industrial ecology approach to management of fly ash from fluidized bed combustion production of slow-release fertilizer and soil conditioner

74 4.1 X-Ray Diffraction and X-Ray Fluorescence...74 4.2 pH and Leaching Behavior of the Pellets...80 4.3 Statistical Analysis of Slow-Release Behavior ...98 4.4 Compressive Strength: R

FERTILIZER AND SOIL CONDITIONER

by

Mario Castañeda Muñoz

A thesis submitted in partial fulfillment of the requirements for the degree of

Gustavo Martínez Rodríguez, Ph.D

Member, Graduate Committee

Date

Ismael Pagán Trinidad, M.S

Member, Graduate Committee

Date

Jorge Rivera Santos, Ph.D

Member, Graduate Committee

Date

Jaime Benítez, Ph.D

President, Graduate Committee

Date

Eric Harmsen, PhD

Representative of Graduate Studies

Date

Ismael Pagán Trinidad, M.S

Chairperson of the Department

Date

José Mari Mutt, PhD

Director of Graduate Studies

Date

3220601 2007

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ii

Coal has been a major energy source since the Industrial Revolution Despite its environmental problems, coal consumption is still growing because of the lack of alternatives such as natural gas and petroleum resources As a result, more than 50 million metric tons of fly ash are generated by the electric utilities in the United States yearly, almost one-third of which is used in a number of applications Alternatives for the reuse of fly ash in the United States and Puerto Rico previously considered are mostly for

the fly ash are currently underway, focusing on the high-technology and high-value areas

An alternative for management and final disposal of the fly ash generated at a fluidized bed (FBC) coal-fired power plant which is in harmony with the principles of industrial ecology was thoroughly studied It was demonstrated that the ash can be pelletized by reacting it with a proper binder (KOH or KCl solutions) and sintering the pellets at temperatures between 400 and 600ºC for periods of time ranging from 30 to

120 min, producing in the process a potassium fertilizer and soil conditioner The

potential value for agricultural purposes, especially for, but not limited to, tropical areas The product was also found to be safe from the points of view of health and the environment The transport of certain trace elements leached from the pellets through the soil was simulated using the software package Hydrus-1D

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El carbón mineral ha sido una fuente mayor de energía desde los comienzos de la Revolución Industrial A pesar de los problemas ambientales que acarrea su uso, el consumo de carbón continúa en aumento debido a la falta de recursos de gas natural y petróleo Como resultado, más de 50 millones de toneladas métricas de cenizas volantes son generadas anualmente por las plantas termoeléctricas de los Estados Unidos, de las cuales aproximadamente una tercera parte es utilizada en varios tipos de aplicaciones Las alternativas para el reuso de las cenizas volantes consideradas previamente en Estados Unidos y Puerto Rico han sido mayormente para aplicaciones de bajo nivel tecnológico y han tenido un éxito limitado Actualmente están bajo estudio diferentes usos para las cenizas, enfocándose estos esfuerzos en áreas de alta tecnología y valor económico

Se estudió intensivamente y se optimizó una alternativa para el manejo y disposición final de la ceniza generada en plantas de potencia que queman carbón en lecho fluido (FBC, por sus siglas en inglés) la cual armoniza con los principios de la ecología industrial Se demostró que la ceniza puede convertirse en perdigones reaccionándola con un agente aglomerador apropiado (soluciones de KOH o KCl) y sinterizando los perdigones a temperaturas entre 400 y 600ºC por periodos de tiempo entre 30 y 120 min, generando en el proceso un fertilizante de potasio y acondicionador

de suelos El producto, conteniendo cerca de 10% por peso de K2O de liberación lenta, tiene un gran valor potencial para propósitos agrícolas especialmente en áreas tropicales

El producto es seguro desde los puntos de vista de salud y ambiente Se usó el programa Hydrus-1D para estudiar el transporte de los lixiviados a través del suelo

iv

“No hay mayor virtud en un hombre, que

el de aquel que sabe entender y

comprender al que no sabe expresar y

decir lo que siente”

“Cuídate de la libertad, pues te puede

dejar sumido(a) en la soledad”

“No hay un ser mas peligroso que un

justo convencido”

Autoría Mario Castañeda Muñoz

This thesis is dedicated to my “I’m God your Lord….”

To my Mother Rosaura Muñoz for her entirety,

My brothers Miguel Antonio, Francisco, Leonardo, and Diego Ferney,

My sisters Rosaura, Rubiela, Nubia and Marina,

All my nephews and nieces,

And, my friend Amira Padilla for her

unconditional support

v

I wish to dedicate this section to recognize the support of several persons and institutions who collaborated directly and indirectly with my research, during the development of my doctoral studies at the University of Puerto Rico for the period of five years 2002 – 2006 Without their support it would have been impossible for me to finish

I am grateful to the Civil Engineering Department of the University of Puerto Rico, Mayagüez Campus for their support of me as a Teaching Assistant, and to all professors that contributed to my academic formation

vi

I greatly appreciate the AES Corporation for providing the funding and the resources for the development of this research Thanks are also extended to Carlos Reyes, Millie Maria Torres, and Neil Watlington for their valuable and authorizing the use of the fly ash from AES Also, I wish to address my special thanks to Dr Hans Schellekens, Director of the Geology Department, for sponsoring running the samples on the X-ray diffractometer instrument

