Precipitate flotation of copper as the sulfide,using recyclable amphoteric surfactants

An experimental study was made to identify surfactants which are effective for removal of copper from dilute aqueous solution (100–500 ppm) by precipitate flotation as the sulfide, and which at the same time can be recovered from the CuS product for recycle. Batch flotation experiments confirmed that a cationic surfactant was necessary for flotation of CuS from such dilute suspensions; however, no satisfactory way could be found for recovering cationic surfactants from the CuS. This led to consideration of amphoteric surfactants, which are cationic at low pH and anionic at high pH. It was found that a change to negative, rather than simply neutral, charge was required for efficient surfactant recovery. It was further found, through the assistance of experiments in which the CuS suspension was agitated with solvents, that certain functional groups which interact chemically with the CuS surface should also be absent from the surfactant molecule. Following this logic, Amphoterge K-2 (Lonza Chemical Co.) was identified as a suitable surfactant, provided CuS was precipitated with S^2? in excess. Tests established that 95% of adsorbed Amphoterge K-2 could be recovered by raising the pH to 11 and boiling the suspension for one hour, followed by decanting. Surfactant thus recovered was effective in a second flotation test. Foamate solids settled rapidly; such behavior would help reduce the consumption of chemicals for the pH change.Column flotation studies were made using Amphoterge K-2 for removal of Cu²⁺ present at 100 ppm and pH = 2. High removals of CuS could be obtained at concentrations of surfactant above about 25 ppm, for which conditions a substantial fraction of the surfactant remains in solution rather than being adsorbed onto the CuS. The recovery of CuS would be improved by introducing the surfactant in a separate feed, below the feed of CuS suspension. Adding some surfactant in the CuS feed, as well as in a lower feed, gave an even better recovery of CuS (99.8%) at sufficiently high surfactant loadings.     

Mechanisms of polytype stabilization during the wurtzite-sphalerite transition

Two mechanisms of solid-state formation of polytypes are suggested. The first is structural-kinetic by nature, the stabilization of short-period polytype (for example, 4H) being due to the fact that there are two possible structural types of nuclei in the wurtzite structure: when new phase growth takes place by means of two-dimensional nucleation, these short-period polytypes become kinetically stable although they do not correspond to the minimum of free energy, and appear as transitional phases. The second mechanism of polytype formation below the transition temperature is influenced by impurities which stabilize the hexagonal modification, in which case polytypes may arise as states that are stable with respect to a diffusionless structural wurtzite-sphalerite transformation and metastable relative to small fluctuations of impurity concentration.     

The crystal chemistry and thermal stability of sol-gel prepared fluoride-substituted talc

Stable, colloidal sols were prepared from the addition of methanolic (Mg(OCH₃)₂) to one equivalent of H₂O₂ in methanol. Fluoride was quantitatively incorporated by treatment of these sols with HF. Stable sols were obtained when sols, prepared from the acid catalyzed hydrolysis of tetramethylorthosilicate (TMOS), were combined with these fluoridated magnesium sols. Solvent removal gave xerogels, which were calcined, and treated with stoichiometric quantities of water at 750 °C and 1.6 kbar. The resulting products were high-purity, single-phase talcs with fluoride substitution as high as 75 mole percent; the fluoride substitution is higher than any previously reported. Powder XRD analysis showed a non-linear decrease in d(060) spacing with increasing fluoride substitution, which is attributed to a decrease in the b-dimension of talc when fluoride replaced hydroxide. FTIR spectroscopy showed a non-linear decrease in v_O-H in talc with increasing fluoride substitution, which was attributed to an increase in hydrogen bonding of the OH groups and an increase in the electronegativity of the octahedral layer in talc with increasing fluoride substitution. The thermal stability of the talcs was studied using DT and TG, powder XRD, FTIR, and fluoride ion-selective electrode analyses. Synthetic talc without fluoride decomposed at 860 °C, whereas talc with 68% fluoride substitution showed essentially no decomposition when heated to 1060 °C. When heated to 1200 °C, 68% fluoride substituted talc formed amorphous material, enstatite, protoenstatite, norbergite, and chondrodite. The upper stability temperature of talc, taken as the maximum rate of the first endothermic event in its DTA profile, was dependent on the extent of fluoride substitution. Talc with 100% fluoride substitution is predicted to be stable up to ～1100°C.     

