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By B. Csoke

In a first stage of our investigations material properties of fly ash (three acidic and one alkaline type originating from combustion of various age coal) obtained from four various dumps have been characterized. In a next step systematic mechanical activation experiments??grinding??and measurements have been performed with various ashes to establish relations between grinding fineness (specific surface area), specific work input demand of grinding and activity. In a third phase utilization of a mixture of mechanically activated fly ash and lime for producing an independent binding composition has been assessed involving determination of interrelationship(s) between the degree of activation of fly ash, the lime concentration and the resultant strength of the obtained concrete. Finally, pilot size experiments were conducted and a test road section was built to explore possibilities for the production of suitable binding composition from the mixture of fly ash and lime as well as the applicability such mixture for road construction. After summarizing major achievements of the first and second stages of the work (history) the present study deals with the research conducted in stages three and four. Experimental results support the conclusion that the obtained binding material is suitable for construction of road bedding.

Jan 1, 2014

By Z. G. Song

As a kind of complex physicochemical process, grinding would affect the subsequent mineral processing such as flotation considerably. In this study, the effect of wet grinding on malachite and calcite flotation using sodium oleate as collector was studied. And the mechanism of the effect of grinding was investigated. Laboratory scale grinding and flotation testing of malachite and calcite samples were performed. Different grinding media were used, including steel balls and zirconia balls. It was the aim of this work to study the effect of grinding on the pulp chemistry paying particular attention to flotation recovery. The effect of grinding media and different addition location of sodium oleate on malachite and calcite flotation was studied. The methodology used in this project involved grinding the ore with and without the addition of sodium oleate in mill, measuring the pH and metal ions produced by minerals after grinding, adding various quantities of sodium oleate and determining the copper recovery. The presence of species of products on the minerals after grinding was probed using X-ray photoelectron spectroscopy (XPS), and the metal ions produced by minerals after grinding were measured by atomic absorption spectrometry (AAS). It is showed that the mil-ling environments evaluated significantly affected the flotation of malachite and calcite. This study also discusses the effecting mechanism of grinding environment on floatability of malachite and calcite.

Jan 1, 2014

By Leonardo Soto, Fernando Villanueva

"Antofagasta Minerals S.A. (AMSA), for its Centinela District Project, is currently developing, at a first stage, a new 90 ktpd Concentrator Plant incorporating Esperanza Sur (ESP Sur) and Encuentro (ENC) ores. In order to dimension properly main equipment, specifically for grinding circuit, a final decision has been taken using geological and metallurgical (comminution) data from both body ores. Data was analyzed internally within AMSA and its consultants to get a final proposed circuit for further engineering studies. Specific Energy Consumption (SEC) parameter is one of the main key factors for proper dimensioning. To get an accurate value different tests have been made and modelled to ESP Sur and ENC ores. Also, operational data from Esperanza operation has been taken into account due to its similar ore characteristics to ESP Sur ore and incorporated as input data for design. Depending on data, quality and amount, it is possible to estimate accuracy for project investment and risk level, hence investment decision can be taken under good and reliable information."

Jan 1, 2014

By Eberhard Gock

The worldwide implementation of corrosion protection of low alloyed automotive metal sheets by zinc coating has led to supply shortages of zinc free non-alloyed steel scrap in the foundry industry. In a collaboration project, partly financed by the German government, with partners from the automotive industry, zinc metallurgy, scrap trading, foundry industry, and plant construction, a new acid-based pre-dezincification process has been developed, and a pilot plant with throughput of about 100 t/d has been put into operation at the Clausthal Umwelt-Institut GmbH (CUTEC) together with the Clausthal University of Technology in Germany. During the treatment process, acid from a zinc metallurgical plant will be supplied, which can be recycled to the primary zinc extraction process after raising the zinc concentration to more than 130 g/L zinc. This way, the separation of small amounts of iron by precipitation and the electrolytic zinc winning are outsourced and, as a result, the pre-dezincification process runs waste-free. In Germany, the amount of zinc coated ?new scrap? is approx. 3 million t per year with a zinc content of approximately 60,000 t per year. The possible additional incomes for the dezincified steel scrap are in the order of ?40 to ?50 per ton of scrap, the gained zinc content during the acid dezincification defrays the costs of the process, if the throughput is more than 700 t/d. In comparison to conventional dezincification during the electro arc furnace process followed by upgrading in a rotary kiln (Waelz process), the acid dezincification process running at a maximum of 50°C will cut the energy costs by up to 74% and the CO2 emission by up to 88%. In fact, a demonstration plant is being designed right now and will be installed for processing a part of the zinc coated metal scrap from the Volkswagen AG in Wolfsburg, Germany. Keywords: steel scrap, zinc-coated steel, dezincification methods, acid

