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By Chao Zhang, Wenhao Xia, Jianxin Fu, Ling Yu, Weidong Song, Yang Li

Sanshandao Gold Mine is the only undersea metal mine in China. To deal with the collapse and pumping of stopes and roadways caused by complex ore-rock occurrence conditions, the mine conducts filling and sealing of some areas, and the remaining ore reserves will be mined after treatment. Therefore, it is urgent to evaluate the stability of rock masses, fault fracture zones, and aquicludes during the secondary mining process. In this study, displacement and microseismic methods are employed to monitor rock deformation and fractures. Additionally, FLAC3D was used to simulate the process of secondary mining, reproducing the evolution of stress fields, displacement fields, seepage fields, and plastic zones at different mining stages. The combination of numerical simulation and on-site monitoring verification demonstrates that the deformation of surrounding rock presents a rapid growth at the initial stage of mining, followed by a gradual decrease in the growth rate, and finally tends to stabilize; the fracture zone area at the 151–159 exploration line on the − 320 m level (near the 7# and 8# stopes) exhibits poor stability, and monitoring measures should be strengthened; the deformation value of the aquiclude is less than the deformation value of I protection level in the Code for Design, the impact of secondary mining on the aquiclude is limited; fault and fracture zone deteriorate rock mass stability, and their impact is related to their spatial locations. Hanging wall fault has a more significant impact on the settlement of the aquiclude, while the footwall fracture zone has a greater impact on the development of the plastic zone.

Feb 21, 2024

By Greg J. Hasenfus, Allison M. Haines, Joshua M. Silvis

The floodable volume of longwall gob can be of great importance in developing accurate coal mine operation plans, particularly for mine water management and environmental control strategies. Given the inaccessibility and difficulty in direct measurement of gob characteristics following gob recompression, hydrologic, geomechanical, and spatial data and principles were used to solve for the porosity and height of the residual gob using a mathematical model framework and bulking-based techniques. Based on this approach, gob porosity of Appalachian longwalls appears to be tighter than previously reported, ranging between 4.99 and 14.31%. Residual gob height, as normalized with respect to mine extraction height, ranges between 1.90 and 2.45. A novel, bedding-based bulking approach is ampliative with respect to existing roof caving and bulking fundamentals, as it has greater explanatory value compared with the traditional, lithologic-based bulking application. The efficacy of using the residual gob characteristics determined by the mathematical model and bedding-based bulking is examined using a causal comparative method, whereby time series prediction of historical groundwater rebound is compared with observed mine pool elevation data. Prediction accuracy is significantly improved using a prototype model to calculate void volume of longwall gob, specifically, the dependence of porosity of the gob material upon the longwall width to overburden depth ratio for movement basins of subcritical and critical panel widths. The potential implication of these findings toward hydrologic, geomechanical, and ventilation studies of longwall gob could be significant.

Aug 13, 2021

By Steven Hoerger

Mixed integer linear programming (MILP) production scheduling models can be used to evaluate if tonnage improvement projects will deliver value over all time periods and whether new bottlenecks will be created. These MILP models can evaluate the interconnected effects of mine and process capacities, mining locations, cutoff grades, stockpiles, and orebody grade/tonnage distributions. A case study compares potential value creation from a mine capacity increase, a mill capacity increase, or a simultaneous increase in all capacities. For perspective, project valuations for capacity increases are compared against valuations for cost reduction projects, mine planning improvements such as phase design, dynamic cutoff grades and stockpiling, and the impact of geostatistics improvements in the areas of block model accuracy and ore control selectivity.

