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By Morin D. H., Battaglia-Brunet F., D'Hugues P.

"In the mineral-processing field, bioleaching of metal sulphide concentrates is currently operated in very large mechanically agitated tanks. Such bioreactors have considerable requirements in terms of power consumption for mixing, aeration and heat transfer. The use of slurry bubble column, where the particles are suspended by gas motion as well as by liquid upward flow, could be an alternative to achieve bioleaching in more economical conditions. In order to compare these two techniques, a unit of stirred reactors in cascade and a bubble column were comparatively operated at laboratory scale in the bioleaching of a pyrite concentrate. For both pieces of equipment, experiments were performed not only in batch mode but also in continuous conditions.Bubble column performances were significantly affected by unpredictable technical difficulties met to maintain continuous feeding in the bubble column and by a significant settling of the heavy solid particles. Nonetheless, theoretical kinetic data, extrapolated from results in batch conditions, could be compared to those obtained in continuous tests, in bubble column and in mechanically agitated reactors. These kinetic data were used to evaluate the influence of reactor design and configuration choice on bioleaching performances."

Jan 1, 2003

By F. Waanders, Campbell. Q.

This project was specifically aimed at using increased acceleration separation, as a method to optimize the recovery of gold in an ore body mainly consisting of hematite where the specific gravity of gold is much higher in comparison to the carrying material, making it possible to separate gold from other materials like silica, base metals and their oxides, usually associated with gravitation-gold-recovery-processes. The ore body investigated in this project originated from a gold reef containing a large portion of gold locked inside the gold pyrite complexes, which was mined and treated in a conventional way. After gold extraction, the material was pumped to a tailings dump and the gold extraction of this dump was investigated. In order to assemble a concentration plant setup, the head grade and size distribution of the dump and bulk sample were determined accurately. Chemical analysis and mineralogical examination were done on a representative sample of the bulk sample, to determine the chemical composition of the material. The results obtained thereof were evaluated and a pilot plant was configured. A bulk sample was processed in the pilot plant and the results were evaluated. The results at optimum acceleration forces applied, resulted in a recovery of 5% of the mass, with a gold concentrate of 90 g/t Au, which represented 58% recovery of the gold. The hematite with high specific gravity as main phase positively influenced the high acceleration separation process. It proved that if the specific gravity of particles in a suspension were increased, high acceleration separation could be applied effectively to separate much smaller particle sizes.

Jan 1, 2014

By H. Tiefel, M. Schneider, T. Neesse, J. Regler, J. Dueck, F. Donhauser

In practice the advantages of high-quality hydrocyclone separation are often reduced due to varying feed suspension properties, solids concentrations and particle size distributions. Control systems of large hydrocyclones are usually fitted with controllable underflow nozzles, which is not practical for small hydrocyclone batteries. Therefore, a new control system for a battery of hydrocyclones with a nominal diameter of 150 mm was invented at the LUR in cooperation with AKW Apparate und Verfahren GmbH & Co. KG. This process was developed for bentonite slurry regeneration associated with tunnel excavation using bentonite slurry as a transport aid and lubricant.

Jan 1, 2003

By E. Hulthén

Crushing plants are widely used around the world as a pre-processing step in the mineral and mining industries and as standalone processing plants in the aggregates industry. Despite automation and different advanced model predictive control, a lot of the process is still managed by operators. The operators affect a lot of the performance. The numbers of the improvement they can achieve are at least as big as the advanced control algorithms?, today. Therefore, it is also important to train the operators so they know how to behave in different situations. Models for crushers and other production units have been developed during the years and the latest add is the different units? dynamic behavior being brought in, which gives the crushing plants dynamic time dependant performance. This can be used as a simulator for operators training. By connecting a Human Machine Interface (HMI) to a dynamic simulator with the models incorporated, a training environment for operators can be achieved. In this paper, a dynamic crushing plant simulator implemented in MATLAB/SIMULINK has been connected to an HMI via a PLC. The HMI is placed in a control room at the university and complemented with monitors showing sequences from the process connected to the simulations, thus creating a realistic control room for training. In the created training environment, the operators can be trained under realistic conditions. Simple training scenarios and how they could be simulated are discussed. Apart from the increased level of knowledge and experience among the operators, the time is an important factor. While a real crushing plant is still being built, the operators to be can already be trained, saving a lot of the commissioning time. Keywords: crushing, cone crusher, simulator, control room, operator, training

