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By E. V. Manlapig

"Some researchers postulate that the floatability of a particle in the streams of an industrial flotation circuit is a function of only its size and liberation properties. They do not discount the importance of reagent or surface contamination on particle floatability but assume that the reagent coverage or surface contamination of the particle surfaces is essentially uniform for particles of similar size and mineralogical properties when subjected to a particular chemical regime.In this paper, samples collected from laboratory batch flotation tests performed on different streams of Cominco Teck’s Red Dog lead cleaning circuit have been characterised with respect to their size, mineral association and mineral surface exposure. An analysis of this data set indicates that the flotation rate of a particle in an industrial flotation environment is a strong function of its size and also of the mineral composition of its surface (Figure 1). It is a function not only of the proportion of the most floatable mineral on its surface but of the floatability of the other minerals on its surface as well.Nodal analysis is a technique developed by the authors that can be used to determine if the ore floatability of a particle class is changing within an industrial flotation circuit. This technique is used within the paper to show that the floatability of all the different types of particle classes studied within the Red Dog circuit did not change significantly during the lead cleaning stage. However, it was also concluded that particles with the same size and mineral composition did not all float with the same rate in the individual streams of the flotation circuit, but with a distribution of rates. It is suspected that the particles within a size mineralogical class in this study have varying degrees of surface oxidation and that this results in varying particle flotation rates. Thus basing particle floatability on size and mineralogical effects, alone, in a flotation model is not always valid."

Jan 1, 2003

By Francisco Vicuña, Miguel Becerra, Nelson Iglesias

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

Jan 1, 2014

By Herman D. Mendoza

"The removal of finely dispersed mercury from the effluent of small-scale gold mining operations and the eventual recycling of the recovered mercury was investigated. The conventional method of amalgamation, or “ball milling”, involves the mixing of a substantial amount of mercury with ore to recover free gold during the grinding stage. During grinding, a portion of the mercury is transformed into minute droplets, which readily float and disperse in the effluent. A kilo of gold ore containing 20-30 g Au/t, when ground with 3 g of mercury, yields 0.005 to 0.050 mg/l of mercury in the effluent, exceeding the concentration of 0.002 mg/l allowed by law for surface water.A rapid recovery/ recycling process was introduced using the surface-chemical properties of finely dispersed mercury in aqueous suspension. It was observed that fine droplets of mercury in an aqueous environment readily attached onto a collector having positive surface potentials for pH 3 to 10. An example of a suitable collector is alumina (Al2O3), which has an iso-electric point of pH 9.8. When an effluent, coming from a settling procedure after an amalgamation-grinding stage, was passed through a column-bed packed with alumina fiber, removal and subsequent collection of finely dispersed mercury occurred under acidic conditions, pH 3-6. Recovery was around 99.5%, yielding an acceptable quality of water safe for disposal into the aquatic environment. The collected droplets of mercury, which are left in the column-bed of alumina fiber, were subsequently treated with a cleansing solution at alkaline conditions pH 10 -12. At these conditions, both mercury and alumina fiber carry negative surface potentials, which results in the eventual detachment of attached mercury from the alumina collector. The effective recovery of attached mercury from the alumina collector by the detachment procedure is only 30-35%. The collected mercury from the cleansing stage can be collected, cleaned and can be used for subsequent amalgamation processes. The attachment and detachment behaviour of finely dispersed mercury onto and from the microscopic collector alumina is shown in Figure 1. The result of attachment and detachment were analyzed using existing interaction energy theories like the Darguin-Landau- Verwey- Overbeek (DLVO) Theory."

