Fine Hematite Research Articles

Enhancement mechanism study on the fine hematite flotation by hydrophobic glass microspheres

Previous studies have primarily focused on the use of coarse mineral particles or hydrophobic materials as carriers, whereas this study was the first to investigate the impact of different hydrophobic glass microspheres (HGM-butane, HGM-pentane and HGM-octane) on the flotation behavior of fine hematite, and it revealed the interaction mechanism through Zeta potential and flotation kinetics analysis. The results of micro-flotation tests indicated that the addition of HGM-pentane can increase the flotation recovery of fine hematite from 65.27 % to 84.64 %, which was significantly better than using the collector NaOL alone. Zeta potential results showed that the incorporation of HGM-pentane caused a further negative shift in the surface potential of hematite, enhancing its adsorption capacity with bubbles. Flotation kinetics analysis demonstrated that the addition of HGM-pentane increased the flotation kinetic constant, promoting the flotation rate of fine hematite. This study revealed that the interaction between hydrophobic glass microspheres and fine hematite was primarily through hydrophobic forces and electrostatic attraction, forming a hematite-HGM complex, which in turn improved the flotation recovery of fine hematite. This provided a theoretical basis for the development of efficient flotation reagents and offers new insights into the efficient utilization of fine hematite.

High efficiency filtration and optimization of pelletizing performance of fine hematite concentrate using sulfuric acid filter aid: Behavior and mechanism

Following the application of anionic reverse flotation to fine low-grade hematite ore, a significant challenge emerges with elevated slurry viscosity and heightened moisture content in the resulting filter cakes. To address the challenge of dewatering during the filtration process of fine hematite concentrate, the impact of sulfuric acid filter aid dosage and filtration temperature on the filtration performance of hematite concentrate was systematically investigated in this study. In addition, the effect of sulfuric acid filter aid on the preparation of hematite pellets was also studied. The results revealed a significant decrease from 1.10 × 1010 1/m2 to 5.7 × 109 1/m2 in the specific resistance of the hematite filter cake when the sulfuric acid dosage was 1.2 g/kg and the filtration temperature was 20 °C. The mechanism underlying the enhancement of filtration performance of fine hematite concentrate by sulfuric acid was summarized. Sulfuric acid compressed the double electric layer on the surface of hematite concentrate particles, reducing the surface zeta potential and causing the aggregation of fine particles into larger ones. This led to an increase in filter cake porosity and compression of the hydration film thickness on particle surfaces, facilitating easier removal of filtrate from the filter cake. The appropriate dosage of bentonite for pelletizing was not significantly affected by sulfuric acid filter aid. Sulfuric acid improved the porosity, drying rate, and burst temperature of hematite green pellets. While the compressive strength of preheated pellets from sulfuric acid-assisted filtration of hematite concentrate showed a slight decrease, the compressive strength of roasted pellets was significantly increased.

Color Origin of Red Beds within the Danxia Basin, Southern China

Sedimentary facies color is an important paleoclimate indicator, but may be unreliable in thick continental red beds. The Danxia Formation is the landscape strata of the Danxia basin, and its color fluctuates between reddish-brown and reddish-purple vertically. This study examined the ferric oxides characteristics, distribution, and mineral composition of the Danxia Formation using a variety of analytical techniques, including optical microscopy, high-resolution scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and micro-Raman spectroscopy. The results indicate that the reddish-brown mineral is composed primarily of fine hematite with traces of goethite, while the reddish-purple mineral consists solely of fine hematite. These hematites exhibit a particle size range of submicron to micron and display various morphologies, including spherical, flake, and fibrous forms. Goethite particles are needle-shaped and often form star-shaped aggregates containing twins. Whole rock geochemical analysis reveals a strong positive correlation between iron and iron group elements, as well as phosphorus and rare earth elements. The findings suggest that the reddening of the Danxia Formation occurs during diagenesis, with fine hematite forming as a result of the alteration of iron-bearing detrital grains. In addition, vertical color variations in Danxia Formation are not attributable to the paleoclimate records, but rather the result of the differentiation of sediment sources. This study provides a novel viewpoint for examining the coloration of thick continental red beds in other regions.

