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By F. C. Appleyard

A couple of miles southwest of the town of Saltville in the western tip of Virginia is a little village called Plasterco. Gypsum has been produced in this area since about the year 1815, being originally found as small outcrops at the surface. Production in the early days was very small, and the use of the mineral was limited to that of "land plaster" or ground gypsum which was spread on the land to sweeten the soil. In the late 1800's, a small calcining plant was constructed and the production of gypsum plaster began. About this same time, the surface rock was depleted and it became necessary to begin underground mining operations in order to maintain a continuous supply of raw material. The United States Gypsum Company became interested in this property in 1909, and has operated there ever since, having enlarged the calcining mill and built a plant for the manufacture of gypsum wall-board in the middle 1920's. Production of gypsum continues from underground' mining operations, and the present mine at Plasterco is now about 1,000 feet below the surface, making it the deepest gypsum mine' in the world.

Jan 1, 1965

By George W. Leney

The iron ore industry might justifiably claim to have originated the science of geophysical prospecting. Their use of geophysical methods was probably the first application of these scientific techniques to the search for economic materials although the exact origin is undoubtedly lost in the unrecorded observations of. some prospector experimenting with compasses or bits of lodestone. Since 1879 when Thalen published "On the Examination of Iron Ore Deposits by Magnetic Measurements" these methods have been a standard supplement to other prospecting techniques. However, many of the great ore bodies of the Precambrian iron ranges were not particularly suitable for geophysical work. The ores were oxidized and enriched through leaching of silica so that they were nearly non-magnetic and other physical properties which distinguished them from the wall rocks were largely destroyed. With the gradual exhaustion of these high grade direct shipping ores, and ores that could be beneficiated by simple means, the iron ore industry turned initially toward the importation of similar high grade foreign ores. At the same time, new processes for concentrating lower grade materials were being developed and older ones improved upon. These concentrates' when pelletized produced such important savings in blast furnace hot metal costs that they now command a premium in the iron ore market and have weakened the competitive position of the remaining high grade ores. The ore bodies now being sought are usually unoxidized and frequently they are also metamorphosed.

Jan 1, 1965

By M. Pope

By 1950, packaged oil and gas fired boilers were on the market for capacities up to 30,000 lbs./hr. By 1962, capacities were up to 100,000 lbs./hr. and even higher when separate heat traps (economizers and air preheaters) were attached to the boiler packages. During this period, complete packaged coal fired boilers were developed into the 10-15,000 lbs./hr. range. Oil and gas fired plant designs became very compact, "basementless", and far: less costly than the coal fired plants of any capacity. Coal fired plants remained large and expensive, required field erection of boilers and required basements. With the spectacular strides made in automation, oil and gas plants became far less costly to operate, requiring only the part-time attendance of a single operator. Some advances were made in coal fired plants, but not to the degree attained by the fluid fuel competition.

Jan 1, 1965

By S. E. Valji

Clay slurries are normally dewatered using flocculents like sulfuric acid or aluminum sulfate. This type of flocculation is based on the electrolytic mechanism. For certain clay dewatering applications, this method of flocculation is unsatisfactory. Flocculation, based on the bridging mechanism, using organic polymers has been utilized to overcome such problem situations. This method of flocculation offers solutions not possible by previous methods. Normally these flocculents are used to assist dewatering. In this case, not only is dewatering promoted, but also further processing is assisted by a change in the dilatant character of the filter cake that is formed. Discharge of filter cake is easier, extrusion of filter cake on to conveyor dryer is possible or improved, and heat transfer and drying rates of the extruded filter cake are substantially higher. Both natural and synthetic organic polymers have been utilized for this purpose. Selection, application techniques, and economics are described.

Jan 1, 1965

By J. P. Vandenhoeck

Sizing devices used commercially are unfortunately not 100% efficient, the splits that can be obtained are usually inferior to the results obtained in the laboratory. Often the capital and operating costs of equipment capable of high sizing efficiency cannot be justified by the economics or requirements of the process. To reconcile the desired sizing efficiency needed to obtain optimum process requirements with the sizing efficiency of equipment economically practical, it is often necessary or desirable to predict the gradation and weight splits of the products obtained based on the expectant efficiency of the contemplated sizing device or method. The less efficient the sizing device one must employ, the more important it is to know the results that may be expected for the establishment of the optimum flow sheet and the more difficult it becomes to estimate the results accurately. Air classification equipment which sizes materials by opposing the drag force created by an air stream acting on a particle with a combination of gravitational, inertial or centrifugal forces are substantially less efficient than, for example, a laboratory sieve analysis. Air classifiers allow oversize material to contaminate the fine fraction and leave undersize material in the coarse fraction. The techniques employed to predict the gradation and weight splits obtained from air classification outlined below are adaptable to other sizing devices less than 100% efficient such as screens, sifters and wet classifiers.