Most importantly, I specially wish to thank my mother for giving me most valuable advice and each member of my family Indeed, while in the distance they have provided their great love, prayers, and support for me including all the things that I have made in

my life My warm thanks to Professor Amira Padilla, for her unconditional friendship and unlimited support during all the phases of this work, helping me to tolerate the difficulties that appear in daily life, and to write this manuscript

vii

LIST OF TABLES IX LIST OF FIGURES XI

1 INTRODUCTION 1

1.1 Objectives of the present study 6

1.2 Strategy 6

1.3 Overview of the Thesis 8

2 THEORETICAL BACKGROUND 9

2.1 Introduction 9

2.2 Characteristics of Coal Combustion By-Products 9

2.2.1 Fly and Bottom Ashes 9

2.2.2 Fluidized Bed Combustion Wastes 11

2.2.3 Types of Coal Combustion Products 18

2.3 Agricultural Use of Coal Combustion By-Products 19

2.4 Environmental Effects of Coal Combustion By-Products 21

2.5 Ion Movement with the Amendment of Soils 23

2.5.1 Lime and gypsum application to correct soil acidity 26

2.5.2 Solute transport in the unsaturated zone (Simunek, et al., 2005) .35

2.6 Powder Metallurgy (German, 1994) 47

2.7 Slow-Release Fertilizers (Bennett, 1992) 49

2.7.1 Pelletized 49

2.7.2 Chemically Altered 50

2.7.3 Coated 50

2.8 Leaching of Solids in a Cross-Flow Cascade of Stages 52

2.9 Industrial Ecology 55

3 METHODS AND MATERIALS 58

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3.1 Introduction 58

3.2 Experiments 58

3.2.1 Materials 58

3.2.2 Equipment 60

3.2.3 Procedure 64

3.3 Analyses 71

4 RESULTS AND DISCUSSION 74

4.1 X-Ray Diffraction and X-Ray Fluorescence 74

4.2 pH and Leaching Behavior of the Pellets 80

4.3 Statistical Analysis of Slow-Release Behavior 98

4.4 Compressive Strength: Rupture Modulus Results 101

4.5 Statistical Analysis of Rupture Modulus Results 106

4.6 Trace Elements in Pellets and Leachates 108

4.7 Potential Environmental Impact of the Pellets 116

4.7.1 Potassium fertilizer requirement of plantains 116

4.7.2 Water requirement of plantains 117

4.7.3 Slow-release behavior of aluminum under field conditions 117

4.7.4 Simulation of the fate of the aluminum released on the field 118

4.7.5 Simulation of the fate of boron 123

5 CONCLUSIONS, RECOMMENDATIONS AND LIMITATIONS 128

6 REFERENCES 132

7 APPENDIX A ANALYSIS OF PH VERSUS WASH NUMBER DATA 145

ix

List of Tables

TABLE 2.1 Typical composition of Class F and C ashes as defined by ASTM

(Ziemkiewicz and Skousen, 2000) 19

TABLE 3.1 Chemical composition of fly ashes (wt%) 59

TABLE 3.2 Amounts needed for the preparation of solutions of KOH and KCl 66

TABLE 3.3 Experimental design for KOH 4.0N 70

TABLE 3.4 Experimental design for KOH 6.0N 70

TABLE 3.5 Experimental design for KCl 4.0N 70

TABLE 3.6 Experimental design for KCl 5.0N 71

TABLE 3.7 Minimum detection limits (MDL) for analyses 72

TABLE 4.1 Crystalline structures in fly ash and pellets 80

TABLE 4.2 pH of fly ash plus binder solutions 81

TABLE 4.3 pH of binder solutions 81

TABLE 4.4 Summary of leaching behavior of pellets produced using KCl, 4N 83

TABLE 4.5 Summary of leaching behavior of pellets produced using KCl, 5N 84

TABLE 4.6 Summary of leaching behavior of pellets produced using KOH, 4N 85

TABLE 4.7 Summary of leaching behavior of pellets produced using KOH, 6N 86

TABLE 4.8 Fertilizer value of best treatments from the point of view of leaching behavior 87

TABLE 4.11 Hydroxyl ion leaching parameters in cross-flow cascade 92

x

TABLE 4.12 Potassium leaching parameters in cross-flow cascade 98

TABLE 4.13 Class level information for statistical analysis of SRI results 99

TABLE 4.14 Type III tests of fixed effects on SRI results 100

TABLE 4.15 Rupture modulus results of best slow-release treatments (kg/m2) 101

TABLE 4.16 Class level information for statistical analysis of rupture modulus results106 TABLE 4.17 Type III tests of fixed effects on rupture modulus results 107

TABLE 4.18 Ceiling concentration limits for biosolids applied to land (USEPA, 1994) 115

TABLE 4.19 Input parameters and conditions for aluminum transport simulation 119

TABLE 4.20 Physical parameters for soil column experiment (Communar et al., 2004) 124

TABLE 4.21 Measured B breakthrough concentrations (Communar et al., 2004) 125 TABLE 4.22 Summary of parameters estimated by Hydrus from column experiment 126

xi

List of Figures

Figure 2.1 Effect of autoliming (Pavan, et al ,1982) 29

Figure 2.2 Schematic of the plant water stress response function β(h), as used by Feddes et al (1978) 39

Figure 2.3 Cross-Flow Cascade of Ideal Stages 53

Figure 3.1 Schematic diagram of fly ash flow in FBC 59

Figure 3.2 Bath reactor immersed in oil bath at 120 oC 61

Figure 3.3 X-ray Fluorescence Spectrometer Instrument 62

Figure 3.4 X-ray Diffractometer Instrument 62

Figure 3.5 Sketch of the geometry of a modulus of rupture determination for a core sample of length! , and radius r (Taylor and Ashcroft, 1972) 63 s Figure 3.6 Compression equipment for measuring the modulus of rupture 64

