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By Ritva Tuunila, Antti Häkkinen

"Wet stirred milling is one of the most effective grinding methods in producing very fine powders in large scale production, but it is a very energy-intensive process, especially when pigments or even nanosize particles are produced. Therefore, optimization of the process parameters is important. The specific energy consumption is a function of stress energy, which describes the effect of tip speed and media characteristics on grinding, and is related to the number of stress events during milling. In effective grinding, a large number of stress events are necessary. The stirrer configuration influences the number of stress events and their intensity, because the motion of the media and the suspension are caused by a rotating stirrer. The effect of three different stirrer types: a pin, disc and blade stirrer, on the grinding rate, i.e. product fineness and specific energy were investigated in this study with a batch laboratory stirred mill with two tip speeds. The material used in the experiments was calcium carbonate. The results obtained with the smaller tip speed showed approximately similar grinding rates and energy consumption for all stirrer types. When looking in closer detail, the blade stirrer seemed to give the finest product with all grinding times compared to the pin and disc stirrers, which both produced almost the same product fineness with the same grinding times. The specific energy consumption was the smallest with the disc stirrer, but not very big differences were obtained. With a higher tip speed, greater differences occurred both in grinding rates and specific energy consumption. The blade stirrer was the most effective in grinding, and the pin stirrer the next. The net energy consumption for the blade and pin stirrers was almost the same, but it was slightly higher for the disc stirrer."

Jan 1, 2014

By Markus A. Reuter, Bernardete Castro, Antoinette van Schaik, Han Remmerswaal

"INTRODUCTIONThis paper describes the inseparable relation between product design, liberation, and metallurgical recovery in the optimisation of the recycling of passenger vehicles. This is illustrated by the use of an optimisation model that uses among others a material combination matrix based on metallurgical process data, which depicts the consequences of the quality of intermediate recycling products on the metallurgical material recovery and final alloy metal quality. Various simulations will illustrate the effect of changes in product design and hence liberation on the recycling of end-of-life vehicles. Although this paper focuses on cars, the discussion is equally valid for any end-of-life product. Calibration of the model will be discussed with reference to experiments carried out in order to study the optimal recovery of aluminium applications used in passenger vehicles.OPTIMISATION MODEL FOR LINKING DESIGN TO RECYCLINGImproving the efficiency of the material cycle of the car is essential to ensure a sustainable development of our society as well as e.g. to comply with the recycling targets imposed by EU legislation. In the design of the car various materials are combined and connected in many different ways, making up the complex 'mineralogy' of the car and its components, which is changing rapidly and continuously over time. The liberation of materials during shredding plays an important role in the composition (and quality) of the intermediate recycling streams. In order to include the influence of product design (mineralogy), liberation, and particle composition (quality of the intermediate recycling streams) in the optimisation of the recycling of end-of-life vehicles, a systems engineering tool for optimisation of the recycling of end-of-life vehicles was developed, including a liberation model. The optimisation model predicts the recovery rate as a function of product design (in this case a car), liberation, efficiency of the different process steps, economy and legislation based on a developed recycling flow sheet for end-of-life vehicles. Optimisation can only be achieved through the combination of the knowledge areas of product design, shredding, mechanical separation technology linked to pyro- and hydrometallurgy, composing a complex interconnected network of unit operations."

Jan 1, 2003

By N. T. Beukes, W. Banda

Recovery of Co from slag is a recent advancement in the extractive metallurgy of nonferrous metals. In this study a DC arc technology at laboratory scale has been applied to investigate the selective recovery of Co from slag, under three different flux types with an emphasis on influencing the activity of FeOx, SiO2 and CoO in the slag. It is known that reduction of slag by carbon is only up to a certain level after which, the recovery will depend on the chemistry of the slag, hence the need to modify the slag chemistry. Two power settings were employed to induce higher temperatures and aggressive agitation. The results were interpreted by comparing how much Co and Fe was in the slag and alloy. TiO2 reduced the amount of Fe in the product alloy compared to when CaO and CaF2 were used. The change in power did not seem to have had a major effect on the recovery although the amount of material lost to flue dust was more at a higher power rate.

