CC-BY 4.0 License requiring that the original work has been properly cited.Occurences of dissolved As in surface and ground waters and observed adverse health effects have emphasized the need for better understanding of reactions that govern As mobility. Precipitation of Ca apatites is quite often used for immobilization of toxic forms P and As in the environment. Hydroxylapatite -Ca 5 (PO 4 ) 3 OH (HAP) and johnbaumite -Ca 5 (AsO 4 ) 3 OH (AsHAP) are isostructural apatite minerals naturally occurring in the oxidation zones.The main objective of this research is identification of systematic relation between structural and spectral properties and As content in the Ca 5 (PO 4 ) 3 3 OH synthesized phases were characterized using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), powder X-Ray diffraction (XRD), Infrared absorption spectroscopy (FTIR) and Raman spectroscopy.SEM-EDS analysis confirms that the products of the synthesis are homogeneous. The crystals size varies between 0.1-1.0 μm and increases with the increase of Ascontent. Semi-quantitative elemental analysis by EDS indicates that Ca, O, P and Asare the only elements detected and that the molar proportions correspond to theoretical composition of HAP, Ca 5 (PO 4 ) 2 (AsO 4 )OH, Ca 5 (PO 4 ) 1,5 (AsO 4 ) 1,5 OH, Ca 5 (PO 4 )(AsO 4 ) 2 OH and finally AsHAP.Systematic shift of peaks is apparent on the diffraction patterns. Hexagonal system and P63/m group of symmetry were used for unite cell parameters calculation. The results show systematic increase in the unit cell parameters with substitution of As for P in the series: parameter a from 9.41 to 9.43 and parameter c from 6.85 to 6.87. Crystal volumes also increase with increasing amount of As in synthesized phases. Calculated values are within the error similar to these reported by Zhu et al. (2009). In contrary to their results, a linear increase of unit cell parameters with As content is observed. This is in accordance with Lee et al. (2009).The intensity and the position of PO 4 and AsO 4 absorption bands varies systematically in the FTIR spectra being shifted towards higher wavenumber with increasing As content. The bands originating from CaO and OH (3400 cm -1 ) are practically not affected in all five spectra.

CC-BY 4.0 License requiring that the original work has been properly cited.-HAP hydroxyapatite Ca 5 (PO 4 ) 3 OH -JBM johnbaumite Ca 5 (AsO 4 ) 3 OH. The phases were synthesized from aqueous solutions at high pH above 8, at ambient temperature, by dropwise mixing of chemical reagents. The products are white, fine, homogeneous crystalline powders. Chemical composition determined by SEM/EDS is close to theoretical. X-ray diffraction confirms their crystalline structure and systematic changes in unit cell parameters with ionic substitution. Dissolution experiments were run in thermostatic bath at 25°C. An aliquot of 0.5 g of apatite was dissolved in 250 mL of 0.05M NH 4 NO 3 background solution at pH in the range of 3.5-5.0. Background solution was used to keep the ionic strength constant. The dissolution was carried out for 3 months. The bottles were manually stirred at least two times a week. The solution was syringe-sampled periodically and filtered through 0.2 μm polycarbonate filter to remove the suspended solids. The concentration of Pb and Ca was determined by atomic absorption spectroscopy. The concentration of dissolved phosphates and arsenates was determined by UV-vis colorimetry using a molybdenum blue method. The plateau on concentration evolution patterns from the dissolution experiments was observed to determine equilibrium in the suspensions.Dissolution of all the phases at the conditions of these experiments is incongruent. An increase in solution pH resulting from dissolution was observed in all cases. The system was considered in Hydroxylapatites are important biomaterials. Substitutions of Pb for Ca and As for P in hydroxylapatites are recently intensively studied due to their significance in the environmental immobilization of Pb and As (Lee et al. 2009, Chlebowska et al. 2015, Motyka et al. 2015. The general chemical formula of minerals in the apatite group is expressed by A 5 (XO 4 ) 3 Z, where A are bivalent cations (e.g., Ca 2+ or Pb 2+ , cations are distributed on two distinct crystallographic sites), XO 4 is a trivalent oxyanion (e.g., PO 4 3-, AsO 4 3-), and Z is a monovalent anion (OH, F, Cl, or O). Positions Z and X may be partly filled with carbonate CO 3 2− . The structure of hydroxylapatite allows for unlimited substitutions of Pb 2+ for Ca 2+ and AsO 4 3− for PO 4 3− . The ability of lead and arsenic apatites to immobilize these toxic elements result from their high durability and low solubility at the conditions on the Earth surface. Various apatites possess different thermodynamic properties including different solubility in aqueous solutions but the systematic variation of these properties in solid solution series is poorly understood.The main objective of this research is determination of systematic variation in the solubilities of hydroxylapatites resulting from cationic substitutions of Pb 2+ for Ca 2+