Figure 3.7 Fly ash samples of 300 g 64

Figure 3.8 Extrusion Machine 65

Figure 3.9 Sintered Pellets 66

Figure 3.10 Experimental Design Diagram 69

Figure 4.1 X-Ray Diffractometer of Fly Ash from AES 74

Figure 4.2 X-Ray Fluorescence Spectra of Fly Ash 75

Figure 4.3 X-Ray Difractometer of Pellets (KOH 6.0N, 30 min Reaction Time; 600oC Sintering Temperature, 120 min Sintering Time) 76

xii

Sintering Temperature, 60 min Sintering Time) 77

Sintering Temperature, 30 min Sintering Time) 78

Sintering Temperature, 60 min Sintering Time) 79

Sintering Temperature, 30 min Sintering Time) 88

Sintering Temperature, 60 min Sintering Time) 89

Sintering Temperature, 120 min Sintering Time) 90

Sintering Temperature, 60 min Sintering Time) 91

Sintering Temperature, 60 min Sintering Time) 93

Sintering Temperature, 30 min Sintering Time) 94 Figure 4.13 Potassium in Leachate from Pellets (KOH 6.0N, 30 min Reaction Time;

600oC Sintering Temperature, 120 min Sintering Time) 95 Figure 4.14 Potassium in Leachate from Pellets (KOH 4.0N, 60 min Reaction Time;

600oC Sintering Temperature, 60 min Sintering Time) 96

xiii

Figure 4.15 Potassium in Leachate from Commercial Slow-Release K Fertilizer (data are

from Yoo and Jo, 2003a) 97

Figure 4.16 Pellets rupture modulus results (KCl 5N, 30 min reaction time) 102

Figure 4.17 Pellets rupture modulus results (KCl 5N, 60 min reaction time) 102

Figure 4.18 Pellets rupture modulus results (KCl 4N, 30 min reaction time) 103

Figure 4.19 Pellets rupture modulus results (KCl 4N, 60 min reaction time) 103

Figure 4.20 Pellets rupture modulus results (KOH 6N, 30 min reaction time) 104

Figure 4.21 Pellets rupture modulus results (KOH 6N, 60 min reaction time) 104

Figure 4.22 Pellets rupture modulus results (KOH 4N, 30 min reaction time) 105

Figure 4.23 Pellets rupture modulus results (KOH 4N, 60 min reaction time) 105

Figure 4.24 Aluminum content of leachates 108

Figure 4.25 Arsenic content of leachates 109

Figure 4.26 Chromium content of leachates 109

Figure 4.27 Copper content of leachates 110

Figure 4.28 Selenium content of leachates 110

Figure 4.29 Zinc content of leachates 111

Figure 4.30 Mercury content of leachates 111

Figure 4.31 Aluminum content of pellets 112

Figure 4.32 Copper content of pellets 112

Figure 4.33 Chromium content of pellets 113

Figure 4.34 Arsenic content of pellets 113

Figure 4.35 Selenium content of pellets 114

xiv

Figure 4.36 Mercury content of pellets 114 Figure 4.37 Zinc content of pellets 115 Figure 4.31 Cumulative water surface flux (cm) for the simulation period 120

) 120 Figure 4.33 Surface and bottom (blue line) aluminum concentration (mmol /L) 121

) 122

) 123 Figure 4.37 Boron breakthrough curve as predicted by Hydrus (units of concentration are mg/L; data are from Communar et al., 2004) 127

1

1 INTRODUCTION

Coal has been a major energy source since the Industrial Revolution Despite its environmental problems, coal consumption is still growing because of the lack of natural gas and petroleum resources Burning coal generates more than half the electricity in the United States As a result, more than 50 million metric tons of fly ash are generated by the electric utilities, almost one-third of which is used in a number of applications

this number is expected to gradually increase The amount of coal ash produced annually

in Puerto Rico, mostly by the Advanced Energy Systems (AES) Puerto Rico Total Energy Plant, is about 0.2 million metric tons (Black&Veatch, 2000) Most domestic power stations in the United States store the collected fly ash in ponds as slurry, but they have had trouble finding suitable sites for disposal

One of the primary driving forces behind the growing interest in recycling and utilization of fly ash is the recognition that this by-product takes up vast amounts of valuable landfill space To illustrate the scope of this problem, consider that if all the fly ash generated in the United States in 1996 were piled onto a 10,000 square foot space (the area of a typical skyscraper foundation), that pile would extend 25 miles into the sky (Gainer, 1996) Presently, most fly ash is still disposed of in landfills or surface impoundments, and adequate handling and disposal is becoming a severe environmental problem On the other hand, fly ash can be considered a valuable, plentiful and economic mineral resource which can substitute for more costly raw materials Where beneficial

uses of fly ash can be found, valuable landfill space is freed up and ash producers are able

to reduce their disposal costs, which usually constitute a significant portion of the total annual cost of operating air pollution control facilities in thermoelectric power plants (Benítez, 1993)

Alternatives for the reuse of fly ash in the United States previously considered are mostly for low-technology uses such as simple pozzolanic material, bricks, and road sub

amendment have been limited by the chemistry of the fly ash In general, fly ash contains only small amounts of beneficial nutrients and often contains potentially toxic trace elements such as arsenic (As), boron (B), cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg), and seleium (Se) A promising new approach to improve the utilization of fly ash is to convert it into a high-charge material with greatly increased cation exchange capacity (CEC) by chemical and thermal treatment Thus, many attempts to utilize the fly ash are currently underway, focusing on the high-technology and high-value areas such

as production of a slow-release granular fertilizer (Yoo and Jo, 2003a; 2003b), zeolitization (Choi, et al., 2001) and production of ceramic membrane filters (Jo, et al., 1996)

