Electrokinetic properties and flotation behaviour of apatite and calcite in the presence of sodium oleate and sodium metasilicate

Calcite is generally associated with apatite minerals in phosphate deposits. To explore the possibility of separating these minerals by a soap flotation technique, their electrokinetic properties and flotation behaviour were studied in the presence of sodium oleate.Microelectrophoresis data indicate oleate adsorption on these minerals, and from Hallimond-tube flotation tests it has been noted that in a controlled pH environment and for a certain sodium oleate concentration range, separation of these minerals is possible.The study of apatite/calcite-sodium metasilicate-sodium oleate systems indicates the preferential adsorption of silicate at the calcite surface. This suggests the potential use of sodium metasilicate as the modifying agent for the separation of apatite from calcite by depressing calcite when using sodium oleate as collector.     

Solution chemistry studies and flotation behaviour of apatite,calcite and fluorite minerals with sodium oleate collector

The maximum flotation response for three naturally occurring calcium minerals, apatite, calcite and fluorite with sodium oleate collector correlated directly with the minimum interfacial tension of the air/solution interface. For fluorite and apatite the minimum surface tension occurred about the mid-pH region and was attributed to the formation of pre-micellar associated species in solution. In the case of calcite the minimum was observed at high pH since the presence of high concentrations of calcium ions in solution appeared to reduce the concentration of amphililic species in the low and mid-pH regions.Microelectrophoresis data demonstrated that the three minerals acquired a negative charge in sodium oleate solution, resulting from adsorption of oleate species on the mineral surfaces.The flotation behaviour of the systems were shown to be related to the species distribution diagrams suggesting that the role of the acid soap dimer, soap dimer, molecular and lattice species could make a significant contribution to the character and composition of the interfacial films.High flotation response was explained by strong adhesion between the hydrophobic particle and bubble. It was suggested that the reduction in surface tension may not be the major factor contributing to the flotation efficiency but indicated the presence of associated surfactant species in solution which could also synergistically adsorb at the solid/liquid interface, increasing the hydrophobic character of the mineral surface. This would maximize the magnitude of the contact angle and hence the strength of the adhesion between particle and bubble. This adsorption behaviour is not in general agreement with conventionally non-hydrolyzable collector theory which is usually based on electrostatic models.     

The electrokinetics of apatite and calcite in inorganic electrolyte environment

Microelectrophoresis technique was used to study the electrokinetic properties of some apatites and calcite. The results indicate that similar to oxide minerals, H⁺ and OH^? ions function as potential-determining ions for apatite and calcite. However, because of their variable compositions, the apatites from different deposits showed different i.e.p. values ranging from pH 3.5 to 6.7, while the i.e.p. of calcite occurred at pH 8.2.Study of the effect of lattice-forming ions on the zeta potential indicates that calcium ions produce specific ionic adsorption effects on apatites, whereas they are potential-determining ions for calcite. On the other hand, as expected, phosphate and carbonate ions function as potential-determining ions for apatite and calcite, respectively.The experimental data suggest that the zeta potential of apatite is a function of mineral—water contact time. The degree of variation in zeta-potential values appears to be influenced by the electrolytic environment of the apatite suspension.     

The effects of dodecylamine, kerosene and pH on batch flotation of Turkey's Tuncbilek coal

The effects of dodecylamine (DDA), kerosene and pH on the recovery of combustible matter and ash content of a lignitic coal from Tuncbilek, Turkey have been studied using a three-variable and two-level (2³) factorial experimental design. The coal sample responded favourably to batch flotation with high recoveries in excess of 95% using both kerosene and DDA respectively. The main effects of all three factors on the recovery are positive. Significance of DDA as a collector, is somewhat greater than that of kerosene, but its selectivity for ash reduction is not significant at the 95% confidence level. The pH-dependence of recovery by these collectors is opposite to each other. The DDA-induced flotation recovery is lowest at pH 9.4, an effect which has been related to precipitation of cationic species of this collector. The kerosene-induced recovery and grade of combustible matter increases with pH and this has been attributed to a better dispersion of coal and its associated clays. The two-way interaction effects are all negative at a smaller level. The main and interaction effects have been discussed on the basis of adsorption at most favourable surface sites, different modes of orientation of DDA species, competition with kerosene, and probable collecting properties of the frother used. The simultaneous effects of the two collectors on the recovery of combustible matter have been discussed at each pH value used.     

