Locked Cycle Tests Research Articles

A computational algorithm coupled with a particle selection routine for the simulation of the Bond locked-cycle test

The Bond’s Equation is commonly used to predict the size-reduction energy in tumbling mills. The calculation of the Bond Equation requires the Bond Index, which is estimated through the results of the locked-cycle grinding tests. However, the tests are time-consuming, labor-intensive, and sensitive to errors. An algorithm is alternatively proposed to simulate the locked-cycle Bond tests by executing cycles of successive breakage events on non-randomly selected particles. The algorithm can yield reproducible Bond work indices fast with negligible computational errors. The algorithm’s applicability was validated against the experimental Bond tests on different ore samples. The results show that the algorithm can predict the grinding behavior of the mill hold-up at successive cycles. However, the simulated grindabilities are lower than the experimental ones, causing the algorithm to estimate slightly higher work indices as compared to the experimental indices. There is no sufficient data to conclude if such differences are because of (i) poor scaling of the breakage events, (ii) sampling/sieving errors, or (iii) varying grinding kinetics.

STUDY OF THE BEHAVIOR OF BINARY MIXTURE GRINDING USING THE FIXED-TIME LOCKED - CYCLE TESTS”.

Ores are generally very heterogeneous in their physical properties. Variation of the ore from a mine can cause the mill feed to vary in grindability. In the comminution of heterogeneous materials, an understanding of how different constituents behave by themselves and how they interact with each other may prove useful not only for understanding grinding mill action but also for obtaining the optimum values which used in mathematical modelling. Locked cycle tests show that in the grinding of mixtures relatively long time is required to attain steady state, during which the composition of the mill contents continuously change. Therefore, the main objective of this work is to study the behavior of the components of limestone-quartz binary mixture at different ratios of mixing from the start point to attain the steady state condition using the experimental fixed-time locked-cycle tests. It is shown that attaining the steady state condition in a fixed time locked cycle is faster with low circulating load for soft material than those for hard one when they ground separately. As admixture, the hard component appearance increases gradually with decreasing the fineness of the product as its percentage increases in the feed.

Laboratory Testing of Scheelite Flotation from Raw Ore in Sangdong Mine for Process Development

Tungsten is an essential metal for the manufacture of special alloys, which is in constant demand due to the development of the industry. The recovery of scheelite from undeveloped tungsten ore in South Korea was investigated to improve the flotation performance for high grade and recovery of concentrate. To investigate the interaction between the flotation reagents and the minerals, the adsorption experiments of oleic acid as a collector on Ca-bearing minerals, such as scheelite, calcite, and fluorite were carried out. This reaction was confirmed chemical adsorption by analysis of zeta potential and FTIR analysis. The batch test was performed using a raw ore to enhance the grade and recovery of the scheelite concentrate. It was obtained at the optimal conditions for high WO3 grade and recovery of scheelite concentrate by using a simple process. In particular, the sodium carbonate used as a pH modifier was investigated to increase scheelite flotation performance by supporting the selective depression of Ca-bearing gangue minerals. Furthermore, a locked cycle test (LCT) was carried out based on batch test results for the design of a continuous pilot plant.

Utilization of petrochemical by-products as a new frother in flotation separation of molybdenum

Recycling of petrochemical by-products is important for environmental protection and sustainable utilization of resources. In this study, petrochemical by-product was analyzed and used for the first time as a cost effective frother in flotation separation of molybdenum to replace terpineol. A significant improvement in molybdenum recovery was achieved by replacing terpineol with petrochemical by-products as frother. Properties of the petrochemical by-product and terpineol solutions, such as foaming, bulk rheology, and foam stability, were investigated through surface tension and rheological measurements. The properties of the petrochemical by-product solution are generally better than that of terpineol. In addition, results obtained in bench-scale flotation showed that the recovery of molybdenum substantially improved by 2.5% in the locked-cycle tests when the concentration of the petrochemical by-product was 100 g/t. Industrial tests showed that the molybdenum recovery obtained by using petrochemical by-products increased by 2.55% which can lead to about 6918192 RMB (1001113 USD) net profit per year. Therefore, these encouraging results suggest that petrochemical by-products can effectively be utilized in mineral processing plants as frothers, and interestingly, Jinduicheng Molybdenum Industry Co., Ltd, China is one that started to use it in industrial production by replacing terpineol.