Covellite formation in low temperature aqueous solutions

Experimentation with cupric salts and aqueous sulphide solutions at room temperature and pressure resulted in the formation of normal and blaubleibender covellite. Blaubleibender covellite is formed at higher pH and lower Eh values than normal covellite. The experimental pH/Eh values for normal covellite formation fall within the theoretical CuS stability field. Blaubleibender was produced at pH/Eh values outside this area. Variations in pH and Eh during the course of the experimental runs showed that normal covellite formed by the simple reaction: Cu²⁺+HS^–=CuS+H⁺; blaubleibender covellite formation on the other hand involves solid state reduction of an initial normal covellite precipitate. Cell volume and formation pH show a straight line relationship in normal covellite which is not observed with blaubleibender. Blaubleibender covellite can be formed from aqueous solution at low temperatures and pressures. The experimental results indicate that it is a metastable intermediary in the reduction of normal covellite to more reduced, stable, copper sulphides. The copper sulphide formed from sedimentary processes in a normal marine environment should initially be normal covellite, or transitory blaubleibender covellite which may be reduced during diagenesis.

---

Zusammenfassung Synthetische Versuche mit Kupfersalzen und wässrigen Sulfidlösungen bei Zimmertemperatur und atmosphärischem Druck ergaben die Bildung von normalem und blaubleibendem Covellin. Blaubleibender Covellin wird bei höheren pH- und niedereren Eh-Werten gebildet als normaler Covellin. Die pH/Eh-Werte für normalen Covellin fallen in das theoretische Stabilitätsfeld von CuS. Die Bildung von blaubleibendem Covellin erfolgte bei pH/Eh-Werten außerhalb dieses Feldes. Systematische Veränderungen der pH- und Eh-Werte während der Syntheseversuche ließen erkennen, daß die Bildung von normalem Covellin nach folgender einfacher Reaktion verläuft: Cu²⁺+HS^–=CuS+H⁺; die Bildung von blaubleibendem Covellin dagegen erfolgt unter teilweiser Reduktion eines vorher gefällten Niederschlags von normalem Covellin. Im Gegensatz zum blaubleibenden Covellin zeigt der normale Covellin eine geradlinige Beziehung zwischen Zellvolumen und Formations-pH-Wert. Blaubleibender Covellin kann aus wässrigen Lösungen bei niederen Temperaturen und niederem Druck gebildet werden. Die Untersuchungsergebnisse zeigen, daß er eine metastabile Zwischenform zu normalem Covellin und stärker reduzierten stabilen Kupfersulfiden bildet. Die Kupfersulfide, die sich während eines Sedimentationsprozesses in einer normalen marinen Facies bilden, werden anfänglich aus normalem Covellin bestehen oder vorübergehend aus blaubleibendem Covellin, mit einer möglichen Reduktion während der Diagenese.

     

Modelling stalagmite growth and δC as a function of drip interval and temperature

Growth and stable isotope composition of stalagmites are affected by climate changes. To understand the underlying mechanisms, we developed a time dependent multi-box model that describes stalagmite growth and stable isotope fractionation of carbon under disequilibrium conditions. The model takes variations of the drip interval, temperature and the amount of mixing between the impinging drops and the solution on top of the stalagmite into account, which allows to quantify the influence of these parameters. To calculate the variations of δ¹³C, the multi-box model was calibrated by comparison with an existing growth model. The results show that drip interval, temperature and the mixing coefficient do have a significant influence on δ¹³C. However, considering the higher natural variability of the drip interval, this parameter might have the largest influence.     

