24-MMP-A3 Mineral Processing · May 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Mining and Mineral Processing Engineering, 09-MMP-A3 Mineral Processing, 2013-May. 3 hours duration, closed book; only an approved Casio or Sharp calculator permitted. Question 3 allows a choice of any six (6) of nine sub-terms. Question 5 and its bonus (page 5) were to be handed in with the exam booklet; Question 4's log-log plot (page 6) is reproduced here as a computed inline figure.
Reference texts: Wills & Finch, Wills' Mineral Processing Technology, 8th ed. (flotation circuit design and metallurgical balances – Ch. 12; comminution, Bond's law and circulating load – Ch. 3 & 6; particle size analysis – Ch. 4; sampling theory, Gy's equation – Ch. 3; gravity concentration, dense medium separation, magnetic/electrostatic separation – Ch. 10, 11 & 13); Taggart, Handbook of Mineral Dressing (classical economic-recovery/economic-efficiency formula used in Question 1(vi)).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
| Item | Clue | Answer | Why |
|---|---|---|---|
| (a) | Main zinc-bearing ore mineral | Sphalerite | ZnS, the principal economic zinc mineral (galena, PbS, is its lead counterpart – the two are commonly co-listed distractors). |
| (b) | % of mineral occurring as free particles | Degree of liberation | Textbook definition – the fraction of a valuable mineral present as fully liberated (unattached to gangue) grains at a given grind size. |
| (c) | Ratio of feed to weight of concentrate | Ratio of concentration | $F/C$ – distinct from "ratio of enrichment" ($c/f$, a grade ratio) and "ratio of reduction" (a crushing/grinding size ratio). |
| (d) | Energy in size reduction ∝ new surface area | von Rittinger('s Law) | Rittinger's hypothesis (as opposed to Kick's Law, energy ∝ volume reduction ratio, or Bond's, energy ∝ $1/\sqrt{P}-1/\sqrt{F}$). |
| (e) | Jaw crusher pivoted at the top | Blake | Blake-type jaw crusher has a fixed pivot at the top (large throw at the bottom); the Dodge type is pivoted at the bottom. |
| (f) | Autogenous mill using steel balls too | SAG | Semi-Autogenous Grinding – ore itself does most of the grinding, supplemented by a modest ball charge (commonly 4–15% by volume). |
| (g) | $(d_{75}-d_{25})/(2d_{50})$ | Imperfection | The classifier sharpness index defined from the (corrected) partition curve – see Q3(ix). |
| (h) | Reagent that conditions the surface so it becomes hydrophobic under later collector action | Activator | An activator (e.g. copper sulphate on sphalerite) modifies the mineral surface chemistry so that a subsequently added collector can adsorb and confer hydrophobicity – the collector itself is a separate reagent, already named elsewhere in the list. |
| (i) | Common flotation depressant for sulphide minerals | Cyanide | Classic depressant for pyrite and other sulphides (e.g. in differential Cu/Zn or Pb/Zn flotation) by complexing surface metal ions and blocking collector adsorption. |
| (j) | Gravity unit using a pulsating water current | Jig | Defining action of a jig (Q3(ii)) – a pulsating water column stratifies the bed by density. |
Bonus (2 marks). Two Canadian mineral commodities routinely processed by dense (heavy) medium separation: metallurgical coal (dense-medium baths/cyclones are the standard coarse/intermediate-size preparation-plant technology at BC's Elk Valley and other Canadian coal operations, rejecting high-SG rock and pyrite from the lower-SG coal) and diamonds (NWT kimberlite operations such as Ekati and Diavik use dense-medium cyclones, typically ferrosilicon-based, to preconcentrate kimberlite ore ahead of final X-ray/optical sorting, rejecting low-value country rock at a coarse size before the diamonds themselves are recovered).