Jan 1, 1965

By Frank E. Sullivan

The separation of liquids from granular materials has been widely studied by a number of: investigators over a period of years in an effort to more fully understand the physical phenomenon which occurs. Liquid may be removed from solids, or partially removed, by gravity separation, mechanical separation' or heat drying. Mechanical separation is advantageous when compared to heat drying principally from a cost saving standpoint and also on certain materials which are heat sensitive. It is realized however that mechanical separation of liquids has certain practical limitations. In order to evaluate the efficiency of mechanical separation and predict the extent of, liquid removal, it is first necessary to study the forces which hold the liquid to the solids. From a very practical observation using gravity drainage, it is soon obvious that a pile of coarse solids will drain faster and retain less liquid than a pile of finely divided solids of the same material. For commercial operations it is important to estimate the residual liquid which will remain after a mechanical separation. Batel (1) explored the various quantities of liquid present in the interstices of the bulk granular material. From his work and other authors which he has correlated in one of his recent papers, various formulas are now available which permit an empirical relationship to be developed showing residual moisture versus mechanical separating forces.

Jan 1, 1965

By Edmund C. Bitzer

The unit costs of dry crushing, within the efficient reduction ranges of equipment now available, are considerably less than those for the reduction of the same material in the same size range by wet mills using grinding media. This is a commonly recognized fact which cannot be disputed; still we find considerable imbalance in costs between the crushing and grinding sections of many operating mills. In other words, there are many instances where more reduction could be accomplished in the lower cost area of dry crushing. In addition, equipment is now available which enlarges this area and makes it possible to consider much finer crushing than has been heretofore economically feasible. There has been a tendency for the past two decades to utilize wet rod-¬milling in the reduction step. This actually amounts to a fourth stage of crushing in a size range formerly served by roll crushers which have fallen from favor on account of high operating costs, Some investigations have indicated that there is not sufficient difference in the operating costs of rolls and rod-mills to give a clear cut advantage to either method, There has for some time been a need and an opportunity for a dry crushing process to improve costs in the range now served by these two systems.

Jan 1, 1965

By Frederick Bradley Henderson

This study was initiated to investigate the occurrence of cinnabar in the oxidation zones of some mercury sulfide deposits. Seven mines or mine districts were visited and samples were taken from both the oxidation and primary zones of these deposits in order to compare their mineralogies and assess Vie chemical changes that took place during oxidation. As a result of the study of these specimens, several limiting factors are suggested for the chemical environments and processes active in both the deposition and oxidation of mercury sulfide deposits. The Mt. Jackson mine, near Guerneville, California (location map, fig. 1), was studied in some detail and forms the basis of this paper. The mine has not heretofore been described in detail in the literature. The Mt. Jackson mine is considered typical of mercury sulfide deposits occurring at the faulted boundaries of serpentinite bodies and enclosing sediments. Such mines are common in the California and Oregon Coast Ranges? Specimens collected by the author from the New Idria and New Almaden districts, the Mt. Diablo, the Culver Bear, and the Buena Vista mines in California, and the Opalite district (Cordero and Bretz, mines) on the Oregon-Nevada border were studied for comparison with the Mt. Jackson samples. The mine description, maps and sketches were composed from field maps kindly provided by Francis Fredericks, consulting geologist to the Sonoma Quick-silver Mine Inc. during the author's visit in 1962. Additional information was obtained from the company maps and minor corrections and interpretations were added by the author.

Jan 1, 1965

By Adrian J. Mathias

For many years excavations were made in rock exclusively by conventional blasting methods, and without concern for damage to the rock surfaces which remained after the excavation was completed. Recently, however, there is an increasing awareness for the importance of making rock excavations with as little damage as possible to the remaining rock surfaces; consequently, several revolutionary new precision blasting techniques have been developed during the past few years. These techniques, variously known as cushion, smooth- wall, perimeter, pre-shear, and pre-split blasting, basically involve the creation of a fracture plane in the rock between a series of blasted holes. The variations in each of these techniques are largely due to the differences in hole diameters, hole spacings, methods of charging, and sequence of blasting used to achieve certain specific results. The development of these precision blasting techniques was initiated by Canadian Industries Limited in 1953 at the time the Sir Adam Beck No. 2 Hydro-electric Project was under construction by the Hydro-Electric Power Commission of Ontario. Since then, these techniques have been somewhat advanced, and they have been applied with varying degrees of success to a number of projects. These projects include railroad and high- way cuts, dam spillway channel excavations, canal excavations, tunnel driving, shaft sinking, and other underground applications.