Mechanisms of pelleting flocculation

Basically speaking, flocculation and coagulation should be theoretically treated as a many-body problem. However, such potential energy theories of coagulation as the DLVO theory have been developed as a two-body problem, i.e., interaction between two plates or two particles in an infinite medium. The concept volume fraction of the constituent particles in the floc, i.e., voidage fraction in the floc is excluded from these theories and, therefore, the traditional theories are not applicable to the phenomenon of “pelleting flocculation”.In an effort to formulate a theory of flocculation that leads to pellet-like flocs, three possible mechanisms of flocculation process are involved, i.e., (1) perikinetic flocculation, (2) orthokinetic flocculation, and (3) an additional process of mechanical syneresis. A few hypotheses are also presented, which may become the prelude to a subsequent flocculation theory.     

Magnetic–hydrophobic coagulation of paramagnetic minerals: a correlation of theory with experiments

A simple theoretical model of magnetic–hydrophobic coagulation considering the total interaction potential energy between two spheres exposed to an external magnetic field as a sum of the van der Waals, electrostatic, magnetic, and hydrophobic components is proposed. The model was used to interpret experiments on coagulation of fine siderite particles in distilled water and 10⁻² M KCl, hydrophobized by sodium oleate. In the experiments, a relative extent of the coagulation/stability equilibrium of the siderite suspension was evaluated photoelectrically. To estimate the model parameters, the ζ-potential and hydrophobicity of siderite particles were measured.A qualitative agreement was obtained between the model predictions (energy maximum and secondary minimum) and the experimental results (voltage changes after a selected interval of sedimentation) of the siderite suspensions. Moreover, a statistically significant correlation was found between the experimental voltages and the calculated energy maximum (a crucial factor of theories on the fine particle coagulation kinetics), which can be represented by a linear regression equation with the correlation coefficient of 0.979.     

Characterization of the chemical structures of natural and synthetic aluminosilicate gels and sols by infrared spectroscopy

Infrared spectra in the 300–1400 cm^?1 region indicate that the non-crystalline products of interaction between hydroxyaluminium species and orthosilicic acid in dilute aqueous solutions of pH < 5 differ markedly in structure from those formed in near-neutral and alkaline solutions of pH > 6. The compound formed in acid solution has an infrared spectrum similar to imogolite, and is termed proto-imogolite; like imogolite, it contains orthosilicate groups and 6-coordinated aluminium, and has an ideal Si:Al ratio of around 0.5, but it can incorporate some excess alumina or silica and it does not have the regular tubular structure of imogolite. Compounds formed in alkaline solutions that are not too dilute have infrared spectra resembling the feldspathoid group of minerals and are termed hydrous feldspathoids. They incorporate a condensed tetrahedral framework with an Si:Al ratio greater than one, but can also contain 6-coordinated aluminium.Natural allophanes of the proto-imogolite and hydrous feldspathoid types exist. The allophane of weathered pumice, however, contains a condensed silicate anion that incorporates little tetrahedral aluminium. Proto-imogolite forms stable sols at pH < 5 and must play an important role in the transport of aluminium in acidic natural waters containing dissolved silica.     

Comparison between thermal–viscous coupling and frictional sliding

We investigated the similarity between thermal–viscous coupling (TVC) and frictional sliding, proposed by Kameyama and Kaneda [Pure Appl. Geophys. 159 (2002) 2011]. We consider a one-dimensional layer composed of viscous material, which is sandwiched and sheared by two thick elastic layers. The rate of viscous deformation depends on the temperature T_c in the viscous layer as well as shear stress τ. The temperature T_c changes owing to heating by viscous dissipation and conductive cooling. We carried out velocity-stepping tests for the steady-state deformation both numerically and analytically, and compared the temporal evolution of small perturbations with that of the spring-block model with rate- and state-dependent friction (RSF). We found that, as is the case of frictional slip stability, the manner of temporal evolution is classified into four regimes depending on whether it is stable or not and whether it is monotonous or oscillatory with time. By further interpreting TVC in terms of general RSF theory by Ruina [J. Geophys. Res. 88 (1983) 10359], we obtained the relations between the parameters appearing in the phenomenological RSF law and the nondimensional parameters which characterize the nature of TVC. A further improvement of this approach might be important for estimating the actual values of frictional constitutive parameters at the deeper portion of seismogenic faults of interplate or inland earthquakes where a ductile deformation is expected to be significant.     