Jan 1, 2003

By Renato Oliveira, Walter Valery, Alex Jankovic, Birol Sönmez

"The ball mill is the most common ore grinding technology today, and probably more than 50% of the total world energy consumption for ore grinding is consumed in ball mills. On the other hand, high pressure grinding roll (HPGR) technology is relatively new to the mining industry, with significant application only since the beginning of the 21st century. Both ball mills and HPGRs are typically used in closed circuit with classifiers. There is a general consensus within the industry that classification efficiency and circulating load both have a major effect on the efficiency of closed circuit ball mills. Metso Process Technology & Innovation (PTI) conducted a laboratory test program to understand the relationship between classification efficiency and circulating load, and the impact on the performance and capacity of ball mill circuits. However, the effects on HPGR performance are significantly different. Metso PTI has initiated a pilot scale test program to evaluate the size reduction performance of the HPGR under different circuit configurations. A series of pilot scale HPGR locked cycle tests were performed to simulate the following circuit configurations: including closed circuit with a screen, partial product recycle and edge recycle. This paper discusses the results from the pilot scale HPGR and laboratory scale ball mill test programs. The effect of circulating load and classification efficiency on the performance of ball mill circuits is compared to the effect on HPGR circuits. The fundamentals of grinding behavior are also discussed in order to explain the difference."

Jan 1, 2014

By S. S. Indi, D. Santhiya, S. Subramanian, K. A. Natarajan

"With the gradual depletion of the high-grade ores and finer dissemination of values in the leaner samples, it has become imperative to develop innovative approaches to process such complex ores. The beneficiation of complex sulphide ores containing copper, lead and zinc minerals, remains one of the most important challenges in base metals metallurgy. The advent of biotechnology in mineral processing has opened up immense possibilities to exploit such difficult-to-treat ores. Bioprocessing techniques thus hold promise as potential substitutes for the conventional technologies in vogue. Several types of autotrophic and heterotrophic bacteria, fungi, algae and yeasts are implicated in mineral beneficiation processes. Adopting a bioprocessing route to mineral beneficiation has attractive benefits, such as lower cost and energy requirements, environmental acceptability and operational flexibility.The interaction of sphalerite- and galena-adapted Bacillus polymyxa (B. polymyxa) cells with sphalerite and galena has been investigated through adsorption, electrokinetic and flotation studies. The amount of sphalerite-adapted cells adsorbed onto sphalerite and galena is found to decrease with increase in pH. On the other hand, the adsorption density of galena-adapted cells onto galena shows a feeble maximum around pH 8, and the amount adsorbed is marginally higher in the pH range of 8 – 11.5. In the case of sphalerite the amount adsorbed is higher in the pH range of 5 to 7. The adsorption density of both the adapted cells is higher for galena vis-à-vis sphalerite. Electrokinetic studies indicate significant surface chemical changes on the chosen sulphide minerals and the bacterial cells, consequent to microbemineral interactions. Selective flotation tests on a synthetic mixture of galena and sphalerite confirm that sphalerite could be preferentially floated from galena, using galena-adapted cells, but not with the sphalerite-adapted cells. The cells adapted to galena assay a higher polysaccharide content and are more hydrophilic, while the sphalerite-adapted cells have a higher protein content and possess greater hydrophobicity. Transmission electron microscopic studies have provided evidence in support of the differences between the cell surface characteristics of sphalerite- and galenaadapted cells (Figure 1). Possible mechanisms of interaction between the minerals and the bacterial cells are discussed."

Jan 1, 2003

By Xiaoping Xu, Tiansong Dong, Guosheng Wang

"Jianfengpo tin ore is located in Jiangxi Province, China. The cassiterite is fine and dispersed. It is hard to separate marmatite from a variety of sulfide minerals. Because the iron-containing sulfide minerals including pyrrhotite, pyrite and chalcopyrite are detrimental to the improvement of the grade of zinc concentrate. Besides, the presence of the iron oxides and ferro-carbonate minerals results in the difficult beneficiation of tin. Therefore, Jianfengpo tin ore is a kind of refractory cassiterite polymetallic sulfide ore. According to the properties of Jianfengpo tin ore, the technology process of "Sulphide ore preflotation-Bulk flotation of sulphur and zinc-Separation of sulphur and zinc -Magnetic separation-Gravity concentration" was developed to recover the valuable materials including marmatite, pyrite, magnetite, cassiterite and indium comprehensively. For the feed ore containing 0.87% Sn and 0.70% Zn, a zinc concentrate of 44.56% Zn with a recovery of 69.10%, a high-grade tin concentrate of 54.38% Sn with a recovery of 53.03% and a low-grade tin concentrate of 6.54% Sn with a recovery of 1.25% can be achieved in the batch flotation tests. In the industrial tests, for the feeding which contains 0.55% Sn and 0.65% Zn, the tin concentrate of 49.10% Sn with a recovery of 48.52% as well as the zinc concentrate of 45.11% Zn with a recovery of 60.10% can be produced. Thus some pyrite and magnetite concentrate are recovered as well. So Zinc, tin, sulphur and iron ores are recovered effectively by the technology."