Jan 1, 1965

By Thomas P. Meloy

There is much interest in the automation of entire comminution circuits, At the present technological level it is possible to automate a circuit but to date it has not been done, To successfully automate a circuit, a number of problems must be solved. Not all of them are engineering problems. The purpose of this paper is to discuss some of these problems, as certain the implications of these problems and indicate solutions to them. In this paper the term "automation" is used loosely but in the popular sense. Namely, that a plant is automated if a computer is used to control the basic flow of the materials as well as setting the critical parameters in the process. Specifically, the discussion will concern itself with the control of comminution circuits from the dumping of the ore into the primary crusher until the final interface between the comminution circuit and say, the flotation mill in the case of a sulfide ore.

Jan 1, 1965

By F. X. Ferney

The centrifuge which will be reviewed in this dis¬cussion is the continuous solid bowl typo. As there are presently approximately 2000 of these units operating in our country, and about 200 of these in use in the coal industry, I expect that most of you are acquainted with its operating principle. How¬ever, for those who are not familiar with the machine a brief introduction is in order. The continuous solid bowl centrifuge was first successfully marketed, worldwide by the Bird machine Company in 1934. The successful development of this unit was based primarily on the invention of a drive mechanism to properly control the differential speed between the two rotating elements. This centrifuge was introduced into the coal industry immediately following the second World War. Today there are five or six additional firms' selling this machine in our country, and approximately twenty others in Europe, England and Japan.

Jan 1, 1965

By G. T. Swanby

Members of AIME, I read to you now a portion of a very fine business letter which we received several years ago. This letter originated in Rangoon, Burma, and reads in part: "Rest assured, if your goodselves see with us eye to eye, sure as certain we should get the business". I don't plan to give anybody "the business" today, but you can rest assured that if some of "you goodselves see with me eye to eye" on what I am about to discuss, I would be most pleased. My talk with you today will discuss the Federal Corporate income tax and its effect on our lives as engineers. In the-engineering-construction business we are faced with all the usual form of taxation which includes such items as sales tax, use tax, school tax, contractor; gross receipt tax, import duties and excise taxes, severance taxes, etc, adinfinutum.

Jan 1, 1965

By Laurence B. James

The California Department of Water Resources is concerned with the development, distribution, and protection of the State's water resources. Geologic activities of the Department relate to planning, construction, and operation of water projects, supervision of the safety of over 900 dams under state jurisdiction, and investigation and control of ground water supply. The Department is engineering oriented, and the role of the geologist is to assist with the solution of engineering problems. Some of these problems require the integration of many talents, including not only those of geologists and engineers, but also those of economists, lawyers, seismologists, chemists, geophysicists, and hydrologists, Frequently, a task force of several disciplines will attack a problem as a team.

Jan 1, 1965

By J. Richard Lucas

Today, the future of the coal industry is extremely bright because coal can be produced at a cost which makes it competitive with other energy sources. However, the industry has been forewarned that further cost reductions must be made if it expects to remain a serious contender in the growing energy market. Surface as well as underground operations must be improved. The very same elements which affected production a. few years ago still exist today and will continue to be present in the future. Improvement's in production mining equipment, mining methods, and auxiliary equipment have resulted in reduced costs over the past few years. Efforts must be continued toward further reducing costs in areas which have been improved previously, and new areas should be investigated for possible improvements. Therefore, new techniques must be developed which will enable the industry to augment its current efforts in reducing the cost of mining. The logical place to begin evaluating the factors affecting production and cost is in the immediate face area where a substantial part of the total cost of mining is incurred. The coal industry stands to gain much through the development of new techniques for analyzing the numerous variables affecting production and by establishing methods for eliminating or minimizing the adverse effect of those variables which can be controlled. Intuition and trial-and-error methods have been the standard means used to resolve many of the factors which influence production. As a result, many elements are overlooked or ignored because their effect on production is not pronounced and cannot be readily resolved. The need for a method of analyzing such factors was recognized by the Office of Coal Research. Therefore, in April 1962, under OCR sponsorship, a. research project was initiated at Virginia Polytechnic Institute (VPI). The objective of the project was to identify the factors which influence mining costs in the immediate production area, and to develop methods and techniques which will enable the coal operator to minimize production costs. The objective of the research at VPI has been successful, and techniques have been developed for establishing quantitative facts concerning the interrelationships of production activities.

