30120140505008

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Partially Lateritised Khondalite (PLK) rocks are the bauxite mining waste materials
generated during mining and dumped at the mining site, create environmental pollution. These waste
rocks can be utilized as filler materials for different industrial applications after grinding to suitable
mesh size. Thermal shock treatment on ore is used for grain boundary breakage and size reduction,
due to thermal shock treatment the surface adsorbed gangue minerals also releases and expose new
surface area in the ore. Comminution study is used after this treatment for further reduction in size.
In comminution study, ball mill has good selective grinding performance. This paper deals with the
effect of thermal shock treatment on grinding characteristics of PLK rock and the overall energy
savings achieved. Alumina based filler/ceramic materials were used in different industries. Thermal
shock of the samples was evaluated using water quench test. Surface deterioration level of samples
was monitored by image analysis before and after quenching. A total energy saving of the order of
52.8 % could be achieved when a sample preheated at 1123 K for 60 minutes followed by coldwater
quenching and grinding.

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30120140505008

  1. 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 83-90 © IAEME 83 AN APPROACH FOR ENERGY CONSERVATION ON PARTIALLY LATERISED KHONDALITE ROCKS USING THERMAL SHOCK TREATMENT 1 Ranjita Swain, 2 R. BhimaRao 1 C V Raman College of Engineering and 2 Aryan Institute of Engineering and Technology, Bhubaneswar, Odisha, India ABSTRACT Partially Lateritised Khondalite (PLK) rocks are the bauxite mining waste materials generated during mining and dumped at the mining site, create environmental pollution. These waste rocks can be utilized as filler materials for different industrial applications after grinding to suitable mesh size. Thermal shock treatment on ore is used for grain boundary breakage and size reduction, due to thermal shock treatment the surface adsorbed gangue minerals also releases and expose new surface area in the ore. Comminution study is used after this treatment for further reduction in size. In comminution study, ball mill has good selective grinding performance. This paper deals with the effect of thermal shock treatment on grinding characteristics of PLK rock and the overall energy savings achieved. Alumina based filler/ceramic materials were used in different industries. Thermal shock of the samples was evaluated using water quench test. Surface deterioration level of samples was monitored by image analysis before and after quenching. A total energy saving of the order of 52.8 % could be achieved when a sample preheated at 1123 K for 60 minutes followed by coldwater quenching and grinding. Keywords: Energy Saving, Grinding, PLK Rock, Thermal Shock Treatment, Work Index. 1. INTRODUCTION In order to produce about 2.1 million tons of alumina per year by National Aluminium Company, about 6.3 million tons per annum of bauxite is being mined. While mining of this bauxite per annum, an equal amount of partially laterized khondalite (PLK) rocks associated with kaolinised khondalite rocks are also being generated and dumped at the mine site as waste material or sometimes used for back filling of abandoned mines. The PLK rocks are associated with different characteristics such as brittle, loose, semi compact, abrasive etc. type of rocks or materials and hence the crushing characteristics of the rock may vary. This waste can be utilized as a filler material in the INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 5, Issue 5, May (2014), pp. 83-90 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2014): 7.5377 (Calculated by GISI) www.jifactor.com IJMET © I A E M E