Jan 1, 2014

By Shenxu Bao, Ying Bian, Xiang Liu, Liuyi Ren, Yimin Zhang, Chun Liu

Efficient enrichment of high-carbon low-grade mica stone coal containing vanadium is a key problem in the mineral processing field, and the mature beneficiation process is yet to be developed and applied. In this paper, a special mineral mica type of stone coal containing vanadium from Tongshan, Hubei Province, China was selected as the research object. Chemical analysis results show that this mineral contains V2O5 0.71%, SiO2 49.28%, C 13.44%, and CaO 6.26%. Scanning electron microscope (SEM) shows that vanadium generally exists in all kinds of mica minerals in 20 µm to 50 µm fractions. Mica stone coal containing vanadium must be ground to a particular fineness (approximately 45 µm). To reduce acid consumption during vanadium extraction from stone coal through acid leaching, a pretreatment process was proposed to enrich micas by using shaking table and flotation methods. A new combined technology process was implemented, resulting in a 0.96% improvement in the vanadium grade of raw materials in the succeeding process. Vanadium losses were controlled to 4.57% through the pre-concentration process, which reduced the burden of the subsequent procedure. The content of high acid consuming minerals was also diminished, such that approximately 6612 CNY was saved from producing 1 t V2O5. Therefore, stone coal containing vanadium should be pre-concentrated by using an appropriate combined process to reduce costs.

Jan 1, 2014

By John Starkey

"The development of the SAG Power Index (SPI) Test in Canada has created a new and accurate way to measure ore hardness in a SAG environment. Coupled with the standard Bond Ball Mill Work Index Test it is now possible to determine from these two relatively inexpensive laboratory tests, the amount of energy required to grind an ore from the primary crushed size to the desired liberation size. By testing multiple samples to discover where the hard and soft ore zones are located, the representative hardness distribution for the ore body can be determined and grinding equipment selected that is capable to meet production targets for all mining areas of the deposit.Previously, it was deemed prudent to select up to 50 t samples of ore for Semi Autogenous Grinding (SAG) pilot plant tests and a second 5 t sample for metallurgical pilot plant work. The methods outlined in this paper show how the 50 t sample is no longer required for SAG design because it is better to measure the representative hardness distribution of the ore body than the hardness of a “chosen” representative sample. This is demonstrated to be true by the fact that the lower horizons of an ore zone cannot initially be accessed to recover 150mm pieces, and the bulk samples taken, rarely represent the desired design hardness of the ore. Median hardness will not yield a good result in most cases and a clear understanding of the location and extent of the hardest zones is imperative to achieve a truly successful grinding circuit design.This paper discusses two plants (Kubaka and Agnico Eagle) that have been designed using SPI and Bond with no pilot plant test backup. Both have been very successful in that they can grind design tonnage on the hardest ores in the mine. This guarantees that the mine’s profitability is protected in any mining sequence. It also allows the extra power to be converted to higher throughput on softer ores if additional cash flow is needed. The advantages from the owner’s point of view are dramatic. This procedure will be attractive as well when considering the costs for test work, and the samples for testing. Existing diamond drill core is normally used and this allows the inclusion of data from the deepest regions of the mine. In addition, it is also clear that the decision to use a crusher can now be made at the design stage of a project based on measured parameters and the estimated capital costs of alternative designs."

