paulofkertzman@uol.com.br lucalu@terra.com.br apmozella@terra.com.br ggodinho@terra.com.br carlosaba

Engineering

Research Paper

E-ISSN No : 2454-9916 | Volume : 2 | Issue : 12 | Dec 2016

STUDIES ON THE GRINDING CHARACTERISTICS OF MANGANESE ORE 1

2

3

3

Dr. CH. A. I. Raju | A. Mahesh Kumar | K. Satyanandam | P. Ratna Raju | K. Prem

3

1

Assistant Professor, Department of Chemical Engg, Andhra University, Visakhapatnam, India - 530003.

P. G. Student, Department of Chemical Engg, Andhra University, Visakhapatnam, India - 530003.

3 Research Scholar, Department of Chemical Engg, Andhra University, Visakhapatnam, India - 530003.

2

ABSTRACT The energy required to liberate a mineral of economic interest from its gangue constituents in the host rock is described in this experiment. Numerous chances to get better energy and environmental presentation are linked with the mineral processing works. The design of equipment use for the purpose is indicated in some details. .

It is now established information that the size reduction by grinding spent for more than half of the total cost. It is true in any mineral beneficiation plant; irrespective of the technique and methodology facilitate to achieve the improvement of the total separation of one or more valuable species in the natural ore. In the present experiment Manganese ore of hardness 6 on moha's scale, specific gravity 3.53 has been taken for grinding tests in a ball mill. The experiments were conducted for three feed sizes (i.e. –1/2" + 3/8", –3/8" + ¼", –1/4" + 3/16") and three ball sizes (i.e. 1", 1/2", 3/4"). The values of selectivity function for giving pre impact to the feed using three set of feed sizes and three feed quantities (150, 100, 50 g) with three different ball sizes have been evaluated.

KEYWORDS: Ball Mill, Grinding, Specific Surface Area, Energy and Feed size.

1. Introduction Most of researchers are working in different fields for a better society with their noble service. The cost effectiveness plays a vital role in the better research. Mineral Engineers are crucial for any product development as the raw material processing plays a key role. The principal operation among many research activities is the basic size reduction. The natural sequence of comminution in the mineral processing plant is crushing and grinding. Crushing is the first mechanical stage in the process of comminution in which the main objective is the liberation of the valuable minerals from the gangue. Crushing accomplishes either by compression of the ore against rigid surfaces or by impact against surfaces in a rigidly constrained motion path. Grinding is the last stage in the process of comminution; in which the particles are reduced in size by a combination of impact, abrasion and attrition of the ore by the grinding media such as balls, pebbles or rods in rotating cylindrical vessels known as tumbling mills [1]. In many industries the final product or the raw materials at some stage of the manufacturing process is of powdered form and cheap preparation of powdered materials is a matter of considerable economic importance [2, 3]. The reasons for the grinding of industrial materials are numerous but the principal reasons may be summarized under the following cases. Ÿ

The liberation of an economically important material from the undesirable constituents of a mixture.

Ÿ

The exposure of a larger surface area per unit mass of material in order to facilitate some chemical process.

Ÿ

To reduce the material to the desired form of the final product.

Ÿ

To assure market product requirements.

The cost of energy consumption is a major factor in the crushing and grinding process that influences the viability of mineral processing operations [4, 5]. Yet grinding operations ought to be carried out for the effective processing of minerals, either to liberate mineral values or to prepare a suitable feed for separating process like floatation, gravity concentration, classification etc. Examples of the first two cases occur in mineral dressing in which size reduction is used to liberate the desired ore from the gangue and also to reduce the ore to such a form in which it presents a large surface to the leaching reagents. The third case may be classed in many medical and pharmaceutical products, food stuffs etc. The fourth case falls under the size reduction of mineral ore and etc, these materials often being reduced to particles of moderate size for ease in handling, strong and loading into trucks [6]. The quantity of the powder to be subjected to such processes of the size reduction varies widely according to the industries involved. The preparation of small quantities of powder is produced by different types of equipment but even so the ball mill is frequently used [7]. For the grinding of largest quantities the ball, rod, tube mill is used almost exclusively, since these are the only types of mill which possesses thorough capacity of the required [8]. In batch grinding, the particle size is continuously reduced with time but minerals of various complexities behave differently. In view of grinding studies, each mineral has to be studied to predict the product size with other influencing parameters