Meanwhile, artificially synthesized fertilizers have been widely used for many decades in domestic agriculture The composition of these chemical fertilizers varies with the type of crops, application time, and nature of the soil Despite their low price in the commercial market, they are often avoided in practical use because they are easily swept away by precipitation, facilitating soil acidification and contributing to surface waters

eutrophication (Ongley, 1996) Such inherent limitations of artificial fertilizer can be solved by using slow-release formulations that rely on suitable media with large surface area to mitigate the loss of fertilizer elements Slow-release fertilizers are excellent alternatives to soluble fertilizers Because nutrients are released at a slower rate throughout the season, plants are able to take up most of the nutrients without waste by leaching, reducing the environmental problems associated A slow-release fertilizer is more convenient, since less frequent application is required Fertilizer burn is not a problem with slow-release fertilizers even at high rates of application; but, it is still important to follow application recommendations Slow-release fertilizers may be more expensive than soluble types, but their benefits outweigh their cost (Bennett, 1992)

The most popular media used in slow-release formulations are artificial or natural zeolites and processed clay However, their high cost often limits application in massive quantity Although waste coal fly ash has sometimes been used as a fertilizer support, and the effects of ash addition on the growth and yield of various crops have been investigated, direct fly ash utilization by simple mixing with the plant nutrients has

pointed out that the work presented in this thesis introduces a new method for using the waste coal fly ash as an effective support for an advanced slow-release potassium fertilizer that can be extended to the other macronutrients (nitrogen and phosphorus)

Preliminary tests show that coal fly ash can be reacted with potassium hydroxide (KOH) in aqueous suspension, filtered, pelletized, and sintered (a powder-metallurgy, or P/M process) at temperatures around 600 °C yielding a slow-release potassium fertilizer

and soil conditioner (Yoo and Jo, 2003) These researchers produced fly ash cylindrical pellets (2 mm diameter, 8 mm in length) that contained 21% by weight potassium

the pellets for a long time

Presently, there is no slow-release potassium fertilizer commercially available in Puerto Rico Such a product, if available at a reasonable price, would be welcomed by local growers of bananas and plantains, heavy potassium feeders According to statistics for the year 2000, plantain growers in Puerto Rico contributed $54.5 million to the Island economy, while banana growers contributed $14.5 million (Cortés, 2003) There are about 6,000 ha of land planted in plantains, and about 2,000 ha in bananas The annual potassium fertilizer requirement for plantains and bananas is estimated at about 500 kg/ha (Irizarry, et al., 1981; Irizarry, et al., 1988)

According to the numbers presented above, the annual potassium fertilizer requirement for plantains and bananas farming in Puerto Rico is about 4 million kg If the potassium content of the fertilizer is 10% by weight, with the remaining 90% made up of pelletized fly ash, 36 million kg (36,000 metric ton/year) of the fly ash would be incorporated into a high-value product Therefore, the waste fly ash generated locally could become the principal raw material for a whole new industry that would benefit the economy of Puerto Rico

For comparison purposes, data were obtained on the slow-release nitrogen fertilizers commercially available in Puerto Rico (Ochoa Fertilizer, 2004) The selling price of conventional-release urea (43% nitrogen) is $345/ton On the other hand, the

price of slow-release urea (TRICOTE™, 43% nitrogen) is $950/ton The value added to fertilizers through the slow-release mode is evident

An important aspect of the modern approach to environmental engineering problems is that of pollution prevention and sustainable development (Bishop, 2000) The concept of industrial ecology is an important part of the philosophy behind pollution prevention and sustainable development Industrial ecology views industrial systems in concert with their surroundings, not in isolation from them It brings together environmental sciences, engineering, management, and policy to study the flows of energy and materials through various systems These flows drive our industrial systems and are vital to determining their sustainability The concept of industrial symbiosis is broadly based on the idea of exchange, where one facility’s waste becomes another facility’s input Thus, industrial symbiosis promotes a collaborative approach to competitive advantage By acting together, businesses seek a collective benefit that is greater than the sum of the individual benefits each company would realize if it optimized its individual performance only (Chertow, 2003) The work that is presented in this thesis fits perfectly into the realm of industrial ecology

AES of Puerto Rico (the source of the fly ash used in this work) is already a participant in an industrial ecology concerted effort initiated by the School of Forestry

and Environmental Studies of Yale University, a project called Puerto Rico: An Island of Sustainability (PRIOS) Students working in this project performed economic and

material flow analyses of the co-generation operations of AES and surrounding system The group found significant environmental savings for both AES and Chevron-Phillips,

its steam host, as well as promising economic returns They also investigated potential uses for other materials such as the high-lime fly ash emitted (Chertow, 2003)

1.1 Objectives of the present study

Two important objectives in this research were:

1 To optimize the procedure for the production of a slow-release potassium fertilizer and soil amendment from fly ash generated during the combustion of coal in fluidized beds by reaction with the proper binder, followed by sintering

2 To evaluate its environmental impact—emphasizing ion movement, retention by the soil, and impact on groundwater—when used for fertilizing plantain and banana plants under the local climate, soil quality, and irrigation schedules

1.2 Strategy

The use of KOH as a binder for pelletization of the fly ash from a conventional pulverized coal-fired power plant has been demonstrated already (Yoo and Jo, 2003) However, KOH is an expensive reagent and that could limit the practical application of these results from the economic point of view On the other hand, the fly ash generated in

hypothesized that KCl can be used as an effective and practical binder for its pelletization, and concomitant production of a slow-release potassium fertilizer and soil amendment

The independent variables considered in this optimization scheme for ash binding and pelletization were:

• Identity of the binder (KOH or KCL)

• Concentration of the binder aqueous solution (4.0N and 6.0N for KOH, and 4.0N and 5.0N for KCL)

• Reaction time at 120°C (30 min and 60 min), followed by filtration and pelletization

• Sintering temperature of the pellets (400°C and 600°C)

• Sintering time of the pellets (30 min, 60 min, and 120 min)

The quality of the pellets generated, from the points of view of slow-release fertilization, soil amendment and environmental safety, was ascertained by measuring the following dependent variables:

• Potassium content of the pellets

• Leaching test of the pellets (to ascertain the rate of potassium release, and the presence of trace elements in the leachate)

