Converting AG to SAG mills: The Gol-E-Gohar Iron Ore Company case

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hmicf thiny an(5epiedheease inimporreasonbrokentheir egle lifte, especall on lakage.ment towards the use of larger diameter steel grinding balls inheight have been incorporated in shell lifter design. Increasing shellling (DEM) computer programs that model charge ow in mills. DEMPowder Technology 217 (2012) 100106Contents lists available at SciVerse ScienceDirectPowder Tee lsorder to increase grinding efciency. A traditional top ball size wasaround 104 mm. Currently, 125 mm balls are in common use withsome mills using 140 and 152 mm balls (165 mm balls are nowbeing proposed). These developments have required a new approachto liner design through consideration of charge motion, especially themotion of the steel media in the mill. Aims of new designs are to im-prove the effective grinding through changes in shell lifter face angleshelps to understand chargemotion in SAGmills for given liner designsand lifters, ball and rock properties and mill operating conditions.Based on the success of the 2-D model of the SAG mill the 3-D modelin DEM was developed. The model could help to study charge motionand energy draft more accurately and also could provide informationregarding the effect of shell liner spacing as well as lifter face angleon charge motion. [3,8,9,11,15,21,22].and the spacing of the lifters [13,20,23,26].It has been known for many years that aon SAG mill shell lifters results in a change Corresponding author. Tel.: +98 341 2515901; fax:E-mail address: banisi@uk.ac.ir (S. Banisi).0032-5910/$ see front matter 2011 Elsevier B.V. Alldoi:10.1016/j.powtec.2011.10.014g to improved mill per-en the parallel develop-The availability of large-scale cost-effective computing power inrecent years has allowed the development of Discrete ElementModel-and improved ball-on-charge impacts, leadinformance [23,25]. Furthermore, there has beThe availability of these mills plays anics of the operation. One of the mainthe time required to change worn orble advantage of SAG over AG mills ising feed hardness variations.The use of liners with large face aner spacing has grown in recent yearsThe claimed benets were reduced bincreased liner lives and less ball bretant role in the econom-s for mills down time isliners [1,27,28]. A nota-xibility in accommodat-rs along with wider lift-ially in large SAG mills.iner impacts, leading toThese reduced packingCharge trajectory modelling has been used to present and interpretaggregate motion of a number of balls critical to the performance ofthe mill [24,25].Lifters are essential elements in the tumbling action of a grindingmill, whose purpose is to prevent slippage of the mill charge. Suchslippage consumes energy without substantial breakage, and themill may not lift the charge sufciently high to promote impactbreakage. Hence, the size, shape and number of lifters have a strongimpact on the tumbling action of the media [4,18].the mineral industry has been on risein capital and operating costs and incro a signicant reductionthe plants throughputs.lifter face angles (for the same mill speed) does reduce the impactpoint of thrown balls and can reduce shell liner damage [19,23,29].The use of large AG (autogenous)/SAG (semiautogenous) mills indue tConverting AG to SAG mills: The Gol-E-GoM. Maleki-Moghaddam, M. Yahyaei, S. Banisi Shahid Bahonar University of Kerman, Mining Engineering Group, Engineering Faculty, Islaa b s t r a c ta r t i c l e i n f oArticle history:Received 30 June 2011Received in revised form 11 September 2011Accepted 10 October 2011Available online 14 October 2011Keywords:SAG millMill llingLifter face angleBall trajectoryAt the concentration plant omills (xed speed) are usedthe target value indicated b515 m and low power drawangle from 7 to 30 while ketrajectory. When the propos5% (v/v balls were added t501 m.1. Introductionj ourna l homepage: www.change in the face anglein the trajectory of the+98 341 2112764.rights reserved.ar Iron Ore Company caseRepublic Blvd., Kerman, P.O. Box 761175-133, I.R. Irane Gol-E-Gohar Iron Ore Company (Iran) three 9 m2.05 m AG (autogenous)parallel in a dry operation. The performance of AG mills has been lower thanincrease in the product size (P80; 