Influence of frothers on floatability. II. Flotation of chalcocite and quartz mixtures

Influence of frothers (α-terpineol or n-amyl alcohol) on the floatability of chalcocite and quartz mixtures, with potassium ethyl xanthate as a collector at pH 5.5–6, was investigated with a Hallimond tube.Activation of quartz by the presence of chalcocite was observed and interpreted as due to copper ionic species originating from chalcocite oxidation products. Best selectivity of separation between chalcocite and quartz was obtained when the frother concentration was kept sufficiently low. Collector—frother interactions during formation of three-phase mineral grain/solution/gas bubble contacts were observed.     

The influence of surface oxidation of chalcocite on its floatability and ethyl xanthate sorption

The results obtained from measurements of potassium ethyl xanthate (EtXK) sorption by synthetic chalcocite (Cu₂S) and the results of chalcocite floatability measurements are presented.Five chalcocite samples, denoted as Cu₂S A, B, C, D and E, were used for the measurements. Chalcocite samples of 60–75 μm were prepared in the same manner but were kept under conditions which differed in their degree to prevent surface oxidation by atmospheric oxygen.Chalcocite surface oxidation has a strong effect both on xanthate sorption and on chalcocite floatability. The maximal amount of xanthate abstracted (Q_max) by chalcocite samples from deoxygenated solutions after a long sorption period increases with increasing oxidation of the samples. The Q_max values give information concerning the total amount of surface oxidation products.Chalcocite decreases its floatability with increasing surface oxidation. Most oxidized chalcocite samples required an about 100 times greater collector consumption to obtain the same flotation results than the least-oxidized samples studied.     

Flotation of oxidized minerals of copper using a new synthetic chelating reagent as collector

A new synthetic reagent containing a mixed aliphatic-aromatic structure, with a hydrocarbon chain and an aminothiophenol chelating group, has proven to be an effective collector for the flotation of chrysocolla minerals. The flotation is optimum in the narrow pH range of 5.5 to 6, falls sharply at pH 5, and is moderate in the pH range 7 to 11. Infrared spectra indicate that copper aminothiophenolate chelates are formed on the surface of the chrysocolla under the conditions of maximum flotation.     

XPS spectra of uranyl minerals and synthetic uranyl compounds. I: The U 4f spectrum

The occurrence and binding energies of the U⁶⁺, U⁵⁺ and U⁴⁺ bands in the U 4f_7/2 peak of 19 uranyl minerals of different composition and structure were measured by XPS. The results suggest that these minerals can be divided into the following four groups: (1) Uranyl-hydroxy-hydrate compounds with no or monovalent interstitial cations; (2) Uranyl-hydroxy-hydrate minerals with divalent interstitial cations; (3) Uranyl-oxysalt minerals with (TO_n) groups (T = Si, P, and C) in which all equatorial O-atoms of the uranyl-polyhedra are shared with (TO_n) groups; (4) Uranyl-oxysalt minerals with (TO_n) groups (T = S and Se), in which some equatorial O-atoms are shared only between uranyl polyhedra. The average binding energies of the U⁶⁺and U⁴⁺ bands shift to lower values with (1) incorporation of divalent cations and (2) increase in the Lewis basicity of the anion group bonded to U. The first observation is a consequence of an increase in the bond-valence transfer from the interstitial species (cations, H₂O) groups to the O-atoms of the uranyl-groups, which results in an electron transfer from O to U⁶⁺. The second trend correlates with an increase in the covalency of the UO bonds with increase in Lewis basicity of the anion group, which results in a shift of the electron density from O to U. The presence of U⁴⁺ on the surface of uranyl minerals can be detected by the shape of the U 4f_7/2 peak, and the occurrence of the U 5f peak and satellite peaks belonging to the U 4f_5/2 peak. The presence of U⁴⁺ in some of the uranyl minerals and synthetics examined may be related to the conditions during their formation. A charge-balance mechanism is proposed for the incorporation of lower-valence U in the structure of uranyl minerals. Exposure of a Na-substituted metaschoepite crystal in air and to Ultra-High Vacuum results in dehydration of its surface structure associated with a shift of the U⁶⁺ bands to higher binding energies. The latter observation indicates a shift in electron density from U to O, which must be related to structural changes inside the upper surface layers of Na-substituted metaschoepite.     

