The substitution of rare-earth elements (REEs) for Pb in the lacunary apatite Pb8Na2(PO4)6 with void structural channels was studied by means of powder X-ray diffraction (including the Rietveld refinement), scanning electron microscopy, energy-dispersive X-ray microanalysis, and IR spectroscopy and also measurements of the electrical conductivity. The substitution limits (xmax in Pb8-xLnxNa2(PO4)6Ox/2) at 800 °C were found to decrease with the atomic number of the REE from 1.40 for La to 0.12 for Yb with a rapid drop from light to heavy lanthanides (between Gd and Tb). The REE atoms substitute for Pb predominantly at Pb2 sites of the apatite structure according to the scheme 2Pb(2+) + □ → 2Ln(3+) + O(2-), where □ is a vacancy in the structural channel. The substitution in lacunary apatite produces quite different changes in the structural parameters compared with broadly studied alkaline-earth hydroxyapatites. In spite of the much lower ionic radii of REE than that of Pb(2+), the mean distances ⟨Pb1-O⟩ somewhat increase, whereas the distances ⟨Pb2-Pb2⟩ and ⟨Pb2-O4⟩ do not change considerably with the degree of substitution. This implies control of the substitution by not only spatial and charge accommodation of REE ions but also the availability of a stereochemically active 6s(2) electron pair on Pb(2+). The high-temperature electrical conductivity shows dependence on the degree of substitution with a minimum at x = 0.2 indicative of a possible change of the type of conductivity.

Pb8‐xLnxNa2(PO4)6 (x = 0—2.0; Ln: Y, La, Pr—Ho, Tm—Yb) with void structural channels are prepared by solid state reaction of PbO, Na2CO3, (NH4)2HPO4, and Ln oxides (Al2O3 crucible, 800 °C, 2—10 d).

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To determine contamination levels of pollutants in all of Baghdad's drinking water sources, all samples were taken from different water sources which are used in research areas and examined by AAS, pH, turbidity and TDS meters. The results indicate the mean concentrations of heavy elements (Cd, Co, Pb, and Cr (except for the concentration of chromium in one site)) were within WHO permissible limit> in the samples of drinking water were higher than the international limits. Mean concentrations of other heavy elements (Cu, Fe, and Ni) in water samples were below WHO recommendations permitted limits. The findings of the sample pH values were within the international acceptable limits. Turbidity values for all samples were within the Iraqi and global limits except 4 sites that exceeded acceptable WHO and Iraqi guideline limits. The levels of TDS in all samples were also lower than WHO except the samples in two sites which show levels of TDS higher than the Iraqi and WHO limits. According to the results above, all the drinking water projects in the Tigris River and water wells in Baghdad city must be monitored, Adequate and new drinking water treatment methods shall also be used. The Heavy Pollution Index (HPI) findings indicate that the drinking water sources in the city of Baghdad have been substantially polluted with Cd, Co and Pb.

Донецкий национальный университет имени Васыля Стуса, г. Винница, Украина Твердофазным методом синтезированы образцы состава Pb(8−x)LnxNa2(PO4)6 (2−x/2)O(x/2), где Ln = Tb, Dy, Ho, Tm и Yb (0 ≤ х ≤ 2,0). В полученных системах рентгенофазовым анализом, в том числе с использованием алгоритма Ритвельда, сканирующей электронной микроскопией и методом ИК-спектроскопии исследовано изоморфное замещение свинца на редкоземельные элементы (РЗЭ) иттриевой подгруппы по схеме: 2 Pb 2+ + → 2 Ln 3+ + O 2-. Установлено, что однофазные образцы образуются в диапазоне от х = 0,00 до х = 0,55. По изменению параметров элементарных ячеек от состава и методом «исчезающей фазы» установлены пределы замещения свинца на РЗЭ: с увеличением номера РЗЭ в ряду Tb − Yb пределы замещений (хmax) закономерно уменьшаются от 0,55 до 0,12 при 800 °C (xmax = 0,53-0,55 для Tb, xmax = 0,45 для Dy, xmax = 0,38 для Ho, xmax = 0,16-0,18 для Tm и xmax = 0,12 для Yb). Проведено уточнение кристаллической структуры и определен элементный состав отдельных образцов. Выявлено, что расстояния Pb(2)-O(1,2,3) и Pb(2)-O(2), несмотря на малую степень замещения, уменьшаются, что свидетельствует о предпочтительном расположении ионов РЗЭ в позициях М(2) структуры апатита. Ключевые слова: апатит, изоморфные замещения, редкоземельные элементы, кристаллическая структура.