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By Q. Cui, Z. G. Song, S. S. Lin, S. Q. Li, S. S. Lu, G. B. Zheng, A. J. Ren

"Mine tailings is one of the most important bulk industrial solid wastes, but its rate of comprehensive utilization is relatively low. Efficient separation, recovery and utilization of the valuable components is one focus of the comprehensive utilization of tailings. Beneficiation recovery of the valuable minerals is the most direct comprehensive utilization method for tailings. There are generally different kinds of nonmetallic minerals contained in the nonferrous metal mine tailings, which are secondary mineral resources waiting for further developing and recovery. Comprehensive utilization test studies on fluorite in tungsten beneficiation tailings and feldspar in molybdenum beneficiation tailings have been carried out by author and good test results are achieved. Some of the technologies developed in the test study have been applied in industrial productions, which have been working well. The economic, social and environmental benefits are remarkable. Our test studies and some production practices will be summarized and current situation and existing problems of comprehensive utilization for nonferrous metal mine tailings will also be discussed. Assumption and prospect for the future study on comprehensive utilization of nonferrous metal mine tailings will be brought at last.INTRODUCTION Mine tailings is one of the most important bulk industrial solid wastes, but its rate of comprehensive utilization is relatively low. Efficient separation, recovery and utilization of the valuable components is one focus of the comprehensive utilization of tailings. Beneficiation recovery of the valuable minerals is the most direct comprehensive utilization method for tailings. There are generally different kinds of nonmetallic minerals contained in the nonferrous metal mine tailings, which are secondary mineral resources waiting for further developing and recovery. Comprehensive utilization of nonmetallic minerals of nonferrous metal mine tailings not only can improve the value of the ore but also reduce the stock of tailings, being the key to reduce emissions at source for exploitation of nonferrous mineral resources (Cai, Yang, 2000)."

Jan 1, 2018

By B. Peszko

There are many measuring methods of grain sizes. Taking into consideration the fine grained materials, one of the existing techniques is measurement of grain size by the Coulter Counter method. This method is based on the measuring the changes of electrolyte resistance during grains flow through the calibrated diaphragm. This method is relatively simple to apply, significantly precise and the results are given quickly. However, the problem is that the measurements are limited by the size of diaphragm. Because of this situation, measurement of grain sizes by this instrument is possible in range from 10% to 60% of diaphragm diameter. This limitation causes the necessity of re-placing diaphragm in case when the measured grain size distribution concerns the material of large size range. In purpose of determining the total grain size distribution, the synthesis of some partial distributions, given for individual grain fractions (with different diaphragm applied), is required. This is possible to do by calculating the mixture of distribution functions, created from the partial distribution functions. Two materials were selected to research: quartzite and glass, which were comminuted in cylindrical crusher, additionally grinded, screened and then analyzed by Coulter Counter for five grain fractions: 0~125 µm, 0~80 µm, 0~56 µm, 0~40 µm and 0~25 µm. For each fraction, five different partial distributions were given (in case of glass ? four), which are the basis for the creating the joined grain composition. To assure the adequacy of the given distribution function, it is necessary to obtain the possibly best approximation of partial distributions. In the work, both the parametric and non-parametric methods of density approximations of investigated random variable. For each grain fraction the approximations were done by three traditional distribution functions: RRB, GSA and log-norm distribution functions and three methods of non-parametric approximation: Gauss kernel, Epanechnikov kernel and orthogonal Fourier series method. As the criterion of the certain distribution function acceptance, the value of the residual deviation was assumed, given by the formulae:

