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By W. A. Barrows, Carl Zapffe

Jan 1, 1913

People in economically developed societies demonstrate inherent human care for Earth and want to stop pollution. Yet efforts to clean Earth seem bogged in confusion from wildly contradictory and alarmist predictions of æclimate crisisÆ. Supposed experts openly disagree yet weÆre told thereÆs universal agreement humans are causing æthe end of life as we know itÆ. The turmoil combines with peopleÆs feelings of fear, guilt, anger, hopelessness and even resignation and apathy to trigger æclimate alarmÆ. The paper enables people to rediscover clarity, hope and support for Earth by understanding how climate alarm and confusion were created and how they actually increase pollution. Many people seem to think global warming is as serious as pollution and worry that questioning alarm will enable pollution. Yet theyÆre different. We need be even more concerned about climate alarm because history shows repeatedly that when buried by ignorance and panic real problems grow overwhelming. Environmental credibility is endangered by confused politicians and sensationalist media. When weÆre willing to re-evaluate what weÆve been told we replace fear and confusion with facts and freedom to identify opportunities. Combining this with practical understanding of human behaviour and leadership enables opportunities to be identified and action taken. The paper shows how confident, informed leadership leads and supports higher productivity and effective care for the natural environment.

Jan 1, 2009

By P. K. N. Raghavan

This paper identifies potential technologies for Carbon dioxide abatement from the mining and metal industry with special reference to the Aluminium industry. Mine reclamation could contribute to this effort to successfully reach the greenhouse gas (GHG) emissions reduction commitments for a nation. An overview of GHG production by the mining and metal industry together with a review of principles used to set the context in which specific options for GHG reduction are described. Options for GHG reduction in the mining and metal industry include reforestation, Addition of soil amendments or neutralizing agents, CO2 capture and storage, initiatives towards energy reduction, waste heat recovery and alternative energy use. An analysis and quantification of the potential GHG reduction of potential carbon sinks and sequestration options for the mining and metal industry are provided. Cost estimates for different options are provided. The paper also identifies sources that could fund research regarding GHG reduction options. The paper concludes with recommendations.

Jan 1, 2011

By L. Schernikau, W. H. Smith

Oil, coal, and gas account for approximately 80% of global primary energy, but only a portion of total airborne CO2 eq (approx. 35% at GWP20 to 65% at GWP100), even though they account for 95% of total measured CO2 emissions. The benefits of these energy sources, as well as their related costs, are not all incorporated in current energy policy discussions. Global greenhouse gas policies must include documented changes in measured airborne CO2 eq to avoid spending large amounts of public funds on ineffective or sub-optimal policies. The authors examined airborne CO2, which is less than half of emitted CO2, as well as reported CH4 emissions and the global warming potential of CH4 as published by the IPCC for coal and natural gas. The surprising conclusion is that surfaced-mined coal appears ‘better for the climate’ than the average natural gas, and all coal appears beneficial over LNG. Therefore, current CO2-only reduction policies and CO2 taxes are leading to unintended consequences and the switch from coal to natural gas, especially LNG, will not have the desired impact of reducing predicted future global warming; in fact, quite the contrary. A large portion of anthropogenic global warming is attributed by the IPCC and IEA to CH4, but it must be noted that CH4 emissions from natural sources and from agriculture account for approximately 40% and 25% of annual global CH4 emissions respectively. Energy accounts for about 20% of documented CH4 emissions. CO2 contributes only approximately 35% of annual airborne anthropogenic GHG emissions after accounting for CH4, over a 20-year horizon. At a 100-year horizon, the contribution of CO2 increases to approximately 60%. Energy policies that do not consider all GHG emissions along the entire value chain will lead to undesired economic and environmental distortions. All carbon taxation and CO2 pricing schemes are incorrect and need to be revised. At IPCC’s GWP20 an approximately 2%1 higher loss of CH4 across the value chain prior to combustion of natural gas versus coal will lead to ‘climate parity’ of coal with natural gas. According to public data, natural gas value chains have high CH4 and undocumented CO2 losses. On a global average, using only IEA-documented CH4 data, natural gas emits approximately 15% more CO2 eq than surface-mined coal, over a 20-year horizon. This difference will increase as the use of shale gas and LNG expands. Investors should support all energy systems in a manner that avoids an energy crisis, including intermittent renewable energy systems where they make sense. If CO2 emissions need to be reduced, one of the most effective ways would be to install ultra-supercritical power plants with CCUS technology. However, the undisputed benefits of increased CO2 concentrations in the atmosphere because of its promotion of photosynthesis and plant growth effects (fertilization) need to be considered in energy policy decisions as well. The authors suggest that future research and development should concentrate on reducing net emissions from fossil fuel power plants and providing cost-effective and reliable new conventional power generation capacity, utilizing clean coal and clean natural gas technology.

