Kaia Tõnsuaadu

Sorption of tartrate ions to lanthanum (III)-modified calcium fluor- and hydroxyapatite

The present article details the formation of lanthanum-modified apatites and the binding process of tartrate ions with these obtained apatites. Chemical analyses, FT-IR and (31)P NMR spectroscopies, XRD powder, TGA, and TEM analyses were employed for studying the reaction between Ca(10)(PO(4))(6)(OH)(2) (HAp) or Ca(10)(PO(4))(6)(F)(2) (FAp) and LaCl(3). The reaction was found to take place mainly through partial dissolution of the apatite followed by precipitation of a new phase containing lanthanum phosphate. When La(3+) was introduced in the presence of L(+)-tartaric acid (TAH(2)), no fundamental changes were observed in the HAp or FAp structures. However, there did occur a formation of a new phase of Ca or/and La tartrate salt.

Hydroxy- and fluorapatite as sorbents in Cd(II)–Zn(II) multi-component solutions in the absence/presence of EDTA

Apatites are suitable sorbent materials for contaminated soil and water remediation because of their low solubility and ability to bind toxic metals into their structure. Whereas in soil/water systems different complexing ligands are present, it is important to examine how these ligands affect apatite metal sorption process. The removal of cadmium (Cd) and zinc (Zn) ions from aqueous solutions by hydroxyapatite (HAP) and fluorapatite (FAP) was investigated by batch experiments with and without EDTA being present in the pH range 4-11. The surface composition of the solid phases was analyzed by X-ray photoelectron spectroscopy (XPS). The surface layer of apatites (AP), according to the (Ca+Cd+Zn):P atomic ratio, remained constant (1.4 ± 0.1) through an ion exchange. The amount of Cd(2+) and Zn(2+) removed increased with increasing pH. The removed amount of Zn(2+) was higher than Cd(2+). In the Cd-Zn binary system, competitive sorption reduced the individual removed amounts but the total maximum sorption was approximately constant. In the presence of EDTA, Cd(2+) and Zn(2+) removal was reduced because of the formation of [CdEDTA](2-) and [ZnEDTA](2-) in solution. XPS revealed an enrichment of AP surface by Cd(2+) and Zn(2+) and formation of new surface solid-solution phase with the general composition Ca8.4-xMex(HPO4)1.6(PO4)4.4(OH)0.4.

Sol–gel chemistry approach in the preparation of precursors for the substituted superconducting oxides

Abstract Sol–gel processing of ceramic materials for advanced applications involves several steps starting from precursor synthesis and ending up with multicomponent metal oxides. A simple sol–gel synthesis technique has been refined to prepare the precursors for the superconducting (Y 1− x Sc x )Ba 2 Cu 4 O 8 and (Y 1− x Ga x )Ba 2 Cu 4 O 8 compounds. The amorphous gel powders were characterized by powder X-ray diffraction, infrared spectroscopy, thermal analysis and elemental analysis. A systematic characterization of precursor gels led us to predict the approximate composition and the chemical reactions involved during gelation. The stability and high level of homogeneity obtained for the gels make them suitable as processable precursors to substituted (Y 1− x Sc x )Ba 2 Cu 4 O 8 and (Y 1− x Ga x )Ba 2 Cu 4 O 8 superconducting compounds.

A novel bisphosphonate-based solid phase method for effective removal of chromium(III) from aqueous solutions and tannery effluents

Effective removal of chromium(III) from waste waters e.g. in the leather industry is required due to continuously tightening environmental regulations, and several methods such as precipitation and adsorption are currently in use. Nevertheless, more efficient, straightforward and inexpensive methods are constantly being sought. The current study describes a novel method to separate chromium(III) from aqueous solutions based on the use of solid bisphosphonates with a P–C–P backbone. Five classes of bisphosphonates with different functional groups and alkyl chain lengths at the center carbon, in all 16 compounds, were prepared and their suitability for metal ion complexing as chelating agents was investigated. Two of the studied compounds, which were almost insoluble in water, were effective in removing chromium(III) quantitatively from aqueous solutions and real waste water samples of tanneries. The results obtained were also compared to the commercially available Diphonix® resin.

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.

Impact of soluble humic substance on Cd2+ sorption on apatite in aqueous solutions

The effect of soluble humic substances (HUM) on Cd sorption and desorption on apatite in aqueous solutions is studied. Batch experiments were carried out using synthetic hydroxyapatite (HAp) and fluorapatite (FAp). Parallel experiments in distilled water, Cd2+, Ca2+, HUM, Cd2++HUM, Cd2++Ca2+ and Ca2++HUM solutions showed that the solubility of apatite did not increase in the initial pH range from 5 to 8 in the presence of dissolved HUM. Dissolved HUM were bound on apatite in suspensions. The pH of suspensions stabilised at 6.4–6.5 in water. The presence of soluble HUM did not change this. Cd uptake resulted in a reduction in pH. The amount of Cd bound on apatite was not changed by HUM, but HUM affected the desorption level of sorbed Cd2+.

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.

THERMAL REACTIONS IN SYNTHETIC APATITE–AMMONIUM SULFATE MIXTURE

The thermal reactions in the mixtures of hydroxylapatite or fluorapatite and (NH4)2SO4up to 500°C were studied with the purpose of elaborating the conditions of obtaining calcium–ammonium cyclophosphate that could be used as fertilizer. Thermal analysis with a simultaneous FTIR analysis of the evolved gases as well as the analyses of chemical and phase composition of solid products were performed. The thermal changes in the mixtures could be divided into three steps: (1) decomposition of (NH4)2SO4and reactions of apatite with these products at 250–420°C, (2) calcium ammonium polyphosphate formation at 290–450°C, and (3) reaction of CaSO4with CaNH4P3O9at 320–500°C. Higher concentrations of NH3in the gas phase promote the formation of CaNH4P3O9and increase its stability. Calcination at temperatures above 350°C causes decomposition of CaNH4P3O9with a decrease in the content of water-soluble phosphorus and evolvement of SO2.