Jan 1, 2014

By T. Sun, J. Kou, C. Sun, D. Gong

"HPGRs (high pressure grinding rollers) have demonstrated higher energy efficiency than conventional comminution equipment due to their application of particle-bed breakage mechanism. In the past decades, a large number of studies have been conducted to understand the characteristics of particle-bed breakage, however, few of them concerned the difference between single-particle and particle-bed breakage in compression comminution. This comparison is able to demonstrate possible advantages of particle-bed against single-particle in a breakage event due to the isolation of the effect of force loading mechanism. The present study investigated progeny fragment size and energy efficiency of these two breakage methods at variable energy inputs and particle sizes. The results show that at low energy inputs of around 0.25 kWh/t, the numbers of fines resulting from the two breakage methods are very similar. However, at higher energy inputs of around 1.0 or 2.0 kWh/t, particle-bed breakage generated significantly more fines. From the perspective of newly generated surface energy, particle-bed breakage is obviously more energy efficient than single-particle breakage at energy inputs between 1.0 and 2.0 kWh/t. It was also found that HPGRs demonstrate high energy utilization rate in generating new surface energy within their typical range of specific energy input. INTRODUCTION Rock comminution is an important and energy-intensive process in mining operations. Nowadays, decreasing head grade and mineral liberation size of ore deposits greatly increase the energy cost of comminution process. HPGRs have been successfully applied in the mining industry to improve the energy performance of comminution circuits. Typically, 10 to 30% of energy saving can be achieved due to the application of HPGR (Wang et al., 2013; Casteel, 2005; Günter et al., 1996)."

Jan 1, 2018

By A. Pirson, J. Souza, A. Araujo, M. Barbosa, F. Guimarães, J. Lima

"Although a large number of processes have been developed and applied to the separation of barite from other minerals, there is a lack of information in the literature about the separation of barite from iron ores. Nowadays, there are millions of tonnes of iron ore disposed as a waste or tailings given its high content of sulphur in the form of barite. In order to effectively separate barite from iron ore and ensure that mining business is truly creating economic and sustainable values, this paper provides a greater understanding of barite properties, the origin and occurrence of this barium-bearing mineral, and the employed beneficiation processes. A test work is conducted in a barite bearing iron ore from a deposit located in the Republika Srpska (Bosnia and Herzegovina) in order to separate the barite and check if a marketable by-product can be produced by drawing upon rich barite tailings. INTRODUCTION The exploration of iron ore containing barite results in a large amount of unrecovered material. The main difficulty in processing and using barite bearing iron ores is given by their high content of sulphur, silica and barium, which are unwanted chemical compounds in the subsequent processes in iron industry. As a result, millions of tonnes of iron ore are discarded every year into tailings or as a waste, which results in production losses, higher operation costs and environmental impacts (Praes et al. 2013). Therefore, the separation of barite from iron ores not only means reducing the environmental impact, but also an opportunity to generate income and beneficiate society. The beneficiation of barite bearing iron ores is a subject which requires a deeper investigation to solve the challenges faced by the iron industry. There are only a few studies that describe flowsheets proposed for the production of barite concentrate of iron ores. The most likely reason for this gap is that barite is frequently exploited commercially as a primary product rather than a by-product. In order to effectively separate barite from iron ore and ensure that mining business is truly creating economic and sustainable values, this paper provides a greater understanding of barite properties, the origin and occurrence of this barium-bearing mineral, and the employed beneficiation processes. A test work is conducted in a barite bearing iron ore from a deposit located in the Republika Srpska (Bosnia and Herzegovina) in order to separate the barite and verify if a marketable by-product can be produced by drawing upon rich barite tailings."