Performance analysis of the HRCTM HPGR in pilot plant

A pilot scale test program was conducted to evaluate the size reduction performance of HPGR (High Pressure Grinding Rolls) operating in different circuit configurations. For this purpose a series of pilot-HPGR locked cycle tests were performed with medium and high pressures to simulate the HPGR operation in closed circuit with a screen, with partial product recycle, and with edge recycle. Logged instrumentation data such as roller speed, working gap, operating pressure, and power draw were used in combination with material test results such as particle size distributions, flake density, flake thickness, and bulk density of the feed for calculation of HPGR operational parameters. The paper reports the results from the pilot HPGR test work. The analysis reported herein includes an evaluation and comparison of different circuit configurations of the HPGR operation in terms of energy consumption, capacity and product fineness and also discusses the benefits of various circuit arrangements.

Grinding kinetics of steady-state feeds in locked-cycle dry ball milling

The size-discrete breakage rate and distribution parameters of the grinding kinetic model are mostly determined in laboratory batch mills using single-size feeds. However, there is evidence in the literature that particle size distribution in the mill affects the breakage parameters. Previous work studying this effect was mostly conducted with feeds whose size distributions were not closely representative of those normally dealt with in industrial mills. This study was undertaken with the main purpose of investigating the effect of particle size distribution on the breakage parameters of quartz and calcite minerals in dry ball milling using steady-state feeds obtained from Bond's locked-cycle tests. Different closing screen sizes were used in the locked-cycle work to produce different feed size distributions that would resemble feeds to industrial closed-circuit ball mills. Experimental results have shown that the breakage rate parameter of the top size interval increases as the feed size distribution in the mill becomes finer. There is some evidence implying grinding-environment dependency of the non-normalizable breakage distribution parameters. The cumulative-basis one-parameter linear population balance model gives a simple and reliable representation of the kinetics of closed-circuit dry ball milling.

Evaluation of a laboratory rod mill when grinding bituminous coal

Laboratory testing was conducted to evaluate the breakage of bituminous coal in a rod mill. A Pittsburgh seam coal, which had been obtained from the product stream of an operating coal cleaning facility, was used as the feed material. This material had an ash value of 6.7% and had been crushed to a nominal −6.35mm. Grinding tests were carried out on a mono-size (2.38×1.68mm) fraction. The tests were conducted using a 193.5mm diameter and 245.0mm long laboratory rod mill, which contained steel rods at a volume loading of 23%. The mill was operated at 70% of critical speed for various grind times. A locked-cycle test was also performed to simulate continuous grinding conditions.The grinding was characterized using the population (or size–mass) balance model. The breakage distribution and rates of breakage were determined from the grinding data. The results indicated first-order breakage. The locked-cycle results indicated that steady state was achieved in several iterations. The simulated results matched the experimental results very well.

Flotation data for the design of process plants Part 1 – testing and design procedures

This paper discusses the methods used in the design of flotation plants, including benchscale batch and locked cycle tests and pilot plant trials. The methods used to establish appropriate flotation circuits as well as the interpretation of the test work data are also discussed in this paper. Careful and appropriate sample selection must be followed by equally carefully designed and executed flotation test work if a successful outcome is to be achieved. These steps are detailed and the correct use of each type of test and the information which can be obtained is described. Practical design considerations such as flotation time, type, number and size of flotation cells, and the means of froth transport are all important and appropriate test work can guide decisions on all these factors.

Flotation data for the design of process plants Part 2 – case studies

The Cadia Hill Gold Mine and the Hellyer copper, zinc and lead plant present different problems with widely different target grind sizes, liberation characteristics. The contrast is between Hellyer's sequential flotation circuit versus Cadia's 'simple' copper–gold flotation circuit. The common theme is that pyrite forms the principal floatable concentrate diluent. Hellyer ore contains finely disseminated chalcopyrite, sphalerite, galena and tetrahedrite. The flotation plant design was based on extensive benchscale test work (including locked cycle tests) on drill core and many months of operation of a 30 t h−1 'pilot plant' using the modified Cleveland Tin Mine processing plant. The Cadia concentrator was designed based on an extensive benchscale variability test work programme. Data from approximately a dozen locked cycle tests conducted on drill core and 2 weeks of continuous pilot plant trials of samples obtained from an adit into the orebody were used as the basis of design. The orebody is a low grade monzonite porphyry with disseminated chalcopyrite/bornite/pyrite (0·17%Cu, 0·73 g t−1 Au). Methods used to establish the appropriated flotation circuits for the treatment of the Hellyer and Cadia ores, as well as the interpretation of the test work data for these particular operations, are discussed. The predicted versus actual operational plant is reviewed and the comparison was found to be satisfactory.

