Mike Kovach, senior supervisor for drilling and blasting at ASARCO’s Ray copper operation, speaks with Gary Carpenter, vice president of sales for Reuter Equipment, an authorized KPI-JCI and Astec Mobile Screens dealer in Arizona.
Mike Kotraba knows that sometimes the most valuable changes to an operation come from posing a simple question.
Kotraba is general manager of ASARCO’s Ray mine in Kearny, Arizona—a 250,000-ton-per-day open-pit copper mine that produces approximately 100 million lb of copper metal each year. ASARCO (American Smelting and Refinery Company) was established in 1899 as a lead and silver smelter and refiner. Today, it is primarily a copper mining, smelting and refining company, and is a wholly-owned subsidiary of Grupo Mexico.
As general manager of the Ray operation, Kotraba is always seeking new ways to keep costs low and improve production throughput. Most recently, the question that plagued him concerned the low-quality copper material that had to be recirculated through the primary SAG mill. What would be the net impact on SAG throughput if the operation could remove the recirculating load from the mill, he wondered.
“The biggest challenge we face at ASARCO Ray is the price of copper, which is something we don’t have any control over,” Kotraba said. “So we try the best we can to be as efficient as we can and mine as safely as we can. We’re really focusing on things we can change and the things that can impact our future.”
Solving A Dilemma
At Ray, copper-bearing sulphide ore is hauled to the primary gyratory crusher, where it is crushed and then fed to the SAG and ball mill circuits. The crushed ore is processed into concentrate and transported via local railroad (Copper Basin Railway) to the nearby smelter where it is transformed into anodes. Oxide ore from the mine is hauled to leach dumps, and the pregnant leach solution is processed through the company’s SX-EW facility to make copper cathodes. The anodes and cathodes from both processes are shipped to ASARCO’s Amarillo, Texas facility, where they are refined and shipped as copper rod to outside customers.
There are two basic types of mineralized material present at Ray; one, a softer meta-sediment rock (schist), and the other, an extremely hard diabase. Tests showed that the pebbles from the harder diabase were nearly barren of copper mineralization after their first pass through the SAG mill. Variability of copper mineralization in the schist pebbles is higher than that seen in the diabase pebbles so the mine closely monitors the pebble grade when milling the schist ore to determine whether or not to reject the pebbles or crush them through their pebble crusher and return them to the milling circuit. Pebbles rejected from the circuit have had nearly all the copper mineralization “washed off” through the SAG grinding process. The nearly-barren pebbles take up precious volume in the SAG, which could be used for additional, higher-grade fresh feed. To eliminate the very low-grade SAG recirculating load, the company decided to remove the pebbles from its production process.
To do this, the mine first needed to invest in a system of conveyors and a telescoping radial stacker. The telescoping action of the radial stacker would be used to load the operation’s fleet of 240- and 400-ton haul trucks.
The Perfect Fit
Mike Kovach, senior supervisor for drilling and blasting at the Ray operation, had previously worked in aggregate operations, and had experience with KPI-JCI and Astec Mobile Screens’ SuperStacker extendable stacker. He sought out Gary Carpenter of Reuter Equipment, an authorized KPI-JCI and Astec Mobile Screens dealer with locations in Tucson and Phoenix, to see if Reuter had a unit available that would give the Ray operation the flexibility it needed based on its objective and site footprint. Ray mine had worked with Reuter Equipment on several projects over the years, and asked the distributor to help evaluate the project’s needs from the very beginning to see what system might work best to accomplish its goal.
“When we were designing the footprint of where we wanted the stacker and conveyors to be placed, placing the conveyors was fairly simple, but trying to get a piece of equipment that could place the material in the back of the truck and allow for stockpiling was a challenge,” Kovach said. “The SuperStacker fit the bill perfectly. It allows us to extend the boom in and out with the stinger and to rotate the entire structure sideways to make a stockpile or hit the truck. It also allows us to raise and lower to hit different heights, which will be important once we move forward with the second phase of our project, which is to place the material into a bin. So it was the perfect fit for what we were trying to do.”
The SuperStacker is a telescoping stacker designed to minimize stockpile segregation and increase stockpile capacity. SuperStackers are often used to build desegregated stockpiles and ensure product quality. By controlling the extension of the stinger conveyor, radial travel and conveyor incline, layered windrows can be built, minimizing stockpile segregation. The Super-Stacker features the Wizard Touch automation control system, which allows for more stockpiling options and produces a higher-quality product. The easy-to-use automation system comes with factory pre-set programming, and provides the versatility of customizing in the field. The SuperStacker also allows 30% more stockpile in the same footprint vs. a conventional stacker, optimizing storage space. It includes as standard a “cam-arm” linkage, connecting the rear undercarriage to the conveyor frame. This maintains a constant radius from the pivot plate to the axle, ensuring true radial movement and uninterrupted stockpiling.
In the future, the mine plans to integrate the stacker’s remote control and automation options, which would allow the stacker to be operated remotely by mill control workers inside the mill, so no employees would have to be outside running the stacker during the scorching Arizona summers.
To ensure the stacker would work in the mine’s application, Kotraba decided on a six-month rental arrangement during which the operation could conduct extensive testing to assess the SuperStacker’s capabilities and ensure it was the right product for the job.
In less than a month, the mine had its answer. Thanks to the SuperStacker, the mine saw increased mill through-put and reduced costs. In the first three months of use, ASARCO removed approximately 500,000 tons of reject material from the SAG mill circuit, saving the company between $750,000 and $1,000,000. These savings come from: 1) reduced costs (by not crushing and recycling the sub-grade recirculating load); 2) increased SAG through- put (by rejecting the sub-grade recirculating load thereby opening-up additional SAG volume for more fresh feed), and 3) increased copper production (by adding higher grade, fresh feed to the process).
“With the help of Reuter Equipment and KPI-JCI and Astec Mobile Screens, we’ve put together a package that, in under a month from full trial implementation, has paid for itself and then more,” Kotraba said. “We’d consider that a very, very successful project.”
In addition to the significant savings earned by the SuperStacker, the mine ingeniously installed drip pans underneath the conveyors to collect the fines that were accumulating with the water from the sprayers. When they tested the material, they found that the grade of the fines material was almost twice their current feed-grade.
“The process is a wet process, so it’s a little different than your typical gravel operation,” Kovach said. “Though the fines in the carryback water do not represent a high volume, they still contain a lot of copper, so we put drip pans on both conveyors to capture the material, and use sprayers to wash the fines back into the mill and back into our process.”
As is the case with any operation as large as Ray, the mine needs to focus on maximizing uptime as much as possible. That included developing a thorough preventative maintenance program with Reuter Equipment and KPI-JCI and Astec Mobile Screens, Kovach said. That program requires scheduled preventative maintenance every other day, which gives the company’s service personnel an opportunity to inspect the equipment for signs of wear and make any necessary adjustments that might prevent a breakdown.
“There’s a responsibility on us to conduct preventative maintenance,” he said. “The program developed in conjunction with Reuter and KPI-JCI and Astec Mobile Screens will ensure we get the best longevity out of the components and the system.” The original version of this article was written by Michelle Cwach, media relations manager for KPI-JCI and Astec Mobile Screens, and appeared in Issue 10, Quarter 2, 2015 of The Feed magazine.