Electrochemical reaction control of contact angles on copper and synthetic chalcocite in aqueous potassium diethyldithiophosphate solutions

The contact angles on synthetic chalcocite in potassium diethyldithiophosphate (KDTP) solutions have been compared with those on copper to delineate physico-chemical factors which might contribute to the flotation response of copper sulfides. The influence of a number of variables such as KDTP concentration, solution pH, gaseous environment and electrochemical pretreatment has been investigated. The results are discussed in terms of the thermodynamic and kinetic aspects of the system.     

Influence of soil minerals on chromium(VI) reduction by sulfide under anoxic conditions

The effects of soil minerals on chromate (Cr^VIO₄ ^2-, noted as Cr(VI)) reduction by sulfide were investigated in the pH range of 7.67 to 9.07 under the anoxic condition. The examined minerals included montmorillonite (Swy-2), illite (IMt-2), kaolinite (KGa-2), aluminum oxide (γ-Al₂O₃), titanium oxide (TiO₂, P-25, primarily anatase), and silica (SiO₂). Based on their effects on Cr(VI) reduction, these minerals were categorized into three groups: (i) minerals catalyzing Cr(VI) reduction – illite; (ii) minerals with no effect – Al₂O₃; and (iii) minerals inhibiting Cr(VI) reduction- kaolinite, montmorillonite, SiO₂ and TiO₂ . The catalysis of illite was attributed primarily to the low concentration of iron solubilized from the mineral, which could accelerate Cr(VI) reduction by shuttling electrons from sulfide to Cr(VI). Additionally, elemental sulfur produced as the primary product of sulfide oxidation could further catalyze Cr(VI) reduction in the heterogeneous system. Previous studies have shown that adsorption of sulfide onto elemental sulfur nanoparticles could greatly increase sulfide reactivity towards Cr(VI) reduction. Consequently, the observed rate constant, k _obs, increased with increasing amounts of both iron solubilized from illite and elemental sulfur produced during the reaction. The catalysis of iron, however, was found to be blocked by phenanthroline, a strong complexing agent for ferrous iron. In this case, the overall reaction rate at the initial stage of reaction was pseudo first order with respect to Cr(VI), i.e., the reaction kinetics was similar to that in the homogeneous system, because elemental sulfur exerted no effect at the initial stage prior to accumulation of elemental sulfur nanoparticles. In the suspension of kaolinite, which belonged to group (iii), an inhibitive effect to Cr(VI) reduction was observed and subsequently examined in more details. The inhibition was due to the sorption of elemental sulfur onto kaolinite, which reduced or completely eliminated the catalytic effect of elemental sulfur, depending on kaolinite concentration. This was consistent with the observation that the catalysis of externally added elemental sulfur (50 μM) on Cr(VI) reduction would disappear with a kaolinite concentration of more than 5.0 g/L. In kaolinite suspension, the overall reaction rate law was:

Radiation-damage-induced defects in quartz. I. Single-crystal W-band EPR study of hole centers in an electron-irradiated quartz

Single-crystal W-band electron paramagnetic resonance (EPR) spectra of an electron-irradiated quartz, measured at room temperature, 110 and 77 K, disclose three previously reported hole centers (#1, G and an ozonide radical). The W-band EPR spectra of these three centers clearly resolve six magnetically nonequivalent sites each, whereas previous X- and Q-band EPR studies reported Centers #1 and the ozonide radical to consist of only three symmetry-related components and interpreted them to reside on twofold symmetry axes in the quartz structure. The calculated g matrices of Center #1 and the ozonide radical show that deviations from twofold symmetry axes are <10°, which are probably attributable to distortion related to neighboring charge compensating ions. The W-band EPR spectra of Center G not only result in improved g matrices but also allow quantitative determination of the nuclear hyperfine (A) and quadrupole (P) matrices of its ²⁷Al hyperfine structure that was incompletely resolved before. In particular, the g-maximum and g-minimum principal axes of Center G are approximately along two pairs of O–O edges of the SiO₄ tetrahedron, while the unique A principal axis is approximately along a Si–Si direction. These new spin-Hamiltonian parameters suggest that Center G most likely involves trapping of a hole between two oxygen atoms related to a silicon vacancy and stabilized by an Al³⁺ ion in the neighboring tetrahedron (hence an O₂ⁿ⁻–Al³⁺ defect, where n is either 1 or 3).     

