Gravity concentration of fines and ultrafines

Concentration of fines by gravity methods remains one of the challenging problems to the world mineral industry. Considering the increasing losses of mineral values and the search for an economic process, it has been the major concern of the researchers and the practicing engineers to develop an efficient fine gravity separator. The development of some of the recent fine gravity separators with the application of high centrifugal forces has resulted in improvement in the separation efficiency. In the last four de¬cades extensive studies have been carried out at National Metallurgical Laboratory (NML), Jamshedpur to develop gravity based processes for low grade ores, fines and industrial wastes involving the conventional separators to the latest equipment like multi-gravity separator for their economic exploitation. In this paper an attempt has been made to briefly present a review of the gravity concentration processes with a particular reference to the recent advances in the processing of fines. The salient results obtained from the recent studies carried out on beneficiation of lean grade finely disseminated tungsten ore, iron ore slimes and chromite slimes at NML using some fine gravity separators like Bartles-Motley Vanner GEC-duplex concentrator and MGS are discussed

Data-Based Performance Modelling of Hydrocyclone for Processing Iron Ore Fines

In this study, a data driven performance characterization model of hydrocyclone has been developed using multiple experimental data set collected from the published literature pertaining to processing of iron ore fines. The cut size, d50, has been determined for a given cyclone operating conditions using Lagrangian interpolation technique. A reduced efficiency curve has been constructed to map the performance and the functional behaviour has been modeled employing three typical distribution functions, namely, Rosin-Rammler, Exponential and Logistic. All pertinent model parameters have been estimated in accordance with the experimental data sets. It has been observed that all these functions fairly mimic the performance of cyclone for processing iron ore in the particle size range 25-300 m. Rosin-Rammler distribution found to be a better function for fitting the experimental data set in comparison to Exponential and Logistic functions to characterize the performance

Designing Process for Concentration of a Low Grade Copper Ore

The paper deals with the results of chracterisation and flotation studies carried out on a low grade and complex copper ore sample with a view to design process for its concentration. Flotation studies were carried out under varying conditions of process parameters. Effects of gran-ulametry of the feed, dosage of sodium iso-propyl xanthate as collector, pH and gangue depressant dispersant were studied. Sulphidization technique and use of potassium octyl hydroxamate as auxiliary collector for flotation of oxidised minerals was observed to enhance copper recovery. Use of sodium silicate as depressant/dispersant for sili-ceous gangues helped in improving grade of copper conce-ntrate. Rougher followed by multi-stage cleaning were found necessary to produce a high grade copper concentrate. Based on the studies undertaken the process was designed for concentration of the low grade copper ore sample

Modelling performance of water-only cyclone as a gravity separator for fine coal cleaning

The performance of a gravity separator treating coal is characterized by plotting a Tromp distribution curve. In this study semi-empirical performance models have been employed to characterize the performance of water-only cyclone on the basis of experimental data modelling for fine coal cleaning. Experiments have been conducted in the laboratory on a 100 mm water only cyclone. Raw coal used for the experiments belong to Patherdih colliery in the Eastern part of India. Washability studies have been undertaken to determine the gravity separation for a desired coal quality. The Mayer curve has been employed to plot float-and-sink analysis from which the Tromp distribution curve has been constructed. A reduced efficiency curve has been obtained and attempts have been made to describe the behaviour using a Rosin-Rarnmler type distribution function characterizing the performance of the cyclone. A simplified approach has been purposed to estimate the model parameters

Performance characterization of water-only Cyclone for processing high ash Indian coal

In this study semi-empirical performance models have been employed to characterize the performance of water-only cyclone on the basis of experimental data modelling for fine coal cleaning. Experiments have been conducted in the laboratory on a 100 mm water only cyclone. High ash coals used for the experiments belong to the Patherdih and Munidih colliery in the Eastern part of India. Separation based on specific gravity was studied on Patherdih sample whereas size classification analysis has been carried out on Munidih sample. Washability studies on Patherdih sample have been undertaken to determine the specific gravity of effective separation for a desired coal quality. The Mayer curve has been employed to plot float-and-sink analysis from which the Tromp distribution curve is constructed. A reduced efficiency curve has been generated based on specific gravity as well as size classification analysis. Attempts have been made to describe the reduced efficiency curve by employing Rosin-Rammler and Logistic distribution function to characterize the performance of the cyclone. A simplified approach has been proposed to estimate the performance model parameters. Experiments were conducted by varying the operating parameters like spigot diameter, feed inlet pressure and percentage solids in the feed to study the sensitivity of operating conditions. The effect of operating variables on the performance of the cyclone in terms of classification function has been investigated. A graphical user interface (GUI) based user friendly software (HYDROSIM) has been developed based on semi-empirical models for calculating the cut-size (d50) under various operating conditions

