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By N. Ahmed

This paper is concerned with the drainage behaviour of gangue mineral in the froth phase. Experiments were carried out in a continuous laboratory flotation cell in which froth depth and bubble size could be changed independently. The fraction of solids returning from the froth to the pulp zone was expressed using a rate constant. A mixture of hydrophilic solids (silica) and floatable particles (glass ballotini) was used as a flotation feed. Samples of glass ballotini of different hydrophobicities were obtained, using controlled silanation. Three samples, with contact angles of 50, 66, 82 degrees, were used. The effect of the initial bubble size (pulp bubble size), concentration of gangue mineral in the froth zone, and froth depth on the drainage of silica, were investigated. The drainage rate of the entrained solids increases with an increase in the degree of hydrophobicity of the floatable particles. Concerning the effect of pulp bubble size on the drainage rate of entrained solids, larger bubbles always give higher drainage rates due to formation of relatively loose froth structures which allow gangue particles to easily move down to the pulp zone. Conversely, smaller bubbles exhibit lower drainage rate constants, in particular at shallow froth depths.

Jan 1, 2003

By C. Dorfling, S. Bradshaw, J. Eksteen, M. Khesa, C. A. Snyders

Titaniferous ores serve as a major feedstock for the production of a white titanium dioxide pigment, a titanium metal and several other titanium-based products. Such ores exist mainly as heavy mineral sands. Ilmenite is upgraded to intermediate products namely synthetic rutile and titania slag through the synthetic rutile route and the reductive smelting route respectively. Tronox KwaZulu Natal Sands (Pty) Ltd recovers high titania slag via the reductive smelting process while slag is used as a feedstock to the pigment industry and furnace dust from the gas cleaning plant is disposed as waste. Previous investigations have shown that such furnace dust can contain significant amount of titanium-bearing minerals. This study looks at the characteristics of the furnace dust obtained from Tronox KwaZulu Natal Sands and investigates a possible high temperature recovery route in detail. The furnace dust was examined by using x-ray fluorescence, x-ray diffraction, microscopy and laser-diffraction size analyses. The characterization work showed that the furnace dust was rich in titanium and iron, containing 49.4 wt% ??????2 and 29.5 wt% ????2??3. These oxides were associated with Si, Mn, K, and Al oxides as impurities. A Carbolite® vertical tube furnace was used to investigate the extent of formation of titania slag and metallic iron on a laboratory scale at 1500°C, 1600°C and 1650°C. The laboratory reduction tests revealed that the slag samples with an equivalent titanium dioxide content ranging from 70.9 -76.9 wt% at 1600°C and 1650°C could be obtained. The Fe content of the metallic iron samples produced ranged between 93.0 and 97.1 wt%. The experimental results were found to be in relatively good agreement with the FactSage simulations, both of which demonstrated the potential of producing a titania slag and a metallic iron from the furnace dust.

Jan 1, 2018

By F. Molhem, S. Banisi, H. R. Montazari, E. Arghavani, Gh. R. Biniyaz, Gh. A. Parsapour

"Water plays a key role in mineral processing plants and to process one ton of ore 2.5 ton water is needed. Thickeners are commonly used for dewatering and recovering water in most processing plants. The underflow pulp density is increased by sedimentation of particles and clear water is recovered from the overflow. One of the issues related with using the process water is the presence of suspended fine particles in the clear overflow water which can create blockage in transfer pipes. The froth formed on top of thickeners is the main cause of this problem. In this study, a method to decrease the froth formed on the Sarcheshmeh Cu-Mo thickener surface was introduced and implemented. At the first stage, the old punched plate feedwell was removed and it was replaced by a vane type feedwell. A spray water ring using fish-tail type nozzles was then installed to break froth layers by water. These modifications led to 63% relative reduction in the water turbidity, 11% relative increase in the underflow solids concentration, 20% relative reduction in torque, 19% relative reduction in its standard deviation and an increase of 6% in water recovery.INTRODUCTION The Sarcheshmeh copper complex, the largest copper producer in Iran, located in southern Iran. In the processing plants of this complex, over 250,000 m3 of water is consumed daily. Because of a lack of water in this area and very low yearly rain fall (150 mm), water plays a vital role in the complex. As a result, it is then aimed at maximum water recovery by taking all necessary measures. The recycled water in order to be used should not contain any suspended solids indicated by low turbidity."