Sep 1, 2012

By Zofia Swierczek

This paper reports the results of a detailed mineralogical study of typical, low-grade Australian nickel laterite run-of-mine ores. Successful development of an effective beneficiation process for upgrading such low grade laterite ores relies on good knowledge of the laterite mineralogy and the value metal(s)? distribution characteristics. Both QEMSCAN and quantitative X-ray diffraction techniques were used to conduct the mineralogical analysis of three types of laterite ores, and the results were compared with those obtained by chemical analysis. Some of the major challenges faced included accounting for the mismatch between the nickel values measured by QEMSCAN and those recorded by chemical analysis. This was primarily due to the relatively low concentration of nickel in the ores and its wide dissemination among several major host minerals in complex association. Careful analysis showed that the limit of nickel detection in iron oxide host mineral grains under normal operating conditions was around 4%. Keywords: nickel laterites, mineralogy, characterisation, QXRD, QEMSCAN

Sep 1, 2012

By B. K. Mohapatra

Small manganese ore bodies in south Odisha, India occurs both as stratiform and stratabound ore bodies. These two ore bodies show contrasting mineralogical, petrographical and chemical characteristics. Stratiform type of Mn-ores consists of manganese, iron and silicate- phases in approximately same proportion. In contrast, stratabound ore bodies contain a high proportion of manganese oxides, silicates and phosphorus phases. Phosphorus is found within apatite in the stratabound ore bodies while in the stratiform ore it occurs as an adsorbed state with iron phase (goethite). Both ore bodies are low-grade (17-23% Mn) therefore do not have a market value. However, the stratabound ores are enriched in phosphorus (P2O5: >1%) compared to the stratiform ores. Both the ore types were processed through gravity, magnetic and roast reduction followed by magnetic separation techniques. The strata bound ore could be upgraded to 33% Mn from a feed of 23% by combination of dry and wet magnetic separation methods. But the phosphorus content also suits up (P2O5: 1.2%) in the processed product making it unsuitable for further use. The stratiform ores do not respond to either gravity or magnetic separation because of close association of manganese with iron phases. However, this could be beneficiated through roast reduction followed by magnetic separation. An ore with 17% Mn content could be upgraded to 40% Mn with a 42% yield and 78% recovery. The goethite, having phosphorus, converts to magnetite and is retained within the magnetic fraction, thereby reducing the concentration of phosphorus in the non-magnetic fraction, which becomes the product. This report demonstrates the influence of ore petrology in determining the up-gradational potential of manganese ore in the southern Odisha, India. Keywords: manganese ore, physical beneficiation, phosphorus rich ore

Sep 1, 2012

By Andrzej Wieniewski, Cezary Regula, Bozena Skorupska, Krystian Cichy

"In this paper, experiences from Polish non-ferrous metals ores enrichment plants in the copper and blende concentrates quality improvement are discussed. The blende concentrate being produced in ZGH Boleslaw S.A., with Zn content of about 54,5% is characterized by the relatively high magnesium content reaching a level of 1% resulting from the dolomite presence, while for the zinc production by electrowinning a concentrate in which magnesium content should not exceed 0,3% is required. The implemented new technology for the quality improvement of blende concentrate is based on the leaching of zinc concentrate with sulfuric acid aimed at dissolving of the contained dolomite, and then flotation of the leached concentrate. It allows to obtain a concentrate with magnesium content below 0,1% at the simultaneously increased zinc content to about 57,5%. In the paper, laboratory tests results on the development of optimal flotation flowsheet for the gypsum removal and the industrial tests results concerning the process optimization of this flotation are discussed. In turn, the copper concentrate being produced in Polish copper ore enrichment plants KGHM PM S.A., is characterized by the increased organic carbon content - above 8%. It creates problems with the smelting of this concentrate because of difficulties with the heat removal derived from the combustion of organic carbon in the flash smelting process. The implementation of segregating flotation to the industrial practice allows the effective production of two concentrates with the differentiated chemical compositions - a concentrate with increased copper content and reduced organic carbon content for the flash smelting process, and a concentrate with lower copper content and increased organic carbon content for the shaft smelting process. In the paper, conditions of the segregating flotation and the achieved results are described."