Variation of Flow Hydrodynamic Parameters and Prediction of Particle Separation Indices in the Spiral Concentrator with the Regulation of Pitch-Diameter Ratio

The pitch-diameter ratio is an important design indicator affecting the separation performance of spirals. Based on the numerical simulation method, this paper systematically investigated the variation of flow hydrodynamic parameters in the spiral concentrator with the regulation of the pitch-diameter ratio. The radial distribution and variation trend of hematite and quartz particles with different particle sizes are further analyzed. Additionally, the separation indices of hematite and quartz with different particle size combinations were predicted. The results show that the tangential velocity, maximum radial velocity, velocity shear rate, and Reynolds number of fluid in each region decrease with the increase of the pitch-diameter ratio. The range of laminar flow gradually expands as the pitch-diameter ratio increases. There are significant differences in depth of water, ratio of inward and outward flows, and secondary flow velocity in different regions. Some flow hydrodynamic parameters at the inner trough reach relative equilibrium at a pitch-diameter ratio of 0.675. Hematite and quartz particles form a selective distribution in the trough surface, which comprehensively reflects the density effect, particle size effect, following flow effect of fine particles, and the effect of interstitial trickling of high-density fine particles. Fine hematite and coarse quartz form a large amount of misplaced material, and there is a corresponding mixing area. With the increase in pitch-diameter ratio, coarse and fine hematite particles migrate inward and outward, respectively. With the increase in pitch-diameter ratio, the misplaced amount of quartz on the inner trough decreases, but the outward migration distance of coarse quartz is smaller. Increasing the pitch-diameter ratio is beneficial to the separation of combined feedings of coarse hematite and quartz but unfavorable to that of fine hematite and quartz. The maximum separation efficiency of coarse hematite and fine quartz can reach 85.74%, and the iron grade of the inner product can reach 65.96% when the pitch-diameter ratio is 0.675 and the splitter location is 115 mm. The changing trend of separation indices in this feeding is closely related to the variation of fluid parameters and the change in the radial distribution of single mineral particles. The research results can provide references for the structural design of spirals, the selection of feed particle size, and the adjustment of splitter location.

Green hematite depression for reverse selective flotation separation from quartz by locust bean gum

Reverse cationic flotation is currently the main processing technique for upgrading fine hematite from silicates. Flotation is known as an efficient method of mineral enrichment that deals with possibly hazardous chemicals. Thus, using eco-friendly flotation reagents for such a process is an emerging need for sustainable development and green transition. As an innovative approach, this investigation explored the potential of locust bean gum (LBG) as a biodegradable depressant for the selective separation of fine hematite from quartz through reverse cationic flotation. Various flotation conditions (micro and batch flotation) were conducted, and the mechanisms of LBG adsorption have been examined by different analyses (contact angle measurement, surface adsorption, zeta potential measurements, and FT-IR analysis). The micro flotation outcome indicated that the LBG could selectively depress hematite particles with negligible effect on quartz floatability. Flotation of mixed minerals (hematite and quartz mixture in various ratios) indicated that LGB could enhance separation efficiency (hematite recovery > 88%). Outcomes of the surface wettability indicated that even in the presence of the collector (dodecylamine), LBG decreased the hematite work of adhesion and had a slight effect on quartz. The LBG adsorbed selectively by hydrogen bonding on the surface of hematite based on various surface analyses.

Properties and potential application of ozone-oxidized starch for enhanced reverse flotation of fine hematite

In this study, ozone as an eco-friendly oxidant was employed to improve the depressive performance of starch in the reverse flotation of fine hematite. Micro-flotation results showed that ozone-oxidized starch (OS) better depressed hematite flotation as compared to the native starch (NS). Particle surface wettability and size distribution analysis suggested that OS rendered the hematite surface more hydrophilic in the presence of an amine collector while maintaining a comparable flocculation performance to that of NS. Solubility, rheology, carbonyl and carboxyl content measurements, together with atomic force microscopy (AFM) imaging were performed to examine the variations in the structure and properties of starch upon ozonation and their correlation with the depressive performance of starch. It was found that ozone treatment not only increased starch acidity and solubility, but also concurrently depolymerized starch with the yield of low molecular weight derivatives. These favorable changes appeared to be responsible for the superior performance of OS. Furthermore, the stronger interaction of OS with hematite was verified by X-ray photoelectron spectroscopy (XPS).

