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By Y. H. Tang, H. Y. Zhang

"Tailings from lead-zinc mine contain plenty of dolomite and low-grade fine-grained barite, which is difficult to enrich by mineral processing. Since the density of barite and dolomite has some differences due to the fine dissemination size in a complex sedimentary, the gravity separation tests were conducted with no results obtained. The magnetic separation was conducted to remove the magnetic gangues, and the results were not satisfactory because of the gangue minerals such as limonite and others were low in content. The results of floatation tests showed that the mineral separation of barite and dolomite is quite difficult because that they have similar mineral floatability. Experimental research shows that the good results can be obtained by “desulfurizationbarite floatation” processing with the new depressant TS. The barite concentrate containing BaSO4 91.27%, BaSO4recovery is 70.25% when sodium dodecyl sulfonate serves as a collector and TS as the depressant.INTRODUCTIONBarite is an important mineral material. Often associated with other minerals, it usually needs to be separated by mineral processing in order to meet the application requirements. The main barite beneficiation methods include hand sorting, gravity separation, floatation, magnetic separation, acid leaching, etc. Usually barite associated with oxide ore such as fluorite dolomite, quartz ore etc. are also associated with sulfide ore such as pyrite, sphalerite and galena. The separation between barite and sulfide ore (such as pyrite) is easy. On the other hand, the separation between barite and oxide ore (such as dolomite and fluorite) is very difficult. There are quite a lot of reports on the separation between barite with fluorite dolomite however the separation between barite and dolomite is seldom discussed.The ore properties are quite complex attributable to mineral assemblage containing a large amounts of dolomite. As the density of barite and dolomite has some differences, gravity separation between them is usually easy. The gravity separation tests were conducted with no results obtained due to the fine dissemination size in a complex sedimentary. The magnetic separation was conducted to remove the magnetic gangues, and the results are not satisfactory as the gangue minerals such as limonite and others were low in content. Due to the fine dissemination and intimate association of minerals, and barite and dolomite contain the same group ions of Ba2+, Ca2+ and Mg2+, the results of flotation tests showed that the mineral separation between barite and dolomite by flotation means problematic. Previous studies have been conducted by several institutions but none to date has come up with a satisfactory process in dealing with the deposit. This may be attributable to: high cost of reagents; unsatisfactory performance. Therefore, the key to the flotation separation of barite and dolomite is the application of selective inhibitors. Based on previous test observations and years of extensive research experience in barite processing technology, with the new depressant TS has selectivity inhibition on dolomite developed and used, good results can be obtained by “desulfurization-barite flotation”, which allows barite in the lead-zinc tailings to a comprehensive recovery."

Jan 1, 2018

By Leopoldo Gutierrez, Esau Arinaitwe, Marek Pawlik

"The effect of various polymers, including: anionic carboxymethyl cellulose (CMC), polystyrene sulfonate (PSS), humic acids (HA) and non-ionic hydroxypropyl cellulose, on the wettability of Athabasca bitumen was evaluated through dynamic contact angle measurements using the captive bubble technique. The tests were carried out as a function of pH at a constant ionic strength (0.01 mol/L sodium chloride). The evolution of the three-phase contact angle between the solution, bitumen and an air bubble was followed as a function of time over a period of ~6 minutes. The contact angle data were modelled using a first-order kinetic equation. The results were analyzed in terms of the initial contact angle, the evolution rate constant, and the steady-state contact angle value. In the case of anionic polymers, a pronounced decrease in the initial contact angle value was observed at pH 3. Under acidic conditions, there was no significant effect of CMC observed on the steady-state contact angle value but PSS and HA significantly decreased the steady-state contact angle value. At pH 8.5. the anionic polymers did not affect the wettability of the bitumen surface but they significantly decreased the contact angle evolution rate. These results suggested that CMC is not capable of permanently lowering the hydrophobicity of bitumen, and the polymer only slowed down the evolution of the contact angle to the steady-state value. The results also showed that polystyrene sulfonate and humic acids were capable of making bitumen hydrophilic but only under acidic conditions. Only hydroxypropyl cellulose (HPC) produced a large decrease in the steady-state contact angle under alkaline conditions (pH 8.5). The kinetics of contact angle evolution in the presence of HPC was also drastically lowered. The results were discussed in terms of the chemical composition of the polymers and their different affinities towards the bitumen surface."

