Laboratory Ball Mill Research Articles

The effects of grinding media shape on breakage rate

Cylindrical grinding media, which have a slightly spherical shape, called Cylpebs have recently been introduced. Comparative tests have been performed using Cylpebs and balls in a laboratory ball mill under the same conditions of mass and feed. Results show that a faster breakage rate is obtained using Cylpebs as the charge.

Effectiveness Of Gravity Concentration For The Beneficiation Of Itakpe (Nigeria) Iron Ore Achieved Through Jigging Operation.

This study investigates the1 effectiveness of gravity concentration for the beneficiation of Itakpe (Nigeria) iron ore achieved through jigging operations. Iron ore obtained from Itapke Iron Ore Mining Project, Kogi State, Nigeria which contains a very high amount of quartz as revealed by x-ray diffraction was crushed using the laboratory dodge crusher and ground in a laboratory ball mill. Particle size analysis was carried out over the range of +4750μm and -75μm in 12 different mesh sizes, and the ore was jigged in a Laboratory Denver Mineral Jig. The operating variables used to determine the recovery effectiveness of jigging include; particle size, dilution ratio and bedding thickness. Recovery of iron ore was assessed by determining the percentages of Fe in the underflow and overflow using the Atomic Absorption spectrometry (AAS) method. Optimum iron ore recovery of 71% was achieved when the jig was operated at medium stroke and speed, with a feed slurry of average dilution and at a particle size of 600μm.

Optimization of continuous ball mills used for finish-grinding of cement by varying the L/D ratio, ball charge filling ratio, ball size and residence time

During the last decade, semi-finish-grinding plants have been used more and more for the energy efficient grinding of high-quality cement. In 1999, it was found that by decreasing the ball charge filling ratio it was possible to lower the specific energy demand for grinding significantly. It was obvious, too, that the L/D ratio influences the specific energy demand and the mill throughput as well. Therefore, a huge test program was carried with a semi-industrial ball mill, which was operated in closed circuit. The mass-specific surface area of the two feed materials (intermediate product) used were quite typical for industrial semi-finish grinding plants. The values were 2200 and 3000 cm 2/g according to Blaine. The product finenesses were 3000 and 3800 cm 2/g, respectively. The L/D ratio of the ball mill was varied in four steps of 1.75, 2.1, 2.79 and 3.49, and the ball charge filling ratio was varied in three steps of 15%, 20% and 25%. The experiments clearly indicated that the optimal L/D ratio and the optimal ball charge filling ratio are different for each feed fineness. The influence of the ball charge grading on the specific energy demand, characterised by the average ball diameter, was tested by means of a discontinuous laboratory ball mill. The results showed that by using a finer ball grading the specific energy demand could be lowered considerably. The obtained results can be explained well by theoretical considerations regarding the ruling stress intensity and the number of stress events. The stress intensity expressed as the power input per ball is dependent on the ball diameter to the third power and only slightly dependent on the inner diameter of the mill. The number of stresses can be characterised by the average retention time of the ground material inside the mill if the ball charge grading remains unchanged. The optimal retention time depends not only on the feed material and the desired comminution result but also on the ball charge filling ratio and particularly on the L/D ratio. On the basis of the present results and considerations, a specific optimisation of ball mills in semi-finish-grinding plants can be done.

Control of ball mill grinding circuit using model predictive control scheme

Ball mill grinding circuits are essentially multivariable systems with high interaction among process variables. Traditionally grinding circuits are controlled by detuned multi-loop PI controllers that minimize the effect of interaction among the control loops. Detuned controllers generally become sluggish and a close control of the circuit is not possible. Model Predictive Controllers (MPC) can handle such highly interacting multivariable systems efficiently due to its coordinated approach. Moreover, MPC schemes can handle input and output constraints more explicitly and operation of the circuits close to their optimum operating conditions is possible. Control studies on a laboratory ball mill grinding circuit are carried out by simulation with detuned multi-loop PI controllers, unconstrained and constrained model predictive controllers and their performances are compared.

A quantitative approach to mechanochemical processes

A complex methodology has been developed in order to quantify the conditions of mechanical treatment in laboratory and commercial ball mills. The experimental determination of the collision frequency and the impact energy has been paralleled by an accurate numerical modelling of the balls and powder dynamics. The obtained results have been further confirmed by a direct inspection of the motion of balls and powder inside a transparent quartz reactor by means of high-speed video recording. The temperature of mechanochemical reactors has been also continuously monitored during the course of mechanical treatments. The methodology has been systematically applied to characterise on absolute basis the kinetic behaviour of a large variety of mechanically-induced structural and chemical transformations. In particular, systematic investigations have been performed on the amorphisation of intermetallic and binary systems, on the formation of extended solid solutions in immiscible systems, on the ignition of combustion-like reactions in metal-metalloid mixtures and on the hydrogen storage in nanocrystalline and amorphous multicomponent metallic alloys. Mechanochemical transformations appeared to be basically ruled by two different mechanisms characterised by simple asymptotic trends and sigmoidal curves respectively. An attempt to rationalise the observed mechanisms on a phenomenological basis has been made.

