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By C. H. Benedict, H. C. Kenny

A 2000-ton ammonia leaching plant has been operated by the Calumet & Hecla Mining Co., at Lake Linden, Mich., continuousl~ since February, 1917, except from April, 1921, to April, 1922, during the period of depression following the European war. A description of this plant has been published elsewhere.1 The present article describes the operation of the plant since 1917, together with the changes in the process that have been found to be advisable. In spite of the fact that this plant and that of the Kennecott Copper Co. are the only ones operating on a large scale, much experimental work is being done on ammonia leaching, as applied to oxidized ores, and it is to aid these and other investigators that this detailed account is given. For the benefit of those unfamiliar with the original article, the following short abstract is given, as an introduction to a more detailed account of the process and the reasons for present practice. Rêsumê of Previous Article Leaching on a commercial scale began in July, 1916, and by Februsry, 1917, the plant of 2000 tons capacity was in commission. The ore treated is a conglomerate containing native copper and no sulfides or oxidized copper minerals. Before leaching, the ore is crushed by steam stamps and Hardinge pebble mills to pass a 28-mesh screen. Free copper is removed, by gravity concentration, on Woodbury jigs and Wilfley tables, and colloidal slime for oil flotation is removed by quadruplex Dorr classifiers. The leaching sand remaining contains about 2 per cent. + 28-mesh material and 15 per cent. — 200-mesh and carries from 8 to 14 lb. of copper per ton, depending on the grade of ore worked. The solvent employed in leaching is a water solution of ammonium carbonate,

Jan 1, 1924

By F. T. Havard

The present truce in litigation between Western smelting and ranching interests gives opportunity for a summary of the results achieved by metallurgists in condensing fume and de-acidifying furnace-gases. In the absence of complete records of past experiments, there ha's been a good deal of unliecessary duplication of attempts and failures. Yet, especially uilder the recent policy of our large corporations, looking to the economic recovery of the values of by- and waste products, . original and, in some cases, effective measures have been developed by American metallurgists. In the case of Bliss us. the Anaconda Copper Mining Co., the Montana Suprenle Court, recognizing the progressive efforts made to render the flue-gases innocuous, and the value to the community of the smelting company's operations, refused to hamper its work, and returned a verdict in favor of the defendant. In the trial, the experimental farms of the company ill the so-called "aff'ected region" were proved to be thriving perfectly, showing that immunity was guaranteed to vegetation and stock by tlle wide distribution of the sulyhurous acid gas in the dry air of Montana. Indeed, L. S. Austin has proved that by the time the fume is 4,000 ft, distant from the stack, the percentage of sulphurous acid has been diminished from 2.28 to 0.00045; and Angus Smith has shown that rain must contain 40 parts per million of free acid before vegetation is affected. The arsenic in the stack-gases is but a very small part of the original content of the ore, of which 80 per cent. and over is rejected in the coilcentrator and furnace waste-products or recovered in the flues, Nevertheless, neither the peace in Montana nor the armistice

Jan 1, 1911

By Z Chang, S A. Mrozek, S Windle

"An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation. It is important to understand skarn-porphyry transitions in order to use exposed skarns to look for associated and potentially larger porphyries. For such purposes, a good start is to understand the transition between porphyry and skarn in known deposits. In this contribution, we report the transition at Antamina, Peru, where skarns occur in and around a Miocene complex comprised of more than seven porphyritic intrusions. There are three types of skarn-porphyry relationships. The earliest intrusive phase, P1A, contains both endoskarn and porphyry-style quartz veins with secondary biotite halos. The porphyry quartz veins and endoskarns formed at the same time. Locally, the intrusion contains only endoskarn without porphyry quartz veins and is surrounded by exoskarns in carbonate wall rocks. In the third scenario, later porphyry (P2) intruding into P1A porphyry and skarns related to P1A contains abundant granular quartz veins and secondary biotite alteration but does not have significant endoskarn. The granular quartz veins also extend into earlier P1A skarns. The scarcity of endoskarn associated with P2 is related to the supply of Ca. The earliest P1A intrusion intruded into carbonates that supplied abundant Ca, therefore both endoskarns and exoskarns formed. In contrast, where the wall rocks of the later P2 intrusion are P1A or skarn related to P1A, there was little free Ca, therefore only porphyry-style quartz veins formed.CITATION:Chang, Z, Mrozek, S A, Meinert, L D and Windle, S, 2015. Skarn-porphyry transition – an example from the Antamina skarn, Peru, in Proceedings PACRIM 2015 Congress, pp 409–414 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Mar 18, 2015

