University of Geological Sciences (Tashkent, Uzbekistan):

Isokov M. U., Vice-Rector, Doctor of Geological and Mineralogical Sciences

Institute of Mineral Resources UGN (Tashkent, Uzbekistan):
Alimov R. S., Head of Laboratory, PhD in Technical Sciences, alimov_rs@mail.ru
Almatov I. M., Senior Researcher, PhD in Technical Sciences, ilkhom90@list.ru
Soatov S. A., Junior Researcher

Coal processing at the Angren deposit in Uzbekistan has led to accumulation of a huge amount of coal tailings, for which an effective and economically viable recycling technology is required. For this purpose, a waste-free technology has been developed, which includes two-stage tailings processing. At the first stage, the tailings are treated with NaOH or KOH hydroxide at the rate of 5–8 g/100 g with the solid/liquid ratio of 1 : 5 for 30 minutes at 80 °C. The humic acid extracts are then filtered, the suspension is adjusted to pH 6.5–7, and dehydration to 50 % moisture is performed to obtain a humate paste. At the second stage, the growth medium is first prepared. First-stage cake is then inoculated with a solution containing an overgrown bacterial medium at a solid/liquid weight ratio of 1 : 3, with the total organic matter present in the form of rice screenings. The resulting mix is placed in waterproof tanks with a layer of up to 2 m and kept for 7–9 days, with six treatments a day. With the mass fraction of bound humic acids (HA) in the residual cake of 13.77 %, bacterial treatment with nine days of cultivation in the active phase results in 11.98 % of free HA passing into the liberated form (available to plants).

1. Ermagambet B. T., Nurgaliev N. U., Syzdykova A. A., Maslov N. A. Prospects for the use of humic substances and their production from oxidized brown coal. Nauka, Tekhnika i Obrazovanie. 2019. No. 2. pp. 20–25.
2. Grechischeva N. Yu., Holodov V. A., Parfenova A. M., Kotelev M. S., Perminova I. V. Study of stabilizing and dispersing ability of humic-clay complexes toward oil pollution of aquaous media. Trudy Rossiyskogo Gosudarstvennogo Universiteta Nefti i Gaza imeni I. M. Gubkina. 2017. No. 1. pp. 133–145.
3. Grechischeva N. Yu., Holodov V. A., Vakhrushkina I. A., Mescheryakov S. V., Perminova I. V. Using of model organicmineral complexes on the base of humic acids and kaolinite to study pahs sorption processes of aqueous and soil medium. Zashchita Okruzhayushchey Sredy v Neftegazovom Komplekse. 2012. No. 5. pp. 21–25.
4. Fisha Ph. C., Budina E. V., Zherebtsov S. I., Malyshenko N. V., Gossen I. N., Klekovkin S. Yu., Sokolov D. A. Comparative assessment of the use of humic substances derived from brown coals for technogenic landscapes reclamation. Pochvy i Okruzhayushchaya Sreda. 2021. Vol. 4, No. 1. pp. 1–10.
5. Zherebtsov S. I., Malyshenko N. V., Votolin K. S., Androkhanov V. A., Sokolov D. A., Dugarjav J., Ismagilov Z. R. Structural-group composition and biological activity of humic acids obtained from brown coals of Russia and Mongolia. Khimiya Tverdogo Topliva. 2019. No. 3. pp. 19–25.
6. Bongiorno G., Bünemann E., Chidinma U., Meier J. Sensitivity of labile carbon fractions to tillage and organic matter management and their potential as comprehensive soil quality indicators across pedoclimatic conditions in Europe. Ecological Indicators. 2019. Vol. 99. pp. 38–50.
7. Federicia E., Massaccesib L., Pezzollac D., Fidatia L., Montalbania E., Proietti P. Short-term modifications of soil microbial community structure and soluble organic matter chemical composition following amendment with different solid olive mill waste and their derived composts. Applied Soil Ecology. 2017. Vol. 119. pp. 234–241.
8. Poeplau C., Don A., Six J., Kaiser M., Benbi D., Chenu C., Cotrufo M. F., Derrien D., Gioacchini P., Grand S., Gregorich E., Griepentrog M., Gunina A., Haddix M., Kuzyakov Y., Kühnel A., Macdonald L. M., Soong J., Trigalet S., Vermeire M. L., Rovira P., Wesemael B., Wiesmeier M., Yeasmin S., Yevdokimov I., Nieder R. Isolating organic carbon fractions with varying turnover rates in temperate agricultural soils — A comprehensive method comparison. Soil Biology and Biochemistry. 2018. Vol. 125. pp. 10–26.
9. Perminova I. V. Humic substances — a challenge for chemists of the 21st century. Khimiya i Zhizn'. 2008. No. 1. pp. 50–55.
10. Enev V., Sedlacek P., Kubíková L., Sovová Š., Doskocil L., Klucaková M., Pekar M. Polarity-based sequential extraction as a simple tool to reveal the structural complexity of humic acids. Agronomy. 2021. Vol. 11, Iss. 3. DOI: 10.3390/agronomy11030587.
11. Ermagambet B. T., Nurgaliev N. U., Khasenova Zh. M., Zaikina A. M., Kholod A. V. Obtaining humic organomineral fertilizer from brown coal. Nauchnyi Zhurnal. 2016. No. 10. pp. 14–16.
12. Dukhovny V. A., Umarov P. D. Water saving as a key factor of sustainable development in the Aral Sea basin. Melioration and water management: collection of scientific papers. Tashkent: SANIIRI, 1999. pp. 9–12.
13. Kamilov O. K. Reclamation of saline soils of Uzbekistan on the example of the Hungry Steppe: dis. for the degree of Doctor of Agricultural Sciences. Tashkent, 1982. pp. 23–49.
14. Land degradation: consequences and solutions for elimination. Ministry of Agriculture of the Republic of Uzbekistan, 2022. URL: https://agro.uz/ru/11-0308 (accessed: 23.05.2022).