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Landfills as biologically-driven terrestrial carbonate factories
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Professor David Manning
White ML, Manning DAC
Conference Proceedings (inc. Abstract)
Frontiers in Mineral Sciences 2007: a joint Meeting of the Mineralogical Society of Great Britain and Ireland, the Mineralogical Society of America, the Mineralogical Association of Canada and the Société Française de Minéralogie et de Crystallographie
Year of Conference
Source Publication Date
26-28 June 2007
Science Magazine, EuroMinScI (ESF) and CrystalMaker
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Carbonate precipitation within sanitary landfills is well known to engineers because of the problems it causes in leachate drainage, handling and pumping systems. Irrespective of variation in landfill operation and fill history, the vast majority of landfills that accept putrescible matter generate leachates that are saturated with respect to calcite. Thus calcite precipitation is one end product of microbially-mediated anaerobic decomposition of household waste. Mass balance considerations have shown that up to 40% of putrescible carbon input to landfill will be fixed as calcite. In this study, we have investigated the extent of Mg, Fe and Mn partitioning into calcite from different locations within landfill sites and have found that Mg substitutes for Ca up to 7 mole% under oxic conditions. In contrast, Fe and Mn substitute for Ca (up to 47 and 8 mole%, respectively) but only when conditions are reducing. Additionally, we have measured the delta 13C values for these calcites and found systematic variation. Calcite formed within landfill has delta 13C values of -3.1‰ to +3.4‰, whereas calcite formed in external leachate handling systems has delta 13C values of +5.2 to +18.8‰. In areas where methane is degassed, delta 13C values of -8.8 to -4.9‰ were recorded. The nature and extent of cationic substitution in landfill calcite and the observed variation in delta 13C signatures are both associated with the processes that occur in different parts of a landfill. Within the waste, pCO2 is relatively high and transition metals exist in their divalent forms in landfill anoxia, whereas in peripheral leachate handling systems degassing is commonly undertaken and oxygenation of leachate occurs through atmospheric interaction. With these details in mind, a model has been produced that explains the partitioning of certain heavy metals into landfill calcite whilst also elucidating C isotope variations. Both of these variables are controlled by landfill operational factors.
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