How to Build a Gold Processing Plant?

Building a gold processing plant is a project in which the ore body, not a standard design, decides almost everything. No two mines are identical, so the flowsheet has to be developed for the specific deposit rather than copied from a previous project. The work below describes the sequence that carries a gold project from ore data to a producing plant.

Start with testwork, not with equipment

Everything begins with the ore. A proper programme establishes the chemical composition and mineralogy of the ore, the occurrence of the valuable and deleterious elements, and the physical and chemical properties that will govern separation. In practice this means mineralogical analysis, grindability and work-index testing, and particle-size analysis, carried out on samples that genuinely represent the deposit.

Sample representativeness deserves attention. Many mines are fed from several ore sources with differing characteristics. A defensible approach is to plan the mining schedule first, sample according to that plan, prepare several distinct samples, then test the main sample with the secondary samples used for verification. This fixes the final recommended flowsheet — and also allows the plant to blend ore from designated stockpile positions later.

Fix the flowsheet

Gold beneficiation commonly draws on cyanidation, flotation and gravity separation, and the flowsheet is tailored to the ore and the plant requirement.

For ores suited to cyanidation, the choice is between agitated cyanidation, which handles flotation concentrates or whole-ore cyanidation, and percolation cyanidation, which handles low-grade oxidized gold ore. Within agitated cyanidation, one route is cyanidation with zinc replacement for solutions after leaching, using counter-current washing and solid–liquid separation followed by solution clarification, deaeration and zinc precipitation to produce gold mud. The other route is carbon-in-pulp or carbon-in-leach, where activated carbon adsorbs the dissolved gold directly from the cyanide pulp without filtration; the loaded carbon is then desorbed, the gold recovered by electrowinning, the sludge smelted into doré, and the carbon regenerated and returned to the circuit.

Gravity separation has a specific role. Most gold ores contain some coarse free gold, above roughly 0.1 mm, that flotation and hydrometallurgy recover poorly. Gravity units therefore recover coarsely liberated gold ahead of, between or after the flotation and leach stages, with a practical lower limit around 0.01 mm. In closed grinding circuits, coarse gold tends to accumulate in the circulating load or lodge in mill liners and grinding media, and because gold is ductile it does not grind fine; cyanidation of this fraction is slow, so gravity recovery during grinding is the usual answer.

Flotation is the route where gold is closely associated with sulphides, producing a gold-bearing sulphide concentrate for downstream treatment.

Establish the plant design

The plant layout and civil and structural scope follow the flowsheet. Design work covers the crushing, grinding, separation, dewatering and tailings stages, and the supporting civil, electrical, automation and structural disciplines. Modular and steel-structure solutions allow reinforced-concrete ore bins, water tanks, platforms, equipment supports, hoppers and chutes to be fabricated as prefabricated steel units and assembled on site, reducing civil work and construction time. Design can also be executed to different national and international engineering standards as the project requires.

Build, commission and operate

Construction covers the mining works, the processing plant and the tailings storage facility, together with equipment installation, process commissioning and operator training. Once built, the plant moves into operation — production, equipment, safety, environmental and human-resources management — which can be delivered under a range of cooperation models depending on what the owner wants to retain.

Practical sequence

The defensible order of work is: define the ore and the target product; run representative testwork including locked-cycle tests; determine the recommended flowsheet and mass balance; complete engineering design to the applicable standard; procure and fabricate equipment and steel structures; construct and install; commission with metallurgical reconciliation against the design; then operate with ongoing optimization. Skipping the early ore-characterization work is the most common reason a plant fails to reach design recovery after start-up.