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By S. A. Kubyshkin, A. A. Agafonov, A. L. Shakhnin, S. M. Sukharzhevsky, A. A. Komlev, N. V. Vorob’ev-Desyatovskii, A. Pichugina

Cyanidation of gold ore results in formation not only of Na[Au(CN)2], but also cyanometallate complexes of some transition metals. During subsequent gold extraction from such solutions and pulps, using activated carbons (??), a number of problems arise. An effective solution of the problem is not possible without detailed knowledge of the interaction mechanism of transition metals cyanide complexes with AC particles. The chemical properties of AC particles and graphene, saturated with [?u(CN)n](n-1)- (n=2, 3), were studied by XPS, ESR, SQUID, and DFT. The obtained results were compared with the data on AC adsorption of anionic form of Ag(I), Au(I), Cd(II), Hg(II), Cr(III), Fe(II), Fe(III), Co(III), Rh(III), Ni(II), Pd(II), Pt(II) and Pt(IV) cyanide complexes. The adsorption of [?u(CN)n](n-1)- (n=2, 3) on AC from aqueous solutions in air is accompanied with oxidation of ?u(I) atoms. Besides, Cu(II) and Cu(III) compounds were found on AC surface. Quantum-chemical calculations confirmed the possibility of formation of Cu(I) complex with carbene-like sites of AC. The reactions of [?u(CN)n](n-1)- (n=2, 3) complexes and aromatic carbenes and their cation-radical were theoretically studied at DFT PBE level to obtain the information on adsorption of cyanometallate complexes on AC. Carbenes with different fragments were regarded as a model of activated carbons, which have free edge sites with paired o and n electrons. It was shown that [Cu(CN)2]- bounds firmly with triplet carbene, if one Cu-CN bond breaks. The dissociation process occurs through a multi-step spin-crossing mechanism to reduce total spin multiplicity of the metal-carbene complex. The behavior of transition element complexes in contact with AC in aqueous solutions is determined by the following characteristics: geometrical structure of ionic complexes; nature of ligands bonded to the central atom; concentration of reactive oxygen species in solution and its pH; nature of binding sites of AC.

Jan 1, 2018

By S. Sheng, Y. G. Huang, W. Chai

"Polyacrylamide (PAM) is a typically synthetic depressant and may be used as a depressor of pyrite. The modification of polyacrylamide may improve its physicochemical properties and performances. Sulfonated polyacrylamides (SPAM) with different sulfonation degree (SD) were prepared using sodium sulfite as the sulfonating agent, and the interactions of SPAM and pyrite were investigated by the adsorption experiment in this work. The adsorption tests of SPAM on pyrite were conducted as a function of sulfonation degree, pH value and contact time. Pyrite and SPAM were constructed and optimized through MS software. The interaction mechanisms of sulfonated polyacrylamide and pyrite were simulated by molecular dynamics simulations. The results show that the adsorption capacities of SPAM at neutral and weak alkaline conditions are higher than that at acidic and strong basic conditions. The high sulfonation degree favors the adsorption of SPAM on pyrite surface. The adsorption process can be described best by the pseudo-second order kinetic model. Molecular dynamics simulations show that the adsorption of sulfonated polyacrylamide on pyrite is better than that of polyacrylamide. Sulfonated polyacrylamide can be used as a potential depressant of pyrite with the main interacting mechanism of hydrogenbond force.INTRODUCTIONPyrite is the most abundant sulfide mineral and often associated with valuable minerals such as galena, chalcopyrite, sphalerite, molybdenite, gold, diaspore as well as coal (Forrest et al., 2001; Jaiswal et al., 2015; Maier and Dobiáš, 1997; Qiu et al., 2017; Xin and Liye, 2010). Froth flotation is the most popular method to remove pyrite from valuable minerals. Pyrite could be floated as the flotation concentrate either by its hydrophobicity or activation by metal ions (Chandra and Gerson, 2009). What is more, pyrite could be seperated as flotation tailing by adding highly selective depressants including inorganic and organic modifiers. Polysaccharides polymers and lignosulfonate-based biopolymers are common natural organic depressants (Deng et al., 2017; Mu et al., 2016). While the synthetic organic products have proved to be particularly versatile in terms of molecule tailing capability and controlled structures (Boulton et al., 2001a; Raffa et al., 2015)."

