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Leaching of Radio-cesium and Other Elements from Cement Solidified MSWI-APC Residues
( Masato Yamada ),( Kazuto Endo ),( Masahiro Sato ),( Satoshi Obokata ),( Tokichiro Yamaguchi ) 한국폐기물자원순환학회(구 한국폐기물학회) 2014 한국폐기물자원순환학회 심포지움 Vol.2014 No.1
The cement solidification is a method to dispose waste containing hazardous substances, such as heavy metals and radionuclides. Recently, cement solidified waste landfills for municipal solid waste incinerators (MSWIs) ash and their air pollution control (APC) residues have been operated in Japan. Also, the radio actively contaminated off-site waste caused by the accident of the Fukushima Dai-Ichi nuclear power plant at above a certain level should be disposed to landfill after solidified by cement. The land disposal of cement solidified waste can provide a containment structure to waste itself in the initial and control fluxes of pollutants to environment in the longer term. Test pieces of cement solidified MSWI-APC residues were made under actual landfill conditions and their leachability of pollutants and structural strength were investigated. Two kinds of MSWI-APC residues were tested. One (hot sample) is APC residues from a MSWI ash melting plant and contaminated by radio-cesium. Another (cold sample) is APC residues from a fluidized bed MSWI. Agents of 6 hazardous inorganics and stable cesium were spiked to the latter one. Both APC residues had been treated by chelate agents at plants before sampling. Same amount of APC residues and the Portland blast-furnace cement class B were mixed at 19 to 38% of the water cement ratio. A certain portions of mixtures were injected to mold of 110 mm diameter, pressed at 0.03 to 25 ton/m<sup>2</sup>. These processes were repeated until height of test pieces raising to 300 mm. Formed test pieces were held in molds and pressed heads for 7 to 19 days. Demolded test pieces were cured for 7 to 28 days in the air. The uniaxial compressive strengths of cement solidified test pieces molded under 25 ton/m<sup>2</sup> were 22 to 71 N/mm<sup>2</sup>. Permeability coefficients of test pieces molded at 25 ton/m<sup>2</sup> were less than 1.59 ×10<sup>-12</sup> cm/sec. These were satisfied conditions in the structural landfill standard in Japan. The tank leaching test with stirring for hot samples showed that around 90% of radio-cesium was leached in 6 hours. Less than 4% of radio-cesium was leached from cement solidified test pieces of hot samples. Leaching ratios for test pieces of hot samples obtained by the tank leaching test without stirring for 32 day were 9 to 17%. Leaching ratios for test pieces of spiked cold samples obtained by same test were 0.002% for total mercury form pieces loaded at 0.003 and 3 ton/m2, 0.4% for cesium from pieces loaded at 0.003 ton/m<sup>2</sup> and less than 0.04% from pieces loaded at 3 and 25 ton/m<sup>2</sup>. All other substances were not detected in leachate. These results suggested that higher compaction would be effective to suppress leaching of substances from the cement solidified waste. Avoidance of contacting the naked surface of cement solidified waste to water would also be important to keep containment of hazardous materials in the waste. This study was partly supported by the Environment Research and Technology Development Fund (3K113015) of Ministry of the Environment, Japan.
Potential of Anaerobic Biological Gas Generation of Waste in the Landfill under Post Closure Care
Tomonori Ishigaki,Masahiro Sato,Kazuto Endo,Masato Yamada,Hiroyuki Ishimori 한국폐기물자원순환학회 2013 한국폐기물자원순환학회 학술대회 Vol.2013 No.2
Stabilization of landfill gas (LFG) generation is recognized as the critical indicator to evaluate the future possibility of environmental impact from the waste landfill. In comparison with leachate quality, the amount of LFG generation is considered more difficult to integrate the sequential monitoring results. Spatially and temporal high variation of the LFG generation and the emission would be influenced by the micrometeorological condition. One of the helpful information to predict the behavior of LFG generation is to estimate the remaining of LFG source in the waste. Biological degradation should decrease the amount of component that should be transformed LFG in the waste. Hence, the LFG generation potential of waste in landfill must be gradually decreased as time goes on. In order to support the assessment of the landfill stability from the viewpoint of LFG, the estimation of the potential of LFG generation of the landfilled waste has been investigated at the landfills that was received the waste incineration ash, slag, C&D inert residue, dredged soil, and so on. The LFG emission behavior has been predicted by using the remaining LFG potential, and it was validated by the investigation of surface LFG emission. Degraded organics by anaerobic incubation had been calculated by Buswell's theoretical equation (Bockreis, et al. 2007). Objected samples that were excavated from 10-15 years old waste layer have shown the little potential of LFG generation (Table 1). A highest content of gasified organics was observed for 2.0m depth of C10 though it was less than 1% of the total weight of sample (dry weight). It would be strongly attributed to intensive pretreatment of waste before the landfilling. Since the landfill operator required the strict quality control for the waste to be disposed of, the content of organics in the waste should be enough low at the initial phase of landfill management. In addition, the effort of the landfill management to promote the biodegradation, such as the lowering of the water level in landfill layer, or ventilation of LFG, had contributed to reduce the biodegradable organics. Fig.1 shows the prediction of methane emission from the landfill. It also exhibited results of investigation of surface LFG emission. The prediction of landfill methane emission was developed by using the parameter that was obtained from excavated waste.
Hiroyuki Ishimori,Hirofumi Sakanakura,Kazuto Endo,Tomonori Ishigaki,Masato Yamada 한국폐기물자원순환학회 2013 한국폐기물자원순환학회 학술대회 Vol.2013 No.2
Prediction method for the long-term chemical leaching amount from by-product/recycled materials such as waste concrete and steel slag and so on is necessary to widely promote their effective utilization and evaluate their environmental safety. Although there are the batch leaching tests and the column leaching test as the testing methods for evaluating the long-term leaching behavior, the leaching mechanism and the testing result compatibility in both tests has insufficiently been clarified yet. Thus, the prediction of the leaching behavior from the by-product/recycled materials used in actual civil works and their environmental safety evaluation are by no means certain. This paper shows the difference between the batch leaching tests and the column leaching tests in the chemical leaching behavior of Cu-slag. The batch leaching tests were conducted under liquid/solid ratio = 10, liquid = distilled water, stirring strength = 0, 30, or 120 rpm. After a certain elapsed time, the leaching solution was exchanged with the pure distilled water and then the stirring was restarted. The elapsed time was set at 1, 2, 4, 8, 16, 32 days. The column leaching tests were also conducted under the same conditions as those of the batch leaching tests in order to evaluate the effects of the pore distribution and the pore flow velocity in the Cu-slag column on the leaching behavior. In the column leaching tests, the effluent passing through the column was circulated as the influent (Fig. 1). The leaching duration in the column tests can be equivalent as that in the batch tests, so that the difference in the leaching behavior between the batch leaching tests and the column leaching tests may be dependent on the pore-scale heterogeneous flow and path generated in porous materials. Figure 2 shows the leaching rate evaluated from the batch leaching tests and the column leaching tests. In the same fluid velocity levels, the leaching rate in the column tests was larger than that in the batch tests. The leaching rate has been considered large with the fluid velocity. Although the fluid velocity generated by the stirring was the same as the flushing velocity on the surface of the Cu-slag in the batch tests, the fluid velocity in the column tests was enhanced because the permeant liquid was concentrated into the limited pore space in the Cu-slag column. Thus, the pore-scale heterogeneous flow and path generated in porous materials should be evaluated in order to clarify the compatibility between the batch leaching tests and the column leaching tests.