Jan 1, 2014

By Markus A. Reuter, Antoinette van Schaik

"INTRODUCTIONGoods and products, such as passenger vehicles, are manufactured by using a wide spectrum of different raw materials to meet highest consumer requirements during use. Due to the time-varying composition and complexity of multi-component products such as cars, recycling is complicated. It involves a network of interconnected processes and material and energy flows. Improving the efficiency of the material cycle of the car to comply with the recycling targets as imposed by EU legislation, requires insight into all aspects influencing the closing of the material cycle (dynamics, technology, economy, legislation, etc.) and their mutual relation. In order to define the link between recycling end-of-life products, their changing composition and design a dynamic model was developed for the resource cycle of cars. The model integrates the optimisation of the material cycle with the dynamic behaviour of recycling systems."

Jan 1, 2003

By E. V. Bratygin, S. P. Elnikova

"In the article carrying out technique of experiments for estimation of power efficiency of process of crushing in cone crushers «in a layer». The conformity of the granulometric characteristics of the crushed products obtained as a result of the tests, the theoretical equations for the size characteristics, and the choice of the optimal equation for the prediction of the granulometric characteristics of the final products obtained by crushing ""in a layer"". Optimization of granulometric composition of power of crushers working ""in a layer"" is carried out with the purpose of reduction of the electric power consumption at reception of a product of required quality. As a result of the experiments, dependencies are obtained, the relevance and applicability of the crushing process ""in the layer"" for obtaining crushed stone of improved quality is proved. INTRODUCTION A number of equations have been proposed for calculating the breakage energy. These include equations by Kirpichev and Kick, Rittinger and Bond (Bogdanov, Olevsky, 1982). Another equation for calculating the specific breakage work in breakage by impact and in stratum was proposed by Devyatkin (Boiko, 2003). In these equations, the breakage energy is proportional to the particle size raised to some power. In the equation proposed by Devyatkin, the ore piece thickness or the feed average diameter is used. The relationship between energy and breakage can be expressed as an equation (Lynch, 1981; Tikhonov, no. 3, 2008) where k is a coefficient characterizing the energy parameter depending on the strength of the feed, l is size in microns. The Rittinger formula is obtained for n = 2, the Kirpichev-Kick formula for n = 1, the Bond formula for n = 1.5. For n = 3 or higher, the equation describes fine and ultrafine grinding. R. Hookey proposed a formula (Lynch, 1981, Tikhonov, no. 3, 2008), where the size exponent n is substituted by a size function In all of the above equations, a single value of the feed and product size is used; for example, in the Bond equation, size is defined as the particle size of the 20% oversize (P80 and F80). However, a single size value can represent multiple distributions, making that the Bond method inappropriate for determining the size (Lynch, 1981). Describing an equation for estimating the grinding energy will allow to design the electric drive and ore preparation circuit for the given breakage method."