LA-ICP-MS analysis of single fluid inclusions in a quartz crystal (Madan ore district,Bulgaria)

A “long-living” crystal of barren quartz from Kroushev Dol Pb-Zn deposit (Madan district, Rhodope Mountains, Bulgaria) was studied. The semitransparent base part (the “root”) of the crystal contains abundant inclusions, predominantly along healed cracks, while the upper half or third of the crystal is clear and poor in inclusions. In order to analyze fluid inclusions in the quartz crystal, it was cut into 4 pieces across and along the c-axis and doubly-polished sections were prepared. Fluid inclusions trapped in this quartz supply information about the temporal evolution of paleofluids depositing ore minerals.     

Influence of biogenic Fe(II) on the extent of microbial reduction of Fe(III) in clay minerals nontronite, illite, and chlorite

Microbial reduction of Fe(III) in clay minerals is an important process that affects properties of clay-rich materials and iron biogeochemical cycling in natural environments. Microbial reduction often ceases before all Fe(III) in clay minerals is exhausted. The factors causing the cessation are, however, not well understood. The objective of this study was to assess the role of biogenic Fe(II) in microbial reduction of Fe(III) in clay minerals nontronite, illite, and chlorite. Bioreduction experiments were performed in batch systems, where lactate was used as the sole electron donor, Fe(III) in clay minerals as the sole electron acceptor, and Shewanella putrefaciens CN32 as the mediator with and without an electron shuttle (AQDS). Our results showed that bioreduction activity ceased within two weeks with variable extents of bioreduction of structural Fe(III) in clay minerals. When fresh CN32 cells were added to old cultures (6 months), bioreduction resumed, and extents increased. Thus, cessation of Fe(III) bioreduction was not necessarily due to exhaustion of bioavailable Fe(III) in the mineral structure, but changes in cell physiology or solution chemistry, such as Fe(II) production during microbial reduction, may have inhibited the extent of bioreduction. To investigate the effect of Fe(II) inhibition on CN 32 reduction activity, a typical bioreduction process (consisting of lactate, clay, cells, and AQDS in a single tube) was separated into two steps: (1) AQDS was reduced by cells in the absence of clay; (2) Fe(III) in clays was reduced by biogenic AH₂DS in the absence of cells. With this method, the extent of Fe(III) reduction increased by 45-233%, depending on the clay mineral involved. Transmission electron microscopy observation revealed a thick halo surrounding cell surfaces that most likely resulted from Fe(II) sorption/precipitation. Similarly, the inhibitory effect of Fe(II) sorbed onto clay surfaces was assessed by presorbing a certain amount of Fe(II) onto clay surfaces followed by AH₂DS reduction of Fe(III). The reduction extent consistently decreased with an increasing amount of presorbed Fe(II). The relative reduction extent [i.e., the reduction extent normalized to that when the amount of presorbed Fe(II) was zero] was similar for all clay minerals studied and showed a systematic decrease with an increasing clay-presorbed Fe(II) concentration. These results suggest a similar inhibitory effect of clay-sorbed Fe(II) for different clay minerals. An equilibrium thermodynamic model was constructed with independently estimated parameters to evaluate whether the observed cessation of Fe(III) reduction by AH₂DS was due to exhaustion of reaction free energy. Model-calculated reduction extents were, however, over 50% higher than experimentally measured, indicating that other factors, such as blockage of the electron transfer chain and mineralogy, restricted the reduction extent. Another important result of this study was the relative reducibility of Fe(III) in different clays: nontronite > chlorite > illite. This order was qualitatively consistent with the differences in the crystal structure and layer charge of these minerals.     

