Natural Dolomite Research Articles

Enhanced La(III) adsorption performance and mechanism of urea-modified dolomite composite adsorbent

Dolomite, a prevalent mineral in rock formations, often coexists with various minerals, impacting their properties and typically being discarded as waste in the extraction process of other minerals. This research introduces a straightforward and effective technique for co-calcining urea with natural dolomite at 550℃, yielding a novel composite adsorbent designated as CN/xDO, where ‘x’ denotes the proportion of dolomite incorporated. During the preparation, urea promotes the conversion of dolomite to nano calcite, and the gas produced by urea pyrolysis during the calcination process has a cavitation effect on the material, enhancing its surface properties. BET analysis reveals that the specific surface area and total pore volume of CN/xDO notably surpass those of pure dolomite, with CN/0.6DO achieving 2.9479 m2/g and 0.0382 cm3/g, respectively. CN/0.6DO demonstrates an adsorption capacity of 237.91 mg/g for La(III) within 360 min at 298 K, which is 16.9 times greater than that of untreated dolomite (14.05 mg/g). The maximum adsorption capacity of CN/0.6DO for La(III) (C0 = 500 mg/L) reaches 382.94 mg/g at 308 K, exceeding the majority of adsorbents documented in the literature. The comparative analysis of batch adsorption experiments and material characterization before and after the adsorption process reveals that the mechanisms adsorption of La(III) adsorption by CN/xDO include physical adsorption, cation-π interactions, ion exchange, and complexation with oxygen-containing functional groups, especially −OH, CO32-. This study broadens the application of dolomite in adsorption and introduces a new strategy for the efficient recovery of rare earth elements from wastewater, consistent with the principles of sustainable development.

Highly-efficient peroxymonosulfate activation by porous nano-MgO for tetracycline degradation: Surface hydroxyl groups and oxygen vacancies synergetic mediated nonradical process

Heterogeneous transition metal activation of peroxymonosulfate (PMS)-based advanced oxidation processes is limited by low cycling efficiency, secondary contamination, and high toxicity. In this study, a non-transition metal porous nano-MgO catalyst from natural dolomite was synthesized and PMS activation was performed to degrade tetracycline (TC). The nano-MgO/PMS system could achieve TC degradation of 88.09 % within 20 min under the optimum parameters (nano-MgO dosage of 0.2 g·L−1, PMS concentration of 0.3 mM), exceeding the efficiency of the PMS-alone system (11.66 %) by 7-fold, which was related to large specific surface area (41.19 m2·g−1) and defect structure of porous nano-MgO catalysts. As revealed by the quenching tests and electron paramagnetic resonance (EPR) analysis, different from transition metal activation PMS where radicals are generated, singlet oxygen (1O2) was essential in the nano-MgO/PMS oxidation process. Notably, the density functional theory (DFT) calculations demonstrated that nano-MgO with surface hydroxyl groups and oxygen vacancies exhibited the longer O-O bond length (1.47 Å), stronger adsorption energy of PMS (-4.07 eV), and faster electron transfer (0.91 e) than the only nano-MgO with surface hydroxyl groups, proving the surface hydroxyl groups and oxygen vacancies active sites in nano-MgO could synergistically mediate the PMS activation process. Furthermore, the proposed three TC degradation pathways and the toxicity evaluation of intermediates suggested that nano-MgO/PMS system have good ecological safety. This work offers an innovative approach for the cost-effective preparation of porous magnesium oxide with highly efficiency, offering a new perspective for understanding the PMS activation mechanism induced by non-transition metal.

Evaluating the role of dissolved silica for dolomite formation in evaporitic environments: Insights from prolonged laboratory experiments

The mineral Dolomite CaMg(CO3)2 is a common constituent of sedimentary rocks. Despite centuries of research, the mechanism of its formation remains elusive and debated. Recent studies have shown the presence of silica in solution promote the incorporation of Mg into the carbonate mineral, forming crystal phases that may be precursors to dolomite. The goal of this study was to evaluate with laboratory experiments whether dissolved silica may play a role for dolomite formation in sabkha (i.e., salt flats) environments. Several models for dolomite formation are based on the studies of sabkhas, which are often cited as modern analogue for ancient dolomite-rich sedimentary sequences. We performed long-incubation time (i.e., up to 600 days) laboratory precipitation experiments at 30 °C with solution mimicking the sabkha pore waters (characterized by a salinity of 23 % and Mg: Ca ratio of 15) to which we added different concentrations of Si. Our results revealed a positive correlation (p-value <0.001) between Si concentration in solution and the mol% Mg of the carbonate minerals forming in the experiment. With 2 mM of Si, the bulk precipitate was comprised of 90 % stoichiometric dolomite with possible signs or ordering. Moreover, the rhombohedral morphology of the crystals is analogue to that of natural dolomite previously described from sabkha sediments. Our results suggest that dissolved Si may play an important role for dolomite formation in evaporitic environments.

