Raw Dolomite Research Articles

Impact of Nano-Cr2O3 Addition on the Properties of Aluminous Cements Containing Spinel

In this paper, the effect of nano-Cr2O3 addition on the properties of aluminous cement containing MgAl2O4 spinel was investigated. For this reason, the raw dolomite was used as raw material along with calcined alumina for the preparation of the aluminous cement. Then, the compositions containing different amounts of nano-Cr2O3 particles were fired at 1450 °C and their mineralogical compositions and microstructures were investigated. The setting times of prepared cements were measured after grounding and ball-milling. Besides, the slag resistance of refractory castables containing prepared cements was evaluated. The results showed that nano-Cr2O3 addition has effect on the increasing of spinel and CA2 and decreasing of CA and C12A7 phases in the cement composition. The decreasing of C12A7 leads to increasing of setting times of cement. Besides, the slag resistance of refractory castables containing prepared cements is improved due to increasing of spinel and decreasing of C12A7 amount in the cement composition.DOI: http://dx.doi.org/10.5755/j01.ms.21.1.5211

Catalytic Energy Production from Municipal Solid Waste Biomass: Case Study in Perlis-Malaysia

A study of energy recovery from municipal solid waste was undertaken. The energy content of the solid waste is 2388 kcal/kg. The elemental composition shows that the municipal solid waste contains 53.84% of carbon and 5.73% of hydrogen. The energy flow (exothermic and endothermic) and thermal degradation analysis were carried out using calorimeter (model: c2000basic) and ASTM standards respectively. It has been observed that municipal solid waste is less reactive to combustion as compared to coal and biomass, but its reactivity can be improved through pre-treating process so as to reduce noncombustible materials such as oxygen and ash content. Also pyrolysis and gasification can be used to convert MSW to liquid or gaseous fuel. This paper also presents analysis of chemical properties and concentration of raw dolomite, calcined dolomite and zeolite for catalytic cracking of tar and enhancing bio-yield production from technologies such as pyrolysis and gasification of municipal solid waste.

Analysis of Ground Dolomite: Effect of Grinding Time on the Production of Submicron Particles

This paper discusses the effect of grinding time on the production of submicron dolomite by using the impact and abrasion technique of high energy planetary ball mill. It is known that grinding process leads to surface activation other than exhibiting particle size reduction. Most of the energy applied during the process will be dissipated as heat that could lead to harmful effects to the structural pattern of the ground material. Thus in order to study the detrimental effects of grinding towards submicron dolomite, sample was ground at 400 rpm speed with various grinding time; 0.5h, 1h, 2h, 5h, 10h and 20h. It was confirmed using X-Ray Diffraction (XRD) method that the crystalline structure of dolomite did not deform even after 20h of grinding time, thus maintained its crystallinity. The morphological structures of ungrind and ground raw dolomite were shown by Scanning Electron Microscope (SEM) morphology.

Removal of a reactive textile azo dye by dolomitic solids: kinetic, equilibrium, thermodynamic, and FTIR studies

Algerian dolomite was treated at different temperatures in the 600–1000°C range and characterized by XRD and SEM. The obtained samples, named dolomitic solids, were used in the removal of Reactive Black 5 (RB5) from aqueous solutions. A literature survey shows that the data about the dye adsorption by dolomites are almost non-existent. Kinetic data, equilibrium isotherms, thermodynamic parameters, pH influence, and FTIR study were considered. The kinetic mechanism is enough complex, involving different models such as those of pseudo-second-order, intraparticle diffusion, and Elovich. For all dolomitic solids, the capacity in RB5, at equilibrium, strongly increases with increasing adsorption temperature. The affinity sequence is D900 (dolomite treated at 900°C) > D800 > D1000 > D600 > raw dolomite. Knowing that D900 adsorbs 125.9 mg g−1, it appears very effective for removing reactive dyes from wastewaters. The isotherms are found to be overall well represented by the Redlich–Peterson equation. The fact that maximum adsorption occurs at isoelectric point emphasizes the prevalence of the nonelectrostatic interaction. A close agreement exists between the evolution of kinetic, equilibrium, and thermodynamic parameters, suggesting chemisorption. The process reflects for D800, D900, and D1000 a weak chemical interaction via a mechanism of inner-sphere complexation. The comprehension of the organic compound–dolomitic solid interactions constitutes a fundamental aspect for developing the application of these materials in the field of wastewater treatment.

