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Poor floatability of fine particles is known to be the main cause of the low recovery of ilmenite in Panzhihua, which is the largest titanium mine of China. To get an optimum ilmenite recovery, selective flocculation, and flotation of fine ilmenite was investigated through flotation tests, particle size analysis, zeta potential tests and scanning electron microscopy. The results indicate that carboxymethyl cellulose (CMC) shows flocculation effect for both ilmenite and titanaugite without selectivity, while selective flocculation could be realized by the combination of water glass and CMC. It is because that competitive adsorption would take place on these two kinds of mineral when water glass and CMC are used together. On the surface of ilmenite, the adsorption ability of CMC is stronger than that of water glass, so that CMC can absorb to the same extent irrespective of the presence of a pre-adsorbed layer of water glass and ilmenite particles is flocculated by CMC. The same cannot be said of the titanaugite phase as water glass strongly adsorbs onto the titanaugite, and the adsorption of CMC is hindered. Therefore, the titanaugite particles keep dispersion. Furthermore, the flotation of fine ilmenite particles is feasible as the ilmenite floccules could react with sodium oleate. In the flotation separation of Panzhihua ilmenite ore, the recovery of TiO2 increased from 52.63% to 68.28% by selective flotation. Keywords: ilmenite, flotation, selective flocculation, adsorption

Sep 1, 2012

By R. T. Dec

Current industrial compacting and briquetting practices are largely based on trial-and-error techniques. This paper introduces a two-dimensional finite element model of briquetting process in the roller press. Compared with other modeling techniques used in the past, finite element method offers the most versatile approach because it incorporates adequate information about powder behavior, geometry and frictional conditions and offers predictions for the density distribution, the velocity field, the stress distribution, roll force and torque. More over, when the model includes elasticity, it offers predictions on the internal stress state in the briquette after its exit from the roll. This enables to perform realistic computer experiments which are helpful for establishing the forming cavity geometry and process conditions necessary to produce briquettes with the desired properties. Three forming cavity profiles are analyzed. Results from model are verified on experimental roller press and best cavity profile is recommended for briquetting of sub bituminous coal fines.

Jan 1, 2014

By Herman D. Mendoza

A rapid recovery/recycling process was introduced utilizing the surface-chemical properties of finely dispersed mercury and alumina (Al2O3) fibers in aqueous environment. The conventional method of amalgamation or .ball milling. involves the mixing of a substantial amount of mercury to collect free gold during the grinding stage. In effect, a portion of the mercury is transformed into minute droplets that readily float and disperse in the amalgamation effluent. The fine droplets of mercury in the dispersion readily attached onto the positively charged macroscopic alumina fibers (i.e. = pH 9.8) at conditions pH 3 to 10. When an effluent from settling procedure after an amalgamation-grinding stage is passed through a column-bed packed with alumina fibers, maximum collection of negatively charged finely dispersed mercury occurred at pH 3 to 6. The collection/attachment efficiency was 99.5%. The collected droplets of mercury, which are left in the column-bed of alumina fibers, were subsequently rinsed with alkaline solution at pH 10 to 11.5. At these conditions, both mercury and alumina fibers carry negative surface potentials and resulted in the partial detachment of mercury from the alumina fibers. The detachment efficiency was only 30-35%. The attachment/detachment mechanisms in this study were analyzed using the DLVO theory.

Jan 1, 2003

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 R. ?. Shishmarjov, Yu. ?. Davidenko, S. V. Bukhalov, ?. S. Baksheev, M. S. Shkirya, N. ?. Aikasheva, D. V. Bogdanovich, ?. Yu. Faustova