Jan 1, 2003

By Y. H. Zhang

Mechanism of BK501 in desiliconization from bauxite was studied by use of flotation test, EDS, ?-potential, FTIR. Results of flotation show that almost all of diaspore can be depressed when BK501 is put into pulp ranging from pH 4~12, in the meanwhile kaolinite is slightly activated. In the light of surface analyses, it is concluded that the adsorption of reagent on the diaspore is dominant by chemical interaction. Moreover, kaolinite may float more by addition of BK501 because of flocculation.

Jan 1, 2014

By Francisco Vicuña, Miguel Becerra, Nelson Iglesias

"The following article presents the development of a dynamic tool for the estimation of Jb/Jc rate (ball filling level / total load filling level) of a SAG mil operating in a single stage mode. Using the methodology detailed in this article, it is now possible to have a dynamic estimation tool in the operation, which enables strategic decision making and achieving a continuous development in process optimization. The estimating of the load filling level (Jc) was conducted using a power model, which in this case corresponds to the C-Model developed by (Morrell, 1993) that was calibrated by measuring the load filling levels (Jc) and balls (Jb) using the FARO laser scanning technology by means of Grind-Out and Crash-Stop procedures during the year 2013 and 2014. Finally, to estimate the dynamic filling level of full charge, Jc, three independent models were developed that allowed to feed the adjusted power model: •,SAG mill discharge grate slot wear model •,SAG mill internal volume wear model •,Ball filling level estimation model."

Jan 1, 2014

By Katarina Theander, Robert J. Pugh

The generation of froth with a critical degree of stability and height is an important aspect of the froth flotation. In this paper we have studied the synergism and anti-synergism in frothing behaviour in a mixed flotation collector/frother mixture (a model fatty acid; sodium oleate and a model frother; nonionic (polyethyleneoxide alkyl C14E6). Values of the collector / frother molecular interaction parameters (the ß-parameters) were determined from the surface tension data using regular solution theory. The frothing characteristics of the system were evaluated using a glass column equipped with a series of conductivity electrodes, which enabled the water content of the froth to be determined. From these measurements, the dynamic frothability and static froth stability were determined. It was concluded that the synergism/anti-synergism in frothability was depended on the molecular composition of the surfactant system, the diffusion of monomer to the thin film interface and on the breakdown of the mixed nonionic/anionic micelles.

Jan 1, 2003

By Wenying Liu, Marek Pawlik

Long-chain ionic surfactants, with fatty acids and amines as the most important representatives, are widely used as collectors in froth flotation. These surfactants, generally referred to as weak electrolyte collectors, frequently form solid insoluble precipitates within a certain pH range. However, the action and behavior of these colloidal precipitates in froth flotation systems are not well understood and has not been well decoupled from those of dissolved forms. The objective of this study was to understand and compare the role of colloidal precipitates with that of the dissolved forms at gas-liquid and gas-liquid-solid interfaces. Using primary amine as the model surfactant, experiments were carried out to measure: the maximum volume of bubbles generated in the presence of dissolved and precipitated forms of the surfactant; surface tension for both forms of the surfactant using the drop shape and maximum bubble pressure methods; and contact angle using the sessile drop method. The experimental results showed that: in the presence of the precipitate, bubble volume was smaller, which was correlated with the lower surface tension and higher contact angle measured; the surface tension of solutions containing surfactant precipitate was affected by the surface age of liquid droplets. This study enhances understanding of the interfacial behavior of long-chain ionic surfactants under different conditions, which would help improve the efficiency of reagent utilization in froth flotation.