Sep 1, 2012

By A. Mainza, H. Hill, L. S. Bbosa

"Impact breakage is the most elementary size reduction mechanism in comminution devices. In comminution research, characterization of breakage is primarily concerned with the energy expended to cause it. The main challenges of this approach have been quantifying the actual energy requirements of impact breakage and developing mechanistic models to accurately describe the process. For engineering load analysis, fracture is characterized in terms of strengths such as yield stress and ultimate tensile stress, which govern the maximum loads specific materials can be subjected to before irreversible inelastic deformation and subsequently complete fracture occur. With this approach, the main challenge has been to elucidate the underlying mechanism, in the means that the load causes weaknesses in the material microstructure to act as sites for stress concentrations, leading to crack initiation, propagation and eventual failure. Studies dedicated to investigating particle fracture under impact loading have led to the development of several devices for conducting breakage characterization tests. These devices include the drop weight tester, split Hopkinson pressure bar, rotary breakage tester and the short impact load cell. All these have different particle loading and breakage methods, and thus can yield distinct information which can be compiled together to study a material and the nature of breakage. This work analyses the single impact breakage data obtained across the listed devices. A homogenous ore commonly known as blue stone is used for all breakage tests. The work is conducted using standard procedures specific to each device as closely as possible. Drop weight and rotary breakage tests were used to obtain hardness parameters based on an existing t10 breakage model, while split Hopkinson pressure bar and short impact load cell measurements provided properties based on conventional engineering load analysis. The results were used to highlight the significance of the loading geometry, impact mechanism and impulse on the extent of breakage."

Jan 1, 2018

By E. V. Zelinskaya, V. U. Starostina

"The Irkutsk region is a raw material region. There are a lot of big enterprises for extraction and processing of oil, gas, coal, iron, gold and rock salt. Besides of it, refractory clays, limestone, mica, gypsum and talc are mined in the region. The most important type of mineral raw material is a gold. More than 8.5% of the total mining in the Russian Federation is extracted in Irkutsk region. It is about 0.7% of the world production. The environmental problems of mining and processing enterprises are a complex set of issues that requires of the searching of effective methods to be solved. One of the key environmental problems remains the reduction of waste generation and the introduction of environmentally safe waste management. After analysing different methods of environmental impact assessment it is established that the method of Life Cycle Assessment is one of the most effective methods for mining production. This method base? on the material balance of flows of raw materials, products and waste. The method of Life Cycle Assessment allows to identify the effects of environmental pollution under the influence of mining and processing at a quantitative level and to show real quantitative forecasts of the possibility of managing the flows of raw materials and waste.INTRODUCTION The Irkutsk region is a raw material region. There are a lot of big enterprises for extraction and processing of oil, gas, coal, iron, gold and rock salt. Besides of it, refractory clays, limestone, mica, gypsum and talc are mined in the region. The most important type of mineral raw material is a gold. More than 8.5% of the total mining in the Russian Federation is extracted in Irkutsk region. It is about 0.7% of the world production. The main provider of precious metal is the Bodaibo region. This is a main location for the major ore companies such as “Vysochaishy”, which produces about 5.0 tons a gold per year; “Pervenets”(PJSC Polyus, the largest gold producer in Russia) - 4.5 tons/year, “Druza” - 0, 5 tons/year. Placer gold is extracted by more than 40 enterprises. In connection with this, there are many plans about a building of new and reconstruction of concentrating factories. Consequently, an increase in the volume of processing is expected. The main projects are the construction of a new mill of the Mining and processing plant GOK “Vysochaishy” with a capacity of 2.6 million tonnes of ore per year; the development of the “Uhakhan” gold-field - 23 km from the “Goltsa Vysochaishy” gold-field; the opening in the Bodaibo region the next parts of the gold-deposit ""Pervenets"". Additional, the growth in a gold production can be achieved by a store of gold in the “Sukhoi Log” deposi"

