Minerals Engineering 39 (2012) 133–139
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Recovering molybdenite from ultraﬁne waste tailings by oil agglomerate ﬂotation Fu Jiangang, Chen Kaida, Wang Hui ⇑, Guo Chao, Liang Wei School of Chemistry and Chemical Engineering, Key Laboratory of Resources Chemistry of Nonferrous Metals, Ministry of Education, Central South University, Changsha, 410083, Hunan, People’s Republic of China
a r t i c l e
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Article history: Received 14 March 2012 Accepted 9 July 2012 Available online 4 October 2012 Keywords: Oil agglomerate ﬂotation (OAF) Molybdenite Waste tailings Recovery
a b s t r a c t Neutral oils like kerosene, diesel, transformer and rapeseed oil were used as collectors or bridging reagents in conventional ﬂotation and oil agglomeration ﬂotation (OAF) process, and a promising OAF process has been developed for the recycling of ultraﬁne molybdenite resources from the waste tailings. p a The average size of collected particles (d50 ), agglomerates (d50 ) and their distribution of the froth concentrate were determined by laser particle size analyzer or sieve analysis. Conventional ﬂotation froth cannot catch the ultraﬁne particles, so it is an ineffective process to recover molybdenum metal in the waste tailings, while OAF has some advantages to recover ﬁne minerals. And the best result was obtained from transformer oil due to its appropriate length of carbon chain, kinematic viscosity and cyclical structure. The oil amount plays a very important role on average size of the particles, with the increase of transa p former oil from 2.0 to 13.8 kg/t, d50 increases from 0.15 to 0.68 mm and d50 decreases from 9.06 to a p 2.05 lm. This ﬁnding suggests the bigger the d50 , the smaller the d50 , and the higher the recovery of molybdenite. The appropriate conditions for recovering ultraﬁne molybdenite were determined as follows: dosage of frother: 0.5 kg/t, natural pH: 6.2, stirring time: 3 min, and stirring intensity:400–600 r/min. Lastly, the closed cycle test and industrial application in the producing scale of 500 t/d were carried out, and result shows 95% molybdenum was recovered with a satisﬁed grade of 22.62%. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction During conventional molybdenite ﬂotation practice, regrinding and multi-stage cleaner are adopted to obtain satisfactory grade and good recovery in molybdenum concentrate. However, because greater size reduction is necessary to liberate the minerals, ﬁne and ultraﬁne rougher or cleaner tailings are inevitably generated in the process (Ansari and Pawlik, 2007; Rubio et al., 2007; Triffett et al., 2008), and these tailings would cause numerous problems in concentration stage and other treatment stages. Since the conventional beneﬁciation techniques like froth ﬂotation and gravity concentration processes are inefﬁcient in the ultraﬁne size range (Sivamohan, 1990; Sönmez and Cebeci, 2003a; Miettinen et al., 2010), a signiﬁcant amount of molybdenum is inevitably lost in waste tailings and discharged to tailings pond. Therefore, the treatment of waste tailings by ﬂotation is an important subject of interest to researchers and engineers. This could potentially conserve the mineral resources and reduce environmental waste. The reuses of waste tailings are investigated in many countries, which have a signiﬁcant advantage in terms of increasing metal productivity and reducing the amount of waste to be rejected ⇑ Corresponding author. Tel./fax: +86 731 88879616. E-mail address: [email protected]
(W. Hui). 0892-6875/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mineng.2012.07.006
