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By C. Scala, F. Bernstein

General expressions are derived relating the streaming potential to the electrochemical potential of a permeable junction separating two electrolytic solutions. By the methods of irreversible thermodynamics, these potentials are related to the flux of mobile species arising from differences in pressure and chemical composition. The flux is conveniently expressed as a transference number, the equivalents of a mobile species transferred through the junction per faraday of electricity. At constant pressure, the flux equation gives the electrochemical potential across the permeable junction. The streaming potential across the junction is obtained by imposing the condition of constant chemical composition. The familiar expression for the borehole SP is shown to be a particular solution of the general flux equation. The derived exprersions were verified in experiments with seven shale samples. Both the theory and experimental data provide additional proof of the presence and magniturle of the streaming potential in shales. INTRODUCTION In the interpretation of electric logs, there has been much concern over the correction to be made to the recorded SP for an electrokinetic or streaming potential originating from the difference in pressure between the mud column and the formation. It was long recognized by M. R. J. Wyllie that such an electrokinetic potential source mas in the mud cake opposite permeable sands.' More recently, M. Gondouin and C. Scala2 showed an additional but opposing electrokinetic source of potential to be in shale beds. Their work was supported by the very extensive and excellent work of Hill and Anderson.3 n the present contribution, the general relationships between the electrochemical potential and the corresponding streaming or electrokinetic potential are examined and clarified. A notable advance towards understanding the relation between the various sources of electrical potential in a borehole has been the application of the now common methods of irreversible thermodynamics to describe the passage of ions and water through charged electrolyte junctions such as in shales.' The advantages of these methods are twofold. Unlike classical thermodynamics, they can be applied to non-equilibrium sys- tems, i.e., systems in which flow takes place, provided the flow processes have reached a steady state. They also permit conventional thermodynamic properties to be related to the steady-state dynamic properties. These methods arc used here specifically to derive expressions relating the potential behavior of shales in terms of ion and water transport. Experimental verification of the expression for the shale streaming potential is given which in turn offers theoretical support to the existence of a streaming potential in shales.' Importantly, the relative contribution of transport parameters to the SP is clarified. The theoretical treatment is essentially that of Lori-mer, Boterenbrood and Hermans3 ut has been extended to derive the general expression for the SP.

Mining software systems have provided a basis for integration of resource, survey, and design functions. They can similarly provide a basis for incorporating ground conditions into the process.Exploration and mine geologists have a prime role to play in this process, extending their responsibilities further across the geological spectrum, into exploration of ground conditions, analyses of results, and assessments of their implications for mining. Ground conditions are as much a part of the geology of a prospect or mine as its mineralisation, and can have critical imnlicationa for mining.

Jan 1, 1993

The Namakwa Sands heavy mineral deposit is located along the West Coast of South Africa and the mine is a world class producer of high quality zircon, ilmenite and rutile concentrates from essentially unconsolidated marine and aeolian sands of Cainozoic age. The objective of this study was to characterize rutile with respect to distribution, grain size, textures, colour and mineral chemistry within the Namakwa Sands orebody with the aim to explain its overall poor recovery. A representative suite of heavy mineral concentrates from various sections of the orebody and stages in the recovery circuit has been investigated microscopically and by means of SEM-EDS and LA-ICP-MS. The rutile grain size distribution displays a wide range and is directly related to its variable chemistry and consequently density. In placer deposits such as Namakwa Sands, mineral sorting is a function of hydraulic equivalence, and high density grains are smaller than the lighter grains when deposited under similar conditions. Grain size is also a function of sediment maturity, and the highly mature red aeolians and (RAS) component of the deposit has a coarser grain size than the less mature orange feldspathic marine sands (OFS). The above primary characteristics of rutile are responsible for the loss of the coarse-grained fraction during screening and, given the empirically determined relationship that increased substitution elements reduce conductivity, also during electrostatic separation. Provenance studies using geothermometry have shown that the heavy mineral suite has been sourced mainly by the proximal medium-to high-grade Namaqualand Metamorphic Complex. The positive relationship between substitution elements and temperature of formation explains their high concentration in rutile of this deposit. The heterogeneity of rutile, produced by the combination of a high temperature primary source and the typical marine-aeolian placer genesis is deposit specific and unfortunately not conducive to high recovery levels in the current Namakwa Sands beneficiation circuit.