Jan 1, 2014

By Venkataramana Runkana, Aditya Pareek, Vishnu Masampally, Nagaravi Kumar Varma Nadimpalli

"Recovery and grade of the ore produced are two important metrics, which define the profitability of a mineral processing plant. Achieving high grade and high recovery at the same time in a mineral processing plant is difficult due to conflicting nature of the two objectives. To explore the operability limits of the plant operations and find the set of operating conditions that can help achieve the best possible recovery and grade, there is a need to solve a multi-objective optimization (MOO) problem. Past research focused on building a plant-wide simulation model or on optimization of individual units or a part of a mineral processing plant like grinding circuit, crushing circuit, etc. However, it is necessary to consider optimization of the complete plant in order to optimize the plant performance. Here, we have formulated the mineral processing plant performance optimization as a MOO problem. We have applied machine-learning algorithms such as random forest to build models to predict the recovery and grade of the ore. A non-dominated sorting-based multi-objective evolutionary algorithm called NSGA-II (Non-dominated Sorting Genetic Algorithm II) was employed to solve the MOO problem. Since the number of parameters that influence recovery and grade are quite large, we have applied machine-learning algorithms for feature selection or identification of key process variables. Pareto optimal conditions were determined for manipulated variables like grinding mill throughput, speed ratio at SAG mill, speed of centrifugal pump, water addition at different locations etc. The results obtained are useful in identifying the operability of a mineral processing plant to achieve the optimum grade and recovery for a given feed grade and the processing circuit. INTRODUCTION Copper is majorly mined or extracted as copper sulfides from large open pit mines in porphyry copper deposits. Among all the available ores, sulfides are the most commercial ores, especially chalcopyrite (Greenwood and Alan, 1997). Copper grade in these ores generally lies between 0.4 to 1.0%. In order to perform smelting operation, the grade of copper has to be improved to around 30% (Biswas et al. 2013). This targeted copper grade is achieved through two stages of mineral processing. Firstly, the copper in the ore has to be liberated by crushing the mineral rock. Secondly, the liberated copper in the crushed ore is then physically separated from other minerals like nickel by froth flotation techniques."

Jan 1, 2018

By Herman Mendoza, Luisa Ciriaco

An investigation of the seeding mechanism using heterocoagulation and the Derjaguin - Landau - Verwey - Overbeek (DLVO) theory of two pure minerals is the objective of this study. The seed was silica with modal diameters of 4.529 µm (fine particles) and 5.216 µm (coarse particles) and the test powder was hematite with a modal diameter of 0.883 µm. Parameters included variations in the concentration and particle size of silica. Both particles were first subjected to size determination and settling tests via Stoke’s Law. The silica-hematite system was then suspended in 0.001 M KNO3 electrolyte solutions where pH was adjusted. Afterward, the suspension was agitated and was allowed to settle at different time intervals while obtaining turbidity readings. Results through settling time and turbidity vs. pH graphs indicate that maximum heterocoagulation occurs from pH 2 to 5 while minimum heterocoagulation occurs from pH 6 to 7. At these pH levels the zeta potentials of silica and hematite are negative and positive, respectively. On the contrary, repulsive forces dominate the system from pH 8 to 11 due to the particles’ negative zeta potentials. Furthermore, the attachment of hematite to silica increases when the parameters become larger thereby increasing the effectivity of heterocoagulation at acidic to neutral pH levels.