"The goal of prospecting operations in the Republic of Altay was to locate gold-sulfide-quartz mineralization. For this purpose we applied the technology of electromagnetic sounding and induced polarization (EMS-IP). These operations resulted in localizing promising sites with presence of sulfidization. The EMS-IP method proved to be highly efficient amongst other prospecting methods targeted at recognizing zones of sulfide mineralization making up 91%, considering that in more than half cases the ore intervals were the case. In the Yakutian diamondiferous province the EMS-IP technology was approbated during three field seasons to accomplish the assignments on searching for kimberlite bodies under conditions of various geological types. As a result, the reference objects were distinguished, and geoelectric parameters of kimberlite pipes of explosion were defined.INTRODUCTION In the time span 2015-2016 in Gorny Altay the EMS-IP technology was approbated in the Novokuznetsk area. The on-land areal geophysical survey was performed by EMS-IP method applied to identify, outline and locate promising sites with Au-Ag-bearing polymetallic mineralization within surveyed areas. Compared to the hosting rocks, the sulfides contained in polymetallic mineralization are typified by low specific electrical resistivity (SER) and high polarization. The areal survey conducted via EMS-IP method provided spatial characteristics of searched object. From July 2016 to August 2017 our expedition group carried out serial test works and laboratory investigations intending to define performance capabilities of EMS-IP technology in searching for kimberlite bodies under conditions of diverse geological types. The prerequisites for serial work were operations accomplished at the «Listvenichny» site lying 35 km away from Mirny town in the Sakha Republic (Yakutia), where the EMS-IP technology was probed for locating position and measuring geoelectric parameters of tuff pipe «Buardakhsky». After successful completion of operations it was decided to evaluate geoelectric parameters of kimberlite pipes of explosion."

Jan 1, 2018

By Z. C. Zhen

Basing on character of fine ores, and employing all the advantage of dissolved-air flotation, the study within the dissertation put forth the methods of superfine metal mineral flotation with dissolved-air flotation equipment, and constructed a full set of laboratory flotation system. Experiments both in water and in slurry were respectively carried out by means of this flotation equipment. Further study was also fulfilled on mechanism of air-dissolved released devices, and the key components of system including ejector, releaser and saturator were designed. Optimizing devices parameters were chosen by taking ideal performance of the devices into consideration, according to orthogonal experiments and tests on bubbles factors, those performance factors were called air release rate, air release efficiency. The results with some minerals are better than JJF flotation machine with 30 litres bulk. The Dissolved-air Flotation(DAF) machine shows great potentiality in treating super-fine metal mineral concentration. The research indicates the Dissolved-air Flotation(DAF) system has superiority over mechanical flotation machine in fine flotation. Air-dissolved released bubbles appear on the surface of hydrophobic minerals in priority, solving collision probability less in the tradition fine mineral separation, such that the metallurgy technology of fine metallic minerals are improved. The exploratory research is a foundation for industrial pilot, commercial test and equipment maturity in the future.

Jan 1, 2014

By John A. Herbst

The Mineral Processing Industry needs accurate Production Simulators for the design of future plants and expansions. To achieve this, these simulators should not only provide an accurate portrayal of the dynamics of individual pieces of equipment they should include the impact of discrete stochastic events such as scheduled and unscheduled maintenance so the relationships between availability, equipment sizes, and plant capacity are understood. To provide such a tool accurate dynamic Population Balance Models need to be combined with solid discrete event modeling. The current paper provides a description of how these two disparate modeling techniques were combined and the associated benefits from this combination. Keywords: dynamic plant simulation, population balance models, discrete event models, prefeasibility and feasibility studies, plant design and expansion

Sep 1, 2012

By Shounak Banerjee, Suresh Babu Dasari, Dharmendr Kumar, Shashank Pardhikar, Beena Rai, Venugopal Tammishetti

Recent increase in steel demand has led to the increased usage of high grade iron ores. During the mining, crushing and washing of ore, huge quantities of fines and slimes (<150 µm) are generated, majority of which is dumped into tailing ponds owing to their high alumina contents (~10-15%). Due to rapid depletion of high grade iron ore, it is the need of the hour to utilize low grade iron ore fines and slimes. These fines and slimes contain high iron values assaying 45-60% Fe. Dumping these valuable resources in ponds locks enormous land space and causes environmental hazards. The constituent minerals present in Indian iron ores comprise of hematite, goethite, gibbsite, kaolinite and quartz. Our research is focused on beneficiation of iron ore slimes through selective flocculation. We use density functional theory simulations to screen the reagents and perform experiments with screened reagents to determine the experimental conditions for effective performance of the reagents. Our studies revealed that reagents like starch, guar gum and carboxymethyl cellulose exhibit excellent selectivity in high alkaline pH range. However, the higher cost of alkali makes the process economically less attractive. In the present study, a commercial reagent from NALCO Water (Hi-Tex 83570) has been explored as selective flocculant for beneficiation of iron ore slimes in wide pH range (4-11). However, the reagent was also found to be the most selective in alkaline pH range only. Full factorial design of experiments was done considering three parameters namely, pulp density, flocculant dosage and settling time. Regression models were developed for yield, iron grade, alumina grade and iron recovery in the concentrate, using experimental results. Further parameter optimization was done to achieve high Fe recoveries and low alumina recoveries. The optimal parameters thus arrived at were validated with the experiments. We were able to achieve a concentrate grade of 60.0% Fe and 5.1% Al2O3 with 68.8% Fe recovery from a feed containing of 53.1% Fe and 8.9% Al2O3. The performance of flocculant Hi-Tex 83570 was also compared with reagents starch and guar gum.

