Julius Kruttschnitt Mineral Research Centre Publications - UQ eSpace

Human factors in control room operations in mineral processing: Elevating control from reactive to proactive

2012-02-16T09:19:33Z

This study applied human factors research approaches to the complex and dynamic environment of mineral processing plants. In this domain, little formal human factors research has previously been undertaken, despite that human performance limitations are frequently noted as a bottleneck to effective production. This article presents a broad, operator-centered investigation on the current status of control room operations and explores the underlying barriers in the operators’ work environment. A total of 20 operators working at two types of Australian mineral processing plants were involved. Multiple data collection methods, including in situ observations and interviews, surveys, and reviews of documentation, were used. The findings revealed that operator control was essentially in a reactive mode, with operators often lacking the will or ability to engage in process optimization. A simplified work domain analysis was used to highlight the essential elements involved in operator control and to explore the gaps between the observed reactive behavior and the required proactive control employed by operators. Also, this study uncovered deficiencies in the current information and organizational environments constraining operator control ability. These deficiencies included poorly designed human-machine interface and alarms, insufficient operator training, and inappropriate task allocations. Further research for enhancing operator capacity is recommended and highlighted.

Hydrophobic Flocculation Applied to Fine Mineral and Coal Processing

2004-02-05T00:00:00Z

This paper highlights hydrophobic flocculation applied to fine minerals and coal processing. Initially, hydrophobic flocculation and its separation technology are briefly described. Then, several examples on the application of this technology to the beneficiation of fine minerals and coals are presented. Finally, the three main parameters affecting hydrophobic flocculation, namely particle hydrophobicity, non-polar oil addition and suspension stirring, are discussed. It is demonstrated that the separation technology based on hydrophobic flocculation is a potential mean to efficiently recover valuable minerals in the fine size range and to effectively remove finely disseminated impurities from coals.

Hydrophobic Flocculation of Galena Fines in Aqueous Suspensions

2004-02-05T00:00:00Z

The hydrophobic flocculation of galena fines induced by potassium amyl xanthate (PAX) in aqueous suspensions has been studied using laser diffraction, electrophoretic light scattering, contact angle, and microflotation measurements. The measurements were performed on <2um, 2-5um, 5-10um, and <30um size galena by varying several parameters, including PAXconcentration, pH, original particle size, kerosene concentration, and suspension stirring. The experimental results have demonstrated that the hydrophobic flocculation was closely correlated with the particle hydrophobicity, but was not lowered upon increasing the particle surface charges due to PAX adsorption, which is contrary to the DLVO theory. This flocculation has been observed to increase with a reduction of the original particle size and an increase in kerosene concentration, and to require sufficient stirring strength and magnitudes of kinetic energy input to achieve the maximum aggregation degree. From the microflotation results, it has been found that the flotation response of galena fines is markedly improved due to the formation of hydrophobic flocs, suggesting that floc flotation is a promising means to recover galena in the fine size range.

Image analysis for mineral processing

2008-06-06T00:00:00Z

Impact of electron beam irradiation on the cathodoluminescence intensity for ZnO and GaN

2010-01-13T00:00:00Z

We have studied the effect of the electron beam irradiation on ZnO and GaN by using cathodoluminescence (CL). The bandedge emissions of ZnO and GaN usually decrease during CL observation, but they can increase in certain cases, such as Zn-plane in ZnO. These variations depend on not only the specimens and the electron beam conditions but also the nature of the luminescence centers and the chemical nature of the material surface. This work suggests that the electron beam induces some modifications near the surface region.

Implementation of control and control issues in mineral sands plants - In-line mass flow meter.

Rivett, T. C. og Pax, R. A. — 2007-08-24T00:00:00Z

Importance of strain to fragment strength in blasting induced pre-conditioning

Michaux, Simon P. og Hocking, Rodney James — 2010-12-13T00:00:00Z

When a rock is blasted, cracks propagate through the rock causing the rock to fracture. This paper focuses on applying the results from a series of small scale blasting tests were designed to show the effect that varying blast variables such as explosive type and explosive energy have on the resulting strength of the post blast fragments. It was shown that the velocity of detonation of the explosive product affects the reduction of fragment strength. This has important implications for the downstream comminution process. The observations from these tests are then explained with reference to the principles of fracture mechanics. A simple but effective prediction of blast induced preconditioning is shown.