Jan 1, 2018

By A. E. Sobolev

The kinetics of hydrochemical oxidation of antimonite in solutions of nitric acid was studied using the rotating disk method and the factor experiment design. The dependences of the antimonite?s oxidation rate on concentration of nitric acid solutions, temperature, disk rotation frequency, and duration of interaction were determined. The adequate kinetic models allowing calculating the specific oxidation rate at any combination of the values of the influencing factors were obtained. The oxidation process is found to proceed in a mixed mode, close to chemically controlled. Gradually, as the sediments of elemental sulphur and Sb2O5 accumulate on the disk surface, the process becomes controlled by internal diffusion. The observed high (more than second) order of the oxidation rate with respect to the concentration of nitric acid was explained by the autocatalytic action of the acid reduction products. The apparent activation energy depends on the stage of interaction. At the initial stage (in a mixed mode of the process proceeding), it depends on nitric acid concentration and varies from 31.5 kJ?mol?1 (in 2 M HNO3) to 36.1 kJ?mol?1 (in 10 M HNO3). This trend indicates the weakening of diffusion limitations with a nitric acid concentration increase. When the process is controlled by internal diffusion, the apparent activation energy was found to be 14.5 kJ?mol?1. The obtained kinetic characteristics enlarge the database on hydrochemical oxidation kinetics of sulphides and can be used for the elaboration of the recommendations for the effective comprehensive exploitation of antimony-bearing ores and concentrates.

Jan 1, 2014

By Kazutoshi Haga, Ryo Kawarabuki, Atsushi Shibayama, Masato Kosugi, Masanobu Kawata, Refilwe S. Magwaneng, Kohei Mitsuhashi, Altansukh Batnasan

"The recovery of copper and iron from carbonaceous sulfide ore is of economic and environmental interest despite its processing difficulty. Hydrometallurgical methods can be used to concentrate sulfide metals of these hard-to treat ores in a simple and eco-friendly manner. In this study, high pressure acid leaching process was comprehensively studied to dissolve metals from an ore with organic carbon and carbonaceous gangue material using autoclave equipment. The sample used for the experiment was reduced to an average particle size of 75 µm after undergoing flotation to reduce carbonaceous gangue minerals. A comparative study on two leaching reagents of sulfuric acid and iron sulfate and their dosage was used to observe dissolution of copper and iron. Other parameters of temperature (90-170 0C), solid-liquid ratio (1:10, 1:5, 1:3 and 1:1) were investigated through kinetic studies to access the influence of organic carbon and carbonaceous material on recovery of copper and iron. Materials balancing analysis was used to evaluate the efficiency of metal dissolution. The effects of parameters on leaching rate and concentration was demonstrated. Results obtained from the experiment indicated low concentrations of copper and iron in pregnant leached solutions, which was attributed to acid consumption by organic carbon and carbonaceous material in feed. However, the high efficiency rates of 92.4% and 86.3 % for copper and iron respectively in sulfuric acid can be concluded that leaching of concentrates of carbonaceous ore is possible provided system control on type of acid, pH and temperature. The purpose of this research is important in understanding mechanism involved in dissolution of copper and iron in concentrates of carbonaceous ore and marks an improvement in leaching of highly contaminated ores."

Jan 1, 2018

By C. Dorfling

Experimental work was performed using a bench scale autoclave to evaluate the effects that leaching temperature, pressure, initial acid concentration, and the solid to liquid ratio have on the behaviour of base metals and platinum group metals in a high-pressure sulphuric acid oxygen leaching system. The concentrations of metals in the leach solution were measured over time at different leaching conditions. At the conditions investigated, the initial acid concentration had the largest influence on the copper leaching kinetics, while the leaching rates of the other precious metals (OPMs: rhodium, ruthenium, and iridium) were highly dependent on the leaching temperature. A set of chemical reactions that can be used to describe the leaching chemistry was proposed, and the associated reaction kinetics were quantified. As a first estimation, the rate expressions were considered first order, and the rate constants were determined using the method of least squares, considering the experimental and predicted concentrations obtained for the different leaching conditions. Of the OPM compounds, the sulphides showed the fastest dissolution rate, followed by OPM alloys, and finally the OPM oxides. During the initial leaching stages, base metals and OPMs competed for the available dissolved oxygen, with oxygen being preferentially used for copper leaching. Precipitation of OPMs during the initial leaching stages can be ascribed to copper and nickel dissolution according to exchange reactions between dissolved OPMs and copper present as digenite or nickel present as polydymite. Control of the autoclave residence time is of particular importance to enhance the selectivity of this leaching step, given the dependence of the PGM leaching rates on the extent of copper dissolution.

Sep 1, 2012

By Z. H. Liu

We experimented with slurry which from one of coal preparation plant in Guizhou province and made researches on double hump gradation, one of critical factor of gradation technology, which can influence pulping character in the process of making coal water mixture (CWM). The purpose for it is to find the best particle gradation which can meet the requirements in concentration, viscosity, and stability for CWM. The final result is that the concentration, viscosity, stability of CWM can meet the requirement for industrial use while the rate of fine particle in the slurry is 70%~75% and the maximum concentration of 62%.

