Methods for determination of coal carbon in reclaimed minesoils: A review

Abstract Organic carbon (OC) of the minesoils reclaimed from coal mining often contains carbon (C) associated with coal particles from mining and the reclamation activities. This C, collectively referred to as geogenic OC (formed as a product of geological processes), must be quantified in order to accurately determine the pools and sequestration potential of OC that originates from recent vegetation input. Reclaimed mined lands can provide significant sink for atmospheric carbon dioxide (CO2) through C assimilation in vegetation biomass, formation and accumulation of SOM. However, the validity of the reported C sequestration potentials in minesoils reclaimed from coal mining activities is questionable due to inability to quantitatively determine the different C sources that may be present in these soils. Due to its high C content, coal particles present in these soils may lead to overestimation of pools and sequestration rates, and can also represent a large C background against which small changes in recent OC must be measured. This is a methodological challenge which must be overcome in reclaimed minesoils (RMS). Standard procedures for quantifying soil organic C (SOC) cannot distinguish geogenic C and recent OC from plant biomass. Appropriate soil C analysis in RMS must differentiate between inorganic C (carbonates), geogenic OC and recent OC from decomposition of plant biomass. Therefore, the purpose of this review is to collate and synthesize the available information on the existing techniques for separating geogenic and recent OC, and quantifying these OC fractions in RMS. Methods for quantifying geogenic OC in RMS have been grouped into microscopic, thermal, chemical, spectroscopic, isotopic, and combination of some of these methods. The major limitation of thermal and chemical methods is the overlap in sensitivity between some types of coal and recent OM fractions. Most of the spectroscopic techniques are semi-quantitative, and generally yield less accurate estimates of geogenic OC. Radiocarbon analysis is one of the most reliable methods for quantifying geogenic OC in RMS. However, the need for specialized instrumentation, advanced computational skills, and high analytical costs precludes its adoption for routine soil analysis. Additional research is needed to further evaluate the existing techniques, develop some reliable and cost-effective methods, and ultimately propose standard geogenic OC quantification methods that can be widely adopted.