On average, 600 tons of ore are sent through the mill grinding circuit—which consists of a semi-autogenous grind (SAG) mill and a ball mill—every hour. Throughput rates, however, fluctuated widely due to the different tendencies of mill operators. The mill could be targeting throughput of 650 tons per hour, for example, but one operating crew might not be comfortable with how a certain pump is running and curb throughput at 600 tons. Another crew, working with the same pump, would come on shift and safely run the mill at the targeted rate.
“You’ve lost 50 tons an hour, which is a lot of money at the end of the day,” says Pam Moyo, Senior Metallurgist at Cortez and Project Lead for the digitization of the mill.
To reduce such variability, the mine recently installed and commissioned an Advanced Process Control system that effectively automates the mill grinding circuit. The system maximizes throughput by automatically adjusting various operating parameters such as mill speeds, reagent levels, power usage and the amount of water and lime used in the grinding circuit. The system is not unlike the automatic pilot on an airplane, Moyo says, adding that the goal is for the system to manage the grinding circuit approximately 90 percent of the time the mills are operating.
Operators are supportive of the initiative
Operators are supportive of the initiative, Moyo adds, because the Advanced Process Control system is an important new tool that will help maximize throughput.
“They bought in because they want to excel and because they’re a big part of the transition,” she says. “They were involved in the testing and implementation of the system, and the system is freeing them up to do things that they haven’t always been able to focus on, like water management, tailings management and supporting other mine processing circuits.”
The Cortez Team is also testing technology that automates reagent dosing levels used at the mill, such as cyanide and flocculant. Cyanide has long been used in gold mining to leach gold embedded in ore. At Cortez, cyanide is added after ore exits the SAG mill and enters the carbon-in-leach circuit. The amount of cyanide used is small and closely regulated, but minor deviations occur and this impacts gold recovery. If cyanide levels are too low, gold recoveries will decline. If too much cyanide is used, it’s a waste of the reagent that could increase operating costs.
To reduce such variability, the mill’s technical services team recently installed a cyanide titrator, a machine that continuously measures the amount of cyanide in the carbon-in-leach circuit and automatically adjusts dosing levels when cyanide volumes are not at optimal levels. This tighter control of cyanide levels—which used to be measured manually—also benefits the operation by reducing the amount of reagents required to detoxify cyanide in waste materials sent to the mine’s tailings storage facility.
Earlier this year, Cortez began conducting equipment inspections using tablets instead of paper. As a result, when mill operators discover equipment that is not in good working order during inspections, they can create a work order on their tablets that is automatically routed to the maintenance department so repairs can be expedited. The transition to a paperless system remains ongoing, but when fully implemented it will ensure more efficient work processes.
“Currently, the operator goes out in the field with a piece of paper and records the condition of equipment, then his supervisor will go over this paper and put in a work request to the maintenance department,” says Matt Majors, Process Maintenance Superintendent at Cortez, who is overseeing the project. “It’s a time-consuming process that will disappear once the transition to a paperless system is complete.”
Looking ahead, digitization will spur even greater efficiencies. One project, called the New Generation Mine to Mill, involves the use of sensors that will be able to detect ore hardness, gold content, sulfide levels and other important mineralogical properties while ore is still being mined. This information will be fed into computer models that quickly analyze the data and develop what Emrah Yalcin refers to as a “Model Informed Process Control” technique. Yalcin, Process Technical Services Superintendent at the Cortez mill, says information gleaned from these models will be fed into the Advanced Process Control system, which will then automatically adjust mill operating parameters, further increasing throughput and operating efficiencies.
“This will take us to another level and allow us to be more proactive than was previously possible,” Yalcin says. “The next step for us is trialing machine learning and artificial intelligence to further refine and improve processing.”