Effect of Humic Acid Binder on the Preparation of Oxidized Pellets from Vanadium-Bearing Titanomagnetite Concentrate

In order to pursue the goal of low-carbon ironmaking, a new type of humic acid (HA)-based binder was applied to the preparation of oxidized pellets from vanadium-bearing titanomagnetite (VTM) in this work. Effects of the HA binder (or with limestone) on the balling, preheating, and roasting behaviors of VTM were comparatively studied with bentonite. The embedded features of each mineral phase in sintered pellets, especially the crystallization and growth state of hematite grains, were deeply investigated by XRD, optical microscopy, and SEM–EDS measures. The binder dosage can be cut down by 50% when HA was used instead of bentonite. Fine hematite grains in HA pellets evolved into plump interlocking grains with ~5% of limestone addition. Pseudobrookite and magnesioferrite spinel phase formed at the optimal sintering temperature of 1250 °C, which could hinder the crystallization of hematite and affect the strength of final pellets.

Cement Bonded Fine Hematite Particles and Carbide Slag as Oxygen Carriers for Chemical Looping Combustion

In this work, cement bonded fine hematite particles and carbide slag (CCIO) were proposed to act as oxygen carrier (OC) for chemical looping combustion (CLC) process. In the tests with CO/N2 as fuel, undecorated iron ore (UIO) and carbide slag decorated iron ore (CSIO) were used for comparison. The results showed that the CCIO oxygen carrier showed better and stable reactivity than UIO, while a lower and continuously decreasing reactivity for CSIO was obtained due to sintering occurring on its surface. The decoration ratio for CCIO was optimized, and the results indicated that CCIO20 displayed the best performance. The investigations on reactivity of UIO and CCIO20 were further conducted with bituminous coal as fuel, and gaseous products, carbon conversion processes and oxidation processes for these two samples were studied comparably. The results indicated that CCIO20 showed better performances than UIO. Twenty cyclic redox tests were performed for UIO and CCIO20, and the results showed better and more stable reactivity for CCIO20. Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses were used to characterize the physical and chemical properties of these two samples, and the results showed that the newly formed phase Ca2Al2SiO7 among combined OC particles exhibited better stability, which contributed to the enhanced reactivity for CCIO20.

Eco-Friendly Collectors for Flotation of Fine Hematite and Malachite Particles

The separation of fine mineral particles, especially using environmentally friendly approaches, is one of the main problems in the processing of low-grade ores and the re-processing of mining tailings. This work assesses the potential of biosurfactants as collectors in the flotation of ultrafine (smaller than 20 μm) particles of hematite and malachite. As biosurfactants, we test acetylated acidic (ac-ASL) and lactonic sophorolipids (ac-LSL). In addition, n-dodecyl-β-D-maltoside (DDM) is used as a model non-ionic alkyl disaccharide surfactant, and sodium oleate (NaOl) is used as a reference. The biosurfactants are characterized using surface tension and foam analysis. The interaction of the minerals with the surfactants is characterized using zeta potential, solubility, and single-mineral flotation. The collecting properties of the surfactants are compared for the ultrafine (− 20 μm) and coarser (38–90 µm) particle size in the two-mineral flotation of hematite and malachite against quartz. The ultrafine particle size improves the grade in the oleate flotation of hematite, as well as the grades in the DDM flotation of hematite and malachite, which is explained by the weak interactions of the metal oxides with fatty acids and DDM. At the same time, the flotation with ac-LSL and ac-ASL is highly tolerant to the ultrafine particle size. These results indicate that biosurfactants are an interesting alternative to conventional petroleum-based surfactants in the flotation of Fe and Cu oxides. Moreover, a proper selection of surfactants can help combat the problem of fines.Graphical

乾式機械的処理を利用した無溶媒均一沈殿法によるヘマタイトナノ粒子の合成

Hematite (α-Fe2O3) nanoparticles were synthesized by a solvent-free homogeneous precipitation method using urea hydrolysis via dry mechanical treatment of urea and ferric nitrate nonahydrate for activation. This novel method consists of high-energy ball milling of the raw materials and subsequent heating of the activated liquid precursor, which can provide smaller-sized nanoparticles than conventional methods. The milling and heating conditions were systematically investigated in detail. It was found that the hematite formation can be promoted by milling ferric nitrate nonahydrate and urea simultaneously under dry conditions even when relatively gentle milling and heating treatments were employed. The hematite nanoparticles had a similar crystallite size and particle diameter regardless of the conditions. This method can contribute to large-scale environmentally-friendly synthesis of fine hematite nanoparticles.

