STUDY OF THE CHEMICAL AND MINERAL COMPOSITION OF DOLOMITE.

JOURNAL OF FOOD SCIENCE VOLUME 3, ISSUE 10, november 2025 ISSN: 2181-385X 155 STUDY OF THE CHEMICAL AND MINERAL COMPOSITION OF DOLOMITE. J.B. Mavlonov., B.Ch. Nurimbetov., E.A. Eseyova. Karakalpak State University, Republic of Uzbekistan, Nukus https://doi.org/10.5281/zenodo.17980514 Abstract. The dolomite of the Djamansai deposit of the Republic of Karakalpakstan (Uzbekistan) has been studied. It was found that the dolomite ore of the Djamansai deposit contains a minimum amount of impurities and a sufficient magnesium content. The temperature intervals of the two stages of dolomite dissociation, as well as the temperatures at which the dissociation rate is maximal, are determined. It is shown that dolomite is suitable for the production of magnesia binding systems. Keywords: dolomite, Djamansai deposits, dolomite ore, dissociation of dolomite, caustic dolomite, decomposition of carbonates. DOLOMITNING KIMYOVIY VA MINERAL TARKIBINI O'RGANISH. AnnotatsiY. Qoraqalpog’iston Respublikasi (O’zbekiston) Jamansoy konining dolomiti o’rganildi. Jamansay konining dolomit rudasida minimal miqdordagi aralashmalar va etarli miqdorda magniy borligi aniqlandi. Dolomit dissotsiatsiyasining ikki bosqichining harorat oralig’i, shuningdek, dissotsilanish tezligi maksimal bo’lgan haroratlar aniqlanadi. Dolomitning magneziyal bog’lovchilar sistemalarini ishlab chiqarish uchun mos ekanligi ko’rsatilgan. Kalit so’zlar: dolomit, Jamansay konlari, dolomit rudasi, dolomitning dissotsiatsiyasi, kaustik dolomit, karbonatlarning parchalanishi. ИЗУЧЕНИЕ ХИМИЧЕСКОГО И МИНЕРАЛЬНОГО СОСТАВА ДОЛОМИТА. АннотаsиY. Исследовано доломит Джамансайского месторождениya Республики Каракалпакстана (Узбекистан). Установлено, что доломитоваya руда Джамансайского месторождениya содержит минимальное количество примесей, достаточное содержание магниY. Определенi температурнiе интервалi двух стадий диссоsиаsии доломита, а также температурi, при которiх скорост диссоsиаsии максимальна. Показано, что доломит пригоден длya производства магнезиальнiх вyaжуshих систем. Клyuчевiе слова: доломит, Джамансайский месторождениya, доломитоваya руда, диссоsиаsиya доломита, каустический доломит, разложение карбонатов. JOURNAL OF FOOD SCIENCE VOLUME 3, ISSUE 10, november 2025 ISSN: 2181-385X 156 Introduction. Magnesite binders include caustic magnesite and caustic dolomite. The former is made from natural magnesite, and the latter from natural dolomite. Magnesite is magnesium carbonate (MgCO3). Dolomite is a mineral that is a double calcium and magnesium carbonate (CaCO3∙MgCO3). Dolomite is grayish-white, sometimes with a yellowish, brownish or greenish tint. Its hardness on the Mohs scale is 3.5…4, and its density is 2.8…2.9 g/cm3. Magnesites and dolomites are used as raw materials in refractory and some other industries. The production process of caustic magnesite and caustic dolomite involves firing the raw materials and grinding the firing products. Magnesite is decarbonized during firing and converted into MgO. The decomposition of magnesium carbonate begins at a temperature of about 4000 ºC, but proceeds at a sufficient rate only at 600-6500 ºC. The practical temperature for calcining magnesite in shaft furnaces is 750-8000 ºC, and in rotary furnaces – 10000 ºC [1]. Currently, with the development of the construction industry, many countries around the world are actively working on the use of magnesia binders as a binding agent, since the Portland cement currently used in construction, the production of which is more energy-intensive, compared to magnesia binders. Therefore, using magnesia binders instead of Portland cement is relevant, since this allows you to reduce energy costs for firing, and in turn, reduce the cost of products based on magnesia binders. The development and implementation of new technologies for magnesia binders for construction