Calcite Impurities Research Articles

Enhancing selective calcite and dolomite flotation in the phosphate ores: Investigation, modeling, and automated mineralogy assessment

This paper presents a comprehensive study on the selective flotation of a multi calcium-bearing minerals ore, focusing on the efficient removal of dolomite and calcite impurities from a carbonaceous sedimentary phosphate ore. Commercial fatty acid (FA) and phosphate ester collectors were investigated in a reverse flotation process, assessing the impact of flotation pH, collector dosage, and type on the selectivity and recovery of calcite and dolomite. The efficiency of FA-based collectors was recognized as they provided higher quality concentrates with reduced carbonated-fluorapatite contents. The response surface methodology was employed to review and model the effects of pH and dosage of each fatty acid collector on flotation performance. Accurate regression models were developed, forming the basis for an optimization study to determine the optimal operating conditions for achieving selective carbonate flotation with high carbonate grade and recovery while minimizing the carbonated-fluorapatite (CFA) content. Automated mineralogical microscopy was conducted on the phosphate ore and the recovered carbonate and phosphate concentrates, confirming the success of flotation while attributing the presence of 12% CFA (≈ 4 % de P2O5) in the carbonate concentrate to mineral associations and fines entrainment.

The impact of calcite impurities in clays containing kaolinite on their reactivity in cement after calcination

The use of supplementary cementitious materials as a partial replacement for Portland cement is the most effective way to reduce the carbon footprint of the concrete industry. Raw clays containing kaolinite (kaolin) are promising substitute materials. In the field, raw clays are often mixed with calcite and this is thought to affect their behaviour after calcination. This study explores the influence of calcite impurities on the mineralogy and reactivity a kaolinitic clay. A kaolin sample was blended with different quantities of calcite. The results show that during calcination calcite is decomposed, but no significant amount of free lime or amorphous calcium carbonate are formed. A granular deposit was observed that partially covers the kaolinite particles. The decomposition of calcite and formation of the deposit is associated with a reduction in specific surface area, which increases with the amount of calcite that is intermixed in the raw clay. TEM-EDS analysis showed that the deposit corresponds to a new phase formed from the interaction of kaolinite and calcite, with an Al/Si ratio ranging from 0.74 to 0.88 and Ca/Si ratio between 0.86 and 1.65. Reduction of the calcination temperature to 700 °C reduces the calcite decomposition and the negative impact on reactivity.

INVESTIGATING MINERALOGICAL AND PHYSIO-CHEMICAL PROPERTIES OF BENTONITE FOR WATER-BASED FLUIDS

Bentonite is a well-known type of clay and the mineralogical and physio-chemical characterization of its suspensions is essential to be investigated. In this study, the mineralogical and Physio-chemical characterization of the nano-porous structure of four industrial-grade bentonite samples namely, B1, B2, B3 and B4 were investigated to determine their mineralogical properties for a specific industrial application. Instrumental analyses of samples using XRD, XRF and BET were investigated along with laboratory tests including swelling and sediment indices, surface area and cation exchange capacity as well in order to select the appropriate sample. XRF along with slurry pH shows alkali metal ions. The results indicate B4 has calcite impurity, 50 cP viscosity reading at 600 r/min, 6 value for yield point/plastic viscosity ratio and 39.05 wt% residue of diameter greater than 75 μm. B3 is the most suitable sample for water-based fluid utilization compared to B1, B2 and B4, which satisfies the best standard requirements.

Wet synthesis of carbonated hydroxyapatite

Carbonated hydroxyapatite of predominant B-type of substitution has been synthesized at various temperatures, carbonate concentrations and time of immersion in mother solution. Carbonated hydroxyapatite synthesized at 80 °C contains the largest amount (up to 9 wt.%) of calcite impurity and has a low specific surface area (40 m2/g). Lowering the synthesis temperature to 20 °C leads to a slight decrease in the content of calcite impurity (up to 5–7 wt.%) and an increase in the specific surface up to 125 m2/g. The introduction of the maturation stage for carbonated hydroxyapatite precipitated at 20 °C for 4 days suppresses the calcite impurity formation and leads to the increase in the specific surface up to 155 m2/g.

