a number of men from these col-leges, sometimes five, six or seven, and put them through this two-year course, which is carefully. laid out so as to give them experience in the various details of our business. A schedule of the typical two-year course laid out for a man who started in July, 1925 shows that he was employed in the mining engineering department first for a period of four months, then for six months in inside mine work, three months in the mechanical and electrical departments, two months in "preparation," which with us means the cleaning of our product for market, one month in the study of statistics, one month on transportation and safety, and seven months in loading coal at the face, working with a shovel, making twenty-four months in all. We started this training in 1915 and in the first year we gave six months in the mining engineering depart-ment. We have now cut that to four. We gave six months in inside mine work and have continued that. We gave four months in the mechanical department, which is now cut to three; five months in preparation, now cut to two; two months in statistics, now cut to one; one month on transportation and safety which re-mains, and we have added seven months in loading coal. This last class of work gives them experience with the miner at the mining face.

Jan 7, 1928

By Thomas T. Read

The fact that certain types of ore-deposits have attained their present condition through the action of descending surface waters was, perhaps, first clearly pointed out by Posepny.l The oxidizing effects of such waters were discussed by Pen-rose,2 and many papers dealing with this phase of the subject have subsequently appeared. That secondary enrichment of sulphide ores, however, might be produced by descending surface waters was not clearly understood until after the copper-bearing veins of the Butte district, Mont., had been carefully studied by the geologists of the U. S. Geological Survey, although De Launay3 had suggested that sulphides might be transported from point to point and re-deposited in the zone above the level of ground-water. As a result of the study of the Butte district, two papers by geologists engaged in the work appeared within a short interval. The first by Weed: dealing with the enrichment of veins by later metallic sulphides ; and the second by Emmons; treating of the secondary enrichment of ore-deposits in general. In the latter paper it was pointed out that a typical vein of sulphide ores which has been subjected to the action of descending surface-waters exhibits four zones,—an upper or surface-zone, in which the changes hare been mainly of removal, the products being typically oxides; a second zone of oxide enrichment, in which the less soluble metals brought from above have been precipitated as carbonates or oxides; a third zone of sulphide enrichment,

Jan 1, 1907

By W. L. Chu

It was observed that chromized coatings on low carbon steel could be embrittled by cooling slowly through the 475°C range. A higher chromium coating was more susceptible to embrittlement than a lower chromium coating. Coating structure and composition could be correlated with the chromizing process and prior carbon content of the steel. IT was recently observed that during the fabrication of rectangular tubings made with chromized thin gage 1010 steel, a high percentage of these parts were fractured readily in a brittle manner under the light impact-forming load employed. Ensuing investigation indicated the cause for such brittle failures to be the so-called 475°C embrittlement of the chromized coatings. The experimental work and results are briefly reported. Rectangular tube sections of normalized AISI C1010 steel, which had a cross-section of 0.5x1.5 in. and a wall thickness of 0.030 in., were chromized to yield coatings having several ranges of thickness, varying from 0.0005 to 0.002 in. Essentially, the chromizing process is similar to that described by Samuel and Lockington,' which consists of heating the parts in a sealed container at about 955°C for 4 hr in intimate contact with a chromizing mixture* samples in a hydraulic press, and the other employed a simple beam bending test of the flat sides of the tubing walls. Neither, however, was able to differentiate the relative brittleness of samples known to include both the brittle and tough types, since the impact-brittle samples were found to deform readily in a manner similar to the tough ones. Both the tough and brittle samples were studied by reflection microscopy. Observation showed that the microstructures of the steel cores were similar in content and distribution of inclusions as well as in the ferritic grain size. Results of Filar micrometer measurements showed that coating thicknesses+ of the brittle samples averaged 0.0007 in., whereas those of the tough samples averaged 0.0016 in. The micrographs of Fig. 2 illustrate the structural differences between coatings of both types of samples. By dissolving the steel cores in nitric acid, coatings of both the brittle and tough samples were isolated. Simple bending tests showed that coatings of the brittle samples cracked readily at about 90" bend, whereas those of the tough samples could be bent nearly 180° without cracking. The coatings as well as the steel cores were analyzed for carbon and