80% passing size) from 450 m (target) to0% of nominal). By simulation it was found that increasing the liner lifter faceng the original lifter height (i.e., 22.5 cm) could provide an appropriate chargeliners installed in one of the AG mills, the throughput increased by 27%; whenthroughput increased by 40%. The product size also decreased from 515 to 2011 Elsevier B.V. All rights reserved.thrown grinding balls. With the development of trajectory generat-ing computer programs, the effects of face angle, packing and lifterchnologyev ie r .com/ locate /powtecYahyaei and Banisi [29] used 3-D liner wear modeling to showthat the liner wear along the mill length is not uniform and providedindustrial data from a SAG mill used at the Sarcheshmeh copper com-plex [28,29]. They developed a spreadsheet-based software to modelcharge trajectory in tumbling mills using Powell's [17] analytical ap-proach and investigated charge trajectory change during the lifetime of a liner set. According to Powell if the grinding media is posi-tioned at the tip of lifter it will start its free ight after the point ofconversion on a smaller scale, which resulted in higher grinding per-formance [12]. A methodology is proposed beginning with nding annumber of lifters are entered. In parameter section, static and dynamicfrictions and mill speed for each liner design are entered.2.2. The model millIn order to determine ball trajectories at different operating condi-tions and liner proles, a 100 cm3.6 cm mill was designed and con-structed. The transparent end of the mill made possible accuratetrajectory determination by image analysis. A 2.5 kW motor with avariable speed drive was used to provide sufcient exibility to testvarious operating speed conditions. A diameter scale down ratio of9 to 1 was used to construct the model mill using the plant mill di-mensions. The mill served as a 2-D model, but there is the possibilityof changing it to a 3-D model mill.In order to exactly duplicate the plant liners arrangement in themill, a polyurethane ring was accurately machined to create 36 liftersin a row (Fig. 1). By this method any number of liners in a row withdifferent designs could be tested. Between the lifters 36 plates werealso included consistent with the plant liner design. Only one of thethree sections of the liners along the mill length was built andinstalled in the 2D model mill.101M. Maleki-Moghaddam et al. / Powder Technology 217 (2012) 100106appropriate charge trajectory by mathematical modelling consideringvarious liner proles, testing physical models of the selected linerproles in a laboratory mill and nally arriving at a liner design forlarge-scale industrial mills. It is believed for the rst time the trajecto-ry obtained for a single ball is corrected with the introduction of asafe operating window concept. In fact, the effects of charge andliner prole which impose extra forces on balls are taken indirectlyinto account on the charge trajectory calculation through using thesafe operating window.2. Materials and methods2.1. Charge trajectory predication softwareIn order to determine charge trajectory, a software called GMT(Grinding Media Trajectory) was used [29]. The approach taken byPowell [17] was used as a base to determine charge trajectory. GMTin comparison with other software packages has the advantages ofusing all MS Excel readily available functions and capabilities. Themain feature of GMT is the ability to show the kidney-type shape ofthe charge along with the trajectory which has not been incorporatedin similar software packages. Morrell's [16] approach was applied todetermine shape of the charge in which he used a laboratory millwith one transparent end and photographed the load under variousoperating conditions. The variation of the toe and shoulder positionsfor three different liner proles at various mill speeds and llingswere studied in his work. Then he proposed various empirical equa-tions to relate the positions of toe and shoulder and inner load radiusto mill speed and lling. Because of the differences in the calculationof charge trajectory for rods and balls an option in GMT has been pro-vided which enables the user to choose the media type. The dataentry section of the software includes ve parts to be completed bythe user: general