Solution chemistry of carbonate minerals and its effects on the flotation of hematite with sodium oleate

The effects of carbonate minerals（dolomite and siderite） on the flotation of hematite using sodium oleate as a collector were investigated through flotation tests, supplemented by dissolution measurements, solution chemistry calculations, zeta-potential measurements, Fourier transform infrared（FTIR） spectroscopic studies, and X-ray photoelectron spectroscopy（XPS） analyses. The results of flotation tests show that the presence of siderite or dolomite reduced the recovery of hematite and that the inhibiting effects of dolomite were stronger. Dissolution measurements, solution chemistry calculations, and flotation tests confirmed that both the cations（Ca^（2＋） and Mg^（2＋）） and CO_3^（2＋）ions dissolved from dolomite depressed hematite flotation, whereas only the 23CO-ions dissolved from siderite were responsible for hematite depression. The zeta-potential, FTIR spectroscopic, and XPS analyses indicated that Ca^（2＋）, Mg^（2＋）, and CO_3^（2-）（HCO_3^-） could adsorb onto the hematite surface, thereby hindering the adsorption of sodium oleate, which was the main reason for the inhibiting effects of carbonate minerals on hematite flotation.

Raman and infrared spectroscopic quantification of the carbonate concentration in K_(2)CO_(3)aqueous solutions with water as an internal standard

Carbonate-bearing fluids widely exist in different geological settings,and play important roles in transporting some elements such as the rare earth elements.They may be trapped as large or small fluid inclusions(with the size down to<1μm sometimes),and record critical physical-chemical signals for the formations of their host minerals.Spectroscopic methods like Raman spectroscopy and infrared spectroscopy have been proposed as effective methods to quantify the carbonate concentrations of these fluid inclusions.Although they have some great technical advantages over the conventional microthermometry method,there are still some technical difficulties to overcome before they can be routinely used to solve relevant geological problems.The typical limitations include their interlaboratory difference and poor performance on micro fluid inclusions.This study prepared standard ion-distilled water and K_(2)CO_(3)aqueous solutions at different molarities(from 0.5 to 5.5 mol/L),measured densities,collected Raman and infrared spectra,and explored correlations between the K_(2)CO_(3)molarity and the spectroscopic features at ambient P-T conditions.The result confirms that the Raman O-H stretching mode can be used as an internal standard to determine the carbonate concentrations despite some significant differences among the correlations,established in different laboratories,between the relative Raman intensity of the C-O symmetric stretching mode and that of the O-H stretching mode.It further reveals that the interlaboratory difference can be readily removed by performing one high-quality calibration experiment,provided that later quantifying analyses are conducted using the same Raman spectrometer with the same analytical conditions.Our infrared absorption data were collected from thin fluid films(thickness less than~2μm)formed by pressing the prepared solutions in a Microcompression Cell with two diamond-II plates.The data show that both the O-H stretching mode and the O-H bending mode can be used as internal standards to determine the carbonate concentrations.Since the IR signals of the C-O antisymmetric stretching vibration of the CO32ion,and the O-H stretching and bending vibrations from our thin films are very strong,their relative IR absorbance intensity,if well calibrated,can be used to investigate the micron-sized carbonate-bearing aqueous fluid inclusions.This study establishes the first calibration of this kind,which may have some applications.Additionally,our spectroscopic data suggest that as the K_(2)CO_(3)concentration increases the aqueous solution forms more large water molecule clusters via more intense hydrogen-bonding.This process may significantly alter the physical and chemical behavior of the fluids.

Dissolution kinetics of Si and Al from montmorillonite in carbonic acid solution

The reaction between carbonic acid and montmorillonite minerals was studied in order to provide a theoretical basis for analyzing changes in the physical properties of coal seams after CO_(2)injection and for optimizing CO_(2) pumping parameters.A single montmorillonite mineral of purity[90%was selected and subjected to reactions at 25,35,and 45℃in carbonic acid solutions of varying acidity.The Si and Al concentrations in the solutions and the structure and elemental compositions of the montmorillonite before and after the reactions were analyzed using a spectrophotometer,an X-ray diffractometer,and an energy-dispersive X-ray spectrometer;kinetic reaction models were established for the dissolution of Si and Al in carbonic acid solutions in order to estimate the apparent activation energy of Si dissolution under different acidity conditions.The results indicate that Al dissolved rapidly and soon reached solubility equilibrium.On the other hand,Si concentration in the solutions increased rapidly and then gradually declined with vibrations,with maximum values at 25,35,and 45℃,which were observed at approximately 96,72,and 48 h,respectively.In addition,Si dissolution fitted the diffusion-controlled reaction model well;as the pH value decreased,the apparent activation energy of Si dissolution decreased,and Si became easier to dissolve.Furthermore,it was concluded that as a weak acid,carbonic acid causes little damage to the mineral structure of montmorillonite.

