U.S. Department of the Interior
U.S. Geological Survey

Chemical Analyses of Coal, Coal-Associated Rocks and Coal Combustion Products Collected for the National Coal Quality Inventory

By Joseph R. Hatch,¹ John H. Bullock, Jr.,¹ and Robert B. Finkelman²

Executive Summary

In 1999, the National Coal Quality Inventory (NaCQI) project was initiated to address a need for quality information on coals that will be mined during the next 20-30 years. The primary objective of this project was to create a database containing comprehensive, accurate and accessible chemical information on the quality of United States coals. This objective was to be accomplished through maintaining the existing U.S. Geological Survey (USGS) publicly available coal quality database and expanding that database through the acquisition of new samples from priority areas. Analysis of the new samples using updated coal analytical chemistry procedures were performed by the USGS and commercial laboratories. Priority areas include those where future sources of compliance coal are federally owned. This project was a cooperative effort between the USGS, various State geological surveys, universities, coal burning utilities, and the coal mining industry. Funding support came from the USGS, Electric Power Research Institute and the U.S. Department of Energy.

Accomplishments include: 1) descriptive information and chemical analyses for 729 samples (697 coal and 32 coal combustion product samples); 2) identification of a mined coal that will be the basis for a new coal analytical standard, to be designated CWE-1 (West Elk Mine, Gunnison County, CO); and 3) five publications.

Introduction

In 1999, the USGS initiated the National Coal Quality Inventory (NaCQI) project to address a need for quality information on coals that will be mined during the next 20-30 years. At the time this project was initiated, the publicly available USGS coal quality data was based on samples primarily collected and analyzed between 1973 and 1985. The primary objective of NaCQI was to create a database containing comprehensive, accurate and accessible chemical information on the quality of mined and prepared United States coals and their combustion byproducts. This objective was to be accomplished through maintaining the existing publicly available coal quality database, expanding the database through the acquisition of new samples from priority areas, and analysis of the samples using updated coal analytical chemistry procedures. Priorities for sampling include those areas where future sources of compliance coal are federally owned.

This project was a cooperative effort between the U.S. Geological Survey (USGS), State geological surveys, universities, coal burning utilities, and the coal mining industry. Funding support came from the Electric Power Research Institute (EPRI) and the U.S. Department of Energy (DOE).

Project Organization

Prior to the start of the NaCQI project, State geologic surveys were invited to submit pre-proposals for geology-based sample collection programs needed to fulfill the goals of NaCQI for their state. The States were asked to include the following parameters in their proposals:

• Most significant coal beds/coal zones: their names, past production, and estimated resources.
• Number of operating mines in each bed/zone. Future plans for production.
• Estimated number of major/minor/trace element analyses available. For analyses done outside USGS, include source and timing.
• Estimated number of new samples needed. Opportunities to collect these new samples, including the number of existing and new mines and new areas to sample.
• List opportunities to obtain core from coal companies.
• Determine whether the coals are usually cleaned before shipping.
• Describe areas where there is little or no current mining, but where significant development is anticipated.
• Comments pertaining to regional or national impact of the beds/zones.
• Other comments concerning the major coal quality issues in that State and/or region.

Fourteen State organizations submitted pre-proposals, of these four proposals were selected for initial funding. These were from the State geological surveys of Colorado, Kentucky, West Virginia, and Wyoming.

In 2000, a second request for pre-proposals was made. This request was for research projects that would generate value-added information on the coal samples collected and/or on the data generated by the NaCQI project. Specifically, requests were for projects that would address the technological behavior (for example, fouling/slagging, combustion, washability), environmental impacts (trace element mobilization, disposal), or economic significance (byproduct recovery or use), or other relevant issues.

Two pre-proposals were received: one from the Indiana Geological Survey, the second from the University of Kentucky Center for Applied Energy Research; both were funded.