Mar 2, 2022

By R. E. Cuthbertson

AN early appreciation by the management that Climax ore presented a challenging problem of economic concentration was responsible for the establishment, in June 1926, of an ore-testing department at the experimental plant of the Colorado School of Mines at Golden, some ninety miles from Climax. An engineering office was later organized in the same community for the design of all ore-treatment units erected at Climax during the period of rapid growth. Work of the ore-testing and design staffs was effectively co-ordinated under a common head. The primary reason for having the ore-testing and plant design departments in Golden, was to place these activities under the able supervision of A. J. Weinig, consultant for the Climax Molybdenum Co., and director of the experimental plant. A secondary consideration was the availability of excellent facilities for research in ore dressing in a highly favorable environment. Concentration of molybdenite by flotation from an ore of simple mineral composition does not appear, superficially, to present a serious problem in ore dressing but experience belies this apparent simplicity. The molybdenite content of average Climax ore is low and it is finely

Jan 1, 1946

By C. Breeds, K. Jeremiah, E. Jennings

Washington State has a well developed set of blasting regulations which have been promulgated by the Department of Labor using extensive stakeholder input, not only from citizens but also from manufacturers and representatives of IME, blasters in charge, blasting engineers, blasting companies, local and federal law enforcement agencies, fire officials, and local and state government representatives. WAC 296-52 therefore provides a foundation or platform for developing city ordinances for Washington State cities should a City wish to do so. On the other hand, Oregon’s code is based on OSHA 1926, Subdivision U, Blasting and the Use of Explosives which provides scant direction regarding the modern use of explosives. Reference is also made to ODOT Section 00335 - Blasting Methods and Protection of Excavation Backslopes. This paper examines two separate programs that have been developed by two Cities, one in Washington State and one in Oregon to further regulate blasting inside City limits and discusses why the lack of a regulatory foundation made one approach more difficult than the other. One of the authors was retained by the City of Kennewick, WA to develop their ordinance and has more recently followed and reacted to a pending ordinance for the City of Redmond, Oregon. The paper will compare and contrast the different approaches and comment on the reaction from both Blasters and the public. We also present a case study that involved blasting in an urban area of Oregon to prepare a foundation for a water tank. Controlled Blasting was carried out within 70-ft of residencies and within a community that had expressed reservations regarding blasting even though the work would make a significant contribution to the betterment of the community. Pre-construction surveys of residencies located in a large area surrounding the site were performed and a well-planned blasting program was carried out. Residencies were subject to vibration levels that were monitored using six seismographs that surrounded the site and these units measured vibration levels that were significantly lower than allowed by statute. There were complaints triggered by individuals reactions to blast vibrations which validated commonly held models of human perception but no damage was caused by the Blasting.

Jan 1, 2024

By J. A. Herbst, Z. Rogovin, Lo. Y. C., K. Rajamani

Knowledge of the amount of time material spends in a continuous mill in a closed grinding circuit is essential for circuit performance analysis and scale-up design. A convenient method for acquiring this information involves the use of pulse tracers in residence time distribution (RTD) experiments. In typical grinding circuit experiments, RTD measurements are done by injecting a pulse tracer into the mill inlet and detecting it in the circuit exit. In this article, an easy mathematical method for calculating mean residence time and the degree of mixing of material in a mill present in a closed grinding circuit is developed. There are no restrictions on the location of the tracer injection or detection points with this method. Any convenient location in the circuit can be chosen without affecting the residence time distribution measured. The analysis of impulse response data obtained from several commercial grinding circuits using this method is presented.