Corrosion Inhibition of Carbon Steel in Hot Hydrochloric Acid Solutions

The dissolution of carbon steel in 5% HCl in the temperature range of 30~90℃ was inhibited by two organic compounds having the general formula: ClR NH2(CH2)n NH2 RCl where R is a benzyl group. The behaviour of these inhibitors in acidic medium were investigated using weight loss method, open circuit potential and linear polarization technique. These inhibitors provided satisfactory corrosion inhibition for carbon steel in hydrochloric acid solutions even at higher temperature and acid concentration (10%). The electrochemical results showed that the polarization resistance (Rp) values increased with increasing inhibitor concentration, also the corrosion current decreased and a higher inhibition efficiency was obtained. The protective properties of these two organic inhibitors were attributed to the chemisorption mechanism

Synergic Mechanism of an Organic Corrosion Inhibitor for Preventing Carbon Steel Corrosion in Chloride Solution

The inhibition effect of dimethylethanolamine（DMEA） and its composite with carboxylic acid was studied with the electrochemical tests. The experimental results indicate that DMEA is not a good inhibitor but the composite of DMEA with caprylic acid exhibits excellent inhibiting efficiency. The synergic mechanism of the organic corrosion inhibitors（OCIs） was studied with quantum chemical calculations. It is found that the DMEA forms a quaternary ammonium salt with the proton in carboxylic acid, and a cyclic complex formed between the salt and Fe may be responsible for the enhancement of inhibiting efficiency. The possible hydrogen bond formed between DMEA and carboxylic acid is not enough for the inhibiting effect. This work is helpful to proposing theoretical interpretation as well as developing a functional organic inhibitor to improve the durability of reinforced concrete contaminated with chloride.

RECOVERY OF URANIURN FROM CARBONATE SOLUTIONS USING STRONGLY BASIC ANION EXCHANGER 3. THE MECHANISMS OF RECOVERY PROCESSES

A moving boundary model under considering the volume change of spherical resin beads during ion exchange processes was employed to recognize the mechanisms of recovering uranium from carbonate solutions using strongly basic anion exchanger Two important factors, swelling and ion exchange, which directly affect the volume of ion exchangers were taken into account. An ion exchange mechanism has been found for the forward reaction RCl/[UO2 CO3)3]4- at pH 8.5～10.0, where the rate is controlled by liquid-film diffusion at low concentration of the tetravalent uranyl complex anion [UO2 (CO3)3]4-, and is partical diffusion governing at high concentration of the complex anion. The mechanism of RCl/U(Ⅳ) at pH 5. 5～7. 5 is a chemical reaction taking place at the moving boundary of the unreacted nucleus. For the reverse reaction RnU/NaCl, the uranyl tricarbonate complex anion in the resin phase is replaced by Cl- ions with an ion exchange mechanism always determined by particle diffusion. The other forms of uranium in the solid phase loaded on the resin at pH 5. 5～7. 5 should belong to non-exchangeable uranium. The mechanism of the reverse reaction RnU/HCl is always chemical reaction which is not restricted to the moving boundary of the unreacted core.

Sulfur phase and sulfur removal in high sulfur-containing bauxite

The sulfur phase in high sulfur-containing bauxite was studied by an X-ray diffraction analysis and a chemistry quantitative analysis.The methods for the removal of different shaped sulfur were also discussed.The results show that sulfur phases in high sulfur-containing bauxites exist in the main form of sulfide sulfur （pyrite） or sulfate sulfur,and the main sulfur forms of bauxites from different regions are not the same.Through a combination of an X-ray diffraction analysis and a chemistry quantitative analysis,the sulfur phases of high sulfur-containing bauxite could be accurately investigated.Deciding the main sulfur form of high sulfur-containing bauxite could provide theoretical instruction for choosing methods for the removal of sulfur from bauxite,and an oxidizing-roasting process is an effective way to remove sulfide sulfur from high sulfur-containing bauxite,the content of S^2-in crude ore in the digestion liquor is above 1.7 g/L,but in the roasted ore digestion liquor,it is below 0.18 g/L.Using the sodium carbonate solution washing technology to wash bauxite can effectively remove sulfate sulfur,the content of the total sulfur in ore is lowered to below 0.2% and can meet the production requirements for the sulfur content.