• Mechanical strength of the pellets (to ascertain the possibility of handling and storage problems due to disintegration of the pellets and the generation of fine dusts)

• Identification of possible crystalline structures formed during the reaction and thermal process by X-ray fluorescence and X-ray diffraction analyses

To evaluate the environmental impact of the slow-release fertilizer and soil amendment developed—when used for fertilizing plantain and banana plants under the local climate, soil quality, and irrigation schedules—some mathematical modeling was

done using the HYDRUS-1D software package developed for such purposes at the University of California at Riverside (Simunek, et al., 2005)

1.3 Overview of the Thesis

In this work, the necessary background theory is developed in Chapter 2, including a detailed literature review of the theory and important principles Chapter 3 gives a detailed description of the materials, equipment and experimental procedures that were

potassium fertilizer from the fly ash generated during coal combustion in circulating fluidized beds (CFBs) Chapter 4 presents and discusses the most relevant results of this investigation Conclusions of the most important findings of the experimental effort and future work are presented in Chapter 5 The thesis also includes an appendix section, which contains additional images and results obtained, as well as supplementary information

2.2 Characteristics of Coal Combustion By-Products

2.2.1 Fly and Bottom Ashes

The physical, chemical, and mineralogical characteristics of bottom and fly ashes depend on a variety of factors, including the composition of the parent coal, combustion conditions, the efficiency and type of emission control devices, and the disposal methods used (Van Hook, 1979; Adriano et al., 1980) Consequently, it is difficult to generalize about the composition of ashes, or their behavior in the environment However, certain characteristics are fairly uniform for most ashes Fly ashes are composed predominantly

of small, glassy, hollow particles, with particle sizes ranging from 0.01 to 100 µm and specific gravities of 2.1 to 2.6g/cc (Adriano et al., 1980) Bottom ashes contain a higher percentage of coarse grained particles and have higher specific gravities than most fly ashes (Santhanam et al., 1979; Adriano et al., 1980) Bottom ash may include a

significant fraction of material greater than 2 mm in size due to the presence of boiler slag (Carlson and Adriano, 1993)

Fly ash is a complex heterogeneous material consisting of both amorphous and crystalline phases (Page et al., 1979; El-Mogazi et al., 1988; Mattigod et al., 1990) It is generally considered a ferroaluminosilicate mineral, with Al, Si, Fe, Ca, K, and Na the predominant elements (Adriano et al, 1980) Fly ash contains all naturally occurring elements, and is substantially enriched in trace elements compared with the parent coal (Van Hook, 1979; Adriano et al., 1980) Studies have shown that many trace elements in the ash are concentrated in the smaller ash particle sizes (Adriano et al., 1980) Among the elements generally enriched in ashes are As, B, Ca, Mo, S, Se, and Sr (Page et al., 1979) Boron is an element to be most seriously considered in the agricultural use of fly ash because it deteriorates vegetation in the case of long-term and massive application (Yoo and Jo, 2003a)

Compared with soils, ashes are typically low in N (due to volatilization during combustion), but re1atively high in most other plant nutrients (Adriano et al., 1980) Ash

pH can vary from 4.5 to 12 depending on the S content of the parent coal, with high-S, eastern coals generally producing acidic ashes and low-S western coals producing a1kaline ashes (Adriano et al., 1980) While fresh (unweathered) ash is characterized by high concentrations of soluble salts, these levels are substantially reduced in weathered or lagooned ash (Townsend and Hodgson, 1973; Townsend and Giliham, 1975; Brown et al., 1976) Some fly ashes also exhibit pozzolanic properties, i.e., they can react with water in the presence of lime to form cement, which can result in reduced infiltration and root

penetration in ash deposits and ash amended soils (Townsend and Hodgson, 1973; Adriano et al., 1980; Bradshaw and Chadwick, 1980)

2.2.2 Fluidized Bed Combustion Wastes

Fluidized bed combustion (FBC) is a process in which the pulverized coal is

(FGD) systems, the sulfur dioxide in the flue gases is scrubbed by countercurrent contact with an aqueous suspension of ground limestone or lime (Benítez, 1993)

The waste from FBC units differs from the FGD waste in several ways: (i) it is a dry product, whereas FGD waste is wet; and (ii) it is composed primarily of anhydrous

mainly of CaSO3 Because of its characteristically high pH (pH ~ 12.5), and relatively high Ca (21-34%) and S (7-13%) contents, FBC wastes have been suggested as a lime substitute and as a source of Ca and S for soils deficient in these elements (Terman, 1978; Terman et al., 1978; Holmes et al., 1979; Stout et al., 1979; Korcak, 1980a, 1985)

to 81% (Terman et al., 1978; Holmes et al., 1979; Korcak, 1979, 1980a,b, 1982, 1985; Stout et al., 1979), much higher than the equivalency reported for fly ash from conventional pulverized coal-fired power plants (Phung et al., 1978)

Terman et al (1978) added FBC waste to two soils, Mountview silt loam (Typic Paleudults, pH = 5.2) and Hartsells fine silt loam (Typic Normudults, pH < 5.5), both of which had been depleted of S by cropping They found that amendment with the waste significantly improved the yields of corn on both soils In addition, low rates (up to 0.4%

by weight) of FBC amendment improved the yield of peanut on the Hartsells fine silt loam However, additions of FBC waste to the Hartsells fine silt loam at rates of 10% or 25% by weight resulted in very little peanut growth, apparently due to the high alkalinity produced by these treatments (leachate pH = 12.5) Boron toxicity was not a problem in these experiments (Terman et al., 1978)