Cobalt(II) removal with dolomite: Use of radiotracer technique in aqueous solution

Industrial processes have the potential to release cobalt into the environment, and exposure to cobalt in quantities higher than specific amounts can have harmful impacts on living organisms. This study aimed to determine whether natural dolomite from the Thrace region of Türkiye could effectively remove Co(II) from aqueous solutions. Batch studies were conducted to examine the impact of various experimental factors, including adsorbent dosage, initial Co(II) concentration, contact time, solution pH, and temperature. The cobalt concentrations in aqueous solutions were determined by employing 60Co radionuclide as a radiotracer. Experimental results revealed that optimum adsorption conditions were obtained at a solid-liquid ratio of 20 g·L−1, initial Co(II) concentration of 128 mg·L−1, contact time of 120 min, and pH 6 with a maximum adsorption capacity of 2.32 mg⋅g−1. The pseudo-second-order kinetic and Redlich-Peterson isotherm models described the experimental data well. The adsorption process of Co(II) ions on the dolomite was spontaneous and exothermic. The results showed the potential use of dolomite to remove such a toxic metal ion from industrial wastewater.

A non-classical crystallization mechanism of microbially-induced disordered dolomite

Non-classical crystallization pathways, involving the formation of complex precursors prior to nucleation, have been observed during the calcification process of invertebrate skeletons and shells. However, these pathways were rarely documented in microbially-induced carbonate precipitation. In this study, we presented experimental evidence demonstrating that a halophilic bacterium (Halomonas sp. strain JBHLT-1) catalyzed the biomineralization of disordered dolomite through an amorphous calcium-magnesium carbonate (ACMC) with a stoichiometry near that of dolomite. During the ACMC formation, strain JBHLT-1 significantly enhanced the incorporation of Mg2+ ions compared to abiotic ACMC that was synthesized without any microbial biomass. In the stage of ACMC crystallization, the presence of microbial biomass reduced the dissolution-reprecipitation rate and induced bias towards a solid-state reaction pathway. This observation was supported by the negligible loss of structural Mg2+ ions in the presence of cells of strain JBHLT-1. The microbially-induced growth of disordered dolomite appeared to follow a spherulitic growth mechanism, as evidenced by its hierarchical structure composed of coalesced nano-spheres, eventually growing into micron-sized spheroids and dumbbells with extended incubation times. Since disordered dolomite is considered as a crucial crystalline precursor of ordered sedimentary dolomite, the findings of this study have important implications for understanding the formation mechanism of natural dolomite.

Magnesium calcites for CO2 capture and thermochemical energy storage using the calcium-looping process

In this study, a precipitation-based synthesis method has been employed to prepare magnesium calcites with the general formula Ca1-xMgxCO3, with the objective of use them in the calcium looping (CaL) process for CO2 capture (CaL-CCS) and thermochemical energy storage (CaL-CSP). The structure and microstructure of the samples have been characterized. It has been found by X-ray diffraction that the samples with a Ca:Mg molar ratio of 0.5:0.5 and 0.55:0.45 are phase pure, while the samples with molar ratios of 0.7:0.3 and 0.8:0.2 are composed by two phases with different stoichiometry. In addition, the sample prepared with calcium alone shows the aragonite phase. The microstructure of the magnesium-containing samples is composed of nanocrystals, which are aggregated in spherical particles whereas the aragonite sample presents a typical rod-like morphology.The multicycle tests carried out under CaL-CCS conditions show that an increase on the MgO content in the calcined samples results in a reduced value of effective conversion when compared to aragonite. On the other hand, under CaL-CSP conditions, the samples with the higher MgO content exhibit nearly stable effective conversion values around 0.5 after 20 cycles, which improve the results obtained for aragonite and those reported for natural dolomite tested under the same conditions.