Jan 1, 2018

By Jia Ma, Lu-De Qiang, Zhi-Chao Liu, Chun-Feng Li, Guang Li, Bao-Bin Tang

"At present, research on the surface chemical properties of uranium minerals is very scanty, which restricts the research progress of uranium ore flotation process research. The research aimed at exploring the surface characteristics of two common uranium minerals and providing basis for flotation process to enrich uranium minerals in ore. This paper selected pitchblende and uraninite as the object of study, which are widely distributed in uranium deposits. We chose out the pure minerals of pitchblende and uraninite from different ores collected from different uranium deposits. By means of Zeta potential test and X-ray photoelectron spectroscopy (XPS) test, a preliminary study on surface characteristics of the pure minerals of pitchblende and uraninite was conducted. And the significance of the change of Zeta potential, the elements composition and valence state on the minerals surface for flotation was discussed. The research shows that, the Zeta potentials of pitchblende and uraninite in pure water are negative mainly when the pH value varies from 2 to 11, which maybe a result of the difference of ionization capacity between two kinds of oxy-compounds on the surface of minerals. On the surface of pitchblende and uraninite, the metal elements are mainly U, Th and Pb. U is mainly in the form of UO2, Th is mainly in the form of ThO2, and Pb is mainly in the form of Pb and PbO. Based on the surface characteristics of pitchblende and uraninite, we can select process and reagents appropriately in uranium ore flotation.INTRODUCTION Globally, the major challenges associated with exploitation of low grade ores are about finding economically feasible processes for reducing the mass of gangue minerals (Filippov et al., 2012). Among the beneficiation technologies of low grade uranium ores with complex minerals assemblage, flotation is the common process which is used to reduce production cost and eliminate the acid-consuming minerals (Li et al., 2016; Liu et al., 2015)."

Jan 1, 2018

By S. I. Anufrieva, N. A. Permyakova, E. G. Likhnikeevich

"Russia’s rare metal reserves are composed of compositionally and structurally complex ores and are characterized by an increased content of natural radionuclides due to their geochemical similarity with rare metals. For instance, concentrates of Zashikhinsky daeposit are characterized by an increased content of uranium (0,06%) and thorium (0,59%); Beloziminsky deposit holds pyrochlore-apatite-magnetite-carbonate ores characterized by increased radioactivity (130 mkR/h) and containing 0,0016-0,0025% of uranium; Etykinsky deposit is characterized by columbite-pyrochlore-microlith mineralization with an average ore grade of 0,013% of uranium and 0,0020% of thorium; eudialyte concentrate of Lovozero deposit (Alluaiv area) belongs to Class II of mineral reserves. Industrial development of these mineral reserves involves the need to comply with environmental standards, public health requirements applicable to finished core and by-products, to take into account the amount and class of the generated radioactive waste, the possibility of disposal or recycling of the radioactive production waste. Concentration processes of radioactive rare metal feeds most often lead to a concentration of natural radionuclides and their accumulation in concentrates. Comprehensive hydrometallurgical processes are currently under development for such concentrates, aimed at producing salable products compliant with the radiation safety standards. The choice of the hydrometallurgical processing method for radioactive rare metal concentrates is based on the mineralogical component of the concentrate, textural and structural features, the distribution of valuable components and impurities, and the content of radionuclides. A systemic approach to the selection of processing methods, in particular integrating several methods, is an effective solution. Methods may not only be combined, but also inextricably linked with each other. Hydrometallurgical processing methods include leaching by acidic and alkaline agents; sulfatization for selectively decomposing the minerals and moving the bulk of U and Th into solution; fluorine extraction process. Methods of precipitation and co-precipitation, extraction (by liquid and solid extractants), sorption, and ion exchange are used to decontaminate the solutions by removing thorium, mezathorium, uranium, and their radioactive decay products. Agents used in hydrometallurgical processing of radioactive rare metal ores include sulfuric, nitric, hydrochloric, hydrofluoric acid, alkali (NaOH, KOH), sorbents (for example, AB-17) for sorption of uranium and extractants (mono- and bidentate organophosphorus compounds, diamides, etc.) for the extraction separation of rare, rare-earth, and radioactive elements."