purposes and the production of modern building materials and products based on them are of scientific and practical interest. It is known from literary data that in the process of firing dolomite at a temperature of about 750 °C, caustic dolomite is formed, which consists mainly of CaCO3 and MgO (at least 15%). At higher temperatures, dolomite cement and dolomite lime can be obtained. Dolomite cement, which includes MgO, CaO and CaCO3, is obtained at a firing temperature of 800–850 °C; dolomite lime (a mixture of MgO and CaO) is formed at a firing temperature of 900–1000 °C. Higher temperatures lead to sintering of dolomite and the formation of dolomite refractories [2]. It is known that the mechanism of firing and then sintering of limestone and dolomites is that small crystalline grains, under the influence of molecular adhesion forces, grow together into a crystalline body, while some of the pores close, and then recrystallization (crystal growth) is observed. During sintering, in parallel with recrystallization, a process of "healing" of crystals with distortions in the original crystalline structure is observed, which is accompanied by a decrease in the activity of the substance [3]. JOURNAL OF FOOD SCIENCE VOLUME 3, ISSUE 10, november 2025 ISSN: 2181-385X 157 In Uzbekistan, only one dolomite deposit has been explored as a refractory raw material – the Farhad Rocks. For other purposes, the Dakhkanabad, Pachkamar, Karakiya, Mamadzhurgat, Navoi and other deposits have been studied in detail. Dolomites in most cases are primary sedimentary formations formed in saline basins. The age of dolomite rocks varies: from the Lower Paleozoic to the Mesozoic and Cenozoic inclusive. Uzbekistan has virtually unlimited reserves of dolomite, estimated at billions of tons, since it is found widely, often in combination with limestones [4]. Methods and materials. The purpose of this work is to study the dolomite of the Zhamansai deposit for the production of low-temperature binders. Dolomite from the Djamansai deposit of the Republic of Karakalpakstan was used for the study. The Djamansai deposits also serve to obtain limestone for soda and cement production. Chemical (Table 1) analysis of dolomite was carried out using an EDX-7000P energydispersive X-ray fluorescence spectrometer, which measures the energy and intensity of secondary fluorescence radiation, determining the elements and their quantitative content in the sample. The chemical and mineralogical composition of dolomite is mainly a mixture of calcium and magnesium carbonates, some amount of silica compounds, alumina, and iron hydroxide, calcium sulfate in the form of gypsum, a small amount of soluble salts of sulfuric and hydrochloric acids. As can be seen from the chemical analysis data, the dolomite content in the sample is almost 99%, which shows the purity of the rock from clay impurities. The CaO:MgO ratio almost corresponds to the theoretical one (1:1). Results and discussion. Table 1. Chemical composition of dolomite samples, % Birthplace of dolomite SiO2 Al2O3 Fe2O3 CaO MgO SO3 Na2O K2O pinning losses  Djamansai 0,34 0,20 0,04 26,31 24,89 0,15 0,02 0,03 47,65 99,63 The phase composition of dolomite ore samples was studied using the X-ray phase analysis method (Table 2). X-ray phase analysis was performed using a RIGAKU Dmax – 2200. Table 2. X-ray phase analysis data for a dolomite sample. d [Å] Line intensity Minerals JOURNAL OF FOOD SCIENCE VOLUME 3, ISSUE 10, november 2025 ISSN: 2181-385X 158 3.7006 71.9 CaCO3 2.8914 1000.0 CaMg(CO3)2 2.6748 34.1 CaMg(CO3)2 2.5437 32.5 CaMg(CO3)2 2.4079 121.7 CaMg(CO3)2 2.1957 243.1 CaMg(CO3)2 2.0679 27.2 CaCO3 1.8078 172.7 CaMg(CO3)2 1.7896 220.5 CaMg(CO3)2 The results of X-ray phase analysis of the ore sample from the Dzhamansai deposit show the presence of dolomite minerals (maximum peak at 2θ = 31.2º) and calcium carbonate (Fig. 1). Figure 1. X-ray