Organic and inorganic carbon
Jutta Laine-Ylijoki1, Päivi Kauppila2, Markku Juvankoski1, Tommi Kaartinen1, Elina Merta1, Ulla-Maija Mroueh1, Jarno Mäkinen1, Emma Niemeläinen1, Henna Punkkinen1 & Margareta Wahlström1; 1VTT Technical Research Centre of Finland Ltd, P.O. Box 1000, FI-02044 VTT, Finland, 2Geological Survey of Finland, P.O. BOX 1237, FI-70211 Kuopio, FINLAND
Elemental carbon forms include charcoal, soot graphite, and coal. The primary sources for elemental carbon in soils and sediments are incomplete combustion products of organic matter (i.e. charcoal, graphite, and soot), geologic sources (i.e., graphite and coal), or dispersion of these carbon forms during mining, processing, or combustion of these materials. In soils, wastes and sediments, there are three basic forms of carbon that may be present. They are: (1) elemental C, (2) inorganic C, and (3) organic C. The quality of organic matter in a certain matrix is critical to the environmental behaviour of many elements and contaminants. (Schumacher 2002)
Inorganic carbon forms are derived from geological or soil parent material sources. Inorganic carbon forms are present in soils and sediments typically as carbonates. The two most common carbonate minerals found in soils and sediments are calcite (CaCO3) and dolomite [CaMg(CO3)2] although other forms may be present (e.g., siderite, FeCO3) depending on where the soils were formed or where the sediment source was located. It should be noted that calcite and to some extent, dolomite, may also be present in soils and sediments due to agricultural input (i.e., liming practices). (Schumacher 2002)
Naturally-occurring organic carbon forms are derived from the decomposition of plants and animals. In soils and sediments, a wide variety of organic carbon forms are present and range from freshly deposited litter (e.g., leaves, twigs, branches) to highly decomposed forms such as humus. In addition to the naturally-occurring organic carbon sources are sources that are derived as a result of contamination through anthropogenic activities. It should be noted that the methods for determining total organic carbon and total carbon contents generally do not distinguish between the sources of the organic carbon forms. (Schumacher 2002)
In mine waste characterisation, the main interest in the carbon analysis is the determination of the abundance of the carbonate minerals in the waste material, as the carbonate minerals, particularly calcite and dolomite, are the primary minerals contributing to the buffering of the acidity produced by the oxidation of sulphide minerals. Carbonate content of the sample is used in the static test CEN/TC EN 15875 to define the amount of acid to be added in the determination of NP potential (Technical Committee CEN/TC 292 2011), and carbonate carbon content can be applied to calculate the neutralising potential of the mine wastes (‘carbonate NP‘).
Methods for determination
Due to the diversity of possible carbon compounds, the quantitative determination of all individual carbon components of natural and anthropogenic origin is not possible. Therefore, it is necessary to rely on the measurement of total quantities and defined parameters, from which total organic carbon (TOC), carbonates and elemental carbon are the most widely and generally used.
Table 1: Methods for organic and inorganic carbon determination (Technical Committee CEN/TC 292).
Standard number and name
|TOC||EN 13137: Characterization of waste –Determination of total organic carbon (TOC) in waste, sludges and sediments||Applicable to wastes from extractive industries for each type (i.e. tailings, waste rock, overburden and topsoil)||Preferred method in EU. The carbonate carbon content can be obtained from EN 13137|
|EN 15936: Sludge, treated biowaste, soil and waste – Determination of total organic carbon (TOC) by dry combustion||Applicable to wastes from extractive industries for each type (i.e. tailings, waste rock, overburden and topsoil)||EN 13137 and EN 15936 are basically the same|
|Elemental C analysis||ISO 10694: Soil quality – Determination of organic and total carbon after dry combustion (elementary analysis)||Applicable to wastes from extractive industries for each type (i.e. tailings, waste rock, overburden and topsoil)|
|ISO 29541: Solid mineral fuels – Determination of total carbon, hydrogen and nitrogen content – Instrumental method||Applicable to coal. It gives both organic and inorganic (carbonate) carbon|
|Carbonate determination||EN 196-2: Methods of testing cement – Part 2: Chemical analysis of cement; section 15 – Determination of the carbonate content|
|ISO 10693: Soil quality – Determination of carbonate content – Volumetric method|
|EN 15936 : Sludge, treated biowaste, soil and waste – Determination of total organic carbon (TOC) by dry combustion||TIC = carbonate is part of the method. Preferred method|
|Carbonate carbon||ISO 925: Solid mineral fuels – Determination of carbonate carbon content – Gravimetric method|
Schumacher, B. 2002. Methods for the determination of total organic carbon (TOC) in soils and sediments. EPA, NCEA-C- 1282 EMASC-001 April 2002.
Technical Committee CEN/TC 292 2011. Characterization of waste – Static test for determination of acid potential and neutralisation potential of sulfidic waste. EN 15875.
Technical Committee CEN/TC 292 2012. Characterization of waste – Overall guidance document for characterization of wastes from extractive industries. CEN/TR 16376:2012.