An Innovative Low Density Synthetic Carbonate with a Composite Structure

A new low density mineral material has been synthesized via a simple, flexible, cheap and easy to control process. This material is a synthetic carbonate produced by carbonation of a solid phase composed of a calcic part and a magnesian part. Typically, its production process includes the calcination of a raw dolomite (general formula CaCO3.MgCO3) into the oxide form, followed by an at least partial hydration of this oxide and a subsequent carbonation step. This process is thus close to the well-known process used for the production of Precipitated Calcium Carbonate (PCC), a common filler and pigment in plastic, paper and rubber, except that the raw material is a dolomite instead of a limestone. It has to be pointed out that flue gases from different industries can be used as a source of CO2 for the carbonation. Many parameters have been studied, such as the hydration conditions or the carbonation conditions, allowing the production of a whole range of products. The products obtained via this process are composed of a calcic part, mainly as calcite and aragonite (CaCO3), and a magnesium containing part, mainly as hydromagnesite (4MgCO3.Mg (OH)2.4H2O). Compared to standard PCC, this material has a particularly low density (100-250 kg/m3 instead of 300-600 kg/m3 for standard PCC), a rather high BET specific surface area (15-35 m2/g instead of 4-15 m2/g for standard PCC) and a specific particle morphology and structure. The particles are indeed commonly spherical particles composed of a core of calcite/aragonite covered by a layer of hydromagnesite. This structure can be described as a core-shell structure. Due to these special features, this product could be used in multiple applications, such as raw material for the manufacture of insulation material, flame retardant, filler in plastics, paints, paper, rubber, and many more.

The Application of Raw Dolomite in Converter

The reaction mechanism of raw dolomite was analysed.The test have been implemented.The effect was generalized.The result is: application of raw dolomite in converter can reduce lime 3.3 kg/t,light burning dolomite 7.2 kg/t,coolant7.4 kg/t,decrease cost 9.74¥/t.

Foaming in Electric Arc Furnace—Part II: Foaming Visualization and Comparison with Plant Trials

The kinetics of slag foaming by limestone particles was studied at 1773 K (1500 °C) with the aid of an X-ray imaging system. Two models were implemented to describe the decrease in foam height with the time on the basis of the lowering of the average temperature and CaO shell formation during decomposition reaction. The energy impact of carbonate additions was studied on an industrial scale in a 100-ton electric arc furnace (EAF). It was found that, in the case of the addition of carbonates after the scrap is completely molten, the heat effects for limestone and dolomite (2255 and 2264 kJ/kg, respectively) were only 70 pct from theoretical values. Comparing these values with similar additions during the scrap melting stage shows that the energy requirements in the case of carbonate additions to steel bath are much smaller. It was found from the trial heats with dolomite addition to the steel bath that the partial substitution of lime by raw dolomite can be made without an increase in energy consumption.

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 °C = 10.01 mg/g; 30 °C = 8.385 mg/g; 40 °C = 6.654 mg/g; and 60 °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 Δ G o and Δ H o specify the spontaneous and exothermic nature of the reaction. The adsorption takes place with a decrease in entropy (Δ S o is negative).

Sintering behaviour and hydration resistance of reactive dolomite

Sintering of raw dolomite and hydroxides derived from dolomite was carried out in the temperature range 1350–1650 °C. The hydroxide derived from dolomite was developed through pre-calcination of dolomite followed by its hydration. For hydroxide development, after precalcination one sample was air-quenched and the other powder was furnace cooled before hydration. The air quenched samples showed better densification than that of the furnace cooling process at the same temperature. Fe 2O 3 addition enhances sintering by liquid formation at higher temperature. The grain size of doloma with Fe 2O 3 addition is bigger than that without additive. Hydration resistance was related to densification and grain size of sintered dolomite.

Synthesis and Characterization of Fe2MoO4 as a Precursor Material for Mo Alloying in Steel