南极三块（L3）陨石球粒结构类型及其矿物学物征

我国第16次南极考察队回收到6块稀少种类陨石-13型,GRV99001,GRV99019,GRV99020,GRV99021,GRV99022,GRV99026。本文对其中3块陨石进行研究,研究它们的球粒结构和矿物化学成分．它们虽然部属于非平衡普通球粒陨石（L3）,但它们的亚类不同,GRV99001为13．4,GRV99026为L3．5,GRV99019为L3．6．它们的球粒结构和球粒内的矿物晶体完整性和矿物组合变化比较大．橄榄石和辉石以高镁为特征．这三块陨石的球粒结构种类比较多．有班状的、炉条状的、扇形的和隐晶质的等．在GRV99001陨石中班状结构的球粒内能见到一个或两个以上完整的单晶橄榄石构成的球粒,也能见到多个细小的或是破碎橄榄石,被包襄在辉石晶体内．而在GRV99019和GRV99026陨石中只能见到多个细小单晶体或是破碎的橄榄石晶体．GRV99001陨石的炉条状结构,好象是由一条带状长石矿物,穿插在单个橄榄石晶体中构成．扇形和伞形结构的球粒,以一个点为中心,向外放射呈扇形．如GRV99019陨石中扇形结构球粒,它们是以辉石为主,陨硫铁充填在低钙辉石缝隙中,形成扇形．另一种是以多个点为中心,如GRV99001陨石,它们是由橄榄石、低钙辉石和长石质的玻璃．构成多个小伞形,形状类似三维立体的球,裂缝中也充填有金属矿物．隐晶质的球粒在GRV99026陨石中有两种,一种是在一厘米等于100un时呈现隐晶质矿物,而放大到一厘米等于5un时,就可以清楚看到两种低钙辉石矿物,在低钙辉石中还有金属矿物．另一种隐晶质结构球粒由极细小破碎的橄榄石和辉石矿物构成．这三块陨石中的橄榄石和辉石都以高镁为特征．班状结构球粒,在GRV99001陨石中橄榄石的MgO～33．37～51．21,辉石为35．9～36．61;GRV99019陨石中橄榄石23．33～56．58．辉石21.38-33.07,GRV99026陨石中榄橄榄石45.91-52.63,辉石34.48-37.35,扇形结构球粒,在GRV99001陨石中橄榄石29.94-46.22,辉石28.17-30.36;GRV99019陨石中橄榄石29.17-34.38,辉石23.11-27.79,炉条状结构的球粒,在GRV99001陨石中橄榄石51.84-56.03,隐晶质结构球粒,在GRV99026陨石中辉石20.17-21.54,橄榄石30.84-32.66,由此看出矿物晶体完整性越好镁的含量越高。     

XPS spectra of uranyl minerals and synthetic uranyl compounds. II: The O 1s spectrum

The O 1s spectrum is examined for 19 uranyl minerals of different composition and structure. Spectra from single crystals were measured with a Kratos Axis Ultra X-ray Photoelectron Spectrometer with a magnetic-confinement charge-compensation system. Well-resolved spectra with distinct maxima, shoulders and inflections points, in combination with reported and measured binding energies for specific O²⁻ species and structural data of the uranyl minerals are used to resolve the fine structure of the O 1s envelope. The resolution of the O 1s spectra includes, for the first time, different O²⁻ bands, which are assigned to O atoms linking uranyl with uranyl polyhedra (UOU) and O atoms of uranyl groups (OUO). The resolved bands in the O 1s spectrum occur at distinct ranges in binding energy: bands for (UOU) occur at 529.6-530.4 eV, bands for (OUO) occur at 530.6-531.4 eV, bands for O²⁻ in the equatorial plane of the uranyl polyhedra linking uranyl polyhedra with (TO_n) groups (T = Si, S, C, P, Se) (TO) occur at 530.9-532.2 eV; bands for (OH) groups in the equatorial plane of the uranyl polyhedra (OH) occur at 532.0-532.5 eV, bands of (H₂O) groups in the interstitial complex of the uranyl minerals (H₂O_interst) occur at 533.0-533.8 eV and bands of physisorbed (H₂O) groups on the surface of uranyl minerals (H₂O_adsorb) occur at 534.8-535.2 eV. Treatment of uranyl minerals with acidic solutions results in a decrease in UOU and an increase in OH. Differences in the ratio of OH : OUO between the surface and bulk structure is larger for uranyl minerals with a high number of UOU and TO species in the bulk structure which is explained by protonation of underbonded UO, UOU and TO terminations on the surface. The difference in the ratio of H₂O_interst : OUO between the bulk and surface structures is larger for uranyl minerals with higher percentages of H₂O_interst as well as, with a higher number of interstitial H₂O groups that are not bonded to interstitial cations, resulting in easier dehydration of interstitial H₂O groups in uranyl minerals during exposure to a vacuum.     