Importance of the feed size distribution and recycle on the HPGR performance

2011-10-13T00:00:00Z

Improved dewatering behaviour of clay minerals dispersions via interfacial chemistry and particle interactions optimization

2011-08-09T00:00:00Z

Orthokinetic flocculation of clay dispersions at pH 7.5 and 22 °C has been investigated to determine the influence of interfacial chemistry and shear on dewatering and particle interactions behavior. Modification of pulp chemistry and behavior was achieved by using kaolinite and Na-exchanged (swelling) smectite clay minerals, divalent metal ions (Ca(II), Mn(II)) as coagulants and anionic polyacrylamide copolymer (PAM A) and non-ionic polyacrylamide homopolymer (PAM N) as flocculants. The pivotal role of shear, provided by a two-blade paddle impeller, was probed as a function of agitation rate (100–500 rpm) and time (15/60 s). Particle zeta potential and adsorption isotherms were measured to quantify the interfacial chemistry, whilst rheology and cryogenic SEM were used to investigate particle interactions and floc structure and aggregate network, respectively. Osmotic swelling, accompanied by the formation of “honeycomb” particle network structure and high yield stress, was produced by the Na-exchanged smectite, but not kaolinite, dispersions. Dispersion of the clay particles in 0.05 M Ca(II) or Mn(II) solution led to a marked reduction in particle zeta potential, complete suppression of swelling, honeycomb network structure collapse and a concomitant reduction in shear yield stress of smectite pulps. Optimum conditions for improved, orthokinetic flocculation performance of negatively charged clay particles, reflecting faster settling flocs comprised (i) coagulation, (ii) moderate agitation rate, (iii) shorter agitation time, and (iv) anionic rather than non-ionic PAM. The optimum dewatering rates were significantly higher than those produced by standard, manual-mixing flocculation techniques (plunging and cylinder inversion) commonly used in industry for flocculant trials. The optimum flocculation conditions did not, however, have a significant impact on the final sediment solid content of 20–22 wt%. Further application of shear to pre-sedimented pulps improved consolidation by 5–7 wt% solid. Higher shear yield stresses and greater settling rates were displayed by PAM A based than PAM N based pulps and this is attributed to the former's more expanded interfacial conformation and greater clay particles bridging ability. It appears that the intrinsic clay particles' physico-chemical properties and interactions limit compact pulp consolidation.

Improved experimental tracking techniques for validating discrete element method simulations of tumbling mills

2009-01-23T00:00:00Z

We report on further developments in the three-dimensional tracking of a particle deep within the tumbling ball charge of an experimental mill. The experimental X-ray program employing the use of bi-planar X-ray angiography now includes the tracking of a typical 6 mm bulk charge particle in three dimensions with a spatial resolution that is accurate to within 0.15 mm. The improved experimental tracking techniques presented were developed for the purpose of generating accurate three-dimensional particle trajectory data against which to validate a numerical method for the simulation of discrete media, namely the discrete element method (DEM). These improvements are complimented with techniques for comparing charge profiles between numerical DEM simulations and three-dimensional experimental trajectory data

Improved slope adjustment functions for soil erosion prediction

2007-08-15T00:00:00Z

Numerous studies in the last 60 years have investigated the relationship between land slope and soil erosion rates. However, relatively few of these have investigated slope gradient responses: ( a) for steep slopes, (b) for specific erosion processes, and ( c) as a function of soil properties. Simulated rainfall was applied in the laboratory on 16 soils and 16 overburdens at 100 mm/h to 3 replicates of unconsolidated flume plots 3 m long by 0.8 m wide and 0.15 m deep at slopes of 20, 5, 10, 15, and 30% slope in that order. Sediment delivery at each slope was measured to determine the relationship between slope steepness and erosion rate. Data from this study were evaluated alongside data and existing slope adjustment functions from more than 55 other studies from the literature. Data and the literature strongly support a logistic slope adjustment function of the form S = A + B/[1 + exp (C - D sin theta)] where S is the slope adjustment factor and A, B, C, and D are coefficients that depend on the dominant detachment and transport processes. Average coefficient values when interill-only processes are active are A - 1.50, B 6.51, C 0.94, and D 5.30 (r(2) = 0.99). When rill erosion is also potentially active, the average slope response is greater and coefficient values are A - 1.12, B 16.05, C 2.61, and D 8.32 (r(2) = 0.93). The interill-only function predicts increases in sediment delivery rates from 5 to 30% slope that are approximately double the predictions based on existing published interill functions. The rill + interill function is similar to a previously reported value. The above relationships represent a mean slope response for all soils, yet the response of individual soils varied substantially from a 2.5-fold to a 50-fold increase over the range of slopes studied. The magnitude of the slope response was found to be inversely related ( log - log linear) to the dispersed silt and clay content of the soil, and 3 slope adjustment equations are proposed that provide a better estimate of slope response when this soil property is known. Evaluation of the slope adjustment equations proposed in this paper using independent datasets showed that the new equations can improve soil erosion predictions.

