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By Wen Tao Liu, Tong Tian, Fu Sheng Niu, Xiu Man Liang

In order to address the difficulty of accurate segmentation of froth images of different sizes, a method of froth image segmentation based on highlight correction and parameter adaptation is proposed. First, a machine vision system on a single-cell flotation machine is built to collect froth images. Homomorphic filtering is used to improve the uneven brightness and shadow of the images. Fuzzy c-means (FCM) clustering is then utilized to classify similar highlights that belong to the same froth. After Otsu threshold segmentation, a parameter-adaptive morphological operation is used to extract the marker points and edge bands and correct the froth edges in the original image. Finally, the modified image is filtered by morphological reconstruction, and the highlight mark is used as the local minimum point for watershed segmentation. Three sizes of froth images are segmented in comparative experiments. The results show that the proposed method is suitable for the segmentation of froth images of different sizes. The position of the extracted segmentation line is close to reality, with average over-segmentation and under-segmentation rates for froth images of 2.6% and 6.8%, respectively. The froth image segmentation performance is stronger than that of the other methods examined.

By C. Vasilescu

Phytotechnologies use plants to remediate various media impacted with different types of contaminants. These technologies can be implemented either in situ or ex situ. The affected media in which phytotechnologies can be applied include soil, sediments, groundwater and surface water. They are best applied at sites with shallow contamination of organic, nutrient, or metal pollutants that are amenable to one of five treatment options: phytoextraction, phytotrans-formation, rhizosphere, bioremediation, phyto-stabilization or rhizofiltration. Phytoremediation can be used along or, in some cases, in place of mechanical cleanup methods. Phytoremediation can be used to clean up metals, pesticides, solvents, explosives, crude oil, polycyclic aromatic hydrocarbons and landfill leachates.

Jan 1, 2006

By Derrick Chambers, George Kevin Chapin, M. Shawn Boltz

Seismic monitoring is one of the few noninvasive technologies with the potential to provide sub-surface geomechanical information to operators of large open-pit mines. Although passive seismic data has been used to refine emerging failure geometries and provide advance indication of surface deformations in the literature, doing so reliably in an operational context is much more difficult. This is due in part to difficulties in estimating and interpreting source locations and parameters in complex, low-stress open-pit environments. Additionally, the high costs associated with implementing, operating, and maintaining deep borehole seismic networks, which are most commonly used to monitor large open pits, can be difficult to justify, especially if monitoring benefits are not readily apparent. In this study, we explore the use of a near-surface nodal seismic deployment, which is commonly used in oil and gas exploration, for monitoring open-pit mining-related seismicity on a short-term basis. A deployment of 18 geophones was conducted on the surface in and around the Bingham Canyon Mine, a large open-pit mine near Salt Lake City, Utah, USA, where we find the small seismic array can detect and locate a variety of mining-related seismic sources, even with an extremely simplified velocity model. We outline the process of creating an idealized velocity model, developing a local magnitude scale, and interpreting the observed seismicity. Of note, we analyze a sequence of mining-induced events associated with a known structure on the south pit wall. We conclude with discussion on how surface-based deployments may be used to augment, or in some cases supplant, borehole seismic networks at large open-pit mines depending on monitoring requirements and objectives.

Apr 26, 2022

By T. L. Barone, J. R. Patts, L. D. Patts, S. J. Janisko

"Controlling float coal dust in underground coal mines before dispersal into the general airstream can reduce the risk of mine explosions while potentially achieving a more effective and efficient use of rock dust. A prototype flooded-bed scrubber was evaluated for float coal dust control in the return of a continuous miner section. The scrubber was installed inline between the face ventilation tubing and an exhausting auxiliary fan. Airborne and deposited dust mass measurements were collected over three days at set distances from the fan exhaust to assess changes in float coal dust levels in the return due to operation of the scrubber. Mass-based measurements were collected on a per-cut basis and normalized on the basis of per ton mined by the continuous miner. The results show that average float coal dust levels measured under baseline conditions were reduced by more than 90 percent when operating the scrubber. IntroductionAirborne coal dust is a byproduct of coal production, and engineering controls exist to deal with both the respirable dust health hazard as well as the float dust explosion safety hazard. Float coal dust, smaller than 75 µm (0.003 in.) in size, can deposit throughout mine entries and propagate explosions that had been initially fueled by methane gas. The inertization of float coal dust with rock dust helps prevent a potential secondary float coal dust explosion, but a preferable course of action is to significantly reduce the hazard by removing float coal dust from the airstream before it has the opportunity to deposit on the mine’s surfaces.Since 1970, disasters due to explosions in underground coal mines have caused 201 deaths in the U.S. mining industry, including 29 deaths in a single mine explosion in 2010 (Wade, 2010; U.S. Mine Safety and Health Administration, 2015). The U.S. National Institute for Occupational Safety and Health (NIOSH) had initiated a fiveyear research project that aims to investigate methods and technologies to reduce the potential for secondary coal dust explosions by the purposeful capture and/or suppression of float coal dust prior to its deposition on the mine roof, rib and floor (NIOSH, 2013). The project aims to evaluate the efficiency of methods to reduce longwall and belt airway float dust in the general airstream as well as methods to capture it at or near the source. Prioritization is given to longwall sections given the amount of coal produced relative to continuous miner sections, but the research is open to technologies that may be adapted from one method of mining to another."

