大量NH_4Cl存在的水盐体系中测定LiCl含量的分析方法研究

根据NH4Cl、LiCl的化学特性,选用烘渣法分析大量NH4Cl存在的水盐体系中LiCl的含量。t≤450℃时,LiCl在烘渣过程中不会发生转变,烘渣得到的LiCl净重与加入时相等。通过调整烘渣温度、烘渣时间、冷却时间等操作条件,得到了最佳的烘渣条件。在此条件下,NH4Cl分解完全,保证了LiCl分析结果的相对误差不超过0.08%。进一步探讨了高NH4Cl与LiCl质量比及低LiCl含量时此方法的适用性。实验结果表明,分析结果相对误差不超过0.1%。     

Modeling and Optimization of Fluoride and Cadmium Trapping in Phosphogypsum Using Design Methodology

The manufacturing of phosphoric acid from natural calcium phosphate generates a solid residue containing 25–30% humidity. This solid residue (phosphogypsum) generates acidic solution (pH ≈ 2.5) containing several toxic ionic species, that coat its grains. Fluorides and heavy metals such as cadmium are considered the most harmful species contained in the released solution from phosphogypsum. The purpose of this work is to study the trapping of fluorides and cadmium in phosphogypsum as well as effluent neutralization before its discharge into natural recipient. Therefore, calcium carbonate finely ground was added and fully mixed with wet phosphogypsum. A four factors central composite design was used to model and to optimize the operating parameters that govern the process. The studied factors were temperature, reaction time, mass, and grains size of CaCO₃. Considered responses were pH, F⁻, and Cd²⁺ concentrations in the released solution after reaction with CaCO₃. The optimum operating conditions were quite efficient to trap, respectively, 99% Cd²⁺ and 97% of F⁻ with a final pH of 6.66. So an original, easy, simple, and cost effective method to trap some toxic species on phosphogypsum through CaCO₃ addition would likely to be integrated in phosphoric acid manufacturing plant.     

Effects of calcium and magnesium on strontium distribution coefficients

 The effects of calcium and magnesium on the distribution of strontium between a surficial sediment and simulated wastewater solutions were measured as part of an investigation to determine strontium transport properties of surficial sediment at the Idaho National Engineering Laboratory (INEL), Idaho. The investigation was conducted by the U.S. Geological Survey and Idaho State University, in cooperation with the U.S. Department of Energy. Batch experimental techniques were used to determine strontium linear sorption isotherms and distribution coefficients (K _d's) using simulated wastewater solutions prepared at pH 8.0±0.1 with variable concentrations of calcium and magnesium. Strontium linear sorption isotherm K _d's ranged from 12±1 to 85±3 ml/g, increasing as the concentration of calcium and magnesium decreased. The concentration of sorbed strontium and the percentage of strontium retained by the sediment were correlated to aqueous concentrations of strontium, calcium, and magnesium. The effect of these cation concentrations on strontium sorption was quantified using multivariate least-squares regression techniques. Analysis of data from these experiments indicates that increased concentrations of calcium and magnesium in wastewater discharged to waste disposal ponds at the INEL increases the availability of strontium for transport beneath the ponds by decreasing strontium sorption to the surficial sediment. Received: 8 November 1996 · Accepted: 6 January 1997     

Rietveld analysis of a new high-pressure strontium silicate SrSi2O5

High-pressure synthesis of a new SrSi₂O₅ phase was performed at 16 GPa and 900°C by using a Kawai-type multianvil apparatus. The powder X-ray diffraction pattern of the compound was analyzed by Rietveld refinement based on the structure of a high-pressure polymorph of BaGe₂O₅, BaGe₂O₅ III. The structure is orthorhombic with space group Cmca and cell parameters of a = 5.2389(1) Å, b = 9.2803(2) Å, c = 13.4406(1) Å, V=653.46(2) Å ³ (Z=8, _calc=4.549 g/cm³). The structure consists of layers containing SiO₆ octahedra and SiO₄ tetrahedra. In a unit layer, oxygen and strontium atoms are arranged in an approximation to hexagonal close-packing. The strontium atom is accommodated in a 12-coordinated site. Each SiO₆ octahedron shares four corners with SiO₄ tetrahedra and the other two corners with another SiO₆ octahedra. The SiO₆ octahedra are linked to each other to form SiO₆ chains along the a-axis. This is the first known example of a silicate with a BaGe₂O₅ III-type structure.     

