21-Mat-B1 Hydrometallurgy and Electrometallurgy · December 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. National Professional Examinations, December 2016 — 10-Met-B1, Mineral Processing. Three hours, closed book, approved Casio/Sharp calculator only. Six numbered Problems plus a two-mark Bonus Question; the rubric requires all problems except Problem 5, which is answered as any SIX of ten short sketch-and-describe topics. All ten topics of Problem 5 are answered here, since this set is a study resource rather than an exam script.
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, sampling theory, classification, gravity concentration and froth flotation — i.e. 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.
Approach. Each statement is matched to the word-list entry whose standard mineral-processing definition it states, with the reasoning given so the match can be checked rather than simply asserted.
| Item | Statement | Answer | Why |
|---|---|---|---|
| (a) | Main lead-bearing ore mineral | Galena | PbS, the principal lead sulphide ore mineral; the list's other lead-bearing entries (Cerussite, PbCO₃, a weathering-zone carbonate; Plombite, an obsolete/minor name) are decoys — galena is the primary ore mineral mined for lead. |
| (b) | % of mineral occurring as free particles | Degree of liberation | Standard definition of liberation: the fraction of a mineral present as free (not locked/composite) particles. |
| (c) | Ratio of concentrate grade to feed grade | Ratio of enrichment | By definition, ratio of enrichment $=c/f$ (a grade ratio); this is distinct from "ratio of concentration," $K=F/C$ (a mass ratio) — the two terms are easy to swap, and this paper's own wording ("concentrate grade to feed grade") pins it to enrichment, not concentration. |
| (d) | Energy ∝ new surface area produced | von Rittinger | Rittinger's law states comminution energy is proportional to new surface area created (Kick's law instead uses reduction ratio/volume; Bond's law uses the reciprocal-square-root form used in Question 1(c)). |
| (e) | Jaw crusher pivoted at the top | Blake | Blake-type jaw crushers pivot the swing jaw at the top (maximum movement at the bottom); Dodge-type crushers pivot at the bottom (fixed discharge opening, more uniform product). |
| (f) | Autogenous mill also using steel balls | SAG | Semi-autogenous grinding: ore itself is the primary media, supplemented by a charge of steel balls. |
| (g) | $(d_{75}-d_{25})/(2d_{50})$ | Imperfection | Probable error is $E_p=(d_{75}-d_{25})/2$ (an absolute size); dividing by $d_{50}$ normalizes it to the dimensionless Imperfection, $I=E_p/d_{50}$ — the formula given here has the $/d_{50}$ term, so it is Imperfection, not Probable error. |
| (h) | Reagent that alters surface chemistry so the collector then renders it hydrophobic | Activator | An activator modifies the mineral surface (e.g. Cu²⁺ activating sphalerite) so that a collector can subsequently adsorb and confer hydrophobicity — the collector itself is a separate list entry, so the reagent described here (which acts BEFORE/WITH the collector) is the activator. |
| (i) | Common flotation depressant for sulphide minerals | Cyanide | Cyanide (as NaCN/KCN) is the classical depressant for pyrite and sphalerite in differential sulphide flotation (e.g. Cu/Pb/Zn separation), forming stable metallo-cyanide complexes that block xanthate adsorption — directly relevant to Question 1's chalcopyrite-with-pyrite-gangue ore. |
| (j) | Gravity unit operation using a pulsating water current | Jig | Jigging separates by density via a pulsating (up/down) water current through a bed of particles on a screen, causing stratification by density; "Pulsator" names one commercial jig design, but the general unit operation is the jig. |
Bonus Question (2 marks). Two metal commodities which currently (Dec 2016) sell for less than $3/kg: aluminum (LME cash price roughly $1.70–1.75/kg in late 2016) and zinc (roughly $2.60–2.80/kg in late 2016, after a strong 2016 rally). By contrast, the Question 1 metal, copper, was trading well above $3/kg (roughly $5.5/kg) at the same date.