Dec 1, 2016

By J. A. Lepinski

The FASTMETSM Process is a coal-based process for converting iron oxide fines into metallic iron. The end product, direct reduced iron (DRI) is used as a low residual charge material in electric arc furnace steelmaking. This paper describes the FASTMET Process and its potential application in the United States. Operating results from a 175 kg/h process simulator are presented. Characteristics of the end product are discussed. Process economics are reviewed along with plans for scaling-up the process to full commercial size.

Jan 1, 1993

By Hongwei Wang, PEIPEI CAO, Yongping Wu, JIANQIANG JIAO

In the fully mechanized top caving mining of steeply inclined, extra-thick seams with variable angles, the mechanisms of roof rock movement, failure, caving and filling are highly complex. This is due to the varying angle of coal seam in different areas, which makes rock–equipment stability control challenging. In this paper, the surrounding rock deformation and failure mechanisms, bearing structure of the overburden, and working characteristics of the supports are elucidated. The principle and key technologies of rock–equipment stability control are presented and applied to control the overburden of the regional failure and realize safe and efficient mining of the working face.

By Z. Jin, D. DePaoli, P. Zhang

"Phosphorite, or phosphate rock, is the most significant secondary rare-earth resource. It contains high amounts of phosphate-bearing minerals along with low contents of rare earth elements (REEs). In Florida, about 19 Mt of phosphate rock are mined annually and most are used to manufacture fertilizers using a wet process, in which sulfuric acid reacts with phosphates to produce phosphoric acid and phosphogypsum. In the wet process, REEs are also leached out into solution and eventually get lost in the leaching residue and phosphate fertilizer. Recovering REEs from Florida phosphate rock in the wet process will be beneficial to broadening rare-earth availability, improving the quality of phosphoric acid product and protecting the environment.This study focuses on the influences of wet-process operating conditions on REE leaching efficiency. The results indicate that REE leaching efficiency increases with phosphoric acid addition in the initial pulp. At a temperature of 75 °C, a stoichiometric ratio of sulfuric acid (H2 SO4 ) to calcium oxide (CaO) of 1.05 and a weight ratio of liquid to solid of 3.5, REE leaching efficiency reached a relatively high value of 52.82 percent. The trends of REE leaching efficiency were similar to those for phosphoric acid (P2O5 ). Extensive tests on the leaching residue showed that during leaching, about 90 percent of the REEs were released from the phosphate rock but only 52.82 percent ended up in the leaching solution. This phenomenon can be attributed to two factors: (1) the effect of phosphate ions (PO4 3-) in the solution, which caused REE ions to form REE phosphates and be precipitated into the leaching residue, and (2) the influence of large amounts of anions such as sulfate (SO4 2-), dihydrogen phosphate (H2 PO4 -) and hydrogen phosphate (HPO4 2-) anions as well as the polar molecule H3 PO4 , which surrounded the REE cations and formed an ion atmosphere that prevented the PO4 3- from contacting and combining with REE cations. Interaction of these two opposite effects determined the REE distribution between leaching solution and residue."