Jan 1, 2010

The Indonesian province of Papua is a remote jungle-clad region covering the western half of the mountainous island of New Guinea. Despite being relatively under-explored to this day,Papua is home to the greatest mineral success story of the 20th century. The Grasberg/Ertsberg minerals district atop the central dividing range contains the worldÆs largest reserve of both copper and gold (Freeport-McMoRan Copper and Gold, 2002). With large mines at Ok Tedi,Por gera and Lihir,and many well-delineated resources such as Frieda River,Wafi and Hidden Valley, neighbouring Papua New Guinea,the eastern half of New Guinea has enjoyed sustained exploration campaigns for gold and copper since the mid 1960s. The combined Grasberg and PNG exploration successes can be measured in terms of ounces of gold produced over the last decade versus available landmass,conf irming the island of New Guinea and surrounding islands as a world-class destination for gold explorers. Yet despite this obvious regional prospectivity and the profitability of the Grasberg operation, a sustained exploration effort in the Papua province in Indonesia has not been achieved. Periodic political constraints, poor infrastructure, high costs, operational challenges, social and environmental concerns and lack of immediate exploration success often impact exploration investment decisions. Accordingly a lesser number of mineral occurrences have been documented in Papua compared to those seen along tectonic strike in geologically similar Papua New Guinea.

Jan 1, 2004

By E. A. Gulbransen, W. S. Wysong

THE behavior of tungsten and its surface oxides in oxidizing and reducing atmospheres and in high vacua at elevated temperatures is a question of considerable technical importance. The use of tungsten as a metal or as an important component in alloys in high temperature oxidizing atmospheres has been limited because of the unprotective nature of its oxide film and the volatility of its oxide. This paper will present results of a microbalance study1,2 of the following problems: (I) the oxidation behavior in the temperature range of 25 to 550°C (2) the reduction with pure hydrogen of thin oxide films formed on tungsten, and (3) the volatility of thin oxide films on tungsten. Tungsten is an interesting metal to study for the following reasons: (1) although the oxide to metal volume ratio is greater than one, the oxide is not considered protective, (2) the metal readily oxidizes at temperatures from 300° to 550°C (3) the oxides W02 and WO3 are reduced at temperatures as low as 500°C. by hydrogen, and (4) the oxide W02 is volatile at temperatures from 800 to 1100°C. LITERATURE The oxidation of tungsten in its thin film range has not been studied critically. In the thick film range Dunn3 has made the only systematic study. He found the oxidation rate to obey the parabolic rate law in the temperature range of 700 to 900°C. The temperature variation of the oxidation rate constant was found to follow an exponential law of the Arrhenius type. An inflection was noticed in the temperature plot of the rate law constant at 850 to 900°C. This was attributed to a phase change in the oxides. Scheil4 has studied the oxidation rate at 500 and 700°C over long periods of time and found a linear rate law. This result was interpreted as evidence for the presence of a nonprotective film. Pilling and Bedworth5 analyses of the oxide volume to metal volume ratio would indicate that a compact protective film should form. McAdam and Geil6 have studied the oxidation of tungsten in the thin film range using the interference color method. A parabolic rate law was found. Their curves showed that tungsten oxidizes faster than nickel but more slowly than iron. The lattice structures found in the oxidation of tungsten surfaces have been studied by Hickman and Gulbransen.7 They have reported that W03 is the stable oxide in contact with the metallic substrate up to approximately 600°C while W02 forms first at 700°C. Hägg and Magneli8 have recently reported a study of the lattice structures observed in the tungsten oxides using the X-ray diffraction method. In addition to an a-phase W03 and a d-phase W02, they reported the existence of two new phases. A ß' phase, homogeneous between

Jan 1, 1947

Robertson Diasol have developed a spectral gamma-gamma tool fully able to withstand borehole conditions. Spectral data is digitally recorded across 256 channels depending on energy levels of the photoelectric effect. Data processing is being developed with the objective of calibrating channel amplitudes to mineral type which will lead to a direct log of selected mineral grade as a continuous trace with depth.