Feb 1, 2024

By K. Luxbacher, A. Haghighat, B. Lattimer

Mine face ignition due to high levels of methane is one of the most common fire incidents in underground coal mines. In continuous miner headings, depending on the magnitude of the ignition or resulting fire, auxiliary ventilation controls may be damaged or dislodged, affecting the ventilation into the area. A computational study was conducted to investigate the effects of different levels of damage to an exhausting ventilation curtain in a continuous miner heading, and the impact on ventilation to the face. The computational fluid dynamics software Fire Dynamics Simulator (FDS) Version 6.0 was used to predict the conditions that develop due to a 200-kW fire in the face following a methane ignition with different levels of assumed ventilation curtain damage. Smoke layer depth, temperature and mass flow inby the last open crosscut were used to evaluate the impact of no damage to the curtain, partially dislodged curtain, and fully removed curtain. As more of the ventilation curtain was damaged, smoke depth and temperature outby the fire increased. With the full removal of the curtain, the smoke accumulated from the last open crosscut to the face, with the ventilation completely bypassing the continuous miner region.

Jan 1, 2016

By J. Drelich

An improved experimental procedure to measure contact angle has been consolidated with coal surface preparation involving polishing with abrasive paper, alumina powder, and a cloth, followed by ultrasonic and mechanical cleaning. Specifically, the captive-bubble measuring technique has been compared with the sessile-drop technique and the former has been recommended for the examination of the hydrophobic properties of coal surfaces. Results of the research program, which is currently under way, on the examination of the effect of the nature, amount, size and distribution of mineral inclusions in coal on its wettability are briefly reviewed.

Jan 1, 1999

By M. S. Tsai

Recovery of uranium from wet-process phosphoric acid is a newly developed source of uranium. Many processes have been developed but the OPAP (octylphenyl acid phosphate) process is still the valuable one because the OPAP reagent compound has the high extraction ,power and cheap cost. The OPAP process was already studied by murthy(1) in 1970 and its complete process flow sheet was first fulfilled by F.T. Hurst(2) in 1974. WCFC(3) (western Co-op Fertilizer Ltd.) in cooperation with ESI (Earth Science Inc.) set up the OPAP uranium recovery pilot plant in Canada in 1978. We have studied the OPAP process since 1974 and first improved the OPAP extractant by proper adjustment of the DOPAP/MOPAP mole ratio with CH3OH-H20 method, resulting in shortening the phase separation time and avoiding the precipitation occurrence in our process. Second, we utilize the reduction and oxidation occurring by DC power supply on either side of the membrane to achieve the extraction and stripping at the same time. An improved OPAP process in which high recovery yield of uranium and acid uncontaminated by iron has been developed in our laboratory.

Jan 1, 1982

By J. Richard Kyle

The Pb-Zn ore bodies in the Pine Point district are localized in paleo-solution structures that developed as the result of post-middle Givetian subaerial exposure of the carbonate barrier complex. Sulfides are concentrated in transgressive pale-solution structures that acted as natural bypasses between aquifers and loci for mixing of fluids of different character, one of which contained metals and the other reduced sulfur. Complex ore textures indicate rapid early sulfide precipitation followed by slower sulfide growth. Evidence for both sulfide-carbonate equilibrium and disequilibrium conditions suggest fluctuations in ore fluid composition. District and ore body metal distribution patterns may reflect the nature and movement of mineralizing fluids.

Jan 1, 1979

By Kevin A. Foo, Murray D. Bath, John H. Canterford, Arnaldo Ismay

There is no doubt that the dominant future source of gold will be the so-called refractory ores, especially those with gold in a pyrite/arsenopyrite matrix. Minproc Engineers is taking an active role in establishing detailed design criteria for a number of apparently competing processes. This involves generating a detailed understanding of the metallurgy involved, systematic pilot plant testing, and the application of advanced engineering technologies. This presentation outlines the approach adopted by Minproc as well as the design criteria for several current projects.