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 83-90 © IAEME 84 industries like paint, pigment, rubber, cement, paper, ceramic and pharmaceutical etc. These filler industries need very fine and some industries also need white fine ground materials. Hence, comminution studies are essential to prepare the bulk rock to very fine grained material. Comminution processes are enormous energy consumption processes. The loss of grinding media through wear is also a significant cost in any mineral beneficiation process. The cost of grinding media is of the same order as that of energy usage during comminution. Thus, any reductions in ore strength (leading to shorter grinding times, or a reduction of milled tonnage in recycle) result in significant cost savings from energy and grinding media conservation. Hence any attempt to reduce electrical energy is one of the important tasks of the researchers. Pretreatment methods are so many such as thermal, electrical, cryogenic, calcinations or microwave heat treatment prior to comminution followed by processing of the ore/ mineral are the alternatives to save energy consumption. The most important properties usually determined for refractories are refractoriness, working temperature and thermal stability. Thermal shock resistance of refractory materials is one of the most important characteristics since it determines their performance in many applications. Thermal shock introduces cracks into the structure and therefore there is need to improve cracking resistance of material. As thermal shock is one of the most efficient techniques in the size reduction. In this process, the solid particles are heated at above 823 K and due to subsequent sudden quenching the particle are subjected to either rupturing or weakening in the interstitial bonds promoting inter granular fractures between particles. In most cases, the action is based on thermal expansion and contraction under sharp and sudden temperatures differential and leading to a potential improvement in grinding performance as well as the downstream operations. Thus thermal shock treatment is one of the methods to improve comminution, liberation and magnetic characteristics of ore by weakening the rock and inducing grain boundary fracture. In thermal shock treatment the ore minerals are subjected to thermal expansion by heat treatment and followed by rapid contraction of minerals by sudden quenching. The literature has been reviewed on the thermal treatment and energy saving on grinding of different samples. Alumina based ceramic fibres and alumina based ceramic [1] were used to produce composite material. Behaviour of composite ceramics after thermal shock treatments was investigated. Thermal shock of the samples was evaluated using water quench test. Surface deterioration level of samples was monitored by image analysis before and after a number of quenching cycles. Ultrasonic measurements were done on samples after quench tests. Dynamic Young modulus of elasticity and strength degradation were calculated using measured values of ultrasonic velocities. Strengths deterioration was calculated using the non-destructive measurements and correlated to degradation of surface area and number of quenches. The addition of small amount of ceramic fibres improves the strengths and diminishes the loss of mechanical properties of samples during thermal shock experiments. Rao etal. [2] discussed in their paper that the crude bauxite requires a magnetic intensity of 14,000 gauss for the removal of ferruginous minerals. The bauxite calcined at 800°C requires magnetic intensity of about 7000 Gauss, whereas the reduced bauxite needs less than 2000 Gauss for separation of iron. Banerjee and Rao [3] investigated that a total energy saving of the order of 32% could be achieved when vanadiferrous magnetite sample is preheated at 800°C for a period of 30 minutes followed by quenching and grinding for 50 minutes in a batch ball mill. It has been earlier [4,5] found that the value added materials such as filler and refractory can be recovered from PLK rocks. To recover these value added materials, the PLK rocks are to be comminuted by stage crushing to obtain a product d80 passing size 100 micron. Thus the recovered value added material contain d80 passing size 100 micron, which has to be ground to very fine size suitable for filler industrial applications. This process is energy intensive. Hence any attempt to save one unit of power per tons in the specific energy consumption is of high significance.
