This is an excerpt from International Mining’s Reprocessing and Tailings Reduction Feature, written by Dan Gleeson in May 2020 edition.
While tailings dam liabilities and falling water resources are affecting the ability of miners to start new mines, or expand existing ones, these issues are strengthening the case for reprocessing and retreating ‘waste’ sites or streams. Dan Gleeson explores an increasingly diverse market focused on revenue generation and risk reduction
With improved transparency around tailings dams and waste stockpiles now part and parcel of being a responsible mining company, investors and the wider mining world are becoming aware of the opportunities to clean up legacy operations, while, at the same time, generate extra revenue.
These opportunities are growing in value and quantity as water scarcity in many major mining hubs accelerates and the ability to expand existing tailings impoundment areas diminishes.
The trend is further aided by the fact costs and liabilities associated with these facilities continue to increase.
At the same time as this, these opportunities are becoming more feasible as the cost of specialised equipment drops – making the upfront capital expense more manageable – and the number of large mining companies looking at removing these ‘liabilities’ from their portfolios expands.
This has seen a new generation of ‘miners’ spring up intent on profiting from processing material previously categorised as ‘waste’.
From Mining Waste to Resource
One company looking to address the availability and cost of specialised technology for reprocessing tailings and other ‘waste’ is CDE.
An industry-leading manufacturer of wet processing equipment for materials processors, CDE has seen a significant rise in proposal requests for dewatering and dry stacking equipment over the previous 12 months, according to Daniel Webber, Regional Manager Australasia at CDE.
Most requests have focused on re-processing existing tailings, recovering the valuable fractions, and dewatering and dry stacking the waste products, he explained.
“We are increasingly approached by clients seeking to recover value from their waste stockpiles, which have accumulated in times where high-grade ore was abundant and lower grades were set aside as waste, or processing technologies were not sophisticated enough to capture fines fractions or suitably upgrade the ore deposit,” he told IM.
Webber said CDE was receiving these requests from smaller mining companies looking to specialise in reprocessing brownfield sites.
“Increasingly we are seeing junior miners adopting a strategy of purchasing waste dumps or historic tails for re-processing as an economic source of commodities,” he said. “This value is easy to recover as the material has already been mined and avoids the substantial extraction costs of virgin mining, yet these tailings deposits contain high recovery rates with existing projects, for example, recovering 2 g/t Au and achieving 63% Fe grade at 50% yield.”
It is the junior and mid-tier miners – not the Tier 1 outfits – able to more easily incorporate the new technologies CDE and others offer to carry out such processing, according to Webber.
“Contrary to the assumption, I think the transition to dry stacked/filtered tailings is more accessible to junior and mid-tier miners who have increased flexibility to incorporate new technologies into their plant design,” she said.
“For Tier 1 miners, the scale of dewatering existing and historical dams presents significant commercial risk due to the expense involved.” The company has a few case studies to back this opinion up.
In working with junior miners from prefeasibility through to development stage, CDE offers cost-effective modular equipment design to achieve minimal tailings and minimise environmental footprint, while also opening new revenue streams for customers, Webber explained.
One of the company’s differentiators is its focus on “life-cycle economics”, with CDE working to identify markets for by-products of mining as part of its zero-waste initiative.
This initiative sees the company look at the entire supply chain in which its customers operate.
In South Africa, for example, CDE has a customer purchasing historic mine waste dump material that it processes through one of its plants to produce a fine sand gold-bearing concentrate that is sold back to the mine for reprocessing.
Simultaneously, the plant produces one sand and two aggregate materials which are sold to the construction industry, while the land where the dumps were once situated is repurposed for development.
In Latin America, the company is also working on projects such as AuVert Mining’s asset in Colombia. Here, AuVert’s technology is being combined with CDE’s experience in dewatering and tailings management to extract the remaining precious metals existing in the ground, while removing up to 93% of residual mercury which has to date prevented this land from being used by the local population.
CDE’s plant designs might also factor in supplying ‘by-products’ to other industries.
“At CDE we try to identify alternative markets for the by-products, such as creating sand and aggregates suitable for construction, as well as land rehabilitation and paste and backfill,” Webber said. “For us, it is important that we strive towards a zero-waste goal.”