Jan 1, 2014

By Indrajit Paul, Atanu Pal, Kapil Modi, Sanjay Chandra, Chandra Sekhar, Srinivas Dwarapudi

"High alumina content in the Indian iron ore fines (2.5% Al2O3) resulted in poor quality pellets at the recently commissioned 6 MTPA pelletizing plant and a study was under taken to establish suitable pellet chemistry through proper fluxing agents. Limestone fluxed pellets were prepared at varying basicity (0 to 0.8) and pyroxenite fluxed pellets at varying MgO contents (0 to 3%) to study their effect on the metallurgical properties. Fired pellets were tested for their strength, RDI, reducibility and swelling. Microstructural studies, optical and SEM-EDS, were carried out to quantify different phases and their chemistry. Acid pellets exhibited poor quality whereas limestone pellets at 0.8 basicity and pyroxenite pellets at 1.5% MgO exhibited optimum metallurgical quality. Formation of widely distributed silicate melt in limestone pellets and high melting point slag & magnesioferrite in pyroxenite pellets found to improve their quality. However during commercial production of MgO bearing pyroxenite pellets, their room temperature and low temperature properties found to be inferior, but exhibited better high temperature properties, viz. softening-melting behavior. Contrary to this, commercially produced limestone pellets, comprising CaO, exhibited better strength and RDI but showed poor high temperature properties. To yield the benefits of both CaO (for good strength and RDI) and MgO (for low swelling and high softening), a dual flux combination was established by using both limestone and pyroxenite/olivine together that resulted in optimum metallurgical properties. Coke rate at the blast furnaces found to be reduced by 1kg for every1% increase of dual flux pellets in the burden.INTRODUCTION Iron ore agglomerate quality plays a vital role in decreasing the reducing agent consumption and increasing the productivity of blast furnace. In most of the integrated steel works, the burden mix for blast furnace is decided as per the availability of the iron ore agglomerates like sinter and pellets. More attention has been given in recent years to the use of fluxed pellets in blast furnace due to their good strength and improved reducibility, swelling and softening melting characteristics. Generally, quality of pellets is influenced by the nature of ore or concentrate, associated gangue, type and amount of fluxes added and their subsequent treatment to produce pellets. These factors in turn result in the variation of physicochemical properties of the coexisting phases and their distribution during pellet induration. Hence properties of the pellets are largely governed by the form and degree of bonding achieved between ore particles and the stability of these bonding phases during reduction of iron oxides (Panigraphy et al., 1990). It is important to note that conditions and parameters of pelletizing are specific to given ore or concentrate; the present study is undertaken for typical Indian hematite ore fines high in alumina. Except authors earlier work on quality of pellets from Indian iron ore (Dwarapudi et al., 2008, 2010), there is no considerable literature reported on the effect of pellet basicity and MgO content in the basicity range of 0 to 0.8 for Indian hematite ore."

Jan 1, 2018

By R. Marandi

The effective removal of heavy metals from aqueous wastes is among the most important issues for many industrialized countries, How ever biosorption, i.e. the uptake of heavy metals by non- living biomass, has gained increased credibility during recent years. Biosorption of Cr(VI) from aqueous solution, on pretreated and immobilized Aspergillus niger was investigated in a batch and countinuous reactors. A.niger biomass pretreated by boiling in 0.5 N NaOH solution for 15 min, exhibited higher Cr(VI) removal capacity than autoclaved biomass. The optimum adsorption pH value observed for Cr(VI) ions was 2. The Cr(VI)removal rate increased with a decrease in pH. The influence of contact time, pH, Cr(VI) concentration, biomass concentration and temperature on Cr(VI) removal were also evaluated. Biosorption of Cr(VI) on pretreated biomass followed the Freundlich and Langmuir adsorption models.In this study A.niger biomass was immobilized in Na-alginate matrix. The biomass beads packed in a column were able to remove metal ions.In this study we used two different flow rate in a column, 1.5 mL/min and 3 mL/min.The breakthrough data obtained for Cr(VI) was adequately by the Thomas and Yan models and the adsorption capacity of the biomass was found to less than the adsorption capacity obtaind in the batch study. When the beads containing biomass become saturated with metal ions, the adsorbed metals were eluted using 0.5 N NaOH solution. Therefor nearly 90% of Cr(VI) was desorbed by NaOH solution.