The objective of the present thesis is to optimize the electric arc furnace (EAF) practice from an environmental view point. Two aspects that meet the requirements of the secondary steelmaking industries today, viz. Mo alloying with maximum retainment of the alloying element in molten steel and optimization of foaming by carbonate addition with a view to optimize the energy need of the process. Both these aspects would also have a significant impact on the process economy. Iron molybdate (Fe2MoO4) has been synthesized from commercial grade materials and proposed as a new potential precursor for steel alloying with Mo. The thermal stabilities of different molybdates, viz. Fe2MoO4, CaMoO4 and MgMoO4, were studied using thermogravimetry analysis (TGA). It was found that Fe2MoO4 is the most stable one and doesn’t evaporate in Ar atmosphere when heating up to 1573 K. The synthesis of Fe2MoO4 requires high temperature (1373 K) and long holding time (up to 16 hours). In a view of this, the possibilities for in-situ formation of Fe2MoO4 and CaMoO4 from their precursor mixtures were studied with the aid of high-temperature X-ray diffraction (XRD) and TGA analysis. Laboratory and industrial trials on steel alloying with Mo were conducted using precursor mixtures as sources of Mo. It was found that the mixture, which contains FeOx, MoO3 and C (Fe2MoO4 precursor), can provide the Mo yield up to 98 % at both the laboratory as well as industrial trials. The Mo yields even in the case of C+MoO3 and C+MoO3+CaO mixtures were around 93 % in these trials. The higher yield for the MoO3+C+FeOx mixture was attributed to the stabilization of Mo in the precursor (marked by the decrease in the Gibbs energy of Mo) and the readiness to dissolve in the steel bath. The heat effect of the slag foaming with carbonates addition was studied at 1623 and 1673 K with the aid of thermal analysis technique with a new crucible design. Experiments were conducted by adding limestone and dolomite pieces of defined shapes (together with iron sinkers) in molten slag and monitoring the temperature changes accompanying the decomposition of carbonates. It was found that the decomposition energies for dolomite and limestone for the studied slag composition are in the range 56-79 % of theoretical values, which is linked to the energy saving effect of slag foaming. No influence of sample shape on decomposition energy was found both for limestone and dolomite. The kinetics of slag foaming by limestone particles was studied at 1773 K with the aid of X-ray imaging system. A model was proposed to describe the decrease in foam height with time on the basis of CaO shell formation during decomposition reaction. The energy impact of limestone and raw dolomite addition was examined in a 100-ton EAF. It was found that, in the case of addition of carbonates after the scrap is completely molten; the endothermic heat effects for limestone and dolomite (2255 and 2264 kJ/kg respectively) were only 70 % from theoretical values. This is indicative of the resistance to heat transfer due to increased foaming.

Preparation, characterisation of thermally treated Algerian dolomite powders and application to azo-dye adsorption

Dolomite powder from Ouled Mimoun, Tlemcen (western region of Algeria) was thermally treated within the temperature range 450–1000 °C. The modifications undergone by dolomite, inherent to thermal treatment, were investigated from X-ray diffraction patterns. The results were also discussed using scanning electronic microscopy and nitrogen adsorption. The XRD data, analysed from X Pert Plus program, showed that the dolomite phase ceases at 700 °C and is relayed by the formation of in situ calcite and periclase. The crystallographic parameters of these two phases tend towards that of pure periclase and calcite at 1000 and 900 °C, respectively. SEM analysis indicated that the morphological properties were profoundly affected. SEM images of D-1000 (sample treated at 1000 °C) indicated that the original particle shape of dolomite (presence of discrete grains having sharp edges with presence of cleavages) was totally destroyed, leading to small spherical particles with a diameter of 0.1 μm. The specific surface area value of D-1000 increased more than 6 times against that of the raw dolomite. Adsorption of azo-dye Orange I from aqueous solutions onto untreated and treated dolomites was also reported. The isotherms were of L-type. The interaction was explained by electrostatic considerations between sulfonate groups of the dye (D-SO 3Na), which are dissociated in the aqueous system, and positively charged adsorption sites. The affinity of orange I for the dolomitic solids follows the sequence D-900 > D-1000 > D-800 > > D-600 > raw dolomite. The maximum retention capacity shown by D-900 was explained and correlated with its crystallographic properties.

Zeta potential study of thermally treated dolomite samples in electrolyte solutions

In this paper, electrokinetic properties of raw dolomite and thermally treated dolomite have been investigated as function of concentrations dolomite of various electrolytes such as NaCl, KCl, MgCl 2, BaCl 2, AlCl 3 and Na 2HPO 4. The dolomitic solids such as D-600, D-800, D-900 and D-1000 were obtained further to calcinations at 600, 800, 900 and 1000 °C, respectively, during 2 h. From the electric potential results, it was found that the zeta potential of dolomite is not affected by the solid concentration. Isoelectric point of dolomite was determined at pH 6.8; H + and OH − are potential determining ions of dolomite. The monovalent cations are indifferent electrolytes for dolomitic solids samples, whereas MgCl 2 and BaCl 2 reverse the sign of surface charge of dolomite, while Na 2HPO 4 is potential determining ion of D-800, D-900 and D-1000.

Adsorption of Cu 2+ and Pb 2+ ion on dolomite powder

Natural Turkish dolomite was shown to be effective for removing Cu 2+ and Pb 2+ from aqueous solution. Selected information on pH, dose required, initial metal concentration, adsorption capacity of the raw dolomite powder was evaluated for its efficiency in adsorbing metal ions. Dolomite exhibited good Cu 2+ and Pb 2+ removal levels at all initial metal amount tested (0.04–0.32 mmol, 20 mL). It is important to note that the adsorption capacities of the materials in equilibrium vary, depending on the characteristics of the individual adsorbent, the initial concentration of the adsorbate and pH of the solution. One hour was enough for the removal of metal ions from (0.2 mmol in 20 mL) aqueous solution. Effective removal of metal ions was demonstrated at pH values of 5.0. The adsorptive behavior of dolomite was described by fitting data generated from the study of the Langmuir and Freundlich isotherm models. The adsorption capacity of dolomite was found as 8.26 mg for Cu 2+ and 21.74 mg for Pb 2+, respectively, from the calculation of adsorption isotherm equation. More than 85% of studied cations were removed by dolomite from aqueous solution in single step. The mechanism for cations removal by dolomite includes surface complexation and ion exchange.

