Early Stage Of Grinding Research Articles

Study on Quantitative Separation Method of Grinding Characteristics of Multi-Component Complex Ore

Based on batch grinding method and normalization idea, a conical ball mill is used and a quantitative separation method of grinding characteristics of multi-component complex ore is proposed. The results show that the feed sizes of polymetallic complex ore have an obvious influence on the particle size distribution of intermediate grinding products in the early stage of grinding. However, the influence of the feed size is relatively insignificant on the particle size distribution of intermediate grinding products in the middle and late grinding stages. The grinding product t10 is negatively correlated with the feed sizes of ore when the grinding force is applied to the ore. At the same time, it has a simple positive linear relationship with the grinding time. The contribution rates of component minerals pyrrhotite, sphalerite and quartz to the grinding characteristics of the ore are 28.64%~37.74%, 39.93%~51.84%, 16.07%~28.39%, respectively. Therefore, the order of contribution of component minerals to the grinding characteristics of ore is sphalerite > pyrrhotite > quartz. The results provide new insights for the subsequent study of grinding characteristics of multi-component complex ores.

Research on the grinding characteristics of lignite based on grinding kinetics

ABSTRACT Aiming to explore the limitation of Hardgrove Grindability Index (HGI) and broken behavior of lignite, coal samples were ground for different minutes in the Hardgrove mill. Experiments show that the grinding kinetics can describe the grinding process of coal well. For the same kind of coal, the grinding kinetic parameters k and m of a certain particle size can be regarded as constants. The particle size of the particles to be ground R has a power function relationship with the parameter k. The initial particles appeared selective grinding during the grinding process. From the perspective of the index T10 (a size of 1/10 of the initial particle size) and grinding rate, HGI has a poor description of continuous lignite grinding. In this case, the grinding kinetic parameter k of the same size of lignite can be used to discuss the grindability of different coal samples. Generally, the larger the k of the same size coal, the higher the grindability. The lattice size and mosaic morphology of ash forming minerals affect the grinding rate of coal samples. Raw coal with low ash content is more likely to liberate a large amount of minerals in the early stage of grinding.

Structural Disorder of Mechanically Activated δ-MgCl2 Studied by Synchrotron X-ray Total Scattering and Vibrational Spectroscopy

A combination of synchrotron X-ray total scattering and molecular simulation is a powerful approach for reliable determination of the structure of δ-MgCl2 as an indispensable component of heterogeneous Ziegler–Natta catalysts. Here, the same approach is applied to mechanically activated MgCl2. Four types of mechanically activated MgCl2 samples are prepared using ball-milling in the absence and presence of different donors. The development of structural disorder along the grinding time is compared. It was found that the presence of donors accelerates the formation of δ-MgCl2 in an early stage of grinding, while elongated grinding eventually results in δ-MgCl2 with similar extents of structural disorder in the absence and presence of different donors. The FT-IR investigation consistently verified the morphological similarity between the firmly ground samples. Thus, the structure of δ-MgCl2 is likely governed by mechanical energy when sufficiently ground.

Effects of dry grinding on the structure and granularity of calcite and its polymorphic transformation into aragonite

The structure and granularity of calcite were measured during dry grinding in a ball mill by X-ray diffraction, Fourier transform infrared spectroscopy and laser diffraction, and its morphology was observed by a scanning electron microscope. During the early stage of grinding (0–10min), the median particle size and X-ray diffraction intensity of the calcite decreased, while the full width at half maximum increased as grinding progressed. During the middle grinding stage (20–300min), the grain size and crystalline degree of ultrafine calcite particles no longer changed with time; this was attributed to aggregation, which hindered the breakage of particles. During the final grinding stage (360–720min), a polymorphic transformation of calcite into aragonite took place.

Effect of Dry Grinding of Pyrophyllite on the Hydrothermal Synthesis of Zeolite Na-X and Na-A

Zeolite Na-X and Na-A were synthesized by mechanochemical activation of pyrophyllite and pyrophyllite-gibbsite mixture followed by hydrothermal reaction in NaOH solution at 75°C under atmospheric pressure. The formation of zeolite Na-X and Na-A was depended on the degree of activation caused by grinding; i.e., grinding accelerated the dissolution of loosely bonded Si substances rather than Al ones of the ground pyrophyllite particles leading the Si/Al molar ratio close to 1.2, which is favorable for the formation of zeolite Na-X. The mixed grinding of pyrophyllite and gibbsite enabled us to synthesize zeolite Na-A monophase. In the early stage of grinding within 60min, the hydroxysodalite (HS) phase was detected, however, HS disappeared completely when the grinding time extended to 120min. The highest crystallinity (I/I0 )o f zeolite Na-A synthesized was estimated to 0.93 at the mixture with Si/Al molar ratio of 1.2. [doi:10.2320/matertrans.M2014127]