Budgetary constraints precluded a comprehensive, nationwide program of sample collection and analysis. Nevertheless, funding from the USGS, EPRI, and DOE and cooperation from State agencies resulted in the collection and analysis of a total of 729 samples of raw or prepared coal, coal-associated shale, and coal combustion products (fly ash, hopper ash, bottom ash and gypsum) from nine coal producing States.

Sampling

For the collection of NaCQI samples, the USGS requested that collection procedures conform to specific American Society for Testing and Material (ASTM) standards. USGS recommended sample collection procedures, briefly outlined below, are described in detailed in Stanton (1989). Application of precise techniques in sample collection helps to ensure that data from each analysis performed on the samples will be useful. For interpretations and comparisons of elemental compositions of coal beds to be valid, the samples must be collected so that they are comparably representative of the coal bed. The effects of differing sample types (see guidelines below) must be considered so that they represent comparable components of the coal bed.

Major steps in sample collection include the following:

1. Select appropriate sample type for collection conditions or opportunity.
2. Obtain sample according to specified procedures.
3. Document all aspects of the sample.
4. Transmit sample in appropriate air-tight containers and in a timely manner.
5. Provide full documentation.

Guidelines

A. Sample Types and Procedures

Samples from selected areas shall consist of the following types:

1. Channel (in accordance with ASTM Standard D4596)
2. Core (in accordance with ASTM Standard D5192)
3. Run-of-Mine or Preparation Plant Sample

[NOTE: Because the objective of NaCQI is to represent a mined product, a properly obtained conveyor-belt sample (ASTM Standard D2234, 1998c) is preferable to channel or core samples. However, if the mine uses a preparation plant to improve the quality of the product, then the sample should be taken from mechanical samplers at the Prep Plant in accordance with ASTM Standard D2234. In some cases, obtaining channel or conveyor-belt samples may not be possible, thus leaving core samples as the only practical alternative.]

Care should be exercised to ensure that the sample(s) represents the resource thickness. If only a part of the bed is being produced, the sample should represent that part. Sample documentation should clearly indicate the nature and extent of the sample and how much of the total bed thickness that the individual sample represents. For core and channel samples, mineral-rich layers greater than 1 cm shall be sampled separate from coal intervals. Run-of-mine or mine product samples shall include all material from the original sample:

B. Sample Descriptions

Include all possible descriptions of the sample. Provide, at a minimum, the locality of the sample; thickness or depth intervals of the sample(s); weather, if a factor; geophysical logs, if core; and any other quality information available from the owner or mine.

Analytical Chemical Methods

Coal characterization analyses listed in the Proximate and Ultimate analyses worksheet in the Excel workbook, NaCQI.xls, were performed by Geochemical Testing (Wyoming, Colorado, Pennsylvania, Tennessee samples), Standard Laboratories, Inc. (Oklahoma and Indiana samples), Detroit Edison (Colorado, ERP150), West Virginia Geological and Economic Survey, and the Kentucky Geological Survey, using methods detailed in American Society of Testing and Materials (ASTM) standards D3172, D5373, D4239, D3176, D3174, D1989, D2494, and D720 (ASTM, 2005).

Analyses for moisture, ash, and major-, minor- and trace-element contents were performed by the Inorganic Chemistry Laboratory of the USGS Energy Program in Denver, CO. Abbreviated USGS methodologies are outlined below. Details of the USGS analytical methods can be found in Bullock and others (2002). Over the project's lifetime (1999-2005), several of the analytical procedures were changed to more closely follow ASTM standards. Analytical standards mentioned below can be found in ASTM (2005).

Moisture

Results from coal samples are reported on an "as-determined" basis as described in ASTM method D3180. Moisture content for each sample is established so that sample submitters can calculate their analytical results to a "dry" basis. Moisture is determined by heating a one-gram coal sample for one hour at 107°C (ASTM standard D3173). After cooling in a desiccator, the coal is reweighed and the percent moisture is calculated. The moisture procedure did not change throughout the study. Analyses are presented both on the as-determined (remnant moisture) basis as well as dry basis in the Excel workbook, NaCQI.xls.