Aggregation process of fine hematite particles suspension using xanthan gum in the presence of Fe(III)

Aggregation is an economical and widely existing method to in hematite mineral processing. In order to achieve the aggregation of hematite particles, high-efficiency agents are required. In this work, the xanthan gum (XG) and Fe3+ were used to explore its aggregation effect on the fine hematite particles. The settling and adsorption experiments were conducted on hematite with XG in the absence and presence of Fe3+. The results show that it is difficult to settle hematite with XG alone, and XG exhibits excellent performance with the mass ratio of 2/1 (XG/ FeCl3) at pH 2–10 in the presence of Fe3+. Zeta potential measurements, Fourier transform infrared (FTIR), Microscope and X-ray photoelectron spectroscopy (XPS) analyses were performed to detect the underlying mechanism. The zeta potential, solution chemistry and FTIR analyses results show that the co-adsorption of XG, Fe(OH)2+, Fe(OH)2+ and Fe3+ is found on hematite surface through specific and electrostatic adsorption, respectively, and the hematite surface is also covered by Fe(OH)3(s) precipitation turned by Fe3+. XPS spectral investigations and microscope observations provide evidence in support of coordination interaction between ferric ions active sites and XG. In addition, the aggregation model of fine hematite particles suspension using XG in the presence of Fe3+ was drawn.

Kinetic analysis of the reduction of hematite fines by cold hydrogen plasma

This study deals with the reduction of hematite fines by cold hydrogen plasma in the temperature range of 360–450 °C. It aims to examine the rate-controlling processes of fine hematite reduction by hydrogen plasma. The gaseous reduction was also performed for comparison. The reduction experiments were performed in a DC pulsed plasma reactor and the phases were characterized by X-ray diffraction. Reacted fraction curves were obtained by using the gravimetric technique. The kinetic analysis suggests that the controlling step of the hematite reduction process by cold hydrogen plasma was the nucleation and growth of iron on the magnetite substrate. The controlling step for the gaseous reduction process was found to be the chemical reaction at the magnetite–gas interface. The activation energy values obtained for cold plasma and gaseous hydrogen reduction processes were 68.5 and 87.2 kJ/mol.

Enhanced effect of fine magnetite on the flotation performance of fine hematite in sodium oleate system

Enhanced effect of fine magnetite on the flotation performance of fine hematite in sodium oleate system

The flotation of fine hematite by selective flocculation using sodium polyacrylate

• Fine hematite was separated from fine quartz by PAAS flocculation flotation . • The hematite particle size increased by 52% due to PAAS selective flocculation. • The adsorption mechanism of PAAS on the hematite surface was discussed in detail. Fine hematite and quartz are particularly difficult to separate using classic flotation and magnetic separation methods because the particles were very small and readily reported to the wrong product. The effect of sodium polyacrylate (PAAS) on the flotation separation of fine hematite from quartz and its mechanism were investigated by micro-flotation experiments using NaOL as a collector, particle size analysis, zeta potential measurements, FT-IR, SEM analysis as well as XPS analyses. The flotation tests found that the flotation recovery of fine hematite increased observably to 94.51% from 68.69% by adding 4 mg/L PAAS before NaOL at pulp pH 7.3; in the separation of mixed hematite and quartz, the separation efficiencies of fine hematite with and without the addition of the PAAS are 85.71% and 68.84%, respectively. After treatment with the PAAS, the fine hematite was well flocculated so that the average hematite particle size increased to 26.73 μm from 17.69 μm, and the particle size distribution of hematite less than 17 μm decreased to 29.58% from 52.51%. Zeta potential variations indicate that the collector NaOL is able to adsorb on the hematite surface after flocculation by the flocculant PAAS whereas the adsorption of the PAAS on quartz plays an inhibitory role in the adsorption of collector NaOL on the quartz surface, considerably improving the floatability of fine hematite, and thus realizing the effective separation of fine hematite from fine quartz. Furthermore, FT-IR, SEM, and XPS analyses suggest that the flocculant PAAS adsorbs on the hematite surface in a scattered punctiform morphology via a chemical bond in which the Fe 3+ of the hematite surface reacts with the –COO – of PAAS to form dimers, including (RCOO) 2 2– or RCOOH-RCOO - .

