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By C. Kleine

Coal sorting with an x-ray-transmission (XRT) sensor has experienced a lot of development since first described by Jekinson et.al. in 1974. Powerful computers and increasingly sensitive X-ray scintillation counters enabled the development of high-performance sensor-based sorting machines. The first industrial installation of a belt-type XRT-sorting for coal is in operation since 2004. It is upgrading high quality coal from 1% ash to 0.7% ash for cathode production. In comparison to the high quality coal which is treated with a belt-type sorter, the chute type sorter has been successfully optimized for high volume coal treatment of lower quality coals. This project was funded by the German Environmental Fund (Project Nr.244444). In cooperation with the RWTH Aachen University and Isambane Processing, CommodasUltrasort(now Tomra Sorting Solutions) conducted extensive pilot test work under production conditions in 2010 for the destoning of power station coal at Arnot Power Station in South Africa. The experience gained during this pilot test phase led to an optimized, redesigned PRO Secondary XRT Chute sorter which is now in operation at a South African coal mine. This flexible semi-mobile modular destoning plant is treating a size range of -120 mm +30 mm at a throughput of 150 tph. The implementation of this plant not only reduces the ash content, abrasiveness index and sulfur content significantly, but also reduces royalties, water treatment and transport costs.

Sep 1, 2012

The flotation of nickel sulphide minerals is normally difficult in the presence of serpentine minerals due to the coating of serpentine particles on the nickel mineral surface. To improve the flotation, dispersants such as polyphosphate and carboxy methyl cellulose are normally used to remove the slime coating. However, in the flotation using high ionic strength process water, these dispersants are invalid due to their ionic nature. In this study, a new type of non-ionic dispersants, Pluronic triblock copolymers were examined with an objective of improving the flotation of ultrafine pentlandite (a nickel sulphide mineral) in the presence of lizardite (a serpentine mineral) in saline water. Three Pluronic triblock copolymers varying in solubility and hydrophile-lipophile balance (HLB) values were studied by flotation tests, settling tests and froth measurement. It was found that two of the copolymers improved pentlandite flotation against lizardite, and one copolymer deteriorated the flotation. The effect of Pluronic triblock copolymers on the flotation was actually linked to their dispersibility and foamability, which were governed by their physical properties. The two copolymers with a higher solubility or HLB value produced more stable mineral suspensions and more stable froth in the flotation resulting in better nickel grade and recovery in both rougher and cleaner flotation. Keywords: ultrafine particle, flotation, slime coating, dispersion, saline water, triblock copolymers

Sep 1, 2012

This paper presents a theoretical investigation on the ionic equilibrium of Fe(III)?Ni(II)?H2SO4?H2O system. A non-ideal speciation model is developed to calculate the concentration distribution of iron and nickel species in a mixed ferric and nickel sulphate aqueous solution over the pH range from 0 to 4 and temperature from 25 to 100°C. A series of speciation diagrams for iron and nickel species is plotted with the effects of ionic strength and temperature on the equilibrium constants being taken into account. The ionic strength-dependent equilibrium constant is treated through a semi-empirical Vasil'eV equation, which is based on an extended Debye?Hückel theory. A Helgeson model is applied to extrapolate the equilibrium constant to elevated temperature. The ionic equilibrium reactions are described by a group of numerical equations containing the temperature and ionic strength-dependent equilibrium constants, which are solved by the Newton-Raphson method. The speciation model is also applied to estimate the hydrogen ion activities and corresponding pH values. The calculated pH values are in agreement with the experimentally measured pH, and are compared to literature data and pH values produced by the Visual MINTEQ® program (a computer code for the calculation of chemical equilibrium in natural aqueous system). This investigation provides a deep insight into the ionic equilibrium behavior of a mixed metal sulphate aqueous system which commonly occurs in hydrometallurgical processing. Keywords: speciation, chemical modelling, thermodynamics, iron, nickel