Improvement of energy efficiency of rock comminution through reduction of thermal losses

Djordjevic, N. — 2009-03-19T00:00:00Z

Improvement of energy efficiency of rock comminution through reduction of thermal losses

Djordjevic, Nenad — 2010-12-19T00:00:00Z

Improving efficiency of the Shahre-Babak copper complex deep cone thickeners

2012-10-08T13:04:04Z

Improving energy efficiency across mineral processing and smelting operations - A new approach.

2009-11-26T00:00:00Z

Improving flotation performance in the good, the bad and the ugly economic times - The Century story.

2009-11-30T00:00:00Z

Improving grinding efficiency with the IsaMill

2009-03-17T00:00:00Z

Improving pentlandite selectivity over pyrrhotite using reagents

2010-12-13T00:00:00Z

The Sheba’s Ridge ore, hosted by the Bushveld Igneous Complex (BIC) in South Africa is exploited for its platinum group elements (PGEs), which are typically associated with the base metal sulfi des pentlandite, pyrrhotite and chalcopyrite. Unusually, in the case of the Sheba’s Ridge ore, pyrrhotite shows little or no association with PGEs. Therefore, the aim of this study was to develop a methodology for the selective fl otation of pentlandite from pyrrhotite using the polysaccharide depressants that are already in use in the fl otation of BIC ores to control the naturally fl oating gangue minerals such as talc. Microfl otation tests were conducted on a high grade Nkomati massive sulfi de ore sample as a probe ore, to investigate the fl otation response of pentlandite and pyrrhotite to four different chain length xanthate collectors (SEX, SNPX, SIBX and PAX) and to different types of polysaccharide depressants (guar, CMC and starch). The effect of oxygen addition and pH modifi cation were also studied. Laboratory batch fl otation tests were then carried out using the Sheba’s Ridge ore, to evaluate the optimum reagent suite and fl otation conditions determined in the microfl otation tests. The results showed that using the different chain length xanthates or polysaccharide depressants on their own did not produce any pentlandite selectivity, but, when these reagents were used in conjunction with one another, some pentlandite selectivity was obtained. The best combination was found to be an intermediate chain length xanthate (SNPX) with guar depressant, where a balance between collector hydrophobicity and selectivity was obtained. Adjustment of the pH to 10, using lime instead of NaOH, together with artifi cial pre-oxidation showed further improvement in the selective fl otation of pentlandite. This was attributed to the faster oxidation rate of pyrrhotite at these conditions, which led to selective depression of pyrrhotite while pentlandite fl oatability was maintained. These results show that there needs to be a synergistic interpretation of the interactions present in the reagent-mineral system. The study has also shown that the reagents used in fl otation cannot be evaluated independently but rather a holistic approach needs to be employed.

Improving the recovery of coarse coal particles in a Jameson cell

2007-08-15T00:00:00Z

It has been observed in several Jameson cell installation where the source for flotation feed is deslime screens, that the recovery of coal particles greater than 0.5 mm is not as great as that of finer material. Consequently, a research project was undertaken at a CHPP in the Bowen Basin Queensland to assess the possibility of increasing the recovery of coarser particles (+0.5 mm) within the downcomer of the Jameson cell. The effect of decreasing turbulence and agitation in a commercial-scale downcomer was investigated to assess the effect oil the recovery of both coarse and fine coal particles. This paper details the findings of the test work, summarising the results relating to differences in the operating parameters within the downcomer. (C) 2005 Elsevier Ltd. All rights reserved.