Jan 1, 1988

By B. Friedrich, A. Weyhe, H. Heegn

"Nickel-metal hydride batteries (Ni-MH) are storers of electrochemical energy, which have a higher specific storage capacity than lead or nickel-cadmium batteries. The demand for Nickel-metal hydride batteries is increasing rapidly since their market launch in the early 1990’s. Today there is no suitable and sustainable recycling process to recover nickel, cobalt and rare-earth metals. The discarded batteries are used today in the steel industry as alloy material because they contain nickel. Cobalt and rare-earth metals (RE) are lost; they are non-recycleable.In a German governmental funded research project, IME Aachen, ACCUREC Mühlheim and UVR-FIA Freiberg are cooperating in processing as well as in creating a feasibility study. The target of this project is the development of a new recycling process for metal recovery from Ni-MH-batteries. The proposed process described in this paper consists of a combination of mechanical, pyrometallurgical and hydrometallurgical processing steps. This process is capable of treating all types of Ni-MH-batteries. After comminution steel and organics are separated. The separated Ni-MH is smelted in an electric arc furnace. The products are a nickel-cobalt alloy and a slag phase enriched with rare-earth oxides for further treatment to ‘mischmetal’. Both the Nickel-Cobalt alloy and the ‘mischmetal’ will be directly used in battery production."

Jan 1, 2003

By Joseph L. Petrillo

In July 1997, Kvaerner Environmental signed a unique contract with Echo Bay Alaska called the Transfer Risk and Accelerate Closure (TRAC). The contract called for Kvaerner to assume the responsibilities and obligations associated with closeout of the Alaska-Juneau (A-J) Mine. Kvaerner is an international engineering and construction company with global interdisciplinary experience in the mining industry and environmental remediation. Echo Bay’s requirements called for Kvaerner to: •Provide a fixed price for closure with no change orders. •Negotiate, prepare and implement a final closeout plan as outlined by Echo Bay. •Complete a closure program that exceeded current regulatory requirements. •Improve, expand and maintain a proactive public and community relations program. •Hire Echo Bay employees where possible. •Provide adequate performance guarantees and judicial relief of environmental claims.

Jan 1, 1999

By J Crosbie, M Lord, R Bitencourt, P Defferrard

The MMG Century mine, which is the largest zinc/lead mine in Australia, began operating in 1999 and ceased mining from the open pit in July 2015, with processing completed in early 2016. Closure plans were developed from 2006, and detailed planning for closure commenced in early 2011 with the appointment of a dedicated closure planning resource. The site will continue to be managed during the active and passive closure phases to complete rehabilitation commitments and demonstrate that closure completion criteria have been achieved.Completion of the mining/processing phase of the project provides an opportunity to reflect on successes, missed opportunities and lessons learnt with respect to planning and execution of mine closure. This paper highlights examples of success at Century and also identifies key learnings and areas for improvement in progressive closure outcomes. Specific examples examine mine planning and execution involving bulk movement of waste rock and construction of permanent waste encapsulation landforms. The paper also provides recommendations for other sites that are planning for closure.Decisions made during the operational phase of the project life can result in a significant increase in closure liability and reduce the likelihood of achieving lease relinquishment. Likewise, it is of paramount importance to assess the consequences and thoroughly understand the risks associated with changes or deferral of closure plans, progressive rehabilitation targets and closure related key performance indicators.CITATION:Lord, M, Bitencourt, R, Crosbie, J and Defferrard, P, 2016. Closure planning lessons Learnt from the Century mine, in Proceedings International Mine Management Conference, pp 207-216 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jun 22, 2016

By B. Balamurugan, D. J. Sellmyer, J. E. Shield, G. C. Hadjipanayis, Damien Le Ror, R. Skomski

