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By Kenneth J. Miller

The Bureau of Mines conducted an investigation to improve the flotation response of coals that are difficult to wash by froth flotation. A literature survey and experimentation showed that, for the most part, refractory coals can be floated with oily collectors and frothers. Collector reagent consumption can be minimized and the selectivity of the flotation enhanced by assuring adequate, but not prolonged, reagent conditioning. Where flotation selectivity is especially poor, two-stage rougher-cleaner flotation is recommended. It was concluded that a major problem with refractory coals is predicting when they will appear in a flotation circuit so that supplementary flotation collectors can be added. Coal losses due to variation in the floatability of the feed might be reduced if a nonpolar collector such as kerosine or fuel oil is used along with a frother as general coal flotation practice.

Jan 1, 1977

By C. E. Jordan

The Bureau of Mines conducted laboratory studies on methods to increase the recovery of brine from slime produced by operating potash plants. The slime was comprised of 80 percent brine saturated with KCl and NaCl, and 20 percent solids. A variety of settling techniques, filtration methods, continuous centrifugation, and novel processing techniques were investigated. Vacuum filtration recovered 6S percent of the brine at 47 gallons of brine per square foot per day. Pressure filtration, on the other hand, recovered 74 percent of the brine at 40.9 gallons of brine per square foot per day. Centrifugation in a 6-inch-diameter continuous decanter-type separator resulted in 42 percent recovery of the brine at a treatment rate of 542 gallons of brine per day. Vertical drains proved to be the most promising novel debrining technique investigated. With this method, 45 percent of the brine was recovered in 3 days.

Jan 1, 1977

By Peter F. Steidl

As part of the Bureau of Mines methane control program, the Upper Free-port coalbed was studied in Fayette County, Pa., where this coalbed lies about 650 feet below the Pittsburgh coalbed and contains the largest remaining reserves of any coalbed in the county. Its estimated recoverable reserves in Fayette County are between 670 and 800 million tons. Coal and overburden isopachs, structure and joint pattern maps, and a fence diagram were prepared using data from gas and oil exploration logs and coal outcrops. These maps will aid in determining the need and/or feasibility of degasifying the Upper Freeport coalbed in the study area. Much of the coalbed in this area is under 600 to 1,400 feet of overburden. By correlation with data from the Pittsburgh coalbed, the gas content at depths of this order is estimated to be between 140 to 300 cf/ton of coal.

Jan 1, 1977

By Peter F. Steidl

As part of the Bureau of Mines methane control program, the Upper Free- port coalbed was studied in Fayette County, Pa., where this coalbed lies about 650 feet below the Pittsburgh coalbed and contains the largest remaining reserves of any coalbed in the county. Coal and overburden isopachs, structure and joint pattern maps, and a fence diagram were prepared using data from gas and oil exploration logs and coal outcrops. These maps will aid in determining the need and/or feasibility of degasifying the Upper Freeport coalbed in the study area. Much of the coalbed in this area is under 600 to 1,400 feet of overburden. By correlation with data from the Pittsburgh coalbed, the gas content at depths of this order is estimated to be between 140 to 300 cf/ton of coal, for a total of 190 to 400 billion cubic feet of methane in this coalbed in Fayette County.

Jan 1, 1977

By Peter F. Steidl

As part of the Bureau of Mines methane control program, the Upper Free-port coalbed was studied in Fayette County, Pa., where this coalbed lies about 650 feet below the Pittsburgh coalbed and contains the largest remaining reserves of any coalbed in the county. Coal and overburden isopachs, structure and joint pattern maps, and a fence diagram were prepared using data from gas and oil exploration logs and coal outcrops. These maps will aid in deter-mining the need and/or feasibility of degasifying the Upper Freeport coalbed in the study area. Much of the coalbed in this area is under 600 to 1,400 feet of overburden. By correlation with data from the Pittsburgh coalbed, the gas content at depths of this order is estimated to be between 140 to 300 cf/ ton of coal, for a total of 190 to 400 billion cubic feet of methane in this coalbed in Fayette County.

Jan 1, 1977

By John C. Edwards

A computer code for laminar, steady-state, incompressible, two-dimensional flow developed by Gosman (2)3 was modified by the Bureau of Mines to calculate shock (minor) loss at the intersections of ventilation ducts. Turbulent flow was simulated using laminar flow equations and an appropriate wall shear stress. Results of the calculation showed good agreement with the experiment.