like specific energy [9]. The present study consists of experiments conducted to relate the specific surface area generated and the energy consumption per unit surface area produced with the above parameters as time grinding, feed size, feed quantity and ball size.

2. Materials and Methods: The ball mill used for the studies is an ordinary cylindrical type vessel with 8'' × 8'' size, closed permanently at one end and with a provision to close the other end by using a lid. The lid in turn is provided with a groove and gasket around the periphery and can be fixed to the mill my means of a suitable nut and bolt mechanism such that material does not leak out of the mill while in operation. The inside surface of the mill is smooth except that it is provided with three baffles of square cross section of 0.5'' × 0.5'' size, along the length of the mill fixed firmly and evenly around the periphery. The thickness of the mill wall is 0.38'' and the theoretical critical speed of the mill is 100 rpm. A stepped pulley framework is connected at one end of the mill by means of the shafts through toothed wheel reduction gear system, which enables the mill to rotate on its horizontal axis. A V–belt connecting the motor and pulley frame work in turn enables the mill to rotate. The stepped pulley framework is provided with four steps and hence the mill can be run at four different speeds namely 23, 41, 66 & 82 rpm. The mill is supplied a with 100 balls of 2.54 cm diameter, 225 balls of 1.9 cm diameter and 800 balls of 1.27 cm diameter. The other accessories used for conducting the experiment include a rotap sieve shaker with an automatic time switch, a set of BSS sieves with mesh numbers 52, 60, 85, 100, 150 & 200 with lid and pan and a stop watch to note the time.

3. Results and discussion: 3.1 Effect of time of milling: The effect of time of grinding in a ball mill has been studied covering a range of 2 minutes to 14 minutes. 50 g of feed of the size 0.475, 0.675 and 1.0 cm were feed to the mill and the mill was run at the speed of 66 rpm. The number of balls of one inch size kept as constant at 100. The specific surface area per each run is calculated and the results are shown in figures Fig 3.1.1, 3.1.2 and 3.1.3 shows the variation of specific surface with time, which shows that the specific surface produced, continues to increase with time. Fig 4 shows the variation of Specific Surface with Energy consumption which reveals that power consumption increases with specific surface. Fig 5 shows the variation of Rate Constant with Time. The Rate Constant is decreasing with increasing time. The reasons for increase in the initial periods are due the fact that coarse particles are being introduced in to the mill are easily ground, but after attaining a certain degree of fineness, further division become a slower process due to the cushioning action of the fines formed.

Also the small particles may agglomerate to form bigger particles with prolonged grinding [10-13].

Copyright© 2016, IERJ. This open-access article is published under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License which permits Share (copy and redistribute the material in any medium or format) and Adapt (remix, transform, and build upon the material) under the Attribution-NonCommercial terms.

International Education & Research Journal [IERJ]

71

Research Paper

E-ISSN No : 2454-9916 | Volume : 2 | Issue : 12 | Dec 2016

Fig. 3.1.1 Variation of specific surface with time

Fig 3.2.1: Variation of Energy consumption with Impact of stress

Fig. 3.1.2 Variation of energy consumed with time

Fig 3.2.2: Variation of E/S with Impact of stress

Fig. 3.1.3 Variation of E/S with time 3.2 Effect of Impact of pre-stress: To study the impact of pre-stress parameter on the performance of the ball mill is measured in terms of the specific surface generated and energy consumed. Three sizes of feed like0.47cm, 0.67cm and 1.0 cm are chosen. The effect of pre stress has been found for a feed quantity of 50g and speed of the mil at 66 rpm.A graph is drawn to show the variation of specific surface with the impact of pre-stress in Fig. 3.2.1 From the figure it can be concluded that the specific surface area increases with increase of pre-stress load. This is because when an external force is applied to break the internal bonds and their deformations, fractures will form resulting in lumps to release individual particles and free the bonds [5, 6, 7, 8, 9].The variation oftheenergy consumption with the increase in pre-stress load.