Jan 1, 1989

By Mingyang Li, Yan Lv, Xiaolong Ma, Xudong Gao, Jie Zhao, Yingyi Zhang

The reduction process of pre-oxidized ilmenite concentrate powder in 30%CO–70%N2 atmosphere was characterized by thermogravimetric and differential thermogravimetric (TG-DTG) analysis system at the temperature from 1073 to1223 K. The isothermal reduction results show that the reduction process is divided into three stages and the corresponding apparent activation energies are obtained by iso-conversional method and model-fitting method, respectively. For the first stage, the conversion degree increases sharply with increasing time, and the reduction process is controlled by the random nucleation and subsequent growth model (A2 model). For the second stage, the conversion degree increases slowly with increasing time, and the reduction process is controlled by the diffusion of carbon monoxide in the reduced layer (D1 model). For the third stage, the reduction processes at different temperatures are controlled by the diffusion of carbon monoxide in the reduced layer (1073 K and D1 model), phase boundary chemical reaction (1123 K and R2 model), random nucleation and subsequent growth (1173 to 1223 K, A2, and A3 models), respectively. For the whole reduction process, the apparent activation energies obtained by iso-conversional method and model-fitting method are 71.72 and 31.92 kJ mol−1 , respectively

By Jacques B. Wertz

However excellent the geologic map of an area is, it can only show what is exposed on the ground. It cannot and should not generalize the information nor complete the picture by inference: this is left to the examiner. Consequently, it becomes justified for him to use all expressions of geologic structure in order to gain an additional dimension in geologic interpretation, and particularly so in mineral exploration. In previous studies related to Arizona, the known faults were the starting points and a host of interpolated, supporting geologic factors described in earlier publications ascertained the presence of a series of structural trends and lineaments found to be rather continuous and persistent, even though unsubstantiated by geologic maps. In present studies pertaining to the humid environment, with the same aim of seeking major structural trends and lineaments, the starting points are morphologic expressions such as straight lakes and straight segments of rivers, among others, because there generally is not enough geology available. An example is given herewith for an area that straddles the International Border, north of Spokane. In both semi-arid and humid environments, one observes that mineral deposits quite often occur close to the intersection of a major fracture or lineament with some secondary trend.

Jan 1, 1971

By M. Akram

Stability assessment of entry roofs is an essential precursor to all underground design. Both multi-seam interaction and longwall mining can subject entries to radical changes in the surrounding stress field. Such loading changes frequently produce instability and failure in the roof, floor and pillars. Roofs are shown to be vulnerable to stress-induced failures, particularly when the load is unsymmetrical. To predict the effects of changes in stress field, roof failure conditions under increasing loads were studied using finite element analysis and body loaded photoelastic models. A large range of geologic conditions were evaluated and incorporated into the model using Monte Carlo methods. Entry analysis using the model showed the roof to be particularly vulnerable to shear with the location of the failure site changing to meet loading and geologic conditions. Results were correlated with field data to determine stress levels at which failure could be expected to occur. Based on this research a roof stability model SESAME was constructed for roof stability evaluation under specified loading conditions.

Jan 1, 1993

By Weiguo Xie, MARK LAPUTKA

The pyrometallurgical industry plays a vital role in producing metals for our modern life. With growing demand of metals and declining grade of mineable ore, innovations become critical for many mining companies. It is necessary to conduct a review of recent improvements to the pyrometallurgical industry on analytical measurement techniques, process and equipment improvements, and computer-based modeling/simulations. Many of those innovations tend to be applied to wider metals, and not be restricted by a specific metal. Therefore, we tried to cover the wide applications of many improvements to wider range of metals to reflect this trend. The challenge of a lack of robust measurement techniques under high-temperature conditions within a furnace hinders optimization of a pyrometallurgical process. Some future opportunities in the pyrometallurgical industry on analytical measurement techniques, computer modeling, and processes and equipment have also been outlined and discussed.