(Szymocha, 2003; Valderrama and Rubio, 2008; Ercikdi et al., 2010). The conventional methods used in China to recover molybdenum from middlings are mainly hydrometallurgical leaching processes, such as sodium hypochlorite oxidation method, chlorine-alkali method and electro-oxidation method (Zhu et al., 2000; Feng, 2008; Xu et al., 2010). Unfortunately, hydrometallurgical processes are not applicable to deal with lower grade waste tailings, because preconcentration is almost unnecessary before chemical processes. Flotation is considered as the best process route for metal enrichment in the mining industry due to its wide range of application and ease of operation and implementation, and the conventional beneﬁciation methods are inefﬁcient in the sub-sieve size below 38 lm. Therefore, column ﬂotation, carrier ﬂotation, selective ﬂocculation and oil agglomeration methods have been developed to recover ﬁne particles (Subrahmanyam and Forssberg, 1990; Cebeci, 2003; Sadowski and Polowczyk, 2004). In these methods, oil agglomeration has some advantages, i.e. simplicity of operation and high recovery (Rossetti and Simons, 2003; Sönmez and Cebeci, 2003a; Valderrama and Rubio, 2008). The oil agglomeration is based on differences in surface properties between the mineral particles. Oil agglomerate ﬂotation process can be considered as a combination of oil agglomeration operation and froth ﬂotation. In this beneﬁciation process, most of the liquid
F. Jiangang et al. / Minerals Engineering 39 (2012) 133–139
hydrocarbons, e.g. kerosene, diesel oil, other petroleum derivatives and vegetable oil, can be used as bridging reagents that is utilized to improve ﬂoatability of ultraﬁne particles by increasing the particle size. Therefore, when small amounts of oil are introduced into agitated slurry, the hydrophobic particles become oil-coated and stick together to form agglomerates, while the hydrophilic particles remain unaffected, and then the agglomerated products can be separated from the suspension by simple froth ﬂotation operation. The basic principles of oil agglomeration and effects of various operating parameters have been investigated by many researchers, and the technique has been used in the mineral industry for the puriﬁcation of coal from sulphur and ashes (Mehrotra et al., 1983; Laskowski and Yu, 2000; Gray et al., 2001; Aktas, 2002; Alonso et al., 2002; Cebeci and Sönmez, 2002, 2006; Sahinoglu and Uslu, 2008), recovery of ﬁne sized gold from ores (Moses and Petersen, 2000; Sen et al., 2005; Valderrama and Rubio, 2008), agglomeration of oxide such as barite (Sönmez and Cebeci, 2003a, 2004), calcite (Sönmez and Cebeci, 2003b; Cebeci and Sönmez, 2004a) and celestite (Cebeci and Sönmez, 2004b) for the separation process, improving the quality of waste-derived char (Hwang et al., 2008), removal of impurities from wastewater (Huang and Fang, 2001; Kang and Shin, 2006) and de-inking of paper (Azevedo and Miller, 2000). To sum up, most of the oil agglomeration studies have been performed with natural hydrophobic particles such as coal and natural gold, but there is nearly no research on oil agglomeration of waste ﬁne mineral tailings. In this study, the oil agglomeration ﬂotation (OAF) process was efﬁciently conducted to recover ultraﬁne molybdenite from waste tailings in industrial scale, and some concrete and appropriate agglomeration conditions had been determined. Therefore, the aim of this work is to obtain a molybdenum concentrate at satisﬁed grade for the next chemical processes with metal recovery as large as possible, and discuss some concerned physico-chemical problems.
