Nuclear Techniques and the Disposal of Non-Radioactive Solid Wastes

FEATURES

Nuclear techniques and the disposal of non-radioactive solid wastes

Heavy metals and other environmental pollutants in solid wastes often are identified and analyzed using nuclear-based methods

by Sheldon Wne of the most vital and persistent public also had wide acceptance in characterizing dif- Landsberger and health challenges facing local, state, and national fusion patterns for metals in soil and aqueous Bruce Buchholz governments is the disposal of solid waste environments and water pollution flows. These produced from industrial, utility, and municipal parameters are important in understanding how sources. mobile or immobile leachates from solid wastes There is a growing interest in the monitor- are in the water table and to predict their general ing, control, and safe disposal of the chemical transport mechanism in the environment. constituents arising from these sources. For instance, it is now well known that the release of byproducts from coal-fired power plants— Nuclear and related techniques namely airborne particulates, bottom ash, and fly ash — can have adverse effects on air and water Neutron activation analysis (NAA). NAA is quality. Another major concern is the disposal of a technique capable of determining 40 to 50 municipal solid waste by incineration and direct elements including many environmentally cru- landfilling, which can result in potentially ad- cial ones (e.g. antimony, arsenic, cadmium, verse affects on the environment due to the high chromium, copper, mercury, nickel, selenium, concentration of heavy metals in the waste itself. vanadium, zinc, etc.). It is also capable of deter- The use of very large quantities of minerals in mining major elements such as sodium, chlorine, many industrial processes can also lead to some- and potassium, as well as many rare earth ele- what complicated waste management problems. ments. The determination of the elemental con- It is therefore important that reliable chemi- centrations is based on the measurement of in- cal analytical techniques are readily available to duced radioactivity following the irradiation of assess the impact of widespread disposal prac- the sample in a nuclear research reactor. The tices of organic and inorganic chemicals. The radioactive decay of each element produces a use of nuclear and nuclear-related analytical characteristic gamma-ray energy spectrum. techniques—such as neutron activation analysis, Hence an individual nuclear "fingerprint" can be energy dispersive x-ray fluorescence and par- measured and quantified. ticle induced X-ray emission—have become Activation analysis measures the total widespread in major areas of science and tech- amount of an element in a material without nology. These methods and techniques have im- regard to its chemical or physical form. It has the portant applications in such work since they can following advantages: be used for both the determination of specific • samples for NAA can be liquids, solids, or individual pollutants (e.g. toxic heavy metals) powders; and multi-elemental analyses for source iden- • NAA is non-destructive and since no pre- tification and apportionment purposes. Other chemistry is required, reagent-introduced con- nuclear techniques, such as isotope tracers, have taminants are completely avoided; • many elements can be readily analyzed simultaneously; • it is highly sensitive to trace elements. Dr Landsberger is an associate professor in the Department of These factors have pushed the detection Nuclear Engineering at the University of Illinois, 103 South limits of many elements of interest to very low Goodwin Ave., Urbana, Illinois, U.S.A. 61801, and an af- filiate at the Institute for Environmental Studies. Mr Buchholz levels, not readily achievable by other analytical is a PhD candidate in the Department of Nuclear Engineering. techniques. NAA is also totally unaffected by