Jan 1, 2018

By Kumar Ranjan, Kumari A. V. Asha, G. E. Sreedhar, Banerjee R. Raja, M. Narasimha, R. Shivakumar

In this paper, numerical simulation of magnetite, medium segregation and coal partitioning have been made in a 350 mm diameter cyclone. An attempt is made to assess the nature of impairment in efficiency in relation to the increasing amount of near gravity materials in coal. The CFD model approaches the Algebraic Mixture (ASM) model with the granular option and Reynolds stress model (RSM) to resolve the air core and turbulent mixing of the medium and coal particles. The partition characteristics of the DMC were modelled using both Lagrangian & Eulerian particle tracking for particles ranging in size from 0.5 to 8 mm and in density from 1200 to 2000 kg.m-3. Lagrangian frame work based Discrete Phase model used to simulate the coal particle trajectories inside the DMC and attempted to understand the residence time of different size and density coal particles. It was observed that coal particles having density near to separation-density (having fifty percent of probability to under flow and overflow) are exhibiting increased residence time than any density particles. As expected the smaller size coal particles shows higher residence time than the coarse coal particles. CFD simulations on effect of NGM mass fraction are simulated and analyzed using ASM model including for coal and magnetite. Coal particles with high NGM content show significant effect in misplacement of coal particles towards wrong products at all relative densities. The residence time of the particles increases because of its increased interaction with near dense particles. The effect of NGM fraction on overall cyclone performance as well as detailed flow assessment in terms of residence time distribution, NGM particle concentration profiles with respect to LZVV is presented.

Jan 1, 2018

By E. Isokangas

The production of minerals for economic use is a two-stage process, involving mining to extract the mineral from the ground, and processing to convert the mineral into a marketable product. Generally, mining and processing have been viewed as self-contained entities. Both have separate objectives, separate cost centres and key performance indicators (KPIs) that do not reflect the customer/supplier relationships that inherently exist. However, mining and processing operations are inter-connected and therefore intimately inter-related with the performance of one operation affecting the performance of another. Optimizing each stage separately without considering the whole system often misses potential economic benefits and energy savings. During the past fifteen years, the authors have been involved in implementing a holistic methodology ?Mine to Mill Process Integration and Optimisation (Mine to Mill PIO)? to maximize the overall profitability of the operation rather than just optimizing any individual process in a mining operation. Metso Process Technology and Innovation (PTI), along with their project partners, have conducted several projects to significantly increase their production- generating typically 5% to 20% higher throughput and improve the overall mine and concentrator performance through PIO methodology. This proven methodology has applications ranging from greenfield projects to long-standing operations with AG/SAG, HPGR or conventional grinding circuits. This paper explains the Mine to Mill PIO methodology and discusses the benefits of such an approach on the energy consumption, the overall costs and benefits of mining operations. The paper also summarizes several case studies illustrating the use of PTI methodology in a variety of applications. Keywords: integration, optimization, simulation, modeling, mine-to-mill, comminution, blast, drill, crushing, grinding

Sep 1, 2012

By Katja Ohenoja

Polymer dispersants, also known as grinding aids, are widely used to reduce the viscosity of mineral particle suspensions and to improve energy efficiency during fine grinding. In this study, the effect of polymer dispersant with different molecular structure on the suspension properties in the wet stirred media milling of limestone was studied. The stability of suspension was studied by combining rheological and zeta potential measurements. The PDI value of polymers corresponds to the width of the molecular weight distribution so that low PDI corresponds to narrow MW distribution and high PDI to the wide one. In this study, two traditionally fractionated polymer dispersants with high PDI (over 2) and one novel polymer dispersant with low PDI (1.2) has been tested. It was noticed that dispersants worked as electrosteric stabilizators and prevented the agglomeration of ground limestone particles. The uses of dispersants could increase solids concentration used in the grinding experiments and at the same time lower the particle size and specific energy consumption. The obtained particle sizes were about 1 µm regardless of which dispersant was used or the amount of it. The novel dispersant with low PDI reduced viscosity most when compared with the traditionally fractionated polymer dispersants. Results indicated that even higher solids concentrations can be used at the same amount of dispersant when the novel low PDI polymer dispersant is used. Alternatively, lower dosage of novel low PDI dispersant can be used compared to traditionally fractionated dispersants.

