Size reduction performance evaluation of HPGR/ball mill and HPGR/stirred mill for PGE bearing chromite ore

In the present study, size reduction experiments were performed on High-Pressure Grinding Rolls (HPGR), ball mill and stirred mill of PGE bearing chromite ore. The performance of HPGR was evaluated in two stages of size reduction to reduce energy consumption. In the first stage of HPGR, the effect of operating variables such as the gap between the rolls, roll speed, and specific pressing force on product size (P₈₀) and energy consumption (E_CS) was investigated. The process to get the smallest product size was optimized within the experimental range of investigation. The crushed product of HPGR was subjected to grinding in the second stage in a ball mill and stirred mill. The effect of mill speed, grinding time, and ball size on the performance of the ball mill was investigated and the product was further investigated in the second stage. A comparative analysis of the ball mill and stirred mill performance and energy consumption at different grinding time intervals was also performed. It was found that the ball mill consumed 54.67 kWh/t energy to reduce the F₈₀ feed size of 722.2 µm to P₈₀ product size of 275.4 µm while stirred mill consumed 32.45 kWh/t of energy to produce the product size of 235.6 µm. It also showed that stirred mill produced finer product than the ball mill at around 40% lesser consumption of energy. It can be concluded that the HPGR-Stirred mill combination was a more energy-efficient grinding circuit than the HPGR-Ball mill combination for PGE bearing chromite ore.     

Grindability of Quartz in Stirred Media Mill

Nowadays, ultrafine grinding in the submicron particle size range is becoming an increasingly conventional process. One of the mostly used ultrafine grinding ways is the size reduction in the so called stirred media mill. This article deals with the experimental investigation of wet grinding of quartz in a stirred media mill. The applicability of the introduced operating Rittinger index and the lower limit size of Rittinger law are studied. Furthermore, the effect of solid concentration of suspension, ball filling ratio, circumferential speed of the stirrer, and size of grinding media on the fineness (median particle size and specific surface area) was examined. Additionally, a relative grindability calculated from the operating Rittinger index is introduced in order to compare the efficiency of stirred media milling. It was found that the grinding conditions greatly affect the applicability of Rittinger's law and its lower limit size.     

Time-dependence of particle size during comminution and a scale-up procedure for stirred media mills

This paper investigates the time-dependence of the median particle size during comminution processes in horizontal and vertical stirred media mills. The shape of the time-dependent function describing the particle size is proposed, and it is shown that this function precisely traces the temporal variation of the particle size in comminution processes. The grinding rate constant is defined as the coefficient of time in the function. The effect of stirrer tip speed and mill size on the grinding rate constant is examined, and it is found that the grinding rate constant can be correlated proportionally with the quantity which is related to specific energy. This correlation provides the basis for scale-up of stirred media mills.     

卧式搅拌磨搅拌叶轮形状对粉碎效果的影响

研究卧式搅拌磨的搅拌叶轮形状对磨矿效果的影响,设计3种搅拌叶轮,在不同搅拌速度的条件下,考察磨矿产品的粒度与能量新生能力。通过对比发现,3种叶轮中圆形孔叶轮的细磨效果最好,磨矿性能最优,是比较适合卧式搅拌磨机进行超细磨的搅拌叶轮形状;在能量输入基本一致的情况下,圆形孔叶轮在1~15μm粒级能量利用率最高,产率最大。     

采用一种高能搅拌磨湿法制备纳米氧化铝粉体

研究用一种先进的高效能搅拌磨湿法制备纳米粒级的氧化铝(α-Al2O3)粉体。采用氮气吸附法测量不同研磨颗粒产品的比表面积,采用X射线沉降粒度仪、电超声粒度分析仪和扫描电镜测定和观察颗粒的粒径和形貌,采用X射线衍射法(XRD)进行晶形分析。结果表明,微米级给料在湿法研磨数小时后可得到一种平均粒径为70 nm和比表面积大于115 m2/g的纳米颗粒产品。经研磨α-Al2O3颗粒的晶体各主晶面均遭到不同程度破坏,但晶相仍为α相。另外,还发现,研磨过程中研磨氧化铝颗粒所需比能耗随着研磨时间的延长而增加,而能量利用效率迅速降低。     

Effect of Various Operating Factors on Wet Stirred Mill Performance

In this study, the effects of various operating factors, such as initial particle size, feed quantity, filling volume of the ball, and ball size distribution on fine grinding of calcite powders (CaCO₃) were studied using a laboratory stirred mill under wet conditions. A series of laboratory experiments using 2⁴ full factorial designs was conducted to determine the optimum grinding parameters. The main and interaction effects on the specific surface area (m²/g) of the ground product were evaluated using Yates' analysis. The test results showed that the main factors that influence the mill grinding performance are the feed quantity and the ball size distribution.     