information, mill, grinding media and liner data,and parameters. In the mill section, the values indicating the effectivediameter, speed and lling are entered. In the grinding media section,the media type (i.e., ball or rod), diameter and density are recorded.equilibrium. Otherwise, it will start to role or to slide on the lifter sur-face until it reaches the edge of the lifter. Then it will fall into freeight. When the grinding media reaches the edge of liner, the refer-ence frame should change to a Cartesian coordination which its originis positioned at the mill center to simplify the calculations. The speedof the particle composed of its linear velocity parallel with the lifterface and angular speed resulted from mill rotation. These two typesof speeds should resolve into components parallel with Cartesianaxes for calculating the charge trajectory. The free ight of chargewill end when it encounter the mill shell. Yahyaei and Banisi [29]showed that the largest difference in the angles of charge impactpoints along the mill length due to non uniform wear was 34which occurred after 3000 h of operation.As the charge volume increases, the greater fraction of the netpower draw is consumed in the form of charge abrasion and lowenergy impacts, while the fraction of net power that leads to highenergy impacts gradually decreases [5].A correct balance between the low and high energy impacts is es-sential for successful comminution practices. This could be achievedby introduction of wide-sized (mature) balls into the mill which inturn provides a broad spectrum of forces to be applied to the particles.This research was carried out to convert existing AG mills to opti-mized SAG mills at the Gol-E-Gohar concentration plant to improveboth grinding efciency and to decrease the sulphur content of con-centrate by increasing the degree of liberation of sulphur bearingminerals. There had previously been at least one report of such aIn the liner section, lifter face angle, liner height, lifter width, andFig. 1. The polyurethane ring machined to scale down the liners arrangement of the2.3. The Gol-E-Gohar iron ore concentration plantThe Gol-E-Gohar iron ore concentration plant located in southeastIran. Three 9 m2.05 m AG mills are used in parallel in a dry opera-tion to grind a feed nominally passing 32 cm, which is the productof a gyratory crusher. The SAG mills is driven by a 4023 hp motorand runs at a constant (12 rpm rotational) speed (i.e., 85% of criticalspeed) in one direction. The mill shell is lined with three series(57 cm each) of 36 row liners. Specications of liners used areshown in Table 1. According to the liner manufacturer recommenda-tion, the liners should be changed when the lifter height reaches100 mmwhich is one third of its initial height. Due to large variationsin feed characteristics and inadequate blending, the performance ofAG mills has been lower than the target value. An increase in P80 ofthe product from 450 m (nominal) to 515 m indicates the extentof the change. Another indication was low power draw of the millwhich was only 50% of the nominal value. Furthermore, the coarserplant mill.product resulted in higher sulphur content of concentrate due tolower liberation of pyrite, which is the main sulphur bearing mineral.ent end of the mill made possible to monitor the charge trajectorythe tests were performed at 14, 16, 18, 20 and 24% llings. Since therotation speed of Gol-E-Gohar concentration plant mills was xed at85% of critical speed, this rotation speed was selected for all tests.Fig. 4 illustrates the charge shape and trajectory for the original andnew liners at 20% lling.Table 1Specications of liners at the Gol-E-Gohar concentration plant used in GMT software.Platethickness(mm)Lifter Liftersin rowNumberof rowsFace angle () Height (mm) Width (mm)75 730 225 125 3 36102 M. Maleki-Moghaddam et al. / Powder Technology 217 (2012) 100106To convert AG to SAG mills 5% (v/v) balls with the sizes andamounts shown in Table 2 were used.3. Results and discussion3.1. Charge trajectory predictionThe charge trajectory of 125 mm balls with 18% total lling, whichwas predicted by the GMT software, is shown in Fig. 2.The balls impact points clearly indicates that with the originalliner design ball addition could results in direct impact of balls onthe