Ash Yield

Ashing improves sensitivity and accuracy by concentrating metals and removing chemical interferences from organic material. Approximately 25 grams of coal is weighed into a ceramic dish and heated in a furnace, following a specific thermal profile, to a final temperature of 525°C. After cooling, the remaining residue is weighed and the ash yield is determined. This ash was used in the analysis of major, minor, and trace elements. For samples ashed after May 2005 (ERP analytical jobs 434, 443, 449, 454, 455, and 650) ASTM standard D3174 was used to produce the ash for major and minor elemental analysis (the ashing procedure for trace elements remained unchanged). The increased furnace temperature (750°C) ensured a more complete ashing and conversion of carbonates to oxides, especially for high-rank coals.

Mercury

Mercury (Hg) is determined by digesting a coal or coal combustion product using a wet-oxidation extraction (D6414 method B). The sample is reduced in a continuous flow manifold, separated using a phase separator, and measured using cold vapor-atomic absorption spectrometry (CVAA). Samples analyzed after July 2004 (ERP jobs 434, 443, 449, 454, 455, and 650) were digested using an acid extraction (a variation of ASTM standard D6414 method A). The mercury was measured by CVAA using a flow injection analysis system. The preparation method change was necessary due to a change in instrumentation.

Selenium

Selenium (Se) procedures varied, depending upon the sample matrix. Coal samples are digested by refluxing a combination of three acids in an open Erlenmeyer flask. Rock and coal combustion byproduct samples are digested using a combination of five acids and heating overnight in open Teflon vessels. The resulting solutions are analyzed for selenium using hydride generation-atomic absorption spectrometry (HGAA). The selenium procedure did not change throughout the study.

Total Sulfur

Total sulfur (S) is determined by combustion using a LECO SC-432 Sulfur analyzer. Coal samples are weighed into a ceramic boat and burned in a tube furnace at 1350°C. Rock and coal combustion byproduct samples are weighed into a ceramic boat along with a promoting agent (to assist with combustion) and burned at 1450°C. Sulfur dioxide is released from the samples and measured by an infrared (IR) absorption detector. The sulfur procedure did not change throughout the study.

Chlorine

Chlorine (Cl) is determined utilizing a sample decomposition technique of Eshka's mixture (two parts magnesium oxide and one part sodium carbonate) combined with the test sample and heated in a furnace, following a specific thermal profile. The mixture is cooled and brought up to a final volume with de-ionized water. The solution is measured using an ion chromatograph (IC). After March 2005 (ERP jobs 434, 443, 449, 454, 455, and 650), samples were analyzed for chlorine using oxidative hydrolysis microcoulometry (ASTM standard D6721). This new technology allows for lower sample reporting limits (from 150 ppm (IC) to 10 ppm).

Multi-element Analysis

Forty-three major, minor, and trace elements were determined using a combination of inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS) on coal ash, coal combustion byproduct, and rock samples prepared using both a multi-acid and a sodium peroxide sinter decomposition technique. After May 2005 (ERP jobs 434, 443, 449, 454, 455, and 650), major- and minor-elements were digested following ASTM method D6349 and trace elements were digested using ASTM method D6357. The elements were still determined using a combination of ICP-AES and ICP-MS. Changing digestion techniques removed the potentially dangerous perchloric acid and sodium peroxide from the preparation procedures.

Results

Chemical Analysis

Identification and descriptive information and chemical analyses for the 729 samples are listed in the accompanying Excel workbook (filename NaCQI.xls). Information and data for the samples are distributed on five worksheets within that file as follows:

1. Identification numbers, locations and descriptive information.
2. Contents of major and minor oxides.
3. Contents of moisture, ash and major, minor and trace elements – remnant moisture basis.
4. Contents of moisture, ash and major, minor and trace elements – dry basis.
5. Proximate, ultimate, calorific value, forms-of-sulfur, etc. analyses.