Recovery of Values from Mining and Industrial Wastes

Studies were carried out on the recovery of valuesfrom wastesfrom magnesite mines and sponge iron plant. Rougher flotation followed by cleaning of the rougher float resulted in decreasing the silica content to below 1 % in thefinal concentrate from the magnesite mines 'waste dump' sample. The apparent porosity, bulk density and water absorption of the pelletsfired at 1750°C were 3.4-4.9%, 3.25 gm/cc and]-1-5% respectively. Results on the 'altered dunite rock'sample from the magnesite mines was also encouraging. Considering the beneficiation characteristics of coal and the associated impurities in the ESP-dust' and 'coal-char'samplesfrom sponge iron plant, a combination of magnetic separation and froth flotation was adopted for their processing. In the f nal products the ash could be brought down to -- 33 %

Mathematical modelling of bagnold effect and separation behavior of a coal-washing spiral using a mechanistic approach

Among the gravity separators, the spiral concentrator is considered to be one of the most efficient and simple unit operations. Complex mechanisms, including the combined effects of different forces, differential particle settling rates, interstitial trickling and possibly hindered-settling affect the stratification of particles. "Bagnold effect" arises at relatively high pulp densities of the feed. This effect is attributed to the velocity distribution along the depth of the flowing film, which gives rise to a distribution of shear rates along the depth of flow. An improved mathematical model incorporating Bagnold effect is proposed to characterize the separation behavior of a coal-washing spiral. Sensitivity studies of the operating parameters on the segregation behavior of particles across the radial width of the trough during their motion along the spiral have been carried out. It is believed that the model reasonably mimics the segregation behavior of a particle during its motion along the spiral with a reasonable degree of realism

Mathematical Modelling of Seperation Behaviour of a Spiral for Washing high ash Coal

Sustained Coal R&D activity has been crucial to the many successful clean coal technology developments that have been achieved globally. The aim has been to enhance the competitiveness of coal by providing technical and envir-onmental improvements whilst at the same time reducing capital and operating costs. In coal preparation, simpler lower cost alternatives to froth flotation, such as the coal dense medium separator and spiral separators, have been adapted for cleaning of fine coal. A mathematical model has been developed to characterize the separation behavior of a typical high ash coal in a spiral. The modeling framework consists of parametric representation of geometry of the spiral and its trough, particulate flow along the helical path and principal forces acting on a particle during its motion. The elements have been combined seamlessly by assuming that the particles event-ually attain dynamic equilibrium in the forward longitu-dinal direction and static equilibrium in the transverse direction. The resulting force function provides a spect-rum of the particles' radial location on the trough according to their size and relative specific gravity. The model predicts relative specific gravity distribution and particle size as a function of equilibrium radial posi-tion. Sensitivities of radial equilibrium distribution of particle size and relative specific gravity with respect to mean flow depth have also been investigated. Simulation results are encouraging and validated with the published data. The model provides an analytical tool for better understanding of the separation behavior of particles in a coal-washing spiral

Mathematical modeling of separation characteristics of a coal-washing spiral

An improved mathematical model to simulate the particle and flow behavior in a coal-washing spiral has been developed. The modeling framework addresses three main components of the spiral system: (i) geometry of the spiral and its trough, (ii) fluid motion along the curvilinear path of the spiral and (iii) principal forces acting on a particle incorporating “Bagnold effect”. This effect has been addressed for both particle–inertial and macro-viscous regimes. The modeling components have been combined seamlessly by assuming that the particles eventually attain dynamic equilibrium in the forward longitudinal direction and static equilibrium in the transverse direction. The resulting force function provides a spectrum of the particle's radial location on the trough according to their size and relative specific gravity. The model predicts relative specific gravity distribution as a function of equilibrium radial position for different particle sizes. It also computes particle size variation as a function of equilibrium radial position for various values of relative specific gravity. Sensitivities of radial equilibrium distribution of particle size and relative specific gravity with respect to mean flow depth have also been investigated. Simulation results validated with the published data, are found to be reasonably consistent. The model provides an analytical tool for understanding of the separation behavior of particles in a coal-washing spiral

Designing Process for Beneficiation of Low Grade Iron Ore Samples from Orissa

The paper deals with the results of characterization and beneficiation studies carried on low grade iron ore samples from Orissa. Beneficiation of the two individual samples and their compostite based on gravity and magnetic separation techniques resulted in products with varying yield and grade of the products.The results of laboratory studies were validated through pilot scale trials. Based on the studies undertaken process was designed for bene-ficiation of the composite sample, comprising 60% S I and 40% S2, to a high grade product assaying over 65% Fe. Detailed material balance for the designed process was also undertaken