Dry Comminution Research Articles

Commercialisation pathway for low energy wet/dry gyratory rolls crusher comminution technology

Comminution for mining and cement industries accounts for over 2 % of global energy consumption and an innovative Gyratory Rolls Crusher (GRolls®) technology has been developed in South Australia to reduce energy and water consumption, providing dry and wet crushing from ∼ 20 mm to 20µm fractions without media, replacing up to two stages of size reduction. The GRolls® is a compression based particle size reduction device, designed to generate fine and ultra-fine products from coarse feeds, by simultaneously applying pulsed compression and shear forces to a packed particle bed. The breakage mechanisms initiated by these forces include compression breakage, inter-particle compression, induced tensile failure and particle shear forces generated by a gyrating roll.The paper presents the commercialisation pathway of the GRolls® technology, from “proof of concept” laboratory scale Alpha prototype and concept design of an upscaled Beta prototype for a pilot plant. A systematic progression of laboratory scale testing of a wide range of feed materials through the Alpha prototype was undertaken to confirm the ‘”proof of concept” design and identify the many design variables and operational configurations that affect the GRolls® crushing and energy performance. The test results were evaluated against currently available comminution solutions such as the High Pressure Grinding Rolls (HPGR) and Vertical Rolls Mill (VRM) in which the mining section is moving towards to provide more economical dry comminution and a progression towards partial to full dry process flowsheets.The commercialisation pathway has confirmed the broad performance range and energy consumption of the GRolls® which could be modularised in the near future to support new and existing low grade mining operations in remote areas restricted by limited water and power infrastructure.

Comparison of particle size and shape distribution of corundum produced by industrial ball mill and material bed compression

Comminution of corundum is a challenging task, as it has very high hardness and compression strength, and it is also a very abrasive material. Selection of the best comminution process for each particle size thus has a great importance. But for this, first we must understand the effects of different type of stresses and comminution methods used for the dry comminution of corundum. In this article the comparison of particle size and shape distribution of corundum produced by material bed compression and classic ball mill grinding is carried out. Comminution experiments were carried out in a laboratory scale piston press, to achieve material bed compression like in HPGR technology, and in a conventional industrial scale ball mill for particle-particle, particle-grinding media interaction. The results showed that the products of the two comminution methods have a significant difference both in particle size and shape distribution.

Effects of Pretreatment on the Yield of Peanut Oil and Protein Extracted by Aqueous Enzymatic Extraction and the Characteristics of the Emulsion.

Effects of comminution on peanut particle size and yield of peanut oil and protein were analyzed. Additionally, the emulsion properties (surface protein concentration, particle size, and ξ-potential) were compared. Moreover, different demulsification methods were used to investigate the emulsion stability. Results showed that the yield of peanut oil and protein was highest (87.23% and 82.05%, respectively) after dry comminution for 72 s. Upon wet comminution for 120 s, the yields of peanut oil and protein were 89.91% and 84.70%, respectively, which were both significantly higher than that obtained after dry comminution (p < 0.05). The surface protein concentration and ξ-potential of emulsion made by dry comminution (DCE) were 7.02 mg/m2 and 12.08 mV, respectively, and those of emulsion made by wet comminution (WCE) were 10.71 mg/m2 and 15.25 mV, respectively, which were significantly higher than that of DCE (p < 0.05). The volume average particle size of DCE was 3.41 µm, which was significantly higher than that of WCE (3.18 µm, p < 0.05). Collectively, these results indicated that WCE was more stable than DCE. Further, the demulsification rate of DCE was significantly higher than that of WCE when treated by freeze-thawing, pH, papain, and phospholipase A2 (p < 0.05). Demulsification effect of Alcalase 2.4L was the best among these five demulsification methods treated, and the demulsification rate of DCE reached 92.77%, which was slightly higher than that of WCE (92.67%), further illustrating the higher stability of WCE.

Fine Comminution of Pine Bark: How Does Mechanical Loading Influence Particles Properties and Milling Efficiency?