Jan 1, 1977

By C. H. Elder, Fred N. Kissell, S. D. Maksimovic

The Bureau of Mines evaluated the hydraulic stimulation of a gob-degasification borehole to determine if this procedure would aid in degasifying a longwall panel. The stimulated borehole did not degasify the longwall panel as expected either before or after mining of the panel started. It reduced the underground methane emission only 11 pct, considerably less than the reductions effected by two unstimulated boreholes in the same panel. Some probable reasons for the reduced methane flow from the hydraulically stimulated borehole are very low reservoir gas pressure, location of hydraulically stimulated zones within the grouted casing, a casing break caused by lateral shifting, possible vertical movement of rock strata during caving, grouting of a 4-inch pipe blocking three stimulated zones, plasticity of shales, and possible hole damage by swelling of water-sensitive minerals. The borehole was also located between two second-mined areas, which may have allowed partial degasification of the overburden and the coalbed in advance of mining. Finally, a period of 3 months is probably not long enough for the borehole to degasify the overburden before mining.

Jan 1, 1977

By S. D. Maksimovic

The Bureau of Mines evaluated the hydraulic stimulation of a gob-degasification borehole to determine if this procedure would aid in degasifying a longwall panel. The stimulated borehole did not degasify the longwall panel as expected either before or after mining of the panel started. It reduced the underground methane emission only 11 pct, considerably less than the reductions effected by two unstimulated boreholes in the same panel. Some probable reasons for the reduced methane flow from the hydraulically stimulated borehole are very low reservoir gas pressure, location of hydraulically stimulated zones within the grouted casing, a casing break caused by lateral shifting, possible vertical movement of rock strata during caving, grouting of a 4-inch pipe blocking three stimulated zones, plasticity of shales, and possible hole damage by swelling of water-sensitive minerals. The borehole was also located between two second-mined areas, which may have allowed partial degasification of the overburden and the coalbed in advance of mining. Finally, a period of 3 months is probably not long enough for the borehole to degasify the overburden before mining.

Jan 1, 1977

By David H. Yee

Because of environmental concerns, the Bureau of Mines investigated an anhydrous chlorination process for the recovery of copper from chalcopyrite, Pelletized concentrate was reacted continuously with chlorine in a vertical shaft reactor at 550° to 750° C to extract copper-iron chlorides and elemental sulfur. The resulting molten metal chlorides drained from the reactor and collected in a receiver while sulfur distilled from the top and condensed in a separate unit. The tests were conducted in a 10-cm-diam reactor constructed of glass and in l5-cm-diam reactors constructed from various refractory materials. A high-alumina ramming mix exhibited the best resistance to molten metal chlorides and elemental sulfur in chlorine atmospheres. A reactor made with this high-alumina refractory was operated for 55 hr under actual chlorinating conditions without suffering any deterioration. Tests results show that more than 96 pct of the chalcopyrite was converted to copper-iron chlorides and elemental sulfur. Good separation of the metal chloride and sulfur products was achieved. After filtration, elemental sulfur of greater than 99 pct purity was obtained.

Jan 1, 1977

By Noel N. Moebs

The Bureau of Mines investigated severe coal mine roof support problems along a section of main entries in the Pittsburgh coalbed in southwestern Pennsylvania to identify the causative factors. The mine roof was examined in detail, and various sedimentary structures are described that contributed directly to irregular and unstable roof. Small-scale paleochannels, scours, and related slickensides were identified as the leading cause of bad roof, and isopach maps were prepared to illustrate a method whereby the presence of these structures could be inferred in advance of mining. Probably second in importance was the occurrence of relatively incompetent flaggy, poorly cemented sandstone, weakened by coal and micaceous laminea. No effect of in situ stresses on roof stability was detected.