By John T. Norton

In spite of the very general errlployment of nitride hardening, there is still considerable doubt as to the real nature of the mechanism involved. Experience has shown that the addition of small amounts of hardening elements to iron or steel results in a wide variety of desirable properties in a nitrided case. Perhaps the foremost of these elements is aluminum and in this investigation an attempt has been made to study the behavior of aluminum during the hardening process. It is believed that the establishment of a complete atomic picture of the metal at various stages of the process will indicate the relationships between the several kinds of atoms and their individual influences on the physical properties in a clear and direct fashion. A consideration of the problem suggests a surprising similarity between the mechanisms of nitride hardening and of age-hardening. It is now generally understood that age-hardening may take place by one of two distinct processes, the first involving the precipitation of a finely dispersed phase and the other being concerned with the modification of an existing phase. Following much the same line of reasoning, two theories of nitride hardening have been suggested. The first explanation, which has been generally discussed, particularly by Fry,' states in brief that the presence of aluminum causes the precipitation of aluminum nitride during nitriding and that this finely dispersed phase is the primary cause of hardening. The second explanation, which has not been published but which has been freely discussed by those interested in the problem, postulates the substitution of aluminum atoms for certain of the iron atoms in the several iron-nitrogen phases in the same manner that the substitutional iron-alurninurn solid solution is formed. The marked increase in hardness, as compared with the aluminum-free system, is attributed to the severe lattice distortion accompanying this replacement.

Jan 1, 1934

By S. Katz, M. E. Nicholson, J. J. Kelly, D. R. Curran

A series of wedges of 1020 steel (2 1/2 by 6 by 8 in.) were explosively loaded, as shown in Fig. 1. A slab of explosive on the surface of the steel wedge was initiated simultaneously along one edge, producing an essentially two-dimensional oblique shock in the metal. Pressure and density in the metal were measured as a function of distance from the explosive-metal interface by a method described elsewhere.' While for pressures below 130 .kbars the technique produces accurate results, for greater pressures the presence of two shock waves in the metalzy3 makes interpretation of the data uncertain. However, the location of the transition in pressure at 130 kbars can be readily identified from the data. The assumption of a single shock in the region above 130 kbars overestimates the pressure computed on a multiple-shock model. After firing, the wedges were sectioned, lapped, and etched with 2 pct Nital. A photograph of an etched specimen is shown in Fig. 2. The specimens were examined metallographically. The dark region, at the top of the specimen, was heavily banded, Fig. 3, while the lighter area was comparatively free from banding, Fig. 4, the boundary between the two regions being quite abrupt. The very light regions at an angle of about 45 deg to the explosive-metal interface show virtually no banding. The origin of these light regions, which are not Luder's bands, is not yet explained. The thickness of the heavily banded area was measured and compared with the pressure at the boundary between the heavily and lightly banded regions. The results of these measurements and calculations are given in Table I. For all shots, the pressure at the boundary is approximately the same

Jan 1, 1960

By R. F. Domagala

SOME of the results of a program designed to study the kinetics of transformation and related mechanical properties of prototype Zr-X binary alloys systematically are presented here. The object of this program was to provide a sound basis for a scientific approach to the realization of optimum properties in binary zirconium alloys. Alloys of Zr-Mo (eutectoid), Zr-Sn (peritectoid), and Zr-Ti (a and ß isomorphous) were prepared and studied. The data herein are confined to a presentation of the results of studying the eutectoid prototype alloys. The Zr-Mo phase diagram has been determined.&apos; A definitive metallographic study of isothermaily annealed samples prepared from high purity elements served to position a sluggish eutectoid reaction, ß?a + ZrMo2, at 780°C. The compositions of the phases involved in this reaction are: ß, 7.5 ±1 pct Mo; a, <0.18 pct Mo; and ZrMo2, 67.8 pct Mo. Inasmuch as a lower purity sponge zirconium was used in this work boundary placements were rein-vestigated with the less pure alloys. Materials and Procedures Hafnium-free sponge zirconium was used to prepare all ingots. The arc melted hardness of a small button of this zirconium was found to be Vpn 168. Chemical analyses conducted at Armour Research Foucdation are shown in Table I, High purity molybdenum sheet was used as the alloy addition. A typical analysis is shown in Table I. Several 200-g Zr-50 pct Mo alloys were made by arc melting. Crushed granules of this material were used to ensure inqot homogeneity Ailoy ingots were prepared by double melting techniques. First, three 5-lb ingots of each alloy composition were are melted in 2 nonconsumable electrode arc furnace. After melting. the ingots were ground to remove surface defects. A subse-