Sep 1, 2012

By Q. Zhang

Phosphate tailings through Flotation contains large amount of dolomite which is difficult to be separated from apatite. In this present research, phosphate tailings is recycled by Flotation i.e. re-processing. High-purity dolomite with purity as high as 91.17% is seperated, which contains 19.82% of MgO. The results of orthogonal test show that the effect of various levels of different factors on the high-purity dolomite floatated. Future utilization of purified dolomite is also discussed: magnesium fertiliser especially magnesium phosphate is expected to be an ideal product from high-purity dolomite.

Jan 1, 2014

By I. Grigoryeva, G. Voiloshnikov, V. Dementyev, N. Moskaeva, N. Voiloshnikova

"Adsorption processes with use of anion exchange resins are widely applied in the gold mining industry of Russia and the former Soviet Union. Anion exchange resin AM-2B and its analogs (with mixed basicity) are used as adsorbents. This paper focuses on the study of weak base anion exchange resin and its comparison with AM-2B resin. Different nature of the ion exchange groups of the adsorbents mentioned above provides essential differences in their properties both during adsorption and elution of gold and silver. Multistage gold elution and resin regeneration procedure is used for AM-2B resin whereas alkaline cyanide solution is used for weak base resin and allows for the reduction Capex and Opex in comparison with AM-2B resin. Anion exchange resins AM-2B and PuroGold S-992 were tested. Weak base resin is sensitive to pH of adsorption medium. Optimal pH value is 10.1-10.3 (at ?? >10.5 gold loading onto resin decreases dramatically). Adsorption isotherms for gold, silver, nonferrous metals, cyanide and thiocyanate ions from synthetic individual metal cyanide solutions were defined. Adsorption of all components onto PuroGold resin was lower than for ??-2? resin. Adsorption of metals from the solution with equal molar metal concentration (0.1 mg-equivalent/L of each metal) was also studied. The affinity of resins to cyanide metals complexes was established. Weak base resin has higher selectivity to gold in comparison with ??-2B resin and is less sensitive to ion composition of cyanide solution or pulp treated. Weak base resin was tested for gold recovery from gold ores. On the base of test results it was recommended to introduce this resin at some new plants in Russia. Commissioning and operation performance of gold plants confirmed efficiency of weak base resin use."

Jan 1, 2014

By Benoit Clermont, Jan Lux

"Magotteaux and Anglo Platinum started a co-operation program with the main aim of establishing the optimum milling configuration measured in terms of throughput, fineness and energy consumption.For this purpose, a fully instrumented pilot milling plant, supplied by Magotteaux (Pty) Ltd, and equipped with a 0.9 x 1.0 m ball mill, was erected at Frank concentrator (Merensky Pt ore). The primary ball mills at Frank concentrator were surveyed in order to set the conditions for the base case. This data was then replicated in the pilot mill under the same configuration. Thereafter, a series of different parameters were varied in order to attempt to optimize the milling system.Some of the grinding parameters that have been studied are:•,Gate versus overflow discharge•,Open versus closed circuit•,Different filling degrees•,Different shell liner profilesOnly grate versus overflow discharge and open versus closed circuit will be discussed in this paper.It should be noted that this paper does not attempt to give a universal solution as to what milling configuration is optimum in all cases. The conclusions apply for this particular case and probably most others, but it would be advisable to consider each case on its own."

