FINAL TECHNICAL REPORT

September 1, 1995, through August 31, 1996

Project Title: BRICK MANUFACTURE WITH FLY ASH FROM ILLINOIS COALS

ICCI Project Number: 95-1/3.1A-14

Principal Investigator: Randall E. Hughes, ISGS

Other Investigators: P. J. DeMaris, ISGS; Gary B.

Dreher, ISGS; Duane M. Moore, ISGS;

Massoud Rostam-Abadi, ISGS

Project Manager: Dr. Daniel D. Banerjee, ICCI

ABSTRACT

This investigation seeks to utilize fly ash in fired-clay products such as building and patio bricks, ceramic blocks, field and sewer tile, and flower pots. This goal is accomplished by 1) one or more plant-scale tests of fly ash mixed with brick clays at the 20% or higher level; 2) a laboratory-scale study to measure and model the firing reactions of a range of compositions of shale, fireclay, and fly ash mixtures; 3) a preliminary study to evaluate the potential environmental and economic benefits of brick manufacture with fly ash. Bricks and feed materials are tested for compliance with market specifications and for leachability of potential pollutants derived from fly ash. The laboratory study combines ISGS databases, ICCI-supported and new characterization methods, and published information to improve predictions of the firing characteristics of Illinois fly ash and brick clay mixtures. Because identical methods are used to test clay firing and coal ash fusion, and because melting mechanisms are the same, improved coal ash fusion predictions are an additional expected result of this research. If successful, this project converts a disposal problem (fly ash) into valuable products- bricks.

During the second year of this project, we collected and characterized three new fly ashes, their feed coals, a suite of fireclays, and three sets of "in-plant" shale and fireclay samples. The three new fly ashes were from coals with 1) a high Ca content, 2) a high Fe content, and 3) an average Ca:Fe:Al+Si. The high-Al+Si fly ash, used in last year's testing, was our fourth standard and gave us fly ashes that represent the extremes and average of the composition of Illinois coals. Analyses by X-ray diffraction (XRD) showed that iron oxide in fly ash is a mixture of magnetite, hematite, and probably maghemite. Sequential dissolution-ICP-XRD experiments were completed and we obtained the ICP analyses of the water soluble fractions of six fly ashes and the LTAs of three feed coals. XRD characterization was completed on all fly ash samples, fireclays, shales, LTAs of coals, and selected fired mixtures of fly ash, fireclay, and shale. Environmental testing was completed on bricks. Laboratory test results were used to design plant-scale tests. These test data also were used to begin a computer model of the firing reactions of brick clays and fly ashes, and to model ash fusion of coals. We will use a high-Ca, "pond-washed" fly ash for our plant-scale runs, which will be made this fall at Marseilles Brick Company. We continue to construct an up-to-date directory of sources of fly ash in Illinois. A summary paper entitled Utilization of Fly Ash in Structural and Decorative Ceramic Products was presented and published at the American Chemical Society Meeting in New Orleans. A slide talk version of this paper was presented at the ISGS Seminar in April and the ISGS Coal Advisory Committee Meeting in May. A paper entitled Sequential Acid Dissolution of Clay Minerals: Tracking Structural Composition was presented in June at the annual Clay Minerals Society Meeting in Gatlinburg (TN). Two of the case studies featured in this paper were performed for this project.

EXECUTIVE SUMMARY

This project seeks methods for the efficient utilization of coal combustion wastes, and precisely meets this purpose by examining the use of Illinois fly ash in the manufacture of bricks and similar fired-clay products. The project is composed of three parts: 1) one or more plant-level manufacturing runs, and 2) a set of laboratory-scale experiments designed to predict the firing properties of mixtures of a range of compositions of fly ashes with clays and shales that represent the range of compositions typical of mines and power plants in Illinois; 3) a preliminary investigation of the potential environmental and economic benefits of brick manufacture with fly ash. The completion of these three program elements provides strategies for maximizing the use of fly ash in bricks and related products.

The first task was to obtain one to three sources of approximately 20 tons of fly ash, ship them to Marseilles Brick Company in Marseilles, Illinois, and conduct plant-scale manufacturing runs with mixtures of Marseilles's brick clays and fly ash at the 20% or higher level. A single plant-scale run would be 3,000-10,000 bricks with fly ash, with pre- and post-fly ash baseline runs of several thousand bricks. A parallel part of the first task was to characterize the chemical and mineralogical content of the feed materials and to test the fired bricks by conventional procedures. A series of leaching tests also were performed on the feed fly ashes, fireclay and shale, and green and fired bricks. This year's leach tests were replaced with more meaningful leach of the bulk fly ash. Chemical analyses of the feed materials were by conventional methods. Methods developed for ICCI were used for mineralogical characterization (¹Kruse et al., 1994; ²Moore, Dreher, and Hughes, 1994). The major goal of the first task was to make realistic tests under manufacturing conditions and detect and solve problems that might occur during scale-up at other sites.