Line-broadening effects in the powder infrared spectrum of apatite

The crystallinity of natural and synthetic apatite samples is often determined from the broadening of ν ₄ PO₄ infrared absorption bands. However, various physical mechanisms contribute to the observed linewidth. In the present study, the factors determining the linewidth in the powder spectrum of synthetic fluorapatite and hydroxyapatite samples are investigated. The temperature dependence of the infrared spectrum (10–270 K) is used to assess the respective contributions of homogeneous broadening, related to the decay of phonons through anharmonic coupling, and heterogeneous broadening related to elastic strain and macroscopic electrostatic effects. This latter contribution is dominant in the investigated samples and depends on the shape of powder particles. It is discussed under the light of the theoretical modeling of the low-frequency dielectric properties of apatite based on first-principles density functional theory calculations. The linewidth of the weak ν ₁ PO₄ absorption band provides a reliable information on microscopic sources of broadening, i.e., apatite crystallinity. In comparison, the other more intense PO₄ bands are more sensitive to long-range electrostatic effects.     

Analogue modelling of the influence of shape and particle/matrix interface lubrication on the rotational behaviour of rigid particles in simple shear

The rotational behaviour of a rigid particle embedded in a linear viscous matrix undergoing cylindrical simple shear (Couette) flow was studied in 2D rock-analogue experiments. The influence of particle shape (elliptical vs. monoclinic), aspect ratio and the nature of the matrix/particle interface (lubricated vs. unlubricated) was investigated. Both matrix (PDMS) and lubricant (liquid soap) were linear viscous, with a viscosity ratio of ca. 10⁴. Without lubricant, the rotational behaviour of all particles closely approximates the Jeffery theory. Lubricated monoclinic particles with the long diagonal initially parallel to the shear direction show back rotation and approach a stable position. Lubricated elliptical particles initially parallel to the shear direction also show back rotation but only transiently stabilize. Weak planar zones in the matrix adjacent to unlubricated elliptical particles do not induce backward rotation. In general for elliptical particles, rotation rate as a function of orientation depends on axial ratio and thickness of the lubricant mantle. For thick mantles (initially >10% of the volume of the particle), rotation rates are faster than Jeffery theory. For very thin mantles they are markedly slower compared with thick mantles, particularly when the long axis is nearly parallel to the shear direction. Rotation rates are never strictly zero, so true stabilization does not occur. However, for more elongate particles (axial RATIO=6) rotation rates are so slow that a very strong shape preferred orientation would develop in a lubricated elliptical particle population. In experiments, the volume of lubricant is constant and the thickness adjacent to the long side of the particle progressively decreases with increasing strain. In natural examples of porphyroclast systems, the weak mantle continually develops by recrystallization and/or cataclasis of the rigid clast core and a steady state between production and thinning could be attained, potentially leading to true stabilization for particles with a high axial ratio.     