Jan 26, 2021

By James J. Meadows, Jason D. Pampena, Emanuele G. Cauda, Lauren G. Chubb

Exposure to respirable crystalline silica (RCS) can cause serious and irreparable negative health effects, including silicosis and lung cancer. Workers in coal mines have the potential of being exposed to RCS found in dust generated by various mining processes. The silica content of respirable dust in one single mine can vary substantially over both time and location. The current monitoring approach for RCS relies on the use of traditional air sampling followed by laboratory analysis. Results generated using this approach are generally not available for several days to several weeks after sampling, and this delay prevents timely and effective intervention if needed. An alternate analytical method is needed to reduce the time required to quantify the RCS exposure of mine workers. The National Institute for Occupational Safety and Health (NIOSH) has developed a new method using commercially available portable infrared spectrometers for measuring RCS at the end of the sampling shift. This paper will describe the application of the new field-based RCS analytical process for coal mines, including the use of the new method with the existing Coal Mine Dust Personal Sampler Unit. In a case study conducted by NIOSH with a coal mine operator in West Virginia, field-based RCS analysis was completed at a mine site to evaluate the new technique. The RCS analysis results obtained by the field-based method in this case study showed sufficiently strong correlation with results obtained by the MSHA standard laboratory analysis method to allow the mine operator to use the field-based method for evaluating process improvements.

By W. A. Haley

The use of diesel engines in underground hard-rock mines dates back to the late 1940s. For the first several years, they were used only occasionally, being limited to a few metal mines that experimented with crawler¬mounted front-end loaders, tractor-trailer hauling units, a few tractors for drill-compressor mounts, and utility cleanup machines. By the mid-1950s, track loaders had become commonplace in limestone mines and uranium mines on the Colorado Plateau in the United States, as well as in Canada. Use of crawler-mounted tractors as drill and compressor mounts also increased. By the end of the 1950s, rubber-tired loaders and some haulers began to replace the track-type machines and rail-mounted cars that had been in use. About 1960, the rubber-tired machines brought about a new era of underground mining mobility and flexibility, centered on a method commonly known as "trackless mining." Ultimately, many of the underground rail-type systems for loading and hauling were replaced by the trackless mining technique. ECONOMIC CONSIDERATIONS The size and nature of mineral deposits, plus ground control techniques, historically had dictated small open¬ings to the surface from many underground mines. The small mine openings led to the development of special rubber-tired loaders and haulers designed specifically for access through the small openings. However, some mines, particularly those in massive mineral deposits, are able to excavate and maintain very large openings, and some use modified room-and-pillar systems. With the large mine openings, the use of larger, more produc¬tive equipment such as that commonly found in surface mining becomes economical. In fact, productivity gen¬erally increases at a more pronounced rate than machine size increases because many of the larger machines were designed for heavy-duty shot-rock applications in surface mines and construction sites where the handling of blasted rock is common. Table 1 can be used as a very Table 1. General Productivity Comparison for Conventional Machines In Underground Use (Shot-Rock Conditions) 2.3 m3 (3 cu yd) 4.6 m3 (6 cu yd) Loader Loader Expected Surface 230 t/h 540 t/h Production (250 stph) (600 stph) Expected Underground 90 t/h 270 t/h Production (100 stph) (300 stph) Expected Total Efficiency: Surface 40%-60% 50%75% Underground 25%.-40% 30%50% Expected Useful Machine 8000 hr 12,000 hr Life Before Replacement general comparison of the production and efficiency between small and large machines. Combining greater productivity often inherent in larger machines, with reduced downtime resulting from using fully developed machines with fast parts and service backup, some mine operators have been able to reduce material handling costs appreciably while reduc¬ing manpower requirements for operators and main¬tenance men. Large mine openings increase the amount of rock that must be handled in the development work, and they sometimes increase the dilution in stopes or rooms, de¬pending upon the dimensions of the ore zone. Providing adequate space for the unrestricted operation of large surface mining machines could, therefore, lead to more waste segregation and handling costs. It could also cause greater ore dilution that would result in a lower grade of ore being delivered to the processing plant. The tradeoffs between opposing cost factors must be reconciled and balanced to achieve the best overall cost of the crude ore, concentrates, or product. EQUIPMENT MODIFICATIONS Loaders and haulers designed for surface mining are seldom used underground in their standard con¬figurations without some modifications. If done, the modifications generally are made by the equipment dealer and/or the user, and the modifications usually include one or more of the following items: 1) The exhaust stack is lowered, and its direction is changed. Usually, it is repositioned horizontally to the rear, or it is fed into the engine fan to diffuse the exhaust gases. 2) The operator's position is lowered by either lowering the seat or changing the seat to a side mount. 3) The operator controls are adjusted to fit the new operator position. 4) Other components, such as the radiator and loader tower, are lowered. 5) Special bumper guards are mounted at the base of the radiator area. 6) An exhaust conditioner is mounted and con¬nected, using either a catalytic or a water-type condi¬tioner, or both. This usually is controlled by the safety and health regulatory authority having jurisdiction. 7) The positions of other components are rearranged