Effects of circulating ash and dolomite on mercury transition during coal step conversion of pyrolysis and combustion

In aim to study the influence of circulating ash used as heat carrier and dolomite used as catalyst on mercury transition during the step conversion of coal pyrolysis and combustion, five experiments with different operating conditions were conducted in this study, including four pyrolysis experiments of raw coal, coal/ash, coal/dolomite, coal and ash/dolomite, and combustion experiment of pyrolysis solid product. By changing the experimental conditions including final pyrolysis temperature, heating rate, coal-ash ratio and dolomite type, the transition path and final mercury distribution in the step conversion process were comprehensively analyzed. Experiments results indicated that mercury completely released out from coal when the final pyrolysis temperature was 600 °C. The individual addition of ash could promote the mercury release from coal at lower temperature. Dolomite could catalyze the oxidation of Hg0 in gas phase, and the modified dolomite had better catalytic capacity for Hg0 oxidation than natural dolomite. The addition of circulating ash and natural dolomite both had a certain catalytic effect on Hg0 emission peaks during the coal pyrolysis. Increasing the coal-ash ratio was conducive to the oxidation of Hg0 in pyrolysis gas. During the direct combustion of coal, the content of Hg0 released into the gas phase could reach to 69.97%. By adding ash, ash/natural dolomite and ash/modified dolomite to the coal pyrolysis process, the content of Hg0 in pyrolysis gas decreased to 58.99%, 34.77% and 31.30%, respectively. The research is able to offer the theoretical foundation for mercury contaminants’ removal and process optimization of the step conversion technology.

Synthesis of Ca-Mg-Al layered double hydroxide from dolomite with ultrasound-assisted method. Application in phosphate removal

The aim of this work was to obtain a Layered Double Hydroxide (LDH) from natural dolomite and to apply the synthetized solid (CaMgAl-LDH) for phosphate removal by adsorption. Both the conventional coprecipitation method and ultrasound-assisted method were used to obtain CaMgAl-LDH. The obtained solids were characterized by N2 adsorption/desorption, size of pores, X-ray diffraction, and FTIR. Batch scale experiments were carried out to evaluate the phosphate adsorption capacity on CaMgAl-LDH using design of experiments (DOE). The studied parameters were pH, solid dosage, contact time and phosphate removal percentage, which was selected as the response function. Experimental data were fitted to kinetics and isotherms mathematical models. The process thermodynamics was also studied. Results showed that the ultrasound-assisted method was more efficient to obtain LDH even in a short period of sonication. The solids presented good crystallization, structure between layers, and high purity. Besides, LDH obtained by ultrasound exhibited a surface area of ​​about 40% greater than the LDH obtained by the conventional method. The results of LDH application for phosphate removal showed high adsorption capacity (>94%) in several conditions of contact time and pH, even in low solid dosage. The kinetics of the process followed the pseudo-second-order model and Redlich-Peterson was the isotherm model that presented the best adjust. The thermodynamic parameters suggested a spontaneous, endothermic, and randomness process at the solid/solution interface, confirming an adsorption system favorable. The results exhibited that the ultrasound-assisted method is promissory to obtain LDH from mineral sources such as dolomite due to decrease energy expenditure and short synthesis time. It was found the ultrasound-assisted method also improve the solid physicochemical characteristics for its use in the adsorption process, enhancing the phosphate removal.

Study on Brittleness Characteristics and Fracturing Crack Propagation Law of Deep Thin-Layer Tight Sandstone in Longdong, Changqing

Tight-sandstone oil and gas resources are the key areas of unconventional oil and gas resources exploration and development. Because tight-sandstone reservoirs usually have the characteristics of a low porosity and ultralow permeability, large-scale hydraulic fracturing is often required to form artificial fractures with a high conductivity to achieve efficient development. The brittleness of rock is the key mechanical factor for whether fracturing can form a complex fracture network. Previous scholars have carried out a lot of research on the brittleness characteristics of conglomerate and shale reservoirs, but there are few studies on the brittleness characteristics of sandstone with different types and different coring angles in tight-sandstone reservoirs and the fracture propagation law of sandstone with different brittleness characteristics. Based on this, this paper carried out a systematic triaxial compression and hydraulic fracturing experiment on the tight sandstone of Shan 1 and He 8 in the Longdong area of the Changqing oilfield. Combined with CT scanning cracks, the brittleness characteristics and fracturing crack propagation law of different types and different coring angles of sandstone under formation-confining pressure were clarified. The results show that there are great differences between different types of sandstone in the yield stage and the failure stage. The sandstone with a quartz content of 100% has the highest peak strength and a strong brittleness. Sandstones with a high content of natural fractures and dolomite have a lower peak strength and a weaker brittleness. There are also differences in the peak strength and fracture morphology of sandstone with different coring angles due to geological heterogeneity. The sandstone with a comprehensive brittleness index of 70.30 produces a more complex fracture network during triaxial compression and hydraulic fracturing than the sandstone with a comprehensive brittleness index of 14.15. The research results have important guiding significance for on-site fracturing construction of tight-sandstone reservoirs.

