EPR, UV-visible and near infrared spectroscopic characterization of dolomite

Dolomite mineral samples having white and light green colours of Indian origin have been characterized by EPR, optical and NIR spectroscopy. The optical spectrum exhibits a number of electronic bands due to presence of Fe(III) ions in the mineral. From EPR studies, the parameters of g for Fe(III) and g, A and D for Mn(II) are evaluated and the data confirm that the ions are in distorted octahedron. Optical absorption studies reveal that Fe(III) is in distorted octahedron. The bands in NIR spectra are due to the overtones and combinations of water molecules. Thus EPR and optical absorption spectral studies have proven useful for the study of the chemistry of dolomite.

A Raman spectroscopic comparison of calcite and dolomite

Raman spectroscopy was used to characterize and differentiate the two minerals calcite and dolomite and the bands related to the mineral structure. The (CO3)2− group is characterized by four prominent Raman vibrational modes: (a) the symmetric stretching, (b) the asymmetric deformation, (c) asymmetric stretching and (d) symmetric deformation. These vibrational modes of the calcite and dolomite were observed at 1440, 1088, 715 and 278 cm−1. The significant differences between the minerals calcite and dolomite are observed by Raman spectroscopy. Calcite shows the typical bands observed at 1361, 1047, 715 and 157 cm−1, and the special bands at 1393, 1098, 1069, 1019, 299, 258 and 176 cm−1 for dolomite are observed. The difference is explained on the basis of the structure variation of the two minerals. Calcite has a trigonal structure with two molecules per unit cell, and dolomite has a hexagonal structure. This is more likely to cause the splitting and distorting of the carbonate groups. Another cause for the difference is the cation substituting for Mg in the dolomite mineral.

Investigations on the adsorption of acidic gases using activated dolomite

In this work activated dolomite adsorption was investigated for removal of acidic gaseous pollutants. Charring was found to be an effective method for the activation of dolomite. This thermal processing resulted in partial decomposition, yielding a calcite and magnesium oxide structure. Adsorbents were produced over a range of char temperatures (750, 800 and 850 °C) and char times (1–8 h). The surface properties and the adsorption capability of raw and thermally treated dolomite sorbents were investigated using porosimetry, SEM and XRD. The sorbates individually investigated were CO2 and NO2. Volumetric equilibrium isotherm determinations were produced in order to quantify sorbate capacity on the various sorbents. The equilibrium data were successfully described using the Freundlich isotherm model. Despite relatively low surface area characteristics of the activated dolomite, there was a high capacity for the acidic gas sorbates investigated, showing a maximum of 12.6 mmol/g (554 mg/g) for CO2 adsorption and 9.93 mmol/g (457 mg/g) for NO2 adsorption. Potentially the most cost effective result from the work concerns the adsorptive capacity for the naturally occurring material, which gave a capacity of 9.71 mmol/g (427 mg/g) for CO2 adsorption and 4.18 mmol/g (193 mg/g) for NO2 adsorption. These results indicate that dolomitic sorbents are potentially cost effective materials for acidic gases adsorption.

Kinetic and thermodynamics of chromium ions adsorption onto low-cost dolomite adsorbent

The chromium bearing wastewater in this study was used to simulate the low concentration discharge from a major aerospace manufacturing facility in the UK. Removal of chromium ions from aqueous solutions using raw dolomite was achieved using batch adsorption experiments. The effect of; initial Cr(VI) concentration, amount of adsorbent, solution temperature, dolomite particle size and shaking speed was studied. Maximum chromium removal was found at pH 2.0. A kinetic study yielded an optimum equilibrium time of 96 h with an adsorbent dose of 1 g/L Sorption studies were conducted over a concentration range of 5-50 mg/L Cr(VI) removal decreased with an increase in temperature (q(max): 20 degrees C = 10.01 mg/g; 30 degrees C = 8.385 mg/g; 40 degrees C = 6.654 mg/g; and 60 degrees C = 5.669 mg/g). Results suggest that the equilibrium adsorption was described by the Freundlich model. The kinetic processes of Cr(VI) adsorption onto dolomite were described in order to provide a more clear interpretation of the adsorption rate and uptake mechanism. The overall kinetic data was acceptably explained by a pseudo first-order rate model. Evaluated Delta G degrees and Delta H degrees specify the spontaneous and exothermic nature of the reaction. The adsorption takes place with a decrease in entropy (Delta S degrees is negative). (C) 2011 Elsevier B.V. All rights reserved.

Removal of ortho-phosphate from aqueous solution by adsorption onto dolomite

An experimental study on the adsorption of phosphate onto cost effective fine dolomite powder is presented. The effect of solution pH, solution ionic strength and adsorption isotherm were examined. The adsorption of phosphate was pH dependent and phosphate adsorption favoured acidic conditions. The adsorption was significantly influenced by solution ionic strength indicating outer-sphere complexation reactions. The experimental data further indicated that the removal of phosphate increased with increase in the ionic strength of solution. The experimental data were modelled with different isotherms: Langmuir, Freundlich and Redlich–Peterson isotherms. It was found that the Redlich–Peterson isotherm depicted the equilibrium data most accurately. The overall kinetic data fitted very well the pseudo-first-order rate model.