Sapphirine I

Microprobe analyses of 26 natural sapphirines from 17 localities indicate that the predominant chemical substitutions in this mineral occur along the solid solution join^VI(Mg,Fe)²⁺+^IVSi⁴⁺=^VI(Al, Fe)³⁺+^IVAl³⁺. Chromium and manganese are minor substituents. Evidence for the substitution SiAl+1/2Mg+1/2 vacancy is absent within the limits of analytical error.A partitioning scheme based on electrostatic charge balance considerations has been devised permitting calculation of Fe²⁺ and Fe³⁺ from total iron content. Results are in good agreement with previous Mössbauer studies which indicate Fe³⁺ is sometimes in octahedral and/or tetrahedral coordination.Distribution coefficients for Fe²⁺-Mg exchange equilibria between sapphirine-spinel and sapphirine-orthopyroxene are similar for most mineral pairs and suggest that most of the assemblages equilibrated at about the same temperature or that the exchange reactions are insensitive to temperature.Compositions of synthetic sapphirines as a function of temperature and pressure are qualitatively predictable from crystal chemical considerations. Changes in sapphirine composition along the MgSi= AlAl solid solution join toward more aluminous compositions stabilize the sapphirine structure at high temperatures and low pressures. The limited extent of MgSi=AlAl solid solution observed in natural sapphirines appears to be related to the requirements of geometrical fit among octahedra and tetrahedra in the almost idealized cubic closest-packed anion framework.     

Electronic structures of sulfide minerals — Theory and experiment

The sulfide minerals exhibit a rich diversity in sturctural chemistry and in electrical, magnetic and other physical properties. Models based on molecular orbital theory and incorporating some elements of band theory can be developed to describe the diverse valence electron behavior in these minerals. Qualitative models can be proposed on the basis of observed properties, and the models can be tested and refined using experimental data from X-ray emission and X-ray photoelectron spectroscopy and quantum mechanical calculations performed on cluster units which form the basic building blocks of the crystals. This approach to chemical bonding in sulfide minerals is illustrated for binary non-transition metal sulfides (ZnS, CdS, HgS, PbS), binary transition metal sulfides (FeS₂, CoS₂, NiS₂, CuS₂ ZnS₂) and more complex sulfides (CuFeS₂, Cu₂S, Ag₂S, CuS, Co₃S₄, CuCo₂S₄, Fe₃S₄). The relationship between qualitative and quantitative theories is reviewed with reference to the pyrite-marcasite-arsenopyrite-loellingite series of minerals. Application of the models to understanding structure-determining principles, relative stabilities, solid solution limits and properties such as color, reflectance and hardness are discussed.     

Silica fume stabilization of an expansive clay subgrade and the effect of silica fume-stabilised soil cushion on its CBR

ABSTRACT

Expansive soil subgrades, which are subjected to dual swell-shrink problem consequent upon absorption and evaporation of water, need to be improved by chemical stabilization or compacted cushion or geosynthetic reinforcement in order that pavements constructed over them are even, stable and safe. This paper presents extensive experimental data on plasticity, free swell index (FSI) and compaction characteristics of a highly swelling expansive clay stabilized with varying silica fume contents. In another series of tests on a laterite soil to be used as a cushion over the expansive clay subgrade, plasticity properties, compaction characteristics and strength characteristics were determined at varied silica fume contents. Further, CBR of the expansive clay subgrade was determined in the laboratory stabilizing it with varied silica fume contents and providing a cushion of 50 mm thickness of silica fume-stabilized lateritic soil. Liquid limit (LL), plasticity index (PI) and free swell index (FSI) of the expansive clay decreased with increasing silica fume contents. The compaction and strength characteristics of both the soils improved with silica fume stabilization. The CBR of the expansive clay provided with silica fume-stabilized cushion improved significantly.     

Stable isotopes in a stalagmite from NW Sweden document environmental changes over the past 4000 years