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 83-90 © IAEME 85 2. EXPERIMENTAL The PLK rock sample was collected from Damanjodi bauxite mine, Orissa, India.The sample was generated at the time of bauxite mining. The sample was prepared by stage crushing to -10 +5 mm size. The representative samples of each 2 kg had been prepared separately and subjected to pre- treatment at various temperatures (823 K and 1123 K) for one hour in a muffle furnace and rapidly quenched in water at ambient temperature. These the sample was dried and ground in a standard ball mill (Fig.1) used for the determination of the Bonds work index. The PLK sample was also subjected to dry grinding without and with pre treatment for comparison study. Percentage of fines generated was determined at different periods of grinding by using standard sieves. The mineralogical phase analysis of the samples was carried out using PANalytical X-Pert X-ray powder diffractometer with Mo-Kα radiation (λ=0.709Ǻ) from 6° to 40° scanning angle at a scanning rate of 0.02°/sec. This technique was based on the Braggs principle. Fig 1: Experimental set up for Bonds work index using standard batch ball mill The Scanning Electron Microscope (SEM) studies were carried out by using HITACHI S – 3400N. High resolution and large depth of field coupled with simple sample preparation technique detected crystal morphology at a microscope. It has High scanning electron resolution of 10nm at 3Kv. The magnification of the instrument used was 5X- 300,00X and alternating voltage 0.3-30 kV. 2.1 Bonds work index: The PLK feed sample was prepared by stage crushing to all passing a 6 mesh sieve. The weight of 700 cc sample was placed in the mill. The grinding conditions are given below. These studies were carried out in a standard ball mill 150 mm X 150 mm size Weight of balls, Kg : 20.125 No. of balls Size, inches Size, mm 43 1.45 36.83 67 1.17 29.72 10 1 25.4 71 0.75 19.05 94 0.61 15.94 Sample weight: Initially weight of 700 cc volume sample Revolutions: Initially the experiment starts with from 100 revolutions Test mesh sieve: 150 micron (100 mesh)
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. The materials with the balls was charged to the ball mill grounded sample was screened with the test sieve and the undersize sample was weighed and fresh unsegragated feed was added to the oversize to bring its weight back to that of original charge. The numbers of revolution required was calculated from the results of the previous period to produce sieve undersize equal to the 1/3.5 of the total charge in the mill. The grinding period cycles were continued until the net grams of sieve undersize produce per mill revolution reache Then the undersize product and circulating load was screen analysed and the last three net grams per revolution (Gbp) is the ball mill grindability. The Bond Work index was calculated from the following equation Where F is the size in microns at which 80 percent of the new feed to ball mill passes P is the size in micron at which 80 percent of the last cycle sieve undersize product passes P1 is the opening in microns of the sieve size Wi is the work index in kWh/ton Power requirement/ton (PG) is calculated in hp ------------------------------------------------------------- Where Wi is the work index in kWh/ton F is the size in microns at which 80 percent of th P is the size in micron at which 80 percent of the last cycle sieve undersize product passes 2.2 Power requirement/ton (PT) for thermal treatment -------------------------------------------------------------- Where M = mass, CP = heat capacity, dT = temperature difference Cp (Cals/deg. Mole) values for Al2 equation 3. RESULTS AND DISCUSSION Physical and chemical analysis of PLK rock sample is given in Table 1 which indicates that the bulk density is of 1.3 g/cm3 , whereas true density is of 2.7 g/cm 4.3% of Fe2O3. XRD of PLK rock is shown in Fig phase along with other phases of gibbsite, goethite and quartz. SEM that this sample contains clay patches with iron content inside these patches which is clearly seen in International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6359(Online), Volume 5, Issue 5, May (2014), pp. 83-90 © IAEME 86 The materials with the balls was charged to the ball mill and ground at 100 revolutions. The grounded sample was screened with the test sieve and the undersize sample was weighed and fresh unsegragated feed was added to the oversize to bring its weight back to that of original charge. The quired was calculated from the results of the previous period to produce sieve undersize equal to the 1/3.5 of the total charge in the mill. The grinding period cycles were continued until the net grams of sieve undersize produce per mill revolution reache Then the undersize product and circulating load was screen analysed and the last three net grams per revolution (Gbp) is the ball mill grindability. The Bond Work index was calculated from the following equation ---------------------------------------- (1) F is the size in microns at which 80 percent of the new feed to ball mill passes P is the size in micron at which 80 percent of the last cycle sieve undersize product