Ultrasonic treatment improves the performance of starch as depressant for hematite flotation

In this study, ultrasonic treatment was introduced to enhance the depressive performance of starch in the reverse flotation separation of fine hematite from quartz. It was found that after ultrasonic treatment, starch was not only able to impart a higher surface wettability of hematite, but also better reduced the degree of entrainment of fine hematite, both of which alleviated the loss of hematite to the froth. Flocculation tests together with starch property characterization were conducted to understand the underpinning mechanism. It is interesting that ultrasonic treatment of starch led to stronger and more selective flocculation of hematite, which accounted for the reduced entrainment loss of fine hematite and benefited the concentrate Fe grade. It was also found that ultrasonic treatment enhanced the dissolution and acidity of starch with a simultaneous increase in the content of amylose, which in turn could contribute to the improved depression and selective flocculation of hematite.

Mineralogical Characteristic of Nanhong Agate with Black Seaweed Pattern Mineral Inclusion

Nanhong from Liangshan Yi Autonomous Prefecture of Sichuan Province, China has gained great popularity in the gem market in China for its vibrant colour. Its attractive orange-red colour is generated by fine hematite concentrations. Recently, a new kind of named seaweed pattern agate, belonging to the family of the Nanhong agates appeared in the local market of Liangshan Prefecture. Microscopic examination showed that the fine red and black grain minerals scattered in various forms such as silkiness and disseminated forms in the sample. Infrared spectrometer, Raman spectrometer and X-ray powder diffraction were used to study the gemmological and mineralogical characteristics of the The results proved that the main mineral component of the was quartz with a low relative content of moganite and high degree of order. The crystallinity of the is about 6.76. FTIR spectra showed a weak peak at 3 674 cm-1 related to OH-. Combined with the XRD testing result (d=8.418 A), it supported the existence of phyllosilicates in the Raman spectrum of red grain mineal showed peaks at 226, 245, 292 cm-1, which matched well with hematite. Meanwhile the spectrum of black grain was consistent with sulfide minerals (peaks at 342, 377 cm-1). Further testing results of scanning electron microscopy and back scattering diffraction confirmed that most of the black grain mineral is pyrite(FeAs(0.015-0.018 5)S(1.826-1.886)), which belongs to isometric system. According to Raman database, the last peak at 289 cm-1 was identical with chalcopyrite. All these evidence showed pyrite had a paragenetic relationship with chalcopyrite in some area of seaweed pattern agate. Another important features were that mineral components and morphological distribution of these black grains were obviously different from features such as Fe and Mn oxides and organic grains that appear in common seaweed pattern from other places, which may indicate that the origin of seaweed pattern agate is from Liangshan.

Reduction Kinetics of Fine Hematite Ore Particles in Suspension

Suspension reduction kinetics of hematite ore particles at 1710 K to 1785 K was described by the Johnson-Mehl-Avrami-Kolmogorov model with Avrami exponent of 1.405. The apparent activation energy is 105.5 kJ mol−1 with the rate determining step of nucleation and growth. The reduction degree of the hematite at the endpoint is a linear function of temperature and the logarithmic oxygen potential of the reacting gas. A peak function of reaction rate constant with particle size has been verified in this work, and the maximum value of the reaction rate is located at around 85 µm particle size. The influence of heat transfer on the reaction process has been evaluated. The results suggest that the heating-up process for large particles, 244 µm particles, for instance, cannot be ignored. It can retard the reaction rate compared to small particles. Normally, the reaction rate constant decreases linearly with the increase of ln[p(O2)] of the reacting gas mixture. However, 95 vol pct CO2 in the reacting gas can accelerate the reaction rate of thermal decomposition of hematite due to the emissivity of CO2 gas. It results in a higher reaction rate of 110 µm particles in 95 vol pct CO2-containing gas than that in other less CO2-containing gases.