"Rare-earth transition-metal (R-TM) alloys show superior permanent magnetic properties in the bulk, but the synthesis and application ofR-TM nanoparticles remains a challenge due to the requirement of high-temperature annealing above about 800 °C for alloy formation and subsequent crystalline ordering. Here we report a single-step method to produce highly ordered R-TM nanoparticles such as YCO5 and SmCO5, without high-temperature thermal annealing by employing a cluster-deposition system, and we investigate their structural and magnetic properties. Nanoparticles of size = 10 nm are monodispersed (s /d ~ 0.15) and have Hc values at T = 300 K of 8.0 and 4.5 kOe for YC05 and SmC05, respectively. Alignment of the easy axes is performed via a field applied to the clusters before deposition. These processing steps are highly desirable to create and assemble R-TM nanoparticle composites for future permanentmagnet applications.IntroductionMagnetic nanoparticles with high magnetocrystalline anisotropies (Ki > 1 MJ/m3) are required for permanent-magnet, recording-media, and other significant applications [1-3]. In this regard, bulk rare-earth transition metal alloys (R-TM) especially RC05 (R = Y and Sm) crystallized in the hexagonal CaCu5-type structure have shown a large Ki = 5 MJ/m3 (YC05) and 22 MJ/m3 (SmCo5) along with an appreciable saturation-magnetic polarization (Js, > 10 kG) and high curie temperatures (Tc > 1000 K) [2]. The challenges in controlling the size, sizedistribution, phase purity and crystalline ordering, however, limit the research on RCo5 nanoparticles [4,5]. The conventional arc-melting technique requires high-temperature annealing for alloy formation and subsequent crystalline ordering, which causes excess growth and thus results in nanocrystalline powders of particles sizes larger than 30 nm [6, 7]. Low-temperature wet-chemical techniques yield SmC05 nanoparticles of sizes smaller than 20 nm [5], but the control of phase purity is challenging due to the presence of surfactants and formation of other secondary phases [8]."

Jan 1, 2012

By P. Dauphin

"CANMET’s Mining and Mineral Sciences Laboratories have developed the Canadian Mining Technology Network (CMT-Net), a website to provide industry with up to date information on technologies in several areas. This paper gives background on the Mineral and Metal Processing sector, describes the steps leading to the development of the websites strategy and gives a tour of CMT-Net. IntroductionThe government of Canada is developing a strategy aimed at fostering the development of value-added activities in the area of mineral and metal processing (MMP). Natural Resources Canada (NRCan) and Industry Canada will partner in delivering on this strategy. Instrumental in defining the main thrusts of the value-added strategy was a series of consultations held across Canada with representatives of companies and organizations active in the sector. The objective of the consultations was to identify barriers to the development of activities which add value in the sector, as well as point to positive factors.Following the consultations, a discussion paper was produced, “From Mineral Resources to Manufactured Products: Towards a Value- Added Mineral and Metal Strategy for Canada” (Natural Resources Canada, 1998). The paper reviews the sector’s structure and main statistical information, lists some of the positive factors and barriers to value-added activities and defines a new partnership between industry and government that will lead to more valueadded activities. The main objective of the paper is to serve as a discussion document between stakeholders during the development of the strategy."

Jan 1, 1999

By Marcia Harris, Richard Mainiero

The New York State Department of Transportation recently commenced highway widening and drainage improvement projects in Clarence and Amherst, NY. Drainage improvements including the installation of storm sewer lines required excavation to a depth of 2.5 m (8.2 ft). In September 2002, NYSDOT stopped further blasting when 800 ppm CO was detected in the basement of a house near the blasting site. At the insistence of NYSDOT, the general contractor developed a new blast plan with the assistance of an environmental consultant. The plan provided for the installation of multi-gas monitors in buildings of special concern and/or with basements and residential type CO monitors in all other buildings within 100m (330 ft) of the blast. The multi-gas monitors would be remotely monitored. The plan provided action levels which would ensure public safety. The blast design was also modified to allow for better venting of CO. Blasts were limited to 20 ft lengths. The overburden was to be removed from the rock and blasting mats put in place to prevent flyrock. Approximately twenty feet of trench adjacent to the blast was left open to allow ground movement and gas release. The use of CO monitors was effective to alert occupants of a building to the presence of CO. The most effective appeared to be the residential type CO alarms with digital readouts. They were simple and easy to use and allowed the public to participate in the process. False alarms were repeatedly received with the more sophisticated instrumentation. Residential type CO monitors are preferable to warn people near blast sites. More sophisticated instrumentation should be avoided unless personnel are experienced in its use. A general overview of the blasting and monitoring is presented and discussed. The use and effectiveness of residential type CO monitors and multi-gas monitors are discussed.