Jan 1, 1958

By R. F. Mehl, M. Gensamer

Creep investigators have made extensive studies to determine the interrelation of stress, temperature and the tensile creep rates of metals. It has been suggested that at small stresses the secondary or constant creep rates obey a simple viscous law. Building upon this suggestion, departure from pure viscosity as stress increases may be expressed mathematically as a consequence of reversibly altered viscosity or "flowability" in the same sense that temperature change reversibly alters viscosity. From the index to alteration of viscosity, a value for the energy of secondary creep may be derived having the magnitude of the free energy of vaporized metal. The suggestion is made that application of stress alters the energy of secondary creep. Strain energy is argued to be but a minor factor in the energetics of secondary creep. A deformation mechanism involving the large energy associated with secondary creep implies a sort of solid self-diffusion process. Evidence indicates that creep strain above the recrystallization temperature takes place by crystallographically directed self-diffusion at grain boundaries and points of crystal defects. A self-diffusion theory of secondary creep is proposed, embracing the principles of the Dushman-Langmuir theory of solid diffusion. An equation is suggested whereby the rate of tensile creep may be related directly to the physical and structural character of the solid metal. Basis of Investigation Much of the investigation that has been given to the creep characteristics of metals and alloys has been directed toward studying the dependence of creep rate upon stress. Great interest has centered upon the approximately uniform rate of flow that has been demonstrated for numerous metals and alloys. At temperatures above the strain-hardening ranges of materials, this uniform rate frequently is attained after a relatively short period of initial rapid flow, and the period during which it persists determines for most practical purposes the useful life of the

Jan 1, 1938

By Joseph Kelly, Christopher Kelsey

This revolutionary super-fine crusher has the unique capacity to generate fine and ultra-fine products from single stage reductions of coarse or fine mineral feeds. The crusher consists of a rotating compression chamber and an internal gyrating mandrel. The axis of rotation of the shell is displaced relative to the axis of the vertically mounted mandrel. The inner surface of the compression chamber is machined as double cone frustums at an angle equal to the displacement angle. Crusher feed is accelerated into a compacted particle bed, which lines the inside of the compression chamber. The depth of the compacted bed progressively increases until the mandrel is engaged. The mandrel is then free to rotate with the compression chamber. Continued feeding increases power draw and triggers the counter rotating mandrel gyration drive. The gyrating mandrel delivers multiple compressions at high pressure to the rotating particle bed. High concentrations of energy are harnessed within a small active volume over short retention times. The combination of extraordinarily high power intensity and extreme compressive force results in primary compressive fracture and induced secondary tensile failure. The axially displaced rotation of the compression chamber effectively distributes the breakage forces throughout the particle bed. This paper covers open circuit, pilot trials on magnetite, perlite, garnet, marble and a copper/pyrite concentrate. Particular emphasis is placed on the extraordinary results achieved with trials on zircon and highly refractory fly ash. The extreme duties were deliberately chosen to demonstrate the crusher’s application scope and potential to impact capital operating and maintenance costs as the technology matures. Super-fine crushing, once considered impracticable has the potential to offer compelling options for the generation of ultra-fine products.