Prediction of rock brittleness using nondestructive methods for hard rock tunneling

Sand production is an undesired phenomenon occurring in unconsolidated formations due to shear failure and hydrodynamic forces. There have been many approaches developed to predict sand production and prevent it by changing drilling or production strategies. However, assumptions involved in these approaches have limited their applications to very specific scenarios. In this paper, an elliptical model based on the borehole shape is presented to predict the volume of sand produced during the drilling and depletion stages of oil and gas reservoirs. A shape factor parameter is introduced to estimate the changes in the geometry of the borehole as a result of shear failure. A carbonate reservoir from the south of Iran with a solid production history is used to show the application of the developed methodology. Deriving mathematical equations for determination of the shape factor based on different failure criteria indicate that the effect of the intermediate principal stress should be taken into account to achieve an accurate result. However, it should be noticed that the methodology presented can only be used when geomechanical parameters are accurately estimated prior to the production stage when using wells and field data.

Polymorph and morphology of CaCO_3 in relation to precipitation conditions in a bubbling system

Simulating the typical carbonation step in a mineral CO_2 sequestration, precipitated calcium carbonate(PCC) was prepared by bubbling CO_2 gas into a rich Ca solution. These carbonation reactions were conducted at three p H ranges, namely 10.0–9.0, 9.0–8.0, and 8.0–7.0, in which temperature and CO_2 flow rate are additional experimental variables. The PCC obtained in experiments was examined by Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction(XRD). It was found that supersaturation determined by p H value and flow rate of CO_2 has significant influence on polymorph of PCC. Vaterite was preferably formed at high supersaturation, while dissolution of metastable vaterite and crystallization of calcite occurred at low supersaturation. High temperature is a critical factor for the formation of aragonite. At 70 °C, vaterite, calcite and aragonite were observed to coexist in PCC because transformation from vaterite to aragonite via calcite occurred at this temperature. Scanning electron microscopy(SEM) technology was performed on prepared PCC, and various morphologies consistent with polymorphs were observed.

Adsorption of phenylalanine from aqueous solution onto active carbon and silica gel

The adsorption isotherms of phenylalanine from aqueous solution on active carbon and silica gel at varying pH,and the influence of inorganic salt upon the ad rption have been studied (at 25℃).The adsorption amount of phcnylalanine on the silica gel is very low due to the strong ad- sorption of water by silica gel.The results on the active carbon show:(1)The adsorption is found to be pH-dependent,within pH 4.1—5.1 it increases with pH,within pH 5.1—11.8 it decreases with pH,at pH 5.1 the adsorption reaches its maximum;(2)The phenylalanine is adsorbed mainly in the form of zwitterion;(3)A certain amount of cations and anions of phenylalanine are also adsorbed with van der Waals interaction;(4)After adding NaCl,the adsorption of phenylalanine increases markedly.

Novel Al-doped carbon nanotubes with adsorption and coagulation promotion for organic pollutant removal

Al-doped carbon nanotubes（Al-doped CNTs） were prepared as a multifunctional integrated material of adsorbent and coagulant aid for organic pollutant removal from aqueous solution. It was observed that aluminum species were dispersed homogeneously on the surface of CNTs, and mainly anchored onto defect structures of the CNTs. The introduction of aluminium efficiently improved adsorption ability for methyl orange（MO） onto the CNTs,and maximum adsorption capacity calculated from the Langmuir isotherm model can reach 69.7 mg/g. The MO adsorption kinetics can be better described by the pseudo-second-order and pore diffusion kinetic models, and the diffusion of MO anions into pores of the Al-doped CNT adsorbent should be the rate-determining step.Thermodynamic analyses indicated that the adsorption of MO onto Al-CNTs-2.0 was endothermic and spontaneous. Moreover, adsorption capacity for MO on the Al-doped CNTs was evidently dependent on the CNT dose, solution p H and adsorbent dose. From the perspective of low-cost and multifunctional, suspension obtained during the Al-doped CNT adsorbent preparation, was tested as coagulant to remove humic acid（HA）. A significant observation is that the suspension exhibited an excellent coagulation performance for HA,because abundant aluminous polymer and Al-doped CNTs existed in the suspension.