14 IAEA BULLETIN, 1/1993 FEATURES

The municipal waste incineration plant in Vienna, whose facade was designed by Viennese painter, Friedensreich • Hundertwasser. (Credit: E. Schauer. Vienna) the presence of organic material in the sample. Worldwide facilities This organic material is a significant matrix problem in several types of conventional chemi- At present there are more than 250 research cal methods. reactors in use for routine environmental Energy-dispersive X-ray fluorescence (ED- monitoring and research using neutron activa- XRF) and Particle induced X-Ray emission tion analysis. More than 100 PIXE facilities and (PIXE). In both of these techniques the quantiza- many more ED-XRF units are also available in tion of elemental concentrations is based on the numerous universities, governmental laborato- detection of X-rays. In ED-XRF, samples are ries, and private institutions. bombarded with X-rays from either a tube or a There are many scientists with significant radioactive source. In PIXE, protons are the analytical expertise to warrant continued use of usual charged particle, which are used to bom- these nuclear and nuclear-related methods in bard the samples and induce X-ray emission. solid waste research. The following sections pre- The methods have similar advantages to those in sent a sampling of a few of the wordwide pro- NAA. In general, fewer elements can be detected grammes that utilize these powerful techniques. with either ED-XRF or PIXE than with NAA. However, it is not possible to detect elements such as sulphur and lead with NAA, although it Airborne particulate matter is using the other two techniques. Isotope tracer technique. This technique is Over the last two decades numerous studies based on the principle that very minute amounts have been initiated to identify and study the fate of radioactivity in the form of a soluble radio- and transport of heavy metals released into the isotope can be injected into a solid or aqueous airborne environment by coal-fired power environmental system and later be detected after plants, incineration facilities, various smelting it has been transported by some mechanism. This processes, automobile exhausts, indoor in- method has been successfully used in hydrology dustrial processes, etc. studies, and its application to environmental There are a variety of reasons to sample and problems has become more widespread. analyze airborne particulate matter. Sampling Typically isotopes of bromine, cadmium, may be done to determine if the concentrations chromium, caesium, chlorine, sodium, and zinc of total particulate matter may be high enough to are used. Most of these radionuclides have rela- adversely affect public health. Thus sampling tively short half-lives when compared to nuclear may be part of an exposure evaluation in which waste. This makes their use ideal for real-time risk is being assessed, information gathered to studies. permit risk management, or monitoring con-

IAEA BULLETIN, 1/1993 15 FEATURES

Nigeria, Slovak Republic, Turkey, United Element Fly ash Soil States, Viet Nam, and Zaire.

Silver 31 .4 - 60 0.1 Aluminum 1.07-11.1% 7.1 % Solid waste Arsenic 75.3 - 229 6.0 Barium <700-1300 500 Perhaps the most widely analyzed solid was- Bromine 1420-5180.00 5 tes by nuclear methods, particularly NAA, are Calcium 8.44-28.1% 1 .37% residues from coal burning; namely coal bottom Cadmium 80.4 - 314 0.06 ash and fly ash. Cerium 4.42 - 51 .90 50 Worldwide there has been a steady increase Chlorine 3.6 - 20.9% 100 in the use of coal to generate electricity for Cobalt 4.78 - 37.3 8 various industrial activities, residential homes Chromium 94.1 - 865 100 and commercial buildings, as well as for heating. Caesium 2 06 - 3 31 6 However, this massive usage has led to the Iron 0.26-2.12% 3.8% disposal of millions of metric tonnes of residual Mercury 18.5-209 0.03 bottom ash and fly ash, which must be properly Indium 0.49-1.91 — managed. There have also been many studies Lanthanum 2.47 - 27.9 30 undertaken to determine which elements, par- Manganese 180-1000 850 ticularly heavy metals such as lead, arsenic, mer- Sodium 1.52-2.83% 0.63% cury, cadmium, antimony, etc., can leach from Rubidium 12.2-40.6 100 the solid waste and potentially become an en- Antimony 618-1665 (2-10) vironmental hazard to groundwater. Scandium 0.89 - 8.37 7 In recent years the disposal of municipal Selenium <2.51 - 109 0.2 solid waste (MSW) has become another impor- Silicon <1.21 - 17.0% 33% tant environmental as well as political issue. Samarium <0.43 - 4.6 — Landfills accommodate most MSW but the Strontium <600 300 vexing problems of leachate generation from Tantalum <0.24 - 3.36 — rainwater permeation and methane gas produc- Thorium 0.79-9.10 5 tion (from decomposition) persist. Replacing Titanium 0.25 - 2.46% 5000 landfills is becoming increasingly difficult and Vanadium <9.93-81.1 100 alternative solutions such as recycling only par- Zinc 8690- 18200 50 tially alleviate the problem. Incineration of MSW reduces its volume and mass by as much Notes: All concentrations are in micrograms per gram unless otherwise specified. Data are from a study at the University of Illinois, USA as 80% to 90%. However, the remaining ash contains high concentrations of many heavy metals such as lead, cadmium, mercury, antimony, zinc, and silver. The potential threat to Summary of the ducted to support epidemiological studies. Sam- groundwater posed by these metals is real and abundance of pling may also be conducted to determine com- long-term studies of the chemical composition, elements in fly ash pliance with air quality laws or regulations. elemental distribution, and leaching charac- and soil from Finally, studies of atmospheric transport, trans- teristics are essential. municipal solid formation, and deposition processes may require Recently, the IAEA has published a detailed waste incineration intensive particle characterization. Essentially technical document with guidelines for leaching air samplers are placed in strategic areas in studies on coal fly ash and other solid wastes urban, rural, and remote locales and then the air with special reference to the use of nuclear filters are analyzed. Subsequent analysis may methods.* Several important aspects were involve various mathematical models to covered including physical characterization, elucidate the sources of the elemental air pollu- distinguishing between different leaching tests, tion and/or evaluate health effects to the general field sampling, and application of radiotracers. public or industrial workers. In our laboratory at the University of Illinois Analysis of air filters, which usually have a we have employed a series of neutron activation very low mass of airborne paniculate matter, has analysis techniques to determine 30 trace ele- greatly benefitted from all the techniques men- tioned here. Some countries involved in such investigations in an IAEA-supported co-or- dinated research programme include Argentina, * Guidelines for Leaching Studies on Coal Fl\ Ash and Other Solid Wastes with Special Reference to the Use of Belgium, Brazil, Chile, China, Canada, Czech Radioanakncal Techniques, IAEA TECDOC-616. Vienna Republic, Germany, Greece, Hungary, India, (1991).