Histological study on the skin of Japanese flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis>

Histological development of Japanese flounder Paralichthys olivaceus larval skin and ultrastructural difference of skin between reared normal and malpigmented Japanese flounder were studied with light microscopy (LM) and transmission electron microscopy (TEM). The results show that the skin develops slowly before the metamorphosis, while at the onset of metamorphosis, the skin develops quickly and becomes complete in structure till about 50d after being hatched. Ultrastructural observation on the normal and malpigmented skins shows that the iridophore and melanophore are adjacent to each other. Profile and structure of the two kinds of pigmcnt cells are more complete in the skin of normal ocular side than in the skin of pigmented blind side. The ultrastructure of typical chloride cell was observed in the skin of Japanese flounder larvae for the first time.     

A new oxygen-deficient perovskite phase Ca(Fe<Subscript>0.4</Subscript>Si<Subscript>0.6</Subscript>)O<Subscript>2.8</Subscript> and phase relations along the join CaSiO<Subscript>3</Subscript>–CaFeO<Subscript>2.5</Subscript> at transition zone conditions

A new oxygen-deficient perovskite with the composition Ca(Fe_0.4Si_0.6)O_2.8 has been synthesised at high-pressure and -temperature conditions relevant to the Earths transition zone using a multianvil apparatus. In contrast to pure CaSiO₃ perovskite, this new phase is quenchable under ambient conditions. The diffraction pattern revealed strong intensities for pseudocubic reflections, but the true lattice is C-centred monoclinic with a=9.2486 Å, b=5.2596 Å, c=21.890 Å and =97.94°. This lattice is only slightly distorted from rhombohedral symmetry. Electron-diffraction and high-resolution TEM images show that a well-ordered ten-layer superstructure is developed along the monoclinic c* direction, which corresponds to the pseudocubic [111] direction. This unique type of superstructure likely consists of an oxygen-deficient double layer with tetrahedrally coordinated silicon, alternating with eight octahedral layers of perovskite structure, which are one half each occupied by silicon and iron as indicated by Mössbauer and Si K electron energy loss spectroscopy. The maximum iron solubility in CaSiO₃ perovskite is determined at 16 GPa to be 4 at% on the silicon site and it increases significantly above 20 GPa. The phase relations have been analysed along the join CaSiO₃–CaFeO_2.5, which revealed that no further defect perovskites are stable. An analogous phase exists in the aluminous system, with Ca(Al_0.4Si_0.6)O_2.8 stoichiometry and diffraction patterns similar to that of Ca(Fe_0.4Si_0.6)O_2.8. In addition, we discovered another defect perovskite with Ca(Al_0.5Si_0.5)O_2.75 stoichiometry and an eight-layer superstructure most likely consisting of a tetrahedral double layer alternating with six octahedral layers. The potential occurrence of all three defect perovskites in the Earths interior is discussed.     

Sorption behavior of heavy metal pollutants onto shales and correlation with shale geochemistry

The sorption of lead (II) and cadmium (II) on seven shales belonging to the Proterozoic Vindhyan basin, central India, and a black cotton soil, Mumbai, India, was studied and compared with sorbent geochemistry. The sorption equilibrium studies were conducted under completely mixed conditions in batch reactors (pH=5.0 and ionic strength= 0.01 M) at room temperature. The Freundlich model provided better fits to the experimental data compared to Langmuir model. High cadmium and lead sorption was observed for the calcareous shales with greater than 5% CaCO₃. The Freundlich isotherm parameter relating to sorption capacity, i.e., K_F, yielded a strong correlation with the calcium carbonate and calcium oxide content across the various geosorbents studied. The observed sorption pattern may be attributed to complex formation of CaCO₃ with Pb²⁺ and Cd²⁺ leading to surface precipitation. Moreover, the Ca²⁺ present in the sorbents may also involve in ion exchange reaction with lead and cadmium.     

