GOLD PROCESSING operations so that miners can take advantage of the record high prices and squeeze every last bit of value out of their asset .”
Gekko ' s 200th ILR
The Gekko Systems team has recently announced a major landmark with the sale of its 200th production scale InLine Leach Reactor ( ILR ) to Marmato Mine in Colombia , operated by Aris Mining Colombia . The InLine Leach Reactor was invented in 1997 by Gekko ’ s Technical Director and Co-Founder Sandy Gray one year after the start-up of Gekko in 1996 .
The concept of chemically treating gravity gold concentrates rather than using physical recovery on a shaking table was driven by the poor recoveries ( 50-60 %) and low security associated with shaking table devices which were standard uses . Typically , gold plants would experience a spike in cyclone overflow and high tailings grades when gravity concentrates were being treated by tables in the gold room and before intensive cyanidation became standard in gold operations . Key people like Nick Mooney and Nick Katsikaros made significant contributions to the concept and efficacy of the operation .
The ILR was the first commercialised intensive leach technology and Gekko says it remains the global technical and market leader in the gold industry worldwide . Gekko adds : “ Sandy and Gekko ’ s award-winning technical and design team continue to constantly review and improve ease of operation and recoveries from the unit which typically run around 98-99 %. Whilst developed in Australia , the concept really took off in Africa first with AngloGold Ashanti installing units in many of their operations in the late 1990s and is now installed worldwide .”
Fully optimised to mining operations , the ILR boasts consistent free gold recoveries of over 98 % as well as superior recoveries of gold from complex sulphide ores . Leaching coarse (> 300 micron ) gravity concentrates and recycling leach solutions delivers low energy and operating costs . Rapid leach kinetics and an automated system provide fast mineral recoveries . In place of open shaking tables that are prone to theft , the enclosed ILR has lockable access points to protect against theft losses and reduce manual handling .
The ILR can be easily retrofitted to any grinding circuit . The modular , small footprint design requires minimal space for integration . The ILR ’ s chemical handling is automated and important leach parameters are electronically controlled , making operations faster and safer . Tailings generated are smaller and can be coupled with the detoxification of cyanide , which protects the environment .
Aachen leach reactor at IMK
The world of gold mining is a relentless pursuit of efficiency , yield , and sustainability . At Indonesia ’ s PT Indo Muro Kencana ( IMK ) gold mine , located in Central Kalimantan , this pursuit recently took a significant leap forward with the adoption of high-shear leach reactor technology – Tom Rigby , Project Metallurgist at Maelgwyn Mineral Services , told IM .
“ IMK faced declining recoveries as its ore became more refractory , or resistant , to conventional extraction techniques . However , with the installation of a single Aachen high shear reactor , the mine has seen impressive improvements in gold and silver recovery , decreased chemical usage , and millions saved in operating costs .”
The challenge at PT IMK began with the mine ’ s complex geology . The gold-bearing ores at IMK contain high levels of sulphides and clays , both notorious for complicating traditional cyanide leaching processes . Rigby : “ Sulphides consume excess oxygen and cyanide , raising costs , while clay particles increase the slurry ’ s viscosity , which combined with boundary layer effects on the surface of gold particles , slow down the leaching process , reducing recovery rates . This led to a reduction in the mine ’ s gold recovery by approximately 4 % and silver by around 7 % - a significant drop in yield that impacted profitability .”
In response , PT IMK introduced additional reagents like hydrogen peroxide to elevate the oxygen levels necessary for effective leaching . Although this helped , it was expensive and fell short of restoring optimal recovery levels . It became clear that a more radical solution was needed to overcome these operational challenges .
Enter the Maelgwyn Aachen high-shear leach reactor - a technology designed to improve oxygen transfer in the leaching process . Rigby : “ While conventional methods inject oxygen into leach tanks , the high-shear leach reactor takes it a step further , using a patented fine-bubble generator to disperse oxygen evenly and consistently throughout the slurry . This design creates ultra-fine bubbles , increasing oxygen surface area and improving dissolved oxygen levels to over 30 ppm . By maintaining these levels , the reactor effectively ‘ powers up ’ the leaching process , enabling higher recovery and greatly improved leach kinetics .”
In April 2022 , PT IMK ’ s team began a one-year trial with the high-shear leach reactor . The results were striking : gold recovery increased by 1.3 %, and silver recovery saw a remarkable 4.9 % improvement . This additional yield translated into an estimated $ 273,000 in extra monthly revenue - a direct boost to the bottom line .
But the benefits didn ’ t stop at increased recovery . By completely reducing the need for hydrogen peroxide , reducing sodium cyanide by
7.3 %, and lime usage by 22.4 %, the high-shear reactor slashed monthly chemical expenses by $ 121,864 . Taken together , these savings and additional revenue amounted to roughly $ 370,000 per month , with a payback period of only 14 days on the initial capital investment . In a world where mining operations often face tight profit margins and high production costs , such an investment was , as the IMK team called it , ‘ a nobrainer .’
Rigby says the improvements at IMK were not purely economic . “ The reactor ’ s ability to maintain high dissolved oxygen levels also had operational and environmental benefits . By reducing the dependence on hydrogen peroxide and cyanide , the reactor helped lower the environmental footprint of the mine ’ s operations - a win for sustainability initiatives . Additionally , with less need for chemical additives , the mine ’ s overall handling and disposal of hazardous materials became safer and more manageable , aligning with industry goals for greener mining .”
The efficiency gains further enabled the IMK team to increase plant throughput by over 17 %, reaching a feed rate of over 200 dry tons per hour . This production boost , achieved without compromising gold and silver recovery rates , demonstrated the technology ’ s versatility and potential to support future expansion at the mine . The value of this increase in throughput could be measured in millions of dollars of increased monthly revenue .
Rigby says the Aachen high-shear leach reactor ’ s success at IMK has sparked industrywide interest . “ Given the increasing complexity of gold ores globally , many mines are facing similar challenges . With its ability to deliver higher recovery rates , reduce chemical usage , and lower operational costs , this reactor technology has the potential to reshape how mining companies approach refractory ores and environmental sustainability .”
Looking ahead , PT IMK is considering additional reactor installations to further optimise their process . A feasibility study is underway to assess the impact of extending leach time , a change that could further improve gold and silver recovery . Early estimates suggest that increasing leach residence time could increase revenue by an additional $ 162,000 monthly , offering a pathway to even greater profitability .
As the gold mining sector embraces technologies that are not only profitable but also sustainable , Rigby argues that Aachen high-shear reactors look set to become a staple in the industry ’ s future , marking a golden opportunity for mines around the world . He also thanks Dadang Prananta , IMK General Manager and Alex Dhayanto , IMK Plant Manager for their cooperation throughout the project . IM
NOVEMBER / DECEMBER 2024 | International Mining 55