Sep 1, 2012

By Xin Tan

In this paper, two types of low-grade complex zinc oxide ores (sandstone and limestone ores) from Yunnan province, China were investigated. A large number of argillaceous and alkaline gangue makes it infeasible to treat the ores with heap leaching. Although wet metallurgy can be considered, the lower efficiency of liquid-solid separation, the high cost, and low revenue limit this technology to be put into practice in large-scale. In order to solve this problem, a new technology combining mineral processing method with metallurgy technique is studied to process this refractory ore that consists of sandstone ore with 5.84 per centZn and limestone ore with 6.50 per centZn. The results of the tests showed that zinc can effectively be recovered from two types of the ores by using the new technology, and the acid consumption can be remarkably reduced. For sandstone sample, 82.96 per cent Zn was recovered by flotation and final Zn recovery by flotation+ hydro-metallurgy can be up to 78.17 per cent from the ore. In addition, for sandstone, acid consumption can be reduced from 270kg/t by direct acid, leaching to 76.92kg/t by flotation + hydrometallurgy combination. For limestone sample, 85.90 per centZn was recovered by flotation and totally 80.95 per cent Zn can be recovered by new technology which is a combination of mineral processing and metallurgy. Besides, H2SO4 consumption can be reduced from 450kg/t for sandstone originally to113.79kg/t after using new technology. One merit of this new process technology is that the zinc sulfides and oxides can be recovered without desliming in the flotation cells at the different stage and make sure the concentrate products as a good feed for hydrometallurgical technology. This study provided pretty good technical support for tapping low-grade refractory zinc oxide ores. Keywords: low-grade zinc oxide ores, limonite, non-desliming beneficiation, flotation + hydrometallurgy combination

Sep 1, 2012

Ca-containing gangue minerals such as Fluorite, Calcite have same surface activity point--calcium ions and approximate floatability with scheelite, it is difficult to achieve good dressing index of rough concentrate of scheelite. Mono-mineral experiments and ore tests indicate that, according to mineral composition, gangue minerals can be inhibited selectively by adopting suitable regulators, then the separation of scheelite from gangue minerals can be realized effectively. Mechanism analysis was taken by zeta potentials measurements and FTIR tests. Good dressing indexes are also obtained in practical ore tests and industrial tests. Keywords: scheelite, fluorite, calcite, regulator, flotation separation

Sep 1, 2012

By M. Panayotova

Most of the quantity of the water soluble xanthates, used in mineral flotation, is consumed in the process. However, the residue amounts are water contaminants downstream the mineral processing operations and can be toxic to aquatic biota at concentrations of 1 mg/L. In order to be able to discharge water from tailing ponds to natural water bodies the concentration of xanthates has to be decreased. The present paper studies the uptake of potassium ethyl xanthate by directly modified with copper and lead ions natural zeolitic rock, without passing through zeolite transformation into homoionic form. Modified zeolite exhibits high, comparable with powdered activated carbon of chemical purity grade, capacity to remove potassium ethyl xanthate from model wastewater, with pH in the range of 7?9 and pollutant concentration in the range of 10-150 mg/L. The pollutant immobilization is fast. Both Cu and Pb modified zeolite behave as selective with respect to xanthate in the model wastewater, and Cu-modified zeolite possesses higher selectivity. The equilibrium is best described by the Freundlich equation. Keywords: xanthate, wastewater, modified zeolite

Sep 1, 2012

By Sharma K. K.

India is the third largest producer with accounting to fifth largest reserves base of coal in the world. Indian coal has high ash content (15-45%) and low calorific value. The basic processes being used in India at different places for coal washing adopts old techniques. Much of the valuable part is being lost during washing processes. With enhancement of the available techniques and use of new processes like flotation process indicates better recovery of carbon values during washing stage. The same will increase the reserve base, improve economy of operation and alleviate environment related problems. In the above backdrop this paper portrays the case study of an existing coal processing plant in India. The case study includes the modifications being incorporated in the existing process to enhance the product value. The existing practices and the future trend of process technology that could be adopted to meet the requirements in this country are also discussed. Keywords: washing, dense media cyclone, magnetite media, flotation

Sep 1, 2012

By D. Moradkhani

Copper metal has important role in the basic industrials, as if it did not exist, modern human life would not develop! Copper leaching, as the first step, is important step in copper production processes. In this research, efficient factors on the leaching have been investigated. For this reason, four efficient factors on leaching namely pH, liquid to solid ratio (L/S), temperature and time, as independent variables, were optimized using response surface (RSM) with D-optimal. A quadratic equation was used to create response and contours. According to the results from analysis of variance (ANOVA), the value of determination coefficient (R2=96.77%) indicates that the model was good fit. Optimum experiment condition also was found: pH of 1, L/S of 8.24, temperature of 26.06 ? and time of 43.64 min. At this condition, the maximum recovery of copper was equaled to 92/38 in which good desirability achieved.

