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By Tsuyoshi Hirajima, Hideyuki Okamoto, Himawan .. T. B. M. Petrus, Keiko Sasaki

"Flotation of arseno bearing minerals from their copper ore has been an interest due to the increasing awareness on protecting the environment by minimizing the possibility of exposed arsenic compound. Some approaches have been proposed, but the mechanisms of separations have not yet fully understood. In this study, oxidation using oxygen was applied. Instead of the complex copper ore flotation results, pure single mineral of tennantite and chalcopyrite foatability was conducted using Hallimond tube. Resembled with the flotation results of copper concentrate containing tennantite, the separation possessed the best result at alkaline condition (pH 11) at where the arsenic content was reduced from 3300 ppm to 1800 ppm. In order to be able to understand the mechanism of the separation atomic force microscope (AFM) was utilized. AFM images showed changes in morphology and behavior when minerals were treated in both acid and alkaline condition. It was found that the morphological change showed the reaction products representing the rate of reactivity of tennantite and chalcopyrite. From the measured force of adhesion, it can be observed that in alkaline condition the surface of both minerals is more hydrophilic than that in acidic condition possessing higher value. This is in accordance with the X-ray photoelectron spectroscopy (XPS) spectra in which hydroxide moieties occupied the mineral surface in alkaline condition while elemental sulfur is in acidic condition."

Jan 1, 2014

By Hajime Miki, Mutia Dewi Yuniati, Tsuyoshi Hirajima, Keiko Sasaki

Acid mine drainage is mainly due to pyrite/arsenopyrite oxidation processes, and suppressing such processes is important issue. As a promising process it is reported that silicate ion can complex with catechol (1,2-dihydroxybenzene) and this complex is oxidized to a solid silica layer on the surface of those sulphide minerals. Detailed behavior was investigated from the result of electrochemical experiments. Results of polarization potential showed that oxidation peak can be seen only in the presence of both silicate ion and catechol addition at this peak potential and this peak can be identified as silicate-catechol complex oxidation to silica. Potentiostatic experiments indicated the dissolution kinetics of pyrite. Untreated pyrite dissolution rates were higher than pyrite treated with catechol and silica solution. To enhance the silica layer reaction on pyrite, the pyrite potential was held at 550 mV vs. SHE in catechol silica solution. This pyrite dissolution kinetics was almost the same as untreated pyrite. Potential hold followed by drying for 30 min process resulted in much lower pyrite dissolution rates. Drying is important for development of the silica layer. Analysis of this potentiostatic curve provided a way to estimate the thickness of the produced silica layer and kinetic information of treated/untreated pyrite. Untreated pyrite showed thinner initial layer thickness on the surface of pyrite (oxidized passive layer, not silica) and higher oxidative kinetics of pyrite compared with silica-coated pyrite.

Jan 1, 2014

By Xiao Jian Li, Dai Xiong Chen, Jian Wen Yang

In one kind of lead and zinc bearing polymetallic ore containing secondary copper, the characteristic of low sulfur, high zinc, and particularly the existing of secondary copper minerals can lead to lead concentrate with high content of zinc because the dissociation of Cu2+ in the grinding process may have an activation influence on sphalerite. Considering its process mineralogy analysis, a new process of seperation of lead and zinc has been put forward. The experiments focused on the analysis of the advantages and disadvantages of the inhibition effect of traditional adjustment reagent + zinc sulfate on activated sphalerite compared with new organic inhibitor, polysaccharide xanthate. According to the numerical calculation and test results, a reagent system of polysaccharide xanthates is developed, which has a good inhibition effect on Cu2+ activated zinc minerals, achieving high-efficiency separation of lead and zinc. A new reagent system and flotation process was developed under optimal conditions. Under the condition of the run-of-mine ore containing 2.37% Pb and 12.48% Zn, lead of 67.69% grade and lead concentrate with the recovery rate of 86.06%, zinc of 60.32% grade and zinc concentrate with the recovery rate of 96.15% were achieved.