Jan 1, 2018

By A. A. Novoselov, U. Kelm

"Large volumes of mine tailings accumulated in surroundings of porphyry copper deposits represent a growing threat to environment. They contain significant concentrations of toxic metal and metalloids which can contaminate river runoff, ground waters or can be transported by wind. Both extreme pH of fluids in tailings impoundments and high surface areas of processed mineral grains provide their increased reactivity. As a result, during only a few decades, As, Cu, and Mo can be mobilized, redistributed through the tailing column and accumulated through post-deposition leaching, evaporation and contamination with natural fluids. Those processes are reflected in the forming of secondary minerals. Gypsum, Fe oxides/hydroxides, efflorescent salts and clay minerals are typical alteration products in tailings. Here we present the results of reactive transport simulations implemented on the base of PHREEQC and SUTRA codes. The one-dimension model emulates the mass balance between rainfall, evaporation and subsurface runoff, the kinetically- and thermodynamically-driven dissolution of tailing minerals, advective and diffusive transport of tailing fluids, and precipitation of secondary phases. A typical tailing column is composed of four unequal layers with predominance of (i) evaporation, (ii) secondary mineralization above, (iii) below water table, and (iv) near the bottom of dump. Those horizons are characterized by contrasting pH, chemical composition and bulk mineralization of pore fluids, distinct accessibility of atmospheric oxygen and, as a consequence, distinct intensity of sulfide oxidation. The modeling and its verification on Chilean tailings impoundments reveal the complexity and high rates of secondary mineralization. The accumulation of toxic alteration products is controlled by fluid transport through the tailing column induced by both rainfall/evaporation and exchange with subsurface runoff. The geochemical modeling is a powerful approach which allows comparing the processes in tailing deposits produced by distinct flotation regimes and providing the long-term predictions of their environmental impact as well as identifying sectors of tailings for possible re-processing."

Jan 1, 2018

By Kaiwen Liu

Activated carbon is widely used in the removal of organic and/or inorganic contaminants from waste water due to its high surface area, porous structure, and specific surface reactivity. However, in practical applications, it is difficult to recover the activated carbon completely by screening or classification. In this project,we prepared a magnetic form of activated carbon (magnetic activated carbon or M-AC) by precipitation of iron oxides on the surface of activated carbon. The M-AC can be easily separated from effluents by applying an external magnetic field, thus it can be recycled and regenerated for reuse. M-AC was characterized by X-ray diffraction (XRD), specific surface area measurement, and scanning electron microscope (SEM).XRD results show that the major phase of coated iron oxides on activated carbon is magnetite (Fe3O4). The specific surface area of activated carbon was found to be reduced after the impregnation of magnetite particles on the surface. The SEM micrograph shows the aggregation of the iron oxides on the surface of activated carbon. M-ACwas found effective in removing DETA (diethylenetriamine) species and metal ions from solutions. Cu (II) with initial concentrations from 5 ppm to25 ppm in solution is removed by more than 99% with the addition of 0.1 wt.%ofM-AC. For the removal of 25 ppm DETA species from solution, an addition of 0.5 wt.% of M-AC is required due to the larger size of the DETA molecule. Moreover, M-AC showed a good loadingproperty for nickel and gold ions from solutions. M-ACshows a better adsorption capacityover activated carbon and its potential applications in carbon-in-pulp for gold leaching and waste water treatment. Keywords: magnetic activated carbon (M-AC),diethylenetriamine (DETA),metal ion,adsorption

Sep 1, 2012

By P. Somasundaran, Tarun Bhambhani, D. R. Nagaraj, P. Patra

"Certain non-sulfide gangue minerals are known to have a detrimental impact on flotation performance. When present in large amounts, they can negatively affect recoveries, grades and throughput at current operations, and dictate the viability and economics of a greenfield project. While the problem has been investigated for a long period of time, a scientific understanding of the mechanisms by which these minerals affect performance has not been obtained, and no acceptable solutions have been developed. This study focused on the role of physical aspects (e.g. shape, size and morphology) of these minerals as the underlying factors for poor performance. Flotation tests were conducted using model mineral systems to understand the impact of one phyllosilicate mineral (muscovite) on flotation kinetics, recoveries and grades. The study reveals that there is minimal impact on flotation kinetics, no impact on recoveries, but a very strong detrimental impact on concentrate grade. The traditional mechanisms of transport such as true flotation and entrainment are not sufficient in describing the extent of transport. The transport is attributed to the unique platy morphology of muscovite, which allows for action of buoyancy forces. Data also shows that the muscovite transport to the froth phase depends on particle size; coarser sized muscovite (100-150@) report to the froth phase in much larger amounts than medium sized muscovite (50-100@). At finer size fractions (<50@) the transport is also increased, and this is likely due to entrainment."