Sep 1, 2012

By N. Dhawan

In the last decades, High Pressure Grinding Roll (HPGR) has gained significant importance in hard rock processing due to numerous metallurgical benefits such as energy savings, particle weakening, preferential damage of coarse particles, and preferential comminution-liberation. There are a limited numbers of lab-scale HPGR units throughout the world. The laboratory-scale HPGR machine at the University of Utah is first-ever lab-scale machine designed by late Dr Klaus Schönert, the inventor of HPGR. This HPGR is constructed with two counter-rotating hardened tool steel rolls, each 200 mm in diameter and 100 mm in width. The HPGR unit is equipped with eight sensors and a robust control system, which serves as an ideal system for fundamental studies and lab-scale testing. In HPGR operation, throughput, energy and product size distribution are intricately linked to specific grinding pressure, roll gap and rolls speed. The nip angle existing during the operation determines the volume of feed material above the rolls that is pulled into rolls without slip. In this paper, scale-up factors and some of the existing models have been reviewed. A number of experiments have been carried out with limestone and a slag material. The influence of operating variables and their complex relationship has been studied.

Sep 1, 2012

By A. Pandey

Over the years, Coal Beneficiation at Tata Steel - West Bokaro has seen varied changes. With increasing R.O.M throughputs & lowering of the concentrate ash, Fine Coal Beneficiation process has thrown up myriad challenges. Development of Synthetic Collector was initiated couple of years back with Technical assistance from NLC Nalco India Ltd. Coal from West Bokaro unit was sent to Nalco?s Naperville (US) research lab for developing Tailor made synthetic collector . After comprehensive lab flotation studies, synthetic collector was developed & recommended for plant evaluation. The lab scale results were very promising in terms of improved separation efficiency & yield at similar ash level. The collector sample received from Nalco research laboratory were revalidated at Nalco Kolkata lab and finally at Tata Steel West Bokaro lab, confirming the promising results. (S.E 25-30 % better than HS Diesel) The key factors playing out for this improvement initiative are a) Scope for improvement in Clean Coal Yield at same or lower ash level coupled with improved Selectivity and Separation Efficiency b) Introduction of a Synthetic Collector with a Green Chemistry and subsequent replacement of H S Diesel, which is highly inflammable with a less inflammable & safer product Trial was conducted at plant scale in two phases and comparative performance of the Collector vis-à-vis Diesel was evaluated across the following Coal Seams of Q- SE (Seam VII, VIII, VI, IX and X). The results generated are very promising and the improvements observed are summarized below. ? Separation efficiency improvement by more than 20% observed. ? Flotation Fines yield increase varied from 0.6- 1.5 % on raw coal basis across different seams. ? Consumption pattern is 20-25 % lower than Diesel. Keywords: synthetic collector, west bokaro, coal beneficiation, HSD

Sep 1, 2012

By Jonas Addai-Mensah

In this paper, the results emerging from the several basic and applied studies performed to provide fundamental understanding of the interplay between clay pulp chemistry, orthokinetic flocculation performance, particle interactions, applied shear and dewaterability of fine clay mineral dispersions are presented, reconciled, and discussed. Modification of pulp chemistry and behaviour was achieved by using kaolinite and Na-exchanged (swelling) smectite clay minerals, divalent metal ions (Ca(II), Mn(II)) as coagulants and high molecular weight, anionic polyacrylamide copolymers: carboxylate substituted (PAM A) and 2-amido 2-methyl propane sulphonate (PAM S) (PAM S), non-ionic polyacrylamide homopolymer (PAM N) and non-conventional, non-ionic polyethylene oxide (PEO) as flocculants. Clear links between pulp interfacial chemistry, particle interactions and dewatering behaviour, resulting from the influence of hydrolyzable metal ion, pH, temperature, polymer structure type and shear, are established. Optimum conditions for improved, orthokinetic flocculation performance of negatively charged clay particles, reflecting faster settling flocs (>10 m/h) comprised: (i) coagulation, (ii) moderate agitation rate, (iii) shorter agitation time and (iv) anionic rather than non-ionic PAM. The optimum flocculation conditions did not, however, have a significant impact on the final sediment solid content of 20 ? 25 wt%. Further application of shear to pre-sedimented pulps improved consolidation by 5 - 15 wt % solid. Application of the findings and new knowledge gained to real plant tails? case studies for marked improvement in dewaterability through thickening is demonstrated.