passes is the opening in microns of the sieve size tested ) is calculated in hp ------------------------------------------------------------- (2) F is the size in microns at which 80 percent of the new feed to ball mill passes P is the size in micron at which 80 percent of the last cycle sieve undersize product passes ) for thermal treatment -------------------------------------------------------------- (3) = heat capacity, dT = temperature difference 2O3.SiO2 at different temperatures were evaluated from Perry’s --------------------------------------- (4) RESULTS AND DISCUSSION ysical and chemical analysis of PLK rock sample is given in Table 1 which indicates that , whereas true density is of 2.7 g/cm3 . It contains 1.66 % of TiO . XRD of PLK rock is shown in Fig. 2 which indicates a highly crystalline kaolinite phase along with other phases of gibbsite, goethite and quartz. SEM studies on PLK rocks reveals clay patches with iron content inside these patches which is clearly seen in International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), and ground at 100 revolutions. The grounded sample was screened with the test sieve and the undersize sample was weighed and fresh unsegragated feed was added to the oversize to bring its weight back to that of original charge. The quired was calculated from the results of the previous period to produce sieve undersize equal to the 1/3.5 of the total charge in the mill. The grinding period cycles were continued until the net grams of sieve undersize produce per mill revolution reaches equilibrium. Then the undersize product and circulating load was screen analysed and the last three net grams per (1) P is the size in micron at which 80 percent of the last cycle sieve undersize product passes (2) P is the size in micron at which 80 percent of the last cycle sieve undersize product passes (3) at different temperatures were evaluated from Perry’s (4) ysical and chemical analysis of PLK rock sample is given in Table 1 which indicates that . It contains 1.66 % of TiO2 and 2 which indicates a highly crystalline kaolinite on PLK rocks reveals clay patches with iron content inside these patches which is clearly seen in
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 83-90 © IAEME 87 Fig. 3. Effect of thermal shock treatment at different temperature on PLK rock sample with respect to the production of fines passing 150 µm size particles are shown in Fig 4. The results of these studies indicate that the grinding time required for a production of 40% fines (below 150 µm size) decreases from 7 minutes to 3.4 minutes. The resultant savings in grinding time is observed to be in the range of 45.7% to 51.4% as compared with the sample without any pretreatment. It is explained as under thermal shock treatment, selective heating of the different mineral components resulted in thermal stress cracking [5]. Table 1: Physiochemical properties of PLK rock sample Physical properties Bulk density, g/cm3 True density, g/cm3 Porosity, % Angle of repose, ° 1.3 2.7 51.9 35.9 Chemical properties Al2O3 ,% SiO2, % Fe2O3, % TiO2, % LOI,% 37.24 40.64 4.3 1.66 16.26 Grain boundary fracture as well as micro-crack formation also occur in thermal shock treated samples. Typical cracks present in the PLK rock sample before and after thermal shock treatment can be seen in Fig 5. Due to development of cracks along the boundary and within the grains the rock mass will become weaken and hence facilitate for selective liberation of minerals or enhance the size reduction of PLK rock sample. Fig 2: XRD pattern of PLK rock
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 83-90 © IAEME 88 Fig 3: SEM of PLK rock samples Fig. 4: Effect of grinding time on thermal shock treatment of PLK rock Fig. 5: Effect of thermal shock treatment on development of cracks within the PLK rock sample Effect of thermal shock treatment on work index of PLK rock and power requirement per ton of ore to be ground is shown in Table 2. It indicates that the work index of natural PLK rock is 7.9 kWh/ton and the corresponding power requirement is 1100.4 kWh, while with increasing thermal shock temperature, the work index is found to be 7.5 kWh/ton and 3.2 kWh/ton at 793ºK and 1093ºK respectively. The corresponding power requirements at these temperatures are found to be 1048.3 kWh and 473.8 kWh. The data on the total power requirement for thermal shock treatment and grinding of the sample to the desired size (150 µm), is shown in Table 2. The data indicate that the power requirement for natural PLK rock is 1100.4 kWh whereas for thermal treated sample at 823 K the total power requirement is 1119.9 kWh. However, it is found that the thermal treated sample at 1123 K temperature for a period of 60 minutes, the total power requirement is units 580.7 kWh/ton. The total energy saving of 52.8 % has been achieved by thermal treatment of the sample. The details