Jan 1, 2003

By Güven Önal, Zeki Dogan, Neset Acarkan

"In general, the processing of glass sand may involve comminution, washing, wet classification and attrition scrubbing. Additional processes may include magnetic separation, flotation and leaching in various combinations.Yaliköy sand dune deposit is located near to Istanbul on the European side by the Black Sea coast. The reserve of deposit is around 70 million tons. Iron content of Yaliköy sand dunes is 0.48 % Fe2O3 and not suitable for glass manufacture. The iron content of glass sand should be less than 0.15 % Fe2O3 for window glass manufacture and 0.05 % Fe2O3 for glassware. In this study, it was aimed to produce glass sand with less than 0.15 % Fe2O3 for window glass and with less than 0.05% Fe2O3 for glassware manufacture from Yaliköy sand dunes. A representative sample with a weight of 200 kg was taken from Yaliköy sand dunes deposit through opening small pits.• Mineralogical studies have shown that iron is present in three forms:• Hematite, limonite, clay and iron silicate minerals such as epidote and garnet occur in free form.• Quartz grains are coated by hematite and limonite.• Iron is also present in the cracks of quartz grains.Free iron minerals such as hematite and limonite and silicate minerals were subjected to magnetic separation and flotation for removal. Iron coatings were tried to be removed by scrubbing and leaching. Iron removal in the cracks of quartz grains was attempted by grinding and leaching.Under optimal conditions, sand concentrate with 0.38 % Fe2O3 was obtained by means of high intensity disc type magnetic separation. Grinding and scrubbing were applied to see the effect of size reduction and attrition at room temperature and 90 ºC, by using non-magnetic fraction. Sand concentrate with 0.13% Fe2O3 was obtained at 90 ºC in this test.Sand sample which was previously ground to minus 0.5 mm and scrubbed, was floated by using sulphonates as collector. After flotation tests, sand Concentrate was obtained with 0.11 % Fe2O3.The optimum iron removal was achieved by H2SO4 leaching at 90 ºC depending on acid concentration and leach duration in static, percolation and agitation leaching. Agitation leaching was done by the use of mixer at 600 rpm, 50% solids and leach duration was 15 minutes."

Jan 1, 2003

By Érica Linhares, Anderson Silveira Lopes, Aline Costa

In the production units of ferromanganese alloys wastewater are generated. They mainly arise from gutters of drainage water from warehouse of raw material (manganese ore, reducing agents and other), product and slag. This wastewater, in general, may contain particles that will suffer difficulty to naturally decant, giving the water turbidity and color characteristics. Thus, this study aims to characterize the effluent, the treated water and the sludge from the sedimentation tank from the one main Brazilian plant. The investigated characteristics were: turbidity, total solids (TS), suspended solids (SS), dissolved solids (DS), pH, Eh, COD (chemical oxygen demand), residue classification and chemical analysis by ICP - OES. The turbidity before treatment was 417 NTU and after passing through the tank, 44 NTU, a figure slightly higher than the emission standards for Class 1 regulated by the Brazilian environmental legislation in force. The values for TS, SS and DS of the effluent were 225, 114.3 and 110 mg/L, respectively. For the treated water the values were 93, 48.3 and 45 mg/L for TS, SS and DS, respectively. The sedimentation process was able to reduce by 21 % of the COD. In the test of loss on ignition (LOI) from the tank bottom sludge were observed losses of 29.35 %, while the volatile analysis found 20.70 % of volatiles in the sample. It was determined that the concentrations of Al, Fe, Mn and S are, respectively, 0.1875 mg.L-1, 0.3071 mg.L-1, 0,789 mg l-1 and 0.00828 mg.L-1, values above the maximum allowed by law. Based on the analysis of X-ray diffraction, the identified minerals in the sludge were quartz, muscovite, kaolinite, calcite and albite.