Arsenic(III,V) adsorption onto charred dolomite: charring optimization and batch studies

In this work, the removal of arsenic from aqueous solutions onto thermally processed dolomite is investigated. The dolomite was thermally processed (charred) at temperatures of 600, 700 and 800 degrees C for 1, 2, 4 and 8 h. Isotherm experiments were carried out on these samples over a wide pH range. A complete arsenic removal was achieved over the pH range studied when using the 800 degrees C charred dolomite. However, at this temperature, thermal degradation of the dolomite weakens its structure due to the decomposition of the magnesium carbonate, leading to a partial dissolution. For this reason, the dolomitic sorbent chosen for further investigations was the 8 h at 700 degrees C material. Isotherm studies indicated that the Langmuir model was successful in describing the process to a better extent than the Freundlich model for the As(V) adsorption on the selected charred dolomite. However, for the As(III) adsorption, the Freundlich model was more successful in describing the process. The maximum adsorption capacities of charred dolomite for arsenite and arsenate ions are 1.846 and 2.157 mg/g, respectively. It was found that both the pseudo first- and second-order kinetic models are able to describe the experimental data (R-2 > 0.980). The data suggest the charring process allows dissociation of the dolomite to calcium carbonate and magnesium oxide, which accelerates the process of arsenic oxide and arsenic carbonate precipitation. (C) 2014 Elsevier B.V. All rights reserved.

Dolomite and phosphogypsum surface application effects on annual crops nutrition and yield

Brazil has extensive area with acid soils. Using phosphogypsum and soil acidity tolerant cultivars are alternatives to crop establishment in no-till system without previous limestone incorporation in many agricultural soils of Brazil. However, it remains unknown how phosphogypsum and limestone surface application affects rice (Oryza sativa L.) and common bean (Phaseolus vulgaris L.) nutrition and yield under a no-till system. A field experiment was conducted in a sandy clay loam, kaolinitic, thermic Typic Haplorthox, previously cultivated under conventional tillage, in Botucatu, Sao, Paulo State, Brazil. Treatments included four dolomitic limestone rates (0, 1100, 2700, and 4300 kg ha(-1)), two phosphogypsum rates (0 and 2100 kg ha(-1)), and two upland rice cultivars (Caiapo and IAC 202). in 2002-2003, and two bean cultivars (Perola and Carioca), in 2003-2004. Both amendments were applied on the surface, without soil incorporation. The content of Ca, Mg, and Mn in flag leaves and rice yield increased with limestone surface application. Liming increased the shoot dry matter of IAC 202 rice. Phosphogypsum increased S contents in leaves of both rice cultivars, and resulted in higher grain yield in the Caiapo rice. Liming increased K contents in leaves of both bean cultivars. In the absence of phosphogypsum, liming increased S contents and grain yield of bean. Content of Mg in leaves was reduced by phosphogypsum in lower limestone rates. In phosphogypsum presence, liming reduced Zn contents in leaves and increased bean shoot dry matter. Phosphogypsum increased Ca and S, and reduced Mg contents in bean leaves. Using soil acidity tolerant cultivars promoted higher crop yields in no-till systems establishment, even when the effective soil amelioration had not yet been achieved.

Investigation of the pore blockage of a Brazilian dolomite during the sulfation reaction

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Investigation of the pore blockage of a Brazilian dolomite during the sulfation reaction

The influence of the temperature and reaction time on the sulfation process of a dolomite is investigated in this paper. The sulfation effectiveness was evaluated and correlated with changes in the physical characteristics of a Brazilian dolomite during the reactive process. Calcination and sulfation experiments were performed under isothermal conditions for dolomite samples with average particle sizes of 545 mu m at temperatures of 750 degrees C, 850 degrees C and 950 degrees C at different times of sulfation. Thermogravimetric tests were applied to establish the reactivity variation of the dolomite in function of the time in the sulfation reaction and evaluate the methodology of the samples preparation. Porosimetry tests were performed to study the pore blockage of dolomite during the sulfation reaction. The highest values of BET surface area were 25.55 m(2)/g, 29.55 m(2)/g and 12.62 m(2)/g for calcined samples and after their sulfation processes, conversions of 51.5%, 61.9% and 42.8% were obtained at 750 degrees C, 850 degrees C and 950 degrees C, respectively. Considering the process as a whole, the best fit was provided by a first-order exponential decay equation. Moreover, the results have shown that it is possible to quantify the decreasing in the dolomite reactivity for sulfur dioxide sorption and understand the changes in the behavior of the sulfation process of limestones when applied to technologies, as fluidized bed combustor, in which sulfur dioxide is present. (C) 2011 Elsevier B. V. All rights reserved.