Jan 1, 2017

By Peter Zhang, Mark Van Dyke, Ted Klemetti, Morgan Sears

Room-and-pillar mining is a mining method used in the United States to extract coal from underground, and pillar recovery is widely practiced for maximizing coal recovery and mining economics. Under certain conditions, room-and-pillar mining can create high stresses in coal pillars resulting in a coal outburst. These outbursts represent one of the more severe safety hazards in underground coal mines, potentially causing injuries and fatalities. Over the past ten years, coal outbursts have resulted in three fatalities in U.S. room-and-pillar mines. Though coal outbursts generally occur under deep cover, they are more likely to occur during pillar recovery and under multiple-seam mining conditions. Coal outbursts are generally associated with strong roof and floor and heavy loading of coal pillars, but it is difficult to predict whether, where, and when they will occur. In this respect, risk management provides a proactive tool to prevent coal outbursts in room-and-pillar mining by identifying mining areas with high risk of outburst and mitigating the risk accordingly.

Apr 26, 2022

By David L. Veith

As the basis for the State of Minnesota's Regional Copper-Nickel Study environmental evaluation, hypothetical mine models were developed ranging in ore capacity from 5.35 to 20.00 x 106 mtpy. Open pit and underground mining operations were defined utilizing conventional methods of ore extraction. Processing of the copper-nickel sulfide material involved conventional bulk flotation of the valuable minerals, with maximum water recycle And tailing disposal. Flash smelting and electrolytic refining of the concentrate resulted in 0.10 x 106 mtpy copper plus nickel metal, plus associated cobalt and precious metals. Variations in model parameters allowed environmental trade-offs to be identified.

Jan 1, 1980

By Lawrence Lien

The reduced need for traditionally trained and educated personnel in the mining industry is systemic to the changing mining industry. Universities and other training institutions are meeting the traditional skill needs required by the industry, but are the skill needs going to be the same in the near future? The answer may be no. Mining is changing because of increased liabilities and costs of environmental and safety is-sues; lower grades of minerals in traditional mining activities and the advent of new bio-chemical processes and robotic equipment. More productive and economic alternatives, and larger, more sophisticated and automatic equipment, are also changing the industry. Engineering is more specific, accurate, precise and expensive. Measurement is more thorough and timely of progress, production, costs and productivity. And, the industry will likely be engaging in more undersea mining, possibly space-based processing, less human interaction and more remote control of events than was previously thought possible.

Jan 1, 2011

By John A. Cherry

Groundwater monitoring conducted at an acidic uranium-tailings impoundment in Wyoming and at one in Ontario indicate that at these unlined impoundments situated on unconfined sand aquifers, there exist well-developed plumes of contaminated groundwater. In the literature similar results are reported for three other unconfined aquifers at mill sites in Wyoming. The plumes extend for distances of several hundred to a few thousand metres from the impoundments. They have a zone of low pH beneath and adjacent to the impoundments and a larger zone of near-neutral pH that extends to the outer limits of the plume. The low-pH zones are generally small compared to the neutral-pH zones because the advance rate of the fronts of acidic tailings-derived water is slower than the average velocity of groundwater which controls the advance of the high pH zone. The retardation of the acid fronts is a result of geochemical reactions that cause hydrogen-ion consumption in a slowly-advancing neutralization zone. Within each of the plumes, the low-pH zone has high concentrations of transition metals, heavy metals and radionuclides. In the neutral-pH zones all of the metals and radionuclides occur at significantly lower concentrations and are generally at levels much below those specified in national drinking water standards. An exception at two of the Wyoming sites is uranium, which exists at levels close to the drinking water limit. A second exception is ferrous iron at the Ontario site, which occurs at high concentrations throughout most of the plume. The carbonate alkalinity at this site is much lower than at the Wyoming sites. The field data indicate that even in very permeable aquifers with a low content of silt and clay, there is normally a considerable capacity for acid-front retardation. To take advantage of this capacity to control contaminant movement in the design, operation and decommissioning of tailings impoundments, it is necessary to be able to predict the rate of acid-front movement. This predictive task has two primary components. The first is to identify the important flow paths from the tailings through the groundwater system and the second is to determine the degree of acid-front retardation that will occur as the tailings-derived water moves along these flow paths. Relative to these two tasks determination of the effects of hydrodynamic dispersion is generally of lesser importance and simple approximations that do not involve field or laboratory tests are probably adequate. In order to effectively apply the acid neutralization concept to the prediction of subsurface contaminant migration at uranium-mill tailings, improved representations of hydrogeochemical behavior of iron and aluminum in the neutralization zone and of the consumption of hydrogen ions through reactions with carbonate and aluminum-silicate minerals are required. Along with the hydrogen ions contained in the tailings water the ferrous iron represents a large potential source of acid but the extent to which ferrous iron converts to ferric iron to produce acid is problematic. Detailed hydrogeochemical evaluation of existing contaminant plumes and the performance of laboratory experiments under appropriate redox conditions ore prerequisites for the improvement of predictive models. However, the existing field and laboratory data provide a basis for preliminary predictions of contaminant migration from acidic uranium tailings impoundments.