Jan 1, 2014

By Chuansheng Luo, Qiuyang Hong, Lili Zhang, Dongyun Liang

"The metallogenic rock of a sandstone-type Cu ore is arkose-quartzite as well as siltstone and the cement is composed of argillaceous minerals including sericite, chlorite, etc. and carbonate minerals including calcite, dolomite, etc. A detailed process mineralogy study on this complex copper ore was carried out using MLA combined with traditional research methods. According to the results, there are many types of Cu minerals including copper sulfideminerals, secondary copper sulfideminerals, copper oxideminerals, copper carbonate hydroxide minerals and copper silicate minerals in the ore. Based on the occurrence of Cu, the copper existing as copper sulfide minerals (bornite, chalcopyrite and chalcocite) and copper oxide mineral (malachite) which have a good floatability accounts for 49.28% while the copper (chrysocolla) hard to be recovered by flotation and the copper existing in the cement (sericite, chlorite, psilomelane and limonite) accounts for 48.65%, and the copper existing in the carbonate minerals (calcite and dolomite) accounts for 1.72%. The process mineralogy study indicates that the process "beneficiation combined with hydrometallurgy" should be applied due to the various occurrence of Cu. The abundance of calcite and dolomite is about 12%, so removing these acid-consuming minerals by floatation is an effective way to reduce the acid consumption in the hydrometallurgical process and the lowest Cu loss is 1.72%. So the process "floating copper minerals-floating calcium minerals (calcite and dolomite)-leaching copper from the tailings" is used in the pilot tests. The recovery of floating copper and leaching copper from tailings is 46% and 30% respectively, so the total recovery of copper is 76%. Compared with the original process "leaching copper from crude ore-floating copper from the residue", the total recovery reduces by 1% but the acid consumption of producing per ton of copper decreases from 37t to 12t. The new technology process has a great advantage."

Jan 1, 2014

By Marco Le Roux, Quentin Campbell

"Most coal supply contracts include strict limitations on the moisture content of the products. This limitation exists because of calorific, transport cost, and handling reasons. Managing the retention time on product stockpiles to facilitate drainage commonly controls the moisture content in coarser coal products. A large-scale pilot rig has been commissioned to facilitate research in this regard. A stockpile of about 15 tonnes of a typical washed power station feed coal from the South African Witbank coalfield was loaded onto a 6 x 6 m platform on load cells. The platform was shielded from the elements, like rain and wind, and an artificial rain sprinkler system was installed. A variety of rainfall intensities and durations were simulated and the water accumulation and run-off was measured. The material was also sampled for moisture and particle size before and after the series of tests. At the same time, the drainage characteristics of the same coal were determined in smaller scale drainage columns for comparison. Data is presented in this paper on the drainage rates, maximum accumulated moisture, final moisture, and the effect of evaporation. The results showed that for all rainfall patterns tested, drainage ceased after 2 - 3 days, but evaporation continued for at least the time period under investigation, albeit at a low rate. Evaporation contributed to dewatering at rates that depended on wind, temperature and humidity conditions. This caused a slow reduction in moisture content even after the run-off had ceased. The value of the final moisture depended on the coal PSD. It was also found that the intensity and duration of the more intense rainfall events did not significantly affect the maximum water accumulation, with drainage rates equaling the corresponding water addition rates which suggested that water ran off over the surface of the stockpile with limited penetration. During more intense rainfall scenarios, some penetration was apparent."