Jan 1, 2014

By M. Maldonado

A flotation bank is a serial arrangement of cells. How to optimally operate a bank remains a challenge. This article reviews three reported strategies: air profiling, mass-pull (froth velocity) profiling and Peak Air Recovery (PAR) profiling. These are all ways of manipulating the recovery profile down a bank, which may be the property being exploited. Mathematical analysis has shown that a flat cell-by-cell recovery profile maximizes the separation of two floatable minerals for a given target bank recovery when the relative floatability is constant down the bank. Available bank survey data are analyzed with respect to recovery profiling. Possible variations on recovery profile to minimize entrainment are discussed.

Sep 1, 2012

By B. S. Moroney

Elemental distribution varies widely in the ores, minerals and beneficiated products depending on the constituents. Accurate analysis of each element present in various beneficiated products is utmost required to assess the grade in view of zero waste technology. Hence, the suitable methods and instrumental technique is of prime importance as the distribution of various elements differs in the beneficiated products. Conventional classical technique of analysis is absolute and due to this, it has not become obsolete. Besides, it is much needed for making standards for various relative techniques. Instrumental techniques comprising of X-ray fluorescence, Induced Coupled Plasma Analyzer, Carbon-Sulphur Analyzer, Atomic Absorption Spectrometer etc. are important for quick and accurate analysis. However, the selection of these instruments depend on the nature of material to be analyzed. This paper highlights the importance and use of various methods/techniques and instruments involved in the analysis of various ores, minerals and beneficiated products. Keywords: wet classical, x-ray fluorescence, induced coupled plasma analyzer, atomic absorption spectrometer

Sep 1, 2012

By S. F. Kaplan, A. S. Dolotov, V. N. Kovalev

"At this point in time, autoclave recovery (POX) followed by sorption cyanidation (CIL) is one of the most promising technologies for the efficient processing of refractory and double refractory gold-bearing sulphide rock. This hydrometallurgical technology requires the use of a large amount of water (up to 5 tons per ton of used concentrate), resulting in highly saline water with high pH (pH 9-11), high content of cyanides (up to 300 mg/l), arsenic compounds, antimony and a number of heavy metals. In order to determine the possibility of using recycling industrial water in POX-CIL technology, several batches of experiments were conducted (using the double refractory flotation concentrate of the Mayskoye deposit). Urban water with a chloride ion content of 10 mg/l was used during the reference POX-CIL experiment as the liquid phase of the ??? feed pulp. At that, gold extraction rate amounted to 89.4 %. A full cycle of POX(200 ºC)-CIL was carried out during the first part of the experiments; at that, fresh concentrate of the untreated recycling water with cyanide ion content of 95.4 mg/l, left after the completion of the previous CIL cycle, was used for repulping. It has been established that direct use of untreated recycling industrial water is impossible due to a sharp decline in gold extraction (preg-robbing) down to 79.5%. The presence of chloride ions, cyanide ions and other ligands in the liquid phase provides effective complexion formation for the recovery gold; complex gold compounds are quickly and firmly sorbed by the natural carbonaceous substances of the concentrate at the stage of autoclave recovery; they are virtually not cyanized onwards, and gold is carried over to the tailings. During the the second batch of experiments, recycling industrial water with cyanide and chloride ions' concentration of 500 mg/l each was subjected to the reverse osmosis desalination (up to 6 times in a successive order). After each desalting cycle, such water was used as the liquid phase of the feed pulp in POX-CIL. 6 cycles of RO desalination enabled the extraction of 86.1% Au (which is close to reference recovery). During the third batch of experiments, recycling industrial water was diluted with distilled water (2, 4, 16, 32, 64 times); after each dilution cycle, this water was used as the liquid phase of the POX-CIL feed pulp. Gold extraction after 64-fold dilution amounted to 82.6%. The results of the conducted researches show that the use of untreated recycling industrial water in POX-CIL hydrometallurgical technology is absolutely impossible due to a sharp decline in gold extraction. Even the 64-fold dilution with pure water is inefficient both from the perspective of gold extraction and of rational use of water. Reverse osmosis desalination solves the problem of water treatment except for the removal of cyanide ion, which requires separate reagent treatment of water."