Thermal Decomposition Analysis of Indonesian Natural Dolomite in Air

Dolomite is widely used in the construction, glass ceramics, iron and steel, pharmaceutical industries, as a source of CaO and MgO and as thermal energy storage material. Thermal decomposition analysis of natural dolomite of the so-called Jeddih limestone has been carried out. A thermogravimetry analysis (TGA) in the air evaluates the thermal decomposition of dolomite. The natural dolomite has been analyzed by x-ray flourescence (XRF) and x-ray diffraction (XRD) to test crystal structure and decomposition phase, fourier transform infra-red (FTIR) was utilized to identify the presence of functional groups. The particle morphology was observed by scanning electron microscopy. TGA curve shows that the thermal decomposition of dolomite occurs in two stages. The first stage is in temperature range of 600 - 779°C and the second one is at the temperature 779°C. The results are in line with the XRD and FTIR measurements. Which shows that calcite begins to grow at a temperature of 600°C and MgO phase is observed at 700 - 900°C. Moreover, CaO phase starts to be found at 800°C.

Characterization and Degradation of Ancient Architectural Red Sandstone in a Natural Erosion Environment

The properties and appearance of ancient architectural red sandstone will be damaged after being eroded by the natural environment for a long time. In order to investigate the weathering and erosion characteristics of the red sandstone structure of an existing ancient building, ultrasonic testing techniques, combined with scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray computed tomography (X-CT), were used to analyze a building in Ganzhou. The variation in chemical substances contained in the red sandstone specimens according to phenology was analyzed by X-ray diffraction (XRD). The characteristic parameters of the CT grayscale images of the red sandstone were extracted and combined with the ultrasonic wave velocity values to comprehensively analyze the degradation characteristics of the red sandstone specimens, and a method to characterize the degradation degree of the red sandstone as a whole plane is proposed. We use the gray model (GM (1, 1)) to predict the surface degradation degree of red sandstone specimens, and gray relation analysis (GRA) to further analyze the correlation between the characteristic parameters of CT grayscale images of red sandstone and its degradation degree. The results show that in the natural erosion environment, dolomite and chlorite are generated on the exposed surface of the red sandstone, which can protect the internal sandstone to a certain extent. The degradation degree of the red sandstone specimens in the horizontal X and Y directions varies, and the proposed method of calculating the overall plane degradation degree of the red sandstone is feasible. The minimum average relative error of the surface degradation degree obtained from the gray prediction GM (1, 1) model is 1.4591%. There is a good correlation between the characteristic parameters of the red sandstone CT grayscale images and the degradation degree.

Diffusion timescale conundrum in contact metamorphism: Oxygen isotope and trace element profiles in dolomite