氯化物对方解石和白云石矿物溶解度的影响

借助PHREEQC软件,文章对方解石、白云石分别在无CO2和大气PCO2条件下NaCl、KCl、CaCl2和MgCl2溶液中的溶解度进行了模拟计算,结果显示:方解石在NaCl、KCl、和MgCl2溶液中以及白云石在NaCl、KCl溶液中的溶解度比纯水中大得多,其原因主要是盐效应。由于同离子效应,在CaCl2溶液中可降低方解石溶解度,而白云石在较高浓度CaCl2或MgCl2溶液中,虽发生同离子效应,其溶解度仍较纯水中有不同程度提高。模拟还显示,方解石在MgCl2溶液中以及白云石在CaCl2溶液中溶解时将分别发生白云石化和去白云石化反应,从而促使不全等溶解继续发生。在常规离子中,按方解石、白云石溶解度提高发挥作用的重要性排序为:阴离子中都是SO24->Cl-;对于方解石溶解,阳离子中Mg2+>Na+>K+>Ca2+;对于白云石溶解,当PCO2=0或PCO2=10-3.5bar且CaCl2浓度大约在1.5mol/L以下时,Na+>K+>Ca2+>Mg2+;当PCO2=10-3.5bar且CaCl2浓度大约在1.5mol/L以上时,Ca2+>Na+>K+>Mg2+。     

Hallimond tube flotation of scheelite and calcite with amines

Hallimond tube flotation experiments have been carried out on the two calcium minerals scheelite and calcite using dodecylammonium chloride as collector. The main variables studied were the calcium ion concentration and the pH.In the case of scheelite, addition of calcium chloride markedly lowered the flotation recovery. Recovery was also lowered when the pH was reduced below about 10. Since it is known that the zeta potential of scheelite is almost independent of pH this confirms that co-adsorption of un-ionized amine is necessary for good flotation. Other un-ionized long-chain molecules can replace the amine; thus it was shown that excellent flotation can be obtained event at about pH 7 by adding dodecanol together with dodecylammonium chloride. With the completely ionic trimethyldodecylammonium chloride recoveries were poor and were independent of pH.In the case of calcite, calcium chloride had no immediate effect on flotation recovery, but at low collector concentrations marked depression occurred after many hours standing in the presence of calcium ions. The effect of pH on flotation of calcite was anomalous and there appear to be two pH regions in which recoveries are high.The results are discussed and attention is drawn to the need for more thorough studies of the calcium carbonate/water interface.     

Oxygen isotope evolution of biogenic calcite and apatite during the Middle and Late Devonian

Oxygen isotope ratios of well-preserved brachiopod calcite and conodont apatite were used to reconstruct the palaeotemperature history of the Middle and Late Devonian. By assuming an oxygen isotopic composition of –1 V-SMOW for Devonian seawater, the oxygen isotope values of Eifelian and early Givetian brachiopods and conodonts give average palaeotemperatures ranging from 22 to 25 °C. Late Givetian and Frasnian palaeotemperatures calculated from ¹⁸O values of conodont apatite are close to 25 °C in the early Frasnian and increase to 32 °C in the latest Frasnian and early Famennian. Oxygen isotope ratios of late Givetian and Frasnian brachiopods are significantly lower than equilibrium values calculated from conodont apatite ¹⁸O values and give unrealistically warm temperatures ranging from 30 to 40 °C. Diagenetic recrystallization of shell calcite, different habitats of conodonts and brachiopods, as well as non-equilibrium fractionation processes during the precipitation of brachiopod calcite cannot explain the ¹⁸O depletion of brachiopod calcite. Moreover, the ¹⁸O depletion of brachiopod calcite with respect to equilibrium ¹⁸O values calculated from conodont apatite is too large to be explained by a change in seawater pH that might have influenced the oxygen isotopic composition of brachiopod calcite. The realistic palaeotemperatures derived from ¹⁸O _apatite may suggest that biogenic apatite records the oxygen isotopic composition and palaeotemperature of Palaeozoic oceans more faithfully than brachiopod calcite, and do not support the hypothesis that the ¹⁸O/¹⁶O ratio of Devonian seawater was significantly different from that of the modern ocean.     