Jan 1, 2018

By Wolfgang Öfner

Many technical processes also yield dusty residues which usually contain appreciable amounts of valuable matter. Often they also accumulate substances detrimental to the process. Dumping them entirely in landfills wastes raw material and causes high disposal costs, but recycling them without prior treatment is often not feasible. Physical separation processes are preferable because of their rather low energy demand. In order to develop such treatment systematically, the residues must be characterized properly. The technique for such a characterization is taken from mineral processing: perfect fractionation according to continuous properties of the particles supplemented with chemical analysis are used for plotting the Henry-Reinhardt chart. This represents the benchmark for assessing actual separation processes and tests. Their results are compared in terms of ?selectivity? and plotted in the kappa chart. In this paper, Henry-Reinhardt chart and kappa chart are applied to several different types of residues from iron and steel production and show their potential for being upgraded before reutilization in the production process. This approach is suitable for virtually all dusty residues from other industrial processes as well. Keywords: residue, dust,iron and steel, process development, Henry-Reinhardt chart, kappa chart

Sep 1, 2012

By J. Sachweh

The last few years have shown a significant increase in the demands for fine products, which means everything under 10µm. There are more and more applications requesting extremely fine ground powders leading to the development of several milling machines which are better adapted to the new products. Cost saving machinery is important for the worldwide competition. Especially the energy consumption is extremely important for any fine ground product. A worthwhile field for mechanical engineering companies is the dry milling machinery as there are not as many solutions available compared with wet milling applications. In many cases wet mil-ling is the only solution to reach the requested quality, but there are also a lot of applications which can be performed in a dry way on the premise that the right mill and classifier are available. Dry milling permits to save energy and allows to influence the particle size distribution more easily, as a classifier can be used in that case. This will significantly reduce production costs and can enable the production of new products with better properties. The Tower Mill is well-known already in the field of wet grinding. Recent research work and end user reports have shown clearly that this mill has a lot of advantages compared to a ball mill. Up to now this advantage is limited to wet grinding as only few mills have been used for dry grinding. There is no doubt about the efficiency of dry grinding, but new and improved feeding and discharg-ing systems have to be developed in order to enable the full range of its advantages. Especially the high production capacities are a challenge for mill and classifier designers. The Tower Mill with its special grinding mechanism allows to cope with very high feed rates, because machines with more than 1 MW are available. Improved grinding efficiency will decrease the circulation load through the classifier and also lead to smaller classifier sizes. Together with im-proved mills the classifier can work more efficiently because the feed material is finer. Results of a test center plant production will be shown together with a comparison between stan-dard machinery and the MaxxMill®. Preferential applications for each mill will be explained.

Jan 1, 2014

In this study, the effect of different regrinding conditions on the depression of fine pyrite at the cleaner stage was investigated. The regrinding condition was manipulated by different grinding media (stainless steel and mild steel). It was found that, after regrinding with mild steel grinding media, the flotation recovery of pyrite is much lower than with stainless steel grinding media, and it is more difficult to restore by adding more collector. This means, regrinding with mild steel grinding media may depress the pyrite flotation more strongly. The copper activation of pyrite during regrinding was also studied. It was found, that the mild steel grinding media is more beneficial to copper activation than stainless steel media. Additionally, the analysis of pyrite recovery based on the particle size indicated, that the fine particles are more susceptible to different grinding environments than intermediate and coarse particles and therefore are more easily depressed with a much lower flotation recovery.