liners causing severe damage. The low throughput of the millcould also be attributed to inappropriate trajectory where the toe ofthe charge does not receive any appreciable direct impacts from thefalling load. The effect of different llings on the positions of theballs impacts was also studied (Table 3). This part of the study wasperformed with the objective of determining whether the ballscould fall on the toe. The distance between impact points and thetoe was measured in degrees. Even at 24% lling which was consid-ered high for the Gol-E-Gohar operation there was 55 difference be-tween the balls impact points and the position of toe.3.2. Safe operating windowsThe analysis performed by the software does not take into accountthe interaction between balls and particles and also the forces actingon the balls due to charge and liner prole. It is also a 2-D analysis anddoes not consider the effect of charge interaction along the milllength. In addition to some simplied assumptions in arriving at thetrajectory, the assumed shape for the charge also is not very realistic.In order to nd safe operating windows where no direct impacts ofballs on liners occur, the charge trajectories of some mills with noliner breakage were determined by the GMT software. The name ofthe plants, and all input data along with the balls impact points mea-sured as the distance between the impact points and the toe areshown in Table 4.Considering the standard deviation of the distances (=4.8), as-suming a normal distribution, the range of distance between the im-pact points and the toe with 95% condence level was found to bebetween 17.4 and 36.2 with the average of 26.8. This value wasused to design the new liners for the conversion from AG to SAG mill-ing in order to be certain that the damage to the liners due to the di-rect impact of balls will be avoided. The wide observed range (7.7 to52.5) difference between impacts points of a single ball with that ofthe charge indicates the effect of differing operating parameters suchTable 2Size and amount of balls added for 5% (v/v) lling.Ball size (mm) Amount (%) Weight (t)125 27.1 5.7115 21.4 4.5100 16.7 3.590 11.9 2.580 22.9 4.8Total 100 21inside the mill. Steel balls within the size range of 412 mm wereadded to provide the desired llings. This size range was selectedbased on diameter scale down ratio of 9 to 1 considering the AGmill feed size distribution. In other words, based on the size distribu-tion of the industrial mill feed the steel balls were chosen to simulatethe feed in the laboratory mill. For both the original and new liners,as amount of charge and mill rotational speed in the studied plants.Since the average difference (26.8) was used in the design of thenew liner, the difference in rotational speed of the mill (85%) withthe surveyed plants (7380%) was not deemed to introduce any sig-nicant error.3.3. New liner designThe new liner not only should provide an appropriate load trajec-tory, but it should also be as similar as possible to the original linerdesign for easy installation and removal. By simulation of charge tra-jectories at various liner shapes it was found that lifter face angle wasthe most effective parameter inuencing the charge trajectory; as aresult for the new design the lifter face angle increased while lifterheight was kept constant.To obtain a lifter face angle which provides an appropriate chargetrajectory, the face angle increased from 7 to 30 and the trajectoriesobtained by the GMT software were compared (Fig. 3). The results in-dicated that when the face angle increased from 7 to 30, the distancebetween the impact point and the toe decreased from 55 to 14 for24% lling and decreased from 63 to 22 for 18% lling.Since balls impact points were within the safe operating windows(i.e., 17.4 to 36.2), the lifter face angle of 30 was selected forthe new design. To ensure the appropriate load trajectory, thelaboratory-scaled models of the original and new liners were con-structed and tested in the 1-m diameter laboratory mill. The transpar-Fig. 2. Simulation of 125 mm ball trajectory for old liner (18% lling) by the GMTsoftware.Table 3The distance between impact points and the toe measured in degrees for various millllings.Total lling (%) Distance between impact points and toe ()14 6916 