Jan 1, 1990

By R. S. Kinasevich, D. D. Crabtree, D. W. Fuerstenau, T. P. Meloy, A. L. Mular

This paper presents details of the concept that size reduction in comminution machines takes place by three mechanisms; namely impact, abrasion, and chipping grinding. Experimental evidence is presented to show that each of these comminution mechanisms produces particles of a characteristic size distribution. The actual product from a comminution device has been postulated to be the result of a composite of these three types of mechanisms. Composite curves are demonstrated for a material following the Gaudin-Schuhmann, Gaudin-Meloy, and Rosin-Rammler size distributions. About forty years ago, Gaudin1 showed that grinding may be considered a combination of impact and attrition. Since that time, major efforts have been devoted to studies, both experimental and theoretical, of impact and compression fracture, while attrition has been almost wholly neglected, at least quantitatively. A significant attempt to distinguish between attrition and impact grinding is the work of Tanaka2 in Japan. By means of an instrumented abrasion grinder and a drop weight device, he determined coefficients relating the increase in surface area of various materials to the energy expended by the two methods of comminution. He showed that physical properties of a material determine its response to attrition and impact grinding. By extending his ideas to ball milling, he concluded that to a large extent the basic comminution process in a ball mill is due to the impact of falling media. Because Tanaka used a mass of particles in his drop weight device, however, he did not obtain pure impact size reduction. The purpose of this paper is to define basic mechanisms of size reduction, to verify that each has a characteristic and meaningful distribution curve, and to show how a combination of these mechanisms results in a size distribution very like that produced by grinding mills. DEFINITION OF COMMINUTION MECHANISMS The product from a grinding device will be considered to be the sum of the contributions resulting from the action of three basic mechanisms of size reduction which operate in a ball and rod mill. These are impact grinding and two forms of attrition, namely abrasion grinding and chipping grinding. Each is defined below. Impact Grinding: If a straight line is obtained when the cumulative weight fraction finer than a given size is plotted on log-log paper as a function of that size, the slope of the line is defined as the distribution modulus. A number of investigators 3,4,5 have shown that impact fracture of single specimens of different composition and shape results in a distribution of daughter particles that exhibit a distribution modulus of unity. This has also been true for materials broken in slow compression. Moreover, under slow compression or impact fracture conditions, theoretical distribution equations6*' which approximate the Gaudin-Schuhmann distribution when the distribution modulus is close to unity agree reasonably well with the experimentally obtained products. If one now considers a comminution process where many impact or compression fracture events are taking place, then any rational summation of the individual events yields, in the finer size range, a Gaudin-Schuhmann distribution whose distribution modulus is also unity. If the size distribution of the product from a mill has a distribution modulus of unity, it is implied that particles are fractured in a manner which results in a comminution event having a distribution like that obtained for the breakage of single specimens. These impact events would occur when a particle is smashed between balls or between a ball and the mill liner. Attrition, on the other hand, is that form of grinding which cannot be called impact grinding, and comprises both abrasion and chipping grinding. Abrasion Grinding: Abrasion is a form of surface wear resulting when particles rub against each other or against balls or the mill liner of a tumbling mill, somewhat like a piece of wood being rubbed over a piece of sandpaper. The surface wears at a more or

Jan 1, 1964

By Marcus A. Grossmann

This paper offers for consideration certain somewhat radical modifications in the iron-carbon diagram, these modifications being the result of the presence of notable amounts of alloying elements. When only small amounts of alloys are present, the standard iron-carbon diagram (Fig. 1) can be used with but insignificant changes; when larger amounts of alloys are present, however, it assumes a distinctly altered appearance. No comment is offered for the present except to call attention to the delta area, A4BM, which represents a region of mixtures of austenite and delta iron, just as area A3SP represents mixtures of austenite and alpha iron. Absence of Carbon We may turn at once to the effect of the presence of alloys. It has been found that in the complete absence of carbon, the gamma change will sometimes disappear entirely when sufficient alloying element is