The energy consumption is decreased with increase in stress 0 to27 psi variation of E/S with pre-stress load. From the Fig.3.2.2 E/S decreased with increase inprestress load. The reason for the above trends is that as stress isincreased the crack surface and crack length will increase leading to weaken the particle bonds and separate them.

3.3 Effect of the size of balls: Three sizes of ball Viz., 2.54 cm (1"), 1.27 cm (1/2") and 1.9 cm (3/4") are chosen. The effect of ball size has been found for a feed quantity of 50g and keeping the time of grinding at 4 min and speed of the mil at 66 rpm. Even though the sizes of the balls are changed, the total weight of the balls was kept constant at 6470g.A graph is drawn to show the variation of specific surface with the size of the balls and it can be concluded that the specific surface area increases with ball size. This is because of the increased void spaces in between the balls of larger diameter.

Fig. 3.3.1 shows the variation of energy consumption with the ball size. The energy consumption is constant in the early stages and then increases with the further increase in ball size up to 2.54 cm. From the Fig 3.3.2 E/S and rate constant is increases with increase in ball size. The ball size must be proportional to feed size; otherwise there will not be nipping of the particles resulting in the particles remaining uncrushed. The nipping is more in case of 1-in. dia. than the other sizes. The speed of the mill in all these three cases is maintained to be 66 rpm. In general, the size reduction due to impact is much more compared to that due to attrition. Further, in case of 1" dia ball, the impact is more compared to ž" dia or a ½" dia ball. Also as per as the impact is concerned, it is the individual ball that counts rather than the total mass; hence the above result [12, 14, 15].

Fig. 3.3.1 Variation of Energy consumption with Ball Size

72

International Education & Research Journal [IERJ]

Research Paper

E-ISSN No : 2454-9916 | Volume : 2 | Issue : 12 | Dec 2016 3.5 Effect of feed size To study the effect of feed size on the performance of the mill measured in terms of the surface area generated and the energy consumption, five samples of sizes –1/2"+3/8" (1.00cm), –3/8"+1/4" (0.67cm), –1/4"+3/16" (0.47cm), etc respectively were taken. In all these systems the feed was ground for a grinding time of 4 min, at a mill speed of 66 rpm using 1" steel balls.A graph was drawn between the feed size and the specific surface as shown in Fig. 3.5.1, reveals that the specific surface area decreases with increase in feed size reveals the variation of energy consumption with the feed size. The energy consumption is continuously decreasing. It is the impact that is significant for size reduction, as the ball size remains constant. But the effect of the impact on the feed for size reduction diminishes with increased size of the feed. The ball size must be proportional to feed size. Otherwise there will not be nipping of the particles resulting in the particles remaining uncrushed. A graph was drawn between the ratios of energy consumption to that of specific surface with the feed size reveals that the ratio of energy consumption to that of specific surface decreases with increase in feed size reveals the variation of rate constant with the feed size. The value of rate constant is continuously increasing [10, 15–18].

Fig 3.3.2 : Variation of E/S with Ball Size 3.4 Effect of feed quantity To study the effect of feed quantity on the performance of the ball mill measured in terms of the surface area generated and the energy consumed, three samples of 50, 100 and 150 g respectively were taken. In all these systems the feed was ground for a grinding time of 4 min, at a mill speed of 66 rpm using 1" steel balls.