The use of lignocellulosic plant biomass as an alternative to fossil feedstocks for chemistry, energy and materials often involves an intense dry comminution step, for which the energy consumed can vary significantly according to the process parameters, the particle size targeted, and the properties of the biomass. Here we studied the fine milling of maritime pine bark in an impact-mill configuration and in an attrition-mill configuration. The properties of the resulting powders (particle size distribution, particle shape, specific surface area, agglomeration level) obtained in each configuration were compared in relation to process energy consumption. Results evidenced that the agglomeration phenomena drive milling efficiency and limit the possibilities for reaching ultrafine particles. Interestingly, impact loading proved more effective at breaking down coarse particles but tended to generate high agglomeration levels, whereas attrition milling led to less agglomeration and thus to finer particles.

Benefits of dry comminution of biomass pellets in a knife mill

The potential benefits of dry comminution in a knife mill for a diverse range of biomass 6 pellets are explored. The impact of dry comminution on energy consumption, particle size and shape, 7 is examined as well as the link between milling and mechanical durability. Biomass pellet comminution 8 energy was significantly lower (19.3-32.5 kW h t-1 [fresh] and 17.8-23.2 kW h t-1 [dry]) than values 9 reported in literature for non-densified biomass in similar knife mills. The impact of drying was found 10 to vary by feedstock. Dry grinding reduced milling energy by 38% for mixed wood pellets, but only 2% 11 for steam exploded pellets. Particle size and shape, particle distribution dispersion, and distribution 12 shape parameters changes between fresh and dry milling were also material dependent. Von Rittinger 13 analysis showed that to maximise mill throughput, pellets should be composed of particles which can 14 pass through the screen and thus have a neutral size change. A strong correlation was found between 15 pellet durability and energy consumption for fresh biomass pellets. Dry grinding has the potential to 16 significantly reduce energy consumption without compromising the product particle size, as well as 17 enhancing product quality and optimising biomass pellet comminution and combustion.

Erratum: Evaluation of HPGR and VRM for dry comminution of mineral ores (2016, vol. 52, no. 1, pp. 11-25)

Erratum: Evaluation of HPGR and VRM for dry comminution of mineral ores (2016, vol. 52, no. 1, pp. 11-25)

Evaluation of HPGR and VRM for dry comminution of mineral ores

The mining industry is searching for more energy efficient and dry comminution equipment as an alternative to conventional crushing followed by wet grinding circuits. This is a result of growing challenges associated with the increasing energy cost, scarcity of water resources and stricter environmental legislation. Dry comminution technologies, such as High Pressure Grinding Rolls (HPGR) and Vertical Roller Mills (VRM), have been successfully used in other industries such as cement and coal for decades, and the literature claims that these technologies are more energy efficient than conventional comminution practices. Pilot scale testing was conducted for each of these technologies using rock with properties similar to many mineral ores to test the claims in the literature and evaluate the applicability for hard rock mining operations. Whilst the test results for the HPGR and VRM are not directly comparable (due to different degree of size reduction), both demonstrated the potential for considerable energy savings compared to conventional ball milling. The HPGR and air classification circuit used 20 - 30 % less energy than the HGPR, screen, ball mill circuit. While VRM was estimated to use 10 - 30 % less energy (depending on the type of VRM) than a ball mill circuit for a similar degree of comminution.

Considerations in the preparation of laboratory samples for the analysis of ochratoxin A in wheat

A process used to prepare the test portion of ground wheat from the whole grain laboratory sample for ochratoxin A (OTA) analysis using dry comminution with homogenisation and sub-sampling via a rotary sample divider was developed and evaluated. With respect to OTA content, the developed process produced a homogeneous sample of ground wheat from 10 kg of whole grain. Relative standard deviations of the mean OTA concentration for five naturally contaminated wheat samples processed using the developed method ranged from 9% to 19% over a relevant concentration range of 1.7 to 7.6 mg/kg. Additional studies demonstrated that OTA was stable in ground wheat with moisture content between 12 to 13% for at least a year when stored at ambient temperatures. Further examination of the developed comminution and dividing procedure demonstrated that higher concentrations were measured in smaller sized particles, indicating that the accuracy and precision of OTA analyses could be affected by the particle size of ground wheat.

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.