The mechanism of fatty acid adsorption in the presence of fluorite,calcite and barite

The interaction of oleic acid with fluorite, calcite and barite has been studied using solubility, oleate abstraction, electrophoretic mobility and Hallimond-tube flotation measurements. Abstraction of oleate from aqueous solution corresponds to the precipitation of the metal oleate. Multilayers of metal oleate inhibits the dissolution of the minerals and prevents true equilibrium from being obtained. Flotation is not only dependent on the amount of oleate abstracted but also on the strength of adhesion of the precipitated metal oleate to the minerals. Selectivity between the flotation of calcite, fluorite and barite is unlikely to be obtained by varying the pH because similar responses are observed.     

The influence of interstitial water on the rheological behaviour of calcite rocks

The effects of pore water on the mechanical behaviour of Solnhofen Limestone and Carrara Marble at various temperatures and confining pressures at constant strain-rate have been experimentally investigated. It is shown that water affects the strength and ductility of calcite rocks through

1.

(1) physico-chemical action at grain boundaries, and     

Molecular-scale surface processes during the growth of calcite in the presence of manganese

This paper deals with the growth behaviour of the Mn-Ca-CO₃-H₂O solid solution-aqueous solution system on calcite {104} surfaces. This system represents a model example, which allows us to study the effect of a number of controlling factors on the crystallisation: (1) the supersaturation function, β(x), and nucleation rate function, J(x), for the Mn-Ca-CO₃-H₂O system, (2) the relationship of such functions to the molecular scale growth mechanisms operating on growing surfaces, and (3) the surface structure of the calcite {104} faces. In situ atomic force microscopy (AFM) growth experiments revealed a wide variety of surface phenomena, such as the transition between growth mechanisms, anisotropic changes in the step rates, and the influence of the Mn-bearing newly formed surface on subsequent growth (step stoppage followed by the formation of two-dimensional nuclei and the reproduction of the original calcite {104} surface microtopography). These phenomena result from the interplay between the controlling parameters and are explained in those terms.     

Removal of lead minerals from copper industrial flotation concentrates by xanthate flotation in the presence of dextrin

Potato starch and dextrins resulting from thermolysis of potato starch in the absence of reagents and presence of -amino acids are promising depressants for separation of lead and copper minerals present in the Polish industrial copper concentrates. The polysaccharides were used for differential xanthate flotation of the final industrial concentrates produced by flotation with sulfhydryl collectors in the absence of depressants. The polysaccharides depressed galena and provided froth concentrate rich in chalcocite and other copper minerals as well as cell product containing lead minerals. The best results of separation were obtained in the presence of plain dextrin prepared by a thermal degradation of potato starch. The industrial concentrate containing 18.5% Cu and 5.5% Pb was divided into a froth product containing 38.1% Cu with 77% recovery of copper and a cell product assaying 7.3% Pb with 83% recovery of lead. It was accomplished using 2500 g/t of dextrin, 50g/t of potassium ethyl xanthate, and 50 g/t of frother (α-terpineol). The pH of flotation was 8.0–8.2.     

Adsorption and flotation behavior of manganese dioxide in the presence of octyl hydroxamate

The adsorption of octyl hydroxamate on electrolytic manganese dioxide was investigated through adsorption studies, electrophoretic mobility measurements, infrared spectroscopy and Hallimond tube flotation. The adsorption measurements at room temperature and flotation studies show that a peak in adsorption density and flotation response occurs around pH 9. IR spectra indicate the presence of basic manganous hydroxamate complex at the surface. The electrophoretic mobility studies suggest that hydroxamate adsorbs specifically at the manganese dioxide/water interface. Adsorption measurements at an elevated temperature show that adsorption density increases with increasing temperature. It is postulated that the reactive species in adsorption could be the hydroxamic acid species.     