6618 6320 6124 553.4. Effect of liner change on the mill performanceTable 4Operating data of the plants along with simulation results of ball trajectories obtained by GMT software.Mine Total lling (%) Ball lling (%) Maximum ballsize (mm)Speed(% of critical speed)Distance between the impactpoints and the toe ()David Bell [14] 25 610 100 75 52.5Kennecott, liner 1 [2] 24 12 120 75 48.2Kennecott, liner 2 [2] 24 12 120 75 25.6Kennecott, liner 3 [2] 24 12 120 75 10Candelaria, liner 8 [10] 29 12 127 73 25.9Candelaria, liner 20 [10] 29 12 127 73 10.5Northparks [6] 20 10 125 78 20.1Anglo Chile, Mill 1 [19] 24 13 125 78 17.6Anglo Chile, Mill 2 [19,20] 18 14 125 74 7.7Newcrest Mining Ltd. [7] 15 - 125 75 12.5Sarcheshmeh [1] 18 12 120 80 47.2Sarcheshmeh [1] 20 12 120 80 44.5103M. Maleki-Moghaddam et al. / Powder Technology 217 (2012) 100106Considering the charge shape and impact points it is evident thatmill llings should be more than 20% to prevent direct impact ofballs to liners. Given the promising results obtained in the laboratorymill, the new liners with 30 lifter face angle and unchanged lifterheight (i.e., 22.5 cm) was constructed and installed in one of thethree parallel dry AG mills. Fig. 5 shows the original and new liners.Because of the higher lifter face angle of the new liner the lifting lugused to move the liner was placed at the top. The weight of the linerswas kept equal to the original design, so as not to increase the totalweight of the mill.Fig. 3. Simulation of 125 mm balls trajectories with different lifter face angles (24%lling).Fig. 4. The charge shape and trajectory of the originalTo evaluate the effects of new liner design, the average through-put of the mill (No. 2) for a period of 18 months before the linerchange was compared with the average throughput of the mill1.5 months after the change. The throughput increased from 419 to532 t/h after the new liners were installed. This signicant increaseof 27% in throughput was attributed to the change in the charge tra-jectory and ball impacts on the toe which led to improved grinding ef-ciency. For further analysis the tonnage range spectrum for the millwas obtained before and after installing new liners for the aforemen-tioned period (Fig. 6). Variation in throughput occurred because ofthe change in the ore hardness, feed size distribution, insufcientore blending and downstream capacity limiting issues. Before linerchange, at 50% of operation time the throughput was within400500 t/h range while after installing the new liners at 74% of theoperation the throughput was within 500600 t/h. The share of600700 t/h range increased from 1 to 5.3% indicating a signicantimprovement in the throughput.Operating three identical AG mills in parallel provided a uniqueopportunity to separate ore characteristics effects from the inuenceof the liner change. The average throughputs of mill No. 1 and No. 2over a period of 18 months before the liner change (in mill No. 2)were 41472 t/h and 41967 t/h, respectively. Given the standarddeviations the difference was not found to be signicant at 95%condence level. During a period of 1.5 months after installing thenew liners, the average throughput of the mills No. 1 and No. 2were 41437 t/h and 53248 t/h, respectively, which indicated asignicant increase.and new liners in the laboratory mill (20% lling).The average product size (P80; 80% passing size) of the mill beforeand after the liner change were 516 and 513 m, respectively indicat-ing no signicant change in the neness of the grind.3.5. Converting AG to SAG milling and grinding performanceAn important prerequisite to convert AG to SAG mills was to as-sure that the mill llings was above 20%. On two occasions the millwas crash stopped and the llings were found to be 22 and 26%. Toprovide 5% (v/v) balls, 21 t balls with sizes and amounts shown inTable 2 were added. The power draw of the mill was used as themain parameter to control the mill lling. Based on the previous ex-perience the power draw was set at 2300 kW. The feed rate was themain manipulated parameter to keep the power draw at the setpoint. The conditions of the liners were checked after 20 h of opera-tion by crash stopping the mill. No broken or cracked liners werefound which veried the appropriate ball trajectory with new liners.The mill