Jan 1, 2014

By Martin Rudolph

"Flotation is without a doubt one of the major processes for the separation of fine minerals and it has been applied for more than a century. A key task of a successful flotation separation is to find the proper chemical treatment to selectively hydrophobize and thus float a certain mineral phase using molecules or ions referred to as collectors, depressants, regulators and frothers. Commonly floatability is determined by microflotation tests using the Hallimond tube with pure mineral phases. This method however requires the pure mineral phase which is very often not even taken from the same deposit which is going to be processed. In this paper we present a new approach to in-situ determine and even map the floatability of finely disseminated mineral phases within cross-sections of an ore. It is based on measuring hydrophobic effects using colloidal probe atomic force microscopy with a hydrophobic polystyrene probe based on force spectroscopy with a lateral resolution of only a few nanometers. Coupled confocal Raman spectroscopy on the same locality enables the identification of the mineral phase. We present the working principles of the method and show which signals in the force spectra characteristic for hydrophobic interactions can be used to define floatability and which can then be mapped as single quantities, e.g. jump-into-contact events due to nanobubble occurrence or parameters of the long range interaction curves most probably due to capillary effects. A finely grained silicate ore containing the valuable rare earth mineral eudialyte from southern Sweden as well as pure samples of magnetite are presented as substrates to demonstrate the capability of this new approach. This method will not only help to find the proper flotation chemistry but it can furthermore help in researching and unravelling problems of floatability within similar mineral phases."

Jan 1, 2014

By Hiroshi Sasaki, Herman D. Mendoza

"The surface-chemical property of nickel slag fiber was modified in aqueous media in order to act as an active and efficient collector of colloidal amorphous silica from geothermal effluent. Colloidal amorphous silica (0.05 µm) from geothermal wastewater causes operational and ecological problems. It clogs geothermal pipes and waterways, and when disposed to the environment poses hazardous effects on both the flora and fauna ecology. Because colloidal amorphous silica is extremely fine and remains in suspension in aqueous media, conventional solid/liquid processes to remove colloidal silica from its bulk liquid are rendered ineffective.A rapid separation technique is then developed to remove effectively amorphous colloidal silica from its bulk liquid by attaching the extremely fine particles of silica onto a nickel slag fiber coated with magnesium hydroxide, Mg(OH)2. The nickel slag fiber has the following characteristics: a high surface area and predominantly possesses negative charge in aqueous media with an iso-electric point at pH ~2.5. When soaked and saturated with Mg(OH)2 solution, the surface of the nickel slag fiber becomes coated with fine and compacted Mg(OH)2 precipitates. This modifies the surface- chemical property of nickel slag fiber transforming the negatively charged surface into a positively charged surface in aqueous media with an iso-electric point of around pH 11.8, which corresponds to the iso-electric point of Mg(OH)2. When geothermal effluent containing negatively charged colloidal amorphous silica particles (i.e.p. of silica is pH 2) is passed through a column-bed packed with surface-chemically modified nickel slag fibers under natural pH conditions, the colloidal amorphous silica particles are recovered by attachment onto the surface of the surface- modified nickel slag fiber. The recovery of colloidal amorphous silica by attachment is 97-99%, resulting in the production of a relatively clean and silica free output. Aluminum hydroxide, Al(OH)3, was also used to modify the surface –chemical property of the nickel slag fiber. In the same way, it also exhibited a positive response with the collection of colloidal amorphous silica from its bulk liquid, but yielding a lower recovery of 90%. This may be attributed to the lower surface potential and iso-electric point of pH 9.3 for Al(OH)3. The separation process was evaluated and analysed using existing potential energy theories. Figure 1 shows a micrograph of the surface of an unmodified and the Al(OH)3 –modified surface of nickel slag fiber."