Jan 1, 2018

By B. Orberger

The fine fraction (< 2 mm) of the high grade Mn-ore from the world class Moanda deposit, Francevillan basin, in Gabon, contains up to 30 wt. % of manganese and about 0.4 wt. % phosphorous. A pilot study at laboratory scale integrating mineralogy and geochemistry before and after ultrasonic treatment was conducted on the fine fraction (< 2 mm) of oxidized Mn ore in order to reduce the phosphorous content and enrich this fraction in manganese. The fine fraction was dried, crushed at 2 cm and sieved at 2 mm. The two fractions (< 2 mm and 2 mm ? 2 cm) were investigated by X-ray diffraction and scanning electron microprobe ? electron dispersive spectroscopy analyses. Both fractions contain lithiophorite, cryptomelane and pyrolusite as Mn carrier, and goethite, muscovite, illite and quartz as contaminants. The Mn hydroxide nsutite was only found in the fraction 2mm ? 2 cm.The < 2 mm fraction is significantly richer in goethite, muscovite/illite, and quartz. Phosphorous carriers are mainly goethite (up to 2.8 wt. % P2O5), while the Mn minerals contain up to 0.8 wt. % P2O5. The Mn minerals are partly included in an agglomerate of goethite, muscovite/illite, and quartz. The < 2 mm fraction was treated by ultrasound for 30 s in normal water. Mineralogical and chemical analyses after ultrasound treatment showed that the Mn-minerals were largely liberated from the goethite-muscovite-illite agglomerate. Mass balance calculations show that after ultrasonic treatment the < 2 mm fraction was ? 50 % enriched in Mn and ?50 % impoverished in P.

Sep 1, 2012

By G. G. Xiong

Water-sealed cyclone is a new efficient equipment to use for grading,concentrating of slurry, it was researched and developed by the Kunming Metallurgy Research Institute in the 1980s , and ac-cessed to the 1990 national invention award and the national patent products (ZL02245313.X ). The equipment and technology are innovative, firstly, we design a set of micro-pressure (0.005~0.008MPa) water-sealed device, which eliminates the gas phase of three-phase of sol-id-liquid-gas of the traditional general hydrocyclone grading process, it only has solid and liquid phases. Secondly, the axial velocity envelope surface which is a factor of controlling the accuracy of grading changes to a wedge rotation; and the interface of upward flow to down flow changes from surface to the solid, it can improve grading accuracy. Thirdly, water-sealed box and catheter devices make the stilling which pass through the cyclone cone centrifugal force fields re-enter the pressure grading zone of catheter. The three innovations make water-sealed cyclone can reduce the loss of overflow and has less mud in stilling product. Because the excellent performance, the water-sealed cyclone has application in non-ferrous metals, ferrous metals, non-metallic and aluminum hydroxide industries for grading, desliming and concentrating since it has successfully developed.

Jan 1, 2014

By T. Badrujaman

In September 2005, after 30 years experiencing in operating an ESF using a falling water film shell cooling system, Antam entered the new era in operating an ESF, after completely modernized its ESF No. 2 from a falling water film shell cooling system to a copper cooling system. Further, in the beginning of 2007, Ferronickel plant No. 3, where its ESF also uses copper coolers, was successfully commissioned. By operating an ESF using a copper cooling technology, Antam has to face some challenges to establish the operation stability. Besides that, the chances to maximize the furnace efficiency are greatly opened. The shielded-arc mode of electrode tip is selected to operate an ESF under relatively high furnace power to produce metal having tap temperature below 1500? and slag having tap temperature below 1600?. It leads to electric current unbalance. Further, operating an ESF using a copper cooler system under high voltage as consequence of the furnace power raise increases metal and slag tap temperature. This condition damages furnace integrity fast. Besides that, relatively high metal temperature increases its pressure during metal tapping. It leads to failure in closing the metal tap hole. The main different ways in operating an ESF using a falling water film shell cooling system and a copper cooling system lie in the electrode tip mode, the water specification used for cooler, metal tap block maintenance and allowed metal & slag level in furnace. Since a copper cooler system allows an ESF to be operated by consuming nickel ore having ratio Fe / Ni up to eight and producing slag having relatively high Fe content in slag, an undesirable silicon reversion phenomenon becomes an obstacle in reaching the operation stability. A copper cooler technology lets Antam to take a chance to increase its capacity. Modernizing the ESF No.2 had increased its furnace power from 17 MWh to 25 MWh. Meanwhile the ESF No. 3 can be operated up to 42 MWh. This technology allows an ESF to be operated under relatively high furnace power above 25 MWh safely as well as prolong the campaign life of ESF brick. Further, lowering ESF power consumption, extending the limitation of ratio S/M in nickel ore consumed and adjusting Ni grade in ferronickel product can be gained by applying this technology.

