Thermal behaviour of Estonian phosphorites from different deposits
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Thermal behaviour of Estonian phosphorites from different deposits Tiit Kaljuvee1 · Kaia Tõnsuaadu1 · Rainer Traksmaa1 · Marve Einard1 · Jekaterina Jefimova2 · Vilma Petkova3 Received: 24 July 2019 / Accepted: 11 November 2019 © Akadémiai Kiadó, Budapest, Hungary 2019
Abstract Thermal behaviour of shelly Estonian phosphorite ores from Iru, Toolse, Ülgase deposits and their concentrates have been studied. The phosphorus-bearing mineral in Estonian phosphate ore is fluorcarbonate apatite (francolite), originated from brachiopod Obolus apollinis shells that makes it different from all other sedimentary phosphate ores. The experiments on a Setaram Labsys Evo 1600 thermoanalyzer coupled with Pfeiffer Omnistar Mass Spectrometer for evolved gases analysis were carried out under non-isothermal condition at the heating rate of 10 °C m in−1 up to 1200 °C in an oxidizing and inert atmosphere containing 79% of Ar and 21% of O 2 or 100% Ar, respectively. The results obtained indicated the complicated character of transformations occurring at thermal treatment of Estonian phosphorites and certain differences depending on the mineralogical composition of sample and gaseous environment. The changes in francolite structure, probable substitution of sulphur additionally to carbonate, were studied by FTIR and XRD. The oxygen in gaseous atmosphere suppresses the liberation of carbonate and sulphate from the structure of francolite. The character of C O2 and SO2 release at heating depending on the atmosphere composition was explained. The impact of thermal treatment of phosphorite on the P 2O5, CaO and SO−2 solubility in 2% citric acid solution and on the particles pore volume, as well as their dependence on each other, 4 was also studied. Keywords Francolite · IR-spectroscopy · Solubility · Thermal analysis · XRD
Introduction The world phosphate rock reserves explored is on the level of 70 billion tons of which 95% are sedimentary and 5% are igneous origin with average content of P2O5 ~ 20% [1]. Phosphate rock is a non-renewable resource which is limited becoming increasingly scarce and expensive [2]. Igneous phosphate is a magmatic rock in which all the elemental phosphorus is incorporated into the crystal structure of apatite. Sedimentary phosphate deposits are bioelemental sediments because they are precipitates of the nutrient element phosphorus [3]. Global phosphate reserves are located unevenly and controlled by several countries, mostly in North Africa (Morocco, Algeria, Tunisia), Middle East * Tiit Kaljuvee [email protected] 1
Department of Engineering, Tallinn Technical University, Tallinn, Estonia
2
Estonian Marine Institute, Tartu University, Tallinn, Estonia
3
Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences, Sofia, Bulgaria
(Saudi Arabia, Jordan, Syria), Brazil, USA, China, etc., but Morocco controlled more than 70% of total resources [1, 4, 5]. In Europe, in addition to apatite–phosphorite deposits in European part of Russia (Kola, Yegoryevsk, Kingisepp, etc.)
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