  7. 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 83-90 © IAEME 89 are given in Table 3. Such power saving has been reported earlier by Banerjee and Rao (Banerjee and Rao, 2000) thermal treated bauxite. Table 2: Power requirement of PLK rock sample Temp, ºK Grindability, gbp Work index, kWh/ton Power/ton for grinding, kWh Natural 3.5 7.9 1100.4 823 3.3 7.5 1048.3 1123 2.7 3.2 473.8 Table 3: Power requirement of PLK rock sample after thermal shock and energy saving Temp,°K Power/ton for grinding, kWh (a) Power/ton for thermal treatment, kWh (b) Total Power/ton for grinding, kWh (a+b) Energy saving, % Natural 1100.4 - 1100.4 - 823 1048.3 71.9 1119.9 - 1123 473.8 106.9 580.7 52.8 The result drawn from this attempt is that the power can be saved in the size reduction of the material. Thermal shock treatment is one of the processes which can be adoptable by the communiation industries. PLK rocks, the bauxite mining waste can be a value added raw material for filler industries which need very fine particles. In view of this, the thermal shock treatment is widely acceptable for size reduction in microns and also saves energy, which can be used further for application in filler industries after suitable beneficiation. 4. CONCLUSIONS Partially Lateritised Khondalite (PLK) rocks are the waste materials generated during mining of bauxite. The results of thermal shock treatment on PLK rock reveal that a total energy saving of the order of 52.8 % could be achieved when a sample preheated at 1123 K for 60 minutes followed by sudden quenching in water followed by grinding. This may be due to a fact that in thermal shock treatment the ore minerals are subjected to thermal expansion by heat treatment and followed by rapid contraction of minerals by sudden quenching. 5. ACKNOWLEDGEMENT The authors are thankful to Professor B.K. Mishra, Director, for his kind permission to utilize infrastructure at CSIR –IMMT, Bhuaneswar and encouraging for publishing this paper. 6. REFERENCES [1] M. Dimitrijević, M. Pošarac, R. Jančić-Heinemman, J. Majstorović, T. Volkov-Husović, B. Matović, Thermal shock resistance of ceramic fibre composites characterized by non-destructive methods, Processing and Application of Ceramics, Vol. 2, No. 2, 2008, pp. 115–119. [2] R. B. Rao, L. Besra, B. R. Reddy and G. N. Banerjee, The effect of pretreatment on magnetic separation of ferruginous minerals in bauxite, Magnetic and Electrical separation, 8, 1997, 115-123.
  8. 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 83-90 © IAEME 90 [3] G. N. Banerjee, R.B Raoand B. R. Reddy, Removal of iron from low grade bauxite for refractory use, Mining engineers’ association of India, 2000, 90-100. [4] R. B. Rao, P. S. R. Reddy, B. Das, S. Prakash, K. K.Rao, A. R. Prasad, S. K. Das, Rajeev, P. S. Mukherjee, M. K.Ghosh, I. N. Bhattacharya and A. K. Sahoo, Studies on production of value added materials from partially laterized khondalite, Phase III, Collaborative project report no T/MPD/598/March/2007 of IMMT and NALCO, Bhubaneswar, 2007. [5] R. BhimaRao and Nivedita. Pattanaik, Preparation of high pure graphite by alkali digestion method, Scandinavian Journal of Metallurgy, Vol. 33, 2004, pp. 257-260. [6] A.Mariajayaprakash, Dr.T. SenthilVelan and K.P.Vivekananthan, “Optimisation of Shock Absorber Parameters using Failure Mode and Effect Analysis and Taguchi Method”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2, 2012, pp. 328 - 345, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [7] Mohammed Yunus, Dr. J. Fazlur Rahman and S.Ferozkhan, “Evaluation of Machinability Characteristics of Industrial Ceramic Coatings using Genetic Programming Based Approach”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 2, Issue 2, 2011, pp. 127 - 138, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [8] S Y Gajjal and Dr. A P S Gaur, “Assimilation of Spa and Pmt for Random Shocks in Manufacturing Process”, International Journal of Industrial Engineering Research and Development (IJIERD), Volume 2, Issue 1, 2011, pp. 80 - 90, ISSN Online: 0976 - 6979, ISSN Print: 0976 – 6987.

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