Jan 1, 1956

By Paul D. Merica

One of the most useful, and at the same time least commonly used, methods of thermal analysis for the determination of transformations in metals and alloys consists in the recording of the time intervals required for successive increments of temperature change during heating or cooling, the temperature of the furnace containing the specimen being altered at a uniform rate. The curve obtained by plotting these time intervals as a function of the mean temperature of the specimen durnig the interval is called the inverse-rate curve. It is probably due to the fact that no simple and convenient method has apparently been available for the measurement of the successive time intervals that this method has not been so generally used as, for example, the differential method, for which several types of automatic or semi-automatic apparatus have been designed. Whenever this method has been used, the intervals have usually been measured with the use of a chronograph; its operation as practised at the Bureau of Standards1 is as follows: The temperature of the specimen is measured by a thermocouple and a dial potentiometer. The operator sets the potentiometer at successive values of the electromotive force differing by equal increments, usually 0.02 millivolt, and records the exact instant on the chronograph, by pressing a contact key, at which the galvanometer coil passes through its null position. Two-second intervals are also recorded on the chronograph record, and the number of seconds elapsing between successive signals is afterward counted from the record and plotted as a function of the electromotive force or of the temperature. This is an admirable method and by it most minute thermal arrests may be detected, but it requires a good chronograph, which is generally difficult to obtain, and the time of one operator during the recording and, subsequently, to read the intervals from the record; the latter operation often takes from one to two hours. There is here suggested a simple, convenient, and, it is believed, equally accurate method of recording the successive time intervals, by which the

Jan 1, 1921

By J. B. Newsom

During July and August, 1931, the Bloomington Limestone Co., at Bloomington, Ind., ran a single wire saw on ledge No. 2 at Maple Hill quarry. The ledge was hard rock, much harder than the average Indiana limestone. It was opened at two ends for a depth of about 20 ft., leaving a 130-ft. section between. During the tests 21 cuts were made in this ledge, to an average depth of 10.42 ft., for a total effective cutting area of 28,445 sq. ft. The actual area sawed was about 20 per cent higher, as we did not level down in the center, preferring to cut deeper on the ends. The various cuts were carefully logged, and the results plotted. A study of these results is interesting, as it enables a forecast of probable future costs to be made, and also because it points out the limitations of wire saws, and the lines development should logically take. Some of the inferences to be drawn are discussed below. Best Length of Cut.—No trouble was due to length of cut, except that we could not easily level down a long cut, and it is probable that longer cuts, say up to 200 ft., can be made. Obviously, longer cuts will result in a higher sawing rate in square feet per hour if they do not cause stoppages. Working Higher Ledges.—The cuts averaged 10.42 ft. high by 130 ft. long. A study of several logs indicated that during only about 15 per cent of the cutting time was the saw cutting to its full efficiency; that is, during about 85 per cent of the time the saw was bedding in at the ends and not cutting well in the center, or the ends were below the floor line and only part of the wire was doing effective cutting. This does not mean that the wire was cutting to only 15 per cent of its capacity, but it means that during about 85 per cent of the time part of the cutting was being wasted. If higher ledges had been worked, the wire would have cut to its full efficiency a large part of the time, as it would have had a greater distance to saw after it had bedded in to the ledge before the ends went down below the floor level. The exact saving to be expected cannot be calculated, but it would be large if really high cuts were made.

Jan 1, 1932

By A. J. Weinig

THE Liberty Bell cyanide precipitate is unique in that it is apt to vary widely in composition in the course of very short, periods of time, and a method of refining and melting that would prove highly satisfactory at one cleanup would yield almost an hopeless "mess" it a second. Table I gives a general conception of the wide range in grade and composition of those raw precipitates. It is evident that no one standard flux could be expected to produce a high-grade bullion with such a widely variable precipitate, and that any method of treatment with acid requires most careful consideration. Refining by Acids Naturally, our first efforts to improve our precipitates were directed along the lines of acid treatment. Table II embodies the results of careful sampling and analysis of one cleanup at the time when wet refining reached its maximum development at this mill. We have now discarded all methods of wet refining, successfully replacing them by amore scientific method of flux calculation described herein, but it is believed that a general description of this wet refining is warranted as it throws some interesting side lights on acid refining in general.