Jan 1, 2018

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 Gabriel C. Aguilera, Juan Arismendy

"The effect of rheological factors inside of a hydrocyclone is very relevant for the fluid mechanics and for the classification of materials on suspension, since parameters such viscosity and thixotropy are intrinsic variables that depend of the particulate system and the continuous phase; they determine the efficiency of classification. Nevertheless, the exact knowledge of the main characteristics and magnitudes of them inside the hydrocyclone is very difficult because of the geometry of the hydrocyclone, even more if the hydrocyclone is of small diameter. Hence is not possible to make a hydrodynamic study with effects over classification regarding these variables. This work studies the rheological variables inside a small diameter hydrocyclone that works at high pressures, using the information given by a model of Computational Fluid Dynamics (CFD). The model used includes the Reynolds Stress Model (RSM) for the evaluation of turbulence, and the Volume of Fluid (VOF) to study the interaction between water and air, which is very important to obtain regarding the effect of the air core over the performance of the equipment. The validation of the CFD model was done with a kaolin suspension at several conditions of solids contents below the critical volume fraction, without chemical additive aid. These conditions are representative of current work parameters on plant. As result it could be established the ranges of evaluation of rheological variables on specific regions inside the hydrocyclone, and through a rheometric study, based on the mechanic characteristics previously obtained, the main rheological characteristics of the mineral suspensions were determined."

Jan 1, 2014

By A. Gueciouer, A. Akkouche, K. Chalah, A. Benmounah

"Drilling solid waste is a typical industrial solid waste, and it is a major pollutant source to ecological environment. Generally, waste management dewatering systems separate solids and fine particles from the liquid phase of drilling fluid, thereby leaving a clarified aqueous solution and allow the cleaning of waste fluids. Typically, dewatering waste management systems clean drilling fluid through coagulation, flocculation and/or mechanical separation. Chemicals used in dewatering are based on the coagulation-flocculation process, which it facilitate the removal of suspended solids and colloidal particles. The factors which can promote the coagulation-flocculation are velocity gradient, contact time, and PH. The objective of this work is to optimize a formulation adequate for dewatering based on the coagulation-flocculation process used coagulant (Aluminum sulphate), anionic flocculants (Partially Hydrolyzed Polyacrylamide) and anionic polyelectrolytes (in solid form with linear chain with very high molecular weight). The results obtained show the good efficiency of the coagulant and flocculants. INTRODUCTION Rig site dewatering of drilling fluids with recycling of processed water can help an operator to comply with environmental rules by reducing volumes of waste and reducing long term liabilities. It can also reduce disposal costs and provide a cleaner drill site overall. Most of the environmental concerns during the 1980s involved hazardous materials and toxic wastes. Drilling fluids, many of which are chemically benign, have escaped many of the difficult-to-comply-with rules and regulations. During the 1990s, however, operators may be required to submit a written plan for liquid waste reduction for even nonhazardous materials. Many states and local agencies may institute total bans on oil field wastes. Drilling rigs typically produce about 1 bbl of liquid waste for every 1 ft of hole drilled. Thus, a typical drilling operation can produce a large quantity of waste [1]. To improve the dewaterability of sludge, different pretreatment processes have been widely studied and developed including thermal, chemical, magnetic, mechanical, acoustic, electric, electro-acoustic and their hybrid treatment processes [2]. Rig site dewatering (figure 1) is the process of injecting coagulants or flocculating chemicals into the mud entering a large clarifying centrifuge. Coagulation occurs when the solid and allowing it to be attracted to other solids by van der waals forces. Flocculation is the binding of individual solid particles into aggregates of multiple particles. It is physical, rather than electrical, and occurs when one segment of a flocculating polymer chain absorbs simultaneously onto more than one particle [3]."

