Stanley J. Mroczkowski

Distribution of trace elements in selected pulverized coals as a function of particle size and density

Abstract Trace elements in coal have diverse modes of occurrence that will greatly influence their behavior in many coal utilization processes. Mode of occurrence is important in determining the partitioning during coal cleaning by conventional processes, the susceptibility to oxidation upon exposure to air, as well as the changes in physical properties upon heating. In this study, three complementary methods were used to determine the concentrations and chemical states of trace elements in pulverized samples of four US coals: Pittsburgh, Illinois No. 6, Elkhorn and Hazard, and Wyodak coals. Neutron Activation Analysis (NAA) was used to measure the absolute concentration of elements in the parent coals and in the size- and density-fractionated samples. Chemical leaching and X-ray absorption fine structure (XAFS) spectroscopy were used to provide information on the form of occurrence of an element in the parent coals. The composition differences between size-segregated coal samples of different density mainly reflect the large density difference between minerals, especially pyrite, and the organic portion of the coal. The heavy density fractions are therefore enriched in pyrite and the elements associated with pyrite, as also shown by the leaching and XAFS methods. Nearly all the As is associated with pyrite in the three bituminous coals studied. The sub-bituminous coal has a very low content of pyrite and arsenic; in this coal arsenic appears to be primarily organically associated. Selenium is mainly associated with pyrite in the bituminous coal samples. In two bituminous coal samples, zinc is mostly in the form of ZnS or associated with pyrite, whereas it appears to be associated with other minerals in the other two coals. Zinc is also the only trace element studied that is significantly more concentrated in the smaller (45 to 63 μm) coal particles.

Toxic substances from coal combustion -- A comprehensive assessment

The technical objectives of this project are: to identify the effect of the mode-of-occurrence of toxic elements in coal on the partitioning of these elements between vapor, submicron fume, and fly ash during the combustion of pulverized coal; to identify the mechanisms governing the post-vaporization interaction of toxic elements and major minerals or unburnt char; to determine the effect of combustion environment (i.e., fuel rich or fuel lean) on the partitioning of trace elements between vapor, submicron fume, and fly ash during the combustion of pulverized coal; to model the partitioning of toxic elements between various chemical species in the vapor phase and between the vapor phase and complex aluminosilicate melts; and to develop a frame work for incorporation of the results of the program into the Engineering Model for Ash Formation (EMAF). A description for the work plan for accomplishing these objectives is presented in Section 2 of this report. The work discussed in this report highlights the accomplishments in the first quarter of this two year program. This includes holding the program kick-off meeting, selection of candidate program coals, preliminary combustion experiments at MIT, and development of a quality assurance/quality control document. Specifically, in Section 3 the authorsmorexa0» briefly discuss the kickoff meeting and some preliminary discussions concerning a collaboration and coordination with other DOE contractors. Section 4 contains a discussion of the criterion used to select the candidate coals, and a brief description of the background for selecting each candidate coal. Preliminary combustion experiments at MIT are discussed in Section 5. Finally, Section 6 discusses the preliminary framework for the QA/QC protocol document.«xa0less

USGS TOXIC SUBSTANCES FROM COAL COMBUSTION -- FORMS OF OCCURRENCE ANALYSIS

Detailed information on trace-element modes of occurrence in coal is essential to understanding and predicting trace-element transformations taking place during coal combustion. The USGS has developed quantitative and semi-quantitative methods for determining the mode of occurrence of trace elements in coal. This information is needed to generate predictive models for trace-element behavior, the ultimate goal of DOE contract DE-AC22-95PC95101 ``Toxic Substances From Coal Combustion--A Comprehensive Assessment awarded to PSI, Inc. USGS activities in support of this contract have a direct bearing on the predictive equations being developed as the primary product of the PSI program.

TOXIC SUBSTANCES FROM COAL COMBUSTION--A COMPREHENSIVE ASSESSMENT, PHASE II: ELEMENT MODES OF OCCURRENCE FOR THE OHIO 5/6/7, WYODAK AND NORTH DAKOTA COAL SAMPLES

This study reports on the second phase (Phase II) of USGS research activities in support of DOE contract DE-AC22-95PC95101 Toxic Substances From Coal Combustion--A Comprehensive Assessment, funded under DOE Interagency Agreement DE-AI22-95PC95145. The purpose of the study was to provide a quantitative and semi-quantitative characterization of the modes of occurrence of trace elements in coal samples investigated under Phase II, including (1) Ohio 5/6/7, an Ohio bituminous coal sample blended from the No.5, No.6, and No.7 beds; (2) North Dakota, a lignite sample from the Falkirk Mine, Underwood, ND, and (3) Wyodak, a sub-bituminous coal sample from the Cordero Mine, Gillette, WY. Samples from these coal beds were selected for their range in rank and commercial applicability. Results of this research provide basic information on the distribution of elements in Phase II coal samples, information needed for development of a commercial predictive model for trace-element behavior during coal combustion.

Preliminary report on the International Energy Agency mode of occurrence inter-laboratory comparison; Phase I, USGS results

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards (or with North American Stratigraphic Code). Any use of trade, product or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Introduction Understanding the mode of occurrence of trace-elements in coal is an important part of predicting element behavior and determining element mobility during coal utilization and storage. A wide range of techniques is currently used to make these determinations. To generate information on modes of occurrence some labortories rely on analysis of density separates, others use various solvents to selectively leach inorganic constituents and yet others use microbeam instruments such as scanning electron microscopes and electron microprobes. No two laboratories use the same approach or rely on the same assumptions. Under these circumstances is it possible to confidently compare the results of different laboratories? To answer this question, the U.S. Geological Survey (USGS) and eight other laboratories* are participating in an international laboratory comparison study of homogenized coal samples. The International Energy agency (IEA) has endorsed this inter-laboratory study and has agreed to publish a summary comparing the results. To date, samples of four coals have been distributed to participating laboratories. Mode of occurrence (chemical speciation) determinations for three of these coals, Gascoigne-Wood #2 (England), Illinois #6 (USA), and Wyee (Australia), are presented in this paper. Results from the 4th coal from Canada will be presented when the data are completed. Information on the rank, ash content and sulfur content of these three samples is given below (Table 1). USGS bulk chemical data and preliminary bulk data from six other participating labs are given in Appendix 1. Because these data are preliminary only the USGS results are identified. We have just begun work on the fourth coal and results are not yet available. As part of this study each of the participating laboratories* are determining trace element modes of occurrence using their own respective techniques. All procedures are unique. Three labs are using leaching procedures, three labs are using density procedures and several labs are using SEM and/or microprobe as their primary or secondary method of determining modes of occurrence. The USGS modes of occurrence data are presented here with comparisons to other results in specific cases. The complete mode of occurrence data set and possibly a statistical comparison of the bulk chemical results will …