Jan 1, 2014

By Nidhi Kumari

This work is based on surface chemical properties of bacteria during adaptation to high grade copper minerals and the projected consequences in Bio-Flotation process. The utility of bio-processing in the beneficiation of copper ore through bio-flotation is demonstrated. An autotroph Acidithiobacillus Ferrooxidans bacterium is adapted to high grade mixed copper ore sample by repeated subcultures. The surface characteristics were studies by analyses at different pH and time intervals. From the studies, it was established that the mineral-adapted cells became more hydrophobic as compared to unadapted cells during bio-flotation. It was also noticed that there was no significant changes in the surface charge of bacteria before and after adaptation. Keywords: bio-flotation, copper, Acidithiobacillus ferrooxidans, hydrophobic

Sep 1, 2012

By A. V. Yevdokimov, Ye. V. Bogorodsky

The paper presents the results of the research on the development of gravity concentrates processing technology (gold grade is from 50 g/t to 1 kg/t and over) using intensive cyanidation with gold recovery to pregnant solutions followed by precipitation of metals from them using various methods. Test work and pilot plant results confirm that a new developed hydrodynamic regime provides an efficient treatment of gravity concentrates of polydisperse composition without their grinding and preliminary desliming. The resulting pregnant and washing solutions are amenable to metals recovery using electrowinning, cementation onto zinc dust and CIS. Cone plants with a lower ball valve for cyanidation of unground gravity concentrates developed by IRGIREDMET JSC have been successfully tested at a number of Russian operations. Currently, a modular plant equipped with gold electric precipitation from pregnant solution unit is successfully operated at a Russian gold processing plant. Cyanidation of the resulting high-grade gravity concentrate is carried out at the concentration of 8-10 g/L NaCN and 10 g/L NaOH. Gold recovery to the solution is 97-98%. Electrowinning is carried out in flow cell GNC-40M. In this case, the residual gold concentration yield is 0.3-0.5 mg/L. Also, a modular plant for relatively low-grade middlings (50-100 g/t Au) of gravity concentration has been introduced. The concentration of NaCN and NaOH is 2-3 g/L and 1.5-2 g/L, respectively, during leaching. This plant is equipped with a unit for gold cementation from pregnant solution with zinc dust. This cementation unit is of original design. It is made in the form of a filtering device and is composed of several layers of carbon fiber which contacts with zinc powder. The residual gold concentration yield from a cementation unit is less than 0.1 mg/L. Gold recovery is 93-97%. In 2017-2018, the introduction of intensive cyanidation modular plants to gravity concentrates will be planned at new projects of Russia and the CIS.

Jan 1, 2018

By A. Shandilya

ACC ECOSAND is finely powdered crystalline silica, which can replace natural sand usage in concrete and plasters. ACC ECOSAND ensures a comparatively denser concrete than those made only with natural sand and / or quarry fines / Manufactured Sand (Artificial Sand). Moreover, there is a significant gain in compressive strength (10-15 %) & durability in concretes (Reduced chloride conductivity leads to increased durability). ECOSAND is a by-product of froth flotation of limestone. At ACC Madukkarai cement works, Coimbatore, Tamilnadu, full-fledged mineral beneficiation process is adopted to enhance the usage of flotation reject in concrete and plasters. Optimum level for usage of ECO-SAND is 50%. With 50% usage of natural sand+50% ECO-SAND in concrete mix, 1 day, 3 day, 7 day & 28 day compressive strength is increased by 30.1 %, 22.6 %, 15.1 % & 11.0 % respectively and with moderate chloride permeability as compare to 100% Natural Sand. Keywords: froth flotation process, beneficiation studies, Denver cell, ECOSAND, siliceous material, durability & compressive strength, RCPT