Jan 1, 1977

By David C. Oyler, Herbert H. Fields, William P. Diamond

A 3-inch pilot hole was directionally drilled to intercept the Freeport coalbed horizon horizontally at Mather, Pa., as part of a Bureau of Mines degasification project. The original concept was to continue the horizontal drilling into the coalbed, after the initial intercept, with a total of three horizontal holes eventually being completed. However, the erratic thickness (0.0 to 4.3 feet) of the Freeport coalbed at Mather was not sufficient to sup- port the horizontal drilling degasification technique, and the site was abandoned after six attempts to locate adequate continuous coal thicknesses. The drilling of coreholes in the immediate vicinity of proposed well paths to evaluate coal thickness is essential prior to future slant hole operations. Although mechanical failures of the new directional drilling equipment, mud pump and rig breakdowns, directional control problems, and exploratory horizontal drilling in the Freeport horizon more than doubled the anticipated cost of the pilot hole, continuing improvements in directional drilling equipment and techniques should significantly reduce the time and costs of future drilling operations.

Jan 1, 1977

By William P. Diamond

A 3-inch pilot hole was directionally drilled to intercept the Freeport coalbed horizon horizontally at Mather, Pa., as part of a Bureau of Mines degasification project. The original concept was to continue the horizontal drilling into the coalbed, after the initial intercept, with a total of three horizontal holes eventually being completed. However, the erratic thickness (0.0 to 4.3 feet) of the Freeport coalbed at Mather was not sufficient to support the horizontal drilling degasification technique, and the site was abandoned after six attempts to locate adequate continuous coal thicknesses. The drilling of coreholes in the immediate vicinity of proposed well paths to evaluate coal thickness is essential prior to future slant hole operations. Although mechanical failures of the new directional drilling equipment, mud pump and rig breakdowns, directional control problems, and exploratory horizontal drilling in the Freeport horizon more than doubled the anticipated cost of the pilot hole, continuing improvements in directional drilling equipment and techniques should significantly reduce the time and costs of future drilling operations.

Jan 1, 1977

By Jack A. Touseull

The Bureau of Mines has developed a simple stereographic method of analyzing the orientation of single and intersecting planes of weakness in vertical pillars of parallel symmetry. From this method, it can be determined if planes of weakness transect the full horizontal cross section of a pillar. A major finding resulting from this method was that intersecting planes of weakness can transect the full horizontal cross section of a pillar even though the individual planes do not. This paper provides step-by-step instructions for using this method.

Jan 1, 1977

By Jack E. Fraley

In this Bureau of Mines study, sealants containing mineral wool, cement, etc, were sprayed through dry-process equipment that propels dry material pneumatically to the water-adding nozzle. Advantages over slurry applications include no mixing, no extensive cleanup, and freedom from hardened cement in equipment should power be lost. Sealants with large mineral wool nodules (>l-inch) were sprayable at rates to 900 square feet per hour for 1/2-inch thickness with little dust and smooth material flow through equipment, but they were weak for mine use, Materials containing small wool nodules (1/4-inch) were stronger but tended to plug lines because the nodules were inadequately separated in the shredder. Increasing the dedusting oil also increased line plugging by holding the nodules together in larger lumps. Best results were obtained using a 3/4-inch-nodule wool with cement binder, which provided both smooth flow through the machine and adequate strength.

Jan 1, 1977

By Richard E. Hucko

The bureau of Mines conducted a laboratory scale investigation of the process of selective flocculation with the objective of developing a method to effect separations on suspensions consisting predominately of ultra-fine-size (minus 400-mesh) particles of coal and refuse. Selective flocculation of coal from coal-refuse slurries could be achieved with a wide variety of reagents. Typically as much as 15 to 20 weight-percent of high-ash solids (70 to 80 percent ash) could be retained in suspension. The flocculated sediment remained a high-ash product, however, and would require further treatment to be regarded as clean coal. No combination of reagents and conditions led to selective flocculation of the refuse component. The dispersing agent was found to be the critical factor; dosages of 3 to 8 lb/ton2 were necessary to stabilize the suspension for subsequent selective flocculation. In addition, most of the dispersants that worked were most effective at substantially elevated pH (11 or so). It was concluded that this process would be prohibitively expensive and, because of yield and quality constraints, it would be of questionable utility in today's coal preparation industry.