Sep 1, 2012

By Egbert Burchardt

"Some of the challenges faced by the mineral industry in the future are the need to process low grade ores at the lowest operating cost, to deal with elevated energy cost and to address scarce water resources in some regions of the world. These challenges will increase the demand to develop highly energy-efficient and less water-consuming mineral processing systems. Experience from other industries suggests that HPGRs could help to achieve these goals, due to their high energy efficiency and their ability to be used as dry grinding systems. Historically, HPGRs have been used mainly as tertiary crushers in mineral applications for the production of ball mill feed. In the cement industry, however, HPGR systems have been successfully applied for grinding limestone, clinker and slag to a final product fineness (p80) of between 30 and 90 µm without the need of downstream ball milling. The total energy consumption of HPGR finish grinding systems in the cement industry has been found to be 30 to 50 % lower than in ball mill systems. This leads to the question of whether the same methodology can be adopted in the mineral industry. Such a step would require the use of dry rather than wet grinding systems. Traditionally, dry grinding systems have been only an exception in mineral processing, since most post grinding processes are wet. However, there are successful - mainly ball mill based - dry grinding examples in gold, nickel or iron ore. Experience from some of these dry grinding references are summarized in this paper. In addition, this paper explores two future-orientated questions: What opportunities does HPGR finish grinding offer the mineral industry? What are general conditions and challenges for adopting this technology for mineral applications?"

Jan 1, 2014

By Venkataramana Runkana, Shantanu Maheshwari

As the world reserves of high quality ores are getting depleted at a rate higher than ever, the liberation of valuable minerals from low grade ores is becoming more and more relevant and imperative. But, liberation of minerals from low grade ores requires grinding of ore to extremely fine sizes. High energy milling in a planetary ball mill is one such option where one can produce particles in the nano-meter range. Although planetary mill is employed extensively for ultrafine grinding, dynamics of grinding inside the mill is not fully understood because of the dependency of grinding kinetics on many interconnected phenomena like collisions between media, particles and wall, time dependent rheology, adsorption and desorption of dispersant, abrasion of media, agglomeration of particles, etc. It was well articulated in literature that media motion and number of media collisions have strong effect on grinding kinetics and final product size distribution. Simulations were carried out using the discrete element method (DEM) to compare the performance of a planetary mill with a ball mill, with and without lifters, in terms of impact energy and number of collisions and it was found that number of collisions is considerably high in the planetary mill. The high number of collisions might be the reason for production of ultrafine particles in the planetary mill. We have also fitted a population balance model (PBM) to experimental data from a laboratory scale planetary mill for prediction of particle size distribution. Unlike previous models, we have incorporated functional forms for the selection function and the breakage distribution function so that the number of parameters in the PBM is just five. The predicted product particle size distributions at different grinding times are in reasonably good agreement with experimental data.

Jan 1, 2014

By J. Drzymala

Ores and raw materials are subjected to mineral processing operations to increase the content of their useful components. Upgrading of these materials can proceed with different selectivity and therefore, there is a need to know and monitor the separation results of the process. The separation results can be evaluated using tables and graphs called upgrading curves. The course of lines in the upgrading curves is usually complex and depends on the graph type and process parameters. The Halbich grade vs. recovery plot is frequently used because is practical and it indicates several characteristic features of separation results. Separations by means of flotation of several different shale, dolomite and sandstone copper ores were performed along with determination of their mineral composition, copper content, liberation degree, and the maximum theoretical copper content in the first concentrate. These data, plotted as the Halbich upgrading curves, allowed to find other characteristic points such as practical maximum copper content in the first concentrate, maximum curvature coexisting with the liberation degree, maximum recovery of ore valuable components, and the slope the recovery-grade line at high recoveries as a measure of liberation. Correlations between theoretical and practical maximum copper contents in the first concentrate as well liberation degree and maximum curvature were also presented. They show that the ore type significantly influences the shape of the Halbich curve and its characteristic points.