Sundqvist, H. S., Holmgren, K., Moberg, A., Spötl, C. & Mangini, A. 2009: Stable isotopes in a stalagmite from NW Sweden document environmental changes over the past 4000 years. Boreas, 10.1111/j.1502‐3885.2009.00099.x. ISSN 0300‐9483. This study of a 4000‐year‐old stalagmite from Korallgrottan in northwestern Sweden highlights the potentials and challenges when using stable isotopes in stalagmites as climate proxies, as well as the fact that the relationship between climate and proxy may change through time. Both the oxygen and the carbon isotopes display an overall trend of enrichment together with decreasing growth rates over the time period covered by the stalagmite, which is considered a generally cooling period according to current palaeoclimate understanding. The stable isotope records show enriched isotopic values during the, for Scandinavia, comparatively cold period AD 1300–1700 and depleted values during the warmer period AD 800–1000. The indication of a negative relationship between measured δ¹⁸O and surface temperature concurs with earlier reported stalagmite records from regions with a seasonal snow cover and is further supported by the fact that the stalagmite δ¹⁸O record shows general similarities with both regional and hemispheric temperature reconstructions available for the past 500 and 2000 years, respectively. Compared with a stable isotope record of lacustrine carbonates from northern Sweden, however, shifting correlations over time between the two records indicate that a local hydrological change may have taken place at Korallgrottan, or at the lake, compared with around 1000 years ago. The earlier part of the stalagmite δ¹⁸O might thus be influenced, to some extent, by another process than the later part, which means that a negative relationship between δ¹⁸O and surface temperature might not hold for the entire 4000‐year‐old record.     

Dephosphorization of phosphorus-rich manganese ores by selective leaching with dilute hydrochloric acid

Leaching of three high-phosphorus manganese ore samples from central India with dilute hydrochloric acid (0.1–0.6 M) has been found to reduce their phosphorus contents below the specified limit of 0.12%. Various process parameters, such as concentration of acid, liquid/solid ratio, temperature and period of leaching, particle size of ore etc., have been investigated in detail and optimum values have been worked out on the laboratory scale. Both liquid/solid ratio (slurry concentration) and temperature of leaching appear to be critical process parameters. While the increase in liquid/solid ratio above 3–4 has no beneficial effect, leaching temperature above 50°C has an adverse effect on the extent of dephosphorization. Grain size of ore finer than 100 mesh (B.S.) in general gives satisfactory dephosphorization. Laboratory-scale results have been, in general, supported by bench-scale work which shows that phosphorus can be effectively removed from high-phosphorus manganese ores of central India by leaching in dilute hydrochloric acid at ambient temperature. Comparative performance of the dilute solutions of all the three mineral acids as leaching agents has been discussed.     

高切坡超前支护锚杆作用机制研究

人工高切坡开挖常常导致边坡失稳破坏,甚至诱发滑坡发生,为此提出了高切坡超前锚杆支护的设计新方法。超前支护锚杆能够约束边坡变形和开挖卸荷带的发展,维持边坡的稳定,对超前支护锚杆的作用机制问题进行了研究,阐述了超前支护锚杆的荷载传递特性,为超前支护锚杆设计提供了理论依据。     

Simultaneous inner- and outer-sphere arsenate adsorption on corundum and hematite

The ability to predict the fate and transport of arsenic in aquatic environments, its impact on water quality and human health, and the performance and cost-effectiveness of water treatment systems relies on understanding how it interacts with solid surfaces. In situ resonant surface X-ray scattering measurements of arsenate adsorption at pH 5 in 0.01 M NaCl on corundum and hematite (012) surfaces demonstrate that arsenate surface complexation is unexpectedly bimodal, adsorbing simultaneously as inner- and outer-sphere species. In addition, this bimodal behavior is found to be independent of the total arsenate solution concentration, and thus surface coverage, over the range of 10⁻⁶ to 10⁻³ M. Alternative mechanisms to produce the observed As distributions, such as arsenate dimerization or surface precipitation of an aluminum or ferric arsenate, are inconsistent with the experimentally-determined total and As-specific density profiles. Based on the location of the outer-sphere arsenate in relation to the surfaces studied, possible binding mechanisms include electrostatic attraction, hydrogen bonding to surface oxygen functional group, and configurational stabilization by interfacial water. Although the observation of outer-sphere arsenate surface complexes on a metal oxide surface is unprecedented, it is unclear if such species were absent in previous molecular-scale studies, as it is difficult for methods commonly used to investigate the mechanisms of arsenate adsorption to conclusively identify or rule out the presence of outer-sphere species when inner-sphere species are also present.     