Storage of CO<sub>2</sub> in Low Al<sub>2</sub>O<sub>3</sub> EAF Oxidizing Slag by Grinding with Vibration Mill

The investigation of the behavior of CO2 absorption into the low Al2O3 electric arc furnace (EAF) oxidizing slag under wet grinding was investigated in this paper. The slag was wet ground in the vibration ball mill in the presence of CO2 at room temperature. The observation of the CO2 absorption was made with constant pressure method. The CO2 absorption increased steeply in the early stage of grinding. It occurred simultaneously with the grinding and immediately ceased when the grinding was stopped. The CO2 absorption occurred at the interface between the slag and the water which was saturated with CO2. The CO2 absorption increased as the finer particles were formed by the grinding process, and as the interface between slag and water was increased by the vibration process. A large amount of CO2 absorption and high conversion ratio was observed in the oxidizing slag with low Al2O3 in comparison with those of the slag with the high Al2O3 content.

Behavior of CO2 Absorption in Wet-grinding of Electronic Arc Furnace Reducing Slag by Vibration Ball Mill

A fundamental study was carried out in order to fix CO2 on slag. The electronic arc furnace reducing slag was wet-ground by a vibration ball mill under CO2 atmosphere. The effect of grinding conditions on the behavior of CO2 absorption was investigated.The rate of the absorption of CO2 under wet grinding was larger than that under dry grinding. The total amount of CO2 absorption increased with the increase in total amount of the slag and water in case that the weight ratio of the water to the slag was kept constant. The CO2 was fixed as CaCO3 and Ca4Si2O6(CO3)(OH, F)2. Any compounds of Mg were not detected by XRD after the experiment. In the early stage of grinding, the CO2 was absorbed even if the grinding was stopped. The concentration of Ca in the water was larger than the solubility of Ca(OH)2. Hence, the absorption of CO2 was determined by the surface reaction that consisted of chemical reaction and mass transfer in liquid. In the latter stage of grinding, the CO2 was not almost absorbed immediately after the grinding was stopped. The concentration of Ca in water was small. Accordingly, the absorption of CO2 was influenced by the dissolution of slag into water.The amount of the exhausted CO2 was calculated from the electronic power which was necessary for operating this experimental apparatus. The amount of CO2 absorption was larger than that of the exhausted CO2 from a solar, an atomic, a wind and a water power plant.

Reaction between CO 2 and CaO under dry grinding

This study was carried out to investigate the reaction between CO 2 and materials that contain CaO under dry grinding. Chemical reagent CaO was used in this experiment, and waste concrete was also tested to examine the feasibility of CO 2 sorption into it. Samples were ground in a CO 2 atmosphere by a centrifugal ball mill. The reaction was measured with the constant volume method. The effects of amount of sample, the number and diameter of balls, the concentration of CO 2 in the mixture of CO 2 and air and the rotational speed on the CO 2 sorption were examined. The amount of the CO 2 sorption under grinding was larger than that without grinding. The grinding enhanced the reaction between CaO and CO 2. The CO 2 sorption steeply increased with time in the early stage of grinding. After that, it increased gradually. The CO 2 reacted with the CaO at the surface layer of the newly exposed surface of the CaO particles during the grinding. The initial sorption rate of CO 2 was related with the shear force. In the latter stage of grinding, the grinding process caused the CaO particles to agglomerate. As a result, the sorption of CO 2 became slow. It was found that the waste concrete had high potential for sorption of CO 2 by means of dry grinding.

振動ボールミルによる電気炉還元スラグの湿式粉砕時の二酸化炭素吸収挙動

A fundamental study was carried out in order to fix CO2 on slag. The electronic arc furnace reducing slag was wet-ground by a vibration ball mill under CO2 atmosphere. The effect of grinding conditions on the behavior of CO2 absorption was investigated.The rate of the absorption of CO2 under wet grinding was larger than that under dry grinding. The total amount of CO2 absorption increased with the increase in total amount of the slag and water in case that the weight ratio of the water to the slag was kept constant. The CO2 was fixed as CaCO3 and Ca4Si2O6(CO3)(OH,F)2. Any compounds of Mg were not detected by XRD after the experiment. In the early stage of grinding, the CO2 was absorbed even if the grinding was stopped. The concentration of Ca in the water was larger than the solubility of Ca(OH)2. Hence, the absorption of CO2 was determined by the surface reaction that consisted of chemical reaction and mass transfer in liquid. In the later stage of grinding, the CO2 was not almost absorbed immediately the grinding was stopped. The concentration of Ca in water was small. Accordingly, the absorption of CO2 was influenced by the dissolution of slag into water.The amount of the exhausted CO2 was calculated from the electronic power that was necessary for operating this experimental apparatus from various power plants. The amount of CO2 absorption was larger than that of the exhausted CO2 from a solar, an atomic, a wind and a water power plant.