Effects of dry density and exchangeable cations on the diffusion process of sodium ions in compacted montmorillonite

As a part of the safety assessment of the geological disposal of high-level radioactive waste, the effects of dry density and exchangeable cations on the diffusion process of Na⁺ ions in compacted bentonite were studied from the viewpoint of the activation energy for diffusion. The apparent self-diffusion coefficients of Na⁺ ions in compacted Na-montmorillonite and in a Na- and Ca-montmorillonite mixture were determined by one-dimensional, non-steady diffusion experiments at different temperatures and dry densities. A unique change in activation energy as a function of dry density was found for the Na⁺ ions in compacted Na-montmorillonite. The activation energy suddenly decreased from 18.1 to 14.1 kJ mol^− 1 as the dry density increased from 0.9 to 1.0 Mg m^− 3, whereas it increased to 24.7 kJ mol^− 1 as the dry density increased to 1.8 Mg m^− 3. Examination of the effect of exchangeable cations on the activation energies determined that the activation energies were almost constant, approximately 25 kJ mol^− 1, for the montmorillonite specimens at a dry density of 1.8 Mg m^− 3. However, three different activation energy values were obtained at a dry density of 1.0 Mg m^− 3. These findings cannot be explained by the conventional diffusion model (the pore water diffusion model), which suggests that the predominant diffusion process alternates among pore water diffusion, interlayer diffusion, and external surface diffusion.     

In situ X-ray diffraction study of an aluminous phase in MORB under lower mantle conditions

In situ X-ray diffraction study was conducted to identify the crystal structure of the “Al-phase”, which was previously reported to form in basaltic compositions at pressures and temperatures of the uppermost part of the lower mantle. Le Bail whole-pattern fitting method was adopted to investigate the structure of the Al-phase under high pressure and temperature as well as ambient conditions. Observed patterns were satisfactorily fitted using the “hexagonal phase” with space group P6₃/m (plus minor amount of garnet) under both of these conditions. On the other hand, the calcium ferrite structure model proposed in some earlier studies based on quench experiments yielded profile-fitting results at significantly lower confidence levels, particularly at simultaneous high pressure and high temperature conditions, suggesting that this phase may not form in oceanic crust materials subducted in the uppermost lower mantle. The difference in densities of hexagonal and calcium ferrite phases, however, is only ~1% under pressures and temperatures of the uppermost part of the lower mantle conditions, which yields a negligible effect on the bulk density of the subducted oceanic crust.     

Ferric chloride treatment to control alakli induced heave in weathered red earth

A detailed experimental investigation has been carried out to study the use of ferric chloride salt to control the undesirable volume changes induced by high concentrated alkali contamination on kaolinitic red earth. X-Ray diffraction studies have revealed that soil alkali interactions produce mineralogical changes and formation of new mineral such as zeolite, which are responsible for observed swelling in non-swelling kaolinitic soil. Loss of ferric oxide, which are known cementing agents has been attributed as one of the reasons for swelling in alkali contaminated soils. The consolidation behaviour of soil compacted with 5% ferric chloride solution by weight of solutions and inundated with alkali solutions as well as soil compacted with alkali and inundated with 5% ferric chloride by weight of solutions has been studied. To study the effect of amount of ferric chloride, the volume change behaviour of soil compacted with different weight percentages of ferric salts by weight of soil (1%, 3%, and 5%) and inundated with alkali solutions has also been studied. The swelling of soil compacted with alkali has been checked by inundating with 5% ferric chloride solutions due to neutralization of alkali and is not controlled when soil compacted with 5% ferric chloride solutions is inundated continuously with alkali solutions. Further, even when the soil is treated with higher amounts of ferric chloride, in the range of 1–5% by weight of soil, the swelling is not controlled. X-ray diffraction studies have shown that the formation of zeolite is not inhibited in the presence of ferric salts.This study clearly shows that ferric chloride treatment can overcome the effects of small concentrations of alkali; it is ineffective to overcome the large and continued exposure of soils with alkali contamination.