Jan 1, 2014

By Arthur B. Cummins, Henry Mulryan

DIATOMITE is a hydrous or opaline form of silica, commonly known as diatomaceous earth, diatomaceous silica or kieselguhr. The term "infusorial earth" has lost its original meaning and today is incorrect in view of the distinctions between diatoms and infusoria. Various locality and variety names are obsolete but some retain local significance. Moler and Celite are trade names that have become associated with diatomite products from certain deposits in Denmark and near Lompoc, California. COMPOSITION Diatomite is essentially silica with some combined water (2 to 10 pct). Frequently it contains organic matter (from traces up to over 30 pct) and varying amounts of inorganic impurities such as sand, cryptocrystalline silica, clay, volcanic ash, calcium carbonate, magnesia and soluble salts. In the natural or crude state, diatomite contains from 10 to 65 pct or more of free water. Table I gives analyses of several diatomites from deposits of different types. PROPERTIES Pure varieties, either massive or stratified, are friable and porous, of low apparent density, and somewhat chalklike in appearance. Varieties containing organic matter vary from sedimentary oozes to peatlike materials. Impure varieties may be more or less claylike, sandy, calcareous or cherty. Compacted types approach porcellanite and silicified shales. COLOR-white, cream, gray, tan, brown, greenish to nearly black. HARDNES-light-weight varieties appear 1 to 1.5 because of porosity, but microscopic particles are 4.5 to 6.5. SPECIFIC GRAVITY-1.9 to 2.35. APPARENT DENSITY---dry block form, 20 to 40 lb per cu ft; dry powder, 5 to 16 lb per cu ft. CRYSTAL SYSTEM-generally amorphous (isotropic by X-ray diffraction) but frequently showing faint cristobalite pattern.67.68,70 MELTING POINT-1400° to 1650°C. STREAK-white. LUSTER

Jan 1, 1949

By Allan J. Clark, W. J. Sharwood

When the cyanide process came into general use, late in the nineteenth century, chlorination was quickly supplanted, but amalgamation yielded place more slowly, being still the major process at many plants, where it is followed by cyanidation of the tailings. The research work of the Denny brothers in South Africa&apos; was probably the most important contribution of its time to the metallurgy of gold. By grading analyses of mill products, they pointed to the necessity of fine grinding to accomplish maximum extraction by cyanide. The work here described is merely an extension of the Dennys&apos; method. Developing the fine-grinding principle, the steps of "crushing in solution" and of "all-sliming" were logical sequels, though both had been attempted early in the history of the cyanide process. Crushing in solution introduced certain complications in amalgamation; when "all-sliming " was adopted it was observed that the omission of amalgamation did not materially affect the total recovery. Thus the field of the older process has become much restricted, being at present confined to ores which, yielding freely to amalgamation, either are too low in grade to show an economic advantage in "all-sliming," or present chemical or other difficulties making the use of cyanide solution unadvisable during the crushing and preparation of the ore. South African ores are typical of the former class; Homestake ores are of both classes, but even in these instances the amalgamation work is being curtailed and greater burdens thrown on the cyanide plants. It is obvious that the time required for the dissolution of gold depends on the size of its particles. In an effort to determine the critical size, the following laboratory method was evolved. A standard amalgamation test2 had already been established, which involves the agitation of about 100 gm. of ore with 20 gm. of pure mercury, the latter then being separated and its gold contents determined. This method was applied directly to certain mill products with interesting results, a few of which may be noted here. The column "Free Gold" gives the value per ton thus amalgamated, as against the " Total Gold " determined by fire assay.

Jan 1, 1923

By C. A. Edwards

Following a brief introduction, an outline is given of the four main conditions in which gases may be associated with metals; namely, (1) adsorbed gases, (2) dissolved gases, (3) gases in chemical combination, (4) gases entrapped in blowholes or cavities. Adsorption is essentially a surface phenomenon and is regarded as the attachment of outside molecules or atoms to the exposed free valencies of the atoms comprising the surface layers. In many cases where adsorbed films of gas are formed this is accompanied by a process of diffusion of the gas into the metal itself. This is particularly true in respect to iron and hydrogen, and experiments have shown that there is no difference between the rate at which hydrogen diffuses through a single crystal of iron arid through the same material after it has been recrystal-lized into a mass of small crystals. This does not prevent a somewhat greater concentration of gas at the boundaries of adjacent crystals, nor does it mean that the effect of the gas will be the same at the boundaries as it is within the body of the crystals. Indeed, under certain conditions, iron is rendered very brittle at the crystal boundaries, as shown in experiments by Pfeil with samples of almost pure iron. Much work has been done by many investigators concerning the temperature and conditions under which dissolved hydrogen, in particular, can be at least partially removed from different metals. With iron, the hydrogen that has diffused into the metal as a result of acid attack by pickling or by electrolytic deposition of the gas on the metal is partly removed by exposing the metal to the atmosphere at ordinary temperatures. Considerably more can be eliminated by raising the temperature, and even greater quantities by jointly raising the temperature and reducing the pressure. Annealing at suitable temperatures completely removes the bad effects of excessive mounts of hydrogen dissolved in or associated with iron. This is shown by the data plotted in Fig. 1, giving values for electrolytic iron sheets after annealing at temperatures between 250" and 950" C. The hydrogen brittleness is rapidly diminished at

