24-MMP-A3 Mineral Processing · December 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Mining and Mineral Processing Engineering, 09-MMP-A3 Mineral Processing, 2017-Dec. 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(v)).
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) | Equation for terminal settling velocity of fine particles | Stokes('s Law) | For fine particles at low Reynolds number, $v_t=\dfrac{g\,d^2(\rho_s-\rho_f)}{18\mu}$ – the classical basis for hydraulic classifier and thickener design; distinct from Newton's Law, which governs coarser, turbulent-regime settling. |
| (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) | Pipe extending down from the cyclone overflow | Vortex finder | The vortex finder is the downward-projecting pipe at the cyclone's top that carries the fine/light overflow product out of the vessel; distinct from the apex (the underflow orifice at the cone's bottom). |
Bonus (2 marks). Two Canadian mineral commodities that are not routinely processed by froth flotation: diamonds (a diamond's surface is not naturally hydrophobic under normal flotation reagent chemistry, so NWT/Ontario kimberlite operations such as Ekati, Diavik and Victor instead use dense-medium separation followed by X-ray transmission/luminescence or optical sorting to recover the stones) and uranium (Saskatchewan Athabasca Basin operations such as Cigar Lake/McArthur River recover uranium by crushing/grinding followed by acid or alkaline leaching and solvent extraction/ion exchange – a hydrometallurgical, not a froth-flotation, flowsheet).
