Adsorption of oleate on fluorite surface as revealed by atomic force microscopy

The adsorption of oleic acid / oleate on fluorite surface could be visualized using tapping mode of atomic force microscopy (AFM). The natural fluorite crystals were equilibrated with 10^− 3 to 10^− 7 M oleate solutions and their AFM images at each concentration along with height profiles were recorded. Even at low oleate concentration of 1 × 10^− 7 M, concomitant monolayer and bilayer structures were observed. It suggests that normal–normal bonding of hydrocarbon chains takes place before the surface is completely covered by the monolayer. Multi-layer adsorption of oleate was observed at oleate concentrations of above 10^− 4 M. The tapping mode AFM can be utilized to visualize the topography of surfaces adsorbed with surfactant molecules.     

Influence of sodium silicate addition on the adsorption of oleic acid by fluorite,calcite and barite

A study has been made of the adsorption of sodium silicate by calcite, fluorite and barite and the effect that this adsorption has on the flotation of these minerals with oleic acid. The results show that sodium silicate depresses these minerals by preventing oleate species from reacting with surface sites. This effect is independent of the total silica concentration. Aged sodium silicate solutions do not produce markedly different results to those obtained with fresh solutions.The concentration of the sodium silicate solutions was generally such that the total silica concentration was below that in equilibrium with amorphous silica. Under these conditions the solutions contained no polymeric silica species and the mechanism of silica adsorption can be generally attributed to interactions of monosilicate ion and monosilicic acid with surface sites.     

The mechanisms of forming iron-base metal gossan minerals

Laboratory studies of the weathering of sulphide ores have centred around using samples of ore as electrodes and accelerating the weathering processes by passing an electric current. The results of reacting 19 different ore types under varying conditions are compared with data from co-precipitating, Fe and Cu, Fe and Ni, Fe and Zn, Fe and Co, and Fe and Pb, over a pH range from 2 to 11. An electrochemical cell specially designed to fit onto an optical microscope has allowed direct observation of the changes in sulphide mineral grains as they are anodically weathered.These experiments are used to demonstrate that the pH of the environment during the weathering of sulphides to sulphates is the most important parameter in determining the initial gossan minerals that form. Factors that will cause the pH to be high are buffering from gangue and wallrock minerals, low iron content in the sulphide and a high metal to sulphur ratio in the sulphide. A low pH is favoured by the converse, namely a sulphide sufficiently massive to override the buffering effects of the wallrocks and any gangue minerals present, a high iron content in the sulphide and a low metal to sulphur ratio in the sulphide.Two mechanisms of iron hydrolysis dominate the weathering processes where iron is a major metal being released from a sulphide.

1. (1) The high pH process. Where there is sufficient buffering for the pH to remain at or above 7, most of the base metals including ferrous iron will be hydrolysed and pyroaurite type of minerals form for Ni, Zn and Co, while mixed Fe-Cu hydroxycarbonates and hydroxysulphates form for Cu, and mixed iron lead hydrocarbonates form for Pb. The iron is located in these initial compounds as a green rust where it is effectively bound as ferrous hydroxide. Subsequent oxidation of this hydroxide produces no further acid. 4Fe(OH)₂ + O₂ + 2H₂0 → 4Fe(OH)₃

2. (2) The low pH process. Where the buffering is insufficient and the pH is below 7, even though some of the ferrous iron will have precipitated as an equivalent to Fe(OH)₂, the solubility is such that sufficient Fe²⁺ will remain in solution so that further oxidation will produce acid. 4Fe²⁺ + O₂ + 1OH₂O → Fe(OH)₃ + 8H⁺ This acid will bring more of the Fe²⁺ into solution to create more acid and the pH will gradually fall even further, so that the gossan forming environment will be at a pH less than 5 and may be as low as 3. At these low pH values, the base metals are soluble and not prone to co-precipitation or adsorption with the gossan minerals. Only elements present in solution as anions, such as Se, As, Mo and Sb, are likely to be bound into gossans forming at low pH.

The results from weathering tests carried out on gossan minerals formed at higher pH show that these minerals are reasonably stable if treated with solutions that have a pH above 7, but they can break down if treated with a solution of pH 5. Thus they could be expected to be leached by rain water saturated with CO₂.When investigating a likely gossan, all aspects — the iron oxides, the silicates, the carbonates and penetrations into the footwall and hanging wall — should be examined carefully, being ever mindful of the effect that pH would have had during the formation and reworking of the minerals. The composition of gossan minerals, their adsorption properties, the solubilities of metal ions, the mechanisms of Fe precipitation, the co-precipitation of other metals with Fe, the stability of carbonates and the binding of humic materials are all pH dependent in the same way. At high pH, metals are immobilized; at low pH, they tend to be in solution.     