Sep 1, 2012

By Chuanyao Sun, Zhenguo Song, Aijun Ren

"Lead-Zinc sulfide ore containing carbon is one of typical refractory resource. Because organic carbon has natural floatability, it has a great negative influence on flotation of lead-zinc sulfide ores. It is difficult to obtain qualified lead concentrate by flotation using conventional reagent system. In order to reduce the influence of organic carbon on lead and zinc flotation, two alternatives, i.e., removal carbon by pre-flotation or adding carbon depressant in lead and zinc flotation, can be adopted. If the flowsheet of removal carbon by pre-flotation is adopted, the lead and zinc recovery which are lost in the carbon tailings is often higher. If conventional carbon depressants are used in lead and zinc flotation, it has a certain depression effect on lead minerals. In the paper, the ore grading 1.49% Pb, 5.73% Zn, and organic carbon 3.14% has been carried out by flotation tests. In the bulk flotation of carbon and lead minerals, Pb concentrate is only about grading 21.00% Pb. In the pre-flotation of organic carbon, it’s hard to remove most of carbon, and the loss of Pb and Zinc recovery is too much in carbon tailings. New carbon depressant BK547 and three conventional carbon depressants including sodium lignosulphonate, Fe-Cr-lignosulfonate, and dextrin, are used in comparative tests of Pb flotation, and results show that BK547 have a good depression on organic carbon, and have almost no effect on Pb flotation. Using BK547 as carbon depressant, cycle test in flowsheet of two-stage Pb and Zn selective flotation and coarse concentrate regrinding have been carried out, and results show that concentrates grading 62.51% Pb and 41.33% Zn are obtained at recoveries of 70.24% Zn and 83.58% Zn.INTRODUCTION Lead and zinc mineral resources are still the main source of lead and zinc metal. For lead-zinc sulphide ore, lead concentrate and zinc concentrate are obtained by flotation. Minerals separation by flotation is a complex process and is dependent, along with other factors, on the relative distribution of hydrophobic (e.g. collector, polysulfide, elemental sulfide) and hydrophilic (e.g. metal hydroxide) species between different particles of the same mineral phase and between mineral phases (Piantadosi & Smart, 2002; Boulton, Fornasiero & Ralston, 2003). Organic carbon has natural floatability and is often associated with lead-zinc sulphide ores. If the content of organic carbon in the ore is more, the flotation index will become worse. The main problem is that the concentrates has too low grade to be qualified grade products for sale. At the same time, the consumption of reagents is more than ordinary ores without organic carbon. In order to solve the influence of organic carbon on the flotation of lead and zinc and other sulphide ores, a lot of research works have been carried out."

Jan 1, 2018

By Y. S. Song

Flotation separation of galena, sphalerite with pyrrhotite in ethanoic acid + sodium acetate sys-tem was studied in this paper. The flotation tests show that galena and sphalerite can float but pyr-rhotite can hardly float in the pH range of 3.6 to 5.6 in ethanoic acid + sodium acetate system. The flotation tests also show that galena can be separated efficiently from pyrrhotite and sphalerite can be separated on the whole from pyrrhotite, but the separation efficiency of the former is much better than the latter. The flotation results have been investigated by ultraviolet spectrum and XPS analysis, and explained by theory of hard and soft acid and base (HSAB), hydrogen bond and galvanic coupling.

Jan 1, 2014

By L. X. Zeng

The low-grade nickel resource is very abundant in the western China. To make the best of the low grade nickel ore, we studied the process mineralogy and beneficiation process of nickel ore in the Yangliuping of Sichuan province. The grade of nickel is 0.45% in the nickel ore and the nickel exists in the sulfide including pyrrhotite, nickel pyrite, chalcopyrite primarily. The nickel distributes in pentlandite and magnetite over 90% and the copper does in the chalcopyrite over 95%. The carri-er minerals of useful elements tend to concentrate in space for concentration. As is shown in grain-size analysis of three major minerals, there are some more fine-grained grains with the percent of from 10% to 15% (<40 µm) and from 3.5% to 5.5% (<20 µm). So there will be some smaller size disseminated sulfide minerals difficulty to liberate in the process of concentration. The liberation degree of sulfide is not high and there are much associativity in the sulfides. Therefore, we should reclaim the sulfide aggregation dominating as pentlandite when concentrating. In addition, the sulphide minerals is so brittle that we should take care of preventing from crashing when grinding. The gangue mineral is mostly metamorphic mineral including serpentine, chlorite and amphibole which is easy to be argillization and difficult to concentrate.

