Optimization of some parameters of stirred mill for ultra-fine grinding of refractory Au/Ag ores

In this study, optimization of some parameters of stirred mill on ultra-fine grinding of refractory Au/Ag ores was performed. A three-level Box-Behnken design combining a response surface methodology (RSM) with quadratic programming (QP) was employed for modelling and optimization of some operating parameters in ultra-fine grinding. Grinding tests were carried out in a laboratory scale pin-type vertical stirred mill. The relationship between the response, i.e. d₈₀ size, and four grinding parameters, i.e. ball diameter, grinding time, ball charge ratio and stirrer revolution was presented as empirical model equations. Analysis of variance showed a high coefficient of determination value (R² = 0.9698), thus ensuring a satisfactory of the second-order regression model with the experimental data.The model equations were then optimized using the quadratic programming method to minimize for d₈₀ size within the experimental range studied. The optimum conditions were found to be 1.61 mm for ball diameter, 11.50 min for grinding time, 80% for ball charge ratio and 745 rpm for stirrer revolution for this grinding process.In order to verify the improvement of grinding performance using the optimal level of control factors three verification experiments were conducted, and the results for d₈₀ was 3.37 μm, which were smaller than those obtained in the initial tests.     

中国超细粉碎和精细分级技术现状及发展

综述了中国超细粉碎与精细分级技术与设备的现状、近5年的进展 .20世纪90年代中期以来,中国超细粉碎和分级技术取得了显著进步,现已具备了研制和生产气流粉碎机、高速机械冲击式超细粉碎机、搅拌球磨机、振动球磨机、塔式搅拌磨、行星球磨机、高压射流磨、旋风自磨机等各类超细粉碎及涡轮式气流分级机和离心式水力分级机等设备的能力,并在流态化床式气流粉碎机、飓风自磨机、搅拌球磨机和砂磨机、行星球磨机、高压水射流磨机以及精细分级原理和分级设备等方面取得了一些进展,具有自主知识产权的新技术、新设备显著增多.指出中国目前在超细粉碎和精细分级领域仍然存在大型设备不足、工艺控制技术落后、磨耗和单位产品能耗偏高、特殊粒形超细粉体的生产工艺和设备落后等问题.最后对21世纪初中国超细粉碎和分级技术的主要发展趋势进行了展望.     

Regrinding sulphide minerals — Breakage mechanisms in milling and their influence on surface properties and flotation behaviour

Changes in surface properties with grinding and regrinding play a key role in mineral flotation performance. Different particle breakage mechanisms in grinding mills may change the mineral surface properties in different ways, possibly leading to different mineral floatabilities depending upon the predominant breakage mechanism. The Magotteaux Mill^® and IsaMill were selected as representations of a tumbling and a stirred mill, respectively. The latter has a greater contribution to particle size reduction from the abrasion mechanism than the former which also has contributions from impact breakage.Mineral recovery decreased with size reduction through stirred mill regrinding (i.e., the IsaMill) employing ceramic media from 90%, achieved before regrinding (d₈₀ 80 μm regrind feed), to 71, 58, 20 and 5% achieved after regrinding to d₈₀ values of 60, 40, 20 and 10 μm, respectively. A similar trend of decreasing recovery was also observed with regrinding in the tumbling mill (i.e., Magotteaux Mill^®). Changes in mineral flotation behaviour were investigated with respect to (i) particle size, (ii) increase in surface area, and (iii) surface contamination with size reduction in the two different mills. The flotation of pyrrhotite with additional reagents illustrated that the total change in recovery through regrinding results mainly from the increase in surface area of the pyrrhotite afforded by size reduction. The effects of the predominating particle breakage mechanism on the change of mineral surface properties were studied through regrinding in the two different mills. In particular it was observed that the hydrophobicity/floatability of the coarse particles decreased to a greater extent with stirred mill regrinding than with tumbling mill regrinding at coarser regrind product sizes (d₈₀ 70 and 60 μm) presumably due to the greater contribution of the abrasion mechanism to size reduction afforded by the stirred mill. It was also observed that the difference in recovery for the same regrind product size from the two different mills decreased when approaching finer regrind sizes, which indicated that the particle breakage mechanisms of the different mills for fine regrind product size were not as influential as for coarse regrind product sizes.     