Improving the recovery of low grade coarse composite particles in porphyry copper ores

2011-08-22T00:00:00Z

Increased profits through mine-and-mill integration

Morrell, S. og Munro, P. D. — 2008-06-06T00:00:00Z

Increasing copper recovery in flotation

Farrokhpay, S. og Manouchehri, H. R. — 2011-08-22T00:00:00Z

Industrial screening

Hilden, M. M. og David, D. — 2007-08-14T00:00:00Z

Wills' Mineral Processing Technology provides practising engineers and students of mineral processing, metallurgy and mining with a review of all of the common ore-processing techniques utilized in modern processing installations. Now in its Seventh Edition, this renowned book is a standard reference for the mineral processing industry. Chapters deal with each of the major processing techniques, and coverage includes the latest technical developments in the processing of increasingly complex refractory ores, new equipment and process routes. This new edition has been prepared by the prestigious J K Minerals Research Centre of Australia, which contributes its world-class expertise and ensures that this will continue to be the book of choice for professionals and students in this field. This latest edition highlights the developments and the challenges facing the mineral processor, particularly with regard to the environmental problems posed in improving the efficiency of the existing processes and also in dealing with the waste created. The work is fully indexed and referenced.

Industry taking the initiative in developing high calibre technical staff

2009-01-27T00:00:00Z

Inferring eye movements on the basis of head and visual target position

Batten, L.M. og Whiten, W. J. — 2007-08-24T00:00:00Z

Influence of charge size distribution on net-power draw of tumbling mill based on DEM modelling

Djordjevic, N. — 2007-08-15T00:00:00Z

Modelling and optimization of the power draw of large SAG/AG mills is important due to the large power draw which modern mills require (5-10 MW). The cost of grinding is the single biggest cost within the entire process of mineral extraction. Traditionally, modelling of the mill power draw has been done using empirical models. Although these models are reliable, they cannot model mills and operating conditions which are not within the model database boundaries. Also, due to its static nature, the impact of the changing conditions within the mill on the power draw cannot be determined using such models. Despite advances in computing power, discrete element method (DEM) modelling of large mills with many thousands of particles could be a time consuming task. The speed of computation is determined principally by two parameters: number of particles involved and material properties. The computational time step is determined by the size of the smallest particle present in the model and material properties (stiffness). In the case of small particles, the computational time step will be short, whilst in the case of large particles; the computation time step will be larger. Hence, from the point of view of time required for modelling (which usually corresponds to time required for 3-4 mill revolutions), it will be advantageous that the smallest particles in the model are not unnecessarily too small. The objective of this work is to compare the net power draw of the mill whose charge is characterised by different size distributions, while preserving the constant mass of the charge and mill speed. (C) 2004 Elsevier Ltd. All rights reserved.

Influence of explosive energy on the strength of the rock fragments and SAG mill throughput

Michaux, S og Djordjevic, N — 2007-08-15T00:00:00Z

Extensive in-situ testings has shown that blast fragmentation influences the performance of downstream processes in a mine, and as a consequence, the profit of the whole operation can be greatly improved through optimised fragmentation. Other unit operations like excavation, crushing and grinding can all be assisted by altering the blast-induced fragmentation. Experimental studies have indicated that a change in blasting practice would not only influence fragmentation but fragment strength as well. The strength of the fragments produced in a blast is clearly important to the performance of the crushing and grinding circuit as it affects the energy required to break the feed to a target product size. In order to validate the effect of blasting on fragment strength several lumps of granite were blasted, under controlled conditions, using three very different explosive products. The resulting fragments were subjected to standard comminution ore characterisation tests. Obtained comminution parameters were then used to simulate the performance of a SAG mill. Modelling results indicate that changes in post blast residual rock fragment strength significantly influences the performance of the SAG mill, producing up to a 20% increase in throughput. (c) 2004 Elsevier Ltd. All rights reserved.