Ceramic materials such as building bricks are among humankind's earliest technologies. However, our understanding of the reactions during the firing of bricks is far from complete. This firing is controlled by the ratio of relatively refractory minerals that maintain the shape of a ceramic body to the easily melted materials that fuse and produce a steel-hard brick. A further consideration is having enough plasticity for good extrusion and enough clay minerals for good green (unfired) strength. The preferred materials for these fired-clay products occur as underclays and roof shales associated with coals. These clays contain variable amounts of three basic mineral groups. They are 1) relatively low-melting-point illite, mixed-layered illite/smectite (I/S), and chlorite; 2) refractory kaolinite and mixed-layered kaolinite/expandables (K/E); and 3) somewhat refractory quartz. Common red-firing roof shales generally contain nearly ideal levels of groups 1 and 2, and adequate firing characteristics are obtained by blending clay-rich shale zones with sandier, quartz-rich zones. It is worth noting that some fly ashes probably will act as a sandier additive in combination with normal brick clays, although the Year 1 test at Colonial Brick seemed to show the opposite. If a manufacturer needs lighter color, greater strength, and/or increased refractoriness, a kaolinitic underclay (fireclay) is normally blended with zones from the shale. The individual minerals within mineralogical groups 1 and 2 are similar enough that the three groups probably can be used as factors in a simplified model. Furthermore, fly ash is made up of burned equivalents of these three mineral groups, so we are modeling the firing reactions of fly ash and fly ash-brick clay mixtures with the same simplifications. In addition, our preliminary data indicated that the mineralogical and water-soluble composition of the feed coal is the best predictor of fly ash composition and its firing reactions.

In general, fly ash has a composition similar to raw materials used in brick manufacture. However, some fly ashes contain amounts of calcium (from calcite) and iron oxide (from pyrite and marcasite) that would be considered too high by many manufacturers. If special procedures are used, fairly high levels of each of these constituents can be accommodated. If present as CaO or Ca(OH)₂, high levels of calcium can be corrected for by adding water in the cool-down part of the firing cycle. This hydration step was the method by which bricks known as "Chicago Commons" were manufactured. Both the color and lower melting point caused by high levels of iron are best adjusted for by increasing the quartz or kaolinite content of the clay-shale, or by removing magnetic iron oxide from the fly ash.

The goal of the second task was to improve the accuracy of methods that predict the firing characteristics of fired-clay products. Part of the uncertainty about the exact level of fly ash that should have been used at Colonial Brick in Year 1 testing was the result of inadequate methods of prediction of firing behavior. Improving the prediction of the firing behavior of fly ash-clay mixtures requires a set of working and practical relationships (predictive tools) that takes into account the firing properties of each of the major components in the feed material. The approach for task 2 was to use the fireclay and shale at Marseilles Brick Company to represent the range of compositional variation that is typical of clay raw materials in Illinois. A set of Illinois fly ash samples was selected to represent the range of composition of ashes from Illinois coals. In particular, fly ashes with high Al₂O₃ + SiO₂, high CaO, and high Fe_xO_y were chosen. To the extent possible, these fly ashes also were chosen from sites near Marseilles and other brick plants. These samples were fully characterized, and about 600 test bricks were made and tested. Laboratory test bricks were made by mixing three clay bodies (100% fireclay, 50:50 fireclay:shale, and 100% shale) with three percentage levels of each of the four fly ashes. A few tests also were performed with high-Ca fly ash that had been "washed" in a waste pond. About half of the test bricks were fired in a reducing atmosphere and half were fired in an oxidizing atmosphere. The mixtures with 30%⁺ fly ash additions were difficult to extrude, and because of lowered green strength, some of these high-fly ash test bricks broke. Scumming was a problem on shale bricks, but we have not yet determined whether and to what degree additions of fly ash exacerbated scumming problems. To see if Ca²⁺ in fly ash could capture pyritic sulfur during firing, samples of the green and fired test bricks were sent out for sulfur analyses by Marseilles Brick Company. They also performed standard water absorption tests on the test bricks.

Characterization of the raw materials showed that fly ash can be used advantageously in bricks. The advantages of fly ash over brick clays are 1) it saves the energy required to dehydroxylate or fire clay minerals, 2) it contains spherical particles and mullite crystallites that are ideal for "opening" the brick and promoting thorough firing, 3) its mixture of mineral components gives similar ranges of refractoriness to those for clays, 4) it can be selected to give special colors or other properties that are not possible from clays, and 5) it contains lime (CaO) or portlandite (Ca[OH]₂) that will capture pyritic sulfur from clays and reduce air pollution. A processed fly ash could provide even greater benefits of these types. The disadvantages of using fly ash in bricks are 1) high levels of ash reduce plasticity to the point that extrusion becomes impossible, 2) most dry fly ashes contain excessive amounts of soluble salts such as calcium oxides and sulfates, which cause chalky deposits on the fired bricks that are called "scumming," 3) high-iron fly ashes can reduce melting points below optimum levels, and 4) fly ash sources sometimes require too much freight for them to be cost-competitive at the brick plant.

Coal samples were collected at the same time as the three standard fly ash samples. To analyze these coals, we used new chemical and mineralogical procedures developed for the IBCSP coals (Kruse et al., 1995). The database for this project was expanded to include chemical and mineralogical analyses of IBCSP coals, chemical analyses of the 34 commercial coals analyzed by ³Demir et al (1994), and this year's research on fly ashes by ⁴DeBarr et al (1996).