Jan 1, 2004

By Richard J. Mainiero, Marcia L. Harris

The New York State Department of Transportation recently commenced highway widening and drainage improvement projects in Clarence and Amherst, NY. Drainage improvements including the installation of storm sewer lines required excavation to a depth of 2.5 m (8.2 ft). In September 2002, NYSDOT stopped further blasting when 800 ppm CO was detected in the basement of a house near the blasting site. At the insistence of NYSDOT, the general contractor developed a new blast plan with the assistance of an environmental consultant. The plan provided for the installation of multi-gas monitors in buildings of special concern and/or with basements and residential type CO monitors in all other buildings within 100m (330 ft) of the blast. The multi-gas monitors would be remotely monitored. The plan provided action levels which would ensure public safety. The blast design was also modified to allow for better venting of CO. Blasts were limited to 20 ft lengths. The overburden was to be removed from the rock and blasting mats put in place to prevent flyrock. Approximately twenty feet of trench adjacent to the blast was left open to allow ground movement and gas release. The use of CO monitors was effective to alert occupants of a building to the presence of CO. The most effective appeared to be the residential type CO alarms with digital readouts. They were simple and easy to use and allowed the public to participate in the process. False alarms were repeatedly received with the more sophisticated instrumentation. Residential type CO monitors are preferable to warn people near blast sites. More sophisticated instrumentation should be avoided unless personnel are experienced in its use. A general overview of the blasting and monitoring is presented and discussed. The use and effectiveness of residential type CO monitors and multi-gas monitors are discussed.

By Kuganathan V

The processing of black coal in Australia segregates waste in the form of coarse reject and fine tailings. The coarse reject is relatively easy to handle, while the tailings can be problematic. Conventionally, the two waste materials are disposed of separately, the coarse reject in dumps, and the tailings in man-made containments. Aqueous tailings slurry is pumped to a 'wet' tailings storage, where the fine particle size of the tailings limits dewatering. Their low bearing capacity and high compressibility result in tailings deposits being difficult to rehabilitate. Disposing of the waste streams separately moves away from the heterogeneous mixture in the undisturbed ground, and concentrates potential problems with each waste stream. The feasibility and desirability of the co-disposal of tailings and coarse reject by combined pumping is demonstrated. This technique is in operation at Jeebropilly Mine and is proposed for a number of other coal mines.

Jan 1, 1992

By Huayi Yin, Wang. Dihua, Wei Xiao, Xuhui Mao, Diyong Tang

"The world production of crude steel reached 1.55 billion tons in 2012,which generated ~2.5 billion tons of CO2. Electrochemical metallurgy especially through high temperature molten salt electrolysis with renewable electricity stands for a great opportunity for producing “green” metals. In recent years, electrolytic production of iron without emission of CO2 in different molten salt systems has been reported. A cost-affordable inert anode is the key to produce acceptable eco-friendly iron by the novel molten salt electrolysis processes. Based on the authors’ research, this paper will discuss iron production by molten salt electrolysis using a nickel alloy inert anode. On the other hand, the paper also covers a novel molten salt CO2 capture and electrochemical transformation (MSCC-ET) process, in which CO2 is effectively converted to value-added carbon and oxygen in a molten bath using a cost-affordable nonconsumable SnO2 anode.1. IntroductionEnergy and materials are cornerstones to support the development of human society. The traditional primary metal production, especially iron and steel, and electricity production are mainly based on the reactions between carbon (coal) and oxygen (represented by equations (1) and (2) respectively), which produce huge amount of CO2.MxOy + 0.5y C = x M + 0.5y CO2 (g) + Q1 ( 1 )C + O2 (g) = CO2 (g) + Q2 ( 2 )In 2012, the world production of crude steel reached 1.55 billion tons, of which 46.3 %, ~0.7165 billion tons were produced in China. Based on the average level of 1.7t CO2 emission per ton steel, more than 1 billion tons of CO2 generated from steel industry in China in the year. Besides the iron and steel industry, thermal power plant leads the CO2 emission in both USA and China. The total consumed electricity in China increased to 4959 billion kWh in 2012, ~70% of it was from coal fired power plant. The average CO2 emission for electricity production in the typical thermal power plant in China is around 0.78 kg kWh-1. It accounts for ~ 3.868 billion tons of CO2 emission from thermal power plant in 2012 in China."