Jan 1, 1965

By A. A. Dor

Recent developments in the design of concentration plants have reflected the increased recognition that has been given to the economic and metallurgical advantages of autogenous grinding. This has manifested itself in the increasing adoption of primary auto genous grinding in iron ore 'beneficiation plants in North America. Table 1 lists eleven major iron ore beneficiation plants which have either been put in operation since 1961 or are under construction at present. Seven out of these eleven plants have adopted primary autogenous grinding. Four of them have coarse grinding mills (8 to 14 mesh) and three have fine grinding primary circuits (48 to 65 mesh). Their nominal capacity totals 26. 2 million ltpy of concentrates or pellets, representing very nearly 75% of the aggregate capacity 135. 3 million ltpy) of the eleven concentrators listed. For a long time there was a tendency to consider that primary autogenous grinding was only applicable to suitable coarse grained ores, However, extensive testing of a very wide variety of ores, and actual operating performance in several commercial plants, seem to have established beyond reasonable doubt, that the majority of mineral ores which the beneficiation engineer may be called upon to process can be ground autogenously. The basis for the selection of autogenous or conventional grinding mills, becomes principally economic and depends on the liberation characteristics of the ores under consideration and their relative hardness and grindability.

Jan 1, 1965

By E. J. Karges

The use of pulverized coal for generating power and performing industrial processes has made an important contribution to our industrial economy during the past half century. Actually, the burning of coal in powdered form is a subject that has held the attention of engineers for a century or longer. Its widespread use, however, is comparatively recent, As early as 1866 patents were granted to Messrs. Whelpley and Storer for a method of feeding pulverized coal into a furnace as an auxiliary to the grate fuel. In the many tests made during the subsequent years with various kinds of apparatus, the experimenters were handicapped in not getting the coal fine enough to obtain complete combustion and to prevent excessive formation of slag.

Jan 1, 1965

By P. C. Kapur

The kinetics of green pelletization in a laboratory balling drum have been studied, using pulverized limestone as a model system. The growth characteristics of green pellets were found to be extremely sensitive to the moisture content of the material. Empirical kinetic equations, which incorporate a function of specific surface of the pellets as the criterion for growth potential, have been found to describe growth in a nucleation region and in a ball growth region. The rate constants in the kinetic equations are strongly dependent on the moisture content of the material being pelletized. Size distributions of the halls at different stages of pelletizing are also discussed.

Jan 1, 1965

By Delbert L. Keenon

The principal concepts of computer control and automation have been successfully applied in industries world-wide, The enthusiasm generated by the proponents of computer control, and the apparent mystery enveloping the techniques of computer control, have caused attention to be focused on this infant industry from all quarters. Consequently, the motivation to "computerize" may be the hope that computers will solve all economic problems. The truth remains that not only have there been monumental successes, but there have been some colossal failures. This paper will attempt to outline a generalized guide to computer control and present methods for avoiding some of the major pitfalls. Since the investment required for computer control systems has been drastically reduced in the past year, small operations will likely find that computerized process control is attractive in areas where it has never been considered before, The discussion presented here is intentionally non-technical and directed towards those who may soon find they have a possible application for a control computer. The primary purpose of computer control is to reduce expenditure and increase profits by improving the quality of product, increasing the efficiency of operation, reducing the materials and man hours required or a combination of these. Success or failure to reach the desired goal depends, to a large degree, on a well-planned approach. This includes recognizing a possible computer application, properly defining the job which is to be accomplished, evaluating computer systems, selecting a capable manufacturer, and following through with sound systems engineering and programming.

Jan 1, 1965

By William H. Lehr

In recent years, we have witnessed many innovations in the equipment used in handling bulk materials. Not too long ago, any sizeable stockpile of coal or iron ore was attended by one or more material handling bridges. More recently, large stockpiles have been built with mobile equipment of' the earth moving type with bulldozers and front end Loaders being utilized in reclaiming operations. The most recent stocking and reclaiming device is the rotary bucket wheel machine. The early bucket wheel machines built in the United States were developed for the strip mining of coal. We understand that the first American machine was built in the Midwest in 1944. This type of unit was developed in an effort to reduce the cost of removing overburden and to provide satisfactory spoil disposal. As the available coal reserves under shallow cover were exhausted, the cost of removing the deeper overburden with conventional equipment became too great for these operations to continue profitably. The first machine has now been followed by six or seven additional units, the largest of which can handle material at a rate of more than 7000 cubic yards per hour.

Jan 1, 1965

By G. H. Friedrich

The distribution of mercury in soils, rocks, and ore was studied in three areas of the Pachuca-Real del Monte District: (1) An area north of the town of Pachuca where ore veins have been found at or near the surface. The mercury content of soil samples taken near the vein zones is far above the background value. The highest value was 1900 ppb (parts per billion) mercury in a soil sample above Veta Vizcaina; the background is about 50 ppb Hg. (2) In the area north of the town of Real del Monte where only a few of the veins are known to crop-out. Regardless of exposure, soils collected over veins show anomalous mercury values ranging from 250 ppb to 1900 ppb. (3) In an area south of the town of Real del Monte. Here, although vein outcrops are lacking, mineralization is known at a depth of about 120 m. All soil samples taken at 50 m. intervals along an east-west traverse contain anomalous amounts of mercury, with peaks corresponding with the known location of the veins.

Jan 1, 1965