Effects of size distribution on flotation kinetics of Turkish sphalerite

The effects of size distribution on the flotation behaviour of sphalerite have been investigated in terms of kinetic parameters. In experimental studies, subsamples of a Turkish sphalerite ore were ground for different times using a laboratory ball mill. Timed batch tests were then undertaken using a pilot flotation column and the resulting recovery/time data were used in kinetic modelling. Results indicated that sphalerite floated rapidly at a medium particle size distribution (d80 = 0·125 mm in this case). In addition, a statistical analysis of data demonstrated that the flotation rate constant corresponded to a first-order model with rectangular distribution of floatabilities given by the equation:r = R∞(1-1/k2t[1-exp(-k2t]}

Effect of Medium Viscosity on Breakage Parameters of Quartz in a Laboratory Ball-Mill

The role and effect of liquid medium viscosity on breakage parameters (S and B values) of the batch grinding kinetic model was investigated by grinding a single feed fraction of quartz (20 × 30 mesh) in a batch ball-mill at fixed mill loadings and at 45 vol % solid concentration, using glycerol−water mixtures of different proportions. The primary breakage distributions (B values) were normalized and separated into three different groups for grinding in media viscosities of 0.001(water), 0.002−0.03, and 0.08−0.16 Pa·s, respectively, with higher viscosity range giving proportionally finer products. The disappearance grinding kinetics of the top size showed that the specific breakage rates (S values) depended both on the viscosity of the liquid medium and on the extent of grinding. The specific breakage rates of the top size increased with the fineness of grinding while the breakage of the smaller sizes proceeded approximately in a first-order manner as characterized by a characteristic breakage rate constant. The acceleration of the top-size breakage rates as grinding proceeded was represented by a parameter called the acceleration factor, which correlated reasonably well with the changing slurry effective viscosity. Alternatively, the acceleration factor can be presented in the form of a single generalized first-order plot for grinding at different medium viscosities. The first-order breakage rate constant decreased with increasing medium viscosity over the range from 0.001 to 0.16 Pa·s but not linearly. The proportional variation of net mill power did not match exactly with that of the breakage rate constant on increasing medium viscosity. On the basis of the analysis of grinding results, three grinding regimes were identified relative to the change in medium viscosity but their existence was not confirmed experimentally.

A liberation model for comminution based on probability theory

Mineral processing plants use two main processes; these are comminution and separation. The objective of the comminution process is to break complex particles consisting of numerous minerals into smaller simpler particles where individual particles consist primarily of only one mineral. The process in which the mineral composition distribution in particles changes due to breakage is called ‘liberation’. The purpose of separation is to separate particles consisting of valuable mineral from those containing nonvaluable mineral. The energy required to break particles to fine sizes is expensive, and therefore the mineral processing engineer must design the circuit so that the breakage of liberated particles is reduced in favour of breaking composite particles. In order to effectively optimize a circuit through simulation it is necessary to predict how the mineral composition distributions change due to comminution. Such a model is called a ‘liberation model for comminution’. It was generally considered that such a model should incorporate information about the ore, such as the texture. However, the relationship between the feed and product particles can be estimated using a probability method, with the probability being defined as the probability that a feed particle of a particular composition and size will form a particular product particle of a particular size and composition. The model is based on maximizing the entropy of the probability subject to mass constraints and composition constraint. Not only does this methodology allow a liberation model to be developed for binary particles, but also for particles consisting of many minerals. Results from applying the model to real plant ore are presented. A laboratory ball mill was used to break particles. The results from this experiment were used to estimate the kernel which represents the relationship between parent and progeny particles. A second feed, consisting primarily of heavy particles subsampled from the main ore was then ground through the same mill. The results from the first experiment were used to predict the product of the second experiment. The agreement between the predicted results and the actual results are very good. It is therefore recommended that more extensive validation is needed to fully evaluate the substance of the method.

助剤添加粉砕による粗粒子の粉砕除去・減量化に関する実験的検討―粉砕媒体材質（密度）の影響―

In this study, we conducted dry grinding tests of silica glass using a laboratory ball mill with and without methanol as well as wet grinding tests. We found that in the early stage of grinding the dry grinding with methanol reduces the coarse feed particles (1, 180-1, 000μm) at a faster rate than dry grinding without methanol and wet grinding. We also investigated the effect of grinding medium density on the reduction rate of coarse particles with size from 1, 000 to 75μm by conducting dry grinding tests with methanol using alumina or zirconia balls. The zirconia balls were more effective for shortening the grinding time than the alumina balls, whereas the alumina balls lowered the input energy required.