Jan 1, 1927

By D. J. McAdam

In 1917 Haighl presented evidence that under simultaneous corrosion and cyclic stress metals may fail at lower stresses than if the corrosion is prior to the cyclic stress. In 1926 the author, while investigating the cooling effect of water on the fatigue resistance of metals, found that under these conditions steel specimens fail at stresses far below the endurance limit.2 (By "endurance limit" is here meant the fatigue limit obtained with specimens as free as possible from stress concentration and corrosive influences.) This led to an investigation (at the Naval Engineering Experiment Station, Annapolis, Md.) of the influence of cyclic stress on corrosion. This investigation may be divided into three parts. The first part was a general survey of the conditions necessary to cause complete failure under corrosion and cyclic stress of relatively high frequency. The entire process by which metals fail under these conditions was called LLcorrosion-fatigue." Corrosion-fatigue limits" for a large number of metals were determined and the relationships of these limits to chemical composition, heat treatment and physical properties were established. The conclusion was reached that corrosion-fatigue is due to the accelerating influence of cyclic stress on corrosion. Results of this part of the investigation were presented in five papers.*-= The second part of the investigation was a preliminary study of the influence of cyclic stress on corrosion. Each experiment was conducted in two stages. The first was a corrosion stage in which the specimen was corroded under cyclic stress; the second was a fatigue stage, in which the previously corroded specimen was tested (without further corrosion) to determine its fatigue limit. The difference between this fatigue limit and the endurance limit was used as a criterion of the "damage" due to

Jan 1, 1932

By J. L. Tokich, A. R. Troiano

INTRODUCTION SINCE 1921, when Hull' discovered that cobalt can exist in the face-centered cubic and hexagonal close-packed modifications, the transitions that occur in cobalt have been extensively studied. It is generally agreed that on heating the hexagonal lattice changes to the cubic structure at temperatures ranging from 400 to 500°C although considerable doubt exists as to the exact temperature. Data concerning the temperature of the transformation on cooling are much less concordant and their interpretation has not been satisfactory. The study is further complicated by the fact that many investigators have reported the existence of a high temperature allotropic change in the range 850 to 1020°C, at which the cubic lattice reverts to the hexagonal modification. The transition on cooling, which has been reported as occurring at various temperatures from approximately 400 to 100°C, is of particular interest. Troiano and Greninger2 have recently suggested and considered the possibility of allotropic transformations occurring in pure metals by a shear-type, diffusionless (martensite) transformation. The case of cobalt was specifically discussed and certain observations of previous investigators evaluated in terms of this type of transformation. Table 1 briefly outlines the methods and results of previous investigators of the transformation temperatures of cobalt. MATERIALS AND METHODS The major portion of this investigation was performed with cobalt sheet containing a total of 0.2 pct impurities with carbon present to the extent of 0.1 pct. After melting in an induction furnace under an atmosphere of hydrogen, the carbon content analyzed 0.03 pct. Some observations were repeated with hydrogen reduced cobalt compresses analyzing 99.9 pct pure. No significant variations in results were observed employing the as-received sheet, the remelted stock, or the cobalt compresses. Filings for X ray diffraction analysis were sealed in evacuated glass ampoules. Pyrex glass tubing was used for temperatures below 600°C and for higher temperatures clear fused quartz was satisfactory. After appropriate heat treatment at various temperatures, the specimen ampoules were furnace cooled, air cooled or quenched by crushing under distilled water. This allowed a range of cooling velocities from less than one degree C per sec to greater than 1,000°C per sec. X ray diffraction patterns were taken with a Debye camera and filtered characteristic cobalt K-alpha radiation. The proportion of the existing phases was roughly approximated by visual examina-