Jan 1, 2018

By A. Tolentino, J. Bravo, M. A. Corona-Arroyo, C. Quintero, R. Zarate, A. Lynch, L. Carillo

"This paper presents the performance of the flotation circuit of Minera Fresnillo PLC, Mexico. A plant survey was carried out on the lead banks and a size-by-size assay on the samples was conducted. The results indicate that the plant is treating fine particles in the flotation circuit. At least 30% of the particles in the feed are finer than 8 microns and that high amounts of Pb, Au, Ag and insolubles are in this particle size. It was also found that higher percentage of insolubles in the -8 micron particles are recovered in the final concentrate rather than being rejected in the tails. The presence of high amounts of insolubles in the concentrate is an issue of the company. The result of the plant survey provided valuable information for effective reduction of the insolubles in the concentrate and for plant optimization. The work conducted is part of the training of the students involved in a mine placement in the Alban Lynch Student Venture. INTRODUCTION Minera Fresnillo is one of the operating mines and the main contributor to the silver production of Fresnillo PLC group, the world’s leading producer of silver from ore. It is located in the mining district of Zacatecaz, Mexico, approximately 650 kilometers from Mexico City. The major minerals that make up the ore are galena, sphalerite, tetrahedrite, pyrargyrite, proustite, polybasite, pyrite and pyrrhotite. Minera Fresnillo has a capacity to treat 8300 tonnes of ore per day. The plant consists of semi-autogenous mill - ball mill – hydrocyclone circuit for primary grinding followed by silver-lead flotation then zinc flotation circuits. This paper reports the plant audit conducted in the silver-lead flotation circuit (Figure 1) of Minera Fresnillo. The circuit includes rougher, scavenger and two stages of cleaning. The tails from the scavenger goes to the zinc flotation circuit while the second cleaner yields the final silver-lead concentrate. The feed to the circuit has a particle size of 90% finer than 75 microns and generates a concentrate with grade of about 35% Pb, 5700 g/ton Ag, 16 g/ton Au and recoveries of 90% Pb, 90% Ag, 64% Au, respectively. Although the plant achieves their target concentrate grade and recovery, the concentrate also contains significant amount of insoluble materials which is about 18%. These insoluble materials consist of gangue minerals. The plant audit was conducted primarily to determine the possibility of further reducing the amount of insoluble materials present in the silver-lead concentrate."

Jan 1, 2018

By Pan, Jian, Siwei Li, Deqing Zhu

"It is great significance to realize the efficiently and comprehensively utilization of iron, manganese and aluminum from refractory high-aluminum and high-manganese iron ores. Aimed at the two types of low grade refractory iron ores, mineralogical characteristics were studied. The direct reduction behaviors and evolution of mineral compositions of single iron ores and their blended ones were analyzed, and the corresponding reduction mechanisms were demonstrated. The results showed that only a part of iron oxides in high-aluminum ore are transformed to metallic iron after reduction, while the other react with aluminum and silica to form fayalite and hercynite which are difficult to be reduced. For the high manganese iron ore, most iron oxides can be reduced to metallic iron and manganese oxides can combined with aluminum-silica minerals to form galaxite and tephroite, promoting the reduction of iron oxides. Co-reduction results demonstrate that reduction of high- aluminum ore can be promoted by adding with high-manganese ore. Metallization and metallic iron grains increase dramatically by elevate high-manganese blending ratio. At the ratio of 60% high- manganese iron ore in the pellet feed, iron-slag separate well with a slag assaying 28.51%~36.35% Al2O3 and the recovery of iron and manganese can be reached 93%, respectively. The high-aluminum rich manganese residue was recycled with H2SO4. INTRODUCTION The growth of the Chinese iron and steel industry has been pushed forward by its rapid economic development in recent years, and 1126 million tons of iron ore have been consumed in 2014, where 933 million tons were imported according to the data from World Steel Association [1]. However, iron resources are limited, and especially the reserves of high-grade iron ores are declining, so it is of significant importance to optimize the mining rate of iron resources [2] and to utilize low- grade refractory iron resources, such as high-aluminum iron ore."