The chemical, mineralogical, and sequential acid dissolution experiments needed for constructing a predictive model of the firing reactions of fly ashes, fireclays, and shales were completed. Pyrometric cone equivalent (PCE or melting point) determinations of 56 mixtures of fly ash and clays are being completed late this summer. Both to predict the effect of pond disposal of fly ash and to determine the composition of water soluble salts in fly ashes, a series of water extractions were performed on six fly ashes, the four standards for our tests and two samples used by ⁴DeBarr et al (1996) for their current ICCI research on fly ash. Five samples of fly ash mined from a disposal pond were analyzed by X-ray diffraction (XRD). This pond-washed ash will be used in a test at plant production scale. If possible, this fly ash test will be continued on a commercial scale. We also expect this fall to advise other brick plants on the closest and best local sources of fly ash, and if possible, we will schedule preliminary tests of fly ash-brick production at those sites.

The high-Ca fly ash from a waste pond for the plant-scale test may solve three problems: 1) Pond storage may wash out most of the salts that caused scumming in bricks; 2) differential settling in the pond may separate low- and high-density fly ash particles, which may have the effect of separating more and less refractory particles; 3) and perhaps most important of all, wet ash will solve dust problems at brick plants. On the negative side, these ashes may be too wet for normal handling at the brick plants and loss of Ca²⁺ will reduce or eliminate the capacity of these ashes to "scrub" pyritic sulfur from brick clays. As time allows, we intend to sample as many fly ash sources within Illinois as possible; the two fly ashes being tested by ⁴DeBarr et al (1996) have been added to our laboratory testing. We also plan to make one or more sets of laboratory test bricks from our four fly ashes after water washing.

Testing was continued on new shale and fireclay samples from mines that supply Marseilles Brick Company. The purpose of these analyses is to make certain that this year's brick clays are chemically unchanged and to investigate the possibility that we could take advantage of natural variations in Marseilles's clays, i.e., use higher plasticity shale with higher levels of fly ash. Sequential HCl dissolution experiments were completed on a heated fireclay, replicate shale samples, and the four standard fly ashes. These experiments gave results that demonstrated significant differences between the mixed-layered kaolinite/expandables (K/E) and kaolinite constituents of the fireclay and proved that the experimental method gives highly reproducible results. Unfortunately, sequential HCl dissolution of fly ashes fails to give the level of discrimination between components that we had expected. For this reason, we will model firing behavior of the fly ash based upon the mineralogical composition of the feed coal.

In consultation with Marseilles Brick Company, we added to our testing goals some objectives that would broaden the range of products that could be made by the Company. In all cases, these larger objectives seek to increase the extent and amount of fly ash that can be used.

The economic feasibility of using fly ash in bricks is controlled by several factors: 1) availability of a stable source of fly ash, 2) distance that fly ash must be transported to the brick plant, 3) whether cost of disposal saved by the utility is used to ship fly ash, 4) whether the utility is libel for product law suits, and 5) the extent to which the ash is processed to improve its properties. In short, feasibility is driven primarily by cost and secondari ly by legalities. Because fly ash sources are relatively near brick plants, our overall judgment is that some level of commercialization is likely. The next few plant-scale tests will probably define this level.

A preprint paper entitled Utilization of Fly Ash in Structural and Decorative Ceramic Products was presented at the ash utilization session of the Fuel Division of the American Chemical Society Meeting, held in late March in New Orleans (⁵Hughes et al., 1996). A slide talk version of this paper entitled Utilization of Fly Ash in Structural and Decorative Ceramic Products (with Additional Comments on New Methods We Developed To Aid This Research) was presented at the ISGS Scientific Seminar Series in April, and at the ISGS Coal Advisory Committee Meeting in May, the slide talk and last year's ICCI poster were presented. A paper entitled Sequential Acid Dissolution of Clay Minerals: Tracking Structural Composition was presented in June at the annual Clay Minerals Society Meeting in Gatlinburg (TN). The basic method and two of the case studies featured in this paper were spin-offs of this ICCI project. Most of our efforts for this fall will be directed at plant-scale firing tests of fly ash-brick clay mixtures and laboratory characterization of samples from plant- and laboratory-scale testing, which in the latter case is research beyond the goals of the project.

¹Kruse, C.W., R.E. Hughes, D.M. Moore, R.D. Harvey, and J. Xu. 1994. Illinois Basin Coal Sample Program, Final Technical Report to the Illinois Coal Development Board, Center for Research on Sulfur in Coal, Carterville, IL;

²Moore, D. M., G. B. Dreher, and R. E. Hughes. 1993. New procedure for x-ray diffraction characterization of flue gas desulfurization (FGD) and fluidized bed combustion (FBC) by-products. Project funded by the Coal Combustion Residues Management Program, Carbondale, IL.

³Demir, I., R.D. Harvey, R.R. Ruch, H.H. Damberger, C. Chaven, J.D. Steele, and W.T.