Analysis of ball mill grinding operation using mill power specific kinetic parameters

With a view to developing a sound basis for the design and scale-up of ball mills, a large amount of data available in the literature were analyzed for variation of the two key mill performance parameters: power specific values of the ‘absolute breakage rate of the coarsest size fraction’, S^*, and ‘absolute rate of production of fines’, F^*, with some of the important operating and design variables such as the mill speed, ball load, particle load, ball diameter and mill diameter. In general, values of both the mill performance parameters were found to vary significantly with the mill operating conditions. The nature and relative magnitude of variation for the two parameters also differed significantly. Moreover, the effect of any particular variable on the S^* and F^* values was found to be significantly different for different sets of operating conditions. It has been emphasized that, as the purpose of grinding is to produce fine particles, the mill design and scale-up work should be based mainly on the F^* parameters. Moreover, it is not correct to regard the S^* values to be independent of the mill design and operating variables as a general rule, especially for a fine analysis of the performance of the grinding systems.     

Effective mechanochemical synthesis of sulfide solid electrolyte Li3PS4 in a high energy ball mill by process investigation

Mechanochemical syntheses have a high potential as environmentally friendly and scalable processes. However, especially in case of solid electrolytes, these syntheses are reported as very time consuming with process times up to several days. In this study, the sulfide solid electrolyte Li₃PS₄ was successfully synthesized in less than 5 h after a systematic variation and subsequently optimization of the process parameters in a high energy ball mill. The synthesized electrolyte samples were characterized according to their composition, morphology, particle size distribution and ionic conductivity. Therefore, a better understanding of the process-structure–property relations and process efficiency was achieved. Thus, the results allow a correlation between the stressing conditions and kinetic rates. The stressing conditions are mainly affected by process parameters such as rotational speed, grinding media size and grinding media filling ratio. The kinetic of the mechanochemical process is highly dependent on the normal power input by head-on collisions, leading to a reduction of conversion time with increasing specific power input. The different sets of investigated process parameters also exhibit systematic effects on the crystallinity and particle size distribution of the solid electrolytes. As a result, a highly enhanced process with lowest specific energy demand was achieved by using the largest grinding media with highest rotational speeds at medium grinding media filling ratio.     

Material characteristics and the breakage parameters in a circular fluid energy mill

Towards analyzing the breakage behavior of materials with respect to their physical properties in the context of simulation and modeling of the process of comminution in a circular fluid energy mill, the present work was taken up to characterize the effect of material hardness on the breakage process of the mill. The breakage parameters of a range of materials, chosen based on their hardness, were analyzed by estimating them using the G-H solution for the size discretized batch grinding equation, with corrections to account for the deviation from first-order kinetics during the initial stages of grinding and a back-calculation scheme. All the operating variables of the mill were kept the same while collecting the primary breakage data using a single-size feed for six successive passes through the grinding chamber of the mill. The breakage distribution values could be related to particle size with the sum of two power function equations, while the breakage rate could be expressed as a power function of the dimensionless particle size and the top size interval disappearance. The coefficients of these functions for different materials indicated inconsistent behavior with respect to the hardness for softer materials, while medium and harder minerals showed specific trends.     

Study on the stability and microstructural properties of barium sulfate nanoparticles produced by nanomilling

Barium sulfate nanoparticles were produced by nanomilling in stirred media mill using sodium salt of polyacrylic acid (PAA-Na) as a dispersant. The particles sizes of the ground product obtained in the grinding mill were determined by dynamic light scattering (DLS), Brunauer–Emmet–Teller (BET) nitrogen gas adsorption method, and transmission electron microscopy (TEM). The mean particle size calculated with various methods yielded different values due to the different characterization techniques. The stability of BaSO₄ nanoparticles produced was analyzed by zeta potential measurement and Turbiscan. The stability of barium sulfate nanoparticles was high in presence of dispersant PAA-Na and higher pH values. Further, the changes in microstructural properties, caused by wet grinding and adsorption of PAA-Na on BaSO₄ nanoparticles, were studied using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The surface activation and amorphization of BaSO₄ nanoparticles were observed due to increased stresses exerted on the particles during wet grinding.     