Influence of feed size on AG / SAG mill performance

Morrell, S. og Valery, W. — 2007-08-23T00:00:00Z

Influence of impact velocity on fragmentation and the energy efficiency of comminution

2012-03-13T00:00:00Z

Influence of Li-dopants on the luminescent and ferroelectric properties of ZnO thin films

2010-01-13T00:00:00Z

Zn1

Influence of milling condition on the mechanochemical synthesis of CaTiO3 nanoparticles

Palaniandy, Samayamutthirian og Jamil, Noorina Hidayu — 2011-11-22T00:00:00Z

Influence of polymer functional group architecture on titania pigment dispersion

2011-08-22T00:00:00Z

The influence upon adsorption of polymers containing different functional groups on the dispersion behaviour of titania pigment particle has been investigated at pH 6.0 and 9.5. The polymers chosen are polyacrylic acid and modified polyacrylamides including homo and copolymers modified with carboxylate and/or hydroxyl groups. A range of experimental methods including polymer adsorption isotherms, zeta potential, rheology and particle size measurements were used to assess the dispersion effect of the polymers. Adsorption of polyacrylic acid and anionic polyacrylamide copolymers onto the titania pigment surface is greatest when electrostatic repulsion is absent. At low pH values, below the pigment isoelectric point (iep), the adsorption density of the anionic polymers on titania pigment was high whilst at higher pH values, above the pigment iep, the adsorption density decreased. However, the adsorption of non-ionic polymers on titania pigment was less influenced by the pH. The presence of carboxylate functional groups in both polyacrylic acid and anionic polyacrylamide copolymer altered the titania pigment dispersion behaviour, reducing the suspension yield stress and mean particle size. The polyacrylamide homopolymer had negligible effect on the pigment dispersion properties at pH 9.5, while it caused pigment particle aggregation at pH 6.0. The hydroxyl-modified polyacrylamide had also a de-stabilisation effect on the pigment dispersion at pH 6.0, but decreased the yield stress and the mean particle size at pH 9.5. The stabilisation effect of both anionic and non-ionic polymers was pH-dependent. The dispersion properties of the pigment particles are largely predicted by DLVO theory.

Influence of slurry rheology on stirred media milling of limestone

He, Mingzhao og Forssberg, Eric — 2010-02-24T00:00:00Z

Influence of slurry rheology on stirred media milling of quartzite

He, Mingzhao og Forssberg, Eric — 2009-12-16T00:00:00Z

The role of slurry rheology in stirred media milling of quartzite has been investigated by varying important grinding parameters such as media bead density and size, addition of chemicals, solids concentration, stirrer rotational speed as well as the combined effect of these factors. Media bead density has an evident but complex effect on stirred milling performance, depending on stirrer rotational speed and solids concentration. The effect of media bead size on the ultra-fine grinding of quartzite is relevant to the feed size. Optimal ratio of media bead size to the median size of a feed is between 150 and 200. The combined effect of grinding bead size and stirrer speed or solids concentration is insignificant. The addition of Dispersant S40 or a lower solids concentration results in better grinding performance (i.e., a higher energy efficiency and a smaller median size) due to the maintenance of lower viscosities at shear rates investigated during grinding. Stirrer rotational speed interacts with solids concentration. For a given solids concentration, an optimal stirrer speed exists. The observed phenomena can be explained by the interaction of slurry rheology and the stress intensity of individual grinding bead. In addition, an empirical particle size-energy model provides a good fit (R2 > 0.904) to the grinding results under the experimental conditions investigated. Furthermore, the wear of grinding media beads is involved. ZrO2 beads have a lowest wear rate whereas the wear of SiO2 beads is most serious. The wear rate of Al2O3 beads is related to bead size.

Influence of the distribution function on modelling and simulation of the Carajas grinding circuit - Part 1 - Model fit

Foggiatto, Bianca og Delboni Junior, Homero — 2012-04-05T00:00:00Z

Influence of turbulence kinetic energy on bubble size in different scale flotation cells

2012-01-09T09:28:40Z

Influence of turbulence kinetic energy on bubble size in different scale flotation cells

2013-04-04T14:34:41Z

Influence of variation in grind size distribution on flotation kinetics of Northparkes copper ore

2010-12-07T00:00:00Z

Influencia da funcao distribuicao de quebra na modelagem e simulacao do circuito de moagem de Carajas. Parte 2: Simulacao

Foggiatto, Bianca og Delboni Júnior, Homero — 2012-04-05T00:00:00Z

Inhomogeneous distribution of dislocations in a SiGe graded layer and its influence on surface morphology and misfit dislocations at the interface of strained Si/Si0.8Ge0.2