Sep 1, 2012

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

Sep 1, 2012

By G. Rajesh

Mathematical modeling of bioremediation has gained importance as it is used as an optimization tool for the remediation process involved in contaminated sites. The bioremediation of Cr(VI) has been studied taking into consideration the initial Cr(VI) concentration Cr(VI)ini, bacterial growth substrate concentration (S), maximum growth rate (µmax), yield coefficient (Y), half saturation constant (Ks), and inhibition constant (KI). As the enzymatic reaction is also affected by initial substrate concentration (Sini) and Ks, different ratios of (Ks/Sini) are analyzed. As the inhibition constant (KI) is not constant for all the enzyme reactions and it varies with Cr(VI)ini, the correlation between (KI) and Cr(VI)ini is developed. A set of differential equations pertaining to bioremediation of Cr(VI) has been solved using FORTRAN 90 program adopting the model developed. The results are verified with the experimental data from the literature and a good correlation has been obtained between the experimental data and the model predictions. Keywords: bioremediation, hexavalent chromium, mathematical model, inhibition kinetics

Sep 1, 2012

By S. Serranti

The recycling of end-of-life concrete into new concrete is one of the most interesting options for reducing worldwide natural resources use and emissions associated with the building materials sector. The possibility to realize a larger re-use of silica aggregates from old concrete, strongly contributes to reduce environmental impact (reduced exploitation of natural resources, reduction of CO2 emissions, airborne dust production, etc.).To reach this goal, innovative processing techniques, as well as innovative sensing units and architectures have to be developed. In this perspective an analytical approach, based on hyperspectral sensing techniques, is proposed, discussed and critically evaluated in order to perform an automatic quality control assessment, finalized to maintain a high standard of concrete demolition waste, from the earliest stage of recycling to the further processing stages, according to the detected in-situ demolition waste characteristics. The paper deals with the analysis and the evaluation of the problems related to the integration of this approach with state-of-the-art demolition and building processes and procedures. Keywords: end-of-life concrete, recycling, hyperspectral imaging, NIR spectroscopy, quality control

Sep 1, 2012

By Mohana Rao Andavarapu

Sandur Schist Belt of Karnataka Craton constitutes a hub of iron ore mining activity. The iron ore deposits of the region are closely associated with Banded Hematite Quartzite (BHQ), Shale, phyllites, & Graywackes. The gradual depletion of high-grade iron ores due to extensive utilization has necessitated the exploitation of low-grade iron ore including BHQ, which are available abundantly in different parts of India. In the present investigation, BHQ samples from Kammaturu mines of Sandur schist belt was studied to assess the possibility of upgrading the iron content to the maximum possible extent, so that it may find the better use in iron and steel industries. The sample collected from the study area analyzing 39.76% Fe, 39.8% SiO2, 0.66% Al2O3, and 1.92% LOI was subjected to beneficiation studies. The mineralogical studies reveals that the samples are predominately consists of hematite as an iron mineral and quartz as gangue mineral. Liberation studies and chemical analysis were carried out prior to the beneficiation process, which is flotation. Cationic Reverse flotation studies were carried out and discussed by varying different process variables such as feed size, depressant, collector cum frother dosage & pH. The results obtained are encouraging with an appreciable improvement in the iron content up to 62.8% Fe with Fe recovery of 50.43%. The concentrate obtained from the flotation can be used for pellet making process.

Sep 1, 2012

By N. Pradhan

In the Sukinda valley, Orissa, India, a large quantity of overburden material is generated during the mining of chromite mineral (on average 10 tons for every ton of ore). The overburden hereby depicted as ?lateritic nickel ore? contains on an average 0.5% Ni. IMMT Bhubaneswar is working on this material for extraction of nickel and cobalt. But for better recovery of metal values, thermal activation or thermal reduction of ore is required. An alternative biotechnological route for reduction of ore is hereby attempted. An anaerobic dissimilatory Iron (III) reducing bacterial consortium (here denoted as IRB), capable of imparting iron phase changes in the lateritic nickel ore was established which improves the subsequent extraction of co-precipitated Co (III) and Ni (II) from the ore. In this study, properties of thermally and microbially reduced lateritic nickel ore are compared vis-à-vis original ore. Due to the phase changes, original light brown color of the lateritic nickel ore changes to dark brown on IRB treatment. This dissimilatory reduction of ore leads to formation of some magnetic particles, which were separable by hand held magnet. Roasting and IRB treated ore on acid leaching with H2SO4 show about 45 % and 36 % leaching of nickel ore compared to about 18 % leaching from the original lateritic ore. If bacterial reduction method is successful, cost intensive method of ore roasting process can be eliminated. Thus, it is possible to make use of dissimilatory iron reducing bacteria for recovery of valuable metals from off grade iron ore/ laterites. Keywords: lateritic nickel ore, bacterial reduction, thermal reduction, dissimilatory fe (iii) reducing bacteria