Jan 1, 2014

By Scott C. Brown, Brij M. Moudgil, Ivan U. Vakarelski

The manipulation of the apparent hydrophobicity of particlute surfaces is necessary to achieve optimal selectivity in flotation processes. Previously a number of works have investigated the role of microscale surface and particulate morphologies on chemically modified substrates. These works have suggested that microscale surface asperities lead to an increase in flotation efficiency by assisting in the rupture of wetting films. Yet, in mineral processing the presence of surface asperities may lead to a reduction in flotation. The reason for this may-in part-be due to the presence of nanoscale irregularities at the interface. In this work, it is proposed that the presence of roughness at the nanoscale may have a dominant impact on the apparent hydrophobicity of mineral surfaces during flotation. It is suggested that as inter-asperity seperation distances are reduced capillary effects are enhanced for high energy mineral surfaces leading to the formation of liquid domains, which adversely impact hydrophobicity. In addition, as these distances approach the surfactant headgroup size obstruction of surfactant self-assembly process may occur, thereby further limiting flotation.

Jan 1, 2003

By Valentine Chanturiya1

We have developed a classification of geochemical barriers according to their origin, i.e. natural and artificial, and according to methods and areas of application. There has been an examination of the interaction between different classes of geochemical barriers with sulfate solutions containing nickel, copper and iron. As natural barriers, carbonates (calcite and dolomites) were used. For artificial barriers, a mixture of serpentine and carbonatite, thermo-activated copper-nickel dressing tailings, and a magnesium-containing sorbent based on brucite was used. Keywords: geochemical barriers, physical-chemical geotechnologies, treatment of natural and waste water, recovery of nonferrous metals

Sep 1, 2012

By David I. Verrelli, Peter T. L. Koh

"Recent experimental measurements of induction time made by direct observation with the ‘Milli-Timer’ indicated that angular particles were able to attach much more rapidly than spherical particles. There was around a tenfold difference in the respective induction periods for particle-bubble attachment. For industrial application, a more holistic comparison is needed, with the induction period for attachment being just one input. Over the years, CSIRO has developed a CFD-flotation model that incorporates both rigorous hydrodynamics, to simulate real industrial cell geometries, and a detailed model of the embedded flotation process, in which the induction period is an important parameter. We conducted transient modelling of batch flotation. First, spherical particles were modelled, as a ‘baseline’, for different particle sizes and levels of hydrophobicity. In the second set of results, the induction period was decreased by a factor of up to ten, simulating flotation of angular particles. Flotation recovery was found to depend upon induction period in a complex manner. For highly hydrophobic or fine particles, the induction period for spheres was already so low that recovery was limited by other factors (e.g. bubble-particle collision frequency). Further decreases in induction period, as for angular particles, did not have a significant effect on recovery in these cases. By contrast, when weakly hydrophobic or coarse particles were modelled, the recovery was predicted to be greatly enhanced for angular particles, in comparison to spheres. For these particles the induction period was limiting recovery, so that the flotation rate constant could be improved directly by reducing the induction period. This is consistent with batch flotation experiments using Ballotini reported earlier. Therefore, when dealing with weakly hydrophobic particles or relatively large particles that are to be floated, an enhancement can be expected for more angular particle shapes. In such cases, judicious specification of the grinding circuit may improve the overall efficiency."

Jan 1, 2014

By Masakazu Niinae, Tasuma Suzuki, Mai Moribe, Yohhei Okabe

Bench-scale electrokinetic experiments were performed to elucidate the electrokinetic remediation mechanisms of arsenate from artificially contaminated kaolinite. The electrokinetic experiments in which a constant voltage was applied demonstrated that high soil pH favored arsenate remediation with respect to both the remediation time and electricity consumption. It was also demonstrated that applying a pulse voltage (1 hour ON, 1 hour OFF) significantly improved the electricity consumption efficiency when the soil pH was maintained at the initial value during the experiments; this trend was not observed when the soil pH was gradually increased from the cathode side. These electrokinetic experimental results indicate that the remediation rate-limiting step varied with soil pH. When the soil pH was maintained at the initial value of 7.2 during the experiments, arsenate desorption was the remediation rate-limiting step rather than the migration of dissolved arsenate toward the anode. Conversely, when the cathode pH was not controlled and the soil pH was correspondingly increased gradually from the cathode side, the migration of hydroxyl and desorbed arsenate ions toward the anode played a more important role in the control of the overall remediation efficiency.