Korcak conducted a series of experiments to evaluate the potential use of FBC waste as a source of Ca for apple trees (Korcak, 1979, 1980a,b, 1982, 1985) He concluded that the waste was an acceptable Ca source, and that fine FBC waste was preferable to coarse FBC waste for this purpose Studies evaluating the impact of incorporating plants grown on FBC waste-amended soils into the diets of rats (Cahill et al., 1988), pigs (Whitsel et al., 1988), and sheep (Cochran et al., 1991; Vona et al., 1992) have shown no deleterious effects on animal elemental concentrations, with tissue concentrations remaining within the normal ranges for these species

The results of studies conducted to date indicate that fluidized bed combustion waste can be used as a lime substitute, and as a source of Ca and S on problem soils The major problems associated with its use are high alkalinity and salinity, which may reduce plant growth at high application rates (Terman et al., 1978; Holmes et al., 1979; Korcak, 1980a) Accumulation of elevated concentrations of trace elements does not appear to be

a problem when this material is used as a soil amendment However, because the transportation costs are also high for this material, its use as a soil amendment would only

be cost-effective for sites located near a fluidized bed combustion plant (Terman, 1978; Holmes et al., 1979)

Coal combustion By-products, including fly ash, bottom ash, flue gas desulphurization waste (scrubber sludge), and fluidized bed boiler waste, and coal gasification ash, account for 90% of all fossil fuel combustion wastes produced in the USA Only about 20% of these materials are utilized, with the remainder deposited in landfills or surface impoundments Because of the physical and chemical characteristics

of these by-products, their utilization or disposal on land can have significant impacts on terrestrial and aquatic ecosystems Environmental impacts of fly and bottom ashes have received the most attention, whereas relatively little is known about the impacts of other coal combustion by-products (ACAA, 2001)

The major potential impacts of ash disposal on terrestrial ecosystems include: leaching of potentially toxic substances from the ash into soils and groundwater; reductions in plant establishment and growth on the ash; changes in the elemental composition of vegetation inhabiting the ash; and increased transfer of elements through the food chain The potential for groundwater contamination due to leachate from ash disposal sites is the primary area of concern regarding the disposal of these wastes due to the elevated concentrations of soluble salts and potentially toxic trace elements, including

As, Ba, Cd, Cr, Pb, Hg, and Se, present in many fly and bottom ashes Leachate pH varies depending on the composition of the ash, with ash from high-S coals generally

producing acidic leachate and ash from low-S coals producing alkaline leachate (Adriano, 1980)

The major factors limiting vegetation establishment on ash disposal sites are: (i) deficient supplies of essential nutrients, usually N and P; (ii) toxicity caused by high pH and/or high soluble salt concentrations, high B, and high concentrations of other potentially toxic trace elements; and (iii) the presence of compacted and/or cemented layers in the ash In many cases, plant tolerance of fly ash parallels tolerance of B Plants growing on ash basins generally accumulate elevated levels of trace elements enriched in the ash, including As, B, Co, Cr, Cu, Hg, Mo, Ni, Pb, Se, and Zn A number of studies have indicated that the Se present in the ash and accumulated by plants is readily transferred up the food chain to animals consuming the plants, resulting in increased accumulation of Se in animal tissues Additional food-chain transfer studies for other potentially toxic elements present in ash are needed (ACAA, 2001)

Adverse physical and chemical characteristics of fly ash deposits can also limit colonization by microorganisms Microbial numbers and diversity generally increase as ash weathers and nutrients accumulate Low supplies of C and N appear to be important factors limiting microbial populations on these sites (Adriano, 1980)

Ash disposal in landfills and settling ponds can influence adjacent aquatic ecosystems directly, through inputs of ash basin effluent and surface runoff, and indirectly, through seepage and groundwater contamination Inputs to aquatic systems from ash disposal sites can affect both water quality and the biota that inhabit receiving lakes and streams Although addition of ash effluents can increase the electrical

conductivity, turbidity, and water temperature of receiving surface waters, in most cases the major impacts are associated with changes in water pH and elemental concentrations Fish kills have been reported when ash basin effluents have been discharged into adjacent aquatic systems High pH, high salinity, and elevated Se concentrations have been blamed in several of these incidents Ash basin discharges have also resulted in reduced densities and diversity of aquatic macro invertebrates (Adriano, 1980)

Because of the large amounts of coal ash generated each year, a great deal of research has been conducted to identify and determine the feasibility of utilizing these wastes in agriculture and industry Amendment of agricultural soils with fly ash can improve soil texture (for both coarse- and fine-grained soils), increase soil water- holding capacity (for coarse-grained soils), increase soil pH (for acidic soils), and increase concentrations of most macro- and micronutrients However, ash amendment can also result in excessive soluble salt concentrations, excess B, and increased concentrations of other potentially toxic trace elements; reduction in the availability of soil N and P; elemental imbalances due to excessively high pH; and cementation or compaction of soil Un-weathered ash has a greater potential for producing adverse impacts than weathered ash At high rates of application (≥ 400 ton ash/ha), salt injury and B toxicity can occur

in plants growing on soils amended with fresh ash (ACAA, 2001)

Addition of fly ash to soil can also affect soil and plant chemical composition, particularly the concentrations of trace elements Changes in soil and plant chemical composition result both from changes in soil pH, affecting elemental solubilities, and from soil enrichment with soluble salts and major and trace elements present in the ash

However, care must be taken in using fly ash as a source of nutrients, since over application could result in phytotoxic levels of B and sufficiently elevated levels of other elements, including As, Mo, and Se, in plant tissues to represent a potential threat to animals consuming these tissues (ACAA, 2001)

Soil amendment with ash appears to result in decreased microbial activity and numbers Decreased soil respiration has been reported by several investigators Reductions in nitrification and N mineralization and increases in denitrification following ash additions to soils have also been reported However, the relatively few studies conducted on the impacts of soil amendment with fly ash on microorganisms do not provide sufficient data to permit generalization (ACAA, 2001)