Jan 1, 2018

By Luís Marcelo Tavares, Daniel Francioli, Malcolm Powell, Mohsen Yahyaei

"Mathematical modeling of the comminution process requires understanding of all breakage mechanisms occurring in this mechanical environment. Modeling of high energy impact breakage is well established, however, modeling low energy breakage including incremental damage breakage, attrition and abrasion is still under development. Free fall incremental impact tests were carried out to investigate the surface fragmentation of a copper-gold ore. This process was achieved by dropping particles individually from a height of four meters onto a metallic plate. The impact specific energy was 0.01KWh/t. The setting of the metallic plate was changed to test the impact angles of 0°, 45°, and 60°. Tests were carried out using fresh angular rocks as well as smoothed particles. Changes to the plate angle and particle shape enabled the study of the influence of the tangential component of the impact energy along with particle shape on superficial breakage. By studying the fractional mass loss variation in each impact, two distinct stages of surface fragmentation were clearly determined: high fractional mass loss dominated in the first 10 impacts and was attributed to chipping, whereas low fractional mass loss occurred for the remainder of the impacts and was attributed to abrasion. Smoothed particles demonstrated higher resistantance to breakage and their surface fragmentation behavior indicated a closer relationship to abrasion, especially when lower impact angles were used."

Jan 1, 2014

By R. Shiva Kumar, G. Sreedhar, S. Sharma

Some of the Indian origin iron ore deposits located in Bellary, Karnataka province are having peculiar characteristics of Iron ore deposits (Hematite) having Iron above 64% and 30-40% lump (-30+6mm) recovery which are not suitable to use in blast furnace due to not meeting the specification of Tumbler Index and Abrasion Index. In general for high grade Iron ores, process flow sheet involves crushing and screening (dry/wet). In the contest of high grade Iron ores located at Bellary sector of Karnataka state in India, lump generated from this process could not attain the required physical properties (Tumbler Index, Abrasion Index) and metallurgical properties , even though the grade of the lump ore is above 64% Fe. Washing techniques like Drum scrubber and Log washer play major role in improving the metallurgical properties of Iron ore lumps by removing the light and hard layers of clay, silica coated over the lumps. In this study the effects were compared of drum scrubbing and log washing on iron ore lumps. It is found that by incorporating simple washing technique i.e. drum scrubbing or log washing, Tumbler Index of Iron ore Lumps could be increased from 74% to 78% which is acceptable for use in Blast furnace. From the Drum scrubber and Log washer tests, it is clear that Log washers have an edge over Drum scrubber in removing hard coated clay on surface of Lumps. This simple washing technique facilitate us to utilize the lumps directly in blast furnace and eliminate the unnecessary crushing and grinding of the ore so as to meet the specifications of Sinter fines and pellet feed.

Jan 1, 2014

By F. S. Hoseinian, K. Filho, D. Deglon, T. Souza, M. Safari

"This paper investigates the reverse flotation of hematite in three laboratory flotation cells with very different contacting environments. The main objectives are to investigate the recovery of coarse quartz by flotation and fine hematite by entrainment. The laboratory flotation cells used were the mechanical, oscillating grid and pneumatic cells. The effect of froth height and solid concentration were investigated in the mechanical and pneumatic cells. The effect of impeller speed and energy input were investigated in the mechanical and oscillating grid cells. Froth height results show that coarse quartz particle recovery decreases almost linearly with increasing froth height due to increased detachment of coarse quartz particles in the froth. Fine hematite particle recovery also decreases almost linearly with increasing froth height due to decreased water recovery and associated entrainment. Agitation/energy input results show that coarse quartz particle recovery increases with increasing impeller speed to an optimum, after which this decreases dramatically. The increase is due to improved gas dispersion, generation of smaller bubbles and increased bubble-particle collision and attachment. The decrease is due to significantly increased bubble-particle detachment at higher impeller speeds. The recovery of coarse quartz particles in the OGC is higher than that in the mechanical cell with an optimum at a much lower energy input. Solids concentration results show that both mass recovery and water recovery increase with increasing solid concentrations. The pneumatic cell achieves higher mass recoveries and lower water recoveries than those in the mechanical cell at equivalent solids concentrations and operating conditions. INTRODUCTIONFlotation is a selective process for separating different minerals from each other. The flotation separation efficiency depends on the recoveries of the mineral species by both true flotation and entrainment (Neethling and Cilliers 2009; Wang et al. 2015). Both chemical variables and hydrodynamic conditions within the flotation cell affect the recovery and selectivity of the flotation process. Cationic reverse flotation of hematite is a common method for selective separation of quartz from iron ores to produce pellet feed. The presence of coarse quartz particles in the tailings and fine hematite particles in the concentrate are two major challenges in the reverse flotation of hematite (Vieira and Peres 2007)."