Jan 1, 2003

By N. Nehoroshev, P. Solozhenkin, N. Voyloshnikova, A. Pshennikov

"Molecular modeling of clusters of major bismuth minerals, Bi2S3, was carried out whereby molecular models of minerals and reagents clusters were created. Their HOMO and LUMO energy levels were calculated and using known modelling equations, the absolute hardness ?, eV and electronegativity were calculated. The charges of separate atoms of clusters and the change of properties of the minerals were determined which allowed predictions of the flotation properties of raw ores containing rare bismuth minerals. Modeled complexes containing the clusters of minerals and various collectors were constructed, consisting of atoms and bonds within clusters of minerals. Major physical and chemical parameters were determined for the complexes created, including the total and electronic energy. Based on the energy calculations, predictions of the collector efficiency were proposed. The efficiency of collector was established for various thiolic reagents, the compounds of phosphorus (III) and mixtures of reagents. Theoretical results were checked and confirmed against laboratory ore flotation tests. A gold-bismuth-magnetite ore type was studied where gold, bismuth and iron (magnetite) are of industrial interest. The ore contains 2.8 g/t Au, 1.0 g/t Ag, 0.26% Bi, 45% Fe and 1.25% As. Sulphide mineralization can be mainly found in the form of pyrrhotite, pyrite and arsenopyrite. Bismuth can be mainly found in the form of bismuthite and native bismuth. Gold is fine. A flow sheet for Zhelezny Kryazh ore treatment was proposed. This flow sheet consists of grinding to 95-98% -74 µm, sulfide flotation with two cleaner with xanthate addition, cyanidation of flotation concentrate and flotation tailings included treatment with with CaO (6 kg, 6 hours), cyanidation (8 hours) and CIL (8+24 hours). Saleable products are gold doré, bismuth and iron concentrate."

Jan 1, 2014

By Luís Marcelo Tavares, Juliana Segura

Comminution is one of the most energy consuming stages in a mineral processing plant. This consumption is not only related to the power supplied to equipment, but also to the indirect or embodied energy, mainly associated to materials that are worn during operation, including grinding media and liners. Until recently, preparation of iron ores in Brazil did not use comminution intensively, given that plants mainly produced sinter feed, natural pellet fines, besides lump ore. However, with decreasing ore grades, size reduction now occupies a centre stage in nearly all new plants. Technologies used up to date for processing low-grade iron ores in Brazil, in particular itabirites, have consisted of three or four stages of crushing followed by ball milling. A number of new plants are either being built or are currently being designed that will process the same type of ore, so that engineers are investigating alternative comminution routes. The paper analyses comparatively four comminution routes for processing a particular itabirite ore, many of which using technologies and layouts that have not yet been used in such application. Using data from bench scale and/or pilot-plant tests, the different routes are compared on the basis of sustainability principles in accordance to the Brazilian energy matrix, which is quite particular. It is concluded that if the sustainability criterion is used, then the optimal route would correspond to a circuit that uses HPGR technology with truncated feed followed by ball milling. Given the particular case of itabirite iron ores and specially to the one in the present work and the source of Brazilian energy, it is evident that indirect energy expenditure in comminution plays a significant role in greenhouse gas emissions when compared to direct energy, being the reason for the great attractiveness of HPGR technology. Evidently that these will have to be balanced against CAPEX, OPEX, NPV and other qualitative criteria, which can certainly lead to a different optimal circuit.

Jan 1, 2014

By K. A. Natarajan

Involvement of various indigenous microorganisms in extracellular and intracellular iron oxide formation is a convincing index for iron ore biogenesis. Biomineralization of various iron oxides such as hematite, magnetite, goethite and limonite with the participation of aerobic and anaerobic microorganisms is well established. Various aerobic and anaerobic bacteria such as Gallionella, Leptothrix, Acidithiobacillus, Thermoplasmales, Pseudomonas, Bacillus spp and Shewanella putrefaciens, which are implicated in the formation of higher and lower oxides of iron have been isolated from different iron ore deposits. Diversity of microbial life in iron ore deposits can be put to beneficial use such as selective removal of undesirable constituents such as silica, alumina, clays, phosphorous and calcite and also to bring about environmental detoxification. Role of microorganisms such as Paenibacillus polymyxa, Bacillus subtilis, Yeasts and a sulfate reducing anaerobe in the biobeneficiation of hematite is illustrated. Surface chemical changes brought about by bacteria - iron ore mineral interactions are discussed with respect to hydrophobcity, adsorption isotherms, zeta potential data and bioreagents generation. Bacterial adaptation to minerals such as hematite, quartz, alumina, calcite, apatite and clays results in secretion of mineral ? specific biosurfactants such as proteins and polysaccharides. Such bioreagents can be used as selective collectors, dispersants and flocculants in iron ore beneficiation. Research results are highlighted to demonstrate silica, alumina, phosphate, calcite and clay removal from hematite. Environmental friendliness of such biobeneficiation processes is demonstrated with respect to biodegradation of toxic amine collectors, utility of ?in situ? organisms in enhancing settlement of fines in tailing dams and water harvesting. Keywords: bio-mineralization, bio-beneficiation, bio-remediation, Gallionella, Leptothrix