Jan 1, 1982

By Dave Southworth

After Abe Lee discovered gold (in April 1860) near the site of present-day Leadville, Colorado, he and is group staked nearly all of California Gulch with "speculative claims." They did so in an effort to grab any property that might be potentially profitable. But the plan did not work. New prospectors demanded a miners' meeting, from which arose the official "Bylaws of California Mining District, California Gulch, Arkansas River." These bylaws, adopted on May 12, 1860, established provisions as to the number, size and type of claims that could be filed. Fair laws invited more newcomers. By mid-summer, 5,000 people with tents and wagons were scattered from one end of the gulch to the other.Among the earliest arrivals to the region that spring were Horace Austin Warner Tabor and his wife, Augusta. H.A.W. Tabor, who was to become a pillar in the development of Leadville, arrived at California Gulch during a food shortage. He sacrificed his oxen so that hungry miners could eat. By doing so, he immediately became the friend of many. Augusta established a little store where she sold her baked goods and provided meals. Like most of the men, Horace prospected the surrounding hills. He only did so, however, for a short time. California Gulch yielded more than $5 million in gold during the next five years. By 1866, however, the placer gold was gone and most of the miners had packed up and left. Charles J. Mullen and Cooper Smith, who were grubstaked by a Philadelphian named J. Marshall Paul, found a new, rich lode at the Printer Boy Mine in 1868. It was the first underground gold mine in the Leadville area and marked the transition from surface mining to underground hard rock mining. Its discovery created a new but modest flurry of activity. Heavy black sand covered the region and made gold mining difficult. In 1875 William Stevens and Alvinus Wood decided to have the sand assayed. They discovered that it contained 15 ounces per ton of silver and was rich in carbonate. Stevens and Wood kept their find a secret for nearly two years. When the word spread in late 1877, the silver boom was on. In 1878 prospectors, merchants and others trickled into town from all directions. Dr. David H. Dougan closed his office. in Alma, crossed Mosquito Pass and set up shop in Leadville. Nobody seemed to need a doctor, however, and Dougan sat in his office for 28 days without a customer. On the 29th day he received word that there had been a mining accident and he was needed immediately. -That was the begin¬ning of his illustrious career in Leadville. Dougan was a successful physician, became mayor in 1881 and was later president of the Carbonate National Bank. Leadville was a simple community of log structures in 1878. By June of the following year, however, it had blossomed considerably. According to Cass Carpenter, as of May 1,1879, Leadville had "...19 hotels, 41 lodging houses, 82 drinking saloons, 38 restaurants, 13 wholesale liquor houses, 10 lumber yards, 7 smelting and reduction works, 2 sampling works for testing ores, 12 blacksmith shops, 6 livery stables, 6 jewelry stores, 3 undertakers and 21 gambling houses where all sorts of games are played as openly as the Sunday School sermon is conducted." Additionally, there were 36 brothels. When George E. King and other architects arrived, Leadville took on an air of elegance and sophistication. In sharp contrast to some of the Victorian-style, gingerbread-laced homes in Leadville, its suburbs were comprised of many tenement shacks and plain cabins mixed with a few commercial buildings, many mines and smelters. Mines sprinkled the area east of Leadville like pepper from a pepper shaker. Wherever there was a cluster of mines, a camp usually sprang up. Most were very close together. South of Leadville the giant Arkansas Valley lead smelter sprawled out between Stringtown and Bucktown in an area known as Smelter Valley. Founded in 1879 as the Billing and Eilers Smelter, the Arkansas Valley plant was operated by the American Smelting and Refining Company. Several other smelters operated in the vicin¬ity. In April 1878, Horace Tabor grubstaked prospectors August Rische and George Hook. For $64 worth of supplies and tools, he was guaranteed a one-third interest in their findings. Rische and Hook discovered the Little Pittsburg (often spelled Pittsburgh) Mine and made Tabor an instant millionaire. Tabor once purchased a "salted" mine, the Chrysolite; but instead of considering it a bad deal, he further developed the property and struck rich silver ore. Later, Tabor purchased the Matchless Mine for $117,000, possibly the only investment he made without partners. During its peak years, the Matchless yielded $1 million worth