Stabilization of extracellular polymeric substances (Bacillus subtilis) by adsorption to and coprecipitation with Al forms

Extracellular polymeric substances (EPS) are continuously produced by bacteria during their growth and metabolism. In soils, EPS are bound to cell surfaces, associated with biofilms, or released into solution where they can react with other solutes and soil particle surfaces. If such reaction results in a decrease in EPS bioaccessibility, it may contribute to stabilization of microbial-derived organic carbon (OC) in soil. Here we examined: (i) the chemical fractionation of EPS produced by a common Gram positive soil bacterial strain (Bacillus subtilis) during reaction with dissolved and colloidal Al species and (ii) the resulting stabilization against desorption and microbial decay by the respective coprecipitation (with dissolved Al) and adsorption (with Al(OH)_3(am)) processes. Coprecipitates and adsorption complexes obtained following EPS-Al reaction as a function of pH and ionic strength were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The stability of adsorbed and coprecipitated EPS against biodegradation was assessed by mineralization experiments for 1100 h. Up to 60% of the initial 100 mg/L EPS-C was adsorbed at the highest initial molar Al:C ratio (1.86), but this still resulted only in a moderate OC mass fraction in the solid phase (17 mg/g Al(OH)_3(am)). In contrast, while coprecipitation by Al was less efficient in removing EPS from solution (maximum values of 33% at molar Al:C ratios of 0.1-0.2), the OC mass fraction in the solid product was substantially larger than that in adsorption complexes. Organic P compounds were preferentially bound during both adsorption and coprecipitation. Data are consistent with strong ligand exchange of EPS phosphoryl groups during adsorption to Al(OH)_3(am), whereas for coprecipitation weaker sorption mechanisms are also involved. X-ray photoelectron analyses indicate an intimate mixing of EPS with Al in the coprecipitates, which is not observed in the case of EPS adsorption complexes. The incubation experiments showed that both processes result in overall stabilization of EPS against microbial decay. Stabilization of adsorbed or coprecipitated EPS increased with increasing molar Al:C ratio and biodegradation was correlated with EPS desorption, implying that detachment of EPS from surface sites is a prerequisite for microbial utilization. Results indicate that the mechanisms transferring EPS into Al-organic associations may significantly affect the composition and stability of biomolecular C, N and P in soils. The observed efficient stabilization of EPS might explain the strong microbial character of organic matter in subsoils.     

On the volume dependence of viscosity of some magmatic silicate melts

Summary Density and viscosity measurements of three melts of volcanic rock composition (basalt and andesite) at low temperatures were carried out to understand the role of free volume in the viscous behavior of a magma and to estimate the flow unit in the melts. The data combined with literature data suggest the following conclusion: free-volume theory is not applicable to these silicate melts; the relation between viscosity and the inverse of free volume does not yield a straight line in a wide temperature range from the glass-transion temperature to 1550°C. However, two depolymerized melts, diopside and Oki-Dozen alkali basalt (OAB), yield almost linear relationships. Thus, the free-volume theory should hold to a fairly good approximation for these two melts. Based on this approximation, the radius of flow unit for diopside melt was calculated to be about 4.7 Å, and that for Oki-Dozen alkali basalt to be about 4.2 Å. The three-dimensional silicate anions which may correspond to the flow unit are Si₁₄O₃₅ ^14– and Si₁₆O₄₀ ^16– for diopside melt, and Si₁₀O₂₅ ^10– and Si₁₂O₃₀ ^12– for OAB melt. The temperature effect on the initial slope of the viscosity-pressure relation has also been examined in the frame of free-volume theory. It was concluded that the relative increase of the initial slope of the relation with increasing temperature might be caused by the increase of free volume.With 6 Figures