Jan 1, 2014

By S. H. Morar

Froth flotation is a physico-chemical separation process that takes place in two phases; pulp and froth phase. It is widely recognised as a complex process, due to the range of interactions present within the system. Of critical importance is the role of the froth phase within the system. The pulp kinetics governs the maximum potential recovery within a flotation cell, while the froth phase governs the selectivity via the froth?s stability. Higher froth stability improves recovery at the expense of grade, and lower froth stability improves selectivity. It is well known that the two major factors affecting froth stability are attached particles and solution chemistry. This paper looks at a flotation bank at different froth depth and frother concentrations. The air recovery to the concentrate is determined at each condition and relates the effect of the operating conditions on froth stability and transport to the amount of solids that are recovered to the froth and concentrate by true flotation. The results presented show that, for a given process objective, which in this case was a consistent mass pull profile, depending on the operating conditions, solids recovery in the pulp is affected by the air rate required to maintain the target mass pull. To a smaller extent, the changes in the pulp composition affect down-stream pulp recovery. The variation in solids recovered into the froth drives the froth stability at the start of the flotation bank, while the frother drives the froth stability at the end of the bank. The performance in between these two extreme conditions arises from an interaction of these two effects. The consequences of these interactions can give rise to counter-intuitive responses that can confound efforts to optimise the performance of the bank.

Jan 1, 2014

By J. Yianatos

The regrinding stage is necessary to achieve the particle size (liberation) for the final upgrade in the cleaning flotation process. At present, vertical mills (Vertimill) are employed at industrial scale, using small steel balls as grinding media. The regrinding process characterization requires mixing regime knowledge along with the mean residence time of the liquid and solid phases. The residence time distribution (RTD) and the actual mean residence time estimations from theoretical relationships are complex due to the presence of three components (solid mineral, balls and water), mass transport characteristics and segregation affecting solid holdup. Therefore, the experimental RTD determination is suitable for industrial mills. In this work, RTD measurements were performed in two different industrial flotation plants. Both plants operate with Vertimills of 1000-1500 HP in the regrinding process with different circuit arrangements according to the plant treatment capacity. The RTD was measured using the radioactive tracer technique. This technique allows for non-invasive tracer detection where the procedure consists of selecting a liquid (Br82 in aqueous solution) or solid (irradiated solid) tracer for RTD data acquisition in real time. The RTD was modelled by the Large and Small Tanks in Series (LSTS) model, which allowed the characterization of the different mixing regimes for both liquid and solids in the regrinding mills. Effective mean residence times in the range 2-11 min were obtained with RTD shapes similar to those obtained in tumbling ball mills. It was found that residence times of liquid and fine particles were similar, which is consistent with results observed in other mixing systems, e.g. mechanical flotation cells. Also, the mean residence times estimated from the RTD allowed the mass balance adjustment to be validated from metallurgical sampling data. RTD estimations are useful for better understanding the Vertimill behaviour and to identify the actual breakage rates. Keywords: vertical mill, residence time distribution, particle size, modeling

Sep 1, 2012

By S. J. Neethling

"This paper examines the impact of several key variables on the performance of flotation cells. The study makes use of a simulator for the froth phase of the flotation vessel, as the main purpose of this study is to separate the impact of different variables from one another. In experiments it is very difficult to separate the effect of variables from one another as a change in a singe input parameter, such as air rate, invariably also affects many of the other key variables, such as bubble size and bubble bursting rates.In order to achieve this a base case simulation that is typical of many of the rougher cells found in sulphide flotation circuits was carried out. Four key variables, air rate, incoming bubble size, surface bubble size and the fraction of the bubbles flowing out of the cell unburst, were varied in order to obtain the system.s response.The most significant results were obtained when the bubble size was varied. An increase in the incoming bubble size has the effect of reducing the pulp zone recovery, but increases the froth zone recovery. If it were possible to vary the incoming bubble size without influencing the overflowing bubble size, the impact of the change would be unclear because of these two competing effects. The effect of a change in the overflowing bubble size has an opposite effect on the froth recovery, with larger bubbles resulting in lower froth recoveries.A final interesting result is that all the effects examined affect the process to a similar degree, which implies that none of these variables can be disregarded, either in industry or in further research."