Jan 3, 1916

By Thomas F. Downing

When examining a coal property it is customary for the engineer to take channel samples at several coal faces. In doing so the extraneous matter, or partings, which can be removed by hand, or mechanically, with the facilities at hand, or proposed, is rejected. Where there is doubt concerning a stratum it is usually rejected from the main sample but part is taken for separate analysis. The samples are forwarded to a chemist for proximate analyses and determination of British thermal units, and, sometimes, ash fusion. Consideration is given all available commercial analyses but frequently the owner presents only the favorable ones. From the results thus obtained a general evaluation is made, monies are loaned or expended, markets are determined, and realization is estimated. In many instances, such grades are not substantiated and it is time we looked deeper for a basis which will prove more practical. Institute committees are working hard on analytic and use classifications and much valuable information has already been assembled and distributed. However, no single grade can be applied to any particular bed or region. Much study has been given the Pittsburgh No. 8 seam, yet that bed is subject to material differences in a single section;i. e., some strata of a face may differ from others in structure and analysis, particularly in sulfur content. From some localities it yields a good carbonization fuel, while in others it is chemically unfit for such use. Traveling south to the Logan, W. Va., field we find the Cedar Grove (Island Creek) seam a hard, gray splint coal., In the same field, and not far distant, the same bed changes, both structurally and chemically, and consists of excellent gas coal. In Illinois the moisture content of a bed may vary greatly in different localities. We have seen mines in which part of the coal is excellent for special purpose use but is spoiled by the product from another part of the same mine. Many other illustrations could be given but these are sufficient to show that application of any grading of coal must be distinctly local. The actual designation of grade can be given only after detail study of the component parts of the seam, or seams, on the property under considera-

Jan 1, 1932

By Alexander Bowie

IN many places throughout the Western mountain plateau regions of the United States coal beds in place have been burned over very extensive, areas, the fire evidently originating on the nakedly exposed outcrop of the coal bed and gradually burning its way into the bed for considerable distances under very heavy cover. . The surface evidences of the burned-out coal beds are seen in the calcined and discolored rocks overlying the places of the outcrop. The greater the mass of the burned coal the higher the results of its combustion can be seen in the overlying strata. I have noted many instances of this condition in the States of South Dakota, Wyoming, Colorado, New Mexico, and Arizona. In the lignite fields of Dakota and Wyoming I noted stretches of level country many square miles in extent where the surface rocks were roasted and vitrified by the burning of a great bed of lignite lying nearly level and with a light cover; this is probably the most favorable natural condition for the burning out of a coal bed. The less the depth of the rock covering overlying the coal bed, the better the .chance for a continuous supply of air to the fire; but when the coal bed clips heavily into the ground, or even if level, if it, passes under a hill or mountain which gives the bed a heavy covering of strata, the fire has more chances of being extinguished from natural causes than in the first condition described. The distance which, a crop fire may extend into a coal field is very much influenced by the dip, the thickness of the coal bed, and the nature of the rock covering immediately overlying it.

Jan 2, 1914

By R. S. Dean

True careful work of Gross and Zimmerley1 has established the fact that the energy actually used in grinding is proportional to the new sur-face produced. This confirmation of Rittinger's law was made by crush-ing quartz in a frictionless drop-weight machine and determining the surface of the quartz by its rate of solution in hydrofluoric acid. The details of this procedure have been described adequately elsewhere and need not be repeated here. The resultant data furnish the only available basis for comparing accurately the efficiency of grinding machines. This method is so cumbersome experimentally that it has been little used. As an alternative all sorts of approximations have been proposed. The best of these is complete size analysis by sieving and elutria-tion. Such procedure is very lengthy and difficult to carry out accurately. Furthermore, any sizing method becomes very inaccurate for determining surface with very fine sizes where the ratio of surface to volume becomes very large. To avoid the lengthy and difficult technique of elutriation it has been proposed to estimate the size distribution below 200 mesh from various probability formulas. Such a procedure is at best an engi-neering approximation; at worst it is a mere guess. Some time ago Dr. V. H. Gottschalk2 found that the coercive forces of magnetite powders were directly proportional to the surface area, regard-less of size distribution. It was at once apparent that this furnished a method for determining grinding efficiency quickly and accurately. The only requirement was a single determination of the relation between the work input of the Gross-Zimmerley drop-weight machine and the coercive force of the resultant crushed magnetite.