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.     

Heavy metal adsorption by sulphide mineral surfaces

The adsorption of aqueous Hg²⁺, Pb²⁺, Zn²⁺ and Cd²⁺ complexes on a variety of sulphide minerals has been studied as a function of the solution pH and also as a function of the nature of the ligands in solution. Sulphide minerals are excellent scavengers for these heavy metals. The adsorption is strongly pH dependent, i.e. there is a critical pH at which the adsorption increases dramatically. The pH dependence is related to the hydrolysis of the metal ions. Indirect evidence suggests that the hydrolyzed species are adsorbed directly on the sulphide groups, probably as a monolayer. The results also suggest the presence of MCI_n²⁻ⁿ species physisorbed on the adsorbed monolayer. A positive identification of the adsorbed species was not possible using ESCA/XPS.     

The effect of Fe on Si adsorption by Bacillus subtilis cell walls: insights into non-metabolic bacterial precipitation of silicate minerals

Si adsorption onto Bacillus subtilis and Fe and Al oxide coated cells of B. subtilis was measured both as a function of pH and of bacterial concentration in suspension in order to gain insight into the mechanism of association between silica and silicate precipitates and bacterial cell walls. All experiments were conducted in undersaturated solutions with respect to silicate mineral phases in order to isolate the important adsorption reactions from precipitation kinetics effects of bacterial surfaces. The experimental results indicate that there is little association between aqueous Si and the bacterial surface, even under low pH conditions where most of the organic acid functional groups that are present on the bacterial surface are fully protonated and neutrally charged. Conversely, Fe and Al oxide coated bacteria, and Fe oxide precipitates only, all bind significant concentrations of aqueous Si over a wide range of pH conditions. Our results are consistent with those of Konhauser et al. [Geology 21 (1993) 1103; Environ. Microbiol. 60 (1994) 49] and Konhauser and Urrutia [Chem. Geol. 161 (1999) 399] in that they suggest that the association between silicate minerals and bacterial surfaces is not caused by direct Si–bacteria interactions. Rather, the association is most likely caused by the adsorption of Si onto Fe and Al oxides which are electrostatically bound to the bacterial surface. Therefore, the role of bacteria in silica and silicate mineralization is to concentrate Fe and Al through adsorption and/or precipitation reactions. Bacteria serve as bases, or perhaps templates, for Fe and Al oxide precipitation, and it is these oxide mineral surfaces (and perhaps other metal oxide surfaces as well) that are reactive with aqueous Si, forming surface complexes that are the precursors to the formation of silica and silicate minerals.     

Infrared studies of the adsorption of oleate species on calcium fluoride

In the study, by infrared spectroscopy, of the nature of the adsorbed species when fluorite or precipitated calcium fluoride are treated with aqueous sodium oleate or oleic acid, a certain amount of confusion has arisen about whether the spectra of the surface products represent sodium oleate, calcium oleate, oleic acid or various combinations of the three. The investigation described in this paper was aimed at resolving the discrepancies, and showed that the spectrum of the adsorbed species had peaks at 1613 and 1562 cm^?1. It is suggested that the former corresponds to a surface chemisorbed calcium oleate and the latter to both surface calcium oleate and physically adsorbed sodium oleate.     

Flotation mechanism of octylic hydroxamic acid on diaspore

Bauxite resources are widely spread in the earth. However, the effective utilization of this mineral is still under infant. The conventional collector for diaspore mineral is oleic acid. It has three main drawbacks which are highly insoluble, large dosages in bauxite flotation, and low selectivity, which hinder its application in industry. In this research, octylic hydroxamic acid was synthesized, and its collecting ability toward two major minerals in bauxite-diaspore and kaolinite was investigated. The collecting power of various reagents for diaspore are shown as follows: oleic acid相似文献   

Adsorption of barium ions by β-manganese dioxide and its activation in oleate flotation

The Ba²⁺ ion adsorption isotherms on β-MnO₂ were of the Langmuir type. The endothermic heat of adsorption (40 kJ mol^?1) is ascribed to entropy contributions associated with the $\text{Na}{}^{\mathrm{+}}\text{Ba}{}^{\mathrm{2+}}$ ion-exchange mechanism. The Ba²⁺ ion adsorption density was higher at pH 10 than that at pH 7, due to the more negative surface charge at the higher pH. Ba²⁺ ions were found to reverse the sign of the ζ potential of the MnO₂ particles.More oleate was adsorbed by β-MnO₂ in the presence of Ba²⁺ ions than in their absence. The oleate adsorption isotherms on Ba²⁺-activated MnO₂ were of the Freundlich type and indicated an exothermic process. Hallimond flotation recovery of Ba²⁺-activated MnO₂ was higher at pH 10 than at pH 7, although less oleate was adsorbed at the higher pH. At pH 7, Mn²⁺-activation led to higher recoveries than Ba²⁺-activation. It seems that the attraction between the surface and the activator plays an important rôle in determining the flotation recovery.     