Application of artificial neural network method to predict the breakage properties of PGE bearing chromite ore

In the present investigation, systematic grinding experiments were conducted in a laboratory ball mill to determine the breakage properties of low-grade PGE bearing chromite ore. The population balance modeling technique was used to study the breakage parameters such as primary breakage distribution (B_{i, j}) and the specific rates of breakage (S_i). The breakage and selection function values were determined for six feed sizes. The results stated that the breakage follows the first-order grinding kinetics for all the feed sizes. It was observed that the coarser feed sizes exhibit higher selection function values than the finer feed size. Further, an artificial neural network was used to predict breakage characteristics of low-grade PGE bearing chromite ore. The predicted results obtained from the neural network modeling were close to the experimental results with a correlation of determination R² = 0.99 for both product size and selection function.     

Use of Wet Grinding and Aging to Produce Narrow Particle Size Distribution

An experimental study on the improvement of particle size distribution of calcite powder (d₅₀ = 3.23 μm) was carried out. Ultrafine grinding of calcite powder was studied under batch wet conditions in a laboratory stirred mill. After grinding, the suspension was allowed to age at 30°C for 12 and 24 h. The results indicated that the fineness narrow particle size distribution is influenced to a small extent by altering some operating parameters, such as suspension temperature and aging time. Further increase in the fineness narrow particle size distribution is likely with additional optimization work on the operating parameters of aging process.     

Production of Submicron Particles by Mechanical Treatment: Width of Particle Size Distribution and Fineness of Product

Calcium carbonate (CaCO₃) powders commonly used as a functional filler in paints, inks, papers, plastics, cosmetics, and so on, are generally produced by mechanical treatment (milling). This research was aimed to produce calcium carbonate submicron particles by stirred milling in wet conditions. The experiments were carried out by a batch operation, and determined the change in particle size distribution (PSD) of calcium carbonate. The product size (fineness) and PSD were used in the evaluation of the test results. The results showed that wet grinding in a stirred bead mill using the smaller grinding media (500 µm) is an effective method for reduction of product size (～500 nm) of the CaCO₃ powder.     

A new approach for the testing method of coal grindability

In this study, a total of 26 hard coal sample (either clean or original) from Zonguldak Coal Basin (17 from Zonguldak, 9 from Amasra) and a total of 17 low grade Turkish coals from various locations in Turkey were collected. So, a total of 69 samples were analyzed initially with standard method of coal grindability, i.e. HGI values were determined. In addition, an alternative method (does not require a standard HGI mill) for grindability measurement was proposed in this study. The abovementioned alternative method includes a ring mill with specified conditions and Malvern Mastersizer. As regards to the procedure of the new proposed method for the determination of coal grindability, samples were prepared in the size range of −1.7 + 1.18 mm size group and they were ground in ring mill. Here, ring mill was chosen because of the fact that it is very widely used for sample preparation and it is very commonly available in every laboratory. Procedure proposed includes placing abovementioned specified samples in ring mill (See Material and Method) and having the samples ground in a previously determined time period. After this grinding process (with ring mill) they have rather different size distribution at the end depending on their nature of grindability. For better understanding, having the ground samples of (−1.7 + 1.18 size group for 20 s for 50 g samples) and analyzing their size distributions with Malvern Mastersizer, ground samples have different D₁₀, D₅₀, D₉₀, D₃₂ and D₄₃ at the end. Comparing these size parameter results with previously determined HGI values, it can be claimed that coal grindability can be easily determined with this method, since evaluated HGI values with the method proposed are ±0.05% different than the determined HGI values.     

