Yanmin Wang

Ultrasonication-assisted synthesis of calcium carbonate nanoparticles

ABSTRACT This article presents a batch carbonation method with ultrasonication to synthesize monodispersed nanoparticles of calcium carbonate (CaCO3). The synthesis processes with and without ultrasonication were compared. The results showed that the application of ultrasonication into the synthesis caused a supersaturation of Ca2+ ions in the synthesis, leading to a rapid nucleation of calcium carbonate and improved the solute transfer as well as. It was also found that the effect of ultrasonication on the grain size of the nanoparticles synthesized was related to other synthesis conditions, such as initial temperature for carbonation, mass fraction of Ca(OH)2 suspension, and CO2 flow rate. The initial temperature applied for the carbonation was increased by at least 5°C when ultrasonication was applied. The nanoparticles formed in the presence of ultrasonication became smaller with a narrower particle size distribution at 6–12 wt.% of Ca(OH)2 suspension or at 1.28 l/h of CO2 consumed by per gram of Ca(OH)2 or more.

Continuous ultra-fine classification in a disc-stack nozzle centrifuge — effects of G-forces and disc geometry

Abstract This paper describes the use of a disc-stack nozzle centrifuge for wet classification of ultra-fine particles of calcium carbonate. The influences of G-force and disc geometry on the performance of the ultra-fine classification have been investigated. The results have demonstrated that the efficiency of the classification can be increased by (1) applying a relatively moderate G-force and (2) the use of stud spacer discs in the centrifuge. The increased extraction of the fine particles is related to the formation of the appropriate fluid velocity profile at a lower G-force and a circumferential motion without meridional barriers for the case of the stud spacer discs.

Aggregation between magnetite and hematite ultrafines utilizing remanent magnetization

Abstract It is indicated that hematite ultrafines ( μm ) in a well-dispersed surry are selectively aggregated with magnetite ultrafines in the absence of aggregating agents, high shear rates or an external magnetic field. The formation of the aggregates is attributed to the presence of their remanent magnetizations, mainly to that of magnetite. The mechanism of an aggregation of this type is discussed.

Sonochemical Synthesis of Magnetic Nanoparticles

Magnetite (Fe3O4) and Zn0.5Fe0.5Fe2O4 nanoparticles (NPs) were synthesized via sonochemical coprecipitation reactions with moderate ultrasound irradiation. The structure and crystalline/particle sizes of the synthesized NPs were determined by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM), and the magnetic properties were measured by vibrating sample magnetometry (VSM). The results show that NPs of smaller size and narrower size distribution can be synthesized via coupling of moderate ultrasound irradiation in coprecipitation reactions. In addition, magnetic NPs prepared in the presence of ultrasonic irradiation exhibit improved magnetic properties.

CARRIER COAGULATION OF CHROMITE FINES IN WET MAGNETIC SEPARATION

A carrier or piggy–back coagulation process was applied to improve the separation efficiency of chromite slimes in wet high–gradient magnetic separation. This was achieved by the addition of a coarse chromite fraction to the slime fraction ( 75, 53 and 38 μm. The results suggested that the 38 μm coarse fraction was the most effective in improving the process efficiency. Superior performance was also found to occur between pH 5 and 6. The results were discussed by computing the various components for potential energy of interaction between the slime particles and the carrier or piggy-back particles at a range of surface potentials in the absence or presence of the magnetic field.

Dry Comminution of Silicon Carbide Particles in a Fluidized Bed Opposed Jet Mill: Kinetics of Batch Grinding

This study investigated the batch grinding kinetics of silicon carbide (SiC) particles in a fluidized bed opposed jet mill by population balance modeling. The selection and breakage functions were obtained by the first Kapur function method. The breakage behaviors for various SiC particles obtained under different experimental conditions (such as inlet air pressure, feed load, and distance between nozzle outlet and jet meeting point) in the jet mill were discussed. In addition, a polynomial model was proposed to predict the relation between the Kapur function and the particle size in the jet mill. The product size distributions obtained under various operating conditions from the jet mill could be simulated by modeling.

Recent Activities in Magnetic Separation in Sweden

This paper describes some industrial applications of magnetic separation in Swedish mineral industry. Recent studies on magnetic treatment of minerals in Sweden are also presented. These studies involve selectivity of wet magnetic separation, wet magnetic recovery of mineral fines and ultrafines, sulphide processing by magnetic means, as well as dry magnetic purification of industrial minerals.

Prediction of Performance of an Industrial Poittemill in Production of Limestone Powders

Experimental data were collected from tests using an industrial-scale high-pressure roller mill named the Poittemill grinding limestone materials for a range of parameters (such as force pressure, circumferential speed of roll, and feed size) in a Nordkalk AB plant located in Ignaberga, Sweden. These data were used to develop models of throughput, size reduction, and energy utilization with the parameters. A performance model with a correction coefficient, which has been developed, is able to describe the Poittemill throughput at various force pressures and circumferential speeds of rolls. The materials leaked beside the rolls are found to be empirically related to the circumferential speed of roll in a given force pressure. It is shown that two major parameters, force pressure and circumferential speed of roll, have an influence on the median size (d50) of the ground product. Product fineness is decreased at a higher circumferential speed of roll or at a lower force pressure. The force pressure is the most dominant effect on energy utilization in the mill. The feed size used has a slight influence on the grinding results. Energy to the Poittemill for the comminution is utilized more efficiently at a lower force pressure or a higher circumferential speed of roll. Empirical models can predict the comminution characteristics with respect to the major parameters in the Poittemill system in dry mode. Product size-energy input relations have been also established, independent of the operating parameters used.

Tensile strength for splitting failure of brittle particles with consideration of poisson's ratio

The core mechanism of comminution could be reduced to the breakage of individual particles that occurs through contact with other particles or with the grinding media, or with the solid walls of the mill. When brittle particles are loaded in compression or by impact, substantial tensile stresses are induced within the particles. These tensile stresses are responsible for splitting failure of brittle particles. Since many engineering materials have Poissons ratios very close to 0.3, the influence of Poissons ratio on the tensile strength is neglected in many studies. In this paper, the state of stress in a spherical particle due to two diametrically opposed forces is analyzed theoretically. A simple equation for the tensile stress at the centre of the particle is obtained. It is found reasonable to propose this tensile stress at the instant of failure as the tensile strength of the particle. Moreover, this tensile strength is a function of the Poissons ratio of the material. As the state of stress along the z-axis in an irregular specimen tends to be similar to that in a spherical particle compressed diametrically with the same force, this tensile strength has some validity for irregular particles as well. Therefore, it could be used as the tensile strength for brittle particles in general. The effect of Poissons ratio on the tensile strength is discussed.

PURIFICATION OF FINE POWDERS BY A SUPERCONDUCTING HGMS WITH VIBRATION ASSISTANCE

In this study, a superconducting high gradient magnetic separator (HGMS) with a matrix vibration system in dry mode was utilised to purify fine calcite and quartz powders smaller than 38 µm. The effects of the operating parameters (particle size, magnetic field/average air velocity (Bo /Vo), the amplitude of vibration as well as the aperture size of the expanded metal matrix) have been presented. The mechanicallybased matrix vibration with the air blowing was recognised to be effective for dry purification of fine powdered materials at high magnetic fields. The function of the matrix vibration has been discussed. In addition, the results have been empirically correlated with the operating parameters used for the purification in the separator.