Mihkel Veiderma

Studies on SO 4 2− Ion Incorporation into Apatite Structure

Calcium sulphate-apatites were synthesised by precipitation from aqueous solutions with different fluorine content and analyzed by chemical, x-ray diffraction (XRD), Raman, and Fourier transform infrared (FTIR) analyses. Their thermal stability was studied by differential scanning calorimetry (TG/DSC) and high-temperature XRD. It was established that the introduction of SO 4 2 m into apatite structure and the thermal changes depend on the fluorine content in the apatite structure. At temperatures above 600;C the structure of apatite reorganizes and CaSO 4 forms a separate phase.

Effect of fluoride and carbonate substitutions on apatites Cd2+ sorption capacity

Effects of fluoride and carbonate substitutions in apatite (Ap) on Cd2+ sorption capacity from aqueous solutions (pH = 6) were examined on precipitated apatites by a batch method. Chemical, XRD, FTIR, BET and TEM analyses were used. The sorption of Cd2+ on Ap proceeds mainly by an ion exchange mechanism. The most important factor influencing Aps sorption capacity is the specific surface area. The amount of Cd2+ bound reaches 58 mmol/100 g Ap for hydroxyapatite, the increase in carbonate and fluoride content diminishes the sorption of Cd2+ to 5.5mmol/100g Ap. The removal of structural water from Ap has no significant effect on the Cd2+ sorption capacity.

Binding of SO2 by Synthetic Substituted Apatites

The reaction of SO2 with synthetic apatites was studied by TG, XRD and IR analyses at 400-1000°C. Due to an interaction of apatite with SO2, destruction of apatite and formation of CaSO4 and diphosphate up to 750°C takes place. The further calcination leads to the formation of β-Ca3(PO4)2 and a part of the SO2 bound is lost again. The amount of SO2 bound with apatite at calcination depends on the substitution ((F- ↔ OH-, PO43- ↔ CO32-, Ca2+ ↔ Mg2+) in its structure.

Fluorhydroxyapatites of Northern Europe and Their Thermal Transformations

Abstract Peculiarities in the composition, structure and thermal properties of fluorhydroxyapatites of Northern Europe have been studied by XRD, FTIR, chemical and thermal analyses.

Removal of Cd2+ and Mn2+ ions from aqueous solutions by synthetic cation substituted calcium‐carbonate‐apatite

Substituted Mg and Na containing carbonate‐fluorapatites were synthesized by the wet method at pH = 9 and T = 80 °C. Their removal characteristics for Cd2+ and Mn2+ from aqueous solutions at pH = 5 were examined by a batch method. The samples were characterized by chemical, XRD, IR, and BET analyses. The amount of Cd and Mn sorbed increases with the increase in the content of Mg in the apatite up to 44.5 mg Cd and 31.0 mg Mn per 100 mg apatite. Ion sorption proceeds either by ion exchange or by the precipitation‐dissolution mechanism.

COMPOSITION AND PROPERTIES OF THERMOPHOSPHATES FROM APATITE AND ALUMINOSILICATES

Abstract Decomposition of Kovdor apatite at 1350°C in the mixture with or without II3PO4 and with aluminosilicates (glauconite, nepheline, pseudoleicite) and the solubility in 2% citric acid solution of the calcined phosphate components (P, Ca, Mg, Fe, K, Na, Si) have been studied by chemical and X-ray powder diffraction analysis. The solubility of P2O5 is 56–73% of its total content in the mixture with G, 42-78% with N and 53–82% with P, as the result of formation of solid solution α-Ca3(PO4)2-α-Ca2SiO4 and β-(Ca, Mg)3PO4)2. The formation of more fluorine-rich apatite during heating was established.

Thermal transformations in systems based on natural apatites.

Abstract The mechanisms of thermal transformations in different types of natural phosphates and their mixtures with H3PO4 and Na2CO3 are discussed.

Synergistic Effects of Fluorine and Carbonate on Cd2+Binding Properties of Apatites

Abstract Most of the studies on heavy metals binding ability of apatites have been carried out on hydroxyapatites (HAP). (HAp)[Ca10(P04)6(OH)2]. As the chemical characteristics of apatite depend substantially on the substitutions in its structure, the apatites with F substitution for OH and CO3 2 for PO4 3 were studied.

Application of the Peak Fitting Programme “Galactic” For FTIR-Analysis of OH-Ions in Natural and Synthetic Apatites

Abstract Most of the studies on heavy metals binding ability of apatites have been carried out on hydroxyapatites (HAP) [Cal0(PO4)6(OH)2]. As the chemical characteristics of apatite depend substantially on the substitutions in its structure, the apatites with F substitution for OH and CO3 2for PO4 3 were studied.

Synthesis and Characterization of Na And Mg Containing Carbonatefluorapatites

Abstract The apatites were precipitated in an aqueous NH4OH-NH4NO3 solution with pH 9–10 at temperatures 20°C and 80°C. The synthesized materials were studied by chemical and thermal analyses (TG/DTG/DTA, TG/ETIR-EGA), IR-spectroscopy, XRD-powder analysis and specific area measurements.