Question 4 of 6: Mineral Processing Term Pairs

Question 4: Mineral Processing Term Pairs (30 marks)

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.

4.1) Coagulation / Flocculation (5 marks)

Both are pre-treatment steps used to aggregate fine (often colloidal, < a few μm) particles ahead of thickening, filtration or clarification, and both work by overcoming the natural electrostatic repulsion between suspended particles so they can collide and stick. Coagulation uses an inorganic salt (alum, ferric chloride, lime) or simple electrolyte to compress the particles' electrical double layer and neutralize their surface charge, letting van der Waals attraction pull particles into small, dense, mechanically weak micro-flocs. Flocculation uses a high-molecular-weight organic polymer that physically bridges across multiple particles (adsorbing at several points along its chain), building large, open, low-density floc structures that settle or filter far faster. In practice the two are sequential: coagulation destabilizes the fine particles first, and flocculation then bridges the destabilized particles into flocs large enough to settle economically in a thickener.

4.2) Jig / Shaking Table (5 marks)

Both are gravity concentration devices that stratify or transport particles by specific gravity in a flowing-water environment, and both are effective on relatively coarse feed (roughly 0.1–25 mm). A jig works on a horizontal screen bed through which water is pulsated vertically (up-stroke loosens/dilates the bed, down-stroke lets particles resettle under hindered settling); repeated pulsation stratifies the bed vertically with the densest particles migrating to the bottom, which are then drawn off through the screen or as a bottom product. A shaking table instead uses an inclined, riffled deck given an asymmetric reciprocating motion along its long axis (slow forward stroke, fast return) combined with a thin cross-flowing wash-water film; heavy particles are caught behind the riffles and carried along the table's shake direction, while light particles are washed laterally across and off the riffles by the cross-flow, producing continuous bands of concentrate, middlings and tailings across the table's width.

4.3) Mechanical Flotation Cell / Column Flotation Cell (5 marks)

Both are froth flotation vessels that use air bubbles to selectively lift hydrophobic (collector-coated) particles into a froth product while hydrophilic gangue reports to the pulp/tailings. A mechanical cell uses a motor-driven rotor-stator impeller that both suspends the solids and shears air into bubbles within the same turbulent zone; froth depth is limited (tens of cm) and the intense agitation, while good for coarse-particle recovery, also promotes some non-selective mechanical entrainment of fine gangue into the froth. A column cell has no moving parts: bubbles are generated by a static sparger near the base and rise countercurrent to the descending slurry through a tall, quiescent column (several metres), while wash water is added at the top to displace entrained gangue-laden water back down out of the froth before it overflows. Columns generally give a cleaner, higher-grade concentrate (better suited to final cleaning stages) while mechanical cells give more robust bulk/rougher recovery, especially of coarser particles.

4.4) Frother / Collector (5 marks)

Both are heteropolar (surfactant-like) flotation reagents with a polar head and a non-polar hydrocarbon tail, and both are dosed at low concentration to the flotation pulp. A collector (e.g. a xanthate) adsorbs by its polar head directly onto the target mineral's surface, orienting its hydrocarbon tail outward into the water; this renders the particle surface hydrophobic so it can attach to a rising air bubble. A frother (e.g. MIBC, a polyglycol) instead adsorbs at the air-water interface of the bubble itself, lowering surface tension so that fine, stable bubbles form and persist long enough to carry particles to a mechanically stable froth layer at the pulp surface. In short: the collector renders the PARTICLE floatable, while the frother renders the FROTH (bubble) usable – flotation needs both acting together but on different surfaces.

4.5) Gyratory Crusher / Cone Crusher (5 marks)

Both are compressive crushers in which an eccentrically-driven mantle gyrates inside a fixed concave, crushing rock caught in the gap between them, and both discharge continuously (no reciprocating jaw). A gyratory crusher has a steep mantle/concave angle and a very large, roughly circular feed opening, making it well suited as a primary crusher taking large, run-of-mine blast rock (up to ~1.5 m) directly and continuously (choke-fed) at very high tonnage. A cone crusher has a flatter head angle and a parallel "choke" zone near the discharge that gives the rock more time under compression at a fixed setting, producing a finer, more closely sized product; it is used as a secondary or tertiary machine, fed already-crushed rock, with a smaller feed opening and a closed-side setting that directly controls the top size of the final product.

