The mining industry is faced with the reality of having to mine and process lower-grade ore from increasingly complex orebodies – a trend that could develop into the blending of different ores and concentrates for collective processing, says State-owned minerals researcher Mintek.

“As lower-grade ores often have particularly difficult components that complicate processing procedures, collective processing may be more efficient, as the ore or concentrates from different deposits can be mixed and diluted for processing,” explains Mintek technology GM Alan McKenzie, adding that there may be several benefits to collective and centralised processing.

McKenzie points out that some platinum mining companies currently buy platinum concentrate from small- scale mines. While the materials are processed at a few plants in a central region, this provides smaller miners with capital cost savings and ensures that larger miners receive a diverse stream of material for processing.

“Centralised processing can also decrease project capital for mining companies developing greenfield projects, as they do not have to invest in separate smelters or refineries,” McKenzie explains.

With this in mind, Mintek developed a central refinery pilot plant for rare earths metals and started running material through the plant’s processes since the completion of the plant in March.

McKenzie says Mintek will process several regional ores at the plant and notes that the research council is focusing more on processing to obtain a better understanding of the quality of products produced, potential operational costs and the plant’s operational efficiency.

He further points out that, while there are several rare earths deposits in Southern Africa, none of these deposits are significant enough in size for individual companies or countries to justify the cost of constructing their own refineries, which is why the material extracted from these deposits should be processed collectively.

“If South Africa aspires to create a local rare earths manufacturing industry, as rare earths metals tend to be the ‘green’ metals of the future, Mintek believes the need exists for a centralised processing and refining plant.”

McKenzie adds that this will stimulate growth in the smaller local mines, as they do not need to invest in separate processing plants or refineries, but can still sell the material.

He emphasises that Mintek’s central refinery pilot plant for rare earths is one example of the type of initiative that can aid industry to process lower-grade, more complex ores.

Key Processes
In addition to researching processing methods for more complex ores, Mintek is focusing on at least half a dozen other key areas to increase productivity and efficiency in the minerals and metals processing industry.

The council secured R150-million in medium-term expenditure framework funding for the 2012/13 – 2014/15 financial years for key projects. These include the rare-earth elements refining pilot plant, energy and water efficiency projects for minerals and metals processing, a metal atomising demonstration plant, a facility focusing on mine effluent, the upgrade of Mintek’s infrastructure, the Savmin acid mine drainage pilot plant and recycling projects.

Mintek developed the Savmin process during the 1990s to treat acid mine drainage and signed a partnership agreement with water solutions company Veolia Water Solutions & Technologies South Africa in 2011 to assist with process engineering and marketing of the technology.

According to the council’s 2013 yearly report, progress on the demonstration plant is proceeding according to plan.

The report further states that Mintek is collaborating with the University of Cape Town to research and develop ways to lower the costs of the process even further through better reagent recycling.

“Having started treating acid mine drainage at the beginning of August, the Savmin water treatment process is in the final stages of demonstration,” adds McKenzie.

Meanwhile, as part of its ‘urban mining’ project, a type of mining beneficiation involving the extraction of value from metal-bearing waste streams, which include electronic waste, industrial waste, mine tailings and residues in South Africa, Mintek is currently running the project’s smelting programme.

The council has started producing copper alloys from the collected metals of the electronic waste. These alloys contain an amalgamation of various metals, including gold, rare earths and platinum-group metals.

McKenzie points out that the smelting programme is proceeding well and that, from here, Mintek will investigate refining possibilities to separate the metals from these copper alloys.

“Although Mintek may have a good idea of the process’s technical viability at the end of this year, several larger-scale stages are necessary to develop additional technical economic data to indicate the process’s commercial viability.”

Meanwhile, McKenzie emphasises that the mining industry needs to become more water and energy efficient. As the industry is becoming aware of competition for water near or at mine sites, there is an increasing need to recycle water, develop dry processing methods and remove chemical reagents from water systems for minerals and metals processing, he says.

McKenzie concludes that, with regard to energy, sensor-based sorting of run-of-mine ores can assist in reducing energy consumption during ore-crushing and milling processes by reducing the amount of waste material sent to these processes.