Jan 1, 2018

By K. Saberyan

Zirconium and hafnium are two important elements in nuclear industries. Zirconium is used in fuel rod for its low neutron absorption. Hafnium should be separated from zirconium, because it has higher neutron absorption cross section. In this research, separation process of the mentioned elements from (Zr+Hf)Cl4 mixture produced in the Zirconium production plant (ZPP) of Iran (Esfahan) was studied employing solvent extraction method in the nitric acid medium by using tributylphosphate (TBP) as solvent, and kerosene as diluent. The effects of nitric acid, sodium nitrate and amount of extractant, zirconium concentration in aqueous phase, phase ratio, agitation time, and mixer agitation rate were investigated on the separation process. The process was optimized at 5 M nitric acid, 1 M sodium nitrate, 60% (v/v) TBP. The optimum values for phase ratio, agitation time and agitation rate were 1.5 min and 500 rpm respectively. In this condition, the zirconium extraction efficiency, and separation factor were 65.1% and 205.59, respectively. Finally, we accessed to nuclear grade in this research.

Jan 1, 2014

By M. Evertsson, E. Hulthén

"In aggregate production and mining the operators are responsible for controlling and monitoring the process to maintain high plant throughput and safe operation. Operators have to make different decisions to control the process due to changed demand on the operation from both management and conditions of the process. The quality of the response and the time it takes for an operator to respond to altered demand relies on what information is available and the experience of the operator. In this work a dynamic simulation platform has been developed to be used for operator training. Models for representing production units and process control for plant simulations have been developed and implemented in MATLAB/SIMULINK to simulate time-dependent plant behavior. Stochastic and scheduled events are included using the discrete events simulation toolbox SimEvents. The human-machine interface was developed using the human-machine interface software ICONICS. The operators’ cognitive process, in interpreting the plants semantic, has been studied by observations and with informal interviews with operators. This was done to get information about the daily operation and the problems that occur in the process. By interacting with operators that experience different physical interactions with the process; more qualitative e-learning software for supporting operator training in a dynamic operator environment could be developed. The quality of the operator training environment was evaluated with a usability study that was performed with operators and others within the production."

Jan 1, 2014

By Matt Kilburn, Liming Lu, Steve Suthers, Alexander Edenton, Rodney Smyth, Matt Adam

"Magnetite concentrate is naturally good for pelletising. However, due to the depletion of reserves of traditional high grade hematite iron ore worldwide, the usage of magnetite concentrate in sintering is expected to increase substantially. Magnetite concentrate is typically high in Fe grade and releases extra heat when oxidised to hematite. This will not only improve the quality of agglomerates produced, but also have a potential beneficial impact on the fuel consumption of the agglomeration process. There are an increasing number of magnetite projects currently being considered and developed. However the concentrates from some of these projects are too coarse as pellet feeds and much finer and denser than normal sinter feeds. Accordingly, special strategies are required in order to utilise the coarse magnetite concentrates at high proportions in pelletising and sintering. This paper discusses various raw material preparation technologies and blending optimization methods demonstrated to be effective for improving the sintering and pelletising performance of coarse magnetite concentrates. Pre-granulation and addition of binders, such as hydrated lime, were found to be particularly efficient in recovering the sintering productivity of sinter blends containing magnetite concentrates. In pelletising, HPGR (High Pressure Grinding Rolls) grinding enabled production of good quality pellets from 100% magnetite concentrates and optimized blends containing up to 70% magnetite concentrates also formed good pellets.INTRODUCTION Magnetite concentrates are often used as feed materials for pellet plants or sinter plants depending on their grades and grain sizes. To achieve the required quality of green and fired pellets, the concentrates often need to be ground very fine (80% passing 38- 45 m), which inevitably consumes a great amount of energy. Therefore, efficient grinding processes are required to reduce the amount of energy consumption needed to achieve the sizing and chemical specification of pellet feeds. The use of magnetite concentrates in sintering has the potential to improve sinter chemistry, which is deteriorating over time due to the slowly decreasing grade of direct shipping iron ores around the world (Yang and Mathews, 1997; Yang and Witchard, 1998, Yang and Davis, 1999; Yang 2005). However, methods are required to allow the utilisation of high levels of concentrates in sintering while maintaining productivity and sinter quality (Han and Lu, 2017)."