2. Materials and methods 2.1. Tailings Samples used in this study were taken from an obsolete molybdenite tailings reservoir (The total inventory quantities of tailings have exceeded 4 million tons) in Zhejiang province, China, and the chemical analysis results are given in Table 1. Those waste tailings had been produced since 1950s, and because of the low-level technological equipments used in the past, they contain a substantial amount of Mo (1.04%). Obviously, such a large amount is worth recovering. The analysis indicates that main components of the tailings are silicate, calcium-bearing minerals (mainly is calcite), iron-bearing minerals, alumina magnesia minerals and some sulﬁde minerals like pyrite. The phase analysis of the tailings indicates that molybdenum mineral mainly occurs as sulﬁdes (98.08%) and only 1.92% amount as molybdenum oxide. Particle size analysis was conducted using standard laboratory wet and dry screening methods. Table 2 shows the particle size and molybdenum distribution of the tailings. As expected, the tailings Table 1 Composition analysis results of the tailings. Components
Table 2 Particle size analysis and molybdenum distribution in the tailings. Size fraction (mm)
Grade of Mo (%)
Distribution of Mo (%)
+0.28 0.28 + 0.125 0.125 + 0.076 0.076 + 0.045 0.045 + 0.038 0.038 Total
2.11 7.69 8.17 10.32 3.66 68.06 100.00
0.13 0.19 0.22 0.36 0.68 1.39 1.04
0.26 1.40 1.72 3.56 2.39 90.67 100.00
exhibit a wide distribution in particle size, and 68.08% of the mass is ﬁner than 38 lm, the d50 (mean diameter) of the tailings is 10.99 lm (Fig. 3). The size of 90.67% molybdenum particles in the tailings is less than 38 lm. 2.2. Chemicals and Instruments In the experiments, kerosene, diesel, transformer and rapeseed oils were used as bridging reagents, respectively. JSR1302 Oil Density Measuring Instrument (JingShi Chem. Eng. Instrument Ltd, Hunan), TSY-1109 Viscosity Measurement (TeAn Ltd, Dalian) and K-11 Tensiometer (SiberHegner Ltd, Hong Kong) were used to determine density, kinematic viscosity and surface tension of these bridging oils, respectively. Pine oil was used as the frother. All oils were industrialized chemicals. In addition, analytical grade calcium oxide (CaO) was used as pH regulator. The physicochemical properties of the bridging reagents are given in Table 3. 2.3. Methods Oil agglomeration experiments were conducted in a 2 L glass vessel with two bafﬂes at the border to create turbulence by using a mechanical stirrer, and prior to the oil addition, the tailingswater mixture was agitated for 2 min at a stirring speed. In each experiment, the oil was injected into the slurry, and then suspension was conditioned before agitation speed to agglomerate molybdenite particles. After these, the pulp was transferred to a XFD-1.5 L ﬂotation cell (Changchun, China), and further conditioned for 2 min, and the agglomerated products were concentrated as a rougher froth product for the subsequent ﬂotation. Similarly, conventional ﬂotation experiments were directly conducted in XFD-1.5 L and XFD-1.0 L ﬂotation cell but without the process of oil agglomeration. Either conventional ﬂotation or OAF, the rougher pulp consistency was ﬁxed at 30%. After ﬁltration, both froth concentrate and ﬁnal tailings were dried in a vacuum oven and then weighed for further analysis and mass balance calculation. The particle size distribution of the raw tailings and froth concentrate were determined by two methods. The average size of a agglomerates (d50 ) was determined using a sieve analysis aiming at the directly dried agglomerates, while the average size of minp eral particles (d50 ) determined using Mastersizer 2000 laser particle size analyzer (Malvern Instruments Ltd. United Kingdom) by dispersing the froth particles in absolute alcohol. In order to get accurate information of the agglomerates, the dried concentrate were soaked and cleared with gasoline1 repeatedly, and the washed concentrate were dried again and then sonicated for 10 min before the measurement. In addition, the morphology of the concentrate was examined with a scanning electron microscope (FEI Sirion 200 FEG SEM). 1 Ethanol and gasoline have a good miscibility, i.e. can be dissolved in any proportion under anhydrous condition, while miscibility of diesel oil in ethanol is worse than gasoline.