Jan 1, 2018

Vanadium-titanium magnetite from Panzhihua was crushed with open and closed circuit process by high pressure grinding roller (HPGR). The particle size characteristics of the crushed product were analyzed and the micro-cracks generated by HPGR during the crushing process were studied. The results showed that, in crushed products, the reduction ratio increases and the size distribution becomes more uniform with increasing of the pressure on roller?s surfaces. The fine fraction content of crushing products from -3.2 mm classification closed-circuit by HPGR increases obviously compared with that by Jaw Crusher and particle size distribution is more uniform. Large amount of intra-crystalline cracks and cleavage cracks are generated in vanadium-titanium magnetite crushed by HPGR, which makes the specific surface area larger and Bond grinding work index (objective particle size is 0.074 mm) decreased by 14.05% than that by Jaw Crusher. And the liberation degree of monomer of the product crushed by HPGR increased compared with that by Jaw Crusher with the similar fineness of grinding. Keywords: iron ore, high pressure grinding roller, micro-crack

Sep 1, 2012

By Stoyan Groudev

Two experimental plots consisting of a slightly acidic soil heavily contaminated with radionuclides (mainly uranium and radium) and non-ferrous metals (mainly copper, zinc, and cadmium) were treated in situ under real field conditions using the activity of some representatives of the indigenous soil microflora. This activity was enhanced by suitable changes in the levels of some essential environmental factors such as pH and water, oxygen and nutrient contents of the soil. The treatment was connected with solubilization and removal of the contaminants from the top soil layer (horizon A) due to the joint action of the soil microorganisms (mainly acidophilic chemolithotrophic bacteria) and leach solutions (diluted sulphuric acid) used to irrigate the soil. In one of the plots, the dissolved contaminants were removed from the soil profile through the drainage soil effluents and were subjected to cleaning by a constructed wetland located near this plot. In the other plot, the dissolved contaminants were transferred to the deeply located soil subhorizon B2 where they were precipitated as the relevant insoluble forms (uranium as uraninite, and the non-ferrous metals as the relevant sulphides) as a result of the activity of the sulphate-reducing bacteria inhabiting this soil subhorizon. This activity was enhanced by injecting water solutions of acetate, lactate, ammonium, and phosphate ions to this soil subhorizon.

Sep 1, 2012

By P. Oliveira, A. Peres, A. Silva

"The decrease in iron content and increase in contaminants grade, associated with greater participation of compact and semi-compact materials, has impacted the recovery of a mechanical cells flotation circuit in the Iron Quadrangle, Brazil. The recovery decrease in the flotation stage motivated the current conventional flotation circuit reevaluation seeking alternatives to restore the recovery, without affecting the final concentrate quality parameters, with low investment. Sampling, chemical characterization of samples, bench scale flotation experiments, and mass balances were conducted. Analysis of the results showed opportunities to improve the circuit performance. The stages prior to the flotation circuit changes were: rougher, cleaner, recleaner and scavenger. In the previous configuration, recleaner was operated as cleaner scavenger and the iron grade in the scavenger concentrate was 23%, representing 38% of the new feed. After the circuit change, the circulating load was reduced from 38% to 15% and the iron content was upgraded to 42%, resulting in increased residence time. The iron content in the global tailings of the concentrator was decreased from 10.9% (year of 2013 average) to 10.2%, representing gains in both mass and metallurgical recoveries.INTRODUCTIONRegarding plant practice, the year 1972 represents a landmark for the concentration of iron ores in Brazil. VALE started up 28 units of WHIMS (wet high intensity magnetic separators) at the Cauê plant in Itabira, each one producing 1x106 t/year of concentrate. Later 17 WHIMS machines were commissioned at Conceição. During the 80’s decade of last century, changes in the ROM required the addition of a cleaner flotation stage to decrease the silica content in the pellet feed.The first company to use reverse cationic flotation as the only concentration operation of iron ore was SAMARCO (start up in 1977). Since 2015 flotation has been utilized at VALE in Itabira as major concentration process, magnetic separation acting as scavenger stage.The Jones matrix type WHIMS were manufactured for decades under patent by KHD Humboldt Wedag. After the expiration of the Jones patent, Eriez Magnetics took the world leadership regarding WHIMS manufacturing. The Brazilian branch of Eriez is Inbras. Based on plant practice experience at the Fabrica concentrator, the Brazilian company Gaustec was established (RIBEIRO and RIBEIRO, 2010) and is now present in different countries. The mega sized WHIMS GHX-1400 (18.000 Gauss, gaps smaller than 1.5 mm) were developed to face the challenge of huge throughput required by iron ore processing (Ribeiro et al, 2017)."