Jan 1, 1935

By S. H. Davis

THE pyrites used in making sulfuric acid in the United States have been largely imported from Spain and Canada, the Spanish imports amounting to nearly 1,000,000 tons per annum in the pre-war period. The greatly increased use of sulfuric acid and the cutting off of these Spanish imports, incident to war conditions, brought about a threatened shortage of sulfur supplies during the war period. The bituminous-coal mines of certain districts have, for many years, furnished a small tonnage of pyrite in the form of coal brasses. A mechanical concentrator at Danville, Ill., for a number of years, has been treating hand-picked lump pyrite and coal from the picking belt and from the mines and a small plant near Gillespie, Ill., for a few months has been recovering pyrite from washery refuse. Many mines throughout Illinois, Indiana, Western Kentucky, Ohio, and Pennsylvania have shipped an occasional car of the hand-cleaned lump pyrite. Only a very small percentage of the available pyrite has been recovered in this way, however, as usually the miners throw such lumps into the gob with slate and other impurities. It has been estimated that the western Indiana coal field could furnish more than 100,000 tons of pyrite per annum. The present production is very small. The possibility of furnishing the domestic trade with pyrites recovered as a byproduct from coal-mining operations appears attractive but there are certain features difficult to overcome. Pyrite, to be used in acid making, must meet with certain requirements as to size and purity. Lump ore for grate burners should be under 3 in. (7.6 cm.) and over 1 in. (2.5 cm.) in diameter. Fines for use in mecnanical roasters should be under quarter mesh. The material should be high in sulfur, free from arsenic and phosphorus, and as low in carbon as possible. The pyrite obtained from coal can be made to meet all the above requirements, but it is difficult to remove all the carbon. The pyrite in coal occurs as bands and nodules of varying thickness and size and of comparative purity, but mixed with this is more or less web sulfur. The web sulfur carries with it admixed coal, which may make the concen-

Jan 8, 1919

By Vladimir Grujic, Milorad Grujic, Ivan Djurkovic, William Riggs

"In this paper, we have studied efficiency of different chemical structures of frothers on copper ore Majdanpek. The goal was to find out the best suitable chemical structure, which allows good bubble formation, size and interaction, forces on mineral surface. The particle size distribution was between 10 and 100 µm. Our research was oriented on three groups of frothers: alcohols, poly glycol ethers and poly glycols.We also used different collectors based on similar or less similar alcohol group in chemical structure as in frothers, expecting higher stability of air bubble in contact with copper minerals. Minimal potential energy was determinate in the hydrodynamic conditions for different particle sizes. It was founded that it is proportional to air bubble volume on 0.88° and contra proportional to the kinematics viscosity of pulp.Analyzing the results, we find out that poly glycols decreased surface tension the most. Also, it increased amount of coarser particles to the top of pulp. This group is less sensitive to pH value compared to the others too.From the class of frothers with higher efficiency in flotation process, we pointed OrePrep X-75 and X-133 as frothers with expressive frothing characteristic in the alkaline and low alkaline circuits. Special suitability of those frothers for floating copper minerals makes their hetero polar molecules with more than one hydrocarbon radicals connected to one polar group. However, those froters have no nether high or low solubility and are non-ionization. Those froters indicate some small collecting characteristics too. In dispersion systems, those two frothers make two types of bubbles: smaller di < 1.2 mm; V = 0.0008 cm3 and middle di < 16 mm; V = 2.2 cm3 (di – Bubble diameter, V – Bubble volume). Transportation speed of air bubbles it is possible to calculate based on equation: ?s = 27.5 * di 1.4 cm/s. Distribution of free surfaces for chalcopyrite is average 80% in the class –74µm +10µm and 20% in the class -10µm. If we get all class sizes, we find that recovery (R) depends from the time by equation:"