ＮＴＣサーミスタ合成に及ぼす粉砕の影響

Starting raw materials prepared by a thermal decomposition of a mixture obtained from aqueous solutions of Mn, Co, Ni nitrates, were ground under dry (in air) and wet (in water and alcohol) conditions by a tumbling ball mill to investigate sinterability and characteristics of NTC thermistor. The dry grinding causes aggregation of fine particles even in early stage of grinding, while the wet grinding reduces the particle size of the product. The sintered bodies from the products ground in wet using water possess large cracks, while they are fairly free from the defects when the mixture was ground in alcohol. Wet grinding in methanol with high (μ/V) value is more advantageous for producting dry fine particles, resulting in the improvement in characteristics of NTC thermistor with high density.

Influence of vibration grinding and calcination on the physico-chemical properties of Egyptian kaolinite

The effects of vibratory grinding and calcination on the structure and reactivity of Kalabsha kaolinite were studied by means of XRD, IR, DTA and surface area determination. Leaching experiments on ground and calcined samples were carried out using 20% HCl for aluminum extraction. At the early stages of grinding, partial destruction of stacked kaolinite layers occurred. These changes were associated with an increase in surface area due to formation of fine grains with numerous boundaries. Further grinding, as well as calcination, led to deterioration of the kaolinite structure. A significant increase of surface area was observed, starting from 18 m2/g for the original sample to a maximum of 42 m2/g after 120 minutes of grinding and 30 m2/g after calcination at 300°C. The extraction of aluminum after 30 minutes leaching time was about 97% for kaolinite ground for 240 minutes, and about 93% for kaolinite calcined at 550°C.

Fracture mechanisms and particle shape formation during size reduction of a model food material

The importance of particle shape to powder properties warrants examination of the effect of size reduction on particle shape formation. In this study, a model food material (dried gelatinized starch) was comminuted in an impact breakage gun, a hammer mill (with and without a screen) and in a blender. After sieving, particle shape at selected sizes was assessed as deviation from sphericity. Generally, particle shapes were elongated at smaller size, except for those produced by unscreened hammer milling. Particle shapes were unaffected by impact velocity in the gun, but were rounded by increased milling. Fractography was used to demonstrate how elongated particles formed. During fracture, fracture fronts were disturbed by air holes in the material, creating cleavage steps. Subsequent undercutting of the steps as fracture planes spread released the elongated particles. Such particle formation mechanisms may account for anomalous size distribution results at early stages of grinding. Particle shape differences between mills and single impact breakage were ascribed to particle selection mechanisms surmised to be operating in the mill. Both material properties and the size reduction method were shown to affect particle shape, thus fracture progress in a given material should be studied if particles of specific shapes are to be produced by comminution.

Effect of dry grinding on ion-exchange characteristics of synthetic mordenite

The changes in ion-exchange characteristics of synthetic mordenite ground by a planetary ball mill under dry conditions were investigated using radioisotopes of 137Cs and 85Sr as tracers. The self-diffusion of Cs + in the mordenite sample was facilitated in the initial stage of grinding, while it was leveled off for the further operation. The relative amount of Cs + immediately exchanged in the mordenite sample was gradually styptic to a constant value with increase in grinding time after showing a rapid reduction in amount in the early stages of grinding. High selectivity of the mordenite sample for Cs + against Sr 2+ observed in acidic solution diminished obviously with an increase in grinding time.

FORMATION OF MULLITE FROM GROUND PRODUCT OF A KAOLINITE-ALUMINUM TRIHYDROXIDE MIXTURE BY SOLID PHASE REACTION

The present paper describe the effect of grinding a kaolinite/aluminum-trihydroxide mixture using a planetary ball mill on the structure of the ground product and the mean thermal expansion coefficients of samples sintered from the unground and ground mixtures. The size reduction of the mixture predominates in the early stage of grinding and the obtained fine particles aggregate subsequently with an increase in grinding time. The crystal structure of the mixture is collapsed easily into a disordered one, of which amount increases with an increase in grinding time. Only mullite phase was detected in the sintered body of the ground products at relatively lower temperature 1523K except for anatase as an inherent impurity, whereas corundum, cristobalite and Al-Si spinel phases besides mullite were formed in the sintered body of the unground mixture. The thermal expansion coefficients of sintered bodies of the 120 minutes-ground mixture are considerably lower than those of the unground mixture by about 10%. Consequently, the planetary milling enables us to improve the uniform mixing state at the atomic scale resulting in direct formation of mullite with high purity at relatively low temperature with a lower thermal expansion coefficient of the sintered body

