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Use of stable isotopes to distinguish mechanisms of calcite precipitation in response to different landfill operational environments

Lookup NU author(s): Maggie White, Professor David Manning

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Abstract

This study proposes a model that associates carbonate mineral precipitation from landfill leachates to (i) biogeochemical processes responsible for waste degradation and (ii) mechanical factors that are an intrinsic part of landfill operation and leachate treatment. Stable isotope techniques can provide the waste management sector with spatial and chemical data that relate directly to site operation and engineering, allowing insight into the future development of waste management facilities. Biogeochemical processes operating within landfill sites play a major role in the degradation of waste fractions (organic and inorganic) by generating large quantities of CO2 and solubilising calcium and other metals. Because of this, carbonate minerals may precipitate from young and ageing landfill leachates as the waste continues to degrade. Mineral scaling in leachate drainage systems can be problematic as it causes blockages, increasing the risk of uncontrolled discharges to the environment. To identify key biogeochemical reactions associated with carbonate precipitation and to elucidate whether precipitation is influenced by mechanical or physical factors intrinsic to landfill operation, solids collected from seven UK landfills sites were subjected to carbon and oxygen stable isotope analysis. Samples analysed included: (1) suspended solids within young leachates from landfill cells, (2) crusty precipitates recovered from surfaces of concrete blocks, submersed in closed leachate tanks outside the landfill, and (3) solids encrusted inside drainage pipes that carried aged leachate from collection tanks to foul sewer. Mineralogical analysis indicated that calcite was typically dominant within solids, comprising 23-95 weight %. Substitution of calcium for magnesium and manganese (<8 mole %) was often evident, although FeCO3 concentrations were more variable and iron was also associated with sulphides or hydroxides. Calcite delta13CPDB and delta18OPDB-values group according to location of sample recovery. Suspended solids (1) and crusty precipitates (2) show increasingly heavy delta13C values (-3.1‰ to +18.8‰) suggesting that bacterial methanogenesis gradually dominates carbon dioxide production with increasing waste degradation, and calcite incorporates progressively heavier carbon which has been kinetically fractionated (delta13CCO2-CH4≈70‰). A pH controlled kinetic fractionation also shifts these delta13CPDB values. Pipe solids (3) show negative delta13CPDB values (-5‰ to -9‰) which are probably explained through bacterial methane oxidation. Calcite delta18OPDB-values range from -5‰ to +12.5‰ and become progressively more positive with leachate age. Increasing kinetic fractionation (Delta18Ocalcite-leachate) with decreasing temperature (to around 5 degrees C, as leachates leave the landfill) in addition to greater interaction with atmospheric carbon dioxide (+9.8‰PDB) during aerobic leachate treatment, in isotopically open conditions, are also undoubtedly significant.


Publication metadata

Author(s): White ML, Manning DAC

Publication type: Conference Proceedings (inc. Abstract)

Publication status: Unknown

Conference Name: Program and Abstracts of the 19th General Meeting of the International Mineralogical Association: Expansion to Nano, Bio and Planetary Worlds

Year of Conference: 2006

URL: http://www.congre.co.jp/ima2006/

Series Title: Program and Abstracts of the 19th General Meeting of the International Mineralogical Association: Expansion to Nano, Bio and Planetary Worlds


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