Sep 1, 2012

By B. Rath

An effective process plan is an important part of maintaining consistent recoveries in mineral processing operations. Traditionally, Mineralogical studies are completed using chemical and metallurgical methods to monitor recovery and elemental distribution. The development of mineralogy and more efficient processes in mineral analysis techniques means that mineralogy is now more accessible as an efficient and comprehensive study tool. As operating costs increase and feed grades decrease it is important to maintain tight control of process and ensured maximum recovery is maintained at all times. Just a few days of losses in recovery caused by changes in ore type or processing conditions can have a large effect on total metal recovery and profit. Mineralogical audits can be used to minimize these losses by monitoring the fundamental behavior of feed ore on a regular basis. Smart use of mineralogical studies can develop mineralogical and ore type benchmarks in a detailed, which can be used in process control and monitoring. Geological ore types can be used to identify key mineralogical parameters that may be used in routine and cost effective analysis. Mineralogical systems ideally suited to this because of the depth of information on everything from modal mineralogy to locking/liberation characteristics and mineral associations. Mineralogical studies can equally be applied to specific unit operations within the process, which can allow more detailed information to be gathered on areas of the process that have been identified as critical. This will be especially effective for flotation or oxidation processes where process parameters can be very sensitive to small changes in mineralogy. This paper deals with the Ore Morphology, Ore Mineralogy, Gangue mineralogy, Photo micrographs under reflected, transmitted light and XRD studies Ore, Mineral studies of Sub grade Iron ore of Bacheli Complex, Bailadila Sector, India. Keywords: mineralogy, liberation, liberation studies, ore mineral, gangue mineral, morphology, jasper, ferruginous clay

Sep 1, 2012

By Nirmal Weerasekara, Malcolm Powell, Mohsen Yahyaei

"The conditions under which rocks become superficially damaged during the grinding process are not well understood. The main purpose of the work presented here is to understand how superficial breakage occurs under incremental low-energy impacts. To enable this study a series of abrasion tests with multi-size pilot mills have been performed. Outcomes of numerical simulation corresponding to each test were examined to investigate the experimental results. Abrasion tests have been conducted using three grinding mill sizes (i.e. 1.8, 1.2, and 0.8 m). Two types of ore were used to investigate different hardness strengths. To ensure abrasion was the dominant mechanism, in all tests the mill speed was reduced to 40% of critical speed. The relationship between the Fractional mass loss rate and particle size was investigated by randomly collecting seven tracer particles from sizes -73+63, -53+45, and -37.5+31.5 mm. It was evident from the results that the Fractional mass loss rate of angular particles declines as the particle size increases whereas the Fractional mass loss rate decreases from fine to coarse in rounded particles. Results of Discrete Element Method (DEM) simulations indicate that fine particles experience higher levels of collision energy per particle and this value reduces as the particle size increases and mill size reduces. This explains the higher Fractional mass loss rate of smaller particles as well as the increase in the Fractional mass loss rate as the mill size increases. Linked DEM and experimental data indicates that under these test conditions surface damage attrition is the dominant mechanism. This work suggests that DEM simulation can be implemented to predict the abrasion wear of particles in mills."

Jan 1, 2014

By Vladimir G. Kochnev

An innovative AG and SAG technology aimed to be applied in grinding of ores and in the production of construction materials is described. A novel design of a cantilever-type mill capable to operate in autogenous, semi-autogenous and ball grinding mode ensures easy delivery and installation even in remote areas, and low capital and operating costs. Results of the tests of the new heel-shaped liners performed by TTD jointly with ALROSA, MINTEK and Anglo-American Corporation are reported. The approach includes also a novel discharge grid design and a technique of treating the material of critical size. These innovations make grinding in AG and SAG mills dramatically more effective, with an increase in the throughput rate and a reduction in power consumption ranging from 1.5 to 2 times.

