Mining in focus
Leon Louw
Gravity concentration separates minerals based on differences in specific gravity. Various concentrator equipment has evolved over time to simulate and automate the panning methods used by the‘ old timers’, but now the recovery of even finer particles of free gold is possible.
pre-oxidation needs to take place. In the 20th century, techniques such as roasting, pressure oxidation, atmospheric leaching( Albion), and even biological oxidation( BIOX) have been developed. Roasting is used to oxidise both the sulphur and organic carbon at high temperatures using air and / or oxygen. BIOX involves the use of bacteria that promote oxidation reactions in an aqueous environment.
The importance of pre-oxidation
Pressure oxidation is an aqueous process for sulphur removal, carried out in a continuous autoclave, operating at high pressures and somewhat elevated temperatures. The Albion process uses a combination of ultrafine grinding and atmospheric, auto-thermal, oxidative leaching techniques.
According to Juan D. van der Merwe, business development manager at Maelgwyn Mineral Services Africa, most contemporary gold mining projects have shown themselves to be more difficult to process than their historical counterparts. Projects have to deal with lock-up aspects such as gold that is not easily accessible to the reactants, the presence of significant portions of fast-reacting sulphide minerals such as pyrrhotite, and gold outright contained in pyrite or arsenopyrite. Alternatively, as is the case in many tailings reclaim operations, the presence of large amounts of unstable oxidation products, such as ferrous iron or meta-stable sulphide oxidation products, places a heavy demand on oxygen and cyanide consumption.
“ To sustain gold leach efficiencies, these inhibiting aspects have directed focus to suitable pre-oxidation steps, followed by CIL, and it is in that phase of the process where our technology becomes applicable,” says Van der Merwe. Maelgwyn Mineral Services Africa is a wholly owned subsidiary of Maelgwyn Minerals Services based in Wales.
One of Maelgwyn’ s prime products is the Aachen High Shear Reactor Technology, which is the enabling technology to achieve efficient high-level oxygen mass transfer along with shear exposure. Slurry is pumped from the process tank through the reactor, where the oxygen is introduced at high shear / high velocity in a specially engineered aerator system. After the oxygen has been transferred under pressure, shear and high velocity, the slurry is returned to the same process tank. If the flow through the reactor is a multiple of the slurry flow rate at plant level, a system of multiple pass rates is established, usually leading to increased benefits.“ The purpose of deploying the Aachen technology is to assist with realising hidden potentials in reagent savings, gold recovery, or throughput increases,” says Van der Merwe.
Although cyanide is a highly toxic substance, it has maintained the position of preferred lixiviant of auriferous oxide-silicate-carbonate ores.
APRIL 2018 MINING MIRROR [ 21 ]