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.     

Arsenate and antimonate adsorption competition on 6-line ferrihydrite monitored by infrared spectroscopy

Arsenate and antimonate are water-soluble toxic mining waste species which often occur together and can be sequestered with varying success by a hydrous ferric oxide known as ferrihydrite. The competitive adsorption of arsenate and antimonate to thin films of 6-line ferrihydrite has been investigated using primarily adsorption/desorption kinetics monitored by in situ attenuated total reflectance infrared (ATR-IR) spectroscopy on flowed solutions containing 10⁻³ and 10⁻⁵ mol L⁻¹ of both species at pH 3, 5, and 7. ICP-MS analysis of arsenate and antimonate adsorbed to 6-line ferrihydrite from 10⁻³ mol L⁻¹ mixtures in batch adsorption experiments at pH 3 and 7 was carried out to calibrate the relative surface concentrations giving rise to the IR spectral absorptions. The kinetic data from 10⁻³ and 10⁻⁵ mol L⁻¹ mixtures showed that at pH 3 antimonate achieved a greater surface concentration than arsenate after 60 min adsorption on 6-line ferrihydrite. However, at pH 7, the adsorbed arsenate surface concentration remained relatively high while that of adsorbed antimonate was much reduced compared with pH 3 conditions. Both species desorbed slowly into pH 3 solution while at pH 7 most adsorbed arsenate showed little desorption and adsorbed antimonate concentration was too low to register its desorption behaviour. The nature of arsenate which is almost irreversibly adsorbed to 6-line ferrihydrite remains to be clarified.     

Gd-DTPA in the hydrosphere: Kinetics of transmetallation by ions of rare earth elements,Y and Cu

The kinetics of transmetallation of Gd³⁺ in diethylenetriaminpentaacetic acid (Gd-DTPA) by rare earth elements (except Yb), Y³⁺ and Cu²⁺ has been studied in test solutions ranging from pH 5 to 6.5 in order to understand the distribution and longevity of their chelates in the hydrosphere. Chelated and non-chelated species were separated by adsorption of the free ions by clay minerals before analysis by ICP-MS. This simple method allows determining the distribution of DTPA chelates at concentration levels as low as a few 10 pmol/l. The transmetallation constants at ionic strength of 0.01 mol/l and room temperature are commensurable with those derived from published formation constants of the corresponding DTPA complexes. It could be proved that DTPA chelates of rare earth elements, Y and Cu are stable at least over 6 months. The pattern of the second-order rate constants shows a strong tetrad effect, which is not displayed by the pattern of transmetallation constants. Based on these results, the rate of transmetallation of Gd-DTPA under natural conditions is derived. The resultant process yields 10% turn-over of initial Gd-DTPA within two months, if Cu²⁺ concentrations are below 1 nmol/l. At higher concentrations, the turn-over increases with elapsed time. Equilibrium among REE and Y is expected only after tens of years. This makes Gd-DTPA a powerful tracer in hydrological studies.     

The interaction of cobalt with hydrous manganese dioxide

Adsorption of cobalt on synthetic hydrous manganese dioxide was studied as a function of pH and surface area in NaCl solutions and solutions containing sea water concentrations of Na, Ca and Mg. The amount of cobalt adsorbed increased sharply at pH 6, a significantly lower pH than that required for significant hydrolysis of Co(II) or precipitation of Co(OH)₂(S) in bulk solution. Sea water concentrations of Na, Ca and Mg have little effect on adsorption until the cobalt concentration is less than 10^?7 M.Micro-electrophoresis experiments from 1 × 10^?3 M to 1 × 10^?5 M to Co(II) show three charge reversals. The first is the pH of zero point charge of hydrous manganese dioxide. The second correlates well with the abrupt increase in adsorption at pH 6 and may reflect both specific adsorption of Co(II) and precipitation of Co(OH)₂ on the surface. The third agrees well with literature values for the pH of zero point of charge of Co(OH)₂.An adsorption isotherm was constructed for cobalt and these data were used to test the hypothesis that the enrichment of cobalt in the suspended matter of the Black Sea is due to adsorption of cobalt from sea water by manganese dioxide. The calculations indicate that adsorption is a feasible explanation for this example.     