Jan 1, 2003

By A. Kurkov

Flotation process is based on the formation of primary collector-based supramolecular associates at the mineral surface and within the pulp. Supra molecular chemistry allows studying within a common framework, all kinds of molecular associates, from dimers to large assemblies, resulting from spontaneous association of a large number of interacting components of the flotation system, where the collective action of non covalent bonds can have an important role. Self-organization of supra molecular assemblies in the flotation process can be controlled by modifying the chemical structure of the collector, the nature and arrangement of functional group in it, by introducing secondary agents (SA) into the process, to adjust the interaction between the collector and the surface and to control the hydrophobicity of the adsorption bed. This offers broad opportunities to build supramolecular assemblies to improve the efficiency of flotation. Besides, the more complex is the system, the weaker are the interactions, that determine its behavior. This powerful factor still is not employed deliberately to control the flotation process. Organophosphorus compounds (OPC) - dialkyl phosphoric acids whose radicals contain ethoxylated groups ? are considered as nanocompounds, that can be used in building supramolecular assemblies. The presence in an OPC molecule of functional groups (P=O, P (O) O-, P (O) OH), ethoxylated groups, and aromatic rings is the basis for the formation of stable supramolecular associates. Gross formula: C54H94KO16P. Molecular weight is 1069.39. Phosphoryl anion has a regular tetrahedral structure with the angle of 109.5°. Lengths of -P-O- bonds in a PN molecule are 1.7345Å; length of the hydrocarbonic radical C42-C72 = 33.942Å. In an alkaline environment, PN is in the form of the anion, in an acidic environment ? in the form of the polycation due to protonation of the oxygen in the EO group. Chem Office software suite was used to generate three-dimensional images of an OPC molecule in acidic and alkaline environments, to reveal the OPC geometry (bond lengths, valence angles, aliphatic radical length), to identify the collector's binding sites with the mineral surface, to find the most stable and energy-efficient molecular conformations of an OPC molecule and its complexes with minerals under various conditions. Mechanisms of interaction between OPCs and the mineral surfaces are different. In ores whose minerals are dominated by ionic bonds (fluorite), the interaction mainly involves the anionic form of the collector; in ores, whose minerals are dominated by covalent bonds - the oxygen of the phosphoryl group (donor-acceptor interaction) and the oxygen of the ethoxylated groups. This difference is responsible for the formation of spatial associates with different surface layer structures. Introduction of supramolecular chemistry concepts into the analysis of flotation phenomena and mechanisms can become an effective tool for better understanding the flotation process and offers new means of consistently improving its effectiveness.

Sep 1, 2012

By Anatoly Usov

The detailed researches of a broad circle of problems connected to development of the electric pulse method destruction materials (EPD) of a various nature and area of use are executed. The electrical and power characteristics of process, physical fundamentals of selectivity of a breakdown and destruction are investigated, the device of electric pulse (EP) disaggregation and ?omminution of materials are developed, the technological efficiency of disintegration of industrial minerals estimated. Due to its technological advantages, the EPD could have a great potential in minerals mining and processing technologies. Low specific power and weight-and-size characteristics of EP installations based on the existing out-of-date electric equipment are at present the main reasons hindering the effective application of the method in mining and processing technologies. The main studies carried out in Russia in the field of electro technical equipment development for EP technology are presented. The pulse capacitors service life affects greatly the economic efficiency of the process because the capacitors cost accounts for a considerable, and in some cases, the most part of the operational costs. Determined and analyzed in the study are the ways which could significantly improve the specific characteristics of high voltage pulse generators (VPG), such as to use of high-frequency voltage transformation to develop a charger; to use pulse transformers (PT) with iron magnetic circuits made of materials characterized by high magnetic permeability, in pulse generating circuits; as well as to use special ways which could produce voltage pulses with a short front. The experiments have proved the possibility to adapt these technological solutions for EP devices, and a further strategy of the EP technologies development and application has been suggested on this base. Keywords: electric pulse disaggregation, electric pulse installation, charger battery, high voltage pulse generator