Application of neural networks to predict locked cycle flotation test results

The performance of a continuous flotation circuit is influenced by the flotation variables and the number of stages of a flotation circuit is dependent on flotation conditions, such that the interrelation between the flotation conditions and the number of stages must be carefully determined to obtain acceptable metallurgical performance from the circuit. The locked cycle test is a useful tool for simulation of continuous flotation circuits. However, it is a time-consuming and tedious procedure. A simulation method used to predict locked cycle test results from data from individual batch tests is available in the literature. In order to develop an optimum circuit configuration for a specific ore, several batch flotation tests for the first cycle of the locked cycle test have to be conducted to predict the metallurgical performance of various circuit types. Therefore, an integrated simulation method, which uses experimental data and the results of this simulation method has been developed to structure a neural network model for prediction of locked cycle tests results without additional experiment and calculation. In training and testing of the neural network model, results of the simulation method were used as the output data set and the flotation conditions of the batch tests were used as the input data set. Apart from the training and testing data, results of the LCT for several circuit types were predicted in order to validate the neural network model and to determine its performance on both: interpolation and extrapolation. Because the neural network model was trained using results of the simulation method, the use of the neural network model did not lead to any improvement in predictions of actual LCT results. However, the results of this study indicate that the neural network model can be used to simulate various circuit types with an error of less than 4%, instead of the simulation method. Consequently, the neural network model, as an alternative to the simulation method, can be used to determine the effects of changes in certain flotation variables on the number of cleaner and scavenger stages in a flotation circuit.

Reverse magnesite flotation

The present investigation deals with the production, at bench scale, of a high purity magnesite concentrate by means of reverse cationic flotation as an alternative to the direct anionic flotation currently employed in a concentrator in Brazil. The specification of the presently produced concentrate, in terms of maximum SiO 2 content, is 0.30% (calcined basis) and the weight recovery of the circuit is approximately 84%. The aim of this study was to produce concentrates with SiO 2 content ≤ 0.20% (calcined basis) and weight recovery ≥ 84%. A two level factorial design was employed in the first stage to optimise the variables that affect the behaviour of the system. In the second stage, the best conditions defined in the first stage were utilised in a locked cycle test, with simulation of circulating load, to predict the stability of the circuit in a continuous process. The main variables investigated were: percent solids and pH of the pulp, collector (ether amine) dosage, depressant (corn starch) dosage and flotation residence time. The aim of the study was achieved and a concentrate with 0.17% SiO 2, at a weight recovery level of 92.17%, was produced in the tests with simulation of circulating load in a rougher - cleaner - recleaner circuit. Lower SiO 2 contents could be reached with a reduction in weight recovery.

Calculation of locked cycle flotation test results

Locked cycle test are frequently used in mineral processing laboratories during the flowsheet development exercise in order to confirm batch results and to get an approximation of a continuous circuit material balance. A review of the literature indicates that there are at least four different methods for calculating the results of a locked cycle test. Only two of these methods offer the opportunity to examine whether or not the test reached steady state and only the cycle-by-cycle method intrinsically calculates the circulating streams. Because of the difficulty and expense of executing locked cycle tests and the frequent failure of the tests to reach steady state it should be of paramount importance to determine whether or not the test reached steady state; thus, the preferred method of calculation is the cycle-by-cycle technique.

Relation between locked cycle tests and continuous plant circuit in flotation

It is important to elucidate the relation between the locked cycle flotation test and the continuous flotation circuit because the locked cycled test has been traditionally the only way to experimentally simulate a continuous circuit. We analytically assessed the mass balances of the locked cycle test in a rougher–cleaner–cleaner scavenger (R–C–CS) system as a function of the iteration number of tests and provided an analytical expression of the mass balance in each separation stage. The mass of the final concentrate and flotation characteristic curves in a continuous circuit and the locked cycle test were calculated using the flotation rate constant k and flotation time T. Based on the comparison of the calculated results between the two tests, a good agreement between the locked cycle test and the continuous circuit can be obtained when the kT value for a product component with the flotation rate constant k and time T is in the range where the mass of a component does not change with kT.

Flotation rate measurements to optimize an operating circuit

Laboratory flotation rate measurements were made on site using pulp generated in an operating plant. The purpose of the measurements was to design an optimized flotation circuit to improve the plant performance. The laboratory tests, which included a locked cycle test, indicated that substantial improvements in the plant circuit were possible. There was excellent agreement between the numerically simulated and the experimentally simulated material balances.

