Flotation of synthetic zinc carbonate using potassium ethylxanthate

An attempt at flotation of fine grains of zinc carbonate using potassium ethylxanthate as the collector and sulphydryl and copper ions as the activators has been undertaken. Results of the flotation tests have been interpreted in terms of the adsorption of activating agents as well as the grain size effect.     

The dissolution of synthetic Na-boltwoodite in sodium carbonate solutions

Uranyl silicates such as uranophane and Na-boltwoodite appear to control the solubility of uranium in certain contaminated sediments at the US Department of Energy Hanford site [Liu, C., Zachara, J.M., Qafoku, O., McKinley, J.P., Heald, S.M., Wang, Z. 2004. Dissolution of uranyl microprecipitates in subsurface sediments at Hanford Site, USA. Geochim. Cosmochim. Acta68, 4519-4537.]. Consequently, the solubility of synthetic Na-boltwoodite, Na(UO₂)(SiO₃OH) · 1.5H₂O, was determined over a wide range of bicarbonate concentrations, from circumneutral to alkaline pH, that are representative of porewater and groundwater compositions at the Hanford site and calcareous environments generally. Experiments were open to air. Results show that Na-boltwoodite dissolution was nearly congruent and its solubility and dissolution kinetics increased with increasing bicarbonate concentration and pH. A consistent set of solubility constants were determined from circumneutral pH (0 added bicarbonate) to alkaline pH (50 mM added bicarbonate). Average or 5.85 ± 0.0.26; using the Pitzer ion-interaction model or Davies equation, respectively. These values are close to the one determined by [Nguyen, S.N., Silva, R.J., Weed, H.C., Andrews, Jr., J.E., 1992. Standard Gibbs free energies of formation at the temperature 303.15 K of four uranyl silicates: soddyite, uranophane, sodium boltwoodite, and sodium weeksite. J. Chem. Thermodynamics24, 359-376.] under very different conditions (pH 4.5, Ar atmosphere).     

Thermoelastic behavior and dehydration process of cancrinite

The high-temperature thermoelastic behavior of a natural cancrinite has been investigated by in situ single-crystal X-ray diffraction. The unit-cell volume variation as a function of temperature (T) exhibits a continuous trend up to 748 K (hydrous expansion regime). The unit-cell edges expansion clearly shows an anisotropic expansion scheme (α _a  < α _c ). At 748 K, a dehydration process takes place, and a series of unit-cell parameter measurements at constant temperature (748 K) for a period of 12 days indicate that the dehydration process continued for the entire period of time, until the cell parameters were found to be constant. After the dehydration process is completed, the structure expands almost linearly with increasing temperature up to 823 K, where a sudden broadening of the diffraction peaks, likely due to the impending decomposition, did not allow the collection of further data points. Even with a very limited temperature range for the anhydrous regime, we observed that the behavior of the two (i.e., hydrous and anhydrous) high-temperature structures is similar in terms of (1) volume thermal expansion coefficient and (2) thermoelastic anisotropy. The structure refinements based on the data collected at 303, 478 and 748 K (after the dehydration), respectively, showed a change in the mechanism of tilting of the quasi-rigid (Si,Al)O₄ tetrahedra, following the loss of H₂O molecules, ascribable to the high-temperature Na⁺ coordination environment within the cages.     

Thermodynamic properties of Fe-rich smectite-nontronite

The results of thermochemical studies are reported for nontronite samples from the Pinares-de-Majari (Eastern Cuba) (Sample I) and Kempirsai serpentine massif (South Urals, Kazakhstan) (Sample II). The enthalpies of formation of dehydrated hydroxyl-bearing nontronites from elements were determined by melt dissolution calorimetry using high-temperature heat-flux Tiana-Calvet microcalorimeter: Δ _f H _el ^o (298.15 K): ?4958 ± 13 kJ/mol for Mg_0.4(Fe _1.5 ³⁺ Mg_0.4Ni_0.1)[Si_3.7Al_0.3O₁₀](OH)₂ (I) and ?5003.6 ± 8.0 kJ/mol for Mg_0.3Na_0.1Ca_0.1(Fe _1.4 ³⁺ Mg_0.5Ni_0.1)[Si_3.7Al_0.3O₁₀](OH)₂ (II). It was determined experimentally that the enthalpy of dehydration (removal of molecular adsorption and interlayer water) of the studied nontronites is 6 ± 2 kJ per 1 mole H₂O. The enthalpy of formation of nontronite of theoretical composition Mg_0.15Fe ₂ ³⁺ [Si_3.7Al_0.3]O₁₀(OH)₂ was estimated at ?4750 kJ/mol. The Gibbs free energies of formation of the nontronites were calculated.     