Sep 1, 2012

By D. I. Verrelli

Within the flotation community a belief has developed that some particle shapes are more ?floatable? than others. This is usually attributed to an influence of particle shape or roughness on the induction period required to achieve attachment between the particles and the air bubbles in the pulp. Up to now, such measurements have not been able to readily isolate the effect on individual flotation subprocesses. In contrast, our experimental apparatus, the CSIRO Milli-Timer, enables us to directly observe the process of particle?bubble interaction and attachment by means of a high-speed video recording, thus providing a direct measure of the induction period for attachment. To assess the influence of particle shape on induction time we used two varieties of methylated borosilicate glass particles ? spheres and angular ?frit? ? in a range of tightly-sized fractions. In doing this, we take care to account for the influence of other factors that could affect the induction time, such as the polar angle of sliding commencement, and approach velocity. These parameters are recorded as variables for each interaction, and corrected for using multiple nonlinear regression. Our results illustrate the importance of particle shape on induction period, with angular particles exhibiting induction periods that were an order of magnitude lower than those of spheres. Furthermore, the induction period was seen to decrease with increasing particle velocity, or kinetic energy on approach, but increased as the trajectory approached the limit of just grazing the bubble. Particle shape in mineral processing is a consequence chiefly of the mineral type and the type of grinding employed. The results presented herein indicate that attention should be paid to the shape of particles obtained from the grinding operation, besides particle size. Keywords: attachment, bubbles, flotation, induction period, particles, shape effects, surface roughness

Sep 1, 2012

Spent automobile catalyst is an important secondary resource of PGMs (platinum group metals) and the recovery is significant. Various methods of recovery technology have been reported and applied in practical production, including pyro- and hydrometallurgical processes. Since the grade of PGMs in the catalysts is so low, approximately 0.5 wt. %, the present recycling technologies require high energy-consumption, it is of great significance to enrich the PGMs with some energy saving physical separation methods as a pretreatment. Automobile catalyst is usually composed of cordierite phase as a substrate and alumina phase, with PGMs, which covers the cordierite phase. We adopted the quenching pretreatment, one method of thermal shock, to generate micro-cracks between the two phases and separate the alumina phase from cordierite. Quenching was carried out by heating the catalysts in an electric furnace of different temperatures followed by rapid soaking into cold water. It was found that the phase boundary between alumina and cordierite was broken in the quenching and selective separation (detachment) of alumina from the cordierite could be achieved in the following surface grinding. The effect of quenching was checked by microscopic observation, hardness measurement, and chemical analysis. This paper figures out the stress formula of the quenching process, which is largely connected with layer thickness and temperature gradient by using an FEM (Finite Element Method) simulation and clarifies the mechanism of crack generation in the quenching process. Keywords: automobile catalyst, PGM, quenching process, FEM

Sep 1, 2012

By David I. Verrelli, Peter T. L. Koh

"Recent experimental measurements of induction time made by direct observation with the ‘Milli-Timer’ indicated that angular particles were able to attach much more rapidly than spherical particles. There was around a tenfold difference in the respective induction periods for particle-bubble attachment. For industrial application, a more holistic comparison is needed, with the induction period for attachment being just one input. Over the years, CSIRO has developed a CFD-flotation model that incorporates both rigorous hydrodynamics, to simulate real industrial cell geometries, and a detailed model of the embedded flotation process, in which the induction period is an important parameter. We conducted transient modelling of batch flotation. First, spherical particles were modelled, as a ‘baseline’, for different particle sizes and levels of hydrophobicity. In the second set of results, the induction period was decreased by a factor of up to ten, simulating flotation of angular particles. Flotation recovery was found to depend upon induction period in a complex manner. For highly hydrophobic or fine particles, the induction period for spheres was already so low that recovery was limited by other factors (e.g. bubble-particle collision frequency). Further decreases in induction period, as for angular particles, did not have a significant effect on recovery in these cases. By contrast, when weakly hydrophobic or coarse particles were modelled, the recovery was predicted to be greatly enhanced for angular particles, in comparison to spheres. For these particles the induction period was limiting recovery, so that the flotation rate constant could be improved directly by reducing the induction period. This is consistent with batch flotation experiments using Ballotini reported earlier. Therefore, when dealing with weakly hydrophobic particles or relatively large particles that are to be floated, an enhancement can be expected for more angular particle shapes. In such cases, judicious specification of the grinding circuit may improve the overall efficiency."

Jan 1, 2014