16 IAEA BULLETIN, 1/1993 FEATURES ments in MSW incineration fly ash.* Size distribution is an important physical characteristic. Note: Data are from a study Results have shown that more than 75% of the at the University of Illinois fly ash consists of particles with diameters less than 63 microns. (See graph.) These smaller particles possess a large total surface area with many possible leaching sites. Our data confirm that most potentially toxic elements are con- centrated on the smallest particles. When compared with normal soil values, the fly ashes contain extremely elevated amounts of numerous elements.(See table.) Elements such as antimony, arsenic, cadmium, chromium, indium, mercury, silver, and zinc are particularly en- riched. These elements may serve as source markers. One crucial area which has been neglected by the vast majority of researchers in MSW in- <20 20-38 38-63 63-106 106-150 150-250 >250 cineration is the elemental characterization of Particle size (microns) ordinary household goods. For instance, it is well known that lead-acid and common dry cell bat- teries contribute significantly to increased levels Environment.** They include studies in the fol- Size distribution of of lead, mercury, cadmium, copper, and zinc in lowing areas: trace elements in the incineration ash. Recently, researchers in the • establishment of the pathways of industrial fly ash from Netherlands and Canada, employing NAA, have effluent discharges at different tidal stages in incineration of shown that various plastics from household was- Malaysia; municipal solid tes are a major source of cadmium. It is therefore • prediction of pollution transport rates from waste extremely prudent to identify common Hungarian landfills and depositories by radioac- household goods which may contain such heavy tive tagging of toxic elements in the soil; metals. Identification of heavy metal sources • determination of residence time distributions may prompt industries to change their process- and flow patterns of waste and sludge in waste ing procedures and eliminate or drastically water treatment facilities of the Czech Republic reduce the quantity of the heavy metals entering and the Slovak Republic; the waste stream. • investigation of the efficiency of Polish in- Another area of great concern is the disposal dustrial sewage treatment plant devices. of industrial solid waste. This differs from Recent French research employing isotope municipal solid waste in that there are generally techniques include risk assessment of iron and fewer different kinds of heavy metals, but the steel industry waste, characterization of en- amounts and concentrations may be orders of gineering cover and containment barriers for magnitude higher. This is particularly true for urban industrial waste sites, and reutilization of mineral based industries. Landfills and water- wastes in forestry and industry. ways are the usual recipients of industrial wastes. There are numerous countries using nuclear and nuclear-related methods to chemically iden- An issue of growing importance tify the waste itself and to study their leaching characteristics. It is unlikely that interest in solid waste dis- Isotope techniques, commonly using radio- posal will diminish. As developing and active tracers, have been successfully employed developed countries increase their use of fossil in many different types of investigations. Some fuels, expand their industries, and increase their applications were reported recently at the IAEA consumption of goods and services to secure a International Symposium on Applications of higher standard of living, solid waste disposal Isotopes and Radiation in Conservation of the will remain an extremely important issue of waste management. The methods of nuclear and nuclear-related * "Elemental Characterization of Size-Fractionated analytical techniques can be judiciously maxi- Municipal Incinerator Ash", S. Landsberger, B. A. Buchholz, mized in the characterization of airborne, indus- M. Plewa and M. Kaminski, /. Radioanal Nucl. Chem (in press, 1993). trial, and municipal solid waste and its leachates, ** See the proceedings of the Symposium, published by the and to predict their transport patterns in the en- IAEA, STI/PUB/904, Vienna, Austria (1992). vironment. D

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