A graph was drawn between the quantity of feed and the specific surface as shown in Fig. 10 it reveals that the specific surface area decreases with increase in feed quantity. This is attributed to the choking of the mill with the increased feed quantity. At larger feed quantities, the chances of balls coming closer are meager; as a result comminution by attrition and impact is greatly reduced. Fig. 12 reveals the variation of energy consumption with the quantity of feed. The energy consumption decreased with an increase in feed quantity. Fig. 12 shows the variation of energy consumed per unit surface area produced with the quantity of feed. The E/S value is decreased with increase in feed quantity. Rate constant decreased with increase in Feed Quantity. In generalwe know that the impact predominantover attrition. The impact is such that, the feed could easily be reduced in size. When the feed quantity has been enhanced by a small increment, still the impact is sufficient, such that the size reduction is “sufficient” As the feed quantity continues to increases the impact has become „insufficient‟ and also the attrition where in the load has been overtaken or submerged by the feed.

Hence the above result [10, 15, 16].

Fig. 3.5.1 Variation of Specific Surface Area with Feed Size

Fig. 3.5.2 Variation of Energy consumption with Feed Size Fig. 3.4.1 Variation of Specific Surface Area with Feed Quantity

3.6 Correlation for Specific Surface Area From the present study, it is clear that the specific surface area produced by milling varied significantly with grinding time, ball size, feed quantity, and feed size.

Hence the grinding rate factor is defined as {SDm/ (N t)} a function of all the variables given below.

Various dimensionless groups along with grinding rate factor correlate the results of the present study. The groups are made dimensionless by using the variables covered in the present study. The dimensionless groups used for correlating the data are Q/WB, Bs/Fs, Fs/Ps, (t/Sta). On regression analysis the following equation is obtained.

SDm/(N t) = 0.059835 (Q/WB-0.20353 (Bs/Fs)-1.2448 (Fs/Ps)0.54593 (t/Sta)-0.315531 Avg Deviation = -3.9128 Std Deviation = + 28.880

3.4.2 Variation of E/S with Feed Quantity

International Education & Research Journal [IERJ]

73

Research Paper

E-ISSN No : 2454-9916 | Volume : 2 | Issue : 12 | Dec 2016

Fig. 3.6.1 Correlation plot for Specific Surface Area(X1)

Fig. 3.6.4 Correlation plot for Specific Surface Area (YCal vs Yreg) 4. Conclusions: As the grinding time increases, specific surface increases. As the specific surface increases, Energy consumption also increases. Energy consumption per unit specific surface increases with time. As the size of the ball increases specific surface increased uniformly. Energy consumption is almost same for all ball sizes and a slight increase is also observed for a particular amount of feed. Energy consumption per unit specific surface area of feed increased with increase in ball size. Ball mill Energy consumption of the feed increase with quantity of the feed. The new specific surface area generated also decreased with increase in feed quantity. The Energy consumption per unit specific surface of the feed is decreased with increase in feed quantity. The study yielded the following regression equation is SρDm/ (Nt) =18.504(Q/WB)-0.069526(Bs/Fs)-0.017495(Fs/Ps)-0.052759 5. Acknowledgment: The authors sincerely thank the Garividi mining for providing the ore and Andhra University, Chemical Engineering Department for providing the equipment.

6. REFERENCES: 1.

CH. A. I. Raju, K. Satyanandam, D.V.S. Sravanthi, P. Hussain Reddy, P. J. Rao, “Studies on Batch Grinding of Bauxite Ore in Ball Mill”, International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 11, May 2013, 140–147.

2.

Antti Mäntynen, Alexey Zakharov , Sirkka-Liisa Jämsä-Jounela , Mats Graeffe, “Optimization of grinding parameters in the production of colorant paste”, Powder Technology 217 (2012) 216–222

3.

Augustine B. Makokha, Michael H. Moys, “Characterizing slurry hydrodynamic transport in a large overflow tubular ball mill by an improved mixing cell model based on tracer response data”, Powder Technology 211 (2011) 207–214

4.

