The North Fork Winifrede deep mine (Logan County Operations, West Virginia) discharges substandard raw water with a low pH and a high loading of iron, aluminium, and manganese. Manual chemical treatment was initiated to treat the raw water. Sodium hydroxide (caustic soda) was used to raise the water’s pH, which allows the heavy metals in the water to take a different chemical form. This pH increase allows the metals that are dissolved in the raw water to change to metals that can be settled out via gravity. As the large water pond reduces the velocity of the particles, gravity settles them in the pond to keep them from discharging into the environment. These particles are cleaned from the ponds periodically to allow room for new settling particles that are being continuously created as the water is treated.
Challenge
With the heavy metals loading and the low pH of the raw water, the pH must be raised to a minimum of 6 pH units, but cannot exceed 9 pH units, as this is the regulatory pH limit at the discharge outlet. The automation of the pH adjustment is needed due to fluctuations in the raw water flows from the deep mine. Without the pH chemical injection automation, the caustic soda infusion may be too high or too low thus not treating the raw water to the correct pH, which would allow substandard water to enter the environment. Without automation, the amount of chemical being added is only set correctly at that moment. Automation enables the amount of caustic soda to be set correctly as the flow changes.
Solution
In May 2023, an automated pH adjustment system was installed at the North Fork Winifrede mine at the Logan Division in West Virginia. The system consists of a pH probe, a computer called a Programable Logic Controller (PLC), and a chemical pump. The mine’s raw water discharges into a 250-gallon plastic IBC tote container. The pH probe is in the tote and tests the pH of the caustic infused treated water. As it senses the pH of the water, it sends real-time signals to the PLC unit that compares the required pH set point to the real time data pH reading. If needed, the PLC initiates the chemical pump that meters the caustic soda into the tote of treated water. The pH probe senses the addition of the chemical in real time and repeats the chemical infusion if needed. If the tote pH is approaching the pH set point, the PLC slows the pump down and the chemical pump shuts off when the pH set point is reached.
Outcomes
With changing volumes of raw water emanating from the mine, the automated pH adjustment system has minimized the manpower previously required to ensure regulatory compliance and reduced the amount of caustic soda required to treat the water by 10%. In addition, another chemical historically used to aid in settling particles in the water was made redundant once the automated system was installed. This system has significantly reduced costs and improved protection of the environment.