diffraction pattern of dolomite The process of carbonate decomposition is complex, with individual stages being diffusion, adsorption and desorption. During the process of carbonate decomposition, chemical reactions and crystalline transformations depend on the nature of the material, as well as on the size of the pieces of the fired material, the heating rate and others [5]. According to A.A. Pashchenko [6], the onset of decomposition of the magnesia component is in the temperature range of 720…760 °C, calcium – 895…910 °C, and according to the studies of V.S. Ramachandran [7], dolomite decomposition is observed at 810 °C and 900 °C. According to the authors [8, 9], the firing conditions should be adjusted so as to exclude decarbonization of CaCO3. Many works are devoted to the study of the chemical and physicochemical properties of carbonate minerals during the firing process and the production of carbonate binder systems based on the raw materials of Karakalpakstan [10-15]. In our case, the raw material for obtaining carbonate binders systems and lime-belite binder (LBB) was natural carbonate marls from the Akburly and Porlytau deposits. In the lime- JOURNAL OF FOOD SCIENCE VOLUME 3, ISSUE 10, november 2025 ISSN: 2181-385X 159 belite binder (LBB)-calcium carbonate-water system, marble flour obtained by highly dispersed grinding of marble (96.5% CaCO3) was used as a carbonate filler [10, 12]. It was established that the optimal mode of heat treatment of the studied marls with and without the addition of quartz sand and the production of, respectively, carbonate binders systems and lime-belite binders IBV1 and IBV2 is a temperature of 1000 ºC with a holding time of 90 minutes. Thermal properties of dolomite ore of Dzhamansai deposit were studied using synchronous thermal analyzer STA409 PCLuxx. This device allows to measure changes in mass and heat of transformations in one experiment for one and the same sample. According to thermal analysis data, two clear endothermic effects are visible on DTA and DTG curves, this shows that dolomite decomposition occurs in two stages. The temperature range of the first stage of dolomite dissociation corresponds to the range of 713–766 ºC, and the second to the range of 780–820 ºC. Figure 2. Thermogram of a dolomite sample There are two steps on the TG curve, characterizing the mass loss of the substance under study. The change in mass, relative to the initial mass, at the first stage is 20.17%, and at the second - 26.79%, in total - 46.96%. The data also show that the DTA curve also shows an exothermic thermal effect, possibly associated with the crystallization of the amorphous decomposition product. The analysis of the obtained data allows us to conclude that of all dolomite binders, dolomite lime has the maximum activity, which is obtained at a dolomite firing temperature of about 1050 ºС. The obtained data agrees well with studies of the firing process of marly limestone and dolomites from other deposits. The presence of magnesium oxide somewhat JOURNAL OF FOOD SCIENCE VOLUME 3, ISSUE 10, november 2025 ISSN: 2181-385X 160 reduces the temperature at which the maximum energy level of the CaO crystal lattice is reached, and a further increase in temperature does not cause an increase in lime activity. Conclusion. The chemical, physicochemical and mineralogical properties of dolomite from the Dzhamansai deposit were studied. From the chemical analysis data it is evident that the dolomite content in the sample is almost 99%, which shows the purity of the rock from clay impurities. According to the results of thermographic analysis, it was established that the temperature ranges of two stages of dolomite dissociation were determined, the first stage of dolomite dissociation corresponds to the range of 713–766 °C, and the second to the range of 780–820 °C. 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