جستجوی مقالات مرتبط با کلیدواژه « آسیای گلوله ای » در نشریات گروه « مهندسی معدن »

A sulfide copper ore was crushed to 100% passing 3.36mm followed by grinding the crushed product through bed breakage process in a piston- die cell or ball mill into to 100% passing 250μm. Revealed by the results of particle size analysis made on the ground products, the bed breakage method provides a finer product compared to the ball mill approach. The liberation analysis of the products in eight size-fractions showed that the chalcopyrite in the ball mill product was more liberated compared to the bed breakage product. The overall percentage of chalcopyrite liberation in the ball mill product was higher than the bed breakage product by 1.82%. The shape properties of particles in the breakage products were examined by analysis of scanning electron (SEM) images. Accordingly, it was found that the circularity and roundness of particles broken by the bed breakage method are higher than the particles broken by the ball mill method, while the ball-milled particles are more elongated. The results of micro-flotation tests indicated the efficiency rate of Cu recovery and separation in the ball mill product were respectively 11% and 15% higher than the bed breakage product. This better metallurgical performance can be attributed to the fact that the bed breakage product was finer, the chalcopyrite was more liberated in the ball milling product, and particles in the ball milling product had less circularity and roundness. Contrary to many previous studies, the results of this study indicated that the bed breakage method did not increase the mineral liberation and improved the performance of the flotation process.

The primary grinding of the concentration plant No.1 at the Sarcheshmeh copper complex includes eight ball mills working in a closed circuit with hydrocyclones. Due to the importance of the density of hydrocyclones in the classification process, the overflow density control loop was included in the initial plant design. Because of high cost, additional maintenance efforts, safety issues and constraints of nuclear density meters, this control loop never became operational. In this research, the percent solids was determined based on the mass balance equations in a format of a soft sensor. These sensors are computer programs that are used as an inexpensive alternative to hardware sensors and their use has increased in the material processing industry in the recent years. After transferring of the measured data to the control room, a program based on mass balances of solid and water the calculations for all 8 ball mills was prepared. To start the overflow density control loop, a control valve was installed on the inlet of the hydrocyclones feed tank. With the installation of hardware and the use of a soft sensor, the hydrocyclones overflow density control loop made operational for one of the ball mills. The monitoring of the circuit showed that the percent solids fluctuation of hydrocyclones overflow decreased from the range of 30.4 ± 4.5 when the percentage of solids was not displayed to a range of 28 ± 0.5 when using the percent solids control loop was operational. Furthermore, the measurement of the size distribution indicated that the percent of material finer than 75 microns of the overflow increased from 63.5% to 67% on account of installation of the control loop.

The present study aims to evaluate the effects of fracture mechanism on physical parameters such as size, shape, and specific surface area and to provide a description on how the grinding mechanisms of ball mill and High-Pressure Grinding Roll (HPRG) work. Moreover, the effects of these parameters on qualitative indicators of green pellets were also investigated. Furthermore, the amount of fine particle and surface shape of the obtained particles were compared. Results showed that the specific surface area of particles produced through HPGR is more than Ball Mill. This feature was recognized as the result of the increasing fine particles in the range of 7-25 µm and the presence of micro and macro cracks and fractures on the surface of the most particles manufactured by HPGR. In addition, pelletizing processes of HPGR and ball mill products at the same particle size distribution of 80% less than 43 and 90 µm showed that green pellets produced with HPGR product in d80=90 µm have more drop number and compressive strength in both dry (D.C.S) and wet (W.C.S) modes compared to ball mill. Also, the green pellets produced from HPGR product at d80=43 µm had higher drop number and W.C.S than ball mill product. But, compressive strength of green pellets in HPGR product showed 63.18% lower values of D.C.S than pellets produced by ball mill product at d80=43 µm. The reason for the lower D.C.S of the HPGR product is the increase of fine particles and specific surface area that consequently led to high water absorption by the fine particles.

When comminution precedes mineral beneficiation processes, the liberation spectrum of the particles in a comminution process is of great importance. The calculation of the liberation spectrum in a continuous closed milling circuit is a vastly more difficult task. Here, a method has been incorporated into the CMCS simulation software to calculate the product size distribution and liberation spectrum in ball mills. The model requires a minimum amount of experimental data and is capable of calculating the detailed liberation spectrum. While, other existing methods account only for the completely liberated particles and a broad group of unliberated particles are not represented. An easy-to-use ball mill simulation environment has been developed and the results are compared with measured grinding data and previously existing simulators, particularly MODSIM, demonstrating firmly tested performance both in terms of accuracy and precision of obtained results.