Thermodynamic stability studies of the basic copper carbonate mineral,malachite

Natural malachite is a well defined solid demonstrating reproducible solubility behavior over a wide range of pH. The following equilibrium constants associated with the malachite dissolution equilibrium at 25°C, 1 atm were determined:

(infinite dilution)

$\text{K}{}^1{}_{\mathrm{sp}}\text{=}\text{[Cu}{}^{\mathrm{2+}}\text{]}{}^2\text{[CO}{}^{\mathrm{2?}}{}_3\text{]K}{}^2{}_{\mathrm{w}}\text{a}{}^2{}_{\mathrm{H+}}\text{= 10. ± 0.2 × 10}{}^{\mathrm{?32}}$

(0.72 ionic strength)

(36.9‰ salinity seawater). The temperature dependence of a “mixed” equilibrium constant, K_sp⁺, of the form:

has been measured at I = 0.72, yielding the relationship:

$\text{log K}{}^2{}_{\mathrm{sp}}\text{= (? 9.8 ± 0.03) × 10}{}^4\text{(}\text{1}\text{T°K}\text{) + (1.52 ± 0.09)}$

within a 5–25°C temperature range. The effect of pressure on the solubility of malachite in water and seawater was estimated from partial molar volume and compressibility data. For 25 °C at infinite dilution $\text{K'}{}_{\mathrm{sp}}\text{(1000 bar)}\text{K'}{}_{\mathrm{sp}}\text{(0)}\text{= 240}$ and in seawater $\text{K′}{}_{\mathrm{sp}}\text{(1000)}\text{K'}{}_{\mathrm{sp}}\text{(0)}\text{= 44}$.Comparison of stoichiometric and apparent malachite equilibrium constants has been used to estimate the extent of copper(II) ion interaction at the ionic strength of seawater. In dilute carbonate medium (total alkalinity, TA = 2.4 meq/kg H₂O, pH 8.3), 2.9% of total dissolved copper exists as the free copper(II) ion and in seawater (S = 36.9%., TA = 2.3 meq/kg H₂O, pH = 8.1), $\text{[Cu}{}^{\mathrm{2+}}\text{]}\text{T(Cu)}$ is 3.1%.Total dissolved copper levels of approximately 450–750 nMol/Kg are necessary to attain malachite saturation conditions in the open ocean. Observations of malachite particles suspended in seawater must be explained by precipitation or solid phase substitution reactions from localized environments rather than by direct precipitation from bulk seawater.     

Thermodynamic properties of organic iodine compounds

A critical evaluation has been made of the thermodynamic properties reported in the literature for 43 organic iodine compounds in the solid, liquid, or ideal gas state. These compounds include aliphatic, cyclic and aromatic iodides, iodophenols, iodocarboxylic acids, and acetyl and benzoyl iodides. The evaluation has been made on the basis of carbon number systematics and group additivity relations, which also allowed to provide estimates of the thermodynamic properties of those compounds for which no experimental data were available. Standard molal thermodynamic properties at 25 °C and 1 bar and heat capacity coefficients are reported for 13 crystalline, 29 liquid, and 39 ideal gas organic iodine compounds, which can be used to calculate the corresponding properties as a function of temperature and pressure. Values derived for the standard molal Gibbs energy of formation at 25 °C and 1 bar of these crystalline, liquid, and ideal gas organic iodine compounds have subsequently been combined with either solubility measurements or gas/water partition coefficients to obtain values for the standard partial molal Gibbs energies of formation at 25 °C and 1 bar of 32 aqueous organic iodine compounds. The thermodynamic properties of organic iodine compounds calculated in the present study can be used together with those for aqueous inorganic iodine species to predict the organic/inorganic speciation of iodine in marine sediments and petroleum systems, or in the near- and far-field of nuclear waste repositories.     