Jan 1, 2014

By T. N. Aleksandrova, A. V. Afanasova

"The research is aimed at solving the problem of enrichment of sulphide ores, counting for more than 40% of the reserves in Russia. The aim of the research is to develop and scientifically substantiate the scheme for processing this type of ores in order to extract fine-dispersed noble metal particles (FNMP). In this work samples of sulfide carbonaceous ore and flotation concentrates were analyzed using complex precision methods of analysis: electron microscopy, spectral analysis with induction plasma, complex thermogravimetric analyzes, etc. Data on the composition of the organic constituent of the samples were obtained with the usage of complex thermogravimetric analysis. The presence of various types of kerogen and bitumen has been established. Experimental studies on the coarsening of FNMP from the initial ore and flotation concentrates using electromagnetic radiation have shown the effectiveness of this coalescence method. The data on the elemental composition of the samples and the amount of FNMP were obtained. Thus, studies on the extraction of FNMP from carbon sulphide ore have shown the possibility of effective usage of combination of electromagnetic action and classical enrichment methods to extract fine particles of noble metals. INTRODUCTION Due to the depletion of free-milling raw materials the involvement of new types of deposits is the strategy of developing mining industry of Russia. The black shale raw materials show interest as a non-traditional source of precious metals since its genetic and positional gold-carbon connection. Muruntau, Sukhoi Log, Bakyrchik, Natalkinsky, Nezhdaninskoye, Olimpiadinsky, Homsen and others are the examples of well-known deposits of the black shale formation [1]. In fact the main gold-dispersed regions of Russia are composed of black-shale strata. Review of literature [2-5] shows that in recent years in almost all deposits of the black shale formation metals of the platinum group (PGM) were detected that significantly increases their practical importance."

Jan 1, 2018

By S. Banisi, A. R. Ghasemi, M. Maleki-Moghaddam

Direct observation of the charge shape and its motion in industrial mills are not possible, it is then customary to use transparent end, small-scale mills (i.e., model mills) to determine the charge trajectory directly by visualization methods. Because of a short length of the model mills, the end-wall effects could introduce a significant bias on the observed charge trajectories and shape. The shorter the mill, the stronger the bias. This could be due to some material bridging between the end walls. In this research, the end-wall effects were investigated by gradually increasing the model mill length and analysing the charge trajectory and shape variation at a given operating conditions (i.e., ball filling, mill speed, liner type). The unbiased mill length was assumed to be beyond the mill length where no significant change observed in the charge trajectory and shape. For all tests, the torque of the charge was also measured by a torque sensor. The special design of the model mill with the diameter of 100 cm made possible to increase the mill length in steps of 3.6 cm up to 21.6 cm. Four types of liners, five steel ball fillings (10, 15, 20, 25, 30% v/v) and three mill speeds (55, 70, 85% of critical speed) were tested. The ball sizes ranged from 4 to 12 mm. The results indicated that when the mill length was below 10.8 cm the end walls prevented the charge from free falling. This resulted in lower impact point angles and lower power draws compared with the case of no end-wall effects. When the same experiments were performed using an iron ore instead of balls with the same size range, the impact of end-wall effects was more pronounced. For an increase of 30% in the speed (from 55 to 85%), the torque due the change in the charge shape decreased by 41% (from 3.7 to 2.2 kgf.m) when mill filling was 30%. At the same operating conditions when steel balls used the torque decreased only by 19% (from 9 to 7.2 kgf.m). This was expected due to irregular shapes of the ore particles which facilitated bridging. Three-dimensional DEM simulations also resulted in the similar conclusions.