Sampling Hazelnuts for Aflatoxin: Uncertainty Associated with Sampling, Sample Preparation, and Analysis

The variability associated with the aflatoxin test procedure used to estimate aflatoxin levels in bulk shipments of hazelnuts was investigated. Sixteen 10 kg samples of shelled hazelnuts were taken from each of 20 lots that were suspected of aflatoxin contamination. The total variance associated with testing shelled hazelnuts was estimated and partitioned into sampling, sample preparation, and analytical variance components. Each variance component increased as aflatoxin concentration (either B1 or total) increased. With the use of regression analysis, mathematical expressions were developed to model the relationship between aflatoxin concentration and the total, sampling, sample preparation, and analytical variances. The expressions for these relationships were used to estimate the variance for any sample size, subsample size, and number of analyses for a specific aflatoxin concentration. The sampling, sample preparation, and analytical variances associated with estimating aflatoxin in a hazelnut lot at a total aflatoxin level of 10 ng/g and using a 10 kg sample, a 50 g subsample, dry comminution with a Robot Coupe mill, and a high-performance liquid chromatographic analytical method are 174.40, 0.74, and 0.27, respectively. The sampling, sample preparation, and analytical steps of the aflatoxin test procedure accounted for 99.4, 0.4, and 0.2% of the total variability, respectively.

Dry comminution and liberation with microwave assistance

This paper presents the experimental results obtained from microwave‐assisted comminution/liberation tests on various minerals. The effects of microwave energy intensity and exposure time on microwave heating behaviour and grind‐ability of materials are discussed. The experimental results indicated that particle size has a significant effect. The coarser particles (−9.50 + 4.75 mm) of some minerals (limestone and quartz) were affected by microwave heating to varying degrees, resulting in an increased fineness of the ground product in a subsequent dry ball milling. It was observed that the silicate and carbonate minerals are difficult to heat at lower microwave energy intensities (&lt;7 kW) during a short exposure (&lt;30 min) due to their principally transparent or reflection to microwave energy. The thermal stress fractures in a copper ore in microwave exposure occurred readily, resulting in a better and cleaner liberation of sulphide minerals from the ore matrix.

Modeling Breakage Kinetics in Various Dry Comminution Systems

In modeling comminution systems, breakage rate (selection) functions are generally influenced more by the comminution machine than are breakage distribution functions, which are controlled by material properties. Linear grinding kinetics can be expressed either in terms of grinding time or specific energy consumption. Nonlinearities are caused by energy transfer mechanisms in the comminution machine whereby coarser particles might be ground preferentially or are protected by fines, by energy dissipation through interparticle friction in compressed bed comminution, and sometimes from heterogeneities produced in the feed particles. This paper discusses modifications of breakage rate functions in the grinding model for a number of situations and compares simulated and experimental results.

Fine dry comminution of calcium carbonate in a Hicom mill with an Inprosys air classifier

The Hicom mill is a high-intensity tumbling mill that can be used for fine and ultra-fine media grinding. Recent investigations on fine dry grinding with the Hicom 25 pilot plant, operating in closed circuit with an IAC 200 Inprosys high-efficiency classifier, have indicated that this milling combination is well suited to the efficient production of fine mineral powders. Closed circuit grinds were performed on 98% passing 94 μm limestone to a range of product sizes from 98% passing 26 down to 6.4 μm to determine the specific energy requirements for the milling of this material. The results from these tests show efficient classifier separation as well as rapid and efficient comminution in the Hicom mill.

Chemically assisted dry comminution of sericite — dry comminution method accompanied by ion-exchange

Chemically Assisted Dry Comminution (CADC) of sericite powder, a kind of mica, was conducted in order to prepare ultra-fine sericite with minimal contamination from the grinding media. CADC of sericite powder is a comminution method in which the sericite powder is first mixed with another powder, “powder B”, and the mixed powder is comminuted in dry conditions, followed by obtaining fine sericite after removing the powder B by use of a simple method such as dissolution. “Assisted” means that powder B assists comminuting the sericite by some interaction with the sericite during the comminution. Various nitrites such as LiNO 3, NaNO 3, KNO 3 and RbNO 3 were used as powder B. Compared with the results of ordinary dry comminution, sericite powder with a large specific surface area and fewer impurities from the grinding media, was prepared by CADC. The specific surface are of sericite obtained by CADC has a correlation with the decrease of potassium ion in sericite. Potassium ion was thought to be exchanged during the comminution.