F. Jiangang et al. / Minerals Engineering 39 (2012) 133–139 Table 3 Physico-chemical properties of the bridging oils. Oil type
Density (kg/m3, 20 °C)
Kinematic viscosity (mm2/s, 40 °C)
Surface tension (mN/m)
Length of carbon chain
Kerosene Diesel Transformer oil Rapeseed oil
800 840 895 915
1.6 3.7 11.5 13.3
24.0 27.2 29.5 27.3
C12–C15 C15–C18 C16–C23 C16–C22
n-Alkanes n-Alkanes Cycloalkanes Unsaturated fatty acid
3. Result and discussion 3.1. Conventional ﬂotation and oil agglomeration ﬂotation The conventional ﬂotation and OAF tests were carried to observe their differences. Kerosene, diesel, transformer oil and rapeseed oil act as both collector and bridging oil, and the test ﬂowsheet is shown in Fig. 1. The dosage of frother was ﬁxed at 200 g/t in conventional ﬂotation. The conditions of OAF were ﬁxed as follows: stirring speed is 800 r/min, stirring time is 5 min and frother dosage is 500 g/t. The ﬂotation results are presented in Fig. 2. The oil amount plays a signiﬁcant role in the recovery of ultraﬁne molybdenite. As shown in Fig. 2, during conventional ﬂotation, though the oil amount was increased to 1.0 kg/t, it forms loose and friable froth or just a little ﬂocs in the ﬂotation cell, because oil cannot act as bridging reagent but just as collector. Such friable mineral-bearing bubbles are very weak, and cannot be recovered completely. In a word, it is hard to be taken as an effective process to recover the molybdenum metal in waste tailings by conventional ﬂotation, because the molybdenum recovery is less than 7.4% when the collector amount is below 1 kg/t. It is well known, molybdenite has natural hydrophobic property. The important question arises why the conventional ﬂotation is not effective for the molybdenum recovery? It is attributed to the mineral particle size. Fig. 3 shows the particle size and distribution of the raw tailings and froth concentrate. As shown, the averp age size of mineral particles (d50 ) in conventional ﬂotation froth concentrate using transformer oil as collector is 10.52 lm, which is close to the raw tailing’s particle size, while the average particle size of OAF concentrate are less than 5.92 lm, and the lowest one is 2.05 lm when transformer oil is used as the bridging reagent. Therefore, it can be inferred that the conventional ﬂotation froth
Fig. 2. Contrast test of conventional and oil agglomeration ﬂotation.
could not recover the ultraﬁne molybdenite particles, but OAF was able to do it. SEM images of conventional ﬂotation concentrate showed that the recovered molybdenite particles are mostly granular and varied size particles with loose structure (Fig. 4a and b). The granular particles are not molybdenite since MoS2 is layered sulﬁde, which indicated that the conventional ﬂotation recovers only a low-grade molybdenite concentrate. Also, the pulp level has to be elevated to meet the scraping requirements to recover loose and friable froth during conventional ﬂotation. On the other hand, OAF concentrate were scraped out from the cell much more easily, and the froth products have ultraﬁne platy shaped particles. These platy shaped particles are believed to be molybdenite, which have layered structure (Fig. 4c and d). 3.2. Type and amount of agglomeration oil
Fig. 1. The ﬂotation test ﬂowsheet.
We have found that the molybdenite tailings can be agglomerated successfully with any of the oil used in this study. Unfortunately, the increase of vegetable oil (rapeseed oil) only has little effect on molybdenum recovery, as presented in Fig. 2. The beneﬁt of naphthenic vs linear chain oils can account for this phenomenon (Smit and Bhasin, 1985). The fundamental ingredients of rapeseed oil are unsaturated fatty acids, e.g. erucic acid, oleic acid and linoleic acid, and they are always used as the collectors of gangues, especially for calcium, iron, aluminium, magnesium bearing minerals. When rapeseed oil is used as the bridging oil, the gangue particles tend to adsorb on the oil droplets, preventing their coalescence. The surface of agglomerates are mostly occupied by gangue minerals, which are the main components of the tailings; while molybdenite particles mostly remain in the water phase and do not attach to oil droplets, so they are not recovered. Obviously, the other three oils can be successfully used in the molybdenite OAF. The molybdenum recovery increases rapidly with increasing the amount of bridging reagent from 2.0 to
F. Jiangang et al. / Minerals Engineering 39 (2012) 133–139
Fig. 3. Particle size distribution of the raw tailings and froth concentrate.
Fig. 4. Product SEM images obtained in conventional and oil agglomeration ﬂotation.