Jan 1, 2018

By P. Harris, D Bradshaw

"Comparison of the two most commonly used classes of depressant in the South African platinum industry is complicated by the fact that these polymers induce different effects on the surfaces onto which they adsorb. The use of carboxymethyl cellulose (CMC), which is ionically charged in solution, can lead to increased particle dispersion in addition to the effect of reduced surface hydrophobicity (depression). Guar is typically only slightly charged in solution. Comparison of these two depressants is complicated since it is uncertain whether differences in their action is a result of either depression of dispersion effects.This work investigates the role of dispersion independently to that of depression in the batch flotation of a platinum bearing ore. An inorganic dispersant, sodium hexametaphosphate (NaHMP) was added in parallel to the uncharged guar depressant to simulate the action of depressants with varying degrees of dispersion. By distinguishing between the material recovered by entrainment and the floatable gangue and by including the effects of froth stability it was possible to decouple the effects of dispersion and depression.The results show that both dispersion and depression led to increased grade of the sulphide minerals. Depression leads to a decreased recovery of floatable gangue minerals. Dispersion leads to an increased recovery rate of these minerals and an accompanying decrease in froth stability."

Jan 1, 2003

By Peter Ay, Elena Geldt, Satyanarayana Narra, Claudia Glaser

"As part of an extensive research and development project, the technical and technological implementation of the patents DE 10 358 245 B4 and WO/2006/056172 was developed with the goal to present a system for the innovative roll- agglomeration method exhibiting a) a modular setup, b) high productivity and c) suitability for the use of fibres of different applications and product qualities (high technical availability). The processability of the rarely adapted raw fibre materials into high-value intermediates brings forward their application in various processing industries dealing with the production of fibre reinforced plastic composites, heat and sound insulation materials as well as with the gas and liquid cleaning systems. The innovative fibre agglomeration presented in this work is performed by a combination of rolling and pressing the fibres inside a geometrically pre-defined roller table, in which the fibres are forced to bound through entanglement / interlocking and develop into agglomerate. The agglomeration process is carried out in a circular roller path with a rectangular cross-section. For improving the adhesive properties, and thus the quality of the agglomerates, the boundary surfaces can be covered / patterned / lined / coated with various materials. The resulting roll-agglomerates are characterized by different quality parameters such as mass, shape, porosity and stability. The properties of the agglomerates can be modified based on the end-product requirements by slightly modifying the process parameters such as filling ratio, residence time, roll-geometry, procurement of the boundary surfaces, etc. as well as the input material properties such as fibre type, fibre fineness, fibre length, etc. This work carries extensive work on the roll-agglomeration system to assess the effectiveness and the variability based on the product specifications. Agglomerates were produced with wide variations of system parameters with varying roller table liners and based on evaluation of the produced agglomerates with respect to their mass, the geometrical dimensions, their porosity and stability."