P. Songfack, R. Rajamani, Hold-up studies in a pilot scale continuous ball mill: dynamic variations due to changes in operating variables, Int J. Miner. Process 57 (1999) 105–123.

5.

Parviz Pourghahramani, “Effects of Grinding Variables on Structural Changes and Energy Conversion during Mechanical Activation Using Line Profile Analysis (LPA)”, Ph.D. Thesis, Department of Chemical Engineering and Geosciences, Lulea University of technology, 2006

Fig. 3.6.2 Correlation plot for Specific Surface Area (X2)

Fig. 3.6.3 Correlation plot for Specific Surface Area (X3)

74

6.

Balaz, P., 2000. Extractive Metallurgy of Activated minerals. Elsevier, Amesterdam,

7.

Heegn, H., 1986. Concerning some fundamentals of fine grinding. In: Leschonski, K.,Editor, 1986. Proc. 1st World Congress on Particle Technology, Part II. Comminution, Nürnberger Messe und Austellungsgesellschaft, Nürnberg, pp. 63–67.

8.

Sahu, P., De, M., Zdujic, M., 2003. Microstructural characterization of the evoluted phases of ball-milled Fe2O3 powder in air and oxygen atmosphere by Rietveld analysis.

Material Chemistry and Physics 82, 864-876.

9.

Bid, S., Banerjee, A., Kumar, S., Pradhan, S. K., De, U., Banerjee, D., 2001. Nanophse iron oxides by ball-mill grinding and their Mössbauer characterization. Journal of Alloys and Compounds 326, 292-297.

10. C. Alamprese , L. Datei , Q. Semeraro, “Optimization of processing parameters of a ball mill refiner for chocolate”, Journal of Food Engineering 83 (2007) 629–636

International Education & Research Journal [IERJ]

Research Paper

E-ISSN No : 2454-9916 | Volume : 2 | Issue : 12 | Dec 2016

11. McFarlane, I. (1999). Instrumentation. In S. T. Beckett (Ed.), Industrial chocolate manufacture and use (3rd ed.). Oxford: Blackwell Science.

12. Arno Kwade, “Determination of the most important grinding mechanism in stirred media mills by calculating stress intensity and stress number”, Powder Technology 105_1999.382–388 13. K. Scho¨nert, in: K.V.S. Sastry, M.C. Fuerstenau_Eds.., Challenges in Mineral Processing, Society of Mining Engineers, Littleton, 1989, p.151.

14. Xi-song Chen ⁎, Qi Li, Shu-min Fei, “Constrained model predictive control in ball mill grinding process”, Powder Technology 186 (2008) 31–39 15. C. Bazin, M. St-Pierre, D. Hodouin, “Calibration of the perfect mixing model to a dry grinding mill”, Powder Technology 149 (2005) 93– 105 16. Oktay Celep, Nevzat Aslan, İbrahim Alp, Gökhan Taşdemir, “Optimization of some parameters of stirred mill for ultra-fine grinding of refractory Au/Ag ores”, Powder Technology 208 (2011) 121–127.

17. O. Celep, İ. Alp, H. Deveci, T. Yılmaz, The investigation of gold and silver recovery from Akoluk (Ordu -Turkey) ore, Proceedings of Int. Conference of Modern Management of Mine Producing, Geology and Environmental Protection-SGEM, Varna, 2006, pp. 251–258.

18. O. Celep, İ. Alp, H. Deveci, M. Vıcıl, Characterization of refractory behaviour of a complex gold/silver ore by diagnostic leaching, Transactions of the NonferrousMetals Society of China 19 (2009) 707–713.

19. A. Guney, G. Onal and T. Atmaca, “Technical Note New Aspect Of Chromite Gravity Tailings Re-Processing”, Minerals Engineering, Vol 14. No I I. pp 1527 -1530, 2001.

20. M.J. Mankosa, G.T. Adel, R.H. Yoon, Effect of media size in stirred ball mill grinding of coal, Powder Technology 49 (1986) 75–82.

International Education & Research Journal [IERJ]

75