Jan 1, 2003

By Å Sandström

Loussavaara-KiirunavaaraAB?s (LKAB) iron ore mine, Kiirunavaara, is of magnetite type and associated with apatite, a calcium phosphate mineral. Rare earth elements (REE) have been found in connection with the apatite but also in other minerals. An apatite concentrate was produced by flotation, in order to investigate the possibilities to extract REE from the apatite by hydrometallurgical means. The content of rare earth elements calculated as oxides (REO) was 0.44% in the concentrate. Initially, leaching was done with large excess of sulfuric acid, hydrochloric acid, and nitric acid to study the REE solubility with different acids. In sulfuric acid, the leaching recoveries of the different REE varied between 35% and 69%. The reasons for the relative low recoveries, were that the rare earth elements precipitated together with huge amounts of gypsum, that was formed during leaching. However, both hydrochloric- and nitric acid gave almost complete extraction of the REE into solution. Analysis of the small leaching residue obtained, revealed, that mainly the light REE remained in the residue indicating that a small part of the light REE were present in the concentrate, in some acid, insoluble mineral other than apatite. With the aim to separate the REE from the phosphoric acid, the solutions from hydrochloric- and nitric acid leaching were neutralized to a pH of approximately 2 with ammonia. During neutralization, REE were precipitated as phosphates with good recoveries and a concentrate of 10.5% REO suitable for further upgrading was obtained, while the remaining solution can be used for fertilizer production. In further solvent extraction studies, it was shown, that after re-dissolution the REE could be effectively extracted by Cyanex 923, thus allowing for purification from calcium and phosphate ions. The REE were finally stripped from the organic phase and a REE nitrate solution was produced. Keywords: apatite, rare earth elements, REE, leaching, solvent extraction, cyanex 923

Sep 1, 2012

By G. Demi

Chromium ore exploitation has commenced in 1948 in Albania and there are produced about 24.3 million tons up to the end of 2006. Last years the prices and need were increased notably. Main export of chromium ores and concentrates was accomplished respectively 114 500 ton and 13 000 ton in People Republic of China during 2006 year. Location, status, reserves and grade of chromium deposits of Albania are presented in the paper. Chromium ore enrichment is related with their composition and Cr2O3 content, as well as with market requests. Actually, high grade chromium ores with Cr2O3 content over 38% ~ 40% are directly exported or treated in metallurgy, but last time have been exported and chromium ores with 28% ~ 30% Cr2O3 content for the reason that dressing plants can not be operated for investment lack. High grade chromium ores have been treated in heavy media separation plant before 1990. It is presented flow sheet, figures and necessity to put in operation HMS plant in the paper. Actually, low grade chromium ores with content 16% ~ 20% Cr2O3 are not enriched for the lack of investments, but before 1990 they have been concentrated in dressing plants producing chromium concentrates grade 48% ~ 50% Cr2O3. In the paper are shown technological schemes and industrial figures during more than 20 years operation and possibilities to reconstruct these mineral processing plants. Only chromium mineral processing plant of Bulqiza is in operation using as raw material its old existing tailings. The flow sheet and figures show that are possibilities to increase recovery and grade of concentrate in the plant. Separation and concentration of slimes in suitable equipment gives visible improvement of Cr2O3 recovery. Several tests have been carried out with flotation and magnetic separation methods for enrichment of low grade chromium ores. Flow sheet and figures of mineral processing ores content olivine as gangue mineral are interesting, because combination of gravimetric with magnetic methods is necessary in this case. In the paper are presented the tests and good results of low chromium ore pre concentration. Metallurgical treatment of chromium ores to produce Ferro chrome, as well as technological process, figures, consume of electrical power and materials in Elbasani and Burreli furnaces are shown and necessary investments to treat in metallurgy all produced chromium ores in Albania are considered.

Jan 1, 2014

By Y. P. Huang

Experiment results and operation practice on reutilizing old tailings dumped at SCIM (Shang-chang Iron Mine) of KISCO (Kunming Iron and Steel Corp.) are presented. In a production period over 30 years SCIM dumped about 8 million tons of iron ore tailings. For improving resources utilization instead of wasting, experiments on processing for reutilization of the old tailings are con-ducted. These tailings are fine size fractions of weathered iluvial ores rejected out by classification- des-liming in ore washing and dressing processes, containing TFe 21%~22% in hematite mainly and limonite occasionally. Their particle size distribution, in average, is of 72.26% minus 0.037mm and 30.88% minus 0.005mm. Existence of plenty of micro-fine particles makes the tailings refractory to process, resulting in poor metallurgy. The whole sample of the old tailings without size-classification is fed into experimental process. Slon-100 type high grads WHIMS (wet high intensity magnetic separator) with cyc-pulsing is adopted, which magnetism-focusing rod?s diameter is changed from 3mm into 2mm. Operational conditions of optimizing rougher separation tests are strengthened. An iron concentrate assaying 52.21% Fe at quantity rate of 18.39% and iron recovery of 44.40% is obtained. Operational practice shows that metallurgy and economy of the old tailings treatment are close to what achieved at experiments. It is estimated, therefore, that some 1.4 million tons of this iron concentrate may be recovered from the old tailings. This means that KISCO has moved its key one-step in re-mining and reutilizing the secondary resources, which would be a good demonstration in this industry. This is also of social and economic significance in response to China government?s request on reducing consumption of resources and establishing society with economy for achieving sustainable development.