Jan 1, 1982

Well designed and maintained haul roads are the key to minimizing truck haulage on-road hazards and costs, as well as increasing productivity. However, practically designing and managing a haul road for optimal performance is often difficult to achieve. Poorly designed and built roads exhibit high rolling resistance - a 1% increase in road rolling resistance can typically reduce speed on ramp by as much as 10% - and on the flat by up to 26%. In the current economic climate, investment and operating decisions come under scrutiny. In the long run, this scrutiny returns improved efficiencies and leaner, healthier operations. The focus of this evolving evaluation process should and will certainly fall on haulage operations ? simply by virtue of their contribution to overall cost of operations ? often in excess of 50% of total costs for deep open-pit mines. Whilst the end result - improved efficiency and reduced cost per ton hauled ? is not in itself problematic, it is the route, or process followed to achieve these savings that needs to be carefully managed. We can be guided on this journey by our understanding of how a road design is developed, and, critically, the interplay between a good design and safe, cost efficient haulage. This paper briefly summarizes the evolution of mine haul road design, from the seminal USBM work of Kaufman and Ault in 1977, through to current geometric, structural, functional and maintenance management design components. These augmented design and management guidelines have been developed over the past decade, both in response to the requirements of mine operators for more safe and efficient haulage systems, and the truck manufacturers? requirements for a more predictable and controlled operating environment. These developments have been paralleled by the need to minimize haulage hazards, both from a health and safety perspective. Whilst improved mine haul road design does indeed reduce haulage accidents, recognition also needs to be given to human factors which are a significant contributor to haulage accidents. The human factor is the most problematic to address in a road design. It is often easier break the link between the interactive effects which may lead to accidents than trying to predict and reduce human error. These human factor interactive effects include the geometric, structural and functional design components and to prevent an accident or reduce the severity of its consequences, a road should be more accommodating to human error. The more that is known about human error, the better a road can be designed to accommodate those actions or non-standard practices that would, on a poorly designed road, invariably escalate an error into an accident.

Jan 1, 2010

The Colorado portion of the Rio Grande rift is clearly defined physiographically from the south in the San Luis valley northward to the latitude of Leadville where sediments of the Dry Union Formation (Tweto, 1961) accumulated within the subsiding rift zone. To the north of Leadville is a system of faults active in the late Tertiary, including the Mosquito fault that offset a portion of the Climax mineralization (Wallace et al., 1968). Tweto (197B) describes remnants of Dry Union Formation against the Mosquito fault north of Dillon in the Blue River valley, so it is apparent that the rift and associated sediments extended well to the north of Leadville. Kelley (1952, 1954, 1956) and Chapin (1971) have noted in New Mexico that the Rio Grande rift is a series of en echelon basins, offset to the east, with constrictions connecting them (Fig. 1). In Colorado the structural basins are offset to the west. The net effect of all the rift zone basins in New Mexico and Colorado is an arcuate pattern (Fig. 1) abutting the Colorado Plateau and Sari Juan Volcanic Province on the west. The width of the rift system gradually decreases northward to about Leadville where rift definition is not apparent.