Automatic quantification of phases and mechanical characterization of materials based on Portland clinker modified with silica and alumina additions

Actual image analysis software allows the automatic quantification of the different main phases present in Portland clinker. This work studies, by optical microscopy analysis, the modification of porosity and relative amount of phases existing in plain clinker when increasing silica and alumina proportions. The compositions were dry mixed in a laboratory ball mill during 30 min. In all cases three different amounts of additions (3, 6 and 9 wt.%) were chosen. The different mixes were pressed by isostatic pressing (in wet bag) at 180 MPa. The sintering was carried out in air at 1400 °C during 30 min. All materials were polished, without etching, to reach the best contrast between porosity and material to analyse the level of porosity. The samples were etched with a mix of acetic acid and ethanol or hydrochloric acid to quantify the relative amount of main phases of materials. The obtained results were correlated with mechanical properties as bending strength and hardness.

Effects of slurry concentration and powder filling on the net mill power of a laboratory ball mill

The tests covered a range of slurry concentrations from 30 to 55 vol.% solid and fractional interstitial bed filling ( U) from 0.3 to 1.75, at a fixed ball load (30% of mill volume) and 70% of critical speed, using batch grinding of a feed of −30 mesh (0.6 mm) quartz. At a fixed slurry concentration, the net mill power versus U went through a maximum, and both the optimum value of U for maximum power and the maximum power varied with slurry concentration. A slurry concentration of about 40 to 45 vol.% solid and a U of approximately 1 gave the maximum power. An empirical equation is given that fits the data reasonably well. It was concluded that the fraction of the slurry that rotates with the balls, the inclination of the resulting rotating charge, and the expansion of the rotating charge are all factors that affect the power; the data were too limited to obtain precise descriptions of these effects. At a constant powder load ( U=1), the specific rates of breakage of the quartz were linearly proportional to the net mill power for the different slurry concentrations. However, this was not true if the mill power was changed by using water–glycerine carrier liquids to vary the viscosity, at a fixed solid concentration (45%). Thus, mill power alone does not define the breakage action.

Fine Dry Grinding of Zeolite in a Laboratory Ball Mill

AbstractThis paper presents the importance and usage of natural zeolites, which was recently recognized in the industry. Therefore, the grinding properties of natural zeolite were studied with the emphasis on a kinetic study in a ball mill. The experimental mill employed was laboratory sized, 200 mm diameter, 191 mm length, providing a total mill volume of 6000 cm3, with a total mass of 5.62 kg of steel balls of 25 mm diameter with a charge of 20% of the mill volume and with a rotation speed of 76 rpm. The breakage parameters were determined by using single sized feed fractions of −850+600 μm, −600+425 μm, and −425+300 μm for the zeolite samples. The Si (specific rate of breakage) and Bi, j (primary breakage distribution) values were obtained for those feed size fractions in order to predict the product size distributions by simulation for comparison to the experimental data. From the experimental results, Si values increased as the feed sizes became coarser, i.e., the highest Si value was 0.85 min−1 for −850+600 μm, while the lowest Si value was 0.65 min−1 for −425+300 μm feed ground in the mill. The Bi, j values obtained for the zeolite sample were γ=0.84, ϕ=0.61, and β=4.25. The breakage parameters obtained showed that the zeolite is broken faster than quartz and slower than calcite and barite in terms of the aT values reported previously at the same experimental conditions. The simulations of the product size distributions of zeolite were in good agreement with the experimental data using a standard ball mill simulation program. The slowing‐down effect was also seen in the mill after 4 min. of grinding.

A Novel Dry Route to ortho‐Functionalized Triarylbismuthanes That Are Difficult to Access by Conventional Wet Routes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Studies on high-performance blended/multiblended cements and their durability characteristics

Number of blends were prepared by intergrinding clinker, gypsum, fly ash, calcined clay, microsilica and limestone in laboratory ball mill in varying percentages, and their physical properties such as fineness, consistency, setting time and compressive strength have been determined. The durability tests on selected compositions were also conducted by exposing the mortar cubes separately in 5% Na 2SO 4 and 5% NaCl solutions till the age of 90 and 180 days. The performance was observed by compressive strength development criteria after various length of exposure. Results have been discussed and found that the durability of blended cement is higher than the ordinary Portland cement.

A novel dry route to ortho-functionalized triarylbismuthanes that are difficult to access by conventional wet routes.