lling was 21% which was sufcient to provide self protec-tion of the mill shell from direct impacts of balls. The rst and themost important effect of conversion to SAG milling was the stabilityof the process judged by the stable power draw of the mill. Thiswas also observed in 34% reduction in feed rate standard deviation(decreasing from 67 t/h with the original liners to 45 t/h) when theconversion to SAG milling practiced.In SAGmilling mode the throughput increased from 532 to 589 t/h(two-month average) with the only liner change. Overall increase of40% in the throughput (419 to 589 t/h) was realized by both changein the liner design and addition of 5% balls. The throughput of themill (No. 2) for a period of 3.6 months is shown in Fig. 7. The steadyincrease in the throughput is evident due to liner change and ballsaddition. The change in the ore characteristics are also seen in thevariation of the throughput in each period (i.e., before changes, afterliner change, and after ball addition).The product size (P80) also decreased from 513 to 501 m.Throughputs and product sizes of the mill along with their standarddeviations before and after changes are summarized in Table 5.Three months after conversion to SAG milling 40% increase inthroughput in addition to 3% decrease in the product size could beconsidered as themain outcome of this change. The balls consumptionFig. 5. The original and new liners used at the Gol-E-Gohar concentration plant mills.l No104 M. Maleki-Moghaddam et al. / Powder Technology 217 (2012) 100106Fig. 6. Throughput range spectrum for milFig. 7. Throughput of mill No. 2. 2 before and after installing new liners.for a period of 3.6 months.was determined to be 37 g/t. Make up balls (125 mm) were addedevery 8-hour shift.3.6. Effect of operational parameters on the SAG mill performancetended to the operating, maintenance, metallurgy and R&D personnelfor their continued help.References[1] S. Banisi, M. Hadizadeh, 3-D liner wear prole measurement and analysis in in-dustrial SAG mills, Minerals Engineering 20 (2007) 132139.Table 5Throughputs and product sizes of the mill before and after liner change and after ballsaddition.Averaging period(months)Throughput(t/h)P80(m)Before change 18 41967 51644After liner change 1.5 53248 51337After balls addition 2 58945 50137105M. Maleki-Moghaddam et al. / Powder Technology 217 (2012) 100106The main manipulated parameter to control the dry SAG mill wasthe exhaust fan power draw. The higher the power draw of the fanthe higher the amount of discharged particles. When the amount ofdischarged particles increased the feed rate to the mill was also in-creased to keep the power draw of the mill at the set point value. Inother words, the power draw of the exhaust fan and the feed rate tothe mill was interrelated. The power draw of the mill was set at2300 kW to provide mill lling of at least 20% depending on the orehardness. At this operating condition (i.e., mill power draw of2300 kW) the effect of power draw of exhaust fan on the productsize was investigated over a period of two months (Fig. 8). Everypoint is a composite sample of four sample cuts each taken at15 min intervals. To reach steady state after any change in the ex-haust fan power draw a period of 2 h was allowed.A liner relationship (Eq. (1)) was found between the exhaust fanpower draw (PEx) and P80. The relationship was then used to ndthe exhaust fan power draw which granted the desired product size.P80 0:28PEx22 1To arrive at the product size of 450 m, the exhaust fan powerdraw should be set at 1650 kW which in turn dictates a certain feedrate. In Fig. 8 for equal exhaust fan power draws (1500 and1750 kW) different values for P80 were found which indicated thechange in the ore hardness over the study period.When the feed rate (F) was plotted vs. P80 for the same study a lin-ear relationship (Eq. (2)) was also obtained (Fig. 9).P80 0:48F 166 2To obtain the product size of 450 m the exhaust fan power drawwas proposed to be between 1650 and 1700 kW. At this operatingcondition the dictated feed rate was 580 t/h.Fig. 8. The P80 of SAG mill No. 2 in different exhaust fan power draws.4. Conclusions The charge trajectory in the AG mills of the Gol-E-Gohar iron oreconcentration plant was simulated by a spreadsheet-based soft-ware called