Karbonat alkalinitesinin hematitin flokülasyonun üzerindeki etkileri.

The main objective in this study is to compare breakage parameters of narrow size fractions of cement clinker taken from the product end and feed end of industrial-scale high pressure grinding rolls (HPGR) in order to assess whether the breakage parameters of clinker broken in HPGR are improved or not. For this purpose, drop weight tests were applied to six narrow size fractions above 3.35 mm, and batch grinding tests were applied to three narrow size fractions below 3.35 mm. It was found that the breakage probabilities of coarse sizes and breakage rates in fine sizes were higher in the HPGR product. This indicated that clinker broken by HPGR contained weaker particles due to cracks and damage imparted. However, no significant weakening was observed for the -19.0+12.7 mm HPGR product. Although HPGR product was found to be weaker than HPGR feed, fragment size distribution of HPGR product did not seem to be finer than that of the HPGR feed at a given loading condition in either the drop weight test or batch grinding test. Also, drop weight tests on HPGR product and HPGR feed showed that the breakage distribution functions of coarse sizes depended on particle size and impact energy (J). Batch grinding tests showed that the specific breakage rates of HPGR product and HPGR feed were non-linear which could be represented with a fast initial breakage rate and a subsequent slow breakage rate. The fast breakage rates of each size fraction of HPGR product were higher than HPGR feed due to cracks induced in clinker by HPGR. However, subsequent slow breakage rates of HPGR product were close to those of HPGR feed due to elimination of cracks and disappearance of weaker particles. Besides, the variation in breakage rates of HPGR product and HPGR feed with ball size and particle size also showed an abnormal breakage zone where ball sizes were insufficient to effectively fracture the coarse particles. Breakage distribution functions of fine sizes of HPGR product and HPGR feed were non-normalizable and depended on particle size to be ground. However, batch grinding of -2.36+1.7 mm and -1.7+1.18 mm HPGR feed yielded the same breakage pattern.M.S. - Master of Scienc

Investigating the effects of random sieving losses on particle size distributions

Sieving analyses are very susceptible to the unavoidable particle losses. Therefore, it is important to assess how sieving losses will affect the particle size distributions. This study aims to simulate sieving losses under a computing environment to further investigate their effects on the particle size distributions. For the purpose of this study, the cumulative size distributions of different particulate materials were generated by using the Gates-Gaudin-Schuhmann (GGS) and Rosin-Rammler-Bennett (RRB) equations. Then, random sieving losses were generated by taking random mass fractions from randomly-selected size intervals. The sums of these random losses were subtracted from the original masses in the size intervals. The calculated residual masses in the size intervals were used to construct the cumulative size distributions of the residual materials. Results show that increasing the mass of sieving losses will only change the position of wide distributions. However, increasing losses will both change the position and shape of narrow distributions. Tolerating all sources of sieving errors may be better to preserve the distribution shapes. The simulation results suggest the rule-of-thumb limit for sieving losses. Sieving losses cause the GGS plots of the grinding products to deviate to bilinear shapes at finer size ranges

Estimating the number-weighted equivalents of the mass-weighted size distribution functions

The number-weighted particle size distributions are difficult to be estimated experimentally. This study offers a simple conversion method to convert mass-weighted distributions to their number-weighted equivalents. Besides, the number-weighted equivalents of the Gates-Gaudin-Schuhmann, Gaudin-Meloy, Pareto, and Rosin-Rammler distributions were determined by the conversion method. The accuracy of the method was successfully confirmed on the artificial populations generated from the Gates-Gaudin-Schuhmann, Rosin-Rammler (Weibull), and Pareto distributions. However, the number-weighted equivalent of the Gaudin-Meloy distribution was found to be trivial. The results also indicate that the conversion method may be applied to a wide range of sieve size distributions that are truncated with upper and lower bounds

The use of non-parametric tests between subsamples and particle population for the assessment of minimum number of particles in microscopic analysis

The use of small and reliable samples in a microscopic analysis can decrease the time to estimate the particle size and mineral grade distributions in a population of particles. This paper attempts to assess the minimum reliable sample size for the above-mentioned distributions, by implementing non-parametric tests on the subsamples taken from a specific population of 2800 particles. The Kolmogorov-Smirnov tests show that the subsamples which contain more than 800 particles (29% of the population) cannot give cumulative distributions of particle size and mineral grade different from their equivalents in the population. On the other hand, Chi-square tests show that 1500-1700 particles (54-61% of the population) may be sufficient to estimate the discrete distributions in the population. The minimum reliable sample size increases with an enlarging population because the sampling errors should increase while taking samples of equal size from larger populations. Nevertheless, the minimum reliable size should be 29-32% of the population if the distributions of mineral grade and particle size in the population are fitted to bimodal and normal distributions, respectively

Development of a supervised classification method to construct 2D mineral maps on backscattered electron images

The Mineral Liberation Analyzer (MLA) can be used to obtain mineral maps from backscattered electron (BSE) images of particles. This paper proposes an alternative methodology that includes random forest classification, a prospective machine learning algorithm, to develop mineral maps from BSE images. The results show that the overall accuracy and kappa statistic of the proposed method are 97% and 0.94, respectively, proving that random forest classification is accurate. The accuracy indicators also suggest that the proposed method may be applied to classify minerals with similar appearances under BSE imaging. Meanwhile, random forest predicts fewer middling particles with binary and ternary composition, but the MLA predicts more middling particles only with ternary composition. These discrepancies may arise because the MLA, unlike random forest, may also measure the elemental compositions of mineral surfaces below the polished section