Adsorption of uranyl onto ferric oxyhydroxides: Application of the surface complexation site-binding model

Uranyl adsorption was measured from aqueous electrolyte solutions onto well-characterized goethite, amorphous ferric oxyhydroxide, and hematite sols at 25°C. Adsorption was studied at a total uranyl concentration of 10^?5 M, (dissolved uranyl 10^?5 to 10^?8 M) as a function of solution pH, ionic strength and electrolyte concentrations, and of competing cations and carbonate complexing. Solution pHs ranged from 3 to 10 in 0.1 M NaNO₃ solutions containing up to 0.01 M NaHCO₃. All the iron oxide materials strongly adsorbed dissolved uranyl species at pHs above 5 to 6 with adsorption greatest onto amorphous ferric oxyhydroxide and least onto well crystallized specular hematite. The presence of Ca or Mg at the 10^?3 M level did not significantly affect uranyl adsorption. However, uranyl carbonate and hydroxy-carbonate complexing severely inhibited adsorption. The uranyl adsorption data measured in carbonate-free solutions was accurately modeled with the surface complexation-site binding model of Davis et al. (1978), assuming adsorption was chiefly of the UO₂OH⁺ and (UO₂)₃(OH)⁺₅, aqueous complexes. In modeling it was assumed that these complexes formed a monodentate UO₂OH⁺ surface complex, and a monodentate, bidentate or tridentate (UO₂)₃(OH)⁺₅surface complex. Of the latter, the bidentate surface complex is the most likely, based on crystallographic arguments. Modeling was less successful predicting uranyl adsorption in the presence of significant uranyl carbonate and hydroxy-carbonate complexing. It was necessary to slightly vary the intrinsic constants for adsorption of the di- and tricarbonate complexes in order to fit the uranyl adsorption data at total carbonate concentrations of 10^?2 and 10^?3 M.     

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.     

粉石英与红柱石的浮选分离机理研究

本文以油酸钠作为捕收剂,研究了磷酸氢二钠、柠檬酸和硅酸钠等抑制剂对粉石英与红柱石浮选分离效果的影响.结果表明,磷酸氢二钠是红柱石与粉石英浮选分离的一种优良的抑制剂;在其最佳浓度0.47×10-2 mol /L,浮选液pH值为8.5时,粉石英与红柱石浮选回收率差高达47.86％.红外光谱及Zeta电位分析结果表明,油酸钠对红柱石兼有物理和化学吸附作用,对粉石英仅有物理吸附作用,因而对红柱石有更强的捕收能力;磷酸氢二钠对粉石英表面起解吸作用,能有效抑制粉石英起浮,从而实现粉石英与红柱石的分离.     

Mg2+ removal in the system Mg2+—amorphous SiO2—H2O by adsorption and Mg-hydroxysilicate precipitation

Two chemical processes can remove Mg²⁺ from suspensions containing amorphous silica (am-SiO₂) at low temperatures: adsorption and precipitation of a Mg-hydroxysilicate resembling sepiolite. Mg²⁺ removal from am-SiO₂ suspensions was investigated, and the relative role of the two removal processes evaluated, as a function of: pH, ionic strength, Mg²⁺ concentration, and temperature.The extent of Mg²⁺ adsorption onto am-SiO₂ decreases with increasing NaCl concentration due to displacement of Mg²⁺ by Na⁺. At NaCl concentrations of 0.05 M and above, adsorption occurs only at pH values above 8.5, where rapid dissolution of am-SiO₂ gives rise to high concentrations of dissolved silica, resulting in supersaturation with respect to sepiolite. Removal of Mg²⁺, at concentrations of 40 to 650 μM, from am-SiO₂ suspensions in 0.70 M NaCl at 25 °C occurs at pH 9.0 and above. Experiments show that under these conditions adsorption and Mg-hydroxysilicate precipitation remove Mg²⁺ at similar rates. For 0.05 M Mg²⁺, at 0.70 M ionic strength and 25 °C, measurable Mg²⁺ removal occurs down to ca. pH 7.5 but is primarily due to Mg-hydroxysilicate precipitation. For the same solution conditions at 5°C, Mg²⁺ removal occurs above pH 8.0 and is primarily due to adsorption.Assuming that increasing pressure does not greatly enhance adsorption, Mg²⁺ adsorption onto am-SiO₂ is an insignificant process in sea water. The surface charge of pristine am-SiO₂ in sea water is primarily controlled by interactions with Na⁺. The principal reaction between Mg²⁺ and am-SiO₂ in marine sediments is sepiolite precipitation.The age distribution of sepiolite in siliceous pelagic sediments is influenced by temperatures of bottom waters and by geothermal gradients.     

