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Effect of high-energy milling and thermal treatment on the solid-phase reactions in apatite–ammonium sulphate system


The phosphorous fertilizers are a product of natural sedimentary phosphorite ores. Using this raw material to produce phosphoric acid and classic phosphorous fertilizers has generated well-known ecological problems. A new and perspective way to use the same materials is creating a new type of time-delayed fertilizers applying high-energy milling (HEM) activation method. The impact of the mechanical forces over the solids is mostly revealed through the changes of the quantities being related to the energetic stability and reactivity of the solid phase. The aim of this work is to report the results from the investigation on the chemical and thermal reactions in composites of natural apatite , which are HEM activated for different times and thermally treated, (from Tunisia) and ammonium sulphate. The Tunisian phosphorite belongs to the ‘basic’ apatites having a Ca/P ratio of 1.70–1.77 and is characterized by a complex mineral composition with major component carbonate-fluorapatite. The used ammonium sulphate—(NH4)2SO4 is obtained as a by-product from cleaning industrial waste gases, using e-beam technology. The composites of Tunisian phosphorite ores and ammonium sulphate, mixed in a mass ratio 1:1, were HEM activated during 10 min to 50 h with 20 mm Fe-milling bodies and temperature treated up to 1,100 °C. As a result, the chemical properties of the treated composites changed. Proofs were found for (i) formation of new phases during HEM activation such as NH4Ca(PO3)3 (NH4)2CaH4(P2O7)2, (NH4)2Ca3(P2O7)2.6H2O, CaH2P2O7 and α-Ca2P2O7; and (ii) decreasing of temperature intervals of phase changes in comparison to untreated composite.

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High-energy milling


Natural carbonate fluorapatite Ca5F(PO4)3


Non-activated mixture Ca5F(PO4)3 + (NH4)2SO4 – mass ratio 1:1


Mixture Ca5F(PO4)3 + (NH4)2SO4 – mass ratio 1:1, HEM activated 5 min


Mixture Ca5F(PO4)3 + (NH4)2SO4 – mass ratio 1:1, HEM activated 10 min


Mixture Ca5F(PO4)3 + (NH4)2SO4 – mass ratio 1:1, HEM activated 30 min


Mixture Ca5F(PO4)3 + (NH4)2SO4 – mass ratio 1:1, HEM activated 60 min


Mixture Ca5F(PO4)3 + (NH4)2SO4 – mass ratio 1:1, HEM activated 5 h


Mixture Ca5F(PO4)3 + (NH4)2SO4 – mass ratio 1:1, HEM activated 10 h


Mixture Ca5F(PO4)3 + (NH4)2SO4 – mass ratio 1:1, HEM activated 15 h


Mixture Ca5F(PO4)3 + (NH4)2SO4 – mass ratio 1:1, HEM activated 30 h


Mixture Ca5F(PO4)3 + (NH4)2SO4 – mass ratio 1:1, HEM activated 40 h


Mixture Ca5F(PO4)3 + (NH4)2SO4 – mass ratio 1:1, HEM activated 50 h


Powder X-ray diffraction


Furies transform infrared


Thermal analyses

P2O sol5 :

Soluble P2O5

P2O tot5 :

Total P2O5


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Authors gratefully acknowledge the financial support of this work by the Central Fund of Strategic Development of New Bulgarian University. The Slovak agency ‘Grant’ and the Ministry of Education and Sciences of Bulgaria are gratefully acknowledged also for the financial support granted under contracts Nos. VEGA 2/0009/11 and DNTS/Slovakia/01/3.

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Correspondence to Vilma Petkova.

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Kostova, B., Petkova, V. Effect of high-energy milling and thermal treatment on the solid-phase reactions in apatite–ammonium sulphate system. J Therm Anal Calorim 116, 737–746 (2014).

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  • Phosphorite
  • Waste ammonium suphate
  • High-energy milling
  • Thermal decomposition