F1y ash can also be used as an amendment to acid mine spoils Numerous studies have shown that ash additions can be effective in increasing soil pH, allowing the establishment of permanent vegetative cover on previously barren sites Because of the high acidity of these materials, high rates of ash addition are usually necessary, but these high rates do not generally appear to cause deleterious effects, and in fact have been shown to improve soil texture (ACAA, 2001)

The environmental impacts associated with the disposal of flue gas desulphurization waste (scrubber sludge) are similar in many ways to those associated with fly ash Flue gas desulphurization wastes are characterized by high pH, high soluble salt contents, and low levels of N and P, and generally contain elevated concentrations of trace elements; including B and Se Principal concerns with scrubber sludge disposal include groundwater contamination from leachate and elevated concentrations of trace

elements in plants and animals in the vicinity of the disposal area An additional problem, unique to FGD waste, is the presence of high concentrations of sulfite in much sludge Under anoxic conditions this can result in the production of H2S gas; under aerobic conditions high levels of sulfite can substantially increase the oxygen demand (due to oxidation of sulfite to sulfate) in surface and groundwater systems affected by these wastes (Adriano, 1980)

A great deal of research has been conducted concerning the environmental impacts of fly and bottom ashes, but there are still some important gaps that need to be filled More research is needed to determine the effects of ash on microbial populations

In addition, relatively little is known concerning the potential for accumulation of potentially toxic elements in animals feeding on plants growing on ash deposits or ash-amended soils More research is needed to determine the best methods of rapidly revegetating abandoned landfills to minimize resuspension and erosion of these deposits The potential for using fly ash as a composting ingredient (e.g., with municipal sewage sludge) need further consideration Innovative, nonagricultural uses of fly ashes on land where the food chain is not involved also need to be explored (ACAA, 2001)

A great deal of research is also needed to determine the environmental impacts of other coal combustion by-products, particularly flue gas desulphurization and fluidized bed combustion wastes Among the areas needing further study are: (i) the impact of the combustion process used on waste characteristics and, subsequently, on the environmental impacts of these materials; (ii) factors inhibiting successful revegetation of disposal sites for these wastes; and (iii) the potential for utilizing these wastes as soil

amendments without adversely affecting soils or the plants grown on them.” (Carlson and Adriano, 1993)

2.2.3 Types of Coal Combustion Products

Coal combustion products (CCPs) are grouped into four main classes: 1) Class F, 2) Class C, 3) Fluidized Bed Combustion, and 4) Flue Gas Desulphurization Class F and

C ashes are produced in large coal boilers where pulverized coal is injected as fuel These two ash types still comprise the bulk of CCPs produced in the U.S They are distinguished by their free lime (CaO) content Class F ashes have less than 10% lime, while Class C ashes have more than 10% lime Nearly all ashes produced by coal boilers

in the eastern U.S are Class F, while those burning western U.S coal are typically Class

C

FBC ashes and FGD solid, result from relatively new, clean coal technologies Both use lime or limestone to generate CaO to capture sulfur oxides in the boiler exhaust

in a strongly alkaline ash (typically 25% to 30% free lime) Table 2.1 shows typical chemical compositions for both Class F and Class C ashes (Ziemkiewicz and Skousen, 2000)

CCPs are typically used in the following beneficial applications at coal mines:

a Neutralization or encapsulation of acid-producing materials

b Barriers to acid mine drainage formation/transport

c Alkaline amendment to neutralize acid-producing rock

d Subsidence control in underground mines

e Filling underground mine voids to control acid drainage

f Pit filling to reach approximate original contour in surface mines

g Soil amendment or substitute

TABLE 2.1 Typical composition of Class F and C ashes as defined by ASTM

(Ziemkiewicz and Skousen, 2000)

2.3 Agricultural Use of Coal Combustion By-Products

Fly ash has potential for use in agriculture because it contains almost all macronutrients as well as micronutrients except organic carbon and nitrogen Fly ash may

be used in conjunction with chemical fertilizer to increase the yield of various agricultural crops, the dose of which will depend on the types of crops as well as the types of soils Although, fly ash may contain moderate quantities of trace and heavy metals, and radioactive elements, its effect on groundwater, soil health and uptake by plants are probably negligible (Kumar et al, 2001)

Alkaline stabilization has been increasingly recognized as a promising alternative for sewage sludge management Chemicals are used in wastewater slurries processing for odor control, pH modification, pasteurization, disinfection, and stabilization Lime and chlorine are the primary chemicals that have been extensively used for these purposes Lime or lime-containing materials, like fly ash, raise pH and increase temperature to inactivate or destroy pathogenic organisms (Grillasca, 1996)

Beneficial agricultural uses of flue gas desulfurization products (FGDs) include application as amendment to acidic soil to mitigate low pH problems (Al toxicity); provide plant nutrients (particularly Ca, S, Mg); improve soil physical properties (water infiltration, soil aggregation, particle stability); help alleviate soil compaction and improve aggregate stability of sodic soils; and inactivate P under high P-soil conditions to reduce P runoff Co-utilization of FGDs with organic materials (manures, composts, biosolids) should also provide benefits when used on land Constraints to use of FGDs on

to cause imbalanced Mg, P, and K in soils and plants; Ca displacement of Al from soil exchange sites to induce Al toxicity in plants; high B to induce B toxicity in plants; excessive sulfite which is toxic to plants; and excessive amounts of undesirable trace elements (As, Cd, Cr, Ni, Pb, Se) which could potentially contaminate water and pose toxicity to plants and animals Most constraints are not, and do not need to be, problems for FGD use on land if these products are used appropriately (Clark et al, 2005)