The effect of dextrin on surface properties and the flotation of molybdenite

The effect of dextrin on molybdenite surface properties has been investigated experimentally through measurements of zeta potentials, adsorption densities, contact angles, Hallimond tube flotation and oil flotation response. These studies indicate that the adsorption of dextrin on molybdenite occurs through physical interaction with the surface, possibly due to hydrophobic bonding. The hydrophobic bonding mechanism is in accord with the magnitude of the adsorption free energy, which was estimated to be—5.4 kcal per mole of dextrin monomers. Dextrin was found to be a very effective depressant for the air flotation of molybdenite in the absence of a collector, whereas it does not effectively depress molybdenite in an oil flotation process using iso-octane. This has been discussed qualitatively from the contributions of electrical double layer repulsion, van der Waals' attraction, and hydration effects.     

High-pressure behaviour and equation of state of calcite, CaCO3

The high-pressure response of the cell parameters of calcite, CaCO₃, has been investigated by single crystal X-ray diffraction. The unit cell parameters have been refined from 0 to 1.435?GPa, and the linear and volume compressibilities have been measured as β _a =2.62(2)?×?10^?3?GPa^?1,β _c =7.94(7)?×?10^?3?GPa^?1, β _v =13.12?×?10^?3?GPa^?1. The bulk modulus has been obtained from a fit to the Birch-Murnaghan equation of state, giving K ₀=73.46?±?0.27?GPa and V ₀=367.789 ±?0.004?ų with K′=4. Combined with earlier data for magnesite, ankerite and dolomite, these data suggest that K ₀ V ₀ is a constant for the Ca-Mg rhombohedral carbonates.     

Micro-environmental controls on biomineralization: superficial processes of apatite and calcite precipitation in Quaternary soils, Roussillon, France

Calcium hydroxyapatite and calcite precipitates around bacteria were observed in 2-week-old alluvial topsoil (Roussillon area, SE France). This observation prompted a laboratory study of Ca²⁺ and PO₄³⁻ incorporation into hydroxyapatite and Ca²⁺ into calcite mediated by bacteria using similar topsoil material, but free from apatite and calcite. Subsamples were prepared using three different grain sizes, and experiments were undertaken using sucrose and different contents of Ca²⁺ and PO₄³⁻. Mineralization experiments proceeded over 5 days. Calcium and PO₄³⁻ sorption onto clay influenced the Ca/P ratio in the solutions. Hydroxyapatite and calcite precipitation only occurred in unsterilized samples. The presence of clay minerals promoted biomineralization.     

Roughing and cleaning flotation behaviour and the realistic simulation of complete plant performance

Data are presented which illustrate a range of flotation behaviour observed for roughing and cleaning operations in industrial plants. Differences are observed in the size by size recoveries in cleaner flotation from those measured in the roughers.The implications of these differences to flotation modelling are discussed, and the importance of conducting confirmatory laboratory batch flotation tests is emphasized.Batch flotation tests have indicated that for certain minerals the flotation characteristics in the cleaner tests are substantially different from those in rougher tests conducted under the same conditions of pulp level, impeller speed, aeration rate and froth removal. The differences are most pronounced for the coarse particles.Computer simulations of a rougher-cleaner circuit have been done to illustrate the effects of these differences on predicted circuit performance. The differences are significant and arise mainly from differences in the behaviour of coarse particles.     

An Atomic Force Microscopy study of the growth of calcite in the presence of sodium sulfate