Jan 1, 1936

By John K. Dienes

The permeability of sands and soils seems to be adequately de- scribed by Darcy's law, but the permeability of rocks is complicated by a number of factors related to the probability of crack intersections. During the last few years we have developed a statistical theory of fragmentation which has been successful in explaining the observed behavior of rocks. In this paper, a theory of permeability is developed which draws on the concepts employed in previous work. The permeability involves three factors, the average fluid flux per crack, the number of cracks per unit area, and the fraction of cracks that are not isolated. Probabilistic ideas are used in connection with the hydrodynamic theory of flow through a single crack to develop an integral expression for permeability. The result has the form of Darcy's law for anistropic media. Although the current work is motivated by the need to develop optimized oil-shale retorts, we believe that the theory can be applied to a variety of other problems.

Jan 1, 1982

B. S. Crocker (Screened Ore Used for Fine Grinding at Lake Shore Mines, P. 499) was born in Toronto, Ont. and attended Saint Andrews College and University of Toronto. He received a B.A. and M.A. degree. He was graduated with honors and received a fellowship in metallurgy. Mr. Crocker did post-graduate research at University of Toronto from 1933 to 1934. He was employed by Beattie Gold Mines in 1933. He did research in milling at Lake Shore Mines from 1934 to 1936 and from 1936 to 1940 was head of experiment laboratory. At the present time he is mill superintendent with Lake Shore Mines at Kirkland Lake, Ont., Canada. Grinding, cyanidation, flotation and roasting are of special interest to him. He is a member of AIME. Mr. Crocker has presented several papers before C.I.M.M. and also holds membership in this society as well as Professional Engineers of Ontario. Skiing, yacht racing and photography are his favorite hobbies.

Jan 1, 1952

By R. S. Shoemaker, F. W. McQuiston

The principle of cyanide recovery or regeneration of cyanide from solution, be it a weak wash or a foul solution, is by acidulation. All or part of the cyanogen is converted thereby into hydrogen cyanide which is fixed by an alkali (generally lime) and returned to the cyaniding system (the Mills- Crowe process). The solution is made acid by bringing it into contact with sulfur dioxide. The acidified solution is stripped in a packed tower by a counter flow stream of air in which the air and the solution are brought into intimate contact. The air leaving the tank charged with hydrogen cyanide is then passed to another tank in which it is mixed with an alkaline solution, the latter absorbing the HCN and leaving the accompanying air clean for reuse in removing more HCN from the acidified solutions. Of the recoverable cyanide, 9770 is usually recovered in a three-unit disperser tower system. When there is a considerable content of copper, the solution is made acid following standard procedure; however, the HCN is not removed until the copper is reduced by regeneration. Copper removal at this point may be as high as 90%. After reduction of the copper, the acidified solution then is contacted with a lime solution which brings down calcium sulfate as a second step. The silver, gold, and copper are recovered in the form of a precipitate which can be shipped to a smelter. At the Hudson Bay Mining and Smelting Company, Ltd., most of the precious metals have been recovered in the copper and lead concentrates, but it has been found profitable to submit the flotation tailings to a scavenger cyanide treatment for the recovery of exposed gold contained in pyrite rejected during flotation. Due to the fine particle size, maximum dissolution is achieved in a four-hour contact period. In the cyanidation plant, the thickened flotation tailing at 70% solids is given a four-hour agitation in weak calcium cyanide solution and filtered. Filter cake is repulped and discharged either to the tailing storage area or to the mine as backfill. Clarification, de-aeration and precipitation of pregnant solutions are carried out in a standard Merrill-Crowe unit. Typical analysis of precipitate is as follows: Au, 0.47%, Ag, 4. 88%; Cu, 46.0%; Zn, 13. 8%. Cyanicides in the form of copper minerals limit the reuse of barren solution. To recover the substantial quantities of cyanogen chemically combined with base metals in this solution, a cyanide regeneration plant is in operation. The barren solution is acidified with sulfuric acid in a spray tower where an upward current of air from a blower sweeps the liberated hydrocyanic acid gas to an adsorption unit where it meets a fine rain of lime suspended in plant solution with which it combines to form calcium cyanide. The lime--water solution carrying calcium cyanide is reused in the cyanide circuit. The return gases are drawn into the blower and back to the disperser tower thus

Jan 1, 1975