4.6) Dense Medium Cyclone / Classification Cyclone (5 marks)

Both are conical vessels that use centrifugal force from a tangentially-fed vortex to split a feed into an overflow (fine/light) and an underflow (coarse/dense) product, and both share the same basic hydrocyclone geometry. A dense medium cyclone (DMC) is fed a suspension of fine ferrosilicon (or magnetite) in water at a controlled density, and the centrifugal field accelerates true density-based separation of the ORE particles across that medium's effective density – the medium is recovered and recirculated, and the cut is essentially independent of particle size, making DMC a true gravity/density (sink-float) separator used for coarse pre-concentration. A classification cyclone (water-only cyclone) uses plain water as the carrying medium and relies on differential settling rates, so its cut is dominated by PARTICLE SIZE (with density only a secondary influence); it is used for sizing duty – classically to close a grinding circuit by returning coarse underflow to the mill while the fine overflow reports as circuit product.

4.7) Upstream Tailings Dam / Downstream Tailings Dam (5 marks)

Both are staged (multi-lift) tailings-dam construction methods that raise dam height incrementally over the life of the mine using cheap, locally-available materials, rather than building the full final height up front. An upstream dam builds each successive raise on top of, and set back toward the pond from, the previously deposited (and often still-saturated) tailings themselves – this is the cheapest method and needs the least fill material, but the resulting structure is founded partly on tailings that may liquefy under seismic loading or high phreatic surface, giving it the lowest stability and the highest failure risk (which is why upstream construction is now banned or restricted in several jurisdictions post-Brumadinho/GISTM). A downstream dam instead builds each raise outward (away from the pond) on new, engineered/compacted fill or the previous raise's structural body, giving a progressively wider footprint entirely founded on engineered material; this is the most expensive and land-intensive method but produces a true water-retaining structure with the highest stability, comparable to a conventional water-storage dam.

4.8) Magnetic Separator / High-Tension Separator (5 marks)

Both are rotating-drum separators (the high-tension unit always dry, the magnetic unit dry or wet) used late in a mineral-sand or industrial-minerals flowsheet to split an already-sized, non-reactive feed into two streams based on a single physical property, with particles fed onto the top of a rotating drum and each product collected by a splitter positioned at the angle where that particle type leaves the drum. A magnetic separator places a magnet (of chosen field strength/gradient, from low-intensity drum to high-intensity induced-roll or rare-earth units) inside or beside the drum; magnetic particles are attracted and cling to the drum surface well past the point where non-magnetic particles fall away ballistically, so the two are collected at different points around the drum's circumference. A high-tension (electrostatic) separator instead charges the particles with a corona-discharge electrode as they pass the drum; electrical CONDUCTORS lose their induced charge to the grounded drum almost instantly and fly off early under centrifugal + gravity force, while NON-CONDUCTORS retain their charge and are electrostatically pinned to the drum much longer, again giving a clean split by collection angle.

4.9) $d_{50}$ / $d_{50c}$ (5 marks)

Both are read from a partition (Tromp) curve, the plot of % of feed reporting to underflow (or sinks) against particle size, and both denote the particle size at which the split is 50/50. $d_{50}$ is read directly off the ACTUAL (uncorrected) partition curve as measured from plant/lab data; at very fine sizes this raw curve typically shows a "fish-hook" upturn because a fraction of fines simply follows the water split into the underflow by mechanical entrainment (bypass) rather than by true classifying action, which lifts the whole raw curve and so biases the apparent cut point FINER. $d_{50c}$ is the corrected cut size, read from the partition curve after mathematically removing the bypass fraction (the curve is rescaled so it runs from 0% to 100% over the range actually attributable to classification); $d_{50c}$ is therefore the better measure of the classifier's true (mechanical) separating performance, independent of how much water/fines short-circuit to underflow. Because the corrected recovery $(R-R_f)/(1-R_f)$ is lower than $R$ at every size, the corrected curve reaches 50% only at a larger size: $d_{50c}$ is always COARSER than $d_{50}$. It is the value normally used to compare classifier efficiency between units or duty conditions.

4.10) SAG Mill / Ball Mill (5 marks)

Both are rotating-drum comminution (grinding) mills that break rock by impact and abrasion as the charge tumbles/cascades inside a rotating steel drum, and both are commonly arranged in closed circuit with a classifier (e.g. the hydrocyclone in Question 6(3)). A SAG (semi-autogenous grinding) mill uses the ore itself as the primary grinding medium, topped up with a small ball charge (typically 4–15% of mill volume) to boost breakage of competent rock; it has a large diameter relative to its length (short L/D), accepts coarse crusher/ROM product directly, and is normally the primary (single-stage, or ahead of a ball mill) grinding step. A ball mill uses a much larger charge of steel balls (typically 30–40% of mill volume) as the grinding medium, has a smaller diameter but proportionally longer barrel (larger L/D), and is fed the SAG mill's (or crushing circuit's) product to grind it down further to final flotation/leach feed size – i.e. it is normally the secondary/regrind stage.