Jan 1, 2014

By Xianjun Lyu, Junxiang Wang, Peng Wu, Minjie Lian

"In recent years, the efficient cementation of mine tailings is a new way to manage mine solid wastes. The traditional cement materials have a slow setting time, large dosage and poor cementation strength for fine aggregate such as mine tailings. Therefore, the preparation of new type cementitious materials for the cementation of fine tailings has great potential in the treatment of mine waste solids. The paper mainly focuses on exploring the critical factors affecting the cementing performance of granulated blast furnace slag and its performance in the cementation of fine aggregate. Results indicate that the fineness of slag has a significant effect on its cementitious activity and Portland cement clinker has a better stimulation effect on the cementitious properties of slag than lime. And, anhydrite has a better early stimulation effect on the cementitious properties of alkali-activated slag compared to semi-hydrated gypsum and dihydrate gypsum. According to a series of tests on the cementation of fine iron tailings, the optimal ratio of slag, Portland cement clinker and anhydrite is determined as 60:30:10. Compared with P.O 42.5 ordinary Portland cement, the new slag based cementitious material shows much better cementing performance on fine tailings sample. Under the dosage of 12%, the compressive strength of fine tailings mortar using slag-based cementitious material in 3 curing days is increased to 168% that of using P.O 42.5 ordinary Portland cement, while the compressive strength in 28 days curing period is increased to 194%."

Jan 1, 2018

By Z. Q. He

This paper introduces the structure and working principle of SLon magnetic separator that has excellent performance in iron removal, and summarizes a part of the examples of applications, which applies this machine to remove iron from non-metallic ores, and shows widespread prospect of application of this machine in the purification of non-metallic ores.

Jan 1, 2014

By Brian Hart, Stamen Dimov

"In refractory ores, a substantial part of the gold content may be present as a sub-microscopic component within the mineral matrix of the various carriers. This type of gold may be present as finely disseminated colloidal size gold particles (<0.5µm) or as a solid solution within the sulphide mineral matrix. Such ores are not amenable to gold recovery by direct cyanidation. In order to liberate the sub-microscopic gold, the ore has to be oxidized before being subjected to gold cyanidation and extraction. Autoclave pressure oxidation (AC POX) of the sulphide ore and subsequent cyanidation is a common technology used to liberate the gold in such refractory ores. The additional presence of active carbonaceous matter in such ores (double refractory ores) represents another major obstacle for efficient gold recovery during the process of pressure oxidation and cyanidation. This carbonaceous matter (c-matter) can adversely affect the gold recovery due to its ability to adsorb, or pre-grob gold from the cyanide solution. Advanced micro-beam analytical techniques such as Dynamic Secondary Ion Mass Spectrometry (D-SIMS) and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) have become powerful tools for characterization of different forms and carriers of gold for the needs of the mineral processing industry. Major advantages of these techniques are related to their ability to analyze individual mineral particles and provide quantitative analysis with detection limits in the low ppm/ppb concentration range. This paper describes various micro-beam techniques and procedures implemented at Surface Science Western (SSW) for quantification and characterization of the sub-microscopic gold and the preg-robbed surface gold as part of full gold deportment studies in feeds and process stream products."

Jan 1, 2014

By V. Buddhiraju

Liberation of valuable minerals from low-grade ores is an important challenge faced by the minerals industry. It is necessary to grind the ore to extremely fine size in order to liberate the mineral from such ores. As it is generally difficult to produce ultra-fine particles of diameter less than 1-10 mm using traditional grinding equipment such as the ball mill and the rod mill, several new types of grinding equipment are being explored to produce ultra-fine particles. The planetary ball mill is promising in that it makes grinding to submicron sizes possible by imparting high energy to the ground powder. It consists of four pots mounted on a disc. The pots and the disc rotate in opposite directions. The high-speed rotation of the pots and the disc makes the grinding media move at high centrifugal velocities leading to high impact energy and thus improving the grinding performance. The planetary mill is currently being explored for its capability to produce ultra-fine particles on a large scale. In this context, there is a need to understand the dynamics of the ultra-fine grinding process within the planetary ball mill. Here, we address this need by studying the movement of media inside the pots and the grinding kinetics, employing both experimental and modeling techniques. The experiments were conducted on a laboratory scale planetary ball mill. The particle size distribution of the powder was monitored to allow an estimate of the grinding kinetics to be made while video images of the media profiles inside the pots were taken to allow quantification of the media movement as a function of process variables such as the media size, percent loading, etc. The population balance modeling (PBM) framework was used to simulate the kinetics of grinding while the discrete element modeling (DEM) approach was utilized to simulate the media motion. The parameters in the population balance model, namely, the specific breakage rate and the breakage distribution function were determined by fitting the batch grinding equation to the experimental data. The predicted powder size distributions were found to be in good agreement with the experimental data. The experimental results have shown that the mean size of product powder decreases as the size of the grinding media decreases. Keywords: population balance modeling, grinding, planetary mill, grinding media, grinding equation