Successful application of diffusion chronometry is based on detailed knowledge of diffusion parameters obtained from laboratory experiments, which also need to be upscaled to be applied to natural samples. While generally applicable, several examples of disagreement with other dating techniques and discrepancies with geological observations highlight the importance of validating diffusion parameters and their use to geochronologic application by testing them on samples from well-characterized geologic environments.The incomplete dissolution and reprecipitation reaction of dolomite associated with infiltration along grain boundaries of a fluid of magmatic origin in a contact metamorphic environment is the starting point of this study. The reaction produces dolomite rims, which are characterized by lower δ18O values (about 16‰) and slightly higher Fe (∼1000 ppm) and Mn (∼200 ppm) concentrations. The cores, in comparison, have no Fe and Mn and a δ18O value of about 30‰. This compositional and isotopic gradient led to chemical re-equilibration through diffusion at the reaction interface. We acquired oxygen isotope profiles using a secondary ion mass spectrometer (SIMS), with spot sizes as small as 3 µm, and iron and manganese profiles with a NanoSIMS and a beam diameter of about 240 nm. These profiles were then compared against cumulative theoretical diffusion distances calculated for a modeled time – temperature path of the contact aureole using the experimentally determined diffusion parameters for O, Fe and Mn in dolomite.The oxygen isotope profiles yielded diffusion distances of ca. 10 µm, corresponding to a formation temperature of about 550 °C, which is concordant with phase petrology and a timing for fluid infiltration at the onset of cooling of the contact aureole (i.e., non-isothermal evolution of the dolomite marbles). The Fe and Mn profiles were very sharp, with a diffusion length of about 150 nm. Such short diffusion length would be achieved at near-surface temperature and corresponding cooling timescale are several orders of magnitude smaller than those derived from the oxygen diffusion profiles. From the mineralogy and textures, a decoupling of the oxygen isotopes and Fe–Mn reaction interface can be ruled out, suggesting that the published diffusion parameters are not fully representative, either due to the experimental conditions or by the assumed diffusion mechanism of natural processes. This case study is not the first example in the literature where the diffusion rate of Fe and Mn in natural dolomite seems to be substantially slower than predicted by experiments. Thus, there is a need to re-assess the experimental diffusivities before Fe and Mn diffusion in dolomite can be reliably used to determine duration, cooling or heating paths of metamorphic processes.

Enhancing the performance of a greenhouse dryer with natural dolomite powder-embedded latent heat thermal energy storage unit and air-to-air heat recovery system

Greenhouse drying systems (GDSs) are grouped in direct-type solar dryers and are widely utilised because of their easy applicability, high product drying capacity and cost-effectiveness. In the present work, it is aimed to improve the drying performance of a GDS by using natural dolomite powder-embedded latent heat thermal energy storage unit (LHTESU) and air-to-air heat recovery system (HRS). In this context, three different types of GDSs have been designed and manufactured including a GDS with paraffin-based LHTESU, a GDS with natural dolomite powder-embedded LHTESU and a HRS-assisted GDS with natural dolomite powder-embedded LHTESU. Designed and manufactured GDSs have been experimentally analysed under the same environmental conditions. According to the experimentally achieved findings, combined utilisation of HRS and dolomite powder in the LHTESU reduced the drying time approximately as 36.36%. Moreover, highest instantaneous outlet air temperature was achieved as 51.4 °C in the system that used natural dolomite-embedded LHTESU and HRS. The exergetic efficiency of the GDS was upgraded as 46.21% by using the mentioned modifications in comparison to the base case (the system contains only paraffin-based LHTESU). In addition, specific moisture extraction rate for the analysed GDSs was attained between 0.96 and 1.52 kg.kWh−1.

The Use of Dolomite to Produce a Magnesium Potassium Phosphate Matrix for Radioactive Waste Conditioning

Magnesium potassium phosphate (MPP) matrix MgKPO4 × 6H2O is a known material for radioactive waste (RW) conditioning; magnesium oxide MgO is used in the classical method of matrix synthesis. The aim of the work was to investigate the possibility of using the widely available natural mineral raw material dolomite, incorporating mixed magnesium and calcium carbonate, for the production of this matrix. To control the quality of the samples obtained, their phase and elemental compositions, microstructure, density, volumetric and apparent porosity, compressive strength, and hydrolytic stability were studied. As a result, it was found that using dolomite powder pre-calcined at 720 °C for 1.5 h, samples of matrix whose properties meet the regulatory requirements for solidified RW were obtained. Thus, a new, cost-effective method of synthesis of the MPP matrix has been demonstrated to solve the RW solidification problem.

A novel and simple approach of rare earth ions (Y3+ and La3+) decorated nano calcium carbonate/ polyethylene glycol for photocatalytic degradation of organic pollutants in wastewater