Jan 1, 2014

By Jens Markowski

The EU Directive 2000/53/EC on end-of life vehicles (ELVs) states that in 2015 at least 85 wt.-% of a vehicle has to be reused or recycled. This result in the obligatory need to separate additionally metallic and other components of the automotive shredder residues (ASR), so that they can be professionally prepared for recycling and reuse further. Currently the iron-containing fines of ASR are deposited as it is not possible to process in blast furnaces due to its particle size (< 4 mm), composition and material properties. Additionally problems are also caused in handling and transportation (dust) of the material. This work focuses mainly on the ASR materials utilization in blast furnaces. Material was further separated into two consecutive fractions by carrying out repeated crushing and magnetic separation twice. The two fractions have significantly higher iron content (up to 75 wt.-%) compared to the initial material mixture. The materials were assessed for their usage in blast furnaces based on the possible pelletisation with and without binders, stability of pellets, shape and size of pellets, etc. Pelletisation of the material was carried out with a single mould pellet press. Further lignite coal was added to the mixture as additive which improved the pelletisation behavior and the mechanical stability of pellets. Lignite coal was chosen as a reducing agent in the blast furnace process contributing towards additional savings in energy supplied. The experiments reveal that the production of pellets from iron-containing fines is possible with a lignite coal admixture of about 15 wt.-%. These pellets displayed good mechanical stability and can be used in blast furnace processes in recovery of the recyclable metals which are currently not recycled. The recycling of not yet recyclable metals would reduce the deposition and can be easily adopted into the economic cycle by their utilization. Keywords: Automotive shredder residue (ASR), FE-fines, pelletisation

Sep 1, 2012

By M. Brozek

The constant of flotation velocity is the value characterizing the kinetics of cyclic flotation. In the statistical theory of flotation its value is the function of probabilities of collision, adhesion and tearing off the grain from the air bubble. The grain ? air bubble collision plays a key role since there must be a prior collision before the grain ? air bubble adhesion happens. The probability of such an event to occur is proportional to the relation of the grain diameter to the bubble diameter. When the grain sizes are given, it is possible to control the value of collision probability by means of the size of air bubbles. Consequently, it is significant to find the effect of physical and physicochemical factors upon the diameter of air bubbles in the form of a mathematical dependence. In the pneumo-mechanical flotation machine the air bubbles are generated by the blades of the rotor. The dispergation rate is affected by, among others, the rotor rotational speed, the amount of air transported to the flotation chamber an time and the liquid surface tension, depending on the type and number of applied flotation reagents. In the proposed paper the authors will present the distribution of air bubble diameters on the grounds of the above factors, according to the laws of thermodynamics. The correctness of the de-rived dependences will be verified empirically.

Jan 1, 2014

By Nirmal S. Weerasekara, Malcolm S. Powell, Mohsen Yahyaei

"An understanding of the fundamentals of different breakage mechanisms is critical for successfully modelling comminution processes. Due to the high frequency of low energy collisions in the grinding process, superficial breakage has a significant role in size reduction in mills. To develop a scaling up methodology for characterising low energy surface damage behaviour of ores, a series of surface damage tests have been conducted using three grinding mill sizes with diameters of 1.8, 1.2, and 0.8 m. Two types of gold-copper ore with different hardness were used: C-ore and T-ore. All tests were conducted using wet mode to remove the products during grinding. To ensure low energy surface damage was the dominant mechanism, in all tests the mill speed was reduced to 40% of critical speed. A surface damage index normalised with product mass and surface based specific energy is determined from the results enabling a study of the grinding performance regardless of mill size, energy level or charge mass. Incremental breakage tests using the JKRBT indicate that the A×b values of the T-ore were 60% higher than C-ore, suggesting the T-ore is considerably softer. The fractional mass loss rate for the T-ore in the 0.8 m and 1.8 m mills started from 16 and 7 (1/kWh/m2) while for the C-ore it was 4 and 2 (1/kWh/m2). After 6 minutes the surface damage index in all tests tends towards steady state a constant value, an indication of steady state surface damage condition. It has been demonstrated that this methodology can be a useful basis for characterising superficial breakage behaviour of ores."