粉砕に伴う合成モルデナイトのメカノケミカル変化 陽イオン吸着特性変化について

The effect of dry grinding on the adsorption characteristics, e. g., distribution coefficient and saturated amount of adsorbed cations, of synthetic mordenite has been studied using a radioisotope of 137Cs+ as a tracer. The grinding operation for different periods of time, i. e., 15 to 360min, was carried out using a planetary ball mill.The grinding operation had no effect on the distribution coefficient onto the mordenite sample at the relatively lower concentration of Cs+ in the neutral and alkaline solutions, though the coefficient significantly decreased in the acidic solutions with an increase in grinding time. The saturated amount of Cs+ adsorbed on the mordenite sample in both neutral and acidic solutions decreased markedly during the early stage of grinding. However, for more than 30 minutes of grinding, the amount of absorbed Cs+ in the neutral solution increased slightly, while in the acidic solution it gradually decreased with grinding time. These observations may be interpreted from the formation of the hydroxyl group on the fractured surface, as well as from the considerable distortion of the channel structure of mordenite induced by grinding.

Effect of Mixed Grinding of Powders on Superconducting Properties of YBa2Cu3O7- Ceramics.

The effect of mixed grinding of Y2O3, BaCO3 and CuO powders using a planetary ball mill before heat treatment of the crystal structure and the superconducting properties of the sintered body has been investigated by XRD, SEM, TEM-EDX, EELS, and measurement of the critical temperature and critical current density.The size reduction of powders predominates in the early stage of grinding, after which aggregation of the obtained fine particles takes place. The homogeneity in the mixture is improved with increase in grinding time. The critical current density of the sintered body changes with increase in grinding time of the mixture and reaches maximum value at 60 minutes grinding, while the critical temperature is almost independent of grinding time.

Effect of Dry Grinding on the Structures and Physical Properties of Pyrophyllite and Talc by a Planetary Ball Mill

The effect of dry grinding by a planetary ball mill on the structures and physical properties of pyrophyllite and talc minerals has been investigated by X-ray diffraction, TG-DTA, density and specific surface area measurements, particle size analysis and SEM observation.Size reduction of these two minerals was dominated in the early stages of grinding. The obtained fine particles of ground talc and pyrophyllite were subsequently found to aggregate with an increase in grinding time. X-ray diffraction patterns showed that the pyrophyllite and talc structures progressively deformed from a crystalline state to a disordered one with an increase in grinding time. Both ground pyrophyllite and talc specimens exhibit lower temperature dehydroxylation and new exothermic reactions. The ground pyrophyllite recrystallizes to mullite and y -alumina, while the ground talc changes to enstatite and amorphous silica when heated.

Thermal behavior of mechanically amorphized talc

Changes in the structure of talc and processes in its dehydration and transformation into enstatite due to mechanical activation have been studied. The structure of talc became amorphous in the early stages of grinding. A decrease in the dehydration temperature and the appearance of an exothermic DTA peak took place following mechanical activation. The amount of heat evolved, estimated from the DTA peak area, increased with grinding time, but the temperature of the exothermic peak remained constant at 822°C. During mechanical activation, substantial dehydration took place, indicating a preferential destruction of the central layer of talc comprising Mg(OH) 2, leaving highly mobile O 2−. The formation of enstatite from mechanically amorphized talc is explained by postulating the recombination of O 2− ions with the partially broken SiO 4 tetrahedra as the rate-determining step.

Effects of Grinding on Dielectric Properties of BaTiO3 Powders

Barium titanate (BaTiO3) powder was mechanically ground over the period of 1 min∼100 h in air using an agate mortar and pestle, and changes in the crystal structure and dielectric properties were studied. The particle size of the BaTiO3 powder was reduced in the early stage of grinding. With increasing the grinding time for more than 100min, the crystallinity of the BaTiO3 powder was lowered and the dielectric constant decreased. However, dielectric dissipation factor (tan δ) and AC impedance of the BaTiO3 powder did not show significant change associated with grinding.

Effect of dry grinding on iori-exchange characteristics of synthetic mordenite

The changes in ion-exchange characteristics of synthetic mordenite ground by a planetary ball mill under dry conditions were investigated using radioisotopes of 137 Cs and 85Sr as tracers. The self-diffusion of Cs+ in the mordenite sample was facilitated in the initial stage of grinding, while it was leveled off for the further operation. The relative amount of Cs+ immediately exchanged in the mordenite sample was gradually styptic to a constant value with increase in grinding time after showing a rapid reduction in amount in the early stages of grinding. High selectivity of the mordenite sample for Cs+ against Sr2+ observed in acidic solution diminished obviously with an increase in grinding time.