6.9 kg/t and then it does not change reasonably at higher amounts. On the other hand, too high concentration of bridging oil in the solution would reduce the grade of ﬁnal concentrate. Considering the recovery and grade relationship for molybdenite, the suitable dosage of bridging oil was determined at 12–14 kg/t (ﬁrst rougher is 10–12 kg/t and second rougher 2 kg/t). In the agglomeration system, the length of carbon chain, kinematic viscosity and cycloalkane structure would make it easy to form compact funicular aggregates, i.e. with larger amounts of oil, funicular bridging occurs and more compact aggregates are formed (Drzymala et al., 1986). The fundamental ingredient of kerosene and diesel is n-alkanes, but transformer oil is naphthenic (Table 3). The transformer oil droplet can catch more ﬁne molybdenite particles and shows the best recovery among the three oils. In addition, it can be found that the average particle size of concentrate using transformer oil as bridging agent was the lowest (Fig. 3e). According to the concept of the critical surface tension of wetting, as developed by Zisman and co-workers, the solid or mineral surface is completely wetted by the liquid if the surface tension of liquid is equal to or less than the critical surface tension of the wet-
ting value of solid or mineral surfaces (Cebeci and Sönmez, 2004a; Ozkan et al., 2005). The critical surface tension of wetting for molybdenite is about 42 mN/m (Kelebek, 1988; Ozcan, 1992). All of the above-mentioned oils’ has surface tensions below this level. Therefore, during OAF the molybdenite particles tend to be drawn into the oil phase. As suggested by Cebeci and Sönmez (2004a), the decisive rules could not put down as evidence of agglomeration success with the critical surface tension of the wetting value as in the ﬂotation, because there are different liquids such as water and oil (bridging reagent) in the agglomeration system. If simply depends on the surface tension of wetting liquid, it is difﬁcult to decide which is the best bridging oil in agglomeration ﬂotation. The effect of transformer oil amount on the average size of colp lected molybdenite particles (d50 ), average size of agglomerates a (d50 ) and ﬂotation recoveries is expressed in Fig. 5. a The mean size of agglomerates (d50 ) increased from 0.15 to 0.68 mm when the dosage of oil increased from 2.0 to 13.8 kg/t (Fig. 5). At the same time, the mean diameter of collected molybp denite particles (d50 ) decreased from 9.06 to 2.05 lm with the increase of the transformer oil amount. The size of agglomerate is not altered with the size of particles. The size of agglomerate can
F. Jiangang et al. / Minerals Engineering 39 (2012) 133–139
Fig. 5. Relationships among oil amount, d50 , d50 and ﬂotation recovery.
not be fully represented by the dry sieve analysis result, but the result should be consistent with statistical laws in the parallel test. a Accordingly, it can be conjectured the bigger the d50 , the smaller p the d50 , and the higher the molybdenum recovery. And it can be explained based on the surface area of small molybdenite particles, which are wetted by the transformer oil, and make aggregates. 3.3. Operating conditions of oil agglomeration ﬂotation There are many factors affecting the OAF process, and the major ones are different oil types and dosages, frother dosages, pH, stirring time and intensity. These operating conditions were tested as follows. Transformer oil was used as bridging reagent with a dosage at 14 kg/t (ﬁrst-stage rougher 12 kg/t and second-stage rougher 2 kg/t), stirring speed is ﬁxed at 800 r/min and stirring time at 5 min. The effect of pine oil amount on OAF was carried out as the ﬂowchart given in Fig. 1, and the results are shown in Fig. 6. There are slight effects on the recovery of rougher concentrate when the amount of pine oil increases from 0.30 to 0.75 kg/t, but it plays an important role in the result, i.e. recovery and grade of ﬁnal concentrate (Fig. 6). The concentrate recovery increases from 79.94% to 85.44% and then to 86.03% when the amount of pine oil increases from 0.30 to 0.50 and then to 0.75 kg/t. At the same time, the grade of the concentrate decreases from 38.21 to 35.84 and then sharply to 16.34%. Hence, 0.5 kg/t pine oil is considered as the proper amount for the ﬂotation separation process.
Fig. 6. The effect of amount of pine oil on oil agglomeration ﬂotation.