Jan 1, 1998

By B. Barry, M. S. Klima

"Testing was conducted to evaluate the effects of hydroacoustic cavitation (HAC) treatment on two bituminous coal slurries and the subsequent separation of each slurry in a classifying hydrocyclone. HAC treatment was performed using a pilot-scale circuit fabricated by Furness-Newburge Inc. The circuit was designed to induce cavitation by means of flow through an ultrasonic resonator chamber or enhanced cavitation by initial flow through a cavitation chamber followed by flow through the ultrasonic chamber. The test materials were nominal -1,500-micron and -150-micron Illinois-basin bituminous coal slurries, which were obtained from an operating coal preparation facility. After 5 sec of HAC treatment, the median size of the -1,500-micron material was reduced, with ash values for certain size fractions decreasing more than 5 percent compared with untreated samples. Extending treatment time led to greater degradation of the +1,180-micron material and an increase in the -25-micron material, with ash reductions occurring for material in the -850+150-micron size range. Size degradation was less for the -150-micron material. Subsequent separation of the treated slurries was carried out in a hydrocyclone with diameter of 102 mm. HAC treatment led to a decrease in the ash value and an increase in the heating value of the underflow stream compared with the feed material. For example, the ash value was reduced by about 16 percent for the -1,500-micron material and 25 percent for the -150-micron material with heating value increases of 7 and 33 percent, respectively, after HAC treatment. Overall, HAC treatment appeared to have a slight effect on the size selectivity curves.IntroductionUltrasound in the range of 20 to 1,000 kHz, referred to as power ultrasound, consists of high energy waves that can create zones of compression and expansion when used to irradiate liquids (Frederick, 1965; Leighton, 1994; Mason and Lorimer, 1988). This action generates varying pressure regions leading to cavitation or the formation, growth and near-immediate collapse of microscopic voids or bubbles (Frederick 1965; Leighton 1994; Mason and Lorimer 1988). Collapse occurs when the bubble reaches critical size and cannot absorb additional sound field energy, and the critical size is governed by the ultrasound frequency (Shchukin et al., 2011)."

Jan 1, 2015

By R. G. McLusky

This paper analyzes the opinion in Bragg v. Robertson, 72 F.Supp. 2d 642 (S.D. W.Va. 1999), a case which threatens the future of surface mining in West Virginia and which will almost certainly result in new policies or rules that will affect surface mining everywhere. This paper addresses: (1) the jurisdictional bases of the action which relies on the federal surface mining laws to enforce a state mining program; (2) settlement agreements reached in the case that threaten to alter federal policies beyond West Virginia borders; (3) a programmatic environmental impact statement on mountaintop mining being undertaken by the federal government; and (4) an opinion by the Court outlawing excess spoil disposal in intermittent and perennial streams.

Jan 1, 2001

By Thornton L. Neathery

The low-grade talc deposits in Tallapoosa County, Alabama, are associated with a mafic-ultramafic rock complex that is part of a widely distributed schist and gneiss group. These rocks form a synform structure overlying Inner Piedmont lithology. Paragenetic sequence of the Tallapoosa talc is interpreted as enstatite-anthophyllitetalc. Talc occurs as massive boulders formed by the alteration of enstatite-anthophyllite and as finely disseminated discrete particles in the enclosing saprolite matrix. Weathered rock reaches depths as great as 60 feet. The quality and quantity of the talc, however, are variable. Mineral analyses of the talc-bearing samples, by petrographic grain count, indicate a talc content of 16 to 26 percent. Most of the talc occurs as plates or scales that are moderately stained with limonite. Fibrous talc also occurs in the deposits and is often mistaken for anthophyllite asbestos which is intimately associated with the talc. The size, shape, and occurrence of the talc deposits precludes any method of min¬ing other than open-cut. A small-scale mining operation began in the district in 1969. Potential capacity of the operation is 5, 000 tons per year. Inferred reserves, based on field investigations, are placed at approximately 8 million tons. Approved for publication by the State Geologist, Geological Survey of Alabama.