Sep 1, 2012

Froth flotation is an industrial process commonly used for the separation of mineral particles. Bubbles sparged in a pulp collect and carry hydrophobic particles to the top layer of a flotation cell, the froth zone. There is a strong correlation between the stability of the froth phase and the flux of solids. However, flotation units placed in series operate, as a whole, in a non-steady state regime with the concentration of particle decreasing from one cell to the next resulting in a decrease in froth stability, which can compromise the recovery of valuables. Organic chemical reagents, frothers, are generally added to prevent fine bubbles from coalescing and to increase the stability of the froth phase. Frothers represent the second largest group of mining chemicals. It is crucial to understand the resulting properties of the frother on the froth phase in order to select the most suitable reagent for a particular operation. The bubble coalescence dynamic of three different surfactants, 1-pentanol, poly (propylene glycol), and tri (propylene glycol) methyl ether, were investigated in this study. In the first stage, the stabilisation mechanism of bubbles in a solution of surfactant was investigated using a specifically designed experimental setup. The coalescence behaviour of bubble pairs was recorded using high-speed video imaging in which information such as the coalescence time and the deformation of the resultant bubble upon coalescence could be extracted. The results were then compared between the different surfactants for several concentrations. It is shown in a study that the coalescence time increases with surfactant concentration until the Gibbs-Marangoni effect is suppressed by bulk diffusion. Conversely, the oscillation of the resultant bubble was found to be affected only at concentrations at which the film is saturated. The implications of the effects of surfactant type and concentration on the coalescence time and bubble oscillation in froth flotation are discussed. Keywords: froth flotation, frother, bubble coalescence

Sep 1, 2012

By Ashish Kumar

High grade ore deposits in the world are fast depleting and the valuables in the low-grade ores are finely disseminated. The feed grade to flotation circuit is also declining. Attainment of suitable grind is preferred, which inevitably creates more fines of the gangue minerals to interfere with the flotation process because of the undue competition between the fines and the valuables for the collector ion adsorption. Besides the use of polymeric or long chain hydrocarbon depressants for the gangue mineral, microbial induced flotation also has potential to float minerals selectively. Thiobacillus ferroxidans and Thiobacillus thiooxidans adhere on the minerals to modify its surface properties and affect the minerals flotation acting as depressants. Hindustan Zinc has conducted laboratory studies to understand the adhesion of microorganism on the mineral surfaces and its impact on the selective flotation. The experiments were further designed to reduce consumption of depressing reagents for graphitic carbon, pyrite, and galena. Preliminary studies reveal that desired quality of concentrate can be achieved with reasonable recovery. Keywords: thiobacillus thioxidans, thiobacillus ferroxidans, bioflotation, microbial induced flotation

Sep 1, 2012

By P. S. Dash

With implementation of stringent environmental regulations, ultra clean coal technology development programs have gained significant importance worldwide. As far as Indian scenario is concerned, most of the coals present in India are of drift origin and low grade, containing high mineral matter varying from 15% to greater than 50%. The inorganic or ash constituents of Indian coals are finely disseminated through the organic or carbonaceous constituents so, that commonly used physical beneficiation techniques are of only limited value in affecting separation. Chemical processes involve addition of chemicals, which react with the mineral matter and allow its easy removal. The present study envisages the effect of aqueous alkali leaching followed by acid washing on the removal of mineral matter from two different captive coals of Tata Steel at elevated temperature and pressure. The experiments are conducted at desired conditions using a bench scale pressure reactor set up having proper data acquisition and control system. The research study revealed, that it is possible to reduce the ash content up to 70% by this method. The alkali content of the product clean coal does not increase whereas the silica and alumina content reduces by nearly 58% and 62% respectively. Significant reduction in the phosphorus content is observed after the acid treatment. The crucible swelling number of the feed coal improves after the treatment. The mechanism of demineralisation was evaluated by analyzing the coal samples before and after the alkali and acid treatment using scanning electron microscope (SEM). Because of the acidic nature of the silicates and aluminates, they dissolve into the NaOH solution and form sodalite. Sodalite is partially soluble in the alkali solution. The hydrates formed during alkali treatment are partially removed due to acid wash. This study in overall provides an insight into possible alternative methods of beneficiation for removal of ash from high ash Indian coals.

Sep 1, 2012

By Xiaoming Wang

This paper describes a new magnetic separator integrating dynamic permanent magnetic force, gravity and flow dynamics to enhance the quality of the iron concentration. This equipment can increase the grade of concentrate by controlling the formation of magnetic agglomerations to reject most gangue. Test results indicates that the compound force field separator can be applied in improving the quality of iron concentrate and has a wide range of potential market applications. Keywords: magnetic separator, compound force field, rotating magnetic system, magnetite concentration

Sep 1, 2012