Pulp pH values can be adjusted from 6.2 to 10.3 by adding calcium oxide from 0 to 1.5 kg/t. The effect of pulp pH values on the OAF is presented in Fig. 7. The ﬁgure shows that the recovery of molybdenum is slightly affected by pH, whereas the grade shows a downtrend and gradually decreases from 35.81% to 15.22% with the pH increasing. During the test, it is found that the foaming ability and viscidity of pulp are improved with the increase of pH value in alkaline solutions, which result in the increase of agglomerate yield and gradual decrease of grade. Therefore, OAF can be carried out at the pH near 6.2, which is the natural pH for tailing suspensions. At optional dosage, the effects of stirring time and agitation intensity were studied in the OAF process, and the experimental data are presented in Figs. 8 and 9, respectively. For a short agglomeration time, the diameters of agglomerates are smaller because of insufﬁcient oil dispersion and the collisions between particles. As the agglomeration time increased, larger agglomerates were obtained due to an increase of particle–particle, particle–microagglomerate, and microagglomerate–microagglomerate contact (Cebeci, 2003). With the increase of agglomerates size, more and more ultraﬁne molybdenites are collected to form large agglomerates. To provide dispersion of oil as ﬁne droplets in the suspension, the oil agglomeration process requires higher stirring speed. When particle–particle collision speed was increased by increasing the agitation intensity, agglomerates of a much tighter structure were formed. However, a too higher stirring speed, partial destruction of agglomerates happened by shear forces and collisions of agglomerates to cell walls and to each other (Sönmez and Cebeci, 2003a). The experimental results indicate that the desired particles can be selectively agglomerated and removed from the slurry under appropriate physico-chemical conditions, i.e. 3 min stirring time with stirring intensity at 400–600 r/min is sufﬁcient for recovering molybdenite from ultraﬁne waste tailings by oil agglomerate ﬂotation. 4. Locked cycle test and industrial application of oil agglomeration ﬂotation A locked cycle OAF test, with the ﬂowsheet of one-stage rougher, one-stage scavenger, four-stage cleaner and middlings return to the former cleaner, has been conducted to assess beneﬁciation performance under simulated continuous operating condition. On this basis, the industrial experiment producing 500 t/d molybdenite was carried out at the spot of tailings reservoir. Results of laboratory locked cycle test and normal production indices are summarized in Table 4. As seen from Table 4, in normal production processes of agglomeration ﬂotation, 95% molybdenum is recovered into the froth products (concentrate) with a molybdenum grade at 22.62%, and only 5% molybdenum still lost in secondary tailings.
Fig. 7. The effect of pH on oil agglomeration ﬂotation.
F. Jiangang et al. / Minerals Engineering 39 (2012) 133–139
Fig. 8. The effect of agglomeration time on oil agglomeration ﬂotation.
Fig. 9. The effect of stirring intensity on oil agglomeration ﬂotation.
Table 4 Results of locked cycle test and industrial application of oil agglomeration ﬂotation. Items
Laboratory locked cycle test
Concentrates Secondary tailings Original tailings
Concentrates Secondary tailings Original tailings
Yield (%) 3.05 96.95 100.00 4.39 95.61 100.00
Mo grade (%)
Mo recovery (%)
The molybdenum grade in the ﬁnal tailings is 0.056%, which is far lower than the feed that is 1.05%. It deserves to be specially noted that the reason for concentrate grade of industrial production is less than that of laboratory test lies in the economic balance consideration, because recovery is more pragmatic than the grade in accordance with the market price. In summary, industrial scale experiment proves that OAF process is a remarkable recycled technology in recovery of ultraﬁne molybdenite from waste tailings. 5. Conclusions In the process of recovering molybdenite from waste tailings, conventional ﬂotation cannot be considered as an effective method, and the most important reason lies on the fact that the mean diameter of the tailings is 10.99 lm and the particles below 38 lm contain 90.67% molybdenum. It is indicated from the experimental data that conventional ﬂotation froth cannot catch the ultraﬁne molybdenite particles, and the mean particle size of froth concentrate is 10.52 lm, which is close to the raw tailing’s particle