Low cost processes for the removal of phosphates in water and wastewater

This paper presents a synopsis of various low-cost techniques employed for the removal of phosphates from water and treated wastewater. Techniques employed include seawater flocculation and coagulation/ flocculation using bittern, adsorption on fluidised raw dolomite bed, and filtration through iron and aluminium coated filter media. Seawater flocculation at a seawater concentration of 10% exhibited highly efficient (>90%) removal of Total Phosphorus (TP) from alkaline oxidation pond effluents. For experiments employing fluidised raw dolomite bed, varying degrees of phosphate adsorption capacities were observed for the different test influents used. Finally, laboratory experiments conducted to determine the efficacy of iron and aluminium coated media in removing low concentrations of phosphates indicated very effective phosphate removals (>90%) when applied to Distilled Water (DW) and synthetic groundwater, and less success when applied to Tap Water (TW) (<80%) and treated wastewater effluents (<70%).

Removal of pentachlorophenol from aqueous solutions by dolomitic sorbents

The partial decomposition of dolomite carried out within the temperature range 600–1000 °C provides new sorbents, called dolomitic sorbents. Their surface properties and identification by X-ray diffraction are discussed. The lowest specific surface area value was found for the raw dolomite, while the highest value was achieved by the D-1000 sample. The adsorption equilibrium of pentachlorophenol from aqueous solutions on the examined sorbents was investigated at 30, 40, and 50 °C via a bath process. Langmuir, Freundlich, Langmuir–Freundlich, and Redlich–Petersen models were fitted to experimental equilibrium data, and their goodnesses of fit are compared. The adjustable parameters of Langmuir–Freundlich and Redlich–Petersen isotherms were estimated by nonlinear least-squares analysis. Langmuir and Freundlich models were found insufficient to explain the adsorption equilibrium, while Langmuir–Freundlich and Redlich–Petersen isotherms provide the best correlation of the pentachlorophenol adsorption onto dolomitic sorbents.

On the Adsorption of Chromium(VI) Ions on Dolomite and ‘Dolomitic Sorbents’

The sorption capability of raw and thermally treated dolomite samples with respect to toxic ions was estimated through the adsorption of chromium(VI) from aqueous solutions. The adsorption isotherms were shown to fit the well-known Freundlich equation. The results confirm the weak adsorption of chromium(VI) on raw dolomite relative to the other dolomite-derived sorbents. The influence of ionic strength on the adsorption was also determined.

Physicochemical Study of 'Dolomitic' Sorbents Prepared under Different Thermal Conditions. Part I. The Influence of Temperature

The partial decomposition of dolomite performed within the temperature range 800-1000°C provides new sorbents, the so-called 'dolomitic' sorbents, composed of calcite and magnesium oxide. Their surface properties, such as their porosity and adsorption capabilities towards hydrocarbons, are discussed. The 'dolomitic' sorbents show a much higher specific surface area and pore volume when compared to the raw dolomite; moreover, their porous structure depends on the temperature of heating. The adsorption of selected hydrocarbons on the examined sorbents was also investigated and the adsorption energy distribution functions calculated from the adsorption data.

Simulating minerals pyroprocessing by thermal analysis

TG and DTA studies on laboratory cement raw mixes and raw dolomite have been extensively reported in the literature. This paper discusses four aspects. (1) Calcination kinetics of raw mix by isothermal TG and calculation of rate constants to derive activation energy by Arrhenius plots. (2) Quantification by TG of minerals in Indian laterites. The amount of goethite appears to influence burnability of raw mix. (3) Determination of practical heat of clinker formation from DTA studies and establishment of enthalpy temperature relationship of raw mix for heat transfer studies in rotary kilns. (4) Prediction of material temperature profile in a dolomite kiln from DTA studies of raw dolomite.

Suitability of Zavadov deposit dolomites for use as raw material

Investigations of raw Zavadov deposit dolomite showed that in strength it belongs to the dense varieties of dolomite with a fine crystalline structure. The weight % of the basic component (dolomite) is 88–98%. The impurities are calcite, quartz, clay particles, and iron oxides.

Preheater for raw dolomite

The vertical annular preheater with double transmission of the gases behind the rotary furnace proved to be workable. The raw dolomite in fractions 12–20 mm is heated to 450‡C.