Sep 1, 2012

By V. K. Gupta

Selection of mill size for reducing a feed material of a given size to the desired product size is generally based on the specific energy estimate obtained from Bond test. Over the last thirty years or so, an attempt has been made to develop a more accurate and powerful alternative approach based on the characterization of the particle breakage kinetics and material transport through the mill over a range of operating conditions of interest and correlating the degree of size reduction achieved with the net specific energy input to the mill. Particle breakage kinetics are described in terms of the specific grinding rate and breakage distribution parameters for the individual size fractions. Precise estimates of these parameters and the net energy input to the test ball mill (a laboratory or pilot scale mill) are important for development of desired energy-size correlations. In this context, three tasks are important: (a) preparation of the feed charge, (b) design of batch grinding experiments and (c) computational technique used for estimation of the breakage rate and breakage distribution parameters. This paper highlights several aspects of these three tasks that have been overlooked by researchers working in this field, and describes a more appropriate approach for estimation of model parameters and specific energy input. Several examples are included based on the data available in the literature and those generated in our laboratories to illustrate important points.

Sep 1, 2012

By S. Mohanta

The air dense medium fluidized bed separator which has been developed for the dry beneficiation of coal is recognized as a low cost and high efficiency process. The success of this separator for beneficiating any specific coal, alone or in combination with other processing methods, mostly depends on the characteristics of run-of-mine coal. Therefore, a thorough knowledge of the mineralogical composition and washability characteristics of representative coal sample is highly essential for correctly and effectively assess the suitability of this process. Available literature conforms that although the characteristics of Indian non-coking coals are well known, the correlations between the particle compositions with its density are entirely lacking. In the present study the washability, proximate, ultimate and elemental analysis was conducted for four typical Indian high-ash non-coking coals and their elemental compositions were well correlated with the specific gravity of coal. The results obtained in this study provide some essential information to the coal-processing engineer for efficiently operate and control the process. Furthermore, the beneficiation potential of air dense medium fluidized bed was experimentally evaluated and compared with the results obtained from an operating wet beneficiation plant. Based on this comparative study the air dense medium fluidized bed is established to be a possible alternative to the conventional wet beneficiation method for beneficiating Indian coals with Ep values in the range of 0.03 to 0.06

Sep 1, 2012

The Indian steel industry is growing at a rapid pace and expected to be the 2nd largest steel producer in the world after China. To cope up with this growth and to sustain it, the industry needs to focus on effective utilization of domestic metallurgical coals. While the importance of indigenous coal has increased, its supply from the domestic sources is declining. This is primarily due to high ash content in Indian coals leading to its difficulty in washing to a low level competitive to imported coals. Non-availability of a suitable beneficiation technology to bring down the ash to such a low level is the other reason. Effective utilization of current technologies has enabled Tata Steel to bring down the ash to 13-16% from its captive collieries. However, further lowering the ash using the conventional beneficiation technologies is difficult and unsustainable. New technologies should be developed for bringing down the ash further. A thrust area research program has been undertaken at Tata Steel for producing clean coal with 8% ash maintaining the yield currently achieved in its washeries. The technologies attempted are based on chemical beneficiation of coal. In leaching process, suitable chemicals are used for extracting ash minerals from the coal. As an alternative process, the combustible part of the coal is being extracted using a suitable organic solvent through an organo-refining process. Both the processes have been successfully developed in the laboratory and are being demonstrated in pilot scales. Various beneficiation processes practiced at Tata Steel including the efforts made for developing new processes for achieving clean coal with 8% ash have been discussed in this paper. Keywords: metallurgical coals, washing, beneficiation technologies, chemical beneficiation, leaching, solvent, and organo-refining process

Sep 1, 2012