Jan 1, 1948

By M. F. Hawkes, R. F. Mehl

The rate of isothermal transformation of austenite to pearlite depends upon the rate of nucleation, N, and the rate of growth, G, of pearlite in austenite. Values of N are given in terms of the number of nuclei forming in unit time per unit grain boundary area of unreacted austenite; values of C are given in terms of the linear rate of radial growth. Variations in the isothermal rate with temperature result from variation of N and G with temperature. Depth of hardening of a steel depends fundamentally upon values of N and G; changes in carbon and alloy content effect changes in N and G and thus affect depth of hardening. Quantitative studies are available on N and G for the formation of pearlite in plain carbon eutectoid steels.3 Systematic studies in this field are necessary if the phenomena are to be well enough known to furnish a proper basis for full rationalization and for theory. Accordingly, the studies are continuing, both with respect to the effect of alloying elements upon the values of N and G in the formation of pearlite and to the values of N and G for the formation of ferrite in hypoeutectoid steels. The present paper is the first relating to the effect of alloying elements upon the values of N and G for pearlite. It offers special interest since cobalt is known to have an anomalous effect upon the rate of formation of pearlite, accelerating it, whereas all other elements retard it.4 It will be shown that cobalt increases both N and G for pearlite and that this effect is inherent in the Fe-Co-C system and not dependent upon factors relating to austenite heterogeneity nor upon any recognizable adventitious factor. Inasmuch as the rate of diffusion of carbon in austenite and the interlamellar spacing of pearlite are variables related to G and possibly to N (in a manner not yet certain), measurements of the effect of cobalt upon them are also reported here. In the course of the work, measurements were made on the effect of cobalt upon the marten-site temperature and these are given. COBALT AS AN ALLOYING ELEMENT IN STEEL Properties of Cobalt Cobalt resembles iron more closely than does any other chemical element. Its atomic number is 27, hence it is the element immediately following iron in the periodic system. The two differ in atomic structure only in the fact that cobalt contains seven electrons instead of six in the third, or transition, level of .the third shell. The next shell, which is the

Jan 1, 1948

By Daniel R. Hull

In 1926 Gendersl reviewed the existing theories of this subject and stated his views in support of the gas-pressure theory. Again, in 1937, the subject was thoroughly reviewed by N. B. Vaughan3 and by Phillips and Brick,2 so that no résumé is called for here. The purpose of this paper is to describe certain observations made in the course of mill work, and to point out that they mostly tend to confirm the gas theory of Genders. Vapor Segregation There is, however, one type of inverse segregation that can be accounted for by considering the volatility of one of the constituents of an alloy. The most familiar case is ordinary brass, which is subject to a zinc enrichment of a few tenths of a per cent at the surface of a chill casting. This has been noted in 70-30 brass by Genders, and a typical example of it is given in Table 1, which represents a cylindrical billet 7 in. in diameter by 55 in. long. After lathe-turning 1/32 in. from the surface, the remaining distance to the center was sampled at six equally spaced intervals. the lead, which is essentially the same throughout, will be mentioned later. Consider a brass-mill mold, either round or rectangular in cross section, standing several feet high. It may require a minute or two for pouring. Before it is full, the metal in the lower end has partly solidified and contracted somewhat away from the mold. The initial shell of solidification follows not far behind the top of the column, even if the central portion is liquid for a long way down. There is, then, a space between metal and mold that is filled with zinc vapor. The vapor has no exit, because the liquid at the top of the rising column is not only in contact with the mold but keeps UP a fresh supply of zinc vapor, which has, perhaps, already begun to condense in the lower portion. The cycle is short. Within a minute or two after the mold is full the bar has cooled enough to condense all the zinc. Some of it may condense on the mold; it might be expected that most of it would condense there, but the mold at that time is well coated with a velvety carbon residue from the oil dressing, overlain by fluffy zinc oxide that commenced covering the inside of the mold as soon as pouring began. The clean skin of the freshly cast brass offers a preferred surface for condensation. Reabsorption is quick and inevitable. A simple experiment indicates that a surprisingly large quantity of zinc vapor is trapped in the space between mold and

Jan 1, 1941

By C. L. Kinney

The rapid increase in the amount of steel produced by the basic open-hearth process is an index of its ability to produce high-grade steel from raw materials of the most, varied physical character and chemical analysis. This inherent adaptability of the process has resulted in a lack of care in the selection of raw materials, so that in far too many cases charges are used of a chemical and physical character not justified by local economic conditions. A practice, or series of practices, should be used that will result in the greatest economy for the plant as a whole; therefore, the operations of blast furnace and open hearth must be considered together. In this paper, an effort has been made to show those variations in both open-hearth practice and cost that follow changes in the analysis of the pig iron arid it may be said that the theoretical costs shown are worthy of careful study and consideration. Carbon, manganese, silicon, phosphorus, and sulfur constitute the principal metalloids in basic pig iron and play the leading role in the production of steel by the basic open-hearth process. The percentages of each of these metalloids, with the exception of carbon, is a variable that has its genesis in the economic relation of the blast-furnace plant to its ore and fuel supplies. As the amount of carbon in the iron is a saturation function of the temperature at which it is produced, the variation in the amount carried is, for any given locality and grade of iron, practically negligible and is so considered in the eight heats discussed in this paper. The melting and refining reactions in an open-hearth furnace, either acid or basic, are essentially oxidizing and vary greatly with the type and age of the furnace, as well as the character of the fuel employed. The outstanding characteristic of the basic process, and the one that explains its predominance over the acid, is its ability to form out of the lime charged and the phosphorus oxidized from the charge a stable

