Chemical Preparations and X-ray Diffraction Data of Cyclotriphosphates Type MnMII2(P3O9)2.nH2O with MII Alkaline Earths

Chemical preparation methods and X-ray powder diffraction data, XPRD, are reported for four cyclotriphosphates associated with manganese MnMII2(P3O9)2.nH2O with MII alkaline earths. These phosphates are MnCa2(P3O9)2.10H2O, MnCa2(P3O9)2, MnSr2(P3O9)2.4H2O and MnBa2(P3O9)2.6H2O. The condensed phosphates MnSr2(P3O9)2.4H2O and MnBa2(P3O9)2.6H2O were prepared by the method of ion-exchange resin, whereas MnCa2(P3O9)2.10H2O was prepared by using nitrates and MnCa2(P3O9)2 was obtained by total thermal dehydration of MnCa2(P3O9)2.10H2O. MnSr2(P3O9)2.4H2O crystallizes in the triclinic system, space group is P-1, Z = 1, the unit-cell parameters are : a = 6,653(1)Å, b = 7,110(1)Å, c = 5,123(1)Å, α = 103,37(2)°, β = 95,81(2)°, γ = 93,04(2)° and the factors of merit, M(20) = 29.6 and F(30) = 34.4. MnCa2(P3O9)2.10H2O crystallizes in the monoclinic system, space group is P21/n, the unit-cell parameters of MnCa2(P3O9)2.10H2O are : a = 9.631 (5) Å, b = 18.173 (7) Å, c = 7.976 (4) Å, β = 109.438 (4), Z = 2 and V = 1045,1 (3) Å3. MnCa2(P3O9)2 an hexagonal symetry, Z = 2, the space group is P3 and the unit-cell parameters are a = 7.392 Å (9) and c = 20.134 (2) Å. MnBa2(P3O9)2.6H2O crystallizes in the triclinic unit cell, , Z = 2, the space group is P-1 and its unit-cell parameters are : a = 7,479 (6)Å, b = 11,942 (8)Å, c = 12,786 (9)Å, α = 105,94(7)°, β = 98,40°(7), γ = 98,16 (7)° and V = 1046,8 (2)Å3.

Trace element fractionation between biotite, allanite, and granitic melt

The partitioning of a large suite of trace elements between biotite and water-saturated granitic melt was measured at 2 kbar and 700—800 ˚C. To reach equilibrium and to grow biotite crystals large enough for analysis, runs usually lasted from 30 to 45 days. In every charge, a few trace elements were initially doped at the 0.1—0.5 wt. % level and analyzed by electron microprobe after the run. First-row transition metal ions are highly compatible in biotite with Dbiotite/melt of 17 for Ti, 35 for V, 47 for Co, 174 for Ni, and 5.8 for Zn. A very notable exception is Cu with Dbiotite/melt < 0.9. This is likely one of the reasons why Cu is enriched together with Mo (Dbiotite/melt = 0.29) in porphyry deposits associated with intermediate to felsic plutons, while the other transition metals are not. Both Nb and Ta are mildly compatible in biotite with Dbiotite/melt being larger for Nb (3.69) than for Ta (1.89). Moderate (15—30%) biotite fractionation would be sufficient to reduce the Nb/Ta ratio from the chondritic value to the range observed in the continental crust. Moreover, the strong partitioning of Ti into biotite implies that already modest biotite fractionation suppresses the saturation of Ti-oxide phases and thereby indirectly facilitates the enrichment of Ta over Nb in the residual melt. The heavy alkalis, alkaline earths, and Pb are only mildly fractionated between biotite and melt (Dbiotite/melt = 3.8 for Rb, 0.6 for Cs, 0.6 for Sr, 1.8 for Ba, 0.7 for Pb). The rare earth elements are generally incompatible in biotite, with a minimum for Dbiotite/melt of 0.03–0.06 at Gd, Tb, and Dy, while both the light and heavy rare earths are less incompatible (e.g. Dbiotite/melt = 0.6 for La and 0.3 for Yb). This behavior probably reflects a partitioning into two sites, the K site for the light rare earths and the octahedral Mg site for the heavy rare earths. There is no obvious dependence of the rare earth partition coefficients on tetrahedral Al in the biotite, presumably because charge balancing by cation vacancies is possible. Allanite was found as run product in some experiments. For the light rare earths, Dallanite/melt is very high (e.g. 385 to 963 for Ce and Nd) and appears to increase with decreasing temperatures. However, the rather high solubility of allanite in the melts implies that it likely only crystallizes during the last stages of cooling of most magmas, except if the source magma is unusually enriched in rare earths.

Investigations of mechanism of Ca2+ adsorption on silica and alumina based on Ca-ISE monitoring, potentiometric titration, electrokinetic measurements and surface complexation modeling

Research on Ca2+ adsorption onto the mineral surface is of significant importance with regard to geochemical processes. Sverjensky (Geochim Cosmochim Acta 70(10), 2427–2453, 2006) assumed that alkaline earths form two types of surface species on oxides: tetranuclear (> SOH)2(> SO−)2_M(OH)+ and mononuclear > SO−_M(OH)+. To look into the above assumption we investigated calcium adsorption on SiO2 and Al2O3 because they are the most widespread minerals in the environment. We have determined the proton surface charge, electrokinetic potential and metal adsorption as a function of pH. The Ca2+ uptake and concentration in the system were monitored by the calcium ion-selective electrode (Ca-ISE). The Ca-ISE measurements indicated a similar affinity of Ca2+ for both materials despite their differently charged surface, negative for silica and mainly positive for alumina. This may suggest that simple electrostatic interactions are not the primary driving force for calcium adsorption, and that solvation of calcium ions at the surface may be crucial. We have analyzed our experimental data using the 2-pK triple-layer model (2-pK TLM). Three calcium complexes on the mineral surface were reported. Two of them were the same for both oxides, i.e. the tetranuclear ($$>$$ > SOH)2($$>$$ > SO−)2_Ca2+ and mononuclear complexes > SO−_CaOH+. Additionally, minor contribution from >SOH…Ca2+ for silica was assumed. In the case of Al2O3 the hydrolyzed tetranuclear complexes ($$>$$ > SOH)2($$>$$ > SO−)2_CaOH+ at pH > 7.5 occurred based on the modeling results. Two types of surface complexes suggested by Sverjensky allowed for the correct description of proton and calcium uptake for alumina. However, the electrokinetic data excluded hydrolyzed tetranuclear surface species for this oxide.