Electron microscope study of the humite minerals: I. Mg-Rich specimens

Natural humite minerals and synthetic fluoro-humites, ideally described as nMg₂SiO₄ · Mg(OH,F)₂ (1<n<4), were investigated by using electron diffraction and imaging techniques. In clinohumite (n=4) and humite (n=3) irregularities in lattice spacings were observed parallel to (001). These were identified, using high resolution lattice images, as upper member lamellae in which n was always even (i.e., n=6, 8, 10 etc.). In fluoroclinohumite the higher members were sometimes perfectly ordered, giving rise to superstructures with relatively large c axes. These supercells always consisted of several consecutive unit cells of clinohumite (n=4) followed by a unit cell of the n=6 member; the largest observed had a d (001) spacing of 169 Å. It was also found that coherent intergrowths of massive portions of humite (n=3) and chondrodite (n=2) often occurred.     

Mechanism of pyroxene and amphibole weathering—I. Experimental studies of iron-free minerals

The short term (2–40 days) dissolution of enstatite, diopside, and tremolite in aqueous solution at low temperatures (20–60°C) and pH 1–6 has been studied in the laboratory by means of chemical analyses of reacting solutions for Ca²⁺, Mg²⁺, and Si(OH)₄ and by the use of X-ray photoelectron spectroscopy (XPS) for detecting changes in surface chemistry of the minerals. All three minerals were found to release silica at a constant rate (linear kinetics) providing that ultrafine particles, produced by grinding, were removed initially by HF treatment. All three also underwent incongruent dissolution with preferential release of Ca and/or Mg relative to Si from their outermost surfaces. The preferential release of Ca, but not Mg for diopside at pH 6 was found by both XPS and solution chemistry verifying the theoretical prediction of greater mobility of cations located in M₂ structural sites. Loss mainly from M₂ sites also explains the degree of preferential loss of Mg from enstatite at pH 6; similar structural arguments apply to the loss of Ca and Mg from the surface of tremolite. In the case of diopside and tremolite initial incongruency was followed by essentially congruent cation-plus-silica dissolution indicating rapid formation of a constant-thickness, cation-depleted surface layer. Cation depletion at elevated temperature and low pH (~ 1) for enstatite and diopside was much greater than at low temperature and neutral pH, and continued reaction resulted in the formation of a surface precipitate of pure silica as indicated by solubility calculations, XPS analyses, and scanning electron microscopy.From XPS results at pH 6, model calculations indicate a cation-depleted altered surface layer of only a few atoms thickness in all three minerals. Also, lack of shifts in XPS peak energies for Si, Ca, and Mg, along with undersaturation of solutions with respect to all known Mg and Ca silicate minerals, suggest that cation depletion results from the substitution of hydrogen ion for Ca²⁺ and/or Mg²⁺ in a modified silicate structure and not from the precipitation of a new, radically different surface phase. These results, combined with findings of high activation energies for dissolution, a non-linear dependence on a_H⁺ for silica release from enstatite and diopside, and the occurrence of etch pitting, all point to surface chemical reaction and not bulk diffusion (either in solution or through altered surface layers) as the rate controlling mechanism of iron-free pyroxene and amphibole dissolution at earth surface temperatures.     