2010-01-15T00:00:00Z

To improve the quality of a strained Si layer on a SiGe virtual substrate, the distribution of dislocations in a graded SiGe layer is characterized using electron beam induced current sEBICd. A crosshatch pattern of dark and bright bands running along the two k110l directions is observed in an EBIC image taken with a 25-keV-electron beam at 80 K. These dark and bright EBIC bands are attributed, respectively, to high- and low-density dislocation regions in the graded SiGe layer, as is confirmed by transmission electron microscopy. The effects of such an inhomogeneous dislocation distribution on the surface morphology and the generation of misfit dislocations sMDsd at the interface of strained Si/SiGe are investigated. Comparison between the EBIC image and an atomic force microscope image shows that the high-density dislocation regions are correlated with ridges on the surface topography. A chemical etching image shows that most of the MDs lie along the edges of surface ridges. Possible mechanisms of MD generation at the interface of the strained Si/SiGe are proposed.

Integrated grinding and flotation simulations for the improvement of circuit performance at BHP Billiton's Minera Escondida

2008-05-08T00:00:00Z

BHP-Billiton's Minera Escondida Limitada is one of the world's largest copper producers. It treats a combined 88 million tons of copper ore per year through its two concentrators: Los Colorados and Laguna Seca. Over the past three years, metallurgical sampling has been performed at the Laguna Seca concentrator to calibrate both the JKSimMet and JKSimFloat grinding and flotation simulators. In the past, the calibrated simulators have been used to predict the effect of changes in operating conditions in the grinding and flotation circuits separately. To assist in the development of future processing options, predictions were required of the effect of changing grinding circuit conditions on flotation performance. This was achieved by using an integrated grinding and flotation simulation. The grinding circuit performance was predicted under different operating conditions (such as tonnage rate and product grind size) using JKSimMet, and these results were then used in JKSimFloat to predict the flotation performance for the new grinding circuit product. This combination of the simulators allows both the effects of residence time and grind size on flotation performance to be investigated. This paper presents the first combined grinding and simulation modelling and simulation case study using JKSimMet and JKSimFloat. The modelling and simulation methodologies for the grinding and flotation circuits are discussed along with the circuit simulations that were performed. The simulator predictions are presented in conjunction with independent laboratory results of the new operating conditions. The ability to predict flotation circuit performance based on changes in grinding circuit performance is also discussed. This methodology provides improved predictions of flotation circuit performance when grinding circuit changes (including grinding capacity increases) are made.

Integrating liner profile evolution and mill performance with 3D DEM modelling

2011-10-13T00:00:00Z

Integrating meso- and micro- textural information into mineral processing: an example form the Ernest Henry Iron-Oxide Copper-Gold deposit, Queensland, Australia.

2009-11-30T00:00:00Z

Integration and analysis of optical and SEM-based microscopy for automated mineralogical characterisation

2011-08-16T00:00:00Z

Interaction of calcium dioleate collector colloids with calcite and fluorite surfaces as revealed by AFM force measurements and molecular dynamics simulation

Fa, K. og Nguyen, A. V. og Miller, J. D. — 2010-03-04T00:00:00Z

Spherical calcium dioleate particles (~10 µm in diameter) were used as AFM (atomic force microscope) probes to measure interaction forces of the collector colloid with calcite and fluorite surfaces. The attractive AFM force between the calcium dioleate sphere and the fluorite surface is strong and has longer range than DLVO (Derjaguin-Landau-Verwey-Overbeek) prediction. The repulsive AFM force between the calcium dioleate sphere and the fluorite surface does not agree with the DLVO prediction. Consideration of non-DLVO forces, including the attractive hydrophobic force and the repulsive hydration force, was necessary to explain the experimental results. The non-DLVO interactions considered were justified by the different interfacial water structures at fluorite- and calcite-water interfaces as revealed by the numerical computation experiments using molecular dynamics simulation.

Interactions of hydrophilic plasticizer molecules with amorphous starch biopolymer - an investigation into the glass transition and the water activity behaviour.