The company’s largest reprocessing project to date has come in Australia and involved “a first-of-kind opportunity” to design a turnkey solution for the upgrading of legacy iron ore waste to a high-value product, she said.
At a combined throughput of 950 t/h, the SIMEC installation is the company’s largest processing facility for low-grade beneficiation.
The project will see almost 18 Mt of low grade, extremely abrasive hematite iron ore, which had accumulated over years of mining the Iron Monarch, Iron Princess, Iron Empress, and Iron Baroness deposits, turned into a saleable product for SIMEC in South Australia.
The two plants on site remove silica and alumina from the feed material, gravity separating low-grade from high-grade ore in the process. Silica levels, which range from 14% to 20% in the barren ore, have reduced to 6.4% after processing; while alumina levels, which range from 5.9% to 8.8%, have reduced to 2.8% after processing.
The iron ore wash plant also removes clays from the feed material, with the combined effect moving the iron content from between 43.4-52.7% Fe in the feed to 63-64% Fe at a yield of 50%, according to Webber.
The plant consists of an initial washing and screening stage using CDE’s M-Series™ modular range equipment followed by scrubbing of the coarser fraction by RotoMax™ log washers. Dry screening using CDE’s patented Infinity Screen™ range follows prior to gravity beneficiation in the coarse and fine jigs, and dewatering and conveying to stockpiles via more than 20 CDE conveyors across the two processing plants.
The finer fraction is further washed and separated prior to being de-slimed in cyclones at 200 mesh and gravity beneficiated through a series of spiral banks. Three of CDE’s A1500 AquaCycle™ thickeners are deployed across the two plants to form a concentrated tailings sludge and recycle process water, the company noted.
Webber said these projects have sparked the interest of many similar providers on a global basis who are increasingly recognising the value retained in legacy waste.
A Fitting Solution
While all in the industry would agree that providing an effective and sustainable tailings management and dewatering solution is easier on greenfield sites, there are few opportunities such as this on the market.
As a result, CDE has designed its EvoWash™ and AquaCycle™ combination to slot into a wet processing circuit for tailings dewatering, while its Filter Press filtration system, which has been in demand as of late, is able to be incorporated into the mix and achieve higher levels of water recovery and dry stacking.
Kevin Vallelly, Director of Engineering at CDE, walked IM through the offering.
“The EvoWash is a compact, modular washing system which integrates a high-frequency dewatering screen, sump and hydrocyclones to provide unrivalled control of silt cut points and eliminate the loss of quality coarser articles to the fines dewatering circuit,” he said.
The system effectively deslimes and dewaters the tailings, while simultaneously creating valuable materials for the construction market and incorporates patented Infinity Screen technology for optimal dewatering results, Vallelly added.
The CDE AquaCycle water management system provides the required high rate thickening to recover up to 90% of the process water for re-circulation around the washing plant while thickening a tailings sludge.
“The AquaCycle offers a fully modular skid mounted option for customers who want to avoid civils work,” Vallelly added.
CDE’s Filter Press filtration system is designed and built to deliver maximum plant efficiency, eliminating the need for tailings dams, or settling ponds and significantly reducing waste handling, according to Vallelly . “The market-leading automated cloth wash system delivers maximum dewatering performance, recycling up to 95% process water,” he said.
The company is also working on an “Ultra-fines solution” to provide a modular tailings dewatering and beneficiation unit that will accept a dredge or dry feed to recover and upgrade the target mineral, while retaining the by-products for use in other applications, according to Vallelly.
“The vision is that of a compact footprint system that can be easily relocated as each area of a tailings deposit is reprocessed,” he said, adding that a combination of this solution with the Filter Press filtration platform, using both membrane squeezing and cake blowing, could achieve moisture contents as low as 8-9%.
Such a solution appears to be aimed at the junior and mid-tier market Webber previously spoke of, allowing for progressive rehabilitation/reprocessing at lower throughputs and cost.
Vallelly said the company is working with strategic partners, customers, and academic institutions to progress the Ultra-fines solution during 2020.