Empirical and scale-up modeling in stirred ball mills

Stirred ball mills are frequently used for ultrafine- and nanogrinding in food, pharmaceutical and chemical industry, but only few investigations have been published on empirical or scale-up modeling of stirred ball mills. Experiments have been carried out with a laboratory scale stirred ball mill. During the experiments the main technical parameters such as stirrer speed, grinding media, filling ratio, grinding time and the solid mass concentration have been systematically adjusted. The particle size distribution of mill products can be well estimated by empirical functions, so an empirical model has been prepared for the laboratory mill. The relation between the grinding fineness, grinding time and specific grinding work was represented for several materials such as pumice, andesite, limestone and tailings of ore mining industry. The power consumption of the stirred ball mill for scale-up was determined by a method based on the dimensional analysis. A new scale-up model has been presented as well by with industrial size stirred ball mills can be designed on the basis of the laboratory measurements.     

Effects of concentration of dispersions on particle sizing during production of fine particles in wet grinding process

Stirred media milling is a prospective technology for producing colloidal dispersions by means of wet grinding process. In the past, many researchers have studied the effects of different operating parameters such as size, shape, nature and quantity of grinding medium, the speed of agitator in grinding chamber, the feed rate of dispersions, etc. in stirred media mills. However, it is still less known how particle sizing which generates valuable information of particle size of the product to interpret, control and optimize the grinding process, is influenced by the concentration of the dispersion during stirred media milling where particles change their size from micron to colloidal range rapidly. One of the reasons of this lack had been our incapability in the past to study the particle size distribution of dispersions without dilution. The recent advent of acoustic attenuation spectroscopy is known to be capable of studying dispersions without dilution, under real process conditions and on line. The study employs acoustic attenuation spectroscopy to investigate the effects of concentration of dispersions of CaCO₃ on its particle sizing during size reduction process in a stirred media mill (LabStar manufactured by NETZSCH). The dispersions of CaCO₃ at 5%, 10%, 20% and 30% (m/m) were studied about six hours under a selected set of operating conditions. Contrary to the existing knowledge obtained through other techniques of particle sizing that are based on the principle of dilution, acoustic attenuation spectroscopy shows that, under certain grinding time at given operating conditions, increase in concentration of dispersion results in better grinding results yielding smaller particles. The causes behind the differences in results of acoustic attenuation spectroscopy and dynamic light scattering have been thoroughly investigated. We find certain limitations of acoustic attenuation spectroscopy in particle sizing. A typical phenomenon which causes misleading trends in particle sizing is multiple scattering in acoustic measurements. Multiple scattering, particularly, influences acoustic results when particles approach to fine size range during size reduction process.     

合纤用砂磨机最新发展

介绍了合纤用砂磨机的发展阶段,影响砂磨效果的主要因素,包括研磨介质种类、尺寸、装填率及研磨介质分离系统等。对现有合纤用砂磨机存在的问题如砂磨机部件材质选错,介质分离系统结构不合理等进行了分析。着重介绍了HDM卧盘式砂磨机的特点及它在合纤钛白研磨中的应用。     

Analysis of ball movement for research of grinding mechanism of a stirred ball mill with 3D discrete element method

A simulation of the three-dimensional motion of grinding media in the stirred media mill for the research of grinding mechanism has been carried out by 3-dimensional discrete element method (DEM). The movement of ball assemblies was graphically displayed with some snapshots from start of the milling to 0.20 s. From these simulation results, the grinding zone in the mill was confirmed to be distributed into two regions, which is near the stirrer and the side wall of mill around the stirrer. The power changing the rotation speed of stirrer was examined based on the micro interactive forces at all the contact points between ball-to-ball and between ball-to-stirrer. DEM is a very powerful tool for the microanalysis of movement of balls, which could not have been solved by a conventional experimental method.     

Application of grinding kinetics analysis of inorganic powders by a stirred ball mill

The need for ultra fine particles has been increasing in the preparation field of raw powders such as fine ceramics and high functional products. A series of wet grinding experiments were carried out on inorganic powders such as calcite, pyrophyllite and talc by a stirred ball mill. The grinding rate constant K’ in the equation of grinding kinetics was examined based on the grinding kinetics analysis as the same type of function of a previous paper on a vertical type planetary ball mill. The experimental particle size distribution of the ground products was obtained in various grinding conditions. The grinding rate constants K and K’ were expressed by empirical equation involving experimental conditions by a stirred ball mill. The empirical equation on the grinding rate constant was expressed in terms of a function involving the ball diameter of grinding balls, the median diameter of feed material, and Bond’s work index of material, in the experimental conditions. The values of empirical constants C1 and C₂ were 21.13 and 0.0109 on K, while C₁ and C₂ were 120.99 and 0.0192 on K′, respectively. And the particle size distribution of ground products of each test material for a given grinding time was found to be expressing the selection function (the specific rate of breakage) which was obtained from the grinding kinetics analysis. In this study, the grinding rate change on calcite and pyrophyllite was similar at the same experimental operation condition. However, in the case of talc, it was observed that the grinding rate was not increased compared with other samples.     