Applications of Raman spectroscopy in art and archaeology

Applications of Raman spectroscopy in art and archaeology

The combination of Raman imaging and LIBS for quantification of original and degradation materials in Cultural Heritage

AbstractQuantification with nondestructive techniques is not very well developed in the field of Cultural Heritage despite its interest. In the last decades, several works have been published using Raman spectroscopy for quantifying. However, depending on the methodology used, the information provided by this technique is not complete, and the results could lead to misunderstanding when dealing with unknown samples. In this work, a novel double quantification using Raman imaging (its representativeness would be higher than point‐by‐point analysis) and Laser Induce Breakdown Spectroscopy (LIBS) analyses is presented for analysis of Cultural Heritage samples. Several dolomitic marble samples, with some calcite impurities, covered or not by a calcium oxalate (whewellite, CaC2O4·H2O) layer were analysed in order to optimize the novel methodology. The agreement between the quantitative results from the independent analyses of the Raman Image data and the LIBS data is consistent within the uncertainty arising from both techniques. Further, the same methodology was applied on the same samples but using point‐by‐point Raman analysis with portable instruments, and portable LIBS information, showing again a great agreement between them and with the results obtained using the laboratory instruments.

Thermal stability of stercorite H(NH4)Na(PO4)·4H2O

Thermogravimetric analysis has been used to determine the thermal stability of the mineral stercorite H(NH4)Na(PO4)·4H2O. The mineral stercorite originated from the Petrogale Cave, Madura, Eucla, Western Australia. This cave is one of many caves in the Nullarbor Plain in the South of Western Australia. The mineral is formed by the reaction of bat guano chemicals on calcite substrates. Upon thermal treatment the mineral shows a strong decomposition at 191 °C with loss of water and ammonia. Other mass loss steps are observed at 158, 317 and 477 °C. Ion current curves indicate a gain of CO2 at higher temperature and are attributed to the thermal decomposition of calcite impurity.

Thermogravimetric analysis–mass spectrometry (TG–MS) of selected Chinese kaolinites

Thermogravimetric analysis–mass spectrometry, X-ray diffraction and scanning electron microscopy (SEM) were used to characterize eight kaolinite samples from China. The results show that the thermal decomposition occurs in three main steps (a) desorption of water below 100 °C, (b) dehydration at about 225 °C and (c) well defined dehydroxylation at around 450 °C. It is also found that decarbonization took place at 710 °C due to the decomposition of calcite impurity in kaolin. The temperature of dehydroxylation of kaolinite is found to be influenced by the degree of disorder of the kaolinite structure and the gases evolved in the decomposition process can be various because of the different amount and kinds of impurities. It is evident by the mass-spectra that the interlayer carbonate from impurity of calcite and organic carbon is released as CO 2 around 225, 350 and 710 °C in the kaolinite samples.

Optical absorption and EPR studies on some natural carbonate minerals

Limestone and dolomite minerals have been investigated by EPR and optical absorption studies. The optical absorption results indicate the presence of ferrous and ferric ion in both the minerals. The bands observed at 24,750, 22,780, 19,415 and 14,450 cm −1 are assigned to 6A 1 → 4T 2 ( 4D), 6A 1 → 4E, 4A 1 ( 4G), 6A 1 → 4T 2 ( 4G) and 6A 1 → 4T 1 ( 4G) d–d transitions of Fe 3+ ions, respectively. A low energy band at 10,638 cm −1 is identified as being due to Fe 2+ ion and can be attributed to 5T 2g → 5E g transition. The weak band in the region 30,000–40,000 cm −1 corresponds to Fe–O charge transfer. Crystal field and Racah parameters evaluated for the Fe 2+ ion are Dq = 990 cm −1, B = 885 cm −1 and C = 3860 cm −1 and that for Fe 3+ ions are Dq = 1040 cm −1, B = 703 cm −1 and C = 3150 cm −1. The room temperature 9 and 35 GHz EPR spectra of the minerals exhibit a sextet hyperfine pattern characteristic of Mn 2+. The EPR parameters obtained for Mn 2+ in limestone are g = 2.00399, A = −9.411 mT, D = −8.19 mT and these values confirm that the Mn 2+ ion are located in the calcite impurity. For Mn 2+ in dolomite are g = 2.0004, A = −9.45 mT for Mn 2+ substituted in the Ca lattice site and g = 2.00984, A = −9.37 mT, D = −9.94 mT for substitution at the Mg site. The EPR spectra of heat-treated limestone and dolomite samples at 950 °C show a signal corresponding to CO 2 − ion.