When an aryl iodide bearing an electron-withdrawing group at the ortho position was milled together with bismuth shots and calcite grains in the presence of Cu powder and CuI using a laboratory ball mill, the corresponding ortho-functionalized triarylbismuthane was obtained in moderate to good yield.

The effect of slurry rheology on fine grinding in a laboratory ball mill

The kinetics of slowing down of breakage rates for fine wet grinding of 20×30 mesh quartz fraction was investigated as a function of slurry concentration in a laboratory batch ball mill. It was discovered that the slowing-down effect occurred to all particle sizes in the charge and at any slurry concentrations even for very dilute conditions. The slowing-down factor was defined and showed good correlation with the relative apparent viscosity of the slurry. Three different grinding regimes in fine grinding region were identified with reference to their rheological behavior. Hypotheses for the mechanisms of slowing-down effect were also given.

A study on the specific rate of breakage of cement materials in a laboratory ball mill

The specific rate of breakage (Si) in the widely accepted first-order expression of grinding rate is one of the important factors required to evaluate a grinding process, particularly for the initial grinding stage in various mill types.In this study, the effects of ball diameter and feed size on the specific rate of breakage were investigated on limestone, trass and clinker samples at batch grinding conditions based on a kinetic model. Eight different monosize fractions were prepared between 1.7 and 0.106 mm, using a √2 sieve series. The specific rates of breakage (Si) were determined from the size distributions at different grinding times, and the specific rates of breakage were compared for three different ball diameters (41, 25.4 and 9.5 mm).The results indicated that the variation of the specific rate of breakage with feed size of cement materials could be expressed. For the specific rate of breakage of each material, empirical equations were developed to express it as a function of feed size and ball diameter.

Experimental study on the grinding rate constant of solid materials in a ball mill

The grinding rate constant, in the widely accepted first-order expression of grinding rate, is one of the important factors required to evaluate a grinding process particularly for its initial grinding stage of various mill types. In this study, we conducted grinding tests on silica glass, limestone and gypsum using a laboratory ball mill, and measured the grinding rate constant of the feed size reduction. We investigated the effects of feed size and ball diameter on the grinding rate constant of the materials used when the mass of balls, mass of feed, and the mill's rotational speed were constant. The results indicate that the variation of the grinding rate constant with feed size of the materials can be expressed by revising the equation proposed by Snow. For the grinding rate constant of each material, empirical equations were developed to express it as a function of feed size and ball diameter.

Effect of carbide fraction and matrix microstructure on the wear of cast iron balls tested in a laboratory ball mill

The effect of carbide volume fraction from 13 to 41% on the wear resistance of high chromium cast irons was evaluated by means of ball mill testing. Martensitic, pearlitic and austenitic matrices were evaluated.The 50-mm diameter balls were tested simultaneously in a 40cm diameter ball mill. Hematite, phosphate rock and quartz sand were wet ground. The tests were conducted for 200h.Quartz sand caused the highest wear rates, ranging from 6.5 to 8.6μm/h for the martensitic balls, while the wear rates observed for the phosphate rock ranged from 1.4 to 2.9μm/h.Increasing the carbide volume fraction resulted in decreased wear rates for the softer abrasives. The almost complete protection of the matrix by carbides in eutectic microstructures caused the eutectic alloy to present the best performance against hematite or phosphate rock. The opposite effect was observed for the quartz sand. The quartz abrasive rapidly wears out the matrix, continuously exposing and breaking carbide branches. A martensitic steel presented the best performance against the quartz abrasive.With phosphate rock, the wear rate of 30% carbide cast irons increased from 1.46 to 2.84 and to 6.39μm/h as the matrix changed, respectively, from martensitic to austenitic and to pearlitic. Wear profiles of worn balls showed that non-martensitic balls presented deep subsurface carbide cracking, due to matrix deformation. Similar behavior was observed in the tests with the other abrasives.In pin-on-disc tests, austenitic samples performed better than the martensitic ones. This result shows that pin tests in the presence of retained austenite can be misleading.

Kinetics of fine wet grinding in a laboratory ball mill

The kinetics of batch wet grinding of quartz from a feed of 600×425 μm to a product of 80% less than 8 μm have been determined using sieving and laser diffractometer sizing for size analysis. A dispersing agent was added while proceeding to longer grinding times to prevent particle agglomeration in the mill. The specific rates of breakage ( S i ) values obtained were higher than those of dry grinding of quartz at the same experimental conditions, but the primary breakage distribution ( B i, j ) values were the same. Non-first order grinding was observed with continued decrease of the specific rates of breakage for finer grinding. The simulations of the product size distributions were in good agreement with the experimental data, providing the decrease in rates was included.