混合捕收剂去除高岭土中含铁矿物试验研究

文章根据高岭土中含铁矿物的浮选试验研究,采用胺类与皂化油酸表面活性剂组合作为高岭土中含铁矿物的捕收剂。高岭土中铁的赋存状态表明,采用分段阳离子/阴离子捕收剂组合试剂,当pH=8～10时,十八胺乳化液以静电力吸附形式捕收含铁硅酸盐;当pH=5～7时,皂化油酸和少量十二烷基磺酸钠通过表面活化反应捕收氧化铁矿,使北海高岭土精矿自然白度达到85%～86%,煅烧白度（1 200℃）达到88%～89%。     

Zn in hydrothermal systems: Thermodynamic description of hydroxide,chloride, and hydrosulfide complexes

The paper presents critical analysis of literature data on the stability constants of aqueous species in the system Zn-O-H-S^?II-Cl. In order to more accurately determine the composition and stability of chloride Zn complexes, additional experiments were carried out to determine the solubility of sphalerite ZnS_c in chloride-sulfide solutions at 175°C and the saturated vapor pressure of the solution. Having processed the data, we obtained the thermodynamic properties at 25°C and parameters of the HKF (Helgeson-Kirkham-Flowers) equation of state (EoS) for hydroxide, chloride and hydrosulfide Zn complexes. The constants of sphalerite dissolution reactions with the formation of hydrosulfide and, particularly, chloride complexes increase with increasing temperature. The predominant Zn transport species in high-temperatures (>250°C) chloride-sulfide hydrothermal solutions are chloride complexes, first of all, ZnCl ₄ ^2? . As the temperature decreases, the concentrations of complexes with smaller numbers of Cl^? ligands increase. The region of weakly acidic to alkaline pH is dominated by hydrosulfide Zn complexes, but their concentrations in equilibrium with sphalerite are relatively low (a few ppm at 400°C and S concentrations <0.1 mol kg^?1) and decreases with a temperature decrease. In the region dominated by chloride complexes, the concentration of dissolved Zn can amount to a few fractions of a percent at near-neutral pH, 400°C, and m(NaCl) = 1.0 and increases if the fluid becomes more acidic. An extremely important factor controlling the concentrations of dissolved Zn is temperature: cooling leads to the effective precipitation of sphalerite, particularly in the region dominated by chloride complexes. The thermodynamic properties of the solid phases and parameters of the HKF model for aqueous species in the system Zn-O-H-S^-II-Cl are presented in the on-line version of the FreeGC database (http://www-b.ga.gov.au/minerals/research/methodology/geofluids/thermo/calculator/search.jsp), which enables calculating the Gibbs energy values of components of the system and reaction constants involving these components at PT parameters up to 600°C and 3 kbar.     

The effect of cobalt ion on nucleation of calcium-carbonate polymorphs

Cobalt, like Mg, may cause the precipitation of aragonite rather than calcite in aqueous solutions due to the adsorption and crystal poisoning of calcite by a hydrated ion. Solutions containing NaCl and CaCl₂, having the ionic strength and Ca content of seawater (35‰ salinity), were spiked with known amounts of CoCl₂. Calcium carbonate was precipitated by the addition of 0.7 ml of 1 M Na₂CO₃. All experimental runs were made at 25°C, and all products were examined by X-ray diffraction. At low concentrations of Co (< 5·^?4M) calcite and vaterite formed. At concentrations from 5·10^?4 M to 2·10^?3M, the products consisted of combinations of calcite and vaterite; aragonite and calcite; aragonite and vaterite; calcite, vaterite and aragonite. In solutions of 3·10^?3M CoCl₂, most precipitates were aragonite with only one sample containing a small amount of calcite. All precipitates from 5·10^?3M CoCl₂ solutions either contained aragonite or were amorphous. Solutions with concentrations of 1 · 10^?2M CoCl₂ produced only amorphous precipitates. All precipitates contained an amorphous violet phase, assumed to be basic cobaltous carbonate (2CoCO₃·Co(OH)₂·H₂O).