Jan 1, 1987

By E. R. Bauer

A primary goal of Ground Control Research, Bureau of Mines, U.S. Department of the Interior, is to develop information that can be used by the mining industry to reduce accidents and fatalities due to failure of mine roof. A specific research objective is to determine methods to detect hazardous coal mine roof. This paper reviews the existing and experimental techniques, and describes a recent Bureau of Mines contract research project that resulted in a simple technique and prototype instrument for evaluating mine roof competence.

Jan 1, 1986

By R. B. Tippin

Great Salt Lake Minerals & Chemicals Corporation (GSL), a subsidiary of Gulf Resources & Chemical Corporation, is located on the east side of the Great Salt Lake, approximately 20 miles from Ogden, Utah. GSL processes brine from the north arm of the lake to produce potash, salt cake, salt and magnesium chloride brine. Potash fertilizer, in the form of K2SO4 is GSL's primary product. The GSL Sulfate of Potash Complex The GSL potash complex (depicted in Figure I) is divided into a solar evaporation pond system and the process plants. The solar,evaporation system consists of a 17,000-acre (68.8 Km2) ponding operation where the various salts deposit during the summer evaporation season, and a harvesting operation which recovers the deposits during the remainder of the year. The harvest is either preconcentrated in the flotation plant or processed directly in the chemical plant where sulfate of potash (SOP) is produced. The chemistry of the lake brine results in a solar deposit con¬taining primarily kainite (KCl-MgSO4.3H20), schoenite (K2SO4?MgSO4^ 6H2O), and halite (NaCI), with some carnallite (KCl.MgCl2.6H20) and epsomite (MgSO4.7H20). Other minor minerals may be deposited, depending upon the weather during the evaporation season. Each year, the solar deposit in the evaporation ponds will greatly depend upon the summer weather conditions, which have in the past proven to be quite unpredictable. Weather may alter both the quantity of the solar deposit and the composition of this deposit. During, a "short" evaporation season, the tonnage deposited decreases, but depending upon the short-term weather, the potash mineral content