Jan 1, 2003

By R. J. Davidson, B. Strong

The piloting and eventual large-scale operation of fixed-bed carbon columns for the recovery of gold from plant effluents is described. A fixed-bed carbon pilot plant comprising three adsorption columns was used for the recovery of gold from clarified plant effluent at the Vaal Reefs Exploration and Mining Company (West Division). The effluent ,which contained 0,1 toO,S g/t of gold and less than 10 g/t of free cyanide, was adjusted to pH 8 prior to use. Daily acid treatment of the carbon circuit with 3 per cent hydrochloric acid was shown to have a most significant effect on increasing the gold adsorption. The acid treatment involved a plant downtime of only I to 2 minutes per day. High loadings of gold (up to 30 k g/t) and copper (up to 75 k g/t) were obtained on the leading column, while the gold recoveries averaged 98 per cent over 17 weeks of continuous operation. The subsequent elution of loaded carbon in a pilot elution column indicated the use of abnormally high amounts of the pretreatment reagent (caustic soda and cyanide) used in gold elution. This was attributed to the high loading of copper on the carbon. However, the elution of both the gold and the copper at 110°C with demineralized water as the eluant was satisfactory. In a similar large-scale operation, three fixed-bed carbon columns each containing 4,5 t of carbon were used to treat 80 to 120 t/h of plant effluent with a gold concentration of about 0,15 g/t. Gold loadings of 5 to 6 k g/t were obtained regularly, while the gold recovery averaged 97 per cent over a 12-month period. The capital cost of the plant was recovered in 2 to 3 months. The evidence presented strongly suggests that copper plays a significant role in the adsorption and elution of gold under the prescribed conditions, and in the subsequent precipitation of gold following acidification of the eluates. The formation of a highly insoluble gold-copper complex produced under acid conditions appears to explain many of the observations made in the investigation.

Jan 1, 1983

By D A. Shushkov

Analcime-bearing rocks are one of the varieties of raw zeolite material, although the characteristics of analcime are not as good as other kinds of zeolites such as clinoptilolite or mordenite. However, some fields of application of analcime-bearing rock have been found, eg a method of water purification has been developed and patented. Analcime-bearing rocks are rather widespread in the Timan region of the Komi Republic of the Russian Federation. They are represented by Upper Permian siltstones and mudstones. The analcime-bearing rocks have the following mineral composition (per cent): clay minerals (50 - 70 per cent), quartz (ten to 30 per cent), analcime (one to 30 per cent), feldspars (two to ten per cent), carbonates (two to five per cent) and pyroclastic material. Analcime aggregates encrust cavities and infill microfissures in rock. Both microcrystalline (crystals &lt;0.01 mm in size) and medium-crystalline (~0.5 mm) aggregates are observed. The mechanical, gravitational, magnetic, sorption and ion-exchange properties of analcime-bearing rocks have been studied. They are characterised by a high index of grindability and a low index of abradability and crush resistance, low values of the benzol-based pore volume and toluene-based specific surface area, and a medium porosity value. The magnesium based ion-exchange capacity (IEC) ranges from 28.7 to 196 mg+equiv/100 g. Analcime-bearing rocks of the Timan region are characterised by low beneficiation potential. Preliminary ultrasonic treatment of the analcime- bearing rocks is efficient for the destruction of intergrowths along their boundaries and production of free analcime aggregates. The proposed beneficiation procedure yields 95 per cent analcime concentrate. In the Komi Republic, analcime-bearing rocks are utilised in agriculture. They are also used for domestic needs (eg as biotoilets for domestic animals) and the solution of ecological problems (regeneration of soil polluted by oil). We have completed experiments on the purification of potable and industrial water using analcime-bearing rock subjected to thermal treatment. The experiments demonstrated that it was possible to decrease water colouration by 20 per cent, turbidity by 79 per cent, permanganate oxidation by 30 per cent and total iron content by 70 per cent.

