GOLD EXTRACTION
The presence of native carbon, graphitic and shale gangues in CIP / CIL circuits can lead to reduced circuit recovery from preg-robbing of gold cyanide complexes. POLYMAX G30 and G35 dispersants were developed to have preferential affinity for carbonaceous surfaces which actively blinds the carbon and reduces the preg-robbing opportunity. These dispersants, when added at 10-50 g / t have been seen to improve gold recovery, which is at a lower dose compared to the typical kerosene or diesel normally used for the same purpose.
The Fosterville HiTeCC facility
Bioleaching
Last year Outotec acquired Biomin South Africa, taking on the full intellectual property and marketing rights of BIOX ® bioleaching technology; a proven method for the treatment of refractory gold ores. BIOX technology complements Outotec ' s portfolio of gold processing technologies. Gold orebodies are becoming more complex to treat and consist of more refractory ores as the less refractory gold ores become depleted. Roughly 20 % of the world ' s current gold projects and a third of upcoming projects are based on refractory ore that needs to be pre-treated before the leaching process. There are three main pre-treatment methods for refractory gold ores; pressure oxidation, roasting, and bioleaching. BIOX is proven technology for bioleaching.
" A significant challenge for gold mining companies is to find an economically viable process to treat more complex orebodies. This acquisition will strengthen Outotec ' s position in the refractory gold ore processing market. Combining BIOX bioleaching expertise with our engineering capabilities and proprietary equipment, such as grinding mills, reactors and thickeners, we intend to provide gold producers complete sustainable plants with life-cycle services”, says Outotec CEO Pertti Korhonen.
In Kazakhstan, Nordgold has launched an innovative Outotec HiTECC( Hot Leach) process at its Suzdal mine to recover gold from both historical and CIL future tailings.
The High Temperature Caustic Conditioning( HiTeCC) process is designed for treatment of double refractory ores. Through the BIOMIN HiTeCC process, gold is efficiently desorbed from the organic carbon by manipulating the ionic strength and temperature of conventionally
The company notes:“ Suzdal is the second mine worldwide to launch a commercial Outotec HiTeCC circuit. The installation of the innovative HiTeCC highlights the strength of Suzdal’ s
management team under Grigorii Iakovenko, General Director and deep technical expertise of
Nordgold’ s international processing team under Philip Engelbrecht, Director of Metallurgy. The first commercial hot Leaching technology was constructed in 2009 at Crocodile Gold Corp ' s Fosterville BIOX ® operation near Bendigo, Australia.”
Biomin says the Fosterville installation has been“ running very successfully with gold increases across the leach plant realising economically attractive recoveries.”
Suzdal produced 75,300 oz of gold in 2015. The HiTeCC circuit will produce an additional 9- 14,000 oz of gold doré per year for 10 years, a total of approximately 90-140,000 oz, generating additional profits. HiTeCC life-of-mine AISC is expected to be some $ 420 / oz. Suzdal AISC decreased to $ 476 / oz in Q1 2016 from $ 575 / oz in Q4 2015 and $ 828 / oz in Q1 2015.
Nordgold CEO Nikolai Zelenski:“ The launch of HiTeCC is an important technical milestone for Nordgold, and highlights our strategy of pursuing operational excellence. Suzdal is a long-time pioneer in the implementation of the best and most innovative operating solutions and we are proud the mine becomes only the second in the world to launch this technology which will have very real financial benefits for the company, both extending the life of mine as well as increasing production. The launch of the new gold recovery circuit using an innovative HiTeCC technology is yet another confirmation of Suzdal ' s leadership as a high-technology gold producer in CIS.”
Construction of the new facility started in July 2015, and it reached full operating capacity at the end of June 2016. HiTeCC will allow Suzdal to process more than 130,000 t of historical and future CIL tailings per year. Suzdal currently has 637,000 t of tailings at 7.17 g / t Au available for retreatment. Test results indicate the possible recovery rate of 40 % to 70 %.
Nordgold invested $ 5.8 million in construction of the state-of-the-art 1,800 m2 HiTeCC facility. The company expects to fully pay back this
investment in less than 20 months( assuming gold price of $ 1,200 / oz and 350 tenge / US $ exchange rate). treated CIL product slurries. Ekato notes that“ biological ore leaching is not only an interesting economic alternative to conventional pressure leaching but it is also ecologically safe – because it operates as a stirred process in closed conditions – in contrast to the usual but questionable heap leaching with respect to ecological balance. The ever increasing plant dimensions as a function of the economies of scale plant dimensions require a stirring technique which is able to suspend heavy ore particles in continuous operation and at the same time to disperse the air supply to the organisms and for the oxidation step.”
The company explains that its COMBIJET technology meets these requirements perfectly, since unlike conventional mixing or agitating, the suspension capacity is hardly affected at higher gassing rates. Thus, a stable operation of ten continuously stirred tanks with volumes of approximately 1,500 to 2,000m ³ is possible despite load variations or varying compositions of the ore.
The good suspending capabilities of the COMBIJET allow a reduction of the power input to that which is required for the mass transfer rate, exhibiting an annual energy saving of about 5 – 10 GWh for a complete system. This is particularly important in remote mining areas without regular electricity supply. In addition, the low power input protects the micro-organisms on the ore particles in an abrasive environment.
The investment costs are not only reduced because of the smaller agitator dimensions; a stable running of the impellers with gassing leads to lower hydraulic loads which also has a
72 International Mining | AUGUST 2016