Effects of phase impurities on vanadium-sepiolite interactions

X-Ray diffraction (XRD), laser Raman spectroscopy (LRS), and solid-state 51V nuclear magnetic resonance (NMR) have been used to investigate the interaction of vanadium with a sample of sepiolite in the presence of phase impurities. After thermal and hydrothermal treatments, sepiolite decomposes forming enstatite (MgSiO 3). In contrast, in the presence of (⩽ 10%) calcite impurities (as found in naturally occurring samples from Nevada) sepiolite decomposes forming diopside (MgCaSiO 6). When the thermal and hydrothermal treatments are repeated in the presence of 5% V, Mg-containing vanadates are not observed, and Ca 2V 2O 7 is the only heat-stable V compound identified. These results suggest that Ca 2V 2O 7 formation is thennodynamically favored over its Mg analog. Formation of this compound is probably responsible for the preservation of cracking activity observed when cracking V-contaminated gas oil with dual-function cracking catalysts (DFCC) containing sepiolite-calcite granules to passivate V impurities.

Lead exchange into zeolite and clay minerals: A 29Si, 27Al, 23Na solid-state NMR study

Chabazite, vermiculite, montmorillonite, hectorite, and kaolinite were used to remove Pb, through ion exchange, from 0.01 M aqueous Pb(NO 3) 2 solutions. These minerals contained 27 (Nachabazite), 16, 9, 9, and 0.4 wt% of Pb, respectively, after equilibration with the solutions. Ion exchange reached equilibrium within 24 h for Na-chabazite and vermiculite, but in less than 5 min for montmorillonite and hectorite. Na-chabazite took up more Pb than natural (Ca, Na)-chabazite (7 wt% Pb), whereas no such difference was observed in different cation forms of the clay minerals. Calcite impurities, associated with the clay minerals, effectively removed Pb from the aqueous solutions by the precipitation of cerussite (PbCO 3). 29Si, 27Al, and 23Na magic angle spinning (MAS) nuclear magnetic resonance (NMR), 23Na double rotation (DOR) NMR, and 23Na variable-temperature MAS NMR were used to study the ion exchange mechanisms. In Na-chabazite, cations in all three possible sites take part in the fast chemical exchange. The chemical exchange passes from the fast exchange regime to the slow regime at −80 to −100°C. One site contains a relatively low population of exchangeable cations. The other two more shielded sites contain most of the exchangeable cation. The exchangeable cations in chabazite and vermiculite were found to be close to the SiO 4 and AlO 4 tetrahedra, while those in the other clay minerals were more distant. Two sites (or groups of sites) for exchangeable cations were observed in hectorite. Lead tended to occupy the one which corresponds to the −8 ppm peak on the 23Na MAS NMR spectrum. The behaviour of the exchangeable cations in the interlayer sites was similar in all the clay minerals studied.

The 9 and 33 GHz EPR Spectra of Mn 2+ impurity ions in polycrystalline calcite—Central transition

