Estimation of absorption capacity of coals metamorphosed to a different extent using the example of potassium fixation

The composition and properties of different coal types, in particular mined in Siberia, are thoroughly studied, but the ecological impact of coals on soil formation process and restoration of technogenic landscapes still lacks sufficient attention. At the same time, one of the main properties of coal, determining its ecological functions, is absorption capacity. The aim of the research was to estimate potassium fixation capacity of coals metamorphosed to a different extent in comparison with loess loam and automorphous soils. We selected three types of coal from West Siberia major fields: anthracite from Gorlovsky field of the Gorlovsky coal basin (54˚34'N, 83˚35'E), coal from Listvyansky field of the Kuznetsky coal basin (53˚39'N, 86˚53'E) and brown coal from Nazarovo field of the Kansko-Achinsky basin (55˚58'N, 90˚23'E). For a comparative assessment of potassium fixation capacity of coals, we took the following samples: loess carbonated loam (hereinafter, loam) as the prevailing soil-forming rock and humus horizon of Luvic Chernozems (hereinafter, agrochernozem) as automorphous soil on the territory of the studied coal basins. Below in the text, as well as in the tables and figure, the samples of three coal types (anthracite, coal and brown coal), loam and agrochernozem are designated as “substrates”. We examined potassium fixation in the laboratory with substrate composting during 150 days in the presence of potassium fertilizers alternating humidification and desiccation. We added 100 g of air-dry substrates sifted through a sieve with 1 mm hole diameter to water solution of potassium fertilizers (KCl) at a dose of 25 and 50 mg of K/100 g (variants K25 and K50, respectively). The experiment also included a variant without fertilization (K0). After fertilization, the substrates were thoroughly mixed and 1, 5, 15, 30 and 150 days later samples were picked for chemical analysis. The experiment was conducted in 2 replicates, thus, the sample size for each substrate was n = 30. Potassium forms were extracted by the following ways: watersoluble potassium (Ws-K) in the ratio of substrate: water 1:5, exchangeable potassium (Ex-K) by 1М CH3COONH4, and non-exchangeable potassium (Nex-K) by 1М НNO3 with boiling. The exchangeable potassium content before the experiment (See Table 1) and during the period after fertilization (See Tables 2 and 3) was calculated with the water-soluble form of the element. At the end of the experiment (150 days), we determined the content of three forms of potassium (Ws-K, ExK and NexK) in the substrates using the difference method (See Table 4 and Fig. 1). Potassium, not extracted by 1М CH3COONH4, was considered fixed. Potassium fixation was calculated in relation to the variant without fertilization (К0) both in absolute values (mg/kg) and as a percentage of the applied dose of fertilizers (fixation percentage). Potassium fixation capacity of anthracite and coal averaged 36% and 30%, respectively in the experiment, which brings them closer to agrochernozem (38%); brown coal was characterized by low potassium fixation (10%), and for loess loam it was high (80%) (See Table 2). Regardless of fertilizer dosage, the applied potassium was never fully fixed by substrates. When potassium fertilizer dosage increased, the absolute value of fixed potassium in substrates significantly rose, but the percentage of the element fixation was at about the same level or even decreased. During potassium fixation by substrates (except brown coal), potassium cations transited not only into non-exchangeable form (extracted by 1М HNO3), but also into a more tightly bound state. Potassium was accumulated in substrates in the following forms: loess loam - non-exchangeable, agrochernozem - exchangeable, coal and brown coal - exchangeable and water-soluble, anthracite - water-soluble (See Table 4 and Fig. 1). After long-term substrate composting, potassium applied with fertilizers was extracted in water-soluble, exchangeable and non-exchangeable forms differently: 100% from brown coal, up to 90% from coal and loam, and around 50% and 40% from agrochernozem and anthracite, respectively. Thus, coals metamorphosed to a different extent are able to deposit biogenic elements and affect the nutrient regime and properties of young soils of coal-mine dumps, and, thereby, are able to determine the rate of restoration of technogenic landscapes. We can assume that more metamorphosed coals (anthracite, coal) will have a greater effect on the functioning of young soils of technogenic landscapes. The fact that coal and anthracite get to dumps with coarse-fragmented rocks having low adsorption capacity enhances this effect. Brown coal comes mainly with loess loam, which minimizes its participation in exchange processes in young soils of technogenic landscapes. Using the results of this experiment will allow a more detailed estimation of the soil-ecological condition and prospects for restoring technogenic landscapes, and, thus, correcting the purposes and reasonably designating the directions of restoration activities. The paper contains 1 Figure, 4 Tables and 39 References.

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