Jan 1, 2018

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 R. X. Li

The overall flow-sheet of producing chromium (III) sulfate is described in this paper. The suitable conditions of each process such as sintering, leaching, aluminum removal, reduction, and de-composition conditions were experimentally studied. The results show it is reasonable to produce chromium (III) sulfate with the flow-sheet pointed out in this research work. The final product is Cr2(SO4)3 solution contained 150~250g/L Cr.

Jan 1, 2014

By P. Braga, A. Chaves, S. França, A. Luz

"In Brazil, there are no official reserves of molybdenum, and the unofficial reserves are modest. Therefore, the molybdenum ore (molybdenite) produced as a co-product or by-product of emerald mining in the region of Campo Formoso, BA, has arisen as the only economic option. The flotation process is commonly used in Brazil for the recovery of molybdenite from emerald mining tailings, but it produces low-content molybdenite concentrates, thereby resulting in a product with low economic value. The molybdenite concentrate produced in Campo Formoso contains 83.5% MoS2 (50% Mo), which is less than the international standard product that contains > 90% MoS2 (54% Mo).This low value is due to the presence of talc, which is a naturally hydrophobic mineral that is also floated with the molybdenite during the flotation process. Separability studies were done in a Partridge-Smith cell using dextrin and quebracho as a molybdenite depressor in solution at different concentrations and pH values to produce a technical-grade concentrate (i.e., 90% MoS2). These basic studies were accompanied by measurements of the zeta potential and contact angle, which was determined by the capillary rise method. The results of these floatability studies were used in bench flotation tests, which were performed in a Denver laboratory flotation cell. A molybdenite concentrate of 93.4% MoS2 was obtained when dextrin was used at a concentration of 100 g/t."

Jan 1, 2014

By Jerzy A. Mielczarski

The separation of albites from quartz by flotation applying the conventional HF-methods is no longer acceptable from an environmental and health point of view. Therefore, the search for a new reagent scheme without using HF depressor for separation of albite from quartz is under consideration. The flotation behaviour of ore mineral components depends on the produced hydrophobic or hydrophilic surface coverage (chemical functionalization). Currently we have excellent possibility of monitoring surface composition and structure at molecular and atomic levels at surfaces of natural minerals contacted with aqueous solutions of collectors, activators, depressants which is vitally important for the understanding of the surface chemistry that govern selective and efficient flotation. Detailed surface characterization of minerals before and after their exposition to different solution conditions was performed by the most modern spectroscopic techniques such as developed by us the infrared external reflection technique combined with spectral simulation and X-ray photoelectron spectroscopy (XPS). It is possible to monitor surface reactions which facilitate the separation process and those which bring disadvantage to selective flotation. At first we found that a small amount of ?mineral impurity? presented in natural ore could play important role in selective hydrophobization process. It was found that the pH of solution (parameter possible to control) and natural mineral impurities present in mineral samples (parameter related to ore origin) play a very important role in the separation process. Another important parameter is interaction between minerals, quartz and albite, present in aqueous solution. The limitation of flotation separation resulting from chemistry will be discussed. Moreover, the most promising scheme for separation of albites from quartz will be examined.