Jan 1, 2003

By F. K. Ikumapayi

An approach to environmental sustainability and improved process economy, in sulphide minerals production is recycling of process water in flotation of complex sulphide ores, although the chemistry of process water may be a critical issue to flotation efficiency. The influence of major components of calcium and sulphate ions in process water on xanthate collector adsorption and flotation response using pure chalcopyrite, galena and sphalerite minerals were investigated by Hallimond flotation, zeta-potential measurement, FTIR and XPS spectroscopy studies, while bench scale flotation tests were also carried out using complex sulphide ores. The impact of the species in flotation was comprehended using deionised water, tap water, process water and simulated water containing equivalent amount of calcium and sulphate species in process water. Hallimond flotation results showed a decrease of chalcopyrite and galena recovery in process water and also in the presence of calcium and sulphate ions in both deionised and process waters, whereas sphalerite does not respond to flotation. The adsorption of calcium and metal ions but not sulphate ions on the minerals is evidenced by zeta-potential data. FTIR and XPS studies revealed the presence of surface oxidized sulfoxy species and surface calcium carbonates on chalcopyrite in the presence of process water and water containing calcium ions, surface oxidized sulfoxy and carbonate species on galena in the presence of deionised water, process water and water containing calcium and sulphate ions, all at flotation pH 10.5, and these surface species influenced xanthate adsorption. The presence of surface oxidized sulfoxy and carbonate species at the sphalerite flotation pH 11.5 were seen in the presence of deionised water, process water and water containing calcium and sulphate ions, but the surface species does not influence xanthate adsorption. Bench scale flotation using two different complex sulphide ores showed that chalcopyrite, galena and sphalerite recoveries are better in process water than tap water. The studies showed that the process water can be recycled in flotation with no detrimental effect on grade and recovery of sulphide minerals. Keywords: sulphide minerals, flotation, zeta-potential, FTIR, XPS

Sep 1, 2012

By Reza M. Rahman

The froth phase plays an important role in the flotation and upgrading of the final concentrate. At present, the techniques that have been used in the mineral industry to measure the froth recovery have limitations. The aim of this paper is to investigate the performance of the froth in an industrial flotation cell. A unique device has been developed which is capable of decoupling the froth zone from the pulp zone. It consists of two concentric tubes. The inner tube acts as a dropback collection chamber or catcher. The particles that detach from the froth phase fall directly into the catcher and are collected as froth dropback. The froth recovery measurements were carried out in a rougher bank of a copper concentrator treating sulphide minerals. The dropback device is designed so that it can be immersed into a plant size flotation cell and plant froth recovery measurements can be taken at any given time. During the experiments, the bubbles laden with valuable mineral particles entered the device from the plant flotation cell, subsequently rising to form a froth layer at the top of the device. The particles that detached from the froth zone were collected in the dropback collection chamber whereas the concentrate sample was collected by a launder. By drying, sizing and chemical analysis of the concentrate and dropback samples, the froth recovery, was estimated on the basis of the valuable component. The effect of air rate on froth recovery was also investigated. Keywords: flotation, froth, dropback, froth recovery

Sep 1, 2012

By C. A. Perez

Estimation of rock composition in mineral plants is important to determine rock size and grindability which in turn may improve control of the grinding process. Variations in ore grindability and size distribution directly affects mills power consumption and throughput. Therefore, it is desirable to develop new tools to estimate rock lithological composition. In this paper, a new method for lithological classification based on machine vision is proposed. The method is based on a single video camera and employs information about texture using several different spatial scales. Texture information is extracted from rock images using Gabor filters that can be adjusted at different spatial scales and orientations. After feature extraction, rock images are classified using support-vector machine (SVM). The method was tested on a database containing sub-images of 64x43 pixels of five ore types as follows: massive sulphide (MS), disseminated sulphide (DS), net textured (NT), gabbro (G), and peridotite (P). These ore types were assigned to three grindability classes: soft (MS), medium (DS and NT) and hard (G and P). The database was divided in 2 subsets for training, cross validation, and for test. Classification accuracy is compared with previously published results on a dataset with three different classes of rocks according to their hardness. Results show that our proposed method reached significant improvements (between 13%-20%) in classification accuracy relative to previously published results. Keywords: rock classification, lithological classification, grindability estimation, Gabor feature extraction, texture features