Jan 1, 2008

By Allan J. Clark, W. J. Sharwood

When the cyanide process came into general use, late in the nineteenth century, chlorination was quickly supplanted, but amalgamation yielded place more slowly, being still the major process at many plants, where it is followed by cyanidation of the tailings. The research work of the Denny brothers in South Africa&apos; was probably the most important contribution of its time to the metallurgy of gold. By grading analyses of mill products, they pointed to the necessity of fine grinding to accomplish maximum extraction by cyanide. The work here described is merely an extension of the Dennys&apos; method. Developing the fine-grinding principle, the steps of "crushing in solution" and of "all-sliming" were logical sequels, though both had been attempted early in the history of the cyanide process. Crushing in solution introduced certain complications in amalgamation; when "all-sliming " was adopted it was observed that the omission of amalgamation did not materially affect the total recovery. Thus the field of the older process has become much restricted, being at present confined to ores which, yielding freely to amalgamation, either are too low in grade to show an economic advantage in "all-sliming," or present chemical or other difficulties making the use of cyanide solution unadvisable during the crushing and preparation of the ore. South African ores are typical of the former class; Homestake ores are of both classes, but even in these instances the amalgamation work is being curtailed and greater burdens thrown on the cyanide plants. It is obvious that the time required for the dissolution of gold depends on the size of its particles. In an effort to determine the critical size, the following laboratory method was evolved. A standard amalgamation test2 had already been established, which involves the agitation of about 100 gm. of ore with 20 gm. of pure mercury, the latter then being separated and its gold contents determined. This method was applied directly to certain mill products with interesting results, a few of which may be noted here. The column "Free Gold" gives the value per ton thus amalgamated, as against the " Total Gold " determined by fire assay.

Jan 1, 1923

By C. A. Edwards

Following a brief introduction, an outline is given of the four main conditions in which gases may be associated with metals; namely, (1) adsorbed gases, (2) dissolved gases, (3) gases in chemical combination, (4) gases entrapped in blowholes or cavities. Adsorption is essentially a surface phenomenon and is regarded as the attachment of outside molecules or atoms to the exposed free valencies of the atoms comprising the surface layers. In many cases where adsorbed films of gas are formed this is accompanied by a process of diffusion of the gas into the metal itself. This is particularly true in respect to iron and hydrogen, and experiments have shown that there is no difference between the rate at which hydrogen diffuses through a single crystal of iron arid through the same material after it has been recrystal-lized into a mass of small crystals. This does not prevent a somewhat greater concentration of gas at the boundaries of adjacent crystals, nor does it mean that the effect of the gas will be the same at the boundaries as it is within the body of the crystals. Indeed, under certain conditions, iron is rendered very brittle at the crystal boundaries, as shown in experiments by Pfeil with samples of almost pure iron. Much work has been done by many investigators concerning the temperature and conditions under which dissolved hydrogen, in particular, can be at least partially removed from different metals. With iron, the hydrogen that has diffused into the metal as a result of acid attack by pickling or by electrolytic deposition of the gas on the metal is partly removed by exposing the metal to the atmosphere at ordinary temperatures. Considerably more can be eliminated by raising the temperature, and even greater quantities by jointly raising the temperature and reducing the pressure. Annealing at suitable temperatures completely removes the bad effects of excessive mounts of hydrogen dissolved in or associated with iron. This is shown by the data plotted in Fig. 1, giving values for electrolytic iron sheets after annealing at temperatures between 250" and 950" C. The hydrogen brittleness is rapidly diminished at

Jan 1, 1935

By Paul C. Schmall, Arthur B. Corwin, Hugh S. Lacy, Derek Maishman

For reasons of hydraulic design and constructability, water supply tunnel systems are often located relatively deep, in competent rock. Where the rock lies below a thick cover of water bearing soils, artificial ground freezing offers a low risk, cost-effective method of constructing access shafts. Several examples, in Kansas City, MO and in Brooklyn and Queens, NY, illustrate the use of freezing to provide structural support and ground water exclusion. In the case histories presented, the shafts range from 6m to 12m (20 to 40 ft) in diameter and soils vary from clays to boulder beds with depths in excess of 73m (240 ft) to competent bedrock. Where tunnels for infrastructure are designed to be driven in rock, vertical access may encounter a considerable thickness of overburden soils with groundwater. In such cases, shaft sinking problems are analogous to those confronted by mining engineers over 100 years ago. At that time, newly developed refrigeration machines were set to freeze the ground water and stabilize running sands. Although modern technology has refined our efforts, the basic features of the ground freezing to be described here are the same as those used in the last century. Vertical holes drilled on a circle surrounding the shaft site are equipped with leak-free steelpipes through which a refrigerated brine is circulated. In this manner, a frozen cylinder, seated in rock, is formed when the earth freezes between adjacent pipes. Shaft excavations take place inside a self-supporting, ground-water excluding structure. For mines, no better method of sinking production shafts through deepwater-bearing ground has yet been established. Indeed, major deposits of coal, potash, and salt would have remained inaccessible to this day were it not for the continued use of artificial ground freezing. If mine shaft freezing became relatively commonplace, early applications to civil engineering were few. Mussche and Waddington (1946) mention only five projects between 1892 and 1935; three of these relate to subway or vehicular tunnels in Paris, Antwerp, and (the most extensive) at five locations of the Moscow Metropolitan Railway development. In the United States, the method was used to spectacular effect in 1936, freezing about 3,000 cubic yards of silt to stop a slide