Jan 1, 2014

By Mingming Zhang, Ramana G. Reddy

"Carbon dioxide (CO2) is one of the most common by-products produced during light metals production. It is considered to be the cause of greenhouse effects. Efficient reduction of CO2 can help minimize the rate of global warming and improving energy sufficiency. In this paper, a novel light metal production process was developed using ionic liquid electrolytes. This process has significant advantages compared to the traditional high temperature processes such as zero CO2 and CF4 emission, low energy consumption due to the low temperature operation and nonconsumable electrodes. Two types of anode materials (graphite, extruded carbon) were tested in electrolysis experiment. The results showed that both anode materials were stable (negligible weight loss). However, the extruded carbon was found to be superior to graphite in terms of current density and current efficiency. The calculated energy consumption for aluminum production was less than 10 kWh/kg at current densities up to 300 A/m2.IntroductionGlobal demand for ultra-light, ultra-strong, recyclable metals is growing as the world switches to low-emission vehicles, energy-saving devices and sustainable products. Aluminum demand is forecast to climb by 30 percent; magnesium demand by 200 percent, while for the emerging industrial light metal, titanium, the demand is expected to be at least double in the next decade. However smelting of light metals is the most energy intensive among all the steps of light metals production. For example, on an average it takes about 15.7 kWh of electricity to produce one kilogram of aluminum from alumina [1, 2, 3]. Advancements in energy efficiency have been steady, but slow, and most U.S. aluminum smelting production operates at 95% current efficiency. Besides high energy consumption, another major concern of the light metals smelting process is the emissions of greenhouse gases (GHG). Electrolysis green house gas emissions in the Hall-Héroult process can be split into three groups: 1) reduction reaction emissions, carbon dioxide (CO2) and carbon monoxide (CO); 2) process upset perfluorocarbons emissions; and 3) hydrogen fluoride (HF) formed from the moisture (H2O) present in the raw materials [2, 3]. Hydrogen fluoride gas can be captured and returned to the cells by the alumina dry scrubbing system used in modern facilities. A total of 5.31 kilograms of CO2 is generated from the reduction process for each kilogram of aluminum produced in the average U.S. primary facility. The perfluorocarbon emissions are related to the “anode effect.” If the concentration of alumina in the bath becomes too low, other reactions between the carbon anode and the bath occur and tetrafluoromethane (CF4) and hexafluoroethane (C2F6) are generated. These gases have high global warming potentials (GWP), which is a ratio developed to compare the ability of each greenhouse gas to trap heat in the atmosphere relative to carbon dioxide"

Jan 1, 2008

By Dolf Gielen

This paper discusses the results of a Western European energy and materials systems engineering study that analyses the impact of greenhouse gas (GHG) emission reduction on the future of the steel and aluminum industry. he technology selection will be significantly affected by future CO2 policies. The avail- ability of C02 removal and storage technology and the social acceptance of this strategy for GHG emission reduction is of key importance for the strategy selection. The use of coal based smelting reduction technologies is optimal in case of weak C02 policies or in case of strong C02 policies and low CO2 removal and storage costs. The selection of CCF or Corex technology depends on the penalty regime. However, if C02 removal proves to be problematic, CCF development fails and strong C02 policies are introduced, the gas based DRI production processes will become more attractive. In both cases, the energy efficiency of the iron and steel industry will further increase in the next decades. The impact of GHG emission reduction on aluminum prices and aluminum use can be significant. However contrary to common notions the aluminum production will be positively affected by GHG emission reduction, notwithstanding the currently high emissions in aluminum production. A combination of emission mitigation in production and significant GHG emission reduction effects further down the product chain cause this effect. A significant potential exists for improved materials efficiency. This potential is generally neglected in energy efficiency and CO2 reduction studies. However improved steel qualities are of similar importance for C02 emission reduction as increased energy efficiency. It remains to see if this potential will be used to its full extent in the next decades. Model calculations indicate that the impact of C02 policies on the competition with other materials will be limited. Greenhouse gas emission mitigation will have much more impact on materials production and waste handling than on materials consumption.