Sample distribution is as follows:

1. Northern Great Plains Coal Province
   • Wyoming – 107 samples
2. Rocky Mountain Coal Province
   • Colorado – 56 samples
   • Wyoming – 11 samples
3. Interior Coal Province
   • Oklahoma – 8 samples
   • Illinois – 11 samples
   • Indiana – 242 samples
   • Western Kentucky – 29 samples
4. Eastern Coal Province
   • Eastern Kentucky – 35 samples
   • Pennsylvania – 33 samples
   • Tennessee – 10 samples
   • West Virginia – 187 samples

West Elk Coal Analytical Standard (CWE-1)

One derivative product resulting from the NaCQI sample collection and analytical program was the creation of a new coal reference standard. The USGS, in cooperation with Quality Associates International (Ontario, Canada), which operates a program called CANSPEX, identified a need for a reference material that is a high-volatile-B or high-volatile-A bituminous coal (minimum of 13,000 Btu/lb, moist, mineral-matter-free basis) with low contents of ash yield and sulfur, and very low, but detectable contents of chlorine, mercury, and other trace elements.

Based on chemical analyses of four coal samples collected by the Colorado Geological Survey (CGS) from the West Elk Mine near Somerset, CO, the coal produced at the West Elk Mine was identified as having a chemical composition that closely matched the requirements for the new coal reference material.

In April, 2003, the USGS and the CGS collected about 1000 pounds of coal from the West Elk Mine. This coal has been crushed, ground, and split. The chemical analysis of the new coal standard is now in the final steps of certification.

Publication List

Finkelman, R.B., and Repetski, J.E., 1999, National Coal Quality Inventory (NaCQI) and U.S. Geological Survey Coal Quality Databases: U.S. Geological Survey Fact Sheet 0120-99 (URL: http://pubs.usgs.gov/fs/fs-0120-99/fs-0120-99.pdf).

Hower, J.C., Mastalerz, M., Mardon, S.M., Lis, G. and Drobniak, A., 2003, Distribution of trace elements in coal combustion products: studies of the combustion of single source coals: paper 27 in Fifteenth International American Coal Ash Association Symposium on the Management and Use of Coal Combustion Products, St. Petersburg, Florida, 27-30 January 27-30, 2003, CD-ROM.

Mardon, S.M., and Hower, J.C., 2004, Impact of coal properties on coal combustion by-product quality; examples from a Kentucky power plant: International Journal of Coal Geology v. 59, p. 153-169.

Mastalerz, M., Hower, J.C., Drobniak, A., and Lis, G., 2002, Chemical properties and petrographic composition of coal and fly ash; examples from Indiana mines and power plants, in Proceedings of the Pittsburgh Coal Conference: CD-ROM.

Mastalerz, M., Hower, J.C., Drobniak, A., Mardon, S.M., and Lis, G., 2004, From in-situ coal to fly ash; a study of coal mines and power plants from Indiana: International Journal of Coal Geology, v. 59, p. 171-192.

Acknowledgments

We acknowledge the time and effort spent by the sample collectors and the cooperation of coal-mine and coal-fired power-plant management and personnel. Important funding support for this project came from the Electric Power Research Institute (EPRI, Barbara Toole-O'Neil) and from the U.S. Department of Energy (DOE, Carl Morande). Detroit Edison (Anthony J. Widenman, III) supplied coal characterization analyses for 24 Colorado coal samples.

References Cited

American Society for Testing and Materials, 2005, Annual book of ASTM standards 2005, v. 05.06, 675 p. (URL: http://www.astm.org)

Bullock, J.H. Jr., Cathcart, J.D., and Betterton, W.J., 2002, Analytical methods utilized by the United States Geological Survey for the analysis of coal and coal combustion byproducts: U.S. Geological Survey Open-File Report 02-389, 14 p.

Stanton, R.W., 1989, Sampling of coal beds for analysis, in Golightly, D.W., and Simon, F.O., eds., Methods for sampling and inorganic analysis of coal: U.S. Geological Survey Bulletin 1823, p. 7-13.

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