21-Mat-B1 Hydrometallurgy and Electrometallurgy · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. National Professional Examinations, December 2014 — 10-Met-B1, Mineral Processing. Three hours, closed book, approved Casio/Sharp calculator only. Six numbered Problems (all compulsory except Problem 5) plus a two-mark Bonus Question. Problem 5's rubric asks for any SIX of eleven sketch-and-describe topics; all eleven topics are answered below.
Nothing on the paper is a hydrometallurgy (leaching, solvent extraction, electrowinning) or electrometallurgy question; the syllabus actually examined is comminution and grinding-circuit mass balance, particle settling, flotation kinetics, and mineral-processing equipment/terminology — the physical/mechanical beneficiation stage that precedes hydro- or pyro-metallurgical extraction.
Reference texts. The answers below are keyed to the works normally recommended for this syllabus code:
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.
Ten one-mark identifications, matched to the word list printed on the exam's page 5.
| Item | Statement | Answer |
|---|---|---|
| (a) | Main lead-bearing ore mineral | $\boxed{\text{Galena}}$ (PbS) |
| (b) | Percentage of mineral occurring as free particles | $\boxed{\text{Degree of liberation}}$ |
| (c) | Ratio of concentrate grade to feed grade | $\boxed{\text{Ratio of enrichment}}$ |
| (d) | Energy proportional to reduction in particle volume | $\boxed{\text{Kick}}$ (Kick's Law) |
| (e) | Jaw crusher pivoted at the bottom | $\boxed{\text{Dodge}}$ |
| (f) | Contact angle of zero | $\boxed{\text{Hydrophilic}}$ |
| (g) | $(d_{75}-d_{25})/2$ | $\boxed{\text{Probable error}}$ |
| (h) | Most abundant metal in the earth's crust | $\boxed{\text{Aluminum}}$ |
| (i) | Common flotation activator for sphalerite | $\boxed{\text{Copper sulphate}}$ (CuSO4) |
| (j) | Separation by electrical conductivity difference | $\boxed{\text{High tension}}$ (electrostatic separation) |
Reasoning. (a) Galena (PbS) is the principal ore mineral of lead. (b) Degree of liberation is the standard mineralogical term for the fraction of a valuable mineral present as fully liberated (mono-mineralic) particles rather than locked in composite grains. (c) "Ratio of concentration" (feed mass / concentrate mass) is a mass ratio, whereas the statement asks for a grade ratio — concentrate grade over feed grade — which is the definition of the ratio of enrichment. (d) Kick's Law assumes geometrically similar strain patterns during fracture, so the energy to reach the elastic/fracture limit scales with the volume (or mass) of material being deformed, independent of the absolute particle size — distinct from Rittinger's Law (energy proportional to new surface area created) and Bond's empirical law (energy proportional to $1/\sqrt{P}-1/\sqrt{F}$, used in Problem 1c). (e) In a Dodge-type jaw crusher the swing jaw pivots near the bottom, so the point of minimum, most-uniform motion is at the discharge (bottom) opening, giving a more consistent product size but a greater tendency to choke; the Blake type pivots at the top, giving maximum jaw movement (and least choking) at the bottom discharge. (f) A contact angle of exactly zero means the liquid wets the surface completely, i.e. the surface is hydrophilic. (g) $(d_{75}-d_{25})/2$ is the textbook (Tromp-curve) definition of the probable error, $E_p$, a measure of classification sharpness. (h) Aluminum, not iron, is the most abundant metal in the earth's crust (about 8 % by mass). (i) Copper sulphate is the standard activator that conditions sphalerite (ZnS) surfaces with Cu$^{2+}$ ions so that a xanthate collector (Problem 5, Topic 8) can then adsorb and float it. (j) High-tension (electrostatic) separation exploits differences in electrical conductivity (or chargeability) between mineral grains, as distinct from magnetic separation (differences in magnetic susceptibility).