Jan 1, 1924

By Yaniuk DW

The sampling of non-ferrous concentrates from trucks and trains has long been carried out either manually or by automatic spears. Very little use has been made of conventional sampling systems for sampling concentrates at transfer points, or cross-belt samplers for sampling from the belt as the concentrate moves along the conveyor.Due to the high value of base metal concentrates and the often extremely heterogeneous nature of the material it is imperative that the sampling procedures adopted are accurate and precise. The basic principle that all particles in the stream have an equal opportunity to be included in the final sample is not fulfilled by accepted traditional concentrate sampling procedures such as the spearing of wagons, trucks or streams. This may lead to significant bias being introduced into the final sample.Consequently, the application of correct sampling procedures, either with conventional cross-stream samplers or the newer cross-belt samplers, is of prime importance.SGS Australia has recently installed a number of cross-belt samplers for the sampling of base metal concentrates both in Australia and overseas. The application of these samplers will be discussed with emphasis on the benefits of their use.

Jan 1, 1976

By Erceg MM

The Waft River gold deposit is hosted by low grade metasediments which have been intruded by a dacite/andesite porphyry complex. Wafi River is classified as a high sulphur, epithermal type gold deposit having: a high sulphur content, a close association with calc-alkalic igneous rocks, zoned advanced argillic and argillic alteration, and enargite group minerals. Gold occurs as minute inclusions in pyrite and pyrrhotite within intermediate dickite/kaohnite - interlayered illitic clay alteration zones. Central leached silicic, alunite and pyrophyllite zones and peripheral chloritic zones are low in gold. The gold mineralisation at Wafi is interpreted to have been predominantly caused by mixing of hot upwelling acidic magmatic mineralised fluids with cool, neutral meteoric/hydrothermal fluids within permeable sediments. Locallised high grade breccia zones are encountered within the porphyry. An initial resource in excess of I million ounces Au has been defined.

Jan 1, 1990

A high volume of slimes which are separated out during the mining of heavy mineral sands has a high environmental impact and results in great capital as well as operational expenses. The presence of clay minerals drastically increases the slimes volume that needs to be catered for due to its low settling capability as well as swelling characteristics. By adding coagulants in the form of cations and organics, one can improve the settling rate of the minerals as well as the degree of solid bed compaction. The addition of flocculant, which is currently used in industry to improve settling rate, is detrimental to solid bed compaction. By combining the cations and flocculant one can dramatically improve the solid bed compaction. This combination is, however, detrimental to the settling rate of kaolinite-rich slimes but improves the settling rate of smectite-rich slimes. Organics can also be used to produce a clear supernatant and improve the settling rate.

Jan 1, 2010

By Tobin GJ

Testwork carried out in the cooling water circuit at the Yabulu treatment plant of the Greenvale Joint Venturers (Metals Exploration Queensland Pty. Ltd. and Freeport Queensland Nickel Incorporated) since 1980 has resulted in significant improvements to both fouling and corrosion control. At the same time corrosion inhibitor costs have been reduced.Acrylate-type silt dispersants were identified as the most effective means of sediment control in the circuit. An increase in the cathodic component of the corrosion inhibitor coupled with a relatively minor adjustment to water pH has yielded a two to three fold reduction in corrosion rate. It has been established that these lower corrosion rates can be sustained in the face of a 20% reduction in corrosion inhibitor addition rate. Further improvements are indicated with a change of raw water algicide.

