SENET boasts a highly technical and competent team of hydrometallurgical experts who have been instrumental in growing the organisation’s successful track record. Process plant performance plays a significant role in a mining project’s overall financial performance and this is the role SENET will continue to facilitate through its extensive skill set in commodities which are performing well at present – including gold, copper and cobalt.
“SENET is adept at evaluating every hydrometallurgical technology available and thereafter determining which is best suited to extracting the greatest economic value – specifically with regard to capital outlay and overall operating costs,” says Process Engineering Director Phil Bundo.
“We take cognisance of our clients’ financial position and processing needs, and design fit-for-purpose plants that deliver the maximum return on investment based on the available cash.” All hydrometallurgical work starts with a testing phase in a laboratory; therefore SENET’s dedicated process engineers are on-hand to prioritise and focus on the clients’ laboratory testing needs. They liaise with the laboratories to interpret the results, from which they then develop the most suitable process flow sheet.
“These initial steps are critical to the entire process and we take great care in translating this information to deliver the best solution for the client,” Bundo highlights.
SENET has developed a formidable reputation for developing suitable processing applications for gold processing projects in Africa and the world over. To ensure that it maintains its position in this field, it continues to explore all the options available as its clients’ needs change/evolve. Traditional gold processing methods include milling and carbon-in-leach/carbon-in-pulp (CIL/CIP), commonly used for easy-torecover oxide material and free milling ores. Mining clients, however, need to consider the best processing options for difficult-to-recover ore bodies as their mines develop over time, Bundo states.
As such, SENET is investing additional focus into assisting companies to develop solutions that are suited to these ores, which specifically entail the following:
• Bacteria oxidation (BIOX) – using bacteria to oxidise minerals
• Pressure oxidation – using high heat and pressure to oxidise the gold
• Albion® process – using ultra-fine grinding with atmospheric oxidation
“We are working with the licence holders of these technologies to ensure that we are fully competent in evaluating all processing technologies.” In 2017, the company investigated the effects and outcomes of all three technologies as part of a definitive feasibility study (DFS) for a gold project in Senegal and determined the BIOX methodology most suitable for the African environment.
SENET has the largest solvent extraction (SX) and electro-winning (EW) process plant footprint in Africa – specifically for copper projects.
On the back of its decades-long success in this commodity, the company has refined a process ideally suited to copper processing – milling in raffinate – which not only improves efficiencies, but also reduces operating costs. “Milling in raffinate replaces the raw water used to grind ore to a slurry state with recovered acidic effluent from acidic tailings as well as from the raffinate bleed to acidic tailings.” Raffinate is an acidic barren solution after copper extraction in solvent extraction. It contains acid and residual copper.
The process does, however, require a stainless-steel mill to withstand the acidic environment. To reduce costs, SENET recommends using an LDX stainless steel, which is more cost effective. The benefits of milling in raffinate are extensive, Bundo outlines:
1) Reduction in environmental damage:
Milling in raffinate is far more environmentally friendly because the process does not use limestone or lime, thereby reducing the carbon dioxide footprint and the amount of lime dust emitted to the environment, respectively.
2) Improvement in the conservation of raw water resources
There is a reduction in raw water usage from natural water sources due to the use of raffinate and a reduction of raw water usage as there is no lime/ limestone make-up activity in the process plant.
3) Reduction in plant operating costs
Milling in raffinate offers substantial operating cost savings due to a 30 –40% reduction in fresh acid usage, as all the recoverable process acid from the tailings is re-used. It also eliminates the need for pre-leach flocculent usage and the associated maintenance costs, as well as lime/ limestone consumables and the associated maintenance costs.
4) Improved copper cathode income (resulting in higher profits)
Leaching of copper starts in the mill, resulting in an improved leach recovery of approximately 1% to1.5% above conventional milling (with extra copper recovered from the acidic return solution).
5) Improved ease of operation
Milling in raffinate translates into a far easier operation because there are no dewatering and re-pulping systems ahead of leaching and no tailings neutralisation. A milling in raffinate plant will also have a reduced plant footprint due to the elimination of the dewatering system ahead of the leach and the elimination of neutralisation facilities.
There are only six plants across the globe that operate by using the milling in raffinate process – most of which were designed by SENET, Bundo notes.
SENET’s engineering experts are equally skilled in designing plants that process copper concentrate, particularly from “difficult” ore bodies such as chalcopyrite and volcanogenic massive sulphide ore bodies.
Thanks to its significant copper portfolio, SENET has also developed a strong skill set for cobalt processing, which is set to benefit the company while the price of cobalt continues to escalate. “We have expertise across all cobalt processing methodologies; including cobalt hydroxide used for various cobalt products, cobalt sulphate including battery grade for electrical vehicles and cobalt metal for use among other things in super magnets and as an alloy in aircraft in parts,” Bundo explains.
HEAP LEACHING (FOR GOLD AND COPPER)
Thanks to its range of proprietary materials handling equipment, SENET has become an engineering leader in designing and building heap leach facilities in Africa. “Both the capital outlay and operating costs are lower than traditional processing circuitry, with lower recoveries of around 75%. It is, therefore, essential to determine if this process holds the greatest economic value for a client, which in many instances it does.”
Image source: SENET