Sep 1, 2012

By W. Pawlos

"The paper will present the methods of visual observation and recording of movement paths of coal grains of different physical properties in the paramagnetic liquid. The paths were recorded with a video camera in the working chamber by means of a specially constructed device, acting as a periscope, which were then transformed into digital images.Experimental movement paths were confronted to the paths obtained in a theoretical way by means of solving differential equations of movement. The outlet level of a grain of the same physical properties from the separator is a random variable with normal distribution which modal value is equal to the outlet level of a spherical grain, calculated from the solution of grain movement equations. At these assumptions it is possible to calculate the height of the passage from the separator working chamber to separate a given product with a given separation accuracy, measured by a probable error and to determine separation conditions."

Jan 1, 2003

By Sanggono Adisasmito

"The quality of the higher education in Indonesia is being improved by implementing a program financed by the World Bank under a project named QUE (Quality for Undergraduate Education). The investments are provided to selected study programs through a competitive selection process. The grant finances staff development, the purchase of equipments, textbooks, consumables, technical assistance, and incentives for outstanding faculties such as teaching grants, project grants, lecture note awards, and educational policy studies. These additional investments are provided to produce chemical engineering graduates that will compete beyond the national market.Chemical Engineering Department of Institut Teknologi Bandung in Indonesia has been selected to receive the QUE grant beginning the year 2000 and ending the year 2004. The department is actively involved in the mineral processing issues, particularly in the aspects of energy supply and the environmental protection. The activities are distributed in different laboratories and areas of expertise, such as: thermodynamics and utility systems, process equipment, chemical reaction and catalysis, microbiology and bioprocess engineering, process control, ceramics, as well as polymer and membrane technology. The main objectives of the QUE project are to improve the undergraduate program in the following aspects: Relevance, Academic atmosphere, Institutional management and commitment, Sustainability, as well as Efficiency and productivity, or abbreviated as RAISE. At the end of every fiscal year, the progress of the program is evaluated to measure the effectiveness of the project.The achievement of the QUE project objectives were assessed using performance indicators developed during the program design. There are six indicators to measure the performance of the individual program of study, such as: (1) Admission Test score, (2) average students' Grade Point Average (GPA), (3) average graduates' length of study, (4) graduates' waiting time before getting first job, (5) Test of English as Foreign Language (TOEFL) score, (6) Graduate Record Examination (GRE) score. Essentially, the RAISE evaluation criteria will be used to perform three main functions, such as (1) to measure the achievement through the six quantitative performance indicators, (2) to support the progress of evaluation and reporting throughout the implementation of the program, (3) to provide a universal framework for qualitative evaluation."