GMT with a view to optimizing the liner prole. The safe operating windows in plants, dened here as milling con-ditions that do not result in liner breakage because of direct im-pacts of balls to the mill shell, corresponded to the ball impactpoints with a distance between 17 and 36 from the predicted toe. Increasing the lifter face angle of AGmill from 7 to 30 while keep-ing the original lifter height (i.e., 22.5 cm) provided an appropriatecharge trajectory. Testing the original and proposed liners in a 1-m diameter 2Dmodel mill indicated that total mill lling should be more than20% to prevent direct balls impacts to liners. Throughput of the AG mill increased by 27% due to the change inthe liner design, without any adverse effect on the product size. Conversion to SAG milling by adding 5% (v/v) balls resulted in anoverall increase of 40% in the mill throughput, and a relativereduction of 3% in the product size. More stable plant operation was obtained in the SAG operatingmode, as quantied by a reduction of 16% and 15% in the standarddeviations of mill power draw and product size, respectively. The target product size (P80) of 450 mwas obtainedwhen the ex-haust fan power draw was 16501700 kW which in turn dictatedthe feed rate of 580 t/h.AcknowledgementsThe authors would like to thank Gol-E-Gohar Iron Ore Companyfor supporting and implementing the outcome of this research andalso permission to publish the article. Special appreciation is also ex-Fig. 9. Product size and feed rate relationship for the SAG mill.[2] S. Bird, A.E. Lamb, W. Lamb, D.W. Partrifge, Evolution of SAGmill shell liner designat Kennecott Utah copper concentrator, Proceedings International Autogenousand Semiautogenous Grinding Technology. University of British Columbia, Van-couver. (2001) pp. 256269.[3] P.W. Cleary, Charge behavior and power consumption in ball mills: sensitivity tomill operating conditions, liner geometry and charge composition, InternationalJournal of Mineral Processing 63 (2001) 79114.[4] N. Djordjevic, Discrete element modelling of the inuence of lifter on power drawof tumbling mills, Minerals Engineering 16 (2003) 331336.[5] N. Djordjevic, F.N. Shi, R. Morrison, Determination of lifter design, speed and ll-ing effects in AG mills by 3D DEM, Minerals Engineering 17 (2004) 11351142.[6] R. Dunn, K. Fenwick, D. Royston, North parks mines SAG mill operations, Proceed-ings International Auogenous and Semiautogenous Ginding Technology, Univer-sity of British Columbia, Vancouver. vol. 1. (2006) 104119.[7] S. Hart, L. Nordell, C. Faulkner, Development of a SAG mill shell liner design atCadia using DEM modelling, Proceedings International Autogenous and Semiau-togenous Grindig Technology University of British Columbia, Vancouver. vol. 3.(2006) pp. 389406.[8] O. Hlungwani, J. Rikhotso, H. Dong, M.H. Moys, Further validtaion of DEM model-ing of milling: effect of liner prole and mill speed, Minerals Engineering 16(2003) 993998.[9] J.T. Kalala, M. Breetzke, M.H. Moys, Study of the inuence of liner wear on theload behaviour of an industrial dry tumbling mill using the Discrete ElementMethod (DEM), International Journal of Mineral Processing 86 (2008) 3339.[10] M.J. Kendrick, J.O. Marsden, Candelaria post expansion exolution of SAG mill linerdesign and milling performance, 1998 to 2001, Proceedings International Autog-enous and Semiautogenous Grinding Technology, vol. 3, 2001, pp. 270287,(Vancouver).[11] A.B. Makokha, M.H. Moys, Towards optimising ball milling capacity: effect of lifterdesign, Minerals Engineering 19 (2006) 14391445.[12] B. Marchant, K. Major, B. Fukuhara, Conversion to SAG Milling at El Limon, Nica-ragua, Proceedings International Autogenous and Semiautogenous GrindingTechnology, University of British Columbia, Vancouver. vol. 1. (2006) pp. 69.[13] R.E. McIvor, Effect of speed and liner conguration on ball mill performance, Min-ing Engineering (1983) 617622.[14] K. Meyer, SAG mill operating experience at the Hemlo, Ontario, Canada David bellmine concentrator, Proceedings International Autogenous and SemiautogenousGrinding Technology, University of British Columbia, Vancouver. vol. 1. (1989)pp. 33347.[15] B.K. Mishra, R.K. Rajamani, Numerical simulation of charge motion in ball mills-lifter bar effect, Minerals and Metallurgical Processing (May 1993) 8690.