Jan 1, 1999

By M. R. Geer Olds, H. F. Yancey

THE increase in the number of coal-cleaning plants employing dense-medium processes occurring since 1946 is especially interesting when viewed historically. Both sand and magnetite were introduced as material for heavy mediums at about the same time, sand in the Chance process in 1921 and magnetite in the Conklin process in 1922, but from that point on their records diverge. The Chance process enjoyed a steady growth from its inception, whereas no additional magnetite plants were built in the United States for over 20 years. Then, following the close of the World War 11, magnetite was again introduced, this time with marked success. During the following years some 47 plants employing magnetite medium were built. This rapid growth of dense-medium cleaning has been concurrent with widespread adoption of full-seam mining on one hand and a return to a more competitive market on the other. At a time when changing mining practice has provided cleaning plants with dirtier coal and changing market conditions have simultaneously demanded a cleaner product, the industry has through necessity turned to improved preparation. The inherently greater sharpness with which dense-medium processes can separate coal from impurity is thus helping to hold the line against ever-increasing mining costs and at the same time assisting materially in retaining badly needed markets. Although dense-medium cleaning unquestionably offers a distinct advantage when the washing problem is difficult, other methods can provide almost equally high efficiency when the coal is easy to wash. Moreover, fine coal cannot yet be treated by heavy medium in a proved process, although the Driessen cyclone is in the pilot-plant stage. Most of the present types of dense-medium equipment have been in use only a few years, and the dearth of information in the literature concerning their performance characteristics is entirely understandable, Nevertheless this information is necessary if the process is to be intelligently applied to individual cleaning problems. Without data on the efficiency of a process in a particular type of separation, it is difficult to assess the advantage to be expected from it. Similarly, the role of particle size in heavy-medium separation is important in some cases, yet there is little published information on this aspect. To mention only one more of the numerous points on which essential information is lacking, the bearing of medium characteristics on performance has been discussed only in qualitative terms. It was with the hope of providing information on some of these points that the Bureau of Mines built a dense-medium pilot plant for cleaning coal at its Northwest Experiment Station in Seattle in 1950. The plant has been operated continuously since that time, and over 50 runs have been made on 7 coals exhibiting a wide range of washability characteristics. An idea of the magnitude of this work will be gained from the fact that examination of the plant products has involved some 600 float-and-sink separations and about 2500 ash determinations. A laboratory pilot plant is especially well adapted to investigate many aspects of performance because close control over test conditions can be exercised and because a large number of tests can be made rapidly. On the other hand, factors such as consumption of medium and other cost items can be investigated satisfactorily only in a commercial plant. Actually, the two forms of investigation should be complementary, with the laboratory work pointing the way for confirming tests in commercial units. Pilot Plant The dense-medium pilot plant employed for this work comprises a 24x30-in. drum-type separating vessel, a 12-in. densifier, a 12-in. magnetic separator, a 26-in. x 9-ft vibrating screen, and the necessary pumps and conveyors for handling materials. Arrangement of these units corresponds with the flowsheet used in most commercial plants, except that a thickener is not provided for the feed to the magnetic separator. Coal and refuse discharge from the separating drum to the vibrator, which is divided longitudinally down the center. Medium draining through the first 3 ft of the screen is recirculated directly to the drum. Sprays on the middle 3 ft of the screen rinse medium from the products, and the last 3-ft section is for dewatering. Dilute medium from the rinsing and dewatering sections is pumped to the magnetic separator, where magnetic solids are recovered. These are pumped to the densifier, from which they return to the medium-drainage sump by gravity through a demagnetizing coil. The drum-type separating vessel is a scale model of a commercial unit. Feed enters axially at one end of the drum just below the surface of the bath, and float material overflows through a circular opening at the other end. Particles sinking to the bottom of the bath are picked up by lifting flights bolted to the inner wall of the drum, elevated out of the bath, and sluiced to the vibrating screen. Baffles suspended in the bath prevent float material from entering the sink-lifting flights. About 8 gpm of medium is used to sluice the feed into the drum. An additional 15 to 24 gpm, depending upon operating conditions, is added through two pipes dipping into the bath behind the baffle on the side where the sink-lifting flights enter the bath. The bath available for separation is 2 ft long and 13 in. wide, giving an area of 2.08 sq ft. Depth of bath from the surface to the top of the sink-lifting flights, measured vertically below the axis, is 6 in.