Jan 1, 2014

By J. Temuujin

Mongolia has some of the world?s largest coal reserves with an estimated total coal reserve of over 150 billion tonnes. At present, over 90% of Mongolian electricity is produced by combined heat and thermal power stations. The main coal deposits used for Central power system's power stations are Baganuur, Shivee-ovoo lignite type coal and Shariin gol bituminous coal. In Mongolia almost 600,000 tonnes of coal combustion by-products are disposed of in waste ponds. In this research, we have thoroughly characterized Mongolian coal combustion by-products including fly ashes sourced directly from thermal power stations and ash retrieved from ponds. It was determined that fly ashes generated from Baganuur and Shivee-ovoo coal deposits are class C, while ash from Shariin gol coal is class F (according the ASTM C618). All ash products were characterized by chemical, mineralogical, granulometrical, porosity, FE-SEM and radiation methods. Fly ashes sourced directly from power stations were found to be more suitable for manufacture of geopolymers for building materials application and zeolite synthesis than ashes retrieved from ash ponds. The adsorption and porous properties of zeolitic compounds were measured and found to be suitable for adsorption of Cr6+ from simulated tannery waste water. Keywords: coal, coal combustion by products, synthesis, geopolymers, zeolitic compound

Sep 1, 2012

By Mohammad Noaparast, Hamed Haghi

"In this research work, it was attempted to reduce the iron contents (Fe2O3) in relatively low grade silica sample which was obtained from Shenin silica mine, using magnetic separation. The prepared sample contained 93.75%SiO2, 0.44%Fe2O3, 2.78%Al2O3, and 0.08%TiO2 and the Fe2O3 had to be reduced to less than 0.08%. Mineralogical studies and XRD analysis indicated the presence of Hematite, Pyrite, and Goethite as the major iron impurity phases. Mineralogical studies of polished and thin sections demonstrated that the degree of freedom of silica is more than 80% in -300+212 ?m size fraction. After primary stages including crushing, milling, scrubbing and de-sliming, various methods such as low intensity magnetic separation (LIMS), high gradient magnetic separation (WHGMS) and dry high intensity magnetic separation (DHIMS) were applied to find out that which process would be appropriate for the elimination of iron impurities from this sample. Different experiments were carried out on the product of wet rod mill and scrubber. However the magnetic field intensity of WHGMS was increased down to 2Tesla, and there was not any acceptable result in reduction of Fe2O3 content lower than 0.08%. Thereafter the product of wet rod mill and scrubber were dried and reported to DHIMS. In these experiments, maximum magnetic field intensity was 1.4Tesla. In this case very significant results were achieved, and Fe2O3 content of final product were reduced to less than 0.05% which meets glass manufacturing standards."

Jan 1, 2014

By M. Narasimha

The flow in a hydrocyclone classifier is highly turbulent complex nature of multi-phase structure, which has led designers to rely on empirical mathematical models for predicting the performance. A number of classifying cyclone models have been developed and successfully used in mineral comminution circuit simulators over the past four decades (Plitt, 1976 and Nageswararao, 1978). However, most of the mathematical models currently available to describe hydrocyclone classifier performance are based on single average mineral density component behavior. In industrial comminution circuits, the feed to the cyclone composed of a mixture of particles of varying degrees of liberation and sizes. The behavior of multi-component particles in a hydrocyclone is poorly understood and unaccounted for in most of the mathematical model equations available in the literature. There is evidence from a number of experimental data sets indicating the significant influence of the multi-component particles on measured cyclone performance. A concept for modeling the performance of hydrocyclones based on multi-component behavior is proposed in this paper. A set of semi-empirical model equations for cut-size, sharpness of separation are presented and the corresponding model parameters evaluated from the measured data are given.

Sep 1, 2012

By M. Eraydin

Dewatering fine particles (e.g., flotation concentrates) is inefficient, energy intensive and often requires large capital and operating costs. To address these issues, a series of advanced dewatering technologies have been developed at Virginia Tech. These include novel dewatering aids and a hyperbaric centrifuge. Typically, the moistures obtained using these methods are 30% to 50% lower than those obtained using conventional methods, as demonstrated in laboratory and pilot-scale test programs. With another novel dewatering technology that has been tested in bench-scale tests, the moistures can be reduced to levels once believed to be attainable only through the use of thermal dryers. In this communication, test results obtained with these advanced dewatering technologies are presented and compared.