Pristine and rare earth ions (Y3+ and La3+) decorated rhombohedral nano CaCO3/PEG were extracted from natural dolomite rock using a novel green route biomimetic synthesis. XRD analysis confirmed the crystal phase and doping of Y3+ and La3+ in the CaCO3/PEG. The FTIR analysis confirmed the presence of various functional groups in the synthesized nanoparticles. The obtained products exhibited good thermal stability at the temperatures up to 844 °C. The absorption and emission peaks were blue-shifted due to the impact of the doping ion concentration. The surface chemical compositions were analyzed using XPS. The direct and indirect bandgap energies of nCY1 (0.02 M Y3+: CaCO3/PEG) and nCL1 (0.02 M La3+: CaCO3/PEG) were 3.95, 3.27 eV (direct bandgap) and 2.52, 2.09 eV (indirect bandgap) respectively. The measured fluorescence quantum yields of nCY1 and nCL1 were 22% and 26%, respectively. FESEM with EDX mapping and HR-TEM with SAED analysis was used to determine the morphology, elemental mapping, and crystalline behavior. The photocatalytic activity of prepared samples were performed against methylene blue under UV irradiation. Based on photocatalytic results, nCL1 showed extremely high photocatalytic activity (92%). The effects of the scavenging agents were investigated using superoxide radicals, photogenerated holes, electrons, and OH radicals. Hence, the prepared samples could be an effective catalysts for significant environmental issues. This is the first study for preparing Y3+ and La3+ doped CaCO3/PEG nanoparticles from natural dolomite rock using a low-cost and nontoxic biomimetic method to get enhanced photodegradation efficiency.

Impacts of fresh bed materials on alkali release and fuel conversion rate during wood pyrolysis and char gasification

Bed materials provide efficient heat transfer and catalytic function in the thermochemical conversion of biomass, but their interactions with the fuel remain incompletely understood. In this study, the effects of bed materials on alkali release and fuel conversion during wood pyrolysis and CO2 gasification are investigated by online alkali detection combined with thermogravimetric analysis. The investigated bed materials include silica, sea sand, alumina and the natural ores olivine, ilmenite and dolomite. Only dolomite has a significant effect on fuel mass loss and alkali release during wood pyrolysis, while all bed materials influence char reactivity and alkali release during gasification. Sea sand, alumina and dolomite enhance the char gasification during the whole or most of the gasification process, which is related to alkali migration from the bed materials. All bed materials affect char reactivity and alkali release when the conversion approaches completion, and small amounts of some bed materials reduce the alkali release by an order of magnitude. The findings can be understood based on the chemical composition of the different materials. Silicon-rich materials reduce the levels of catalytically active alkali by formation of stable alkali silicates, and a similar explanation applies for ilmenite that captures alkali efficiently. Magnesium and calcium in contrast promote alkali release through their influence on alkali silicate chemistry. Analysis of char surfaces using scanning electron microscopy with energy dispersive spectroscopy indicates that low amounts of several elements are transferred from the bed material to the char where they may be directly involved in the char conversion process. The transferred elements are specific for each bed material and relates to their chemical composition. Mechanisms for material exchange between bed material and char are discussed.

Sustainable and economical dolomite-modified biochar for efficient removal of anionic dyes

Dyes induce acute to chronic illnesses in humans and aquatic animals. This study tested dolomite-modified rice husk biochar (DRHB) to eliminate anionic reactive dyes Remazol Brilliant Blue (RBB) and Reactive Black 5 (RB-5) from simulated wastewater solutions. DRHB was produced by pretreating rice husk biomass with the natural mineral dolomite (CaMg(CO3)2) solution following pyrolysis step at 700 °C for 4 h at 8 °C min−1. Pristine rice husk biochar (PRHB) was made by pyrolyzing rice husk for 4 h at 700 °C. The DRHB and PRHB were characterized via different techniques including, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and Scanning electron microscopy (SEM). Afterwards, DRHB was used to get rid of the dyes in the wastewater solutions, and the effects of dose, pH, and contact duration were studied. Both RBB and RB-5 exhibited maximal adsorption capacities of 52.07 and 35.518 mg/g at 50 °C, respectively, and the findings matched well with the Langmuir model, demonstrating monolayer adsorption. For this system, the pseudo-second-order fit is optimal, pointing to chemisorption of both substances. The outcomes presented higher adsorption for RBB (95.63%) compared to RB-5 (85.20%) at 70 mg/L concentration, pH 6, 4 hr. contact time, and 0.3 mg of DRHB dosage. The primary mechanism to remove of both dyes was chemisorption via π-π bond and hydrogen bond. These findings provide insights to build an economical, and sustainable anionic dyes removal technique especially for the third world nations.