size. While the average particle size of OAF concentrate is less than 5.92 lm, and the products have ultraﬁne compact layered molybdenite structure, so OAF has some advantages to recovering ﬁne minerals. The molybdenite tailings can be successfully agglomerated with kerosene, diesel, transformer oil or rapeseed oil, but rapeseed oil shows little effect on increasing the recovery of molybdenum, due to the fact that rapeseed oil is an unsaturated fatty acid, which is also the gangue collector. When rapeseed oil is used as the bridging oil, most of the surface of agglomerates is occupied by undesired particles. The best result is obtained from transformer oil because its length of carbon chain, kinematic viscosity and cycloalkane structure are all in favorable conditions. The average particle size of agglomeration concentrate using transformer oil as bridging oil is the lowest one, 2.05 lm. The oils amount plays a very important role on the average size of p a collected particles (d50 ), average size of agglomerates (d50 ) and ﬂotation recoveries. With the increase of transformer oil from 2.0 to a p 13.8 kg/t, d50 increases from 0.15 to 0.68 mm and d50 decreases from a 9.06 to 2.05 lm. Accordingly, it can be conjectured the bigger the d50 , p the smaller the d50 , and the higher the molybdenum recovery. There are many factors affecting the OAF process, and the dosage of 0.5 kg/t frother, natural pH and stirring time of 3 min, stirring intensity of 400–600 r/min are considered as the appropriate conditions. Practice has proven that OAF process can be considered as a remarkable improvement technology in recovery of ultraﬁne molybdenite from waste tailings. Lastly, the locked cycle test and industrial experiment in the producing scale of 500 t/d have been carried out, in normal production processes, 95% molybdenum is recovered with a satisﬁed grade of 22.62%. Acknowledgements The authors acknowledge the Key Laboratory of Resources Chemistry of Nonferrous Metals, Ministry of Education (Central South University) for the laboratories and ﬁnancial support, and we would like to express our sincere appreciation to the anonymous reviewers for their insightful comments, which have greatly aided us in improving the quality of the paper. References Aktas, Z., 2002. Some factors affecting spherical oil agglomeration performance of coal ﬁnes. International Journal of Mineral Processing 65 (3–4), 177–190. Alonso, M.I., Valdés, A.F., Martínez-Tarazona, R.M., Garcia, A.B., 2002. Coal recovery from ﬁnes cleaning wastes by agglomeration with colza oil: a contribution to the environment and energy preservation. Fuel Processing Technology 75 (2), 85–95. Ansari, A., Pawlik, M., 2007. Floatability of chalcopyrite and molybdenite in the presence of lignosulfonates (part II): hallimond tube ﬂotation. Minerals Engineering 20 (6), 609–616. Azevedo, M.A.D., Miller, J.D., 2000. Agglomeration and magnetic deinking for ofﬁce paper. Technical Association of the Pulp and Paper Industry (TAPPI) Journal 83 (3), 66–72. _ 2002. The investigation of coal–pyrite/lignite concentration Cebeci, Y., Sönmez, I., and their separation in the artiﬁcial mixture by oil agglomeration. Fuel 81 (9), 1139–1146. Cebeci, Y., 2003. Investigation of kinetics of agglomerate growth in oil agglomeration process. Fuel 82 (13), 1645–1651. _ 2004a. A study on the relationship between critical surface Cebeci, Y., Sönmez, I., tension of wetting and oil agglomeration recovery of calcite. Journal of Colloid and Interface Science 273 (1), 300–305. _ 2004b. Investigation of spherical oil agglomeration properties Cebeci, Y., Sönmez, I., of celestite. Journal of Colloid and Interface Science 273 (1), 198–204. _ 2006. Application of the Box–Wilson experimental design Cebeci, Y., Sönmez, I., method for the spherical oil agglomeration of coal. Fuel 85 (3), 289–297. Ercikdi, B., Cihangir, F., Kesimal, A., Deveci, H., Alp, I., 2010. Utilization of waterreducing admixtures in cemented paste backﬁll of sulphide-rich mill tailings. Journal of Hazardous Materials 179 (1–3), 940–946. Feng, X.L., 2008. Study on the process of producing MoO3 by recovery from a lowgrade molybdenite. Tianjin Chemical Industry 22 (4), 20–23 (in Chinese). Gray, M.L., Champagne, K.J., Soong, Y., Finseth, D.H., 2001. Parametric study of the column oil agglomeration of ﬂy ash. Fuel 80 (6), 867–871.
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