Jan 1, 2003

By R. Roufail

In this paper, the effect of different operating parameters of high speed stirred mill on the particle breakage mode is addressed. Morphological features of broken particles is investigated and related to the types of forces generated in the mill using Discrete Element Method (DEM). The stress intensities generated in the mill are varied by changing the agitator speed. The investigated agitator speeds were 1000, 1500, and 2000 revolution per minute (rpm). The minerals considered in this study are hard minerals (quartz) and soft, sulphide minerals (galena). The morphological features examined are roughness, roundness and elongation, which shed light on the mode of breakage during the grinding process. Particles that are rough, less round and elongated would imply that they broke via fracture, along their grain boundaries. On the other hand, the smooth, less elongated particles would mean breakage occurred across the grain, which is abrasion mod. DEM study complemented the understanding of particle breakage mechanism via tracking the types of forces applied on the particles. Normal forces imply compressive loading, which is presumed to impose fracture breakage along the grain boundaries, whereas tangential forces imply abrasion loading. Stirred mill grinding has been regarded as an attrition/abrasion process, whereas, this study showed that about 60% of total particles that are morphologically analyzed for both minerals were rough particles. Such an observation indicates that the fine product, which contain a significant amount of progeny from the coarse fractions are consistently broken via fracture. The morphology results agreed with the DEM findings, which indicated that the agitator speed, mineral type, and residence time would dictate the type and mode of particle breakage. Keywords: DEM, high speed stirred mill

Sep 1, 2012

By Marzio Piller, Girolamo Belardi, Jure Mencinger, Paolo Bozano, Gianni Schena

"The hydrodynamics of the Tri-Flo™, a two stage cylindrical cyclone used in dense media separation, is studied using Computational Fluid Dynamics. The flow field is simulated with an Euler-Euler Volume of Fluid two-phase approach and the Reynolds stress turbulence model.A unique feature of the device is that the separation medium suspension is pumped and introduced tangentially into the two cylindrical compartments while the raw feed is conveyed to the feed hopper and fed at the axial inlet. This feature allows to use less pumping energy and limits the unavoidable production of fines. The Tri-Flo™ complex flow pattern is little known but central to the efficiency of the separation.The velocity field is computed within the two compartments of the separator. The interface of the air-core that forms in the inner axial part of the cylindrical sections is identified and visualized. The numerical results for a reduced-size 100 mm ID Tri-Flo™ are compared against laser Doppler measurements on a transparent acrylic model (Chinè, 1995) operated with water. The robustness of the model and its prediction capability are verified.The possibility to accurately predict the velocity profiles within the vessel and their dependence on the main Tri-Flo™ operating and geometrical variables paves the way to a better understanding of the functioning of the separator, its design improvements and scale-up."

Jan 1, 2014

By Y. Y. Zhou

This paper introduces the application of CRIMM high-gradient magnetic separator in refinement of feldspar powders as well as the supporting technical outfits needed by the refining process with the high-gradient magnetic separator as main equipment. It could reduce the content of Fe2O3 to 0.03% with a deferrization rate of 85.88% from the feldspar raw ore containing 0.17% Fe2O3by using the above refining technology, producing an ultrapure feldspar product.

Jan 1, 2014

By Y. Q. Qui

In the bauxite flotation process for desilication, the middling treatment mode is the important factor to raise the flotation recovery of the preparation concentrate. The middling treatment mode mainly depends on A/S and the size composition. However, similar ratio of A/S should not be the single factor of re-dressing, size composition plays an important role also. Re-dressing the middling mixed with the tailings of concentrated to the rough ground for desilication and the concentrate of scavenged to the fine ground for desilication to raise the recovery of 5.83%, when compared two flow sheet schemes.

Jan 1, 2014

By V. Tsyplakov

This article reviews factors of preg-robbing effect, occurring in the course of pressure oxidation of ore and concentrates, containing chloride compounds and so-called &apos;organic carbon&apos;. The article also summarizes the main results of the studies and testwork conducted to overcome this effect. The following efficient preg-robbing mitigation methods have been noted: higher temperature of pressure oxidation process, preliminary removal of natural carbonaceous material from concentrate, chloride removal prior to concentrate pressure oxidation, and addition of water-soluble organic blanking agents, which suppress the adsorption activity of the native ore adsorbents. Keywords: preg-robbing, double-refractory gold concentrates, pyrite, arsenopyrite, blanking agents, pressure oxidation, autoclave leaching

Sep 1, 2012