Jan 1, 2014

By M. Schneider, J. Regler, Th. Neesse, AKW A. + V GmbH & Co., J. Dueck, F. Donhauser

"In practice the advantages of high-quality hydrocyclone separation are often reduced due to varying feed suspension properties, solids concentrations and particle size distributions. Therefore, a new control system for a battery of hydrocyclones with a nominal diameter of 150 mm was developed for bentonite slurry regeneration associated with tunnel excavation using bentonite slurry as a transport aid and lubricant.As can be seen from Fig. 1, the hydrocyclone battery has been modified for regulation purpose. The battery was manufactured with an overflow collector as a closed pressure chamber (1) with a discharge pipe (2) where the throttling valve (3) was installed.With increased stepwise throttling of the overflow, the volume split is changed with the effect that the solids discharge in the underflow is increased. To stabilize the total throughput, the feed pump speed is simultaneously increased so that the pressure drop ?p across the hydrocyclones (9) remains approximately constant. However, this causes the increasing pressure inside the hydrocyclones, which results in a further intensification of the underflow discharge. After the detection of the break through of the air core (transition state) by the capacitive sensor (4), the throttle valve is shortly opened, and a new regulation interval can start again. The control concept is focused on maintaining the optimum operating state, characterized by the underflow discharge shape at the transition state between rope and umbrella discharge."

Jan 1, 2003

By Ray Everson, Henry Kasaini

"Adsorption of Pd (II) anions on the surface of activated carbon (Norit 0.8) occurred at high proton concentration (0.01 – 2.5M, HCl) in the feed and averaged 27 mg/g. The adsorption process was interpreted in terms of surface ionisation and adsorption model. Enthalpy of adsorption averaged 0.4 kJ/mole indicative of an instantaneous physical adsorption process. We found that the Toth isotherm fit the adsorption data fairly accurately. A combination of the Langmuir and Freundlich equations yields an effective three-parameter Toth equation (1) which is frequently used to describe adsorption on heterogeneous surfaces.Figure 1 shows the comparison between experimental results and the model isotherms. We found that Langmuir isotherms underestimated the adsorption capacity on the porous surface while the Freundlich isotherm overestimated adsorption. Furthermore, the surface coverage at equilibrium was well described by both the Langmuir and Toth isotherms. But, Freundlich isotherm predicted a surface fraction coverage that was higher than unit. Based on better prediction of surface coverage and a reasonable fit to adsorption data, we concluded that the Toth isotherm best described the adsorption data of palladium. The adsorption process was limited by mass transfer resistance through the external film. We estimated the rate constant from equation (2), where e, ?b, and rp are porosity, fluid density and particle radius, respectively"

Jan 1, 2003

By Yuriy V. Gulyaev, Galina V. Sedelnikova, Valeriy D. Lunin, Valentin A. Chanturiya, Igor J. Bunin

"Probable mechanisms of disintegration of mineral particles in gold-containing sulphides and benefication products exposed to high-power electromagnetic pulses are discussed. Experimental data are presented to confirm the formation of breakdown channels and selective disintegration of mineral complexes as a result of pulse irradiation, which makes for efficient access of lixiviant solutions to precious metal grains and enhanced precious metal recovery into lixivia during leaching. Experiments with different gold-containing products revealed a synergetic effect of high-power electromagnetic pulses with widely varying parameters and moisture in mineral pores on breaking-up and gold extraction processes for various resistant goldcontaining mineral products.Several series of tests performed in IPKON RAS, IRE RAS and TsNIGRI yielded an absolute gain in precious metal recovery, up to 30-80 % for gold and 20-47 % for silver, with resultant gold recovery as high as 90 %. An essentially new, environmentally safe and energy-saving breaking-up technology has been developed for resistant gold-containing products. This new method would shorten the way from raw minerals to final products and help significantly reduce the cost of these products as it obviates the necessity for using the expensive procedures of energy-intensive and environmentally hazardous oxidative roasting and autoclave breaking-up for ore concentrates."

