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exm301i20081 - ”‘1 UNIVERSITY PERTH WESTERN AUSTRALIA...

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Unformatted text preview: ”‘1 UNIVERSITY PERTH, WESTERN AUSTRALIA Egg MURDOCH Examinations — Semester 1, 2008 ExamType : Internal Reading time : 10 minutes (Note taking allowed onto Exam Paper ONLY) Exam Duration : 3 hours ANSWER ONLY FIVE QUESTIONS ALL QUESTIONS CARRY EQUAL MARKS AS INDICATED Provided by the University GRAPH PAPER (A4 1MM) GRAPH PAPER (LOG-LOG) Provided by the Candidate CLOSED BOOK EXAM - CALCULATOR PERMITTED (NOT GRAPHICS) b) b) b) ANSWER ONLY FIVE QUESTIONS ALL QUESTIONS CARRY EQUAL MARKS AS INDICATED It is required to evaluate options for a comminution circuit to prepare the feed to a flotation plant. Suggest a flow sheet for the comminution circuit comprising of a primary crusher, SAG mill, pebble crusher, hydrocyclones and a regrind mill. Briefly discuss the characteristic features of each unit and the size range of material passing through each stage. . (10 marks) Discuss the merits of using a SAG mill over the alternative of secondary crushing followed by ball milling? Under what conditions would the choice of SAG milling not be favourable. (5 marks) What are the beneficial effects of having a recirculating load in the comminution circuit? (5 marks) Describe a sub-sieve technique for measuring particle size distribution. (5 marks) In an Andreason pipette experiment to determine the size distribution of a silica sample, the three 10 m1 samples taken at 0, 100 and 200 seconds yielded 200, 130 and 60 mg of solids respectively. Depth to the sampling point below the surface is 20 cm. Determine: i) The largest size of particles remaining in suspension above the sampling point at 100 and 200 seconds respectively. (4 marks) ii) The percentage of particles in the silica sample within these sizes. (6 marks) Stoke’s Law is given by: V = gd2(pS—pf)/18|J Viscosity of water = 0.001 Nsm'2 The size distribution data of a magnetite sample is shown in figure 1 below as a Rosin-Rammler plot. Evaluate the model parameters. (5 marks) Briefly discuss: 1) Factors affecting the size of a sample taken for assay purposes ii) Effects of increasing the speed of a tumbling mill (3 x 2 marks) A 3m diameter ball mill wet grinds a gold ore of work index 14 kWh/tonne at the rate of 250 tonne/h. The 80% passing size of the feed is 2.3 cm and that of the product is 180 microns. Determine the power of the motor required to drive the mill if the efficiency of power transmission is 90%. (10 marks) Under what conditions would the power requirements determined by Bond formula be valid? How are the non—standard conditions taken into account? (4 marks) a) Briefly describe the regions within an operating hydrocyclone (4 marks) b) The performance curve of an operating hydrocyclone is shown in Figure 2. i) What is the fraction of the feed water reporting to the underflow. (2 marks) i) Plot the corrected performance curve on the same graph paper and determine the corrected cut size (dsofi) (attach graph) (8 marks) ii) Hence plot the reduced performance curve of the hydrocyclone. (6 marks) a. What are separability curves and what do they represent? (5 marks) b. The performance curves of an operating jig and a dense medium cyclone are shown in Figure below. Estimate the cut SG, probable error and imperfections for the two devices. ' (6 marks) 05- Performance curves for Jig and Dense medium cyclone “’0‘ P: v: t 3 80 ~ 3: — mi i.-- .E 70 _ i - . _-_ NW _ m l r t _ .9 60 ‘i‘ I L_ w m +JIG 3 50 ‘ ' ‘ I ' _-_-_ :-:_ “Jr: +DMC E 40 J “ i: .: E 30 — — -- me» 1 ——~ a 3 _ i. _ _. .4. 0 20 “ :__-;i:‘ :‘i‘ if ,: 1O -. ”FEM _ .\ __L L- 0 FL“ :‘ ‘“" ”WW 1 3 1 4 1 5 1.6 1 7 1 8 1 9 SG c. A coal of —32 + 0.5mm size Whose sink/float data are given in the table 1 below is to be processed using one of these devices. Which device would you recommend and what would be the yield and ash content in the clean coal product. (9 marks) TABLE1:$NKNIOATDATA FOR COAL -32mm+0.5mm ash° Discuss the following: i) ii) iii) The differences between electrostatic and high tension separators and how the charges are developed in the particles in each case. (6 marks) Factors affecting the performance of industrial screens. (6 marks) Single measures of efficiency used to evaluate separator performance and their drawbacks. (8 marks) Y 1100iI|IIIII= - fle>lcp{- (x/k)n} ] where n Is sIope of line and k Is intercept vI/Ifh Y' = 36.79. “meme mummmmmmmmm mmmmmmm II “I“ Imam mm mm IIIIIInIm .uIIII. Immmu “IMHIIImImnmum “mummmmmmnl m MmmmmMMWIIIIIII II IIIMmmnuuaIIfimI .IumIIusmHu-u nmnmamImII narruu mm IIHII llml I III-II- I IIIIum “I““m IIIII II IIIII- I“"“" m "m“I M“ In". I mmnmmm mllnlnfllnlll “In“ IIflu—nnIIIlul II II I :nunIIII munllnlnln ll "nunflfluuuuuu"unannnflufl"Human".IIm"WW""unnunInflnflfluunnmuunflnnununnIllI-“nI V. ulluflunufiafianun.uunnmnnunnunnuu“muuuuunununnflflnunnlld“nuulflnlIlunulIa "nflflnufimtmmnnmumllumammmmmmum.mmmmmnmmmumuflflflflflnlllnnflflflflnfi I III-IlllIlmIIIIIIF. IRWmMIIHIW IMIMMIuImu-mmmfimmmum- ImmmmmmmnmIMMMMMMMHIIIIIa INHIIIIMHIHIHInInmnmImImImeMuI II ,mm mumm mummmmnmmmnummmmmmmlmmflnflmmmmmmflflfi5 "IIIIIIIIIIII IIIll ! IIII' mammal! II' III" IWummmmmmmmmmmmmmflmmmummEmmmmmmummmmmmm ”III Wan“. 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