Jan 1, 2014

By N. Tsoni

The separation and recovery of fine and ultra-fine particles during the processing of mineral commodities by conventional separation methods is difficult and inefficient. This is due to the problems posed by the very small size of the mineral particles. The fine and ultra-fine mineral particles are either generated during size reduction processes or are necessitated by liberation size. This problem is expected to deteriorate, as deposits of even lower grade are processed. The inefficiency of the conventional separation methods with regards to the processing of very fine particles leads to the loss of considerable quantities of mineral commodities to the tailings. Novel methods and techniques as well combinations of known methods have been tested over the years. Among them, selective aggregation, along or in combination with flotation, has been given much attention. This study deals with the application of hydrophobic agglomeration as a separation method for very fine particles. The selected mineral system is magnesite/quartz, due to its sensitivity to physi-cochemical separation methods. The aim was the selective agglomeration of magnesite using sodium oleate. Tests on single minerals revealed that separation seems feasible and efficient. The parameters examined were: pH, quantity of sodium oleate, conditioning time, and, finally, settling time. Tests carried out on artificial mixtures of the two minerals, under various proportions, confirmed the results obtained from single mineral tests but they were slightly inferior. Finally, hydrophobic ag-glomeration tests were carried out on single and artificial mixtures of minerals using sodium oleate and petroleum as reagents. The results show that the addition of petroleum improves the results. In conclusion, hydrophobic agglomeration can be applied successfully even for fine particles of difficult-to-be-separated systems such as magnesite and quartz.

Jan 1, 2014

By Q. W. Jiang

This paper presents a new process for producing industrial magnesium sulphate using waste water from titanium white plant and magnesium oxide from calcinations of magnesite ore as raw materials. With the laboratory experimental equipment, the waste liquid and magnesium dioxide react effectively at ambient temperature and under atmosphere pressure. Via the press filter, a clear liquid predominately containing magnesium sulphate is obtained. It is further evaporated and crystallized by cooling, separated by centrifuge and dried. Consequently a high quality of industrial magnesium sulphate is achieved as the final product. In the course of process, as the majority of valuable component (SO42-) is recovered in the final product, most of impurities from waste acid is being removed into the by- product. With the simple operational process, it is possible for titanium dioxide plant to resolve the environmental problem completely and benefit from the industrial magnesium sulphate product as well. The filter cakes containing valuable elements such as Mg, S, Fe, Mn, V, Ti are by-product proposed to be used for manufacture of agriculture fertilizer particularly for peanut planting.

Jan 1, 2014

By A. Vidyadhar

Printed circuit boards (PCBs) constitute a majorpart of electrical and electronic equipment containing valuable metals such as Cu, Ni, Au, Ag, Pd, Fe, Sn, Pb, etc. The concentration of base and precious metals in PCBs is observed to be several times more than those in their respective ores. Therefore, the recycling of PCBs is necessary to recover the valuable materials. However, the ultrafine particles pose a big challenge. Removal of them is suggested prior to processing by flotation. Froth flotation is observed to be a promising technique for rejecting the plastics from the comminution product. In the present work, enrichment of ground 1.0 mm PCB powder was investigated through flotation route by varying the operating variables such as frother dosage, pulp density, air flow rate and rotational speed of the impeller. The liberation studies indicate that excellent liberation of metal values is achieved from the non-metallic constituents at -1.0 mm size and below. The particulate system is quite rich in metal value with about 23% total metal content. The non-metallic constituents such as plastics are observed to possess strong hydrophobicity while the metal particles in the pulverized mass are hydrophilic in nature. Froth flotation kinetics is studied in depth with a view to facilitate high rejection of plastics and identify optimum operating conditions for the same. A number of experiments are performed to establish the influence of the operating variables on flotation performance. The conditions for achieving higher yield of the metal-rich fraction with respect to a specified grade are discussed in the light of the experimental results. It is found that the requirement of reagents is negligible which could be a very important factor from the commercial stand point. Single-stage flotation increases the metal content from 23% to over 32% with a mass yield of around 75% and over 90% recovery of metal values. 32% of the materials in the feed could be effectively rejected in the float fraction losing less than 4% metal values. The dependence of kinetics on the process variables is also discussed. It was concluded that a high rotor speed helps in efficiently rejecting the plastics. Frother should be added to help stabilize the froth and enhance the kinetics. A moderate air flow is required while pulp density must be kept low for efficient pre-concentration. It is established that the entire -1.0 mm comminution product could be treated by flotation for generating a pre-concentrate. Keywords: printed circuit boards, recycling, froth flotation, kinetics, recovery

Sep 1, 2012