Reduction of the porcelain firing temperature by preparation of the raw materials

An innovative way of reduction of firing temperature of porcelain tableware is reached by preparation of raw materials down to submicron- and nanoscaled powder for higher reactivity. In this study a common slurry was ground in an agitator ball mill from d₅₀ = 5.0 μm to 0.9 μm, green bodies were prepared, and glost firing was simulated in a dilatometer. The sintering temperature has been decreased by approximately 180 °C. A reflection between ball mill and agitator ball mill regarding the grinding cost shows no difference which means that the ball mill could be replaced. The energy consumption during the grinding process will be discussed regarding to energy savings resulting from reduced firing temperature. Furthermore a comparison between experimental and literature data will be done. The effect of grinding of raw material is finally evaluated concerning sintering behaviour and material properties.     

A statistical approach for estimation of significant variables in wet attrition milling

Production of ultrafine particles by grinding in attritor mill has been successfully applied in chemical, pharmaceutical and mineral processing industries. It has also been demonstrated as a cost effective and efficient method for production of nanoparticles. The present study attempts to relate the effects of operating variables on the Rosin Rammler equation parameter (X_d), which is indicative of the size of product. Operating parameters considered for the investigation are initial size of particles, ball loading, slurry mass fraction, diameter of grinding media, pin tip velocity and ratio of Young's modulus. The results indicate that the ratio of Young's modulus and initial size of particles have significant effects; ball loading, diameter of grinding media and pin tip velocity have moderate effects; and slurry mass fraction does not have a significant effect on the final size of the powder. The paper illustrates how statistical analysis, when appropriately applied, can be used to analyze complex unit operations such as the attritor mill and can be effective in gathering of process understanding.     

Fine grinding of mica in the Szego Mill

The Szego Mill is a planetary ring-roller mill with radially mobile, helically grooved rollers. It has a high capacity for its size and is suitable for continuous dry or wet grinding, including pastes with high solids concentration. It reduces size rapidly, and with a relatively low power consumption. In this paper, results for mica grinding are presented for both dry and wet operation. Particle size distribution, power consumption and mean particle aspect ratios are correlated with operating conditions, including use of special rollers to enhance shearing and flake delamination. Aspect ratios in the 30–40 range can be attained; for grinding to 15 μm median size, the specific energy requirement is about 80 kWh/t.     

HRM立式磨水泥半终粉磨系统节能分析

目前的辊压机水泥联合粉磨系统电耗多在30~36 kWh/t范围。若要进一步降低水泥粉磨电耗,可选择HRM预粉磨立磨和半终粉磨工艺,粉磨电耗可控制在26 kWh/t以内。HRM型低阻外循环立磨作为水泥预粉磨设备,以其粉磨系统电耗低、耐磨材料使用寿命长、操作维修简单、系统投资省等优点,在水泥节能粉磨工艺中得到了很好的应用。     

Ultra-fine grinding mechanism of inorganic powders in a stirred ball mill

An experimental investigation on grinding mechanism for calcite used in a stirred ball mill was carried out. The slurry concentration and the amount of grinding aids were chosen as main experimental factors of the grinding process. The effect of grinding aids on particle size distribution and grinding efficiency, defined as the increases of specific surface area per the specific grinding energy, was investigated. It was demonstrated that the grinding rate for calcite could be improved by addition of grinding aids. The grinding energy efficiency by adding a specific grinding aids was improved approximately 45.2% in comparison with and without grinding aids (n=700rpm, J=0.7, d_B= 1.0 mm, C_s=60wt%). This paper was presented at the ‘First Asian Particle Technology Symposium’ held at Bangkok between December 13 and 15, 2000.     

Production of transparent suspensions by real grinding of fused corundum

Suspensions containing ceramic nanoparticles (x₉₀ < 30 nm) are supposed to have an important property: transparency, this opens up a wide field of applications, especially scratch resistant or UV-absorbing films. Common processes for preparing transparent suspensions are based on dispersing aggregates produced by pyrolysis or precipitation. However, in this paper the possibility to produce transparent suspensions by real grinding in a stirred media mill is shown. The grinding of fused corundum down to values near the grinding limit is a very time and energy consuming process. According to the property of transparency, the grinding media wear is one of the greatest challenges to overcome. Therefore, a two-step grinding process was introduced to keep the wear values as low as possible. To produce a transparent suspension by real grinding, the operation mode and operating parameters have to be chosen very carefully, since the amount and size of the wear particles as well as the width of the product particle size distribution determines whether a suspension turns transparent or stays opaque.     