Jan 1, 2003

By Dilip Kumar Mohanty

In today?s world, Sustainability is the key issue before the mankind. With the ever-increasing population & unimaginable boost in industrial growth to cope up with a steady increase in demand and fast change in life style of a human being, the natural resources are exploited to such an extent that the very existence of living beings in this earth planet is threatened. In such devastating situation, the concept of Sustainability emerges out as a great savior. This concept focuses on minimum/ judicious use of natural resources, thereby preserving the resources for future generation while meeting the bare minimum requirement of the present generation. For an emerging economy like India, Mining and Mineral based industries form the back bone of our economic development. Thus, sustainability of mining and mineral processing industry has a far reaching impact on sustainable economic development of our nation. While at a macro-economic level, we have to strike a balance between economic development vis-à-vis socio-economic & environmental impacts, Industries have to ensure judicious and frugal use of natural resources by making use of energy efficient plants & machineries and adopting befitting technology for reduction & recycling of waste. In the context of the above, it would be interesting to look into the sustainability measures taken up by National Aluminium company (Nalco) at its Crushing & conveying plant at Panchpatmali Bauxite Mine, which is incidentally Asia?s largest Bauxite Mine. In the backdrop of the above stated facts, in this paper the authors make an attempt to bring out the sustainability issues in areas of energy conservation, environmental impact/pollution vis-a-vis mitigation measures adopted in crusher & conveyor plant of Panchpatmali Bauxite Mine & CSR / peripheral developmental activities undertaken by Nalco to mitigate the socio- economic impacts. Keywords: sustainability, energy efficiency, recycle, csr, peripheral development

Sep 1, 2012

The flotation of nickel sulphide minerals is normally difficult in the presence of serpentine minerals due to the coating of serpentine particles on the nickel mineral surface. To improve the flotation, dispersants such as polyphosphate and carboxy methyl cellulose are normally used to remove the slime coating. However, in the flotation using high ionic strength process water, these dispersants are invalid due to their ionic nature. In this study, a new type of non-ionic dispersants, Pluronic triblock copolymers were examined with an objective of improving the flotation of ultrafine pentlandite (a nickel sulphide mineral) in the presence of lizardite (a serpentine mineral) in saline water. Three Pluronic triblock copolymers varying in solubility and hydrophile-lipophile balance (HLB) values were studied by flotation tests, settling tests and froth measurement. It was found that two of the copolymers improved pentlandite flotation against lizardite, and one copolymer deteriorated the flotation. The effect of Pluronic triblock copolymers on the flotation was actually linked to their dispersibility and foamability, which were governed by their physical properties. The two copolymers with a higher solubility or HLB value produced more stable mineral suspensions and more stable froth in the flotation resulting in better nickel grade and recovery in both rougher and cleaner flotation. Keywords: ultrafine particle, flotation, slime coating, dispersion, saline water, triblock copolymers

Sep 1, 2012

By R. Hejazi, Saghaeian. M., H. Abedini

Continuous vacuum belt filters mainly carry out an important duty in the solid-liquid separation processes such as iron ore concentrate dewatering. However as the particles become finer, the resistance to filtration and dewatering would increase and as the result cake moisture content tends to increase. So in recent decades, using additives in order to improve the filtration performance has been considered by many researchers. In the present study, the effect of several surfactants on the filtration rate and cake moisture content of Chadormalu iron ore concentrate (80% =40 micron) was investigated using a laboratory scale vacuum filter. The results of several tests indicated that a non-ionic surfactant (Lauryl Alcohol Ethoxylated, LAE) has the best performance on reducing the moisture content of the cake and reducing the cake formation time. The optimum dose of LAE was found to be 300 g/ton which reduced the concentrate cake moisture content from 13.76 to 11.28% (wet weight base). Some industrial filtration tests were performed in Chadormalu iron ore concentrate plant to prove the effectiveness of this surfactant. The surfactant is mixed with water and added to the concentrate slurry before distributing on the vacuum belt filter. The industrial and experimental results were almost similar, so that adding about 300 g/ton of LAE would reduce the final cake moisture content from 12.87 to 10.76%.