Sep 1, 2012

By Bruce Mathema, Steven Huynh, Terry Cheng, Gerry Gomez

"The use of PM40N, a specialty precious metals promoter in conjunction with a standard Xanthate based collector was extensively investigated in the flotation of a complex, silver-bearing, lead-zinc ore containing naturally occurring graphitic gangue. The ore, considered difficult to treat with conventional reagents, was tested at plant scale to determine the impact of the promoter on silver recovery, lead grade and also on the amount of zinc misplaced to the final lead concentrate.Initial laboratory-scale rougher flotation testing implied significant improvements in the recovery of silver and lead with a marginal amount of zinc displaced. Subsequent mini pilot flotation tests further revealed that a gain in selectivity and recovery could be achieved by adjusting PM40N promoter dosage and incorporating a cleaner flotation step, further improving rejection of sphalerite. Plant trials resulted in an improvement of 3% in Silver recovery coupled with a 2% increase in recovered lead whilst maintaining lead grade in the lead circuit.To date, the use of PM40N as a promoter has enabled the processing operation to significantly increase its plant economics. The partial replacement of the standard Xanthate based collector has also reduced the overall quantity of Xanthate required in the standard circuit by approximately 10% - which is a positive impact on the environment. It is envisaged that further optimization of plant parameters will favor stable operation and continue to boost revenues generated by subsequent improvements in silver metallurgy."

Jan 1, 2014

By Cristiane Ericksson, Ananda Scomazzon, Irineu Schadach, Juliano Tonezer

The state of Rio Grande do Sul, southern Brazil, appears on the national and international scene as an important producer of precious stones and the main gems are amethyst, citrine and agate. However, despite the immense potential of this mining activity, the extraction and processing of gemstones in Brazil present critical issues of infrastructure, which prevents a better development of these activities. In general, local production is still concentrated in small rudimentary mining. Recently some of these mines have begun to regularize their activities, in conjunction with the National Department of Mining Control. Besides these problems best practices for extraction activities and environmental control are not usually observed. Another problem which is placed in a critical way is the absence of aggregate value for the products of small mines. In this situation, the miners have great problems to obtain access to technology and adequate infrastructure. In most cases miners need negotiate their gems without processing, transferring most of the profit to intermediate traders. These results in heavy losses for the producer and for the communities involved. Given this scenario, the present study aimed at defining systems technically and operationally viable to be implemented in these communities in order to add value to gemstones. In this study best practices to thermochemical coloring systems, analysis of effect of raw materials and operating parameters on the final color of the gem were analyzed with attention.

Jan 1, 2014

By Ljudmil S. Grigorov, Eric Forssberg, Hanumantha Rao Kota, Robert J. Pugh, Lidia B. Alexandrova

"The effects of mixed collectors on some physicochemical parameters (thin film lifetime, kinetics of expansion of the three-phase contact, equilibrium three-phase contact angle and surface tension) involved in the elementary act of flotation were investigated experimentally.We have used the microscopic thin balance developed by Scheludko et al (1970) to study the stability and interactions within the thin film between the silica surface and air bubble with (i) a long chain C10 amine and (ii) a cationic/anionic surfactant systems consisting of mixtures of a long straight C10 chain amine with long straight chain C8, C10 and C12 sulfonates at 1:1 molar ratio. The experiments were performed at a range of concentrations at pH 6.5. The equilibrium contact angle was measured with a microscope technique using the modified Mingins-Sheludko method (Mingins and Scheludko, 1979). The surface tension was measured by the method of Wilhelmy (Adamson, 1960). It was found that the mixed surfactants caused lower contact angles, lower rates of the thin film rupture and longer film lifetime, compared to the pure amine system."

Jan 1, 2003