Jan 1, 1985

By David E. Jones, Dean K. Hunt, C. Y. Chen

INTRODUCTION Of all the numerous geological hazards that threaten the well-being of urban areas in the United States, probably none is so widespread, persistent, and diversified as surface subsidence (HRB-Singer, Inc., 1977). Simply defined, subsidence is the vertical displacement or sinking of the ground surface caused by either natural phenomena or man's activities. The downward movement, however, can be accompanied by horizontal movement, strain, tilt and even by a locally upward movement. Damage to structures and the environment can result from any of these movements. Extracting subsurface materials, fluids and solids, accounts for most man-induced subsidence in the United States. Among all the mining-related subsidences, the collapse of voids created by underground coal mining has been the major cause in inflicting surface damage (Comptroller General of the United States, 1979). Subsidence from coal mining may occur within a few weeks or be delayed for years, depending upon the mineral layer's depth below the surface, the overlying rock strata's characteristics, the extent and methods of mining that were employed, and the time deterioration of pillar and mine structure. Unless underground resources are not mined or control measures are implemented to prevent or minimize damage, some degree of surface subsidence and its accompanied deleterious effects are often inevitable. The ways to control the subsidence and minimize surface damage may include: 1. Precautionary measures built into new structures or surface features. 2. Preventive works applied to existing structures or surface features. 3. Mine design incorporating special underground layouts. 4. Any combination of the above measures. Upon the enactment of Public Law 95-87, the Secretary of the Interior, through the recently created Office of Surface Mining (OSM), was authorized to promulgate rules to regulate mining reclamation including subsidence control. Proposed on September 18, 1978, these rules were finalized, following public comment and hearings, on March 13, 1979, as part of the permanent regulatory program for the regulation of surface mining and reclamation operations which include the surface effects of underground mining. On January 28, 1981, Secretary Watt of the Department of the Interior issued an order to re- quire all agencies to identify with recommendations all regulations which are believed to be excessive, burdensome or counterproductive. Also on February 17, 1981. President Reagan issued Executive Order No. 12291 requiring all Federal agencies to conduct a regulatory review to make a determination that each promulgation of a regulation is clearly within the authority delegated by law and consistent with Congressional intent (Federal Register, 1981). As a result, OSM initiated the regulatory reform to revise the permanent regulatory program. Following a brief discussion of the technical aspects and the effects of subsidence on man and his environment, this paper presents a historical overview of how rules and regulations are used to govern the subsidence related problems. The development of the regulation of subsidence under Public Law 95-87, the Surface Mining Control and Reclamation Act of 1977 (SMCRA or the Act) are also discussed, including the new regulations being developed under the regulatory reform program. SOME TECHNICAL ASPECTS Am EFFECTS OF FINE SUBSIDENCE An extensive historical review of mining subsidence is given by Zwartendyk (1971) and Shadbolt (1978). Comprehensive technical presentations have been given by Henry (1956), King and Whetton (1957), Hall and Orchard (1963). Muller, et al. (1968). Grard (1969), Voight and Pariseau (1970). Kapp and Williams (1972), Cummins and Given (1973), Brauner (1973) , and NCB (1975). A theory of surface subsidence due to underground mining was perhaps first fundamentally stated by a French engineer, Toillez, in 1838, and formulated by a Belgian engineer, Gonot, in 1839 (Goldreich, 1913, cited by Zwartendyk, 1971). Since that time,