Experimental investigation of the impact breakage characteristics between grinding media and iron ore particle in ball mills

The particle breakage of the ball mill is an extremely complicated breakage process. It is difficult to quantify and describe the particle breakage behavior. In this study, a drop-ball experimental setup was developed to demonstrate the impact process of grinding media on ore particles. The quantitative analysis of the effects of particle size, impact energy, and the number of impacts on particle breakage behavior was performed separately. The results show that the breakage probability model and product size distribution model used can be excellent to predict the particle breakage behavior for the single-particle impact experiments. The breakage probability of particles is highly sensitive to impact energy and particle size, exponentially increasing with the increase of impact energy. In addition, the application of the t_n-t₁₀ relationship provides a convenient means to characterize and predict the particle size distribution. In multi-layer particle impact experiments, the captured thickness of ore particles is approximately 2 layers during the crushing process. The broken mass of iron ore particles is proportional to the number of concessive impacts at different impact energies. This paper provides theoretical and methodological support for the evaluation and optimization of particle breakage in ball mills.     

Preparation of submicron calcite particles by combined wet stirred media milling and ultrasonic treatment

This paper investigates the grindability of calcite powder (D₅₀ = 6.68 µm) to submicron particle sizes using stirred media mill (0.75 l) and ultrasonic generator (400 W, 24 kHz). The present study focuses directly on the comminution of calcite powder in water media by combined stirred milling and ultrasonic treatment and effects of some operational parameters such as grinding time (10–30 min), ultrasonic power (40–100% µm as amplitude settings), and solid ratio (10–30% w/w) on comminution. Experimental results have been evaluated on the basis of product size and width of particle size distribution.     

A study on the effect of process parameters in stirred ball mill

An experimental study on the fine grinding of calcite powder (d₅₀ = 62.16 μm) using a 0.75 l laboratory stirred ball mill has been carried out. The effects of various operating factors, such as grinding time (min), stirrer speed (rpm), slurry density (wt.%) and ball filling ratio on fine grinding was studied under batch wet conditions using alumina balls, 95% purity with diameters 3.5–4.0 mm. A series of laboratory experiments using 2⁴ full factorial designs was conducted to determine the optimum grinding parameters. The test results showed that the stirrer speed and grinding time have strong effects on the grinding efficiency, based on the value of specific surface area (m²/g).     

Doppler broadening measurements of the electron-positron annihilation radiation in nanocrystalline ZrO<Subscript>2</Subscript>

ZrO₂ powders have been ground by ball mill grinder to achieve the particle size down to 10 nm. Typical defects introduced during ball mill grinding have been studied by positron annihilation lifetime measurement technique and coincidence Doppler broadened positron annihilation radiation spectroscopic technique. Coincidence Doppler broadened positron annihilation spectra for ball mill ground and unground ZrO₂ samples have been analyzed by constructing ratio curve with defects free Al single crystal. Results indicate an increase of cation defects in ZrO₂ samples due to the reduction of particle size by the ball mill grinding process.     

Media Wear in Stirred Milling

ABSTRACT

A method for measuring media wear using a commercially available 0.751 stirred mill is described. Five material groups, namely steel, ceramics, natural materials, glass, and ore pebbles (autogenous grinding) were tested using water alone and a 60% by weight slurry of sulfide ore. Other variables were stirrer speed and media size. The relative wear rates of the different materials and their effects on grinding efficiency are reported. Relative costs of media were taken into account in the assessment. Ottawa sand was the most cost effective medium for wear, and steel shot for grinding efficiency.     

Practical strategy to produce ultrafine ceramic glaze: Introducing a polycarboxylate grinding aid to the grinding process

In this work, a polycarboxylate comb-like polymer was used as grinding aid for ceramic slurry, and the effect of addition of this grinding aid on ceramic process property was highlighted. The grinding efficiency of the polycarboxylate grinding aid (PG) in terms of the particle size distribution and specific surface of unit volume of the ceramic slurry being ground were investigated. Consequently, the PG that was synthesized via free radical polymerization under the condition of an APEG/AA/MA molar ratio of 0.3:1:1, an initiator dosage of 5 wt%, and a reaction time of 6 h at 90 °C, provided better grinding efficiency than those of the triethanolamine and other commercial grinding aids. Specifically, with a dosage of 0.21% and 2 h of grinding, the d₉₇ and d₅₀ of ceramic slurry decreased from 13.956 μm and 2.043 µm to 3.739 µm and 0.561 µm, respectively. The cumulative distribution, frequency distribution and SEM results exhibited a uniform particle size distribution for ceramic ground with PG-C. Furthermore, the sintering experiment indicated that a lower processing temperature was capable of producing ultrafine ceramic. These improvements indicated the potential application of the PG as an efficiency ceramic grinding aid, which further facilitating the preparation of uniform ultrafine slurry by a sand mill.