2012-07-24T00:00:00Z

In this article, we demonstrated that within a hydrophilic biopolymer-plasticizer system, the molecular "activity" of the plasticizer also influenced the extent of these interactions. We demonstrated through an analysis of crystallinity and calorimetry results that the equilibrium moisture content within the starch matrix can preferentially interact with the hydrophilic plasticizers and modify the polymer recrystallization process to an extent that the commonly acknowledged relationship between the crystallinity and the glass transition behavior is disrupted. Two plasticizers, glycerol (three -OH groups) and xylitol (five -OH groups), were selected. The water sorption isotherm of polymer samples with 5-20 wt % (dry basis) plasticizers were examined across a water activity range from ∼0.11 to ∼0.95 and using Guggenheim-Anderson-de Boer analysis, we compared the molar sorption enthalpies of various starch-plasticizer mixtures. Finally, the competitive plasticization between water and plasticizer molecules at different water activities was also discussed using known glass transition models. The analyses validated the antiplasticization limit for glycerol to be ∼10-15 wt %, but for xylitol, its antiplasticization behavior did not manifest till 20 wt %.

Interactive effects of the type of milling media and copper sulphate addition on the flotation performance of sulphide minerals from Merensky ore Part I: Pulp chemistry

2010-01-12T00:00:00Z

It is well known that the chemical environment determines the success of the flotation process, however its characterisation and control is difficult to achieve. This paper, as two parts, Part I and Part II, evaluates the use of various measurements and their interpretation to gain an understanding of the influence of varying parameters such as the type of milling media and copper sulphate addition on the flotation performance of sulphide minerals from a platinum group mineral (PGM) bearing Merensky ore. It shows the complexity of interpretation and the importance of analysing flotation performance holistically. Part I focuses on the pulp chemistry and mineral potential measurements have been used to show the differences in the response of the various mineral electrodes to different conditions. The final flotation recoveries of the sulphide minerals in the ore followed the same trend as the decrease in mineral potential due to collector addition viz. chalcopyrite > pentlandite > pyrrhotite. Type of milling media and copper sulphate addition slightly affected the mineral electrode potential and flotation recovery of chalcopyrite. Addition of copper sulphate increased the recovery of pentlandite and particularly pyrrhotite due to activation by copper (II) ions. The copper activation mechanism was likely to be in the form of initial adsorption of copper hydroxide followed by reduction to Cu+ at the surface. However, the changes in flotation performance of the different minerals in the ore could not be completely described by the electrochemical changes, demonstrating the limitations of these measurements. Part II addresses the effect of froth stability as demonstrated by the variations in the mass and water recovery data resulting from the different milling conditions and addition of copper sulphate which emphasised the importance of considering the froth phase in the evaluation of flotation data.

Interactive effects of the type of milling media and CuSO4 addition on the flotation performance of sulphide minerals from Merensky ore Part II: Froth stability

2010-02-19T00:00:00Z

The limitations of pulp chemistry measurements in the flotation of a platinum group mineral (PGM) bearing Merensky ore were demonstrated in Part 1 of this article. In this paper the importance of the contribution of the froth structure due to changing froth stability is analysed using the batch flotation data. The effects of mild steel (MS) and stainless steel (SS) milling media and the addition of copper sulphate on the flotation performance of the sulphide minerals in Merensky ore have been evaluated in relation to the changes in stability of the froth phase. The effects of pulp chemistry and froth stability on the flotation of sulphide minerals were distinguished by using two different rate constants (kt and kw). The rate constant (kw) calculated as a function of cumulative water recovery was used to describe characteristics of froth phase and kt was calculated as a function of flotation time. The results revealed that the type of grinding media and copper sulphate addition had an interactive effect on the froth stability. While mild steel (MS) milling increased the froth stability due to the presence of hydrophilic iron hydroxides and colloidal metallic iron, the addition of copper sulphate reduced the stability, especially with stainless steel (SS) milling. Copper sulphate addition had a dual role in the flotation of Merensky ore in that it caused destabilisation of the froth zone as well as activation of selected sulphide minerals. The dominant effect was found to depend on the type of milling media and floatability of the mineral in question and this work has demonstrated the importance of using a combination of measurements to evaluate flotation performance holistically.

Interparticle collision of particle composites: Finite and discrete element simulations

Khanal, M. og Tomas, J. — 2009-02-02T00:00:00Z

Interpreting the individual contribution of reagents on a plant and laboratory scale

2010-01-25T00:00:00Z