Laboratory flotation separation of INCO bulk matte

Laboratory batch flotation tests were performed on a sample of bulk slow cooled converter matte (Cu:Ni = 1) to optimize the time in each of the separation stages. Numerical simulations were carried out to estimate a continuous circuit material balance for the conditions selected. An experimental simulation of a continuous circuit (locked cycle test) readily came to steady state and there was reasonable agreement between the numerical and experimental results. The use of nitrogen as the flotation gas and the addition of collector to the grinding mill minimized the oxidation of chalcocite, which has previously resulted in increasing circulating loads, and led to a stable circuit with very low weights in the recycle streams.

Influence of preheating on grindability of coal

Enormous quantities of coal must be ground as feed to power generation facilities. The energy cost of grinding is significant at 5 to 15 kWh/ton. If grindability could be increased by preheating the coal with waste heat, energy costs could be reduced. The objective of this work was to determine how grindability was affected by preheating. The method was to use population balance grinding models to interpret results of grinding coal before and after a heat treatment. Simulation of locked cycle tests gave a 40% increase in grindability. Approximately 40% grinding energy saving can be expected. By using waste heat for coal treatment, the targeted energy savings would be maintained.

Simulation of locked-cycle grinding of multicomponent feeds and its implications for stability and control of industrial comminution circuits

A mathematical algorithm is described for cycle-wise simulation of locked-cycle grinding tests in a ball mill using multicomponent feeds. The simulation is in good agreement with extensive experimental data for quartzite and limestone mixture feeds ranging in composition from 1:3 to 3:1. The simulation model is employed for generating transients in the locked-cycle tests by imposing either relatively large step changes or random fluctuations in a narrow band width on the composition of the feed, its fineness and the grinding time. Because locked-cycle tests mimic closed-loop grinding circuits with plug flow transport through the mill, the simulation provides useful insight into the stability and control of industrial comminution circuits where ore composition and hardness and the feed rate are invariably subjected to minor fluctuations on a more or less continuous basis, and occasionally to rather abrupt large changes.

Analytical evaluation of locked cycle flotation tests

A locked cycle test is one of the testing methods used to develop the optimum mineral recovery process. In order to understand the behavior of locked cycle tests, material balance equations are set up at the nth cycle of locked cycle tests consisting of three and four stages, called rougher, scavenger, cleaner and recleaner, and analytical solutions are obtained. From the analytical solutions, it becomes clear that the iteration number of the locked cycle tests required to reach a steady state depends on the flotation rate constant, the flotation time, the arrangement of the flotation stages and the total mass of recycled middlings which are discharged from the nth cycle of the locked cycle tests and fed into the subsequent ( n + 1)th cycle. In addition, flotation characteristics obtained from analytical solutions of a locked cycle test are compared with those of a continuous flotation circuit on the assumption that each flotation stage is composed of the same number of perfectly stirred cells of the same volume. As a result, it is found that good agreement between the theoretical locked cycle test and continuous flotation results is obtained when the number of cells in each stage is large.

Simulation of locked-cycle grinding tests using multicomponent feeds

Locked-cycle grinding tests using multicomponent feeds provide valuable insight into the dynamics of industrial closed-grinding circuits processing heterogeneous ores. These tests, however, are very laborious and time consuming. We present one general and two simplified mathematical algorithms for cycle-wise simulation of locked-cycle tests grinding mixture feeds. The algorithms have been tested against experimental data on locked-cycle grinding of calcite-quartz feed. Whereas single-component feeds require 3 to 6 cycles to attain steady state, mixture feeds need anywhere up to 35 cycles. The higher the hard mineral content of the feed, the greater is the change in the circulating load from one cycle to the next. The steady state recycle values vary steeply and almost linearly with the composition. These results imply that the closed-circuit grinding of heterogeneous ores is inherently less stable than those processing nominally pure minerals. The predominance of a soft matrix in the ores should enhance the stability of the circuit somewhat. Random and unintended variations in ore characteristics and feed rates, even relatively minor ones, make it virtually impossible to assure a stable performance for any length of time.

The comminution of multicomponent feeds under batch and locked-cycle conditions: Kinetics, simulation and energy distribution

The results of a detailed investigation of batch and locked-cycle dry grinding of quartz-calcite mixtures in a laboratory ball mill are presented. Batch grinding tests showed that the breakage rate function of the components is time-independent but composition-dependent and is normalizable with specific energy. Locked-cycle tests on the mineral mixtures revealed that approximately 25 2-min cycles are required before the composition of the circuit product and the recycle material attains steady state. The circulating load, after steadily increasing during the first 15 cycles, continued to fluctuate over a narrow range. These findings indicate that industrial-scale grinding circuits may also have long transient periods as the grindability of the ore changes and that circuits might be in transience perpetually.