Jan 1, 1970

By Hans Treichl

1. INTRODUCTION For Europe the Arlberg road tunnel signifies the elimination of the largest traffic barrier between Bucharest and Paris in the east-west transversal. Apart from that the tunnel will serve the feeder system to the two north-south links Ulm - Milano, and the Brenner motorway, and links the Inntal and the Rheintal motorways closer together.. Thus, the supraregional road system carrying traffic through the Tyrol and Vorarlberg will considerably be emproved by the Arlberg road tunnel. 2. THE PROJECT The 16.1 km contract section of expressway S 16 includes a ramp section of approximately 2.6 km, the access points at St.Anton and at Langen, and the main 13.98 km section of the road tunnel. This section cuts the link between St.Anton and Langen by 3.7 km, and saves 475 m in altitude. The Arlberg road tunnel is planned to have two tubes with two lanes each. In the first stage the southern tube was under construction. Its traffic capacity is 1,800 car units per hour. The tunnel has a cross section of 9o to 103 m2. The sloping gradients are by 1.3o and 1.67 per cent. Fresh air is supplied and used air removed through a ventilation system, fed at the portals and through two vertical ventilation shafts. One of them, at Maienwasen, is 222 m deep, its cross section 66.5 m2. The diameter in clear is 8.32 m. The vertical shaft Albona is 736 m deep, the diameter in clear is 7.37 m. The tunnels is 9,4o m wide, providing for a 7.5o m roadway plus o.95 m sidewalks on each side of it. 4.7o m above the traffic area the conduits for fresh and used air. A transverse ventilation system with reduced exhaust air has

Jan 1, 1979

By II Browne

After a decade of high copper prices, major mining companies are renewing their interest in purchasing operating properties and/or development of ore bodies. An existing operation carries with it a history that can present unique opportunities, while a greenfield operation allows for the establishment of a defined culture. Capital investments are distinctly different. A comparison of BHP Copper Robinson Operation, a greenfield property, and BHP Copper Tintaya Operation, a government owned Peruvian property, will provide insights into mining, concentrating and cultural differences between North and South American Operations.

Jan 1, 1997

By Liangguo Kang

Coal, as one of the vital sources of energy in China, has raised widespread concerns regarding its safety issues amidst the country’s economic growth driven by coal. To address this concern, this study employed the Kuznets curve, multiple linear regression, and data envelopment analysis models to investigate the impact of Chinese coal economic development on coal mine deaths from 1992 to 2021. The findings revealed a clear correlation between the Chinese coal economy and coal mine deaths. Specifically, per capita coal output, the death rate per million coal tons, and the death rate per hundred thousand persons exhibited positive, negative, and negative correlations, respectively, with the growth of coal income over the past three decades. Moreover, when the coal workers and coal output factors remained unchanged, the income of coal demonstrated a negative correlation with future changes in coal mine deaths. Notably, with three decades of coal economy development, substantial improvements in coal mine safety have been observed in China. Consequently, this research provides valuable insights for formulating safety measures and policies in coal mines across different economic levels, as well as a useful framework for assessing safety development in the coal industry.

Jan 20, 2024

By James K. Wright

This chapter will discuss the use of financial models as an evaluation tool for various phases of decision making from exploration strategy to the analysis of a producing mine. The text of this chapter was not received in time for printing.

Jan 1, 1979

By Philip R. Whitney

Precipitation of hydrous manganese/iron oxides in streams can be readily observed in much of the northeastern United States, and is apparently a common phenomenon in other glaciated areas (1,2,3,4). Deposition occurs when Mn-enriched ground or surface water enters the stream environment and encounters conditions of higher Eh and pH. The preferred location for deposition is in shallow, fast-flowing segments of stream; the oxides usually form as coatings on detrital material. The experimental studies of Hem(5) and a considerable amount of work on marine and lacustrine manganese nodules(6,7,8) suggest that given an appropriate substrate, deposition of manganese oxides may occur even when the water is undersaturated in Mn with respect to the oxides, due to catalysis by organisms or by silicate, carbonate, or ferric hydroxide surfaces. Once begun, manganese oxide deposition is autocatalytic (9). Studies of the distribution of oxides in various size fractions of stream sediments indicate that the thickness and prevalence of the coatings commonly increases with increasing particle size in the coarse sand and gravel size ranges. Figures 1 and 2 show a fairly typical distribution of leachable metals over nine size fractions from 62 microns up to 8-16 mm. The leaching solution used was neutral ammonium citrate with hydroxylamine hydrochloride, which effectively removes the oxide coatings without significantly attacking most silicates, carbonates or sulfides. Figure 1 shows metal content as ppm of the total sample; figure 2 shows' the same data as micrograms of metal per square millimeter of surface area.

Jan 1, 1975