Jan 1, 1977

By Theodore Christos

The Bureau of Mines sponsored an investigation of the thermal oxidative degradation characteristics of selected ingredients employed in the formulation and manufacture of conveyor belts. This work was done to supplement similar studies of samples from finished conveyor belts and thus provide basic data for correlation of the potential toxic behavior of a finished belt with that of the individual ingredients. This report covers the study of (1) basic polymers (styrene-butadiene, neoprene), (2) reinforcing fibers (Nylon 6,6, Dacron, viscose rayon), (3) flame-retardant plasticizers (tritolyl phosphate-isomeric mixture, tri-p-tolyl phosphate, tributyl phosphate, tris (dichloropropyl) phosphate), (4) plasticizers (diphenylphtha1ate, di-(2-ethylhexyl) sebacate), and (5) a vulcanization accelerator (2-mercaptobenzothiazole).

Jan 1, 1977

By d&apos, Dennis V. Andrea

The Bureau of Mines and El Paso Mining and Milling Co. conducted a cooperative in situ leaching research program at the Emerald Isle mine near Kingman, Ariz. The objective of this research was to develop in situ leaching methods for 200,000 tons of ore exposed in the pit bottom and also 3,000,000 tons of ore under 200 feet of overburden adjacent to the pit. The research included core drilling for fragmentation analysis, inplace permeability testing, seismic surveys, blasting tests, blast vibration measurements, inplace leaching, and ground water monitoring. A l5,000-ton test area in the pit bottom was blasted and leached inplace for 117 days. This successful test was followed by leaching 100,000 additional tons of unblasted pit bottom ore. Two test blasts, under 205 feet of overburden and extending to 290 feet, were detonated in an area near the open pit. The second blast was detonated because the first blast did not create adequate permeability for leaching. Pit bottom leaching was discontinued and the test area under 200 feet of overburden was not leached because the company terminated operations at the Emerald Isle mine. Based on the research completed, an expanded in situ leaching system was designed, but not implemented, to recover copper from a 1,500,000-ton area at the Emerald Isle mine.

Jan 1, 1977

By Robert F. Droullard

The Bureau of Mines has investigated techniques of using gross alpha or beta detectors to continuously measure working levels. Both methods measure radioactive particulates collected on a filter paper using a constant airflow. Inherent-error studies indicate a value of about ±3 percent for the gross alpha method and about ±8 percent for the beta method in typical mine atmospheres. However, the beta method avoids problems associated with alpha detectors and is therefore more useful. Applications of these continuous working-level detectors include work area monitoring of exposure levels in underground openings, such as mines and caves, and calibrating personal dosimeters exposed over extended time intervals.

Jan 1, 1977

By Byron S. Gottfried

This Bureau of Mines report presents a method for combining the distribution curves at different specific gravities of separation, for a given piece of coal-cleaning equipment and a given raw coal feed, into a single, generalized distribution curve normalized with respect to specific gravity and, therefore, independent of the specific gravity of separation. Illustrative generalized distribution curves, based upon Bureau of Mines collected data on industrial operations, are presented for five different types of coal-cleaning equipment. The well-known concept of probable error is extended to the generalized distribution curve. It is shown that the conventional probable error is directly proportional to the specific gravity of separation. A number of sample calculations, illustrating the use of the generalized distribution curve and generalized probable error, are presented in the appendix.

Jan 1, 1977

By Kenneth J. Miller

The Federal Bureau of Mines coal-pyrite flotation process has been modi¬fied to produce a concentrated final clean coal slurry underflow that could be dewatered more effectively by filtration or centrifugation. This change was accomplished by redesigning the Bureau's two-stage flotation pilot plant facility and running the second-stage flotation step with undiluted or only partially diluted first stage coal froth concentrate. Results of the pilot plant flotation tests showed that substantial sulfur reduction could be achieved by flotation with undiluted pulp but some dilution is recommended for maximum selectivity. For example, coal-pyrite flotation in slurry of 25 percent solids yielded clean coal products analyzing as low as 0.7 percent pyritic sulfur and froth reject products containing slightly over 3.0 percent pyritic sulfur. In comparison, coal-pyrite flotation with pulp diluted to about 12.5 percent solids yielded clean coal containing as low as 0.4 percent pyritic sulfur and froth reject of 5.6 to 6.7 percent pyritic sulfur. Despite the need for some dilution, it was concluded that excellent coal-¬pyrite flotation selectivity could be achieved without diluting to 6 or 7 per¬cent solids as done in the earlier work. Thus the economics of coal-pyrite flotation would be improved by easing clean coal dewatering problems and by reducing second-stage flotation cell volume requirements.

Jan 1, 1977