Brushy Creek Mill employees faced a challenge when the quality of its lead and zinc concentrates unexpectedly declined. An investigation discovered that poor process water quality was to blame. Thanks to collaboration within the team, and with water partner Neo Solutions, Doe Run discovered a sustainable solution located 1,200-feet underneath the mill.
Brushy Creek Mill processes approximately 50,000 tons of lead concentrates each year. The lead ore also contains smaller amounts of zinc and copper. Processing these other elements helps Doe Run diversify its revenue streams and fulfill its sustainability commitments, getting the most from all the natural resources in its mining operations.
However, a decline in concentrate quality was caused by the process water being used in flotation, which separates lead, zinc and copper minerals from the mined rock. As good stewards of the estimated 38 million gallons of water that flow into Doe Run’s six mines and other facilities, Brushy Creek Mill was using water pumped from the mine and held in its tailings ponds for the flotation process to separate the minerals.
“Over time, the use and reuse of the process water made the quality too poor to filter lead concentrates effectively,” said Brian Mangogna, mill manager at the Southeast Missouri Mining & Milling Division (SEMO). “The lead concentrates contained too much moisture, so they had to dry longer before being shipped. It affected our business, our transportation partners and our customers.”
A Solution Right Under Their Feet
Doe Run and Neo Solutions, a water management partner, evaluated a number of solutions that would both improve the quality of lead and zinc concentrates and maintain the company’s stewardship of the water at its property. Instead of reusing process water after it reaches the tailings ponds, they developed a system that enables them to tap the high quality, naturally occurring mine water directly from Brushy Creek Mine below.
An adjustment in the piping now allows the mine water to enter directly into the mill. Not only was the quality better suited for the flotation process, the year-round 65-degree water temperature has provided unexpected benefits.
“We know temperature plays a role in the quality of outputs for our mill,” said Mangogna. “But the switch to using mine water improved zinc recovery and mill efficiency more than anticipated, especially during the winter months when the outdoor tailings pond is very cold.”
Today, a cross-functional team at the mill stays in communication to make the process work. They monitor water within the mines, in the tailings pond and in the mill process and make adjustments as needed. For example, during heavy rainfall, the mill may need to draw more water from the tailings pond than the mine to help balance the increased volume caused by the rain.
“We often celebrate when we make substantial leaps by building new technologies, but simple changes and improvements can create significant positive change,” said Mark Yingling – vice president, environment, health and safety. “With the new mine water process, in combination with the capabilities of the water treatment plant added to that site in 2014, Brushy Creek Mill serves as an example of how we can optimize our infrastructure to be a better steward of our natural resources and environmental responsibilities.”
The team from Brushy Creek Mill has shared its knowledge about managing water systems for sustainable reuse of water resources with Doe Run’s other locations. In 2017, Fletcher Mine and Mill began similar work to pump underground water for use at the mill.
Doe Run discharged approximately 3 percent more water to the environment in 2016 based on discharge monitoring reports submitted to MDNR. Improved water treatment efforts contributed to a decrease in the total amount of lead and zinc in discharged water from all Doe Run facilities by approximately 56 percent and 22 percent respectively.
Additional Water Management Efforts
In 2017, Doe Run will complete a $75 million overhaul of its water management program at SEMO. The five-year program to upgrade and advance the company’s water management adds high-tech water treatment plants that use a chemical process to treat mine and mill water to meet permit limits. Two water treatment plants, costing $28.6 million, opened in 2016 at Sweetwater Mine and in Viburnum. A final plant at West Fork Mine is scheduled to be completed in the summer of 2017.
The new plants improve flexibility and treatment options at the facilities. The plants can treat up to 10,000 gallons of water per minute, 5,500 gallons more than the first plant, which was constructed at Brushy Creek Mine. The final plant at West Fork Mine will be able to process up to 18,000 gallons per minute.
“We’ve learned that we needed more flexibility in our water capacity given the types of weather we encounter in Missouri, and made the necessary adjustments,” said Samantha Anderson, senior environmental scientist at SEMO.
The four completed water treatment plants processed more than 5 billion gallons of water in 2016.