The 293 K EPR spectra of Mn 2+ impurity ions in polycrystalline natural and synthetic calcite and in the calcite impurity in various coal samples have been studied at 9.2 and 33.3 GHz. The spectra obtained at these two frequencies were found to differ dramatically. At 9.2 GHz, the lineshapes of the central transition hyperfine resonances are in good agreement with previous measurements. The 33.3 GHz EPR spectrum has some features which have not been reported previously at Mn 2+ concentrations below 1000 ppm. Computer simulation programs for both spin-Hamiltonian perturbation and diagonalization techniques were used to describe the mono- and polycrystalline spectra. It was found that the simulated spectrum using the spin-Hamiltonian diagonalization method agrees with previous 9.3 GHz monocrystal data within an error of 0.1 mT for the central transitions and of 0.13 mT for the noncentral transitions, whereas the simulation using the perturbation method had errors of 0.2 and 0.6 mT, respectively. An analysis of the polycrystalline hyperfine resonance lineshapes observed at 9.2 and 33.3 GHz for 1, 50, and 520 ppm Mn 2+ concentrations has been performed using both simulation methods. The hyperfine resonance lineshapes observed at 9.2 GHz are due to the magnetic field angular variation caused by the axial zero field splitting (ZFS) term C 0 2( S). The hyperfine resonance lineshapes observed at 33.3 GHz are shown to be due to the combined effect of A-tensor and g-tensor anisotropy, the axial ZFS, and the spin-spin interaction. The Mn 2+ impurity ion EPR spectrum observed in an Alberta coal and several Argonne coal samples is shown, using lineshape analysis, to originate from their calcite mineral impurity. The lineshape broadening observed in coal samples is characteristic of a strong spin-spin interaction and may be due to interactions with the free radicals and other impurity ions as well as between Mn 2+ ions.

The Mn 2+ HFS spectrum in argonne and Alberta coals at 9 and 33 GHz

The 13°C 9 GHz and 20°C 33 GHz CW EPR spectra of the Δm = 0 and Δm = ±1 HFS transitions of Mn 2+ impurity ions were observed in six Argonne premium coal (APC) samples and one Alberta by bituminous coal. The EPR spectral parameters are in good agreement with previous measurements: g av = 2.00176(30) and A av = −9.395(5) mT at 9.2 GHz; g av = 2.00138(30) and A av = −9.397(8) mT at 33 GHz. The first direct estimation of the zero field splitting parameters D and F for the APC and Alberta coal samples has been obtained using the weak HFS of the ΔM = ±1, Δm = 0 | ± 5 2 〉 → | ± 3 2 〉 and |± 3 2 〉 → |± 1 2 〉 outer transitions; the values are D = 7.88(6) mT and F = 3.2(5) μT for five of the six APC and D = 8.04(8) mT and F = 2.8(1) μT for the Alberta coal. These values confirm that the Mn 2+ ions are located in the calcite (calcium carbonate) impurity. The calcite Mn 2+ ion concentration in the Argonne premium coals and the Alberta coal were estimated. It is found that only a small fraction of the Mn 2+ concentration determined by chemical analysis for the APC samples is in the calcite impurity whereas a large fraction is present in the Alberta coal calcite component.

The International Mineralogical Association (IMA/CNMMN) pyroxene nomenclature scheme: Computerization and its consequences

A FORTRAN-77 program is documented, PXTAB, which automates the 1988 IMA/ CNMMN pyroxene nomenclature. PXTAB calculates formula units to 4 cations/6 oxygens by reallocation of Fe2+/3+ (pIus MD2+/3+ and Ti3+14+ if necessary), checks for certain analytical errors, names pyroxenes, and tabulates results in batches. K2O, P2O5 and CO. can be calculated out as K-feldspar/biotite, apatite and calcite impurities respectively. PXTAB attempts to computerize the IMA report as it stands, but some rules given in the report are incomplete, inexact and often ambiguous, so that certain assumptions have to be made in programming. The lack of defined compositional boundaries for certain rare (e.g., Mn-rich and Zr-rich) pyroxenes is one problematical omission. The report also inexplicably names pyroxenes which lie outside its own stated compositional limits. Further problems related to adjectival modifiers may particularly concern petrologists: (a) many modifiers remain formally undefined, so that there is no way of consistently distinguishing, say, ‘subcalcic augite’ from ‘augite’; (b) other modifiers are applied inconsistently in the report; (c) there is imbalance among modifiers: for example, aluminian applies to many more pyroxenes than titanian, even though the defined limits (>0,1 PFU) are the same. Overall, the IMA pyroxene nomenclature is at variance with its 1978 amphibole nomenclature in both principle and practice, posing problems for nomenclatural consistency.