Performance of a fluidized bed jet mill as a function of operating parameters

Fluidized bed jet mills are used for the dry comminution in the μm range. The application of the jet mill ranges from deagglomeration purposes to grinding of hard materials. This indicates the wide field for the usage of this grinding technique. The comminution effect is based on particle-particle impact in expanding gas streams. A dynamic classifier is integrated in the fluidized bed jet mill. There are two parameters which can be used to control the performance of the fluidized bed jet mill: the speed of the classifier rotor and the pressure of the gas used for grinding. As a characteristic value the “spin-number” was defined. The “spin-number” is given as the ratio of the circumferential speed of the classifier rotor and the flow-through velocity of the classifying gas in radial direction. Results of limestone grinding were presented. The comminution of limestone represents a grinding process, not just a deagglomeration step. The fineness achieved, expressed by the mean particle diameter, can be modelled as a function of the “spin-number” and the pressure of the gas used for grinding. A similar dependency was found for the parameters of the RRSB-distribution, describing the shape and the position of the distribution. The dependencies could be backed-up with experiments performed with an easily grindable rubber chemical. A few experiments performed at the base-points of the working range of the fluidized bed jet mill enable to establish a characteristic field of performance for a given product. The knowledge of this characteristic field simplifies the selection of the optimum operation conditions of the fluidized bed jet mill for a given grinding task. Moreover it enables to include milling processes in more advanced process control systems.

Chemically assisted dry comminution of an inorganic powder

Chemically assisted dry comminution (CADC) of an inorganic powder was conducted in order to obtain fine powder with large specific surface area. Soda glass powder was comminuted with lithium nitrate under dry conditions. The interaction of lithium nitrate with soda glass powder during the comminution assisted the soda glass powder in being comminuted. Soda glass powder of about 180 m 2/g was prepared by CADC, whereas the specific surface area in ordinary dry comminution (DC) of soda glass powder was only 3.8 m 2/g. Zirconia content as a contaminant was lower in CADC than in ordinary DC. The prevention of agglomeration of the comminuted soda glass by lithium nitrate and the ion-exchange between lithium and sodium ions in the soda glass powder during CADC were thought to help the comminution.

Grinding Aids

The use of chemical additives for improving the efficiency of both wet and dry comminution is reviewed. Although such additives can affect breakage strength under general comminution conditions crack velocities are probably too great to involve adsorption effects. Additives in dry grinding systems appear to function by coating the particles and preventing reagglomeration. In wet grinding systems, their main influence on grinding is through their effect on slurry rheology. Such additives do not affect the specific energy for grinding but only regulate mill power draft and kinetics.

乾式化学的微粒子化促進法による粘土鉱物セリサイトの微粒子化 硝酸塩類の粉砕性に及ぼす影響

Chemically assisted comminution, in which chemical and/or physicochemical actions are introduced into powders to be ground, was conducted under dry conditions. The comminution method is called “chemically assisted dry comminution” (CADC). In the CADC sericite powder, a kind of mica, was first mixed with a nitrate, and the mixed powder was comminuted under a dry condition, followed by obtaining finely ground sericite after removing the nitrate by water cleaning. Lithium, sodium, potassium and rubdium nitrate were used as the nitrates.The sericite powder obtained by every CADC had a much larger specific surface area and a smaller amount of impurity than that obtained by an ordinary dry comminution. On the other hand, the median diameters of sericite by CADC were slightly smaller than those by an ordinary dry comminution.Potassium ions in sericite decreased only in the case of the CADC, which suggested that potassium ions were exchanged with alkali ions in the nitrate during the CADC. There was a correlation between the amount of exchanged potassium ions and the specific surface area of the sericite by the CADC. Stabilisation of the nascent surface and the prevention of agglomeration of the sericite by nitrate during comminution was considered to be another reason for the enhanced grindability by CADC.