Tumbling mill liners transfer the energy to the mill charge and have a significant effect on the load behavior. A plant audit at the Sarcheshmeh_copper complex indicted that due to the inappropriate design of ball mills liners the liners wear and tear increased and the grinding efficiency decreased. With the objective of investigating the design of initial, current and proposed liners, the simulation of charge trajectory was performed by the GMT and KMPCDEM software packages. It was observed that the charge impact point for the current liners design was above the toe and on the shell liners. By simulation it was found that increasing the liner lifter face angle from 0 to 15° and the lifter height from 18 to 21cm could decrease the difference between the impact point and the toe and direct balls impact to liners. Given the promising results, the new liners were designed, constructed and installed in the ball mill 4. The result of sampling for a period of one liner life indicated that the amount of particles smaller than 75 microns for ball mill 4 product (proposed design) compared with the ball mill 3 (current design) increased by 2.5% and the liners life of the first half and second half increased by 18% and 20%, respectively.

Steady-State simulation of grinding circuit is an efficient tool for achieving reasonable estimates of the process and improving its performance. In this study، along with coding the grinding simulator for a closed circuit and providing applicable sub-routins for calculation of breakage and selection functions and etc in MATLAB and creating a user friendly interface، it was attempted to calibrate the models of this software using sampling data of Zarshuran gold processing pilot plant. Models’ Calibration was done using raw، average and also reconciled data using bilinear method and in each stage، simulation results and measured data were compared. Results of simulations showed that selecting valid models for the units and using reconciled data in model calibration process، leads to calculating true parameters for selected models and consequently، resulting in better simulations. Maximum error reduced from 153. 16 percent in water flowrate of hydrocyclone underflow calculated using raw data down to 4. 57 percent while reconciled data were used. In addition، it was shown that repetitive sampling of every sapmling point and averaging the data could reduce the errors to some extent.

At the grinding circuit of the Share-Babak copper concentration plant two 503 cm ×762 cm ball mills with motors of 2984 kW which are working with 10-cyclone (66. 8 cm diameter) clusters are used. In the initial design of the plant، it was assumed that this circuit could grind a feed rate of 721 t/h with size of 789 μm (80% passing size) to a product size of 90 µm (80% passing size). The study of the circuit during the last year indicated that due to variation of feed characteristics and non-optimized operating conditions P80 of the cyclone overflow (i. e.، flotation feed) was 128 µm with the standard deviation of 12 µm. In order to provide proper operating conditions، the ball mill percent solids was increased from 66 to 70%، and the ball load was also increased from 23 to 35%. On the account of increase in ball load، the mill power draw increased by 28%. To increase the performance of the cyclones، the cyclone feed solids concentration was decreased from 52 increased to 48 %. These changes decreased the P80 of the cyclone by 22. 7% and also lowered its variations by 40%.

Grate and its specification can significantly affect the performance of ball mills، semi-autogenous grinding (SAG) and fully autogenous grinding (FAG) mills equipped with this type of discharge mechanism. The grate design، open area and grate aperture size affect grinding throughput. In SAG and FAG mills، the inadequate design of discharge grate can lead to inefficiency of comminution device and creation of a slurry pool which practically stops particles'' breakage. In optimization projects، investigation on discharge grate and its effect on grinding process is critical due to particle size classification at mill exit، which necessitate the effect of grate to be considered in process modeling and simulation. In this project، discharge grates of Esfordi and Gol-e-Gohar plant ball mills and their effect on mill performance were investigated in details to make sure that the modeling and simulation and subsequent optimization studies are accurate as much as possible. To study and determine the effect of the discharge grate، samples were collected from mill feed and discharge streams when the circuits were under steady-state operation. After mass balancing، the discharge streams were simulated by BMCS®. Then the observed and simulated PSD of output were compared. The obtained results showed that the grate inside Esfordi ball mill does not affect the particle size distribution of mil output. In Gol-e-Gohar pilot plant ball mill the grate behaves like a fine screen which should be considered in mill mathematical modeling and simulation.