PSFL立轴式破碎机在粉磨工艺中的应用

为提高粉磨效率、降低粉磨消耗,山东鲁碧建材有限公司先后在原料粉磨系统和水泥粉磨系统的工艺布置均配置了“筛分＋破碎”的细碎工艺。其中破碎设备选择了PSFL立轴式破碎机。生产实践表明,该破碎机破碎不同物料适应性强,破碎后的物料粒度均匀、细小,破碎机使用寿命较长,使用效果良好。使用细碎工艺后,入磨石灰石粒度由25mm左右降至8mm;入磨熟料粒度由20mm降至6mm,从而使粉磨系统的台产提高,电耗降低。其中原料磨台产提高23．08％,电耗下降了2．7kWh／t;水泥磨台产提高11．54％．电耗下降了2．54kWh/t。     

Φ3.8 m×13 m闭路粉磨系统节能改造

肇庆金岗水泥有限公司2 500 t/d新型干法旋窑水泥熟料生产线~#1、~#2水泥粉磨系统各采用1套Φ3.8m×13m球磨机单闭路工艺系统,为响应国家节能减排的号召,金岗水泥公司对其中~#1水泥磨系统进行节能技术改造,新增1套HFCG180-160辊压机预粉磨系统与原#1球磨机组成"一拖一"的联合粉磨系统。技改后,台时产量大幅度提高,由原来的60～65t/h提高到平均192.0t/h,粉磨系统工序电耗由平均45kWh/t降低到平均29.2 kWh/t,节电效果显著。     

Mathematical modeling of fluid energy milling based on a stochastic approach

In this study, the stochastic method is used to simulate the grinding process in a fluid energy mill: the product particle size distribution is regarded as the result of repeating elementary breakage events, i.e. M_p=M₀[T_m]^m, where M₀ is the row vector of the size distribution of feed particles, M_p is the row vector of the size distribution of product particles, m is the number of elementary steps, and T_m is the matrix of transition probabilities representing the elementary breakage event. The matrix of transition probabilities can be related to the breakage rate function and the breakage distribution function of the elementary breakage event. A specially designed apparatus, named single-event fluid mill, was employed to experimentally estimate those two breakage functions of the elementary breakage event with a breakage rate correction factor θ. The classification effect is taken into consideration by defining a cutting size under which the particle will not break any more. Using this strategy, the product particle size distribution is calculated. The good consistency between the simulation and the experimental results indicates that this model is valid to quantitatively estimate the grinding performance of the fluid energy mill.     

立磨预粉磨在水泥粉磨系统技改中的实践

某水泥粉磨站为Φ3.2 m×13 m单球磨机组成的开路粉磨系统,将其改造为Φ1 700 m立磨预粉磨组成的联合预粉磨开路粉磨系统,水泥粉磨系统的平均产量由40t/h提高到70 t/h,增产幅度高达75%;平均电耗由39.5 kWh/t降到了28.5 kWh/t,节电幅度为27.5%,增产节能效果显著。技改后的工艺流程精简,设备少,系统投资少,为业主以后的生产和设备维护提供了方便。     

磨矿条件对湿式细磨重质碳酸钙的影响

通过ＧＳＤＭ－４００型超细盘式搅拌磨的工业型试验，考察了物料粒度，矿浆浓度，助磨剂用量和研磨介质填充率等对搅拌磨细磨重质碳酸钙的影响。经对各项磨矿条件的优化，取得了最佳的技术和经济指标。     

An analysis of wet grinding operation using a linearized population balance model for a pilot scale grate-discharge ball mill

Batch and continuous wet grinding experiments were carried out in a 40 × 40 cm grate-discharge ball bill. Well-distributed ?4 and ?20 mesh feeds of two complex pyritic ores were used. The vol. % solids in the pulp ranged from 30 to 40, the particle load from 5 to 8 kg, and the solids feed rate from 70 to 110 kg/h.Analysis of the experimental data showed that over the range of operating conditions investigated, a linearized model could be used to predict the size distributions of both the mill product as well as the mill hold-up of the solids, very accurately. The breakage rate parameters, S_i, were found to be dependent on the mode of operation, independent of the percent solids in the pulp, and approximately inversely proportional to the mill hold-up weight of the solids. In the case of the continuous mode of operation, with decrease in particle size the rate parameter values became increasingly smaller by comparison with the corresponding expected batch operation values.