Jan 1, 1999

By J. M. Ohm, C. M. Bunker

Two special tools for recovering gamma-ray probes and logging cable from drillholes have been designed by Ohm and Bunker and constructed by Ohm. Though intended specifically for U. S. Geological Survey equipment, they may be used with other equipment of the same general type. Fishing Tool for Probes: A fishing tool of the overshot type (Fig. 1) was designed to retrieve logging probes (sondes) that become disconnected from the logging cable and are trapped in the drillhole. When the tool slides over the top of the gamma-ray probe, studs on the bottom engage the shoulder near the top of the probe (Fig. 2), which is then pulled to surface. The barrel can be constructed from brass or steel tubing. Wall thickness is not a critical dimension, but the tool should be heavy enough to sink through mud or water in the drillhole. The internal length of the tool must be enough to prevent interference with the upper end of the probe head as the tool slides over it. The design of the probe head used by the USGS required a minimum free space of 2 1/2 in. inside the fishing tool, which was made 7 1/2 in. long to increase the weight. The lower end, which engages the shoulder of the upper end of the probe, contains three studs placed at 120" around the circumference of the tool and held in the engaging position by the tension of a spring wire. The studs can be made of any metal, such as steel, having high tensile strength. As the tool slides over the probe the studs are pushed outward from the center against the spring tension, allowing the tool to slide into position below the shoulder of the probe head. The spring tension forces the studs inward into the engaged position after they pass the shoulder. When the tool is raised the studs stop against the shoulder, preventing the tool from sliding up over the top of the probe. Once it engages the shoulder of the probe it cannot be freed until both probe and fishing equipment are recovered from the drillhole.

Jan 1, 1960

F. JOHNSON,* Birmingham, England (written discussion t).--. Mr. Skowronski&apos;s first melting experiments tend to show that ingots with a "level set" may be obtained without oxygen. Now it is characteristic of all metals which occupy a smaller volume when solid than they do when molten to "pipe." In vertical-cast ingots, this pipe resembles a horn-shaped cavity, with the wide mouth uppermost. In horizontal-cast ingots, the pipe is a longitudinal furrow along the center-line of the ingot surface. If copper be successfully deoxidized and degasified, this furrow will inevitably be produced. In the author&apos;s oxygen-free ingots, it is. clear that gases were occluded and these gases effectively opposed the formation of a pipe or furrow by shrinkage (fluid contraction). It is riot a special property of any particular gas which produces this effect. Hence it is not surprising that the author has succeeded in producing level and overpoled ingots through the agency of sulphur. dioxide gas. That he has counteracted the overpoling influence of sulphur by means of oxygen is somewhat difficult to explain, since the well known reaction between cuprous sulphide and cuprous oxide should result in the production of sulphur dioxide gas. Why the presence of excess cuprous oxide should neutralize the overpoling influence of this gas without eliminating sulphur is not at all clear. It is to be regretted that the oxygen was not determined in the bars given in Tables 3 and 4. It is by no means established that sulphur is responsible for the over, poling of ingots given in Table 4, since carbon was used for overpoling. If, however, the same kind of poling treatment was given as that applied in the case of ingots in Table 1, the responsibility of sulphur assumes more definite shape. The author rightly points out that Mr. Johnson&apos;s theory of the equilibrium between gases and cuprous oxide does not explain why a simple addition of cuprous oxide does not correct an overpoled charge. Such a charge must be re-worked to "set" copper. This re-working (rabbling) undoubtedly forcibly removes the excess gases, which are not removable by cuprous oxide.

Jan 11, 1918