[16] S. Morrell. The prediction of power draw in wet tumbling mills. Doctorate Thesis,[26] D. Royston, Developments in SAG mill liner design, Advances in Comminution(2006) 399412.[27] M. Weidenbach, P. Grifn, Liner optimisation to improve availability of the ridge-way SAG Mill, Proceedings Mill Operators' Conference 2007, 2007, pp. 125129.[28] M. Yahyaei, S. Banisi, M. Hadizadeh, Modication of SAG mill liner shape based on3-D liner wear prole measurements, International Journal of Mineral Processing91 (2009) 111115.[29] M. Yahyaei, S. Banisi, Spreadsheet-based modeling of liner wear impact on chargemotion in tumbling mills, Minerals Engineering 23 (2010) 12131219.Mostafa Maleki-Moghaddam obtained his B. Eng.(Exploitation) andM.ENG. (Mineral Processing) fromMin-ing Engineering Departemnt of Shahid Bahonar Universityof Kerman, Iran. He worked for two years in titanium con-centration plant and then returned to the university. He iscurrently a Ph.D. student in the Mineral Processing group.Mohsen Yahyaei obtained his B. Eng. in mining explora-tion from Sahand University of Technology, IRAN. Thenhe joined mineral processing group at Shahid BahonarUniversity of Kerman where obtained he M.ENG. (2002)and Ph.D. (2011). For 3 years (20042007) he workedcessing research center at Shahid Bahonar University ofKerman.106 M. Maleki-Moghaddam et al. / Powder Technology 217 (2012) 100106[17] M.S. Powell, The effect of liner design on the motion of the outer grindingelements in a rotary mill, International Journal of Mineral Processing 31 (1991)163193.[18] M.S. Powell, Liner selectiona key issue for large SAG mills, Proceedings Interna-tional Autogenous and Semiautogenous Grinding technology, University of Brit-ish Columbia, Vancouver. vol. 3. (2001) pp. 307322.[19] M. Powell, P. Condori, I. Smit, W. Valey, The value of rigorous surveysthe LosBronces experience, Proceedings International Autogenous and SemiautogenousGrinding Technology, University of British Columbia, Vancouver. vol. 1. (2006)pp. 233248.[20] M. Powell, I. Smit, P. Radziszewski, P. Clear, B. Rattray, K.G. Eriksson, L. Schaeffert,Selection and design of mill liners, Proceedings Advances in Comminution, 2006,pp. 331376.[21] M.S. Powell, N.S. Weerasekara, S. Cole, R.D. LaRoche, J. Favier, DEM modelling ofliner evolution and its inuence on grinding rate in ball mills, Minerals Engineer-ing 24 (34) (2011).[22] R. Rajamani, A.D. Joshi, B.K. Mishra, Simulation of industrial SAG mill charge mo-tion in 3D space, Proceedings 2002 SME Annual Meeting, SME Publication, Phoe-nix, Arizona, 2002.[23] R. Rajamani, Semi-autogenous mill optimization with DEM simulation software,Advances in Comminution, SME Publication, Part 4, 2006, pp. 209214.[24] D. Royston, Interpretation of charge throw and impact using multiple trajectorymodels, Proceedings International Autogenous and Semiautogenous Grindingtechnology vol. 4, 2001, pp. 115123.[25] D. Royston, A review of recent experience with large-angle wide-spaced shell lifterliners, Proceedings 2003 SME Annual Meeting, SME Preprint 03056 (Cincinnati,Ohio), 2003.Samad Banisi graduated from Isfahan University of Tech-nology, Iran, in 1985, with a B.Eng. in mining engineering.He obtained his M. Eng. in 1991 and Ph.D. in 1994, in min-eral processing from McGill University, Montreal. He ispresently professor of mineral processing at the MiningEngineering Department of Shahid Bahonar University ofKerman. His research interests include plant trouble shoot-ing and optimization, column otation and modeling ofgrinding.as superintendent for coal processing plant (Interkarbon).He is currently research fellow at Kashigar mineral pro-University of Queensland, Australia, 1993.Converting AG to SAG mills: The Gol-E-Gohar Iron Ore Company case1. Introduction2. Materials and methods2.1. Charge trajectory predication software2.2. The model mill2.3. The Gol-E-Gohar iron ore concentration plant3. Results and discussion3.1. Charge trajectory prediction3.2. Safe operating windows3.3. New liner design3.4. Effect of liner change on the mill performance3.5. Converting AG to SAG milling and grinding performance3.6. Effect of operational parameters on the SAG mill performance4. ConclusionsAcknowledgementsReferences

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