Structural and thermal transformations on high energy milling of natural apatite

Abstract

In this work we investigated the isomorphic substitution and thermal decomposition of sedimentary fluor apatite (FAp) (with Ca/P ratio [ 1.67) from Tunisia after high-energy-milling (HEM) activation at different times from 10 to 600 min. The chemical composition of the material includes: 29.6 % P 2 O 5 total and 46.5 % CaO (main components) and 3.5 % F; 0.55 % R 2 O 3 (R = Al, Fe); 1.1 % SO 3 ; 1.9 % SiO 2 (a low content in a comparison with other natural apatites from North Africa or Asia); 0.35 % MgO; 0.05 % Cl; 6.6 % CO 2 are impurities. HEM is a well-known approach for preparing various solid materials and for increasing their reactivity. The solid-state transformation of the initial and HEM-activated apatite samples was examined by chemical analysis, BET, powder XRD, FTIR spectroscopy, and thermal analysis. The structure of natural apatite allows isomorphic substitutions of carbonate, hydroxyl, and metal ions by PO 4 3-, Ca 2? , and F -. The obtained powder XRD data indicate an increased defectiveness of the apatite structure in the course of the HEM. The solid-state transformations of the initial and HEM-activated apatite are examined by TG-DTA analyses. It is found that the thermal stability of the activated samples decreases as compared to the initial sample. This is related to the increased defectivity of the apatite structure during the high-energy milling shown by the XRD data. The thermal analysis allows the differentiation of the structurally bonded A, B, and A-B types carbonate ions from these originating from the calcite and dolomite admixtures. The results obtained demonstrate that the mechanical distortion and the structural changes related to the migration of the carbonate ions from B type to A-type channel positions are the main factors responsible for the enhanced solubility of the high-energy activated FAp.

Effect of mechanochemical activation of natural phosphorite structure as well as phosphorus solubility

“…In our previous study, the maximum of phosphorus solubility in citric acid of Huangmailing phosphorite was 46.53% after milling for 21 min by a planetary ball mill [9]. Petkova et al (2015) used a an exponential equation to describe the relationships between the phosphorus solubility, which reached the maximum (60%) at 300 min and milling time [7]. According to the fertilizer criterion in Brazil [12], phosphorite can be applied in the field when the phosphorus solubility in citric acid is more than 30%.…”

“…It was suspected that the decreasing and destroying of calcite and dolomite crystals might reduce the consumption of citric acid, and that there was enough citric acid to dissolve the apatite to increase the phosphorus solubility phosphorus in citric acid. The absorption peaks belonging to the CO 3 2- ions (1425–1459 cm -1 ) of the apatite were wider and relocated, which is a characteristic of PO 4 3- substitution by CO 3 2- (Type B) and for the incorporation of CO 3 2- resulted from the destroyed calcite and dolomite crystals, not only CO 2 from the air (2300 cm -1 ) during the mechanochemical activation [7]. The level of substitution of CO 3 2- with PO 4 3- should be studied in future.…”

“…The level of substitution of CO 3 2- with PO 4 3- should be studied in future. With the extension of the activation time for more than 30 min, the absorption bands of the newly generated OH - ions (3530 and 660 cm -1 ) in the apatite structure, which indicated the formation of the fluorine-hydroxide bonds (-F…HO-), were perhaps detected due to adsorbed water in apatite structure, not only the absorption of water vapor from the air [7]. It can be concluded that the hydroxyapatite formed partly during the mechanochemical activation which was consistent with our previous results before [9].…”

“…Previous researches mainly focused on the optimization of the processing parameters of milling equipment [6] and on structure analysis with infrared spectroscopy (IR) and X-ray diffraction (XRD) methods [7, 8]. In our previous study, the physical and chemical characteristics of Huangmailing phosphite (total phosphorus solubility in citric acid, P 2 O 5 27.4%) after mechanical activation were compared with the initial ore by scanning electron microscope (SEM) and XRD [9].…”

Synthesis and characterization of strontium-doped hydroxyapatite for biomedical applications

“…Strontium could be substituted with calcium in the whole range of composition in the HA structure [15][16][17][18][19][20]. Until this time, substitutions in HA have been made in order to assimilate the structure to chemical composition of the natural bone, improving biological, mechanical and antibacterial properties or decreasing solubility [11,[20][21][22][23][24][25][26][27].…”