Jan 1, 2014

By Ben Murphy, Alejandro Yanez, Tatu Miettinen

"Flotation using large volume cells has grown in importance during recent years, particularly given the increasing demand for minerals whilst ore grades are decreasing. Outotec introduced the TankCell® e300 in 2007 to enable concentrator plants to process these higher tonnages. From the beginning, TankCell® e300s with FloatForce® mixing mechanisms have demonstrated good metallurgical performance with decreased operating costs and high availability. This paper deals with specific engineering challenges that need to be considered when installing these units rather than giving examples of performance. Today there are over 100 TankCell® e300s operational worldwide. As more of these units are installed new technical challenges are encountered and solutions developed to maximize their productivity. Lessons have been learnt by operators, engineering companies and the cell manufacturers on how best to design and layout these cells in modern concentrators to ensure smooth transition from design to installation to operation. This paper presents information on important design considerations and learning that has been obtained through the design, installation and commissioning of the TankCell e300 around the world. Areas pertaining to cells layout such as feed and discharge arrangements along with items of metallurgical concern such as sampling, reagent addition and the potential benefits of installing a variable speed drive on the motor will be covered in depth."

Jan 1, 2014

By A. Güney

Currently, recycling technologies use relatively homogeneous plastics because hand-sorting waste feed is too expensive. Many promising technologies for separating mixed thermoplastics are being investigated, but they are still uneconomical and unreliable. Burning plastics for recycling is not used because of poisonous gases released when their burning. PET and PVC cannot be separated using conventional gravity separation techniques because their specific gravities overlap; PET density changes from 1.33 g/cc to 1.37 g/cc and PVC density is between 1.32 g/cc and 1.37 g/cc. For this reason, plastic recycling needs new techniques. Among these techniques froth flotation, also used in mineral processing, can be useful for its cost and simplicity. In this method, a plastic is selected from mixture, tried to regain its natural property, hydrophobicity. In this study the experiments were applied by using plasticizer reagents to make the selected plastics hydrophobic and us-ing NaOH to render the other hydrophilic. Post-consumed PET and PVC are evaluated by concerning the effects of selected parameters (particle size, concentration of plasticizer reagent, amount of NaOH, conditioning time and the effect of conditioning temperature). At the end of the experiments, optimum parameters for selective flotation of PET from PVC was found as particle size of -4.76 + 3.36 mm, NaOH amount of 30 kg/t, conditioning temperature of 75°C, conditioning time of 30 minutes, reagent amount of 300 mg/L. Consequently, PET was re-covered with 99.7% purity and 57% efficiency.

Jan 1, 2014

By J. Jávor

The response of the air/water interfaces to deformation in presence of surfactants is affected by the adsorption/desorption rate, re-orientation and exchange rate of surfactant. These surface properties can be observed using equilibrium and dynamic surface tension and surface elasticity measurements. However, the effect of these parameters on bubble size in dynamic conditions has not been studied due to the difficulty in capturing freshly formed bubbles in dynamic conditions. The paper presents a new experimental set-up designed and built at the Aalto University, called Shear Force Observation Chamber(SOC). The setupallows the monitoring and analysisof freshly formed air/liquid interfaces in dynamic conditions and facilitates the study of the effect of dynamic surface tension and surface elasticityon freshly formed air bubblesin presence of surfactants. The method helps to establish correlation between bubble size and dynamic interfacial properties and bubble-bubble interaction in turbulent flow. Dowfroth 200, Nasfroth 240 and Dowfroth 250 commercial flotation frothers were tested in this study. The results show a marked difference between results obtained in dynamic conditions compared to the static conditions. The results are presented and the reasons and implication to flotation modelling are discussed in the paper. Keywords: shear force observation chamber, flotation frothers, flotation bubbles, critical coalescence concentration

Sep 1, 2012