Mechanism of sulfur migration and conversion in pyrolysis/combustion staged conversion process of high sulfur coal

To investigate the effects of circulating ash heat carriers and dolomite catalysts on sulfur migration in the coal pyrolysis/circulating fluidized bed combustion staged conversion process, five experiments of coal pyrolysis, ash/coal co-pyrolysis, coal pyrolysis catalyzed by dolomite, ash/coal co-pyrolysis catalyzed by dolomite and combustion of pyrolysis solid products were designed and carried out. By examining the effects of pyrolysis temperature, heating rate, coal-ash ratio and dolomite species on sulfur migration, the final distribution of sulfur-containing pollutants throughout the staged conversion process was systematically analyzed. The results showed that the separate mixing of ash heat carrier at final pyrolysis temperature of 600 °C increased the residual sulfur in solid phase from 79.29 % of raw coal pyrolysis to 90.00 %. When dolomite catalyst was added individually, the sulfur released into gas phase and tar was reduced from 18.28 % and 2.43 % of the raw coal to 13.14 % and 1.94 %, respectively. And Fe additive significantly improved sulfur resistance of the dolomite catalyst. The regeneration process has little effect on the sulfur fixation capacity of natural dolomite. When ash heat carrier and dolomite catalyst were simultaneously added to the system, the sulfur fixed in ash increased from 79.29 % of the raw coal to 91.27 %, and the sulfur fixed in natural dolomite and modified dolomite accounted for 4.32 % and 4.46 % of the total sulfur, respectively. In the combustion experiments of pyrolysis solid phase products, 43.57 %, 65.57 % and 61.44 % of sulfur was retained in the solid phase residue after combustion with circulating ash, circulating ash/natural dolomite and circulating ash/modified dolomite were added, respectively. Compared with direct combustion of coal, the staged conversion process resulted in a 55 % reduction of sulfur in the boiler flue gas. This study provides a theoretical basis for the purification of sulfur-containing pollutants in the staged conversion process.

New analytical method for the evaluation of heterogeneity in cation compositions of dolomites by micro-XRF and Raman spectroscopies.

Dolomite (CaMg(CO3)2) is an abundant carbonate mineral contained in sedimentary rocks and plays significant roles in water and carbon cycle in geo/cosmochemical environments. Since the cation compositions of carbonates are sensitive to the aqueous environment where they were precipitated and persisted, quantitative analysis of their cation compositions provides valuable information on the aqueous environments and their changes. The difficulty for the analysis of natural dolomite is that Mg2+ is continuously substituted by Fe2+ or Mn2+, and hence they sometimes possess micrometer-scale heterogeneity. Such heterogeneity carries quite important information on the gradual changes in aqueous environments due to changes in thermodynamic conditions and/or aqueous chemical compositions. In the present study, we explored a new quantitative scale to assess such heterogeneity of cation composition in natural dolomite and ferroan dolomite by combining X-ray fluorescence (XRF) and Raman spectroscopy. While the Fe + Mn content differed spot-by-spot, it was found that the Raman wavenumber and Fe + Mn content linearly correlated with each other. Since the spatial resolution of micro-Raman spectroscopy is as high as 1μm, it does not require vacuum conditions, and is free from so-called matrix effect faced in other methods utilizing X-Rays and electron beams, the proposed qualitative analytical scale can provide a useful tool to assess the cation compositions in dolomites found in nature.

Experimental investigation of a double-flow photovoltaic/thermal air collector with natural dolomite powder-embedded thermal energy storage unit

Photovoltaic/thermal (PV/T) systems have ability the produce both electrical and thermal energy in a same surface area. Additionally, utilizing PV/T systems help to reduce the solar panel temperature and therefore, improving the electrical output of the system. In this survey, it is aimed to improve the electrical and thermal effectiveness of a double-flow PV/T (DPV/T) system by using natural dolomite power-embedded thermal energy storage unit (TES). In this regard, three various types of DPV/Ts have been modelled, fabricated and experimented in the same test conditions. The first DPV/T structured as a conventional system. Second (DPV/T-TES) and third (DPV/T-DTES) systems have been upgraded with only paraffin-based and natural dolomite powder-embedded TESs, respectively. The experimentally obtained results indicated that utilizing dolomite particle-enhanced TES in the DPV/T system improved the electrical, thermal and total exergetic efficiencies as 10.83 %, 32.62 % and 54.07 %, respectively when compared to the conventional PV/T. Additionally, mean performance ratios of the tested systems were acquired between 0.62 and 0.69. The experimentally obtained findings showed the positive effect of utilizing natural dolomite particles-embedded TES in the DPV/T system on both electrical and thermal efficiencies.