Our world is dependent on all the copper wire distributing electricity and communications signals over great distances and throughout our homes and businesses. Mining and refining this copper into the purity required poses safety, efficiency and reliability challenges for global miners.
That’s why I wanted to revisit the 2018 Mining Engineering magazine article, Improved flow measurement and control are key to efficiency, by Emerson’s Alena Johnson.
Alena opens describing the heap leaching process for copper:
Copper ore is excavated from the ground, crushed and then spread in uniform layers on a pad. A slow trickle of sulfuric acid is distributed over the pile, where it percolates to the bottom and a collection point. The acid leaches out the copper, along with other minerals, which can be extracted chemically.
This continuous process is performed on a massive scale:
A typical pad measures 1.6-km (1-mile) long and 0.8-km (0.5-miles) wide. Working day after day, the stacker creates individual piles or modules on the pad, each 122 x 61 m (400 by 200 ft) and 3 m (10 ft) deep. When one module is filled, it moves across the pad to the next, filling the area in one continuous pile.
Much like a drip irrigation system for a garden, mining technicians lay plastic pipes on the surface. Dripping out of this network of pipes is:
…diluted sulfuric acid, called raffinate, is pumped through the pipes so it can be distributed over the module, allowing the acid to soak through the ore and leach out copper as it percolates to the bottom.
Monitoring the even flow of raffinate, which is critical for efficient extraction of copper from the ore, has been a manual operation since everything on the surface is moved around manually.
If it hits one area heavily, it will quickly leach out the copper, and then the rest of the raffinate will simply sink and be wasted on the layers of spent calcite. Eventually this flooding causes porosity and destabilizes the pile. Other areas with inadequate coverage will leave behind unrecovered copper. Hitting some average value where there are still highs and lows does not help.
One miner turned to the Emerson team for a solution to improve the overall efficiency of this leaching process. They needed movable, modular skids that two technicians could lift and move around on all-terrain vehicles. The skids would measure and control the flow of raffinate. Since they were movable, a wireless DP flow meter, wireless pressure transmitter and manual regulating valve were needed per skid.
Once a solution was developed and tested, the skids were built and deployed. Part of the planning process was the miner’s recognition that:
…its biggest product had become data. With every unit sending its reports, there were more than 1.2 million data points created daily.
This wealth of big data provided the opportunity for analysis and optimization. They:
…created a quality score system based on an ideal pressure target using very strict performance expectations. A deviation of 0.05 psi from the ideal value at the skid causes a 1 percent score deduction. With so tight a measure, the plant thought it would be an accomplishment to run at better than 80 percent across the site. After using the new system for a few months, they routinely scored higher than 87 percent.
Be sure to check out the refreshed Emerson Mining, Minerals, and Metals web page to access resources on how you can improve your mining operations. Also, take a few minutes to read Alena’s article for more information on the heap leaching process, requirements for the skids, skid solution, improvements made from access to the real-time, and historical data.