Jan 1, 2014

By G. Prabhulingaiah, D. M. R. Sekhar

"A phosphate deposit of estimated 6 billion tons of P2O5 is located 180 to 300 meters below the sea level, 185 kilometers north of port Luderitz, Namibia. The ore bed is 6 kilometers wide and 220 kilometers long. The ore deposit analyzing 16% P2O5 is loose sediment of 1.5 meters thick without over burden. Sizing of the ore to - 1.4 mm + 0.150 mm improves the grade to 23.54% P2O5 with a P2O5 recovery at 83.75% containing phosphate pellets and flakes of sea shells. Clay, bacterial debris as organic matter, flakes of broken sea shells and fine phosphate containing particles report to - 0.150 mm fraction and + 1.4 mm fraction contains sea shells and few phosphate containing pellets. The mineralogical composition of phosphate containing pellets is estimated (Droste, T.C., 2004) 80% frankolite, 6% pyrite, 4% illite, 3% quartz, 3% amorphous SiO2, 1% carbonates, 1% organic carbon and = 1% ilmenite, magnetite, zircon etc. The phosphate content in the pellets is around 27.7% P2O5. Trials to separate by gravity or flotation processes were not successful. Leaching of carbonates (sea shell flakes) under mild acidic condition (= 2% acetic acid or HCl solutions) or calcinations followed by leaching however yielded residues (concentrates) of grades 27.85 - 32.74% P2O5 at P2O5 recoveries ranging from 78.45 - 96.8% P2O5."

Jan 1, 2014

By I. Gombköto, G. Mucsi, S. Nagy, F. Kristály, Á. Rácz, R. Szabó, B. Egyed

"Present paper deals with the investigation of a Hungarian pumice. Grinding experiments were carried out in a stirred media mill for various residence time. Ground samples were tested with laser particle size analyzer to determine and calculate the material fineness (particle size distribution and specific surface area). The lime adsorption capacity was measured to monitor the reactivity. Alkali activated cement paste was prepared using ground pumice with various alkali activators. Cube shaped specimens were produced from the paste and the uniaxial compressive strength was measured at the age of 7 days. The resulted alkali activated material structure was investigated by XRD and FTIR. The results of the experiments show that pumice fineness has strong impact on its hydraulic activity, hence on the compressive strength and the structure of the resulted binder. Relationships between grinding fineness, material structure and strength of the raw and mechanical activated material as well as the alkali activated cement were revealed. INTRODUCTION Pumice is a natural pozzolan which can be used as raw material for cementitious materials in limited portion owing to its low reactivity. Furthermore, due to its mineralogical composition it can be used for developing a new environmental friendly binder, namely alkali activated cements (AAC) which are inorganic alumina-silicate materials with good cementitious properties (Almalkawi et al., 2017; Özodabas and Yilmaz, 2013; Najimi et al. 2018; Yadollahi et al., 2015). Despite being a rather recent research topic, many papers and books have been published focusing on various aspects of alkali activation. There is great variety of raw materials that can be utilized for AAC production. However, primary raw materials are very expensive and secondary materials are heterogenous in composition. Therefore, a more homogeneous and low price silicate would help to balance the properties and cost of resulting cement and easing the way for commercialization of AAC. However, the control of its reactivity is of great importance which can be realized using mechanical activation by grinding (Juhász and Opoczky, 1990; Djobo et al., 2016; Mádai et al., 2015). The goal of present paper is to investigate the effect of mechanical activation of pumice on the properties of the resulted alkali activated cement."

