Evaluation of the Environmental Risk from the Co-Deposition of Waste
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World Academy of Science, Engineering and Technology International Journal of Environmental and Ecological Engineering Vol:8, No:6, 2014 Evaluation of the Environmental Risk from the Co-Deposition of Waste Rock Material and Fly Ash A. Mavrikos, N. Petsas, E. Kaltsi, D. Kaliampakos [5], leaching behavior of trace elements and heavy metals [6], Abstract —The lignite-fired power plants in the Western [7], as well as the correlation of trace elements and heavy Macedonia Lignite Center produce more than 8 ⋅10 6 t of fly ash per metals in the lignite with the respective compositions in fly year. Approximately 90% of this quantity is used for restoration- ash [8]. However, there are not any available data on the reclamation of exhausted open-cast lignite mines and slope environmental behavior of mixtures of waste rock material stabilization of the overburden. The purpose of this work is to evaluate the environmental behavior of the mixture of waste rock and and fly ash that are being used for the restoration of open-cast fly ash that is being used in the external deposition site of the South mines. Field lignite mine. For this reason, a borehole was made within the Therefore, the present study deals with the evaluation of the site and 86 samples were taken and subjected to chemical analyses environmental behavior of the co-deposited waste rock and fly and leaching tests. The results showed very limited leaching of trace ash based on chemical composition and leaching potential elements and heavy metals from this mixture. Moreover, when tests. For this purpose, a large number of samples were compared to the limit values set for waste acceptable in inert waste landfills, only few excesses were observed, indicating only minor risk collected from the external deposition site in the South Field for groundwater pollution. However, due to the complexity of both mine. The site contains materials with a wide variety of the leaching process and the contaminant pathway, more boreholes composition (marl, sandy marl, sand, clay etc.), granulometry and analyses should be made in nearby locations and a systematic and stratigraphic origin due to the exploitation of the mine, as groundwater monitoring program should be implemented both well as fly ash from the TPP Agios Dimitrios. downstream and within the external deposition site. II. FLY ASH AND ENVIRONMENTAL INFLUENCE FROM Keywords —Co-deposition, fly ash, leaching tests, lignite, waste BACKFILLING OPERATIONS rock. A. Fly Ash I. INTRODUCTION Fly ash is a fine powder, consisted mainly of spherical, HE lignite basin of Kozani – Ptolemaida – Amyntaio is glassy particles that originate from burning of pulverized coal Tthe biggest and most important in Greece. The proved [9]. According to the European standard ΕΝ 197-1, fly ash is lignite reserves contained in this basin are more than 4·10 9 t, divided into two main categories, i.e. siliceous fly ash (V), which account for 65–70% of the country’s total coal which contains less than 10% CaO, and calcareous fly ash resources [1]. There are 5 lignite mines currently in operation (W), which contains 10–35% CaO. Siliceous fly ash has in this area that feed 4 thermal power plants (TPPs). These pozzolanic properties, while calcareous fly ash may also have plants have a total installed capacity of 4000 MW and cover hydraulic properties. 32% of the total energy generation in Greece. The American standard ASTM C 618 classifies fly ash into As a consequence of lignite burning, large quantities of fly three Classes, namely Class N, which includes raw pozzolans, ash are produced. In the Western Macedonia Lignite Center with a minimum of 70% of SiO 2+Al 2O3+Fe 2O3, Class F, (WMLC), the annual quantities of fly ash exceed 8·10 6 t [2]. which originates from anthracite and bituminous coals, with a Over 90% of this fly ash is used in exhausted open-cast lignite minimum of 70% of SiO 2+Al 2O3+Fe 2O3 and Class C, which mines restoration-reclamation with overburden. Fly ash acts as originates from sub-bituminous and lignite coals, with 50– binder for the increase of slope stabilization of the overburden 70% SiO 2+Al 2O3+Fe 2O3. Class F fly ash usually has less than in the restoration process. 