Cathodoluminescence (CL) and electron paramagnetic resonance (EPR) studies of clay minerals

Summary ?Sheet silicates of the serpentine–kaolin-group (serpentine, kaolinite, dickite, nacrite, halloysite), the talc–pyrophyllite-group (talc, pyrophyllite), the smectite-group (montmorillonite), and illite (as a mineral of the mica-group) were investigated to obtain information concerning their cathodoluminescence behaviour. The study included analyses by cathodoluminescence (CL microscopy and spectroscopy), electron paramagnetic resonance (EPR), X-Ray diffraction (XRD), scanning electron microscopy (SEM) and trace element analysis. In general, all dioctahedral clay minerals exhibit a visible CL. Kaolinite, dickite, nacrite and pyrophyllite have a characteristic deep blue CL, whereas halloysite emission is in the greenish-blue region. On the contrary, the trioctahedral minerals (serpentine, talc) and illite do not show visible CL. The characteristic blue CL is caused by an intense emission band around 400 nm (double peak with two maxima at 375 and 410 nm). EPR measurements indicate that this blue emission can be related to radiation induced defect centres (RID), which occur as electron holes trapped on apical oxygens (Si–O centre) or located at the Al–O–Al group (Al substituting Si in the tetrahedron). Additional CL emission bands were detected at 580 nm in halloysite and kaolinite, and between 700 and 800 nm in kaolinite, dickite, nacrite and pyrophyllite. Time-resolved spectral CL measurements show typical luminescence kinetics for the different clay minerals, which enable differentiation between the various dioctahedral minerals (e.g. kaolinite and dickite), even in thin section. Received December 3, 2001; revised version accepted February 27, 2002     

Mechanodestruction of minerals at the crack tip (overview): 2. Theory

The terminal velocity of a crack determines whatever classical or quantum approaches are appropriate to describe phenomena at the crack tip. The expression for the fractoemission intensity of crystals accounting for the quantum character of the energy transfer at the crack tip is obtained. Relationships of classical mechanics and statistical physics are applied to numerical aspects of energy balance on the front of a main crack, with reference to the cleavage of alkali halide crystals. The possibility of nanoparticle emission during dynamic fracture of solids is confirmed theoretically.     

Iron(II) oxide determination in rocks and minerals

The determination of FeO of geologic materials by modern instrumental methods (such as atomic absorption spectroscopy (AAS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray fluorescence (XRF), etc.) cannot distinguish between different oxidation states of elements. In many cases, the oxidation state of Fe has to be known in order to perform several chemical calculations (norms, etc.) and discuss the reactions that occur during weathering, hydrothermal alteration and other processes. A modified Wilson method is proposed, giving reproducible results in a much shorter time than the classical method. Back-titration with potassium dichromate and an Fe(II) and ammonia sulphate solution is used, after dissolution of the sample powder in a heated HF/H₃PO₄ mixture and an ammonium vanadate solution. This modified method, tested with several international reference materials, gives reliable results, equivalent to the ones cited in the literature for the reference materials.     

Experimental growth of quartz in petroleum environment. Part I: Procedures and Fluid Trapping

The quartz-water-oil-gas system has been experimentally studied with the objective of investigating the trapping of petroleum and aqueous inclusions in quartz at different water/oil (W/O) ratios (0/100, 5/95, 10/90, 20/80, 50/50, 100/0). Experiments were carried out in both a gas-pressure autoclave (GPA) under CH₄ pressure control, up to 250°C and 212 bar, and in a fluid-pressure autoclave (FPA) up to 350°C and 400 bar. High p-T conditions have notably allowed the growth of quartz at high oil saturation levels (W/O ratios from 10/90 to 50/50). Petroleum inclusions have been synthesised inside quartz microfractures (W/O ratios from 0/100 to 50/50; 209-350°C; 175-400 bar), and also inside quartz overgrowths (W/O ratios from 10/90 to 50/50; 289-350°C; 350-400 bar). Aqueous inclusions have been synthesised in presence of oil inside quartz microfractures from 185°C-163 bar up to 400°C-400 bar, and inside quartz overgrowth from 277°C-330 bar. Synthesised petroleum inclusions are representative of the parent oil up to 250°C. At 350°C, evidence of a cracking process has been observed with the consequent formation of methane. The segregation of the oil/gas/water column inside the GPA autoclave may also have prevented methane diffusion into the water phase when oil is present. This experimental approach shows that the trapping of fluid inclusions and the formation of quartz cement, under conditions of high oil saturation, have not been suppressed or prevented.