gold recovery Archives - International Mining

The latest innovation in semi-continuous gravity separation from FLSmidth is delivering a key breakthrough in performance that increases recovery and cuts maintenance downtime, according to the OEM.

For decades, Knelson gravity concentrators have been recognised for their recoveries of gold and precious metals, but the development of the new Knelson GX Concentrating Cone is set to take this performance a step further.

The new patented GX Cone delivers impressive recovery enhancements due to enhanced water distribution within each ring, according to the company.

FLSmidth explains: “As water enters from the base, it flows through zone separator nozzles for a customisable fluidisation profile. This allows for even distribution of water in each ring; the new design also significantly increases the active recovery surface area. The result is a step change in overall coarse and fine gold recovery.”

Test data shows that gold recovery in all size fractions, from course to fine, improved significantly with the GX Cone, according to the company.

By incorporating an advanced distribution of fluidisation water across the entire concentrating cone, the Knelson GX facilitates the highest possible recovery of coarse and fine gold. At the same time, balanced water distribution across the concentrating cone allows for a significant reduction in fluidisation water requirements while improving recovery.

The third major benefit of the Knelson GX is easier maintenance. Because it is made of a customised, abrasion-resistant and durable polyurethane compound, maintenance frequency and operational costs are significantly reduced, FLSmidth says.

Mike Lefler, Head of Global Product Line Manager for Precious Metal Recovery at FLSmidth, said: “The new Knelson GX Concentrating Cone is the culmination of over 40 years of research and operational experience and is exciting news for our customers. It delivers a win-win-win scenario: better recovery, less water use and less downtime due to easier maintenance.

“In short, it helps customers produce more with less resources – a central tenet of our MissionZero ambition to cut water and energy waste in mining by 2030.”

Production looks like increasing at Northern Vertex Mining’s recently started up Moss gold-silver mine, in Arizona, USA, as recent modifications to the Merrill Crowe facility and additional output from the heap leach kick in.

The company produced 7,482 oz of gold and 45,876 oz of silver during the three months to the end of June, compared with 6,057 oz of gold and 25,558 oz of silver, marking the company’s strongest quarter to date. In June, alone, Northern Vertex saw 2,580 oz of gold and 18,051 oz of silver come out of the operation.

The Moss open pit and heap leach gold and silver mine hit its commercial straps in September 2018, at which point the company said expected fiscal 2019 production guidance was 36,000-40,000 oz of gold equivalent production.

Northern Vertex said this week that its operations team has made progress in correcting issues that have hampered the process plant since started up, with modifications to the filter press piping, clarifiers and vacuum pump system nearing completion.

“We have observed a large decrease in reagent consumption and an immediate improvement in recoveries of gold and silver from the pregnant solutions,” the company said.

Such improvements to the Merrill Crowe facility recently resulted in the company’s single largest gold shipment to date – of $1.2 million representing nine days of production.

The Moss team initiated a recovery study of the heap leach pad in May 2019, with the purpose to confirm consistent moisture percolation throughout the pad; measure solution volume and solution grade retained in various areas (panels) of the pad, in order to determine the gold and silver inventory remaining on the pad; obtain samples for further bottle roll testing, in order to estimate the amount of gold inventory that can be recovered by re-leach; and design and implement a leach solution application plan to recover additional gold from the leach pad inventory.

Results from the first panel (known as the ‘Central Panel’), which contains approximately 235,000 t of ore have been received, the company said. “Results show remarkable consistency in the percolation of solution, both laterally and vertically. Furthermore, the study confirms there are no dry areas, channelling is not occurring, the pad is retaining its moisture as expected and that the recoverable gold and silver in inventory will meet or exceed feasibility predicted recoveries.”

While the full study, which will include an additional five panels is ongoing, Jim Gubler, Process Manager at Northern Vertex, said the results from the Central Panel indicated there are around 5,000 oz of recoverable gold contained in this area, of which an “estimated 3,000 oz have already been dissolved in the water held in the heap and need only to be flushed and collected”.

He added: “With the leach solution application plan that we have designed, we are projecting that a significant portion of this gold will be recovered over the next several months, which should add to our normal monthly production.”

The ongoing column test program (using crushed ore samples) is predicting ultimate recoveries of approximately 80% for gold and 60% for silver from the heap leach. The column test work on the crusher samples and the heap leach pad recovery study described above will also be used to optimise and shorten the recovery curves going forward, using live ore panels for testing rather than bulk samples that were used in the feasibility, Northern Vertex said.

“Every current test being run indicates that we should be able to outperform the feasibility recovery curves,” the company concluded.

FLSmidth takes gravity separation to a new level with Knelson GX Concentrating Cone

Northern Vertex Mining ready for more gold at Moss mine