Jan 1, 2014

By A. Kuriwada

Dolomite is a mineral, which consists of CaCO3 and MgCO3. In this work, a series of experiments were carried out in order to adsorb boron from a boron-containing solution using a calcinated dolomite sample, and then to desorb it from the loaded adsorbent. A particular modification on the surface of dolomite was observed when it was thermally treated at certain temperature, ranging from 750 oC to 1050 oC; in turn, it is the specific surface was increased. In other words, the experimental results suggested that the calcinated dolomite exhibited a high adsorption capacity for boron, indicating its effectiveness in effectively adsorbing boron from drinking water or wastewater.

Sep 1, 2012

By K-O. Mickelsson, S. Töyrä, H. Esbensen

Accurate information of physical, chemical and metallurgical quality characteristics such as moisture content, iron grade and particle size are crucial for successful process control and for producing products within customer specifications. Correct moisture content of pellet feed is an important variable for successful balling of iron ore pellets and to minimize power consumption in the sintering process. Control of the filtering process in the pelletizing plant is therefore essential for both productivity and high product quality. The current measurement systems for moisture content at LKAB are based on two types of manual grab sampling, subsequently analyzed with rapid moisture determination methods. Previous studies of the measurement systems have indicated high sampling variability resulting in lowered possibilities for successful process control. The objective of the present study is to evaluate an alternative filter sampling approach and testing of on-line Infra-Red analysis (IR-analysis). On-line IR-analysis has the advantage of eliminating physical sample extraction and allowing for continuous monitoring of moisture content. However, this approach is sensitive to the surrounding environment, making careful calibration and control crucial for the quality of measurement results. Furthermore, as IR-sensors only target the surface of the conveyed pellet feed, several incorrect sampling errors need to be considered and counteracted to eliminate sampling bias and reduce the remaining measurement variability. Variographic characterization was applied to the two current grab sampling approaches of combined filtered material, to the alternative filter sampling method, and to the On-line IR-analysis. The results indicate that both the sampling of separate filters (using composite sampling and ISO-standardized moisture analysis), as well as a calibrated and well- maintained IR-sensor can improve the relative variability significantly, by lowering the total measurement system variance from 60% to 25%.

Jan 1, 2018

By G. X. Du

Reaction kinetics of serpentine and hydrochloric acid is theoretical basis for optimizing reaction process conditions of serpentine and hydrochloric acid. Kinetics of serpentine and hydrochloric acid was studied in this paper. The results indicated that apparent reaction order to hydrochloric acid was two and reaction kinetic equation could be expressed as: 2HClHCl,ddtckct-=·. The diffusion rates of hydrogen ions in liquid film on surface of serpentine particle and in amorphous silica layer generated in the reaction and chemical reaction velocity during the reaction had important effects on to-tal reaction velocity. And chemical reaction velocity had the most significant influence. The relation of conversion rate of magnesia xMgO with reaction time could be expressed as: 1(1)xkt--=·.

Jan 1, 2014

By Aldo Cipriano, Fernando Estrada

The mining industry is in search of control strategies that allow considering a global optimization of their processes, ensuring their stability. This has led to the application of recently developed control techniques on large-scale systems in the mining processes. One of the most important process of the mining industry is the mineral grinding, as the product particle size impacts, in a significant manner, the recovery rate of the valuable mineral in the separation stages. As a solution, a centralized hybrid model predictive control (HMPC) is presented; this control approach maintains the product particle size on a defined range and minimizes energy consumption, maintaining the grinding plant in a stable operation. As a comparison, a conventional model predictive control with an expert system to handle discrete events was developed, showing HMPC is a suitable solution that can used in the grinding process, with the benefit that it handles in the same controller both discrete and continuous dynamics and events.