Jan 1, 2014

By Chen Zhiqiang, Luo Chuansheng, Chen Ziqiang, Liu Jianguo, Rao Jinshan

To comprehensively utilize the valuable resource in tailings, increase the economic benefit of mine, reduce the amount of tailings, prolong the service life of tailing dam, the comprehensive utilization of tailing resource is arousing the attention of more and more mines. Research of comprehensive recovery of feldspar and silica from Cu-Mo floatation tailings has been furthered. Technology of "De-sliming-Magnetic Separation-Reverse Flotation-Feldspar and Silica Separation" has been developed to utilize the resource. Slime is removed and reagents cost is reduced by de-sliming. The specific effective collector ZL is used in gangues reverse flotation, and GZ-818 is the collector in feldspar and silica separation. The grinding operation is vital to ensure the liberation degree of feldspar and to eliminate the reagents pollution on minerals surface. To a Cu-Mo flotation tailing assaying K2O 5.22%, Na2O 2.22%, Fe2O3 1.95%, Al2O3 12.05%, SiO270.66%, superfine K-feldspar and silica concentrates can be produced. The feldspar concentrate productivity is 29.67% assaying K2O 8.99%, Na2O 2.86%, Fe2O3 0.16%, Al2O3 16.99% and SiO2 68.92%. The silica concentrate productivity is 14.20% assaying 0.17% K2O, 0.04% Na2O, 0.01% Fe2O3, 0.55% Al2O3 and 98.17% SiO2. The technology provides technological reference model for the similar mines.

Jan 1, 2014

By Hakan Gürsoy, Kemal Bilir, Bahri Öteyaka, Ali Uçar, Oktay Sahbaz

"Jet diffuser flotation column (JDFC) is a flotation device resembles Jameson flotation cell (JFC) in terms of operational principles, but it has significant difference structural points of view. This difference is an essential change in the downcomer to provide an increase of performance of the cell for the coarse particles. By using the hydrodynamic and fluid mechanics principles (Sahbaz et al., 2013) downcomer was changed as a diffuser, therefore turbulence at the end of the downcomer was reduced to provide better aggregate stability and homogeneous dissipation of the bubbles in the separation tank. According to experimental results carried out in pilot scale JDFC, not only higher flotation performance comparing with Jameson cell was obtained specifically for coarse talc particles in a certain condition, but also quiescent froth layer was acquired. In these tests, vertical pipe of JDFC having inlet diameter of 6 cm and outlet diameter of 11.5 cm was used with separation tank having the diameter of 39 cm. By using the data, pilot scale JDFC having 410 cm vertical pipe integrated with separation tank was produced and flotation tests were carried out by using the naturally hydrophobic mineral (talc). Finally, the talc recovery obtained as 94% by the use of JDFC, while Jameson cell has the recovery of 77% for the particle size of 250 µm."

Jan 1, 2014

By Rodolfo Silva, Antonio Peres, Afonso Martins, Gilberto Ramalho, Mario Cabello

The consumption of aggregates in civil construction has increased considerably in Brazil for the last years. The extraction of sand and gravel generates significant environmental impacts. As the quarries and sand deposits are getting exhausted near the big cities, the price of aggregates is increasing. Meanwhile, the extraction of quartzite (dimensional stone) in the state of Minas Gerais has been done mostly in small quarries, with very low recovery, generating approximately six million tons of wastes a year, which causes pollution, increases final prices of products, decreases the life time of quarries and ends up in the closure of enterprises. The government agencies and the quarries’ owners understand that only by finding applications to wastes there will be development to the sector. The aim of this investigation was to study the application to the quartzite wastes as aggregate in the civil construction. Samples of quartzite wastes collected in a quarry were characterized by petrographic analyses. Laboratory tests of crushing and grinding were done to analyze the viability of reducing the size of coarse material to a finer one to be used as raw material in industrialized mortars and concrete pre-molded components.

Jan 1, 2014

By Graeme Lane, Yuqing Feng, Kaixi Jiang, Junwu Zhou, Zhengchang Shen, Tao Song

"Airlift reactors are used in a wide range of industries, such as hydrometallurgy, biochemical processes, chemical process industry and waste water treatment. With increasing superficial gas velocity three circulation regimes can be defined: no gas bubbles in the downcomer, gas bubbles remain stationary in the downcomer and gas bubbles in the circulating regime. In this paper a numerical modelling method was presented for gas-liquid flow in airlift reactors under different bubble recirculation regimes. Gas-liquid flow was modelled using the Eulerian two-fluid equations, and extra user defined subroutines were incorporated to consider the complex physics, such as bubble induced turbulence and turbulent dispersion force. Some alternative correlations of drag coefficient were used to capture the bubble distributions in the riser and downcomer of the airlift reactor, with consideration of the interaction between bubbles. As using constant bubble size is hard to describe global characteristics of the flow in airlift reactors for three circulation regimes, a model including multiple bubble sizes was presented to get more accurate simulation results of gas holdup and water velocity. Also, the inhomogeneous MUSIG model was used, as an exploration, to compute the complex flow regimes. The MUSIG model is a population balance method to predict the bubble sizes, taking break-up and coalescence into account. The modelling method was applied to a laboratory internal loop airlift reactor, and the simulation results were compared with the experimental measurements of Simcik et al. (2011) for gas holdup and water velocity. The three bubble circulation regimes were observed from simulation figures. Reasonable agreement was obtained over a range of operating conditions, and an improvement was demonstrated using the proposed methods."