Jan 1, 1954

By M. A. Elliott

The technology of gasifying coal to produce synthesis and pipeline gas has advanced significantly in the Past 20 to 30 years. This period has seen the extensive use of oxygen in coal gasification, the development of suspension gasification processes and fluidized-bed gasifiers, the operation of various gasification processes at elevated pressures, and operation of gasifiers under slagging conditions. These developments are discussed, and their application to commercial and pilot plant gasifiers is reviewed. Typical processes for synthesis gas production are described, and operating results are compared. Pipeline or high-Btu gas may be produced from coal either by catalytic conversion of synthesis gas to methane, or by the direct reaction of coal with hydrogen (hydrogasification) to produce a methane-rich gas. Neither of these methods has been applied commercially, but developments pertaining to each of them are reviewed, and general processing schemes are discussed. The use of coal as a raw material for manufacturing gas has a long and distinguished history. In fact, the gas industry began in the early 1800's when William Murdock demonstrated that it was feasible to produce and distribute gas made by retorting coal. Coal was used exclusively for gas manufacture until the middle of the 19th centruy, when Lowe invented the carbureted water gas process. In that process, coke was one of the raw materials used, so coal was still an important factor in gas manufacture. However the availability and relatively low cost of natural gas in the United States, and its widespread distribution by long-distance pipelines in recent years, has virtually eliminated the use of coal as a raw material for gas manufacture in this country. It should not be inferred from the foregoing that the technology of coal gasification has remained static in the United States and abroad. In fact, in the past two decades many new concepts have been developed in both the science and the technology of gasification. This progress has been a result of the considerable expansion in research on the fundamental chemistry and physics of gasification reactions, and in development work on gasification processes. This expansion in effort stems in part from increased interest in the use of gas as a raw material for the synthesis of chemicals and liquid fuels, and in part from the need to develop methods for gasifying coal and other solid fossil fuels to ensure a long-range supply of energy in the form of gaseous fuel. In these uses of gas, synthesis gas, a mixture of hydrogen and carbon monoxide in various proportions, is the starting material. It may be converted catalytically to gaseous and liquid hydrocarbons and other chemicals, or to hydrogen for use in hydrogenation or reduction reactions. Since coal is our most abundant fossil fuel, it is inevitable that one day it will regain its prominence as a raw material for gas manufacture. It is of interest, therefore, to consider the present status of gasification technology, directing attention particularly to advances made in recent years. Inasmuch as many comprehensive treatises l-3 and review4-7 of gasification technology are available, no attempt will be made in the present review to cover all processes in detail. Instead, the discussion will be concerned chiefly with typical processes embodying the advances that are most likely to be generally applied. ADVANCES IN GASIFICATION TECHNOLOGY For purposes of this discussion the starting point will be the conventional processes that were used for many years for the complete gasification of coal. These were: 1) carbonization in coke ovens followed by gasification of coke with air and steam in cyclic water-gas generators, and 2) fixed-bed air-blown producers. Both of these methods have obvious deficiencies when we consider that the ideal complete gasification process would be a single-stage, continuous

Jan 1, 1961