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 ]