In situ atomic force microscopy (AFM) has been used to compare the growth of pure calcite and the growth of calcite in the presence of sulfate ions from aqueous solutions at a constant value of supersaturation (S.I. = 0.89) with respect to calcite. The effect of sulfate ions on calcite growth rates is determined and a potential incorporation of sulfate ions is identified in the calcite during growth. Solutions supersaturated with respect to calcite with solution concentration ratio of one and a constant pH of 10.2, were prepared and sulfate was added as Na₂SO₄ aqueous solution. The solution composition was readjusted in order to keep the supersaturation and pH constant. PHREEQC was used to determine relevant solution concentrations. In situ AFM experiments of calcite growth were performed using a fluid cell and flowing solutions passed over a freshly cleaved calcite surface. Growth rates were determined from the closure of the rhombohedral etch pits induced by initial dissolution with pure water. The spreading rate of 2-dimensional nuclei was also measured. At low concentrations of sulfate (≤ 0.5 mM), no effect on the growth rate of the calcite was observed. At higher concentrations (2 to 3 mM) of sulfate, the growth rate increased, possibly because a higher concentration of calcium and carbonate was necessary to maintain the supersaturation constant. At much higher concentrations of additional sulfate (up to 60 mM) the growth rate of the calcite was substantially decreased, despite the fact that a further increase of calcium and carbonate was required. The morphology of 2-dimensional growth nuclei became increasingly elongated with increasing sulfate content. Measurements of step height showed that newly grown steps were approximately 1 Å higher when grown in high sulfate concentrations, compared to steps grown in sulfate-free solutions. At sulfate concentrations above 5 mM the growth mechanism changes from layer growth to surface roughening. These observations suggest that the new growth has incorporated sulfate into the calcite surface.     

Effect of pretreatment of the electrokinetic properties of quartz

Effects of various commonly used pretreatments such as desliming, ultrasonic scrubbing and leaching with dilute nitric, hydrofluoric and sodium hydroxide solutions on the electrokinetic properties of quartz in aqueous solutions are reported. The study showed that treatments with various reagents often used in mineral processing research in the past to clean minerals can affect, sometimes severly, the electrokinetic properties of quartz. The change in these properties during subsequent aging is also found to be governed by the type of treatment used. This study also shows the need in mineral research for standardization of mineral preparation techniques in order that the discrepancy in data reported for surface properties in literature can be minimized.     

In situ AFM study of the dissolution and recrystallization behaviour of polished and stressed calcite surfaces

We investigated the dissolution behaviour of polished calcite surfaces in situ using a fluid-cell atomic force microscope. Polished calcite surfaces enabled us to study the effects of applied surface stress and crystallographic orientation on calcite dissolution pattern formation. Thin-sections of Iceland spar single-crystals polished either parallel or with a 5° miscut angle to cleavage planes were studied. Compressive surface stresses of up to 50 MPa were applied to some of the thin-section samples by means of elastic concave bending. Experiments were carried out in semi-stagnant deionized water under mainly transport limited dissolution conditions. Samples polished parallel to cleavage planes dissolved by the formation of etch-pits originating from polishing defects. The dissolution behaviour of 5° miscut surfaces was relatively unaffected by polishing defects, since no etch-pits developed in these samples. Dissolution of the miscut samples led to stepped or rippled surface patterns on the nanometer scale that coarsened during the first 30-40 min of the experiments. Possible reasons for the pattern-coarsening were: (i) progressive bunching of retreating dissolution steps and (ii) surface energy driven recrystallization (Ostwald ripening) under transport limited dissolution conditions. A flat polished miscut surface in calcite may recrystallize into a hill-and-valley structure in a (near-)saturated solution so as to lower its total surface free energy in spite of a larger surface area. No clear effect of applied stress on dissolution pattern formation has been observed.     

Transformation of curite into metaautunite paragenesis and electrokinetic properties

Genesis of metaautinute [Ca(UO₂/PO₄)₂ · 7H₂O] starting from curite hints at the existence of an intermediate hydrogen autunite stage [HUO₂PO₄ · 4H₂O]. The substitution of protons in hydrogen autunite by Ca²⁺ ions is proved by electrokinetic measurements. As a consequence of the similarity between X-ray powder patterns of hydrogen autunite and meta-autunite a glycolation method has been applied in order to distinguish the two species. The cell dimensions have been determined from Guinier X-ray diffraction patterns. Both minerals are tetragonal with a=6.981±0.005 Å and c=8.448±0.005 Å for metaautunite and a=7.084±0.005 Å and c=8.777±0.005 Å for hydrogen autunite. For both minerals, the zeta-potential is mostly negative and is strongly influenced by temperature, pH and concentration of cations in the suspension. The surface conductivity has been calculated from the value of the zetapotential. The electrokinetic properties of metaautunite are very similar to those of metatorbernite.