Reduction Mechanism of Fine Hematite Ore Particles in Suspension

In order to understand the pre-reduction behaviour of fine hematite particles in the HIsarna process, change of morphology, phase and crystallography during the reduction were investigated in the high temperature drop tube furnace. Polycrystalline magnetite shell formed within 200 ms during the reduction. The grain size of the magnetite is in the order of magnitude of 10 µm. Lath magnetite was observed in the partly reduced samples. The grain boundary of magnetite was reduced to molten FeO firstly, and then the particle turned to be a droplet. The Johnson-Mehl-Avrami-Kolmogorov model is proposed to describe the kinetics of the reduction process. Both bulk and surface nucleation occurred during the reduction, which leads to the effect of size on the reduction rate in the nucleation and growth process. As a result, the reduction rate constant of hematite particles increases with the increasing particle size until 85 µm. It then decreases with a reciprocal relationship of the particle size above 85 µm.

Tannin: An eco-friendly depressant for the green flotation separation of hematite from quartz

Reverse cationic flotation is the most known beneficiation method for the separation of fine hematite particles from silicates. In this process, the depression of the hematite surface is an essential factor. Thus, the development of environmentally friendly depressants plays a critical role. Tannin (TA) as a natural and eco-friendly organicreagent has not yet been considered for such a purpose. Through the reverse cationic flotation, the depression effect of TA was investigated by single and mixture of minerals. Micro-flotation tests and wettability analysis based on contact angle measurements by the captive bubble method (CBM) were conducted. The surface adsorption mechanism of TA on the hematite and quartz was explored through turbidity, zeta-potential measurements, surface adsorption tests, and Fourier transform infrared (FT-IR) analyses. The micro-flotation results indicated that TA could selectively depress more than 90% of hematite, while its effect on quartz floatability was negligible (<8% depressing). Surface wettability analysis demonstrated that TA in the presence of 30 mg/L collector could significantly increase the work of adhesion of hematite from 135.5 to 143.1 erg/cm2, whereas it increased the work of adhesion of quartz from 117.1 to 120.7 erg/cm2. Surface adsorption analysis depicted that in the presence of 100 mg/L TA, the adsorption amount of TA on the hematite surface was 0.99 mg/g, while this amount for quartz was 0.17 mg/g (around 6 times lower than hematite). Turbidity measurements, applied to clarify the aggregation – dispersion behavior of pure minerals in the TA presence, showed that TA had a dispersion effect on the quartz particles, whereas TA caused hematite aggregation. Surface analyses proved that TA selective adsorption occurred on the hematite surface mainly by chemisorption. In contrast, poor physical adsorption was the main interaction between TA and the quartz surface.

Influence of aggregation/dispersion state of hydrophilic particles on their entrainment in fine mineral particle flotation

Mechanical entrainment of −10 μm gangue particles affects flotation selectivity and dilutes concentrate grade in fine minerals flotation. This study investigated the effect of aggregation/dispersion behaviors of fine hydrophilic particles on their entrainment in batch flotation using quartz and hematite as model minerals. Two structurally similar polysaccharides corn starch and corn dextrin were used as polymer depressants and octadecylamine acetate (ODA) was used as a collector. Batch flotation of fine hematite-quartz mixtures indicated that lower percentages of Fe was recovered into froth using corn starch than corn dextrin; however, similar Fe recoveries in froth were obtained in coarse hematite-quartz mixtures with the two reagents. It was confirmed that the amount of Fe recovery in froth was positively correlated with the proportion of fine hematite in the feed when corn dextrin was used as a depressant. Experimental data collected from batch flotation were fitted to Warren’s models, indicating that the fine hematite was primarily recovered into froth through entrainment rather than true flotation in the presence of high dosage of corn starch or corn dextrin as a depressant (>500 g/t). The surface wettability of mineral particles was studied by micro-flotation and solvent extraction methods. The results showed that the surface hydrophilicity of hematite induced by corn starch or corn dextrin in the presence of ODA was in an identical range. The real-time FBRM measurements coupled with microscope imaging were carried out to monitor particle aggregation/dispersion behaviors in suspension. The results showed that corn starch can aggregate fine hematite and thus reduce their entrainment in batch flotation, while hematite remained dispersed in slurry by corn dextrin and aggravate its entrainment. In addition, a two-stage aggregation process and the formed flocs were observed in FBRM and microscope tests, which provide evidence for the feasibility of the proposed two-stage aggregation/flocculation flotation concept for fine and ultrafine mineral particles.