Jan 1, 2014

By A. I. A. Salama

In this paper, the problem of sedimentation and consolidation of poly-disperse suspensions is considered. The solid particles are assumed to be of different densities. If the sediment solids stresses are dropped out of the system equations and using the Richardson and Zaki hindered settling model, it has been found that in the limit, i.e., as time approaches infinity, the fluid is completely displaced to the top of the sediment zone. Furthermore, the species segregate completely with the heavier and coarser particles at the bottom of the sediment and the lighter and finer particles at the top of the sediment. Practical observations do not support these behaviors and physical-ly such behaviors do not exist; consequently, results of this kind in the literature are unrealistic. Here, a mathematical structure of the poly-disperse sedimentation and consolidation problem has been proposed. In this case the compaction zone species solids stresses are introduced in the momentum balance equations of the system. The species solid stresses in the sediment are constrained so that the system equations are consistent, i.e., sedimentation and consolidation of two or more identical species should behave as a mono-disperse system. Such a condition has not been recognized and imposed in some of the studies in the literature, which has led to unreliable results. Two practical forms of species stresses that satisfy the system consistency condition are here proposed. It should be noted that the study of sedimentation and consolidation of poly-disperse suspensions could result in more realistic suspension interfaces compared to mono-disperse suspensions, and could lead to more reliable engineering designs of tailings ponds. Predictions of sedimentation and consolidation in models of poly-disperse suspensions are demonstrated using published data.

Jan 1, 2014

By L. O. Filipov, N. E. Menad, A. Geneyton

"Zeta potential of synthetic monazites presenting various compositions were measured to investigate the effect of the main lanthanides substitutions on electrophoretic mobility and resulting IEP. The measurements are performed in a CO2 depleted and enriched solutions showing both reduced influence of monazite chemistry and strong influence of ions resulting from the solubilization and dissociation of CO2. The influence of oleic acid on the electrophoretic mobility of those monazites was also investigated. The influence of pH on oleate adsorption was studied using a bubble/particle adhesion system. Adhesion strength measurements were performed on pure synthetic monazite-(Ce) and monazite-(La). An extensive thermodynamic model of monazite in water was developed to highlight correlations between lanthanides hydroxides/carbonates species concentrations in the bulk solution and oleate adsorption. Based on electrophoretic measurements, advanced thermodynamic consideration and adhesion measurements, further details of the oleate adsorption model on monazite surface were proposed.INTRODUCTION Electrophoretic and potentiometric data on monazite and, a fortiori, other rare earth semi-soluble salts such as bastnaesite are extremely erratic (Chelgani et al. 2015). The isoelectric points measured with electrophoretic mobility methods range from 4.7 to 6.5 although sporadic data indicates an IEP (isoelectric point) far from that range. Different explanations are proposed in the literature to explain the IEP variability notably the numerous chemical substitutions that frequently occurred within monazite crystal lattice (Chelgani et al. 2015). Based on lanthanides speciation diagram, several authors highlighted the influence of specific lanthanide species on the flotation performance of rare earth semi-soluble salts when carboxylate or hydroxamate collectors are used. Although lanthanides ions have a great affinity for carbonates groups (Kragten et Decnop-Weever 1987), lanthanide (hydrogen) carbonates were not implemented in speciation diagrams. In this work, an advanced thermodynamic model is proposed to highlight correlation between flotation performance and lanthanide species predominance but also concentrations. Qualitative measurement of the monazite surface hydrophobicity are performed through tests of adhesion of coarse monazite particles onto bubbles. Since flotation and microflotation technics are highly influenced by hydrodynamic parameters, this method was investigated to obtain a sharp contrast between appropriate and inappropriate pH conditions. This paper is to investigate 1) the effect of lanthanides substitution on monazite surface properties through zeta potential measurements, 2) the mechanism of adsorption of carboxylates on monazite surfaces and 3) the effect of CO2 on monazite surface properties and carboxylates adsorption."

Jan 1, 2018

By Richard K. Komarek, Antonios Zavaliangos, Roman T. Dec

Roller presses are widely utilized in mineral industry for fine milling and compaction. Recently used models are providing only limited information about the material behavior in the roll bite. This paper introduces a 2-dimensional finite element model for analyzing those two basic processes. A pressure-dependent plasticity model with linear elasticity was used as a constitutive model for the particular material. Coulomb friction law was used to describe phenomena on the material/roller surface interface. Two basic roller geometries are considered: smooth (used for milling and compaction) and with cavities, commonly used for briquetting. Comparison of the results obtained from the model with experiment indicates that they are following the general trends of experimental values recorded with laboratory roller presses. It is shown, that the model is suitable to analyze material behavior through all stages of the rolling process: feeding zone, nip region, neutral plane and release section. It can predict pressure, shear stress, slip of the material over the roller surface, material velocity field, failure of the compact during release and the course of other important process variables. This allows the process engineer to gain an improved understanding, leading to a better process and equipment design and control.

