Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
EGBC National Exam — Mining and Mineral Processing Engineering, 09-MMP-A3 Mineral Processing, 2018-Dec. 3 hours duration, closed book; only an approved Casio or Sharp calculator permitted. Four questions constitute a complete exam paper (100 marks total).
Reference texts: Wills & Finch, Wills' Mineral Processing Technology, 8th ed. (comminution, crushers and mills – Ch. 6; classification, hydrocyclones and partition curves – Ch. 9; gravity concentration – Ch. 10; froth flotation, cells, reagents and flotation columns – Ch. 12; metallurgical balances, recovery/enrichment ratio – Ch. 1 & 12; solid-liquid separation, thickening and filtration – Ch. 15); SME Mining Engineering Handbook, 3rd ed. (porphyry copper mill flowsheets); BC Health, Safety and Reclamation Code for Mines, and the MEND/GARD Guide (Global Acid Rock Drainage Guide) for acid mine drainage prediction and control in the Canadian regulatory context.
Question 1: Bell Concentrator Flowsheet (15 marks)
Given. A block flow diagram for a 13,000 t/d porphyry-copper concentrator (Bell Mine, central BC, 1972–1992). Fixed boxes are labelled: Primary crusher, Primary screen, Regrind Hydrocyclone and 3rd cleaner flotation cells. Fourteen unlabelled boxes A–P must each receive one of the fourteen named unit operations (a one-to-one match), consistent with the drawn arrows (feed, splits and recycle loops).
Find. The unit operation identity of each box A, B, C, D, E, F, G, H, J, K, L, M, N, P.
Approach. Read the connectivity directly off the source diagram and match each box to the comminution/classification/flotation/dewatering stage its position in the loop structure requires: a three-stage closed-circuit crush ahead of the mills, a rod-mill/ball-mill/hydrocyclone grind loop, a rougher–scavenger–regrind–three-stage-cleaner flotation train, and a thickener–filter–dryer concentrate-handling train.
Fig. 1 – Bell Concentrator flowsheet with all fourteen unit operations identified. Given boxes (Primary crusher, Primary screen, Regrind Hydrocyclone, 3rd cleaner flotation cells) are shown for context; solved boxes A–P are labelled with both their letter and the matched operation.
Three-stage closed-circuit crushing (A, B, C, D). Primary screen oversize is still coarse and must be crushed again, so A = Secondary crusher. Its product and a returning oversize stream both enter a screening box, so C = Secondary screen: C's undersize (properly sized) joins the primary screen's undersize on the way to the mill, while C's oversize recycles to B = Tertiary crusher — the classic "screen closes the tertiary stage" closed-circuit crushing arrangement (all of A, B and C's own arrows form exactly this loop in the source figure). The combined, correctly sized crusher product then feeds D = Rod mill, the coarser of the two grinding stages.
Closed-circuit grinding (E, F). The rod mill (D) discharges into a box whose output splits two ways and which also receives a return stream from below — the signature of a classifier closing a mill loop: E = Hydrocyclone. Cyclone underflow (still coarse) recycles through F = Ball mill, whose discharge rejoins the rod-mill product ahead of E; cyclone overflow (correctly sized, ready for flotation) is the only other exit from E and reports forward to rougher flotation.
Rougher / scavenger / regrind (G, H, J). The cyclone overflow enters G = Rougher flotation cells. Rougher tailings pass to H = Scavenger flotation cells, whose own tailings are the (given) final Tailings — standard practice for scavenging the last recoverable copper before rejection — while H's concentrate recycles to the rougher feed (the line from the top of H back into the E→G stream). Rougher concentrate is not yet liberated enough for cleaning, so it reports down to the Regrind Hydrocyclone (given); the hydrocyclone's underflow (still coarse) is reground in J = Regrinding ball mill, whose discharge recycles back into the Regrind Hydrocyclone feed — a second, independent closed grinding loop dedicated to the rougher concentrate.
Three-stage cleaning (K, L). The Regrind Hydrocyclone overflow (now finely liberated) feeds K = 1st stage cleaner flotation cells; K's tailings reject to the final Tailings line and K's concentrate advances to L = 2nd stage cleaner flotation cells, combined with the tailings recycled back from the 3rd cleaner cells (given) one stage downstream. L's concentrate feeds the 3rd cleaner cells, whose own tailings recycle back to L — the standard reverse-cascade cleaner arrangement that keeps middling copper circulating forward rather than reporting to waste. L's own tailings return to the Regrind Hydrocyclone feed (joining J's discharge), so 2nd-cleaner middlings get a further regrind rather than being rejected.
Concentrate dewatering (M, N, P). The 3rd cleaner cells' final concentrate is still a dilute slurry and must be dewatered and dried before shipment, in the order bulk water removal → cake filtration → thermal drying: M = Thickener (bulk settling, thickened underflow), N = Filter (filter cake, ~85–90% solids), P = Dryer (final moisture removal), whose output is the Final concentrate shipped from the mill.