Jan 1, 1982

By Leendert de Witte, Fred J. Radd

In many areas caring failures can be directly related to electrical currents observed in the casings. It is the thesis of this paper that the observed casing currents are mainly due to electrochemical potentials of the type in evidence on spontaneous potential curves of electrical logs. The general nature of these potentials are discussed and an equivalent circuit is given for current and potential distributions around open holes. The casing forms a short circuit to these potentials and tends to average the effects of local cells. The case of casing corrosion opposite the Dakota water sands in the salt-mud area of Kansas is discussed anil used us a qualitative, illustration of the relation between SP's and casing currents. A method of quantitative derivation of casing current distribution frorn electric log SP curves, using linear transform theory, is described and results are compared with a measured current profile. The effects of hydrogen over-potentials at the cathodic portions of the pipe are considered and some laboratory data are given in support of conclusions regarding the over-1.01tuge.s. INTRODUCTION To date an appreciable amount of work has been done on the measurement of oil well casing currents and on the correlation of the anodic portions of the current profiles with corrosive casing failures. Speculations on the origin of the casing currents have, however, remained rather vague; and although almost every plausible cause has been mentioned, there is to the writers' knowledge no clear-cut expose' on the details of the causes of the corrosive currents in the literature. A study of current surveys and casing failures in the N.W. Burnett field, Ellis County. Kan.. indicated the probability that concentration cell emf's between the Wellington salt section and the relatively fresh waters in the Dakota sands were a major cause of the corrosion currents. A more general concept evolved upon analysis of the severe corrosive conditions in the Pleistocene sands in the Ventura Avenue and San Miguelito fields in California. In this area no major variations in the salt content of the formation waters occur and yet large casing currents are observed. An explanation is found in the fact that the local spontaneous potentials which are set up due to concentration contrast between the drilling fluid and the connate water are short circuited when casing is set. The very conductive path through the casing increases the magnitude of the currents and has the tendency to average local sources over fairly large intervals. Current will flow between the sections that are predominently shaly and the sections that are mostly sandy. At the places where the current leaves the pipe, corrosive attack will occur. This same phenomenon will be present wherever unprotected pipe is set through sections that show large SP kicks on the electric logs over reasonably thick interval~. GENERAL- NATURE OF THE SPONTANEOUS POTENTIALS When a sequence of sedimentary rocks is penetrated by a drill hole filled with a mud which has a different salt concentration from that in the formation waters, various types of electrochemical potentials are established between the formations and different parts of the mud column. Opposite clean sand sections. a simple liquid-liquid junction potential will be observed; while opposite argillaccous formations, a membrane potential, often referred to as shale potential, will be established. The first quantitative analysis of these emf's in terms of liquid junction and membrane potentials is due to Wyllie.1

Jan 1, 1956

By Boyd Davis, Vladimiros Papangelakis, Douglass Duffy, Michael Carlos

"The processing of lateritic saprolite in hyper-concentrated magnesium chloride brines offers several potential advantages for the hydrometallurgical production of nickel. An aggressive HCl-MgCl2 leach at atmospheric pressure can significantly reduce magnesium dissolution, and offers the ability to recover HCl and MgO by a less energy intensive process than conventional techniques via the formation of magnesium hydroxychlorides. Inevitably, the high chloride concentration renders iron fully soluble during leaching and thus requires subsequent iron control and disposal steps. Experimental measurements coupled with OLITM modeling were conducted to investigate the behaviour of iron in concentrated magnesium chloride brines, in terms of chemistry (nature of iron species) and solubility limits. The solubility of ferric chloride in magnesium chloride solutions of concentrations and temperatures relevant to this process was controlled by a previously unreported solid phase: 2.5FeCl3·MgCl2·7.5H2O. Iron precipitation tests on synthetic leach solutions without seeding indicate a metastable akaganeite precipitate which transitions to hematite upon equilibration. Magnesium chloride solubility in ferric chloride solutions was also investigated to allow the simulation of a ternary phase diagram for the MgCl2-FeCl3-H2O system, in order to determine process conditions that avoid unwanted chloride precipitation.INTRODUCTION In the search for more economical processes to treat lateritic saprolite for nickel production, chloride hydrometallurgy has been increasingly investigated. While High Pressure Acid Leaching (HPAL) can frequently economically treat lateritic limonite, the presence of saprolite negatively affects process economics. The higher magnesium content of saprolite increases acid consumption, because magnesium sulphate, unlike iron and aluminum sulphates, does not hydrolyze in HPAL. This soluble magnesium decreases the sulphuric acid strength by an amount greater than the amount of acid stoichiometrically required to leach magnesium, which must also be disposed of or recovered (Jankovic, Papangelakis, & Lvov, 2009). Due to these issues, pyrometallurgy is most commonly employed to treat lateritic saprolite, via the Rotary Kiln-Electric Furnace (RKEF) process; this process uses a rotary kiln to dry and partially reduce nickel and iron oxides before sending the calcine to an electric furnace for smelting to produce a ferronickel product for the stainless steel market. Although the problems encountered during hydrometallurgical processing are avoided and nickel recoveries are high, high capital and energy costs prevent the application of this process to lower grade lateritic saprolite deposits (De Bakker, 2011)."

Jan 1, 2016