2.4 Environmental Effects of Coal Combustion

By-Products

Coal combustion by-products are most commonly classed as a special waste, though some states regulate under RCRA subtitle D, and some expect FBC ashes to receive mandatory subtitle D or even subtitle C requirements when the Bellville amendment exemption runs out The mentality that combustion by-products are a sinister waste product from an industrial plant has caused a presumption of environmental liability and a general neglect of environmental enhancement potential Much regulation and concern centers around the notion that industrial waste products release dangerous leachate into the water supply Fugitive dust concerns are receiving more attention as companies move to dry disposal alternatives Finally a last concern with coal combustion byproducts, noticed most frequently by mine reclamationists, is the general lack of organic material to spur plant growth (Paul, et al 1996)

Combustion by-products have been looked upon as dangerous waste products prone to degrade the ground and surface waters, cast dangerous dust clouds into the air,

or create sterile organic free piles for anemic plant growth Large field scale pilot projects that have followed laboratory tests suggest that most of these fears are unwarranted (Paul

et al, 1996) A 50,000 ton scrubber-sludge backfill in a final strip cut was instrumented with monitoring wells that showed no evidence of heavy metals contamination of the groundwater One hundred and fifty tons of FBC fly ash was used to neutralize an acid lake and heavy and toxic metals concentrations all dropped, even though the ash was expected to leach toxic metals that would not precipitate with changing pH A 1,000 ton

test bed of FBC fly ash and gob was instrumented with a 15 by 20 foot lysimeter catchment basin beneath to determine if the leachate carried heavy metals or other toxics The bed is so impermeable that in 2 years it was not possible to get a 10 ml water sample for analysis A 7-acre cap made of FBC ash and spoil has yielded no leachate to sample Run-off from the cap area showed a slight elevation in potassium and sodium concentrations but no indication of heavy or toxic metals There were no adverse impacts detectable in an adjacent stream Engineered mixes of coal combustion by-products and mine wastes seem to bind even mobile elements like boron Open frame-less dump trailers filled with dry FBC fly ash have been unloaded in the field with practically no dust emissions Much of the dust in handling can be avoided with attention to minor details in construction sequences Experiments are under way to design mobile field systems that will render FBC fly ash non-dusty while retaining its dry fine granular characteristics (Paul et al, 1996)

A power plant in Illinois produces forced-oxidized synthetic gypsum from scrubbing operations that is more pure than the natural product and enhances plant growth The low cost, high volumes and excellent properties of combustion By-products make them suitable for beneficial use in the mines they are hauled back to (Paul et al, 1996)

In studies done in Spain in the vicinity of a mine reclaimed with fly ash, it was found that the existing conditions of Eh-pH in the zones rich in ashes diminished the accessibility of heavy metals for the plants (Macías, et al., 1992; Errecalde, et al 1991)

A similar study was done in Poland, where the impact of fly ash runoff in ground water

quality was investigated Assuming that the criteria to be met by drinking water were those specified by the European Union and WHO documents, it was established that the heavy metals content in the fly ash and slug mixtures did not have a negative effect on underground water quality (Zerbe, et al., 2001)

Most of the health and environmental concerns related to the use of coal combustion by-products stem from the presence in them of trace elements Some of their potential health and environmental effects are summarized in Table 2.2

2.5 Ion Movement with the Amendment of Soils

In southeastern US and Puerto Rico, many soils are acid and the subsoil is acid and infertile For example, there are 209,894 ha of soil belonging to the Ultisols order and 64,801 ha of the Oxisol order in Puerto Rico (Santiago, 1994) Of these, 36,532 ha of the Ultisols are soils of the Consumo series, and 5,262 ha of Oxisols are in the Coto series These soils, in contact with water and in the presence of aluminum, form AlOH+2 type compounds, which are poisonous for plants and release hydrogen which increase the soil acidity Besides, Al and H in solution limit the availability of other ions necessary for plants

TABLE 2.2 Health and environmental effects of trace elements

• Damage to the roots of plants

• Decreased production of red and white blood cells

• Skin changes and lung irritation

• Intensify the chances of cancer development, especially the chances of development of skin cancer, lung cancer, liver cancer and lymphatic cancer

• Infertility and miscarriages with women

• Can damage DNA

likely to accumulate

• When animals absorb large amounts of boron over a relatively long period of time through food or water, the male reproductive organs will be affected

• When animals are exposed to boron during pregnancy their offspring may suffer from birth defects or

delayed development

• Boron toxicity is an important disorder that can limit plant growth on soils of arid and semi arid

concentrations of B may occur naturally in the soil or in groundwater, or be added to the soil from mining, fertilizers, or irrigation water

• Contamination of land by by-products of fossil fuel combustion, such as fly ash, can lead to high soil B concentrations (Adriano, et al., 1980)

• Boron concentrations in fly ash as high as 700 mg/kg are often reported

• The predominant forms of B in fly ash are probably soluble borates and less soluble borosilicates Alkaline conditions in the soil decrease B solubility in fly ash, while neutral and acid reactions promote its solubility and release into solution, therefore liming of the soil will reduce the potential for B toxicity (Nable, et al., 1997)

(Cont.) TABLE 2.2 Health and environmental effects of trace elements

• Upset stomachs and ulcers

• Respiratory problems

• Weakened immune systems

• Kidney and liver damage

• Alteration of genetic material

• Vomiting and diarrhea

• Can interrupt the biological activity in soils, as it negatively influences the activity of microrganisms and earthworms

and headaches

birth defects and miscarriages

chains that they are part of

• Rashes, heat, swelling of the skin and severe pains

• Eyes burning, irritation, and tearing

• Poisoning may even cause death

• Skin irritations,

• Vomiting, nausea, and anaemia

• Can damage the pancreas

• Disturb the protein metabolism

• Respiratory disorders

• Zinc can be a danger to unborn and newborn children Source: Lenntech, 2006