Crystal structure of nitrate cancrinite synthesized under low-temperature hydrothermal conditions

Doklady Earth Sciences -     

Thermodynamic properties of almandine-grossular garnet solid solutions

The mixing properties of Fe₃Al₂Si₃O₁₂-Ca₃Al₂Si₃O₁₂ garnet solid solutions have been studied in the temperature range 850–1100° C. The experimental method involves measuring the composition of garnet in equilibrium with an assemblage in which the activity of the Ca₃Al₂Si₃O₁₂ component is fixed. Experiments on the assemblage garnet solid solution, anorthite, Al₂SiO₅ polymorph and quartz at known pressure and temperature fix the activity of the Ca₃Al₂Si₃O₁₂ component through the equilibrium: 1 $$\begin{gathered} {\text{3CaAl}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{8}} \rightleftarrows {\text{Ca}}_{\text{3}} {\text{Al}}_{\text{2}} {\text{Si}}_{\text{3}} {\text{O}}_{{\text{12}}} \hfill \\ {\text{Anorthite garnet}} \hfill \\ {\text{ + 2Al}}_{\text{2}} {\text{SiO}}_{\text{5}} {\text{ + SiO}}_{\text{2}} \hfill \\ {\text{ sillimanite/kyanite quartz}}{\text{.}} \hfill \\ \end{gathered}$$ This equilibrium, with either sillimanite or kyanite as the aluminosilicate mineral, was used to control \({\text{a}}_{{\text{Ca}}_{\text{3}} {\text{Al}}_{\text{2}} {\text{Si}}_{\text{3}} {\text{O}}_{{\text{12}}} }^{{\text{gt}}} \) . The compositions of the garnet solutions produced were determined by measurement of their unit cell edges. At 1 bar Fe₃Al₂Si₃O₁₂-Ca₃Al₂Si₃O₁₂ garnets exhibit negative deviations from ideality at the Fe-rich end of the series and positive deviations at the calcium end. With increasing pressure the activity coefficients for the Ca₃Al₂Si₃O₁₂ component increase because the partial molar volume of this component is greater than the molar volume of pure grossular. Previous studies indicate that the activity coefficients for the Ca₃Al₂Si₃O₁₂ component also increase with increasing (Mg/Mg+Fe) ratio of the garnet. The region of negative deviation from ideality implies a tendency towards formation of a stable Fe-Ca garnet component. Evidence in support of this conclusion has been found in a natural Fe-rich garnet which was found to contain two different garnet phases of distinctly different compositions.     

富CO2深部流体对碳酸盐岩的溶蚀-充填作用的热力学分析

由于广泛而强烈的岩浆作用,我国东部的松辽、渤海湾、莺歌海以及西部的塔里木等盆地中都有富CO₂深部流体的活动。富CO₂深部流体与碳酸盐岩相互作用可用Duan and Li(2008)所建立的CO₂-H₂O-CaCO₃-NaCl体系的热力学模型来进行模拟计算。计算结果表明,富CO₂深部流体在自深部向浅部运移过程中对CaCO₃的溶解度会逐渐增加,到达一定深度后溶解度达到最大值,再向浅部溶解度开始逐渐降低; 也就是深部流体具有深部溶蚀碳酸盐岩-浅部沉淀碳酸盐矿物的规律。与浅部地层中的流体发生混合会使流体的CO₂含量和盐度降低,会导致CaCO₃的沉淀充填; 深部流体进入开启性断裂/裂缝体系中时,由于压力的降低,也会发生CaCO₃的沉淀充填。深部流体的CO₂含量、盐度、温度和压力的变化影响着实际的溶蚀-充填过程。塔中地区钻井也揭示了深部下奥陶统碳酸盐岩中发育有丰富的溶蚀孔隙,而在相对浅部的奥陶系灰岩和志留系砂岩中见有大量方解石的充填,这是富CO₂流体深部溶蚀-浅部充填的一个较好的实例。基于理论和实际分析,本文认为在岩浆火山作用广泛发育的塔里木等盆地中下古生界深部优质碳酸盐岩储层存在的可能性。     

Single-crystal polarized FTIR spectroscopy and neutron diffraction refinement of cancrinite