Investigating the effects of water pretreatments on chromite liberation

Many studies investigated the effects of grinding aids on mechanical and breakage properties of particles, as well as the flowability of ore-water slurries in wet grinding mills. Only recently, it was showed that grinding aids can promote grain-boundary fracturing. This paper aims to observe the effects of water pretreatment on chromite liberation, to underlie some reactions between water and chromite samples which promote the liberation of coarse chromite grains, i.e. the grain-boundary fracturing. For the purpose of this study, two different chromite ore samples were initially pretreated under water at different sets of pH, temperature and pretreatment time. Then, the untreated and pretreated samples were broken in a drop-weight tester (J/g). Finally, the grade-recovery plots in the selected progeny size fractions of the untreated and pretreated samples were compared. The results show that the hydrolysis of ore samples in 15 min of pretreatment improves the grain-boundary fracturing. The results also suggest that mineral carbonation may be beneficial for chromite liberation

Simulating probabilistic sampling on particle populations to assess the threshold sample sizes for particle size distributions

The primary objective in sampling is to acquire the smallest sample as a reliable estimate of a particle population. This study aims to assess the threshold (minimum) sample sizes for reliable estimation of particle size distributions. For that purpose, samples were simulated from particle populations artificially generated from the Gates-Gaudin-Schumann model. Then, two-sample Kolmogorov-Smirnov and Chi-Square Goodness-of-Fit tests were implemented between the number-weighted size distributions of samples and their parent populations. Results suggest that continuous size distributions can be estimated with at least 36-40% of the number of population particles. Corresponding masses to estimate continuous distributions varies between 34% and 68% population mass, where smaller populations may require larger samples. Results indicate that probabilistic sampling may be insufficient to estimate the discrete number-weighted size distributions. Probabilistic sampling seems insufficient to estimate the mass-weighted size distribution of widely sized population particles. Estimating mass-weighted distributions requires larger samples than their number-weighted equivalents. Mass-weighted size distributions of samples better fit at the finest or the coarsest size ranges than the mid-size range of their population. If a population is large, the percent population mass taken as a sample is nearly equal to the percent number of population particles

Correlating common breakage modes with impact breakage and ball milling of cement clinker and chromite

Understanding the mechanisms of the breakage of ore particles is important to predict the particle size distribution in size reduction operations. This paper aims to show the presence of common breakage modes in impact breakage and ball milling of the cement clinker and chromite samples. For that purpose, narrow size fractions of the two samples were broken in a drop-weight tester or ball mill by changing the degree of applied energy. Then the resultant size distributions were evaluated to seek evidence for the common breakage modes. The results showed that increasing the breakage energy will produce a systematic change in the shapes of the size distributions, suggesting a sequential set of breakage modes. The breakage is initially due to tensile stresses at low breakage energies and compressive stresses at high breakage energies. Further studies should be done to assess if these breakage modes occur at size-reduction of different ores. (C) 2020 Published by Elsevier B.V. on behalf of China University of Mining & Technology

Kimyasal ön işlemin tanelerin kırılma şekli ve mineral serbestleşmesine etkisi.

The conventional approach in mineral beneficiation is to increase ore fineness for achieving sufficient degrees of mineral liberation. However, achieving finer products requires higher grinding energies, and finer products generate problem in slurry flow at further processing steps. Then, the emphasis should be given to foster breakage along grain-boundaries between minerals, so that sufficient liberation can be achieved without excess breakage. The purpose of this study is to assess if the aqueous species can make surface complexes at the grain boundaries to promote grain-boundary fracturing, and consequently chromite liberation. For this purpose, chromite ore samples were treated under water, dilute surfactant and electrolyte solutions at varying pH and temperature. The treated samples were broken in drop-weight tester, and then the liberation spectra and mass distribution of the resultant progenies were evaluated with the ones of untreated feed. Besides, some microscopic and spectroscopic tools were used to find evidence for structural changes at the grain boundaries in the case of improved liberation. Results show that hydrolysis of silicates tends to improve grain-boundary fracturing since it preferentially dissolves Si-layers which are located near to or at the grain-boundary regions. However, protonation tends to remove Mg-layers in silicates and hinder grain-boundary fracturing since Mg-layers are accumulated at the bulk texture. Aqueous salt and surfactant species enhance grain-boundary fracturing, and consequently chromite liberation if they form surface complexes and dissolve Al-layers at the grain boundaries. Grain-boundary fracturing yields exposed chromite surfaces and enriched chromite content in coarser progeny classes.Ph.D. - Doctoral Progra

A Pseudo-matrix model coupled to a particle selection algorithm for simulating batch grinding

The kinetic population balance model (PBM) is widely used to predict the particle size distributions of ball milling products. The matrix model can be easily used for the same purpose if the grinding time can be incorporated into the relevant model. This study proposes and demonstrates an accurate algorithm that uses a pseudo-matrix model to simulate the product size distributions (PSDs) of successive breakage events in batch grinding. The simulation results indicate that the breakage events in the mills may be determined by attraction forces between particles and grinding media. The algorithm is shown to be widely applicable to different combinations of samples and grinding equipment. The algorithm can even work with arbitrary sets of parameters that are irrelevant to the mill feed. Therefore, the proposed algorithm with its mathematical framework may be fundamental to different size reduction methods. Also, the algorithm is shown to have a potential for predicting the product PSDs of continuous milling