5% CaO, while Class C fly ash has a higher CaO content (10– International Science Index, Environmental and Ecological Engineering Vol:8, No:6, 2014 waset.org/Publication/9998419 Several studies have been conducted on Greek fly ashes 35%). regarding their mineralogical and chemical composition [3]– Greek fly ash in the WMLC is calcareous (W) according to EN 197-1 and Class C according to ASTM C 618, due to its Dr. A. Mavrikos is with the School of Mining and Metallurgical high CaO levels (Table I) [5]. Engineering, National Technical University of Athens, Athens, 15780, Greece Fly ashes also contain trace elements (As, Pb, Cr, Ni, Zn, (phone: +30 2107722190; e-mail: [email protected]). Dr. N. Petsas and E. Kaltsi were with the Generation Environment Cu, Ba, Th, Se, Mo, etc.) in relatively high concentrations. Department of Public Power Corporation S.A., Athens, 10432, Greece (e- Table II shows the main trace elements of fly ash in the mail: [email protected], [email protected]). WMLC [7]. Prof. D. Kaliampakos is with the School of Mining and Metallurgical Engineering, National Technical University of Athens, Athens, 15780, Greece Environmental concerns from the presence of trace (phone: +30 2107722211; e-mail: [email protected]). International Scholarly and Scientific Research & Innovation 8(6) 2014 385 scholar.waset.org/1307-6892/9998419 World Academy of Science, Engineering and Technology International Journal of Environmental and Ecological Engineering Vol:8, No:6, 2014 elements depend mainly on their form within the fly ash and and analytical information on the properties and the potential on their mobility capability (e.g. Mo shows high leaching risks of the substances, based on toxicological and ability in alkaline environment). Thus, many trace elements ecotoxicologal data. remain entrapped in fly ash, despite the fact that they may The producers of fly ash have registered their product for come in contact with rain water in the deposition areas. There use in the construction industry under REACH. All are, however, other circumstances that favor trace element information about chemical, physical, toxicological and leaching and create risks about possible degradation of ecotoxicological properties was compiled and submitted in a groundwater quality. The issue of leaching, which could affect registration dossier. Fly ash has been registered as a UVCB the environment, is of major importance for a proper substance (substance of unknown or variable composition, evaluation of the environmental compatibility of fly ash [9]. complex reaction products or biological materials) and has been assigned with the EC number 931–322–8. All TABLE I commercial uses of the substance have also been described. CHEMICAL COMPOSITION OF FLY ASH IN THE WMLC Main oxides Typical range (% wt.) Details of the chemical composition and the properties of the registered fly ash are publically available at the ECHA website SiO 2 25,35 - 35,30 Al 2O3 9,22 - 13,51 (www.echa.europa.eu). Fly ash in the WMLC, according to its Fe 2O3 4,98 - 6,35 chemical composition as given in Table I, is covered from the CaO 29,10 - 41,00 substance that has been registered. MgO 2,85 - 4,76 As a result of the hazard assessment and PBT/vPvB Na 2O 0,35 - 0,62 assessment it has been found that the registered fly ash does Κ2Ο 0,92 - 1,49 not meet the criteria for classification as hazardous (according TiO 2 0,47 - 0,77 to Directive 67/548/EEC and Regulation 1272/2008/EC) and SO 3 3,55 - 6,92 does not meet the criteria for PBT/vPvB substances. LOI 3,38 - 6,17 C. Environmental Influence from Backfilling Operations with Fly Ash TABLE II TRACE ELEMENTS OF FLY ASH IN THE WMLC The problems that relate to the vast production, combined Trace element Typical range (mg/kg) with certain properties of the material, led to alternative ways As 20,8 - 38,8 of utilizing fly ash. Since 1930, fly ash has been used in road B 0,28 - 0,34 construction as mineral filler in asphaltic mix, in embankment Ba 124,2 - 229,4 soil stabilization, sub-grade base course material, as aggregate Cd 0,65 - 1,49 filler and bituminous pavement additive [6], [13]. Currently, Co 14,9 - 20,7 fly ash applications have expanded and include cement Cr 148,9 - 201,1 production and related products [13], [14], restoration and Cu 30,3 - 74,9 remediation of polluted soil [15], [16] and production of Mn 102,3 - 246,8 synthetic zeolites [17]. In Greece, the main application of fly Mo 5,0 - 7,3 ash is the backfilling for restoration of exhausted open-cast Ni 217,4 - 265,5 Pb 20,4 - 27,2 mines. Almost 70% of the total produced quantities are used in Sb 0,82 - 1,33 this direction. Another 10%, with a trend to decrease lately Se 10,0 - 25,7 due to the recent financial crisis, involves the utilization in Sr 318,9 - 385,5 other commercial applications, mainly in the cement industry, V 89,4 - 116,2 which is rather low when compared to the European average Zn 63,0 - 130,0 of 18% [2], [4]. Internationally, there is a widespread utilization of fly ash in B. Fly Ash as a by-Product – REACH Regulation filling applications of abandoned mines and embankments. In It is well established that fly ash can be utilized as a by- this respect, various studies have been published that examine product in the building material industry, in civil engineering, possible influence of the groundwater, adjacent to the in road construction, for construction work in underground deposition areas, from trace element leaching.