REPROCESSING AND RETREATMENT
The Multotec pulping chutes consist of patented wave generators , using energy from the slurry flow to create a turbulent mixing action to release mud , clay and slime sticking to the kimberlite particles
“ Scrubbers are equipped with large drives with gears and gearboxes to rotate the drum . They are high consumers of power and require mechanical component maintenance , which means higher operating costs .”
Substantial structures and supports are also needed for the scrubber and its drive mechanisms , the company explained .
In designing the pulping chute , Multotec sought a simplified solution , Britton said . In addition to improving scrubbing efficiency , the objective included reducing the cost of replacing scrubber liners and the downtime this demanded . The cost of replacing the steel shell of a scrubber – which is constantly subject to stress , wear and fatigue – was another cost consideration .
“ The pulping chute , by contrast , is a stationery and much simplified innovation , focused on the scrubbing of fines less than 32 mm in size ,” the company said . “ Slurry deflectors located at the top end of the scrubbing chute direct at least part of the slurry away from the scrubbing chute floor . This curls into an arched form which flows backwards into the approaching flow of slurry , creating the turbulent scrubbing effect .”
Britton said : “ We custom-design the chutes to suit the application and can increase chute capacity to up to 800 t / h . This is achieved with no moving parts , bearings , hydraulic packs or girth gears ; the only power required is to supply material and water to the receiving chute . These actions are also required to feed the scrubber , then gravity takes over and provides the required energy .”
Maintenance is also streamlined by designing the chute in segments . Should one segment come in for more wear than others , it can be quickly removed and replaced – putting the chute back into operation while the original segment is refurbished as a spare .
Britton said the pulping chute , which can also be applied in commodity sectors such as coal , platinum , chrome , iron ore and mineral sands , has drawn interest from other diamond producers in southern Africa , Australia and Canada .
CDE ’ s patented modular scrubbing and classification system , AggMax™ , has also found favour with the diamond sector . This AggMax logwasher seeks to maximise product yield from clay-bound feedstock in industries such as mining . It offers a compact combination of screening , scrubbing sizing and organics removal in one package , according to CDE .
The ability to recover larger-stone sizes using this technology has further increased demand for the AggMax , according to CDE Middle East & Africa Regional Manager , Ruchin Garg .
The AggMax system cleans and scrubs material without causing damage to the stones , also removing contaminants from the feed material and increasing the potential of discovering stones before passing to the crushers , Garg said . It acts as a pre-concentration technology , which is very important considering the potential revenue destruction that comes with prematurely allowing larger-carat stones to flow through to the comminution circuit .
Sixth time lucky ?
It is the ability to recover gold from tailings that has GreenGold Engineering and Heritage Minerals Pty Ltd trying its luck at the historic Mount Morgan gold mine in Queensland , Australia .
The story behind Mount Morgan dates to 1882 when a syndicate was created to open a gold mine at Ironstone Mountain , 39 km south of Rockhampton . Having operated as an open-pit and underground mine intermittently in the years that passed , it closed in 1980 . From 1982 to 1991 , however , it was back producing gold from a tailings treatment operation .
At different stages over the life of the mine , copper has proven to be either a bonus or a nuisance . When copper grades are high , copper was a financial benefit ; when the copper grade was low , the metal increased the operating cost associated with gold recovery .
Yet , this more than century of mining and processing came with consequences .
The pyrite remaining in the mine and tailings dumps is acid-forming and has generated a significant environmental legacy that remains today . This legacy has become the responsibility of the State of Queensland ( 1993 ) and is managed by the Department of Natural Resources and Mining ’ s ( DNRM ) Abandoned Mines Division .
Despite these environmental liabilities , five companies have come back to Mount Morgan since Peko Wallsend stopped processing tailings in the early-1990s , encouraged by higher yellow metal prices and improved processing options for the refractory ore .
“ We ’ re the sixth company to have a shot at reprocessing the tailings , with none of the companies before us getting past the feasibility study stage into financing ,” Peter Mellor , Corporate Secretary at Heritage Minerals , told IM last year .
All of them were unsuccessful primarily because of the presence of nuisance copper and the high cyanide consumption that comes with removing this , according to Mellor .
After gaining rights to the project from Norton Gold Fields following Carbine Resources ’ exit , one of the first things Heritage did was appoint GreenGold to carry out the definitive feasibility study ( DFS ).
GreenGold is equipped with its ReCYN resinbased technology that has been shown on other projects to reduce cyanide consumption by up to 50 % through capturing free cyanide from plant tailings and recycling it back into the leach circuit .
The company could potentially detoxify the tailings stream and clean up the water discharge at Mount Morgan . This would be a boon for the Department of Natural Resources and Mining ’ s ( DNRM ) Abandoned Mines Division , which currently treats the water from the open pit and tailings deposits before being released into the local creek due to the low pH levels caused by the acid-forming pyrite .
“ Our process plant will use this water , treat it and send it out as clean water down the creek ,” Mellor explained .
The ReCYN resin plant to be built will be able to deal with the higher cyanide consumption needed to treat the copper at the back end of the flowsheet , which will allow the company to focus on the gold – which represents 90 % of revenue – that can be processed by a technically-simple carbon in leach plant .
The open pit is partially filled with previously processed tailings , with Mellor saying the reprocessing of 10 Mt of tailings ( averaging 1.1 g / t Au ) can help complete the rehabilitation process .
54 International Mining | APRIL 2021