A Look Inside the 3rd PTFI SAG Mill That Adds More Power to Better Process Underground Ore
10 May 2023
Hundreds of millions of dollars are being invested in high-tech comminution power to break up underground ore into fine particles. In Papua’s Southernmost Outback, that’s happening with PTFI's third SAG mill.
The finer the particles, the less tonnage capacity is required to process the copper and gold
During the fourth-quarter of 2019, PTFI completed mining the final phase of the Grasberg open pit. The mine has transitioned to large-scale underground mining, achieving important milestones in ramping-up production of large-scale quantities of copper and gold from its significant underground ore bodies.
When the Grasberg open pit was in operation, crushing and grinding the ore into those fine particles was a lot easier, as naturally occurring gravity from the Grasberg Pit ore was available.
The Grasberg mill got a great head start on making rocks into finer particles, from the open pit, because pit ore was dropped down through 600-meter ore passes. The switch from processing ore from the open-pit above to underground meant the loss of that free comminution.
Adding another SAG mill to the two existing ones at the mill
A SAG or semi-autogenous mill uses steel ball and the ore itself to break up the rock into fine particles in order to separate the copper and gold from all the non-valuable constituents of the ore, or gangue.
Before 2019, the mill could operate at 250 ktpd. As the mine has transtitioned from open pit to underground mine, the mill face difficulties to keep up with the ore processing capacity compared to what it had when the Grasberg open pit was still operating.
Imanuel Hutahaean, General Superintendent-Metallurgical Services revealed that, in the period 2020 to 2021, when all ore came from underground mine, the mill never reached the production capacity to operate at a 200 ktpd rate.
In 2020, the Concentrating Division sped up action on the SAG #1 and SAG #2 surveys. They were conducted by grinding model simulations and the result indicated de-rate tonnage factors of SAG #1 and SAG #2.
“De-rate tonnage factors of SAG #1 and SAG #2 was found on the surveys with the cause was the characteristics of the ore from the GBC underground mine having higher levels of hardness and abrasiveness than the ore from the Grasberg open pit,” Imanuel said.
To maintain milling capacity despite de-rate of SAG #1 and SAG #2, Anthony Manuel, Vice President-Concentrating said that a third SAG mill installation will provide sufficient capacity to enable the mill to operate at a 240 ktpd rate.
“SAG #3 in conjunction with SAG #1 and SAG #2 and refurbished Crusher Master Plant will have the required capacity to support the safe ore processing from the Grasberg Block Cave underground mine.” Anthony added.
The construction of the third SAG Mill in a new building located in the vicinity of the old MP74 lime-mixing station and the decommissioned ARD Fluid Bed Reactor plant required a high level of engineering and planning, said Bayu Swandharu, Manager-Concentrating Technical Support.
The project, began in December 2019 with the demolition work and is scheduled to be completed in the fourth quarter of 2023, a deadline that poses a significant challenge to the team.
“While the overall construction progress of SAG Mill #3 is nearing 41%, we are currently investigating ways to optimize the schedule and cost for the project in order to expedite the project slow-down due to the COVID crisis,” Bayu said.
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