Jan 1, 2003

By Nikkam Suresh

Dense medium cyclones have been in use for washing coarse and small coals for more than 50 years. There have been modifications in its design and today these units have become indispensable for washing of Indian coals possessing difficult washing characteristics. About 53 percent of the Indian coals (coking and non-coking) are being washed in jigs, about 38 per cent are washed in dense medium cyclones while the remaining 9 per cent is treated in other units like Barrel Washers, Heavy Media Baths and Drum Separators etc. The present paper deals with the attempts made for design of industrial Dense Medium Cyclones for enhanced coal recovery. Two industrial units of 500 mm diameter and 650 mm diameter were designed with their washing capacities being 200 m3/hr and 350 m3/hr, respectively. The results of the pilot tests conducted on 500 mm cyclone treating very high Near Gravity Material coals crushed to -3.0+0.5 mm gave an ash reduction of up to 19.5 percent with the new design i.e., from a feed ash of 34.5 percent to 15.06 percent in clean coal with an appreciable yield of 45 percent in one stage.

Sep 1, 2012

By V. A. Luganov

Methods of treatment of pyrite concentrates differ, depending on the content of pyrite and non-ferrous metals: oxidation roasting, sulphatization roasting, smelting, direct hydrometallurgical treatment and so on. Existing technologies do not provide for high recovery of metals, expenses associated with existing technologies are high, and environmental issues, associated with the existing technologies need serious attention. We have developed universal technology of the activating-dissociating autogenous roasting of pyrite concentrates using air based, or air, enriched with oxygen, blow. The basic process is taking place in accordance with the following reaction: (1-x)FeS2 + (1-2x)O2 = Fe1-xS + (1-2x)SO2 +Q The products of this reaction are pyrrhotinized cinder and roasting gases, rich in SO2 (up to 18 % in case of air blow) and poor in SO3, that contain up to 1 % of elemental sulphur. Cinder contains different forms of pyrrhotite. These forms of pyrrhotite differ by its content (from Fe0.843S to Fe0.945S), thermodynamic, magnetic (from 4.10-1 to 3.6 SI units), flotation properties (with pyrite dissociation the ?-potential of the product is moving towards more electrically positive charge, from 0.95 for pyrite to 0.2 for dissociation products) and other properties that depend on the conditions of roasting. The combination of pyrrhotizing roasting with different methods of cinder treatment allows to increase the level of sulphatization of non-ferrous metals during the roasting; reduce the amount of blow used during the processing; reduce dust losses to the gas phase; reduce the capacity of gas cleaning system and increase resistance to corrosion of the gas-treatment system, used for the production of sulfuric acid from pyrites. This combination of treatments also allows to use magnetic separation and flotation for separation of ferrous and non-ferrous metal compounds during cinder treatment; perform de-arsenation of arsenic containing concentrates and by-products. Pyrrhotinized cinder may be treated by oxidizing and non-oxidizing hydrometallurgical methods. Keywords: Pyrite, polymetallic ores, sulphidization roasting, pyrrhotite, magnetic separation, arsenic sulphide

Sep 1, 2012

By S. Banisi, E. Arghavani, Gh. Parsapour, S. Mousavi

Maximization of water recovery in thickeners is an essential step in the mineral processing industries. The Gol-E-Gohar iorn ore processing plant uses a center pier thickener with a diameter of 38 m and depth of 4 m. The feed rate is 50 t/h solids with a concentration of 5% (w/w), and it has been designed to provide an underflow containing 50% solids. The performance of the thickener was not as expected judged by the overflow stream containing 0.6% solids and water loss of 52 m3/h in the underflow. A criterion called the index of flocculation incorporating the perimeter-based fractal dimension of flocs, floc size, and settling velocities was proposed and used to determine the optimum flocculant dosage which was found to be 20 g/t. The fractal dimension of flocs in a pulp containing 5% solids was found to be between 1.16 (no flocculant) and 1.56 (40 g/t flocculant) which indicated highly branched and loosely bound structures for the flocs as flocculant dosage increased. At these conditions, the size of the flocs which was recorded by a digital microscope increased from 93 µm to 403 µm. A new feedwell with a special design with the aim of preventing flocs breakage and maximizing energy dissipation of pulp was constructed and installed. These modifications led to an increase in the thickener drivehead torque from 5% to 18% of the rated torque, indicating a higher bed depth. Finally, installation of a PID controller reduced the drivehead torque relative oscillation from 52.0% to 12.7%. These changes increased the solids concentration of the underflow from 49.0% to 56.9%, decreased the overflow solids concentration from 0.6 % to values smaller than 0.01% and resulted in a reduction of 27% in water loss in the thickener underflow.

Jan 1, 2014