Jan 1, 1977

By A. E. Desrosiers, R. L. Kathren, D. L. Haggard, J. M. Selby

INTRODUCTION The radiological health significance of thorium-230 stems from its tendency to separate from the uranium238 parent, concentrate in bone tissues, and to subsequently irradiate the radiosensitive tissues lining the bone surfaces and the bone marrow. Indeed, thorium-230 may be the radionuclide which contributes the major dose following intake of natural uranium (Hartley and Pasternack 1979). This is reflected by the most recent recommendations of the International Commission on Radiological Protection, which specify the limits shown in Table I for the annual intake of radionuclides by occupationally exposed workers (ICRP 1979). TABLE 1. Occupational Annual Intake Limits (microcuries per year) for Selected Uranium Nuclides and Daughters (ICRP 79) [Radionuclide Ingestion Inhalation] [Uranium-238 200 0.05 Uranium-235 200 0.05 Uranium-234 200 0.03 Thorium-234 300 200 Thorium-230 3 0.02 Radium-226 2 0.5] Clearly, the relatively low annual limit of intake for thorium-230 shows it to be of greater radiological concern than its parent radionuclides. Because of the greater toxicity and different metabolism of thorium-230, monitoring only for uranium-238 does not satisfactorily identify the possible hazard from thorium-230 nor does it provide any real indication of the metabolism or biodynamics of these two radionuclides. Thorium-230 has a half-life of 80,000 years and can be detected by direct counting of the alpha particles or photons emitted during its transformation to radium-226. The 4.69 and 4.62 MeV alpha particles are distinctive and specific indicators of thorium-230 and are emitted with abundances of 76% and 24%, respectively. The principal photon, a 68 keV gamma ray, is emitted in only 0.37% of the transformations and is, therefore, not useful for low level measurements. The other photons emitted have even lower yields, or, in the case of radium L x-rays, are non-specific and, hence, useless for quantification. High sensitivity measurements of thorium-230 currently are usually accomplished by wet washing of the sample substrate, quantitative chemical separation of thorium atoms, and, finally, direct measurement of the alpha particles emitted from a massless deposition. This procedure is complicated, expensive, and time-consuming, and subject to interferences from uranium, other actinides, and other thorium isotopes. Recently, the feasibility of low-level measurement of thorium-230 by neutron activation analysis (NAA) was demonstrated (Kathren, Desrosiers and Church 1980). Two principal variations of the NAA method were used in this study: 1) instrumental NAA technique and 2) post-irradiation radiochemical separations (RCS). Instrumental NAA procedure is a nondestrucive technique which is preferred because of its simplicity. The procedure is as follows: after irradiation with a known neutron fluence, the samples are transferred to a clean container and quantitative gamma spectroscopy performed. With the radiochemical separations procedure, the sample is initially treated as in the instrumental technique. However, after irradiation, a known amount of "carrier" is added to the sample. The element(s) of interest are then separated from the rest of the matrix by distillation, precipitation and extraction techniques. The resulting sample, now free of interferring elements, is then ready for gamma-ray analysis. The use of a "carrier" is to determine the loss of element-of-interest during the chemical separations process. The neutron activation cross section of thorium-230 has an epicadmium resonance value of 1,010 barns (Mughahghab and Garber 1976) and a thermal neutron cross section of 23 barns. The 25.52 hr thorium-231 produced releases two photons of significance: an 84 keV complex, (6.5% yield) and 25.6 keV (15% yield) (Lederer and Shirley 1978). The 84 keV complex is particularly useful for quantification since neither natural uranium, thorium, their daughters, or activation products emit photons in this region. However, the higher yield of the 25.6 keV photon may result in increased sensitivity if there are no other photons of similar energy emitted by other radionuclides in the sample. PRELIMINARY STUDIES Thorium-230 standard stock solution was prepared from a pure sample of the oxide purchased from Oak Ridge National Laboratory. From this stock solution a series of samples were prepared for irradiation in the TRIGA Mark I reactor at Reed College. Various dilutions were prepared as well as thorium-230 spiked urine samples. Irradiation times varied from 1 to 54 minutes in a neutron fluence rate of 1.84 x 1012 n/ cu m-sec. The neutron spectrum was abundant in thermal neutrons, having a Cd ratio of approximately 10. Treated urine samples were also analyzed by the NAA instrumental method. Analysis of untreated urine samples was not possible due to the high background

Jan 1, 1981

By P. B. Queneau

An operating problem encountered at the Moa Bay operation in Cuba, where nickeliferous laterite ore is processed by sulfuric acid pressure leaching, is the formation of alunite and hematite deposits on the autoclave walls. The AMPX Extractive Research & Development, Inc., metallurgical laboratory (Golden, Colorado) has made substantial improvements in the Moa Bay process in the areas of metal recovery, energy consumption, and feed versatility. One of the advantages of AMAX's process is its ability to treat substantial portions of nickel- and magnesium-rich serpentine while maintaining acid utilization efficiency. The process minimizes scale formation by combining staged acid addition with vigorous agitation and 270°C operation, but does not eliminate scaling. This paper describes how advantage can be taken of MgSO4?XH20 precipitation both to inhibit alunite scaling and to disperse hematite scale within the MgSO4?XH20 matrix. Cooling the autoclave from its 270°C operating temperature down to 180°C takes advantage of the reverse solubility of magnesium sulfate. The magnesium dissolves, liberating entrained hematite, thus providing a means for control of autoclave scale with minimum process disruption.

Jan 1, 1984