Jan 1, 2014

By Henrique Kahn, Daniel Uliana, Juliana Antoniassi, Viviane Shimizu

"Mineral exploration and geometallurgy require a large number of samples for physical, chemical and mineralogical assays. The combination of all these data and their spatial distribution define the ore variability. This is important in exploration programs and crucial in feasibility studies as well as at the production operation level. Ore mineralogical composition and its associations, characterizing the geological formation and mineralization, are the main keys to define the ore domains and its variability, which can be quickly assessed by cluster analysis and by modern automated mineralogy tools. One hundred and ten copper ore samples from Sossego mine, in Brazil were compared and classified by X-ray diffraction cluster analysis based on the position and the intensity of the diffracted peaks. Initially four ore types were categorized based on content of major minerals: quartz, feldspar, amphibole, iron oxides, mica and chlorite. Results showed a strong correlation between the grouping and the samples location in Sequeirinho and Sossego orebodies, with a straight link to types/intensities of hydrothermal alteration prevailing in each body, which reflects the mineralogical composition and thus the X-ray patterns. Samples from four recognized ore types were submitted to detailed automated mineralogical studies by electron beam image analysis and differ strongly from each other regarding their chemical and mineralogical compositions and relevant parameters for mineral processing. Chalcopyrite is essentially the only valuable mineral, occurring both as submillimetric grains included in other minerals and as larger crystals. Except for pyrite, other sulfide minerals occur as traces. Chalcopyrite liberation curves indicate that samples from Sossego have higher liberation degree than those from Sequeirinho. The proposed method proved to be very efficient and accurate to classify a large number of samples within a short time frame, allowing the distinction of the ore types regarding their mineralogical composition as well as the mineral processing parameters."

Jan 1, 2014

By Nicolus Rotich, Ritva Tuunila, Louhi-Kultanen. Marjatta

Most minerals, their ores, and gangue require sorting in order to maximize the recovery of the primary product during concentration. Gravity separation though old, is not obsolete and is continually playing an important role in mineral processing and many other industries, especially where plant energy efficiency is of concern. Screen designs e.g. material of construction, deck angle of inclination, the feed throughput, and physical as well as chemical properties of the particles, are critical factors to consider when using gravity for solid separation. Solids loading and screen geometry are significant, and easily manipulated operational parameters that affect both the screening rate and efficiency to a large extent. In this paper we applied nonlinear least squares optimization technique, and response surface methodology first, to assess the significance of the two factors, and secondly to select the best mathematical models that optimize both capacity and efficiency of the screening process. Initial experiments and confirmation tests were conducted on a prototype screen of 846.51cm2 effective area, (2100 cm2 total area). For glass beads of sizes 0.75-3mm, with feed loads of 10g up to 160g, and inclination angles from 5-20o, a maximum efficiency of 66.7%, and a screening rate of 22g/s was achieved with a screen loading of 86.5g, and an inclination angle of 12.43o. These results were then subjected to nonlinear least squares optimization, in which afterwards an optimum theoretical efficiency of 72% and screening rate of 31.2g/s were achieved at a loading of up to 104g. There was excellent performance at angles 12.5=?=17.5, but poor at the angles outside this range. The screening efficiency did not seem to respond significantly to changes in screen loading. Confirmation tests conducted at selected optimum parameters achieved an efficiency of 72.1% (at 17.5o with 88g load), and a rate of 27g/s at 16.5o with 104g.

Jan 1, 2014