Jan 1, 2014

By Vinay Jain

Beneficiation of alumina rich iron ore slimes is a major challenge for the Indian iron ore industry. One of the methods by which this problem might be addressed is by design/screening of suitable reagents (flocculants/depressants/collectors) which act selectively towards either aluminum containing minerals (gibbsite and kaolinite) or iron bearing minerals (hematite and goethite) in order to separate them. Our earlier work indicates that separation of iron oxide minerals from gibbsite is relatively more difficult than from kaolinite. Accordingly, our research work has been focused on finding selective reagents for iron oxide ? gibbsite separation. We have performed density functional theory (DFT) computations to evaluate the interaction energies of seven different reagent groups - carboxylic acid, flotol, hydroxamic acid, phosphonic acid, iminobismethyl phosphoric acid, xanthate and starch with hematite and gibbsite surfaces. The objective was to identify if any of these groups show selective adsorption towards one of the mineral surfaces. Among all these reagents, starch exhibits the highest selectivity towards the hematite surface with a difference in interaction energy of ~63 kcal/mol between hematite and gibbsite surfaces. This is consistent with experimental findings at our laboratories on slime samples from Noamundi mines wherein it is being observed that usage of starch as a flocculant does lead to an improvement in the final grade of the ore with significant reduction in the Al-content. A binuclear complexation mechanism based on affinity between Fe and Ostarch atoms combined with a geometrical templating effect, arising out of a close correspondence between Fe-Fe distance on the hematite surface and O-O distance in starch, is proposed to explain the strong adsorption of starch on hematite surface. Keywords: slimes, iron ore, alumina, hematite, gibbsite, DFT, adsorption, flocculants

Sep 1, 2012

By Carina Ulsen

The existing construction and demolition (C and D) waste recycling technologies and standards have been essentially focused on the production and use of coarse recycled aggregates. Very few papers focus on the production of recycled sand, although some previous results show that fine aggregates fraction represents around 40 to 60% (in mass) of the Brazilian waste and it is usually used as road sub-base or disposed in landfills. The quality of the recycled aggregate is strictly related to the content of porous and low strength phases, mainly the patches of cement remaining on recycled aggregate surface. Some technologies have already been described in the literature, even though, to the moment none of these technologies has clearly succeeded in reaching the large market available. This paper presents a summary of the main properties of the sand produced from C and D waste by tertiary crushing at vertical shaft impact crusher (VSI). Additionally mineral processing technologies were applied on the attained product, such as gravity concentration by shaking table and spirals and removal of cement paste by attrition. The main properties of recycled sand are discussed and compared to the previous C and D waste, respectively: particle size distribution, particle shape, chemical composition, cement paste content and porosity. The results demonstrates that the crushing allowed producing a VSI-sand with low porosity and water absorption due to the increasing on the content of silicates from natural rock phases and increasing liberation between these phases and porous cement paste; the particles from the attained product presented also a better shape (sphericity and aspect ratio). The attrition tests assayed on VSI recycled fine aggregates accomplished a further selective disaggregation of cement paste and other porous materials - the porosity was reduced from 10% to 7%. The concentration by shaking table at narrow sieve fractions led to a product with low porosity and reduced content of cement paste, however, concentration on spirals did not succeed since separation was performed essentially by the size of the particles. The heavy product from shaking table represented almost 75% in weight and has less than 60% recovery of CaO+LOI, and expressive reduction on porosity. The aim of producing sand from construction and demolition waste through mineral processing unit operations changes the recycling approach and contributes for up cycling the recycled sand. The exhaustion of sand deposits on Brazilian large centers, the increasing price and the construction boom encourages the development of alternative materials as construction raw material. Keywords: recycled sand, construction and demolition waste, technological characterization

Sep 1, 2012

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

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

Jan 1, 2014