Jan 1, 2018

By F. Boylu

In this study, Ca-bentonite was subjected to a series of systematic hydrocyclone tests with the aim of developing separation procedures and in turn achieving optimum recoveries. In hydrocyclone tests, vortex and apex diameters and also feed pressures were investigated. In each hydrocyclone set, vortex diameter was kept constant while the other two parameters varied to produce bentonites con-centrates of various smectite contents. The separation efficiencies were evaluated based on the cation exchange capacity (CEC), particle size and swelling index. The detailed hydrocyclone tests showed that, upgrading of Ca-bentonites require procedures different from the bentonites reported in the literature. Sodium and mixed bentonites are easy- to-disperse and easy-to-separate whereas calcium types need to be scrubbed rigorously for disintegration. Scrubbing properties of ca-bentonite were investigated as a function of scrubbing time and percent solids by weight (PS). The scrubbing conditions at 700 rpm for 1.5 hours and percent solids of 30 % were found more effective for achieving a better quality bentonite. In addition to the parameters mentioned above, the effect of percent solids on hydrocyclone separation was also studied. Although Ca-bentonites permit studying at higher percent solids, increasing solids content of the pulp deteriorated the quality of the clean products. Application of an appropriate separation scheme enabled the development of a unique separation procedure involving stage wise scrubbing followed by hydrocycloning which yielded calcium bentonite concentrates with CEC of 90 meq/100 g and high swelling indexes of 12 mL from the original bentonite of 65 meq/100 g and 7.0 mL, respectively. These results indicate that upgraded bentonite products can be conveniently used in various diverse industrial applications including bleaching earth, desiccant, cat litter, paper etc.

Jan 1, 2014

By T. Mütze

The progress in comminution is often described by the specific surface area and the energy utilization or the brakeage ratio and breakage function. The principal mechanisms of size reduction are therefore, well known. All four parameters share a common disadvantage: They are limited in describing the behavior of a feed material with fine particles and a wide particle size distribution. An alternative is to describe the progress in comminution with ? The particle size distributions Q(x) before and after the stress or ? The particle concentration ratio pcr(x), which combines these two states. In the case of a self-similar fracture behavior, (in short: self-similarity) the progress in comminution can be simplistically described by the relationship between a reference particle size and the stress intensity. Self-similarity means self-similar breakage functions of geometrically similar particles of the same strength, a certain stress situation and stresses up to the breakage point. Self-similar breakage functions show the same curve at different stress intensities when the fragment size x is normalized with a reference particle size xNorm. This behavior was demonstrated for single particle comminution repeatedly and unequivocally. In the field of particle bed comminution, these results differ in literature. Therefore, the self-similarity in particle bed comminution was systematically investigated at the Institute of Mechanical Process Engineering and Mineral Processing of the TU Bergakademie Freiberg as part of a research project. Limestone, quartz, silicon carbide and glass beads, were examined with a hydraulic press. The particle sizes covered monodisperse fractions in the range of 1-1000 µm, bimodal mixtures of these fractions and polydisperse fractions. The results obviously show that there is no self-similar fracture behavior in the case of glass beads, quartz and silicon carbide. Statements on the self-similarity of limestone are much more difficult: Only some of the investigated limestone fractions show a similar clear, non-self-similar behavior. Self-similar curves appear particularly for fine monodisperse fractions as well as bimodal mixtures, which stressed with pressures above 200 MPa. Considering the measurement accuracy of particle size analysis the coincidence of the curves can be explained by the fact that progress in comminution almost ends above 200 MPa. At this point, a hydrostatic stress state is reached in the particle bed which is known from the literature. This stress state inhibits further fractures. Overall, it has been verified for the investigated materials that there?s no self-similar fracture behavior in particle bed comminution. One reason for the diverse opinions in literature is that there are three types of particles after the comminution in the particle bed: ? Particles which are stressed below their breaking point, ? Particles which are stressed right up to the break point, and ? Particles which are stressed beyond their breaking point.

Sep 1, 2012