We relate a single-crystal FTIR (Fourier transform infrared) and neutron diffraction study of two natural cancrinites. The structural refinements show that the oxygen site of the H₂O molecule lies off the triad axis. The water molecule is almost symmetric and slightly tilted from the (0001) plane. It is involved in bifurcated hydrogen bridges, with Ow···O donor–acceptor distances >2.7 Å. The FTIR spectra show two main absorptions. The first at 3,602 cm^?1 is polarized for E ⊥ c and is assigned to the ν₃ mode. The second, at 3,531 cm^?1, is also polarized for E ⊥ c and is assigned to ν₁ mode. A weak component at 4,108 cm^?1 could possibly indicate the presence of additional OH groups in the structure of cancrinite. Several overlapping bands in the 1,300–1,500 cm^?1 range are strongly polarized for E ⊥ c, and are assigned to the vibrations of the CO₃ group.     

Thermodynamic properties and phase stability of wadsleyite II

The thermodynamical stability of a newly observed wadsleyite II phase in the Mg₂SiO₄ system is studied by the density functional theory. The wadsleyite II equation of state has been derived. The phase boundaries of Mg₂SiO₄ polymorphs: wadsleyite, wadsleyite II and ringwoodite are studied using the quasi-harmonic approximation at high external pressures. Clapeyron slopes determined for wadsleyite II–ringwoodite and wadsleyite–wadsleyite II boundaries are 0.0047 and 0.0058 GPa/K, respectively. It is shown that the wadsleyite II phase is not thermodynamically preferred in the pure Mg₂SiO₄ system and will probably not occur between wadsleyite and ringwoodite phases.     

碳酸盐岩中烃类包裹体的人工合成实验研究

运用Sterner和Bodnar在1984年提出的愈合裂隙的实验技术,利用冰洲石作为主矿物,进行了烃类包裹体的合成实验研究.并将实验产物磨制成双面抛光的薄片,在普通光学显微镜和荧光显微镜下对合成的包裹体进行了岩相学观察.结果表明本次研究在冰洲石中成功地合成了含液态烃类的包裹体,这也是国内外首次在碳酸盐岩矿物中成功合成的烃类包裹体,它为研究碳酸盐岩中油气藏的形成机理提供了一种新的手段,也为正确理解和解释自然界碳酸盐岩油气藏中烃类包裹体的资料提供了重要的参考.     

不同植被下碳酸盐岩石发育形成土壤属性研究

为探究喀斯特地区不同植被条件下碳酸盐岩石发育土壤属性的分布特征及其影响因素,以贵阳市花溪区范围内的碳酸盐岩石（石灰岩、灰质白云岩和白云岩）发育土壤为研究对象,采集不同植被类型下0~40 cm土壤,分析不同植被类型、基岩类型、土层层次对土壤性质分布特征的影响。结果表明：基岩和植被类型是影响碳酸盐岩石发育成为土壤的主要影响因素,其次是土壤层次。在0~20 cm和20~40 cm土层中,石灰岩、灰质白云岩和白云岩发育土壤的肥力和颗粒均差异显著,而0~20 cm与20~40 cm土层间,除石灰岩发育土壤石砾含量（SLC）和细颗粒比（<0.002 mm）,白云岩发育土壤速效磷（AP）和有机质（SOM）含量外,同类基岩发育土壤性质无显著差异;在0~40 cm土层,基岩类型显著影响土壤pH、AP、SLC、速效氮（AN）、全氮（TN）、SOM、0.2~0.25 mm和0.002~0.02 mm颗粒的分布;植被类型显著影响石灰岩发育土壤pH、AP、TN含量,白云岩形成土壤的pH、SLC、粗颗粒（0.25~2 mm）和细颗粒,灰质白云岩形成土壤的AN、SOM、粗颗粒和细颗粒;土壤层次显著影响石灰岩发育土壤的SLC、粗颗粒和细颗粒及白云岩发育土壤的AP的分布。研究区内荒草坡和草被下土壤,以及石灰岩发育的土壤可能正遭受侵蚀的破坏。因此,结合母岩岩性,改变植被种植结构,对提高土壤养分、改善土壤颗粒组成和增强土壤的抗侵蚀能力具有积极作用。