The Probe monitor uses non-contacting ultrasonic technology to provide reliable measurement of froth levels in the flotation cell.

Phelps Dodge Mining Company, the mining and metals division of Phelps Dodge Corporation, is one of the world's leading producers of copper and molybdenum and is the world's largest producer of continuous-cast copper rod. The Bagdad copper mine, located in Arizona's Yavapi County, produces copper and molybdenum ore, and has a history that dates back to the late 19th century. 

The facility uses a large series of cone crushers and ball mills to reduce copper ore to very fine particles. Then the solids are "pulped" or mixed with water to create a slurry. To this slurry, they add milk of lime to raise the pH. Small amounts of special reagents are also added, including a frother to make bubbles, as well as a collector chemical that causes the copper minerals to stick to those bubbles. This material is pumped to a series of froth flotation cells to concentrate the copper. Air is blown into the flotation cell tank, and the pulp mixture is vigorously agitated like a high-speed blender. Rising bubbles carry the copper particles up and over the edge of the flotation tank. The bubbles break soon after they flow over the edge. The copper is then ground even finer and purified by additional flotation processes.
 

It is critical to measure the level of both the pulp and the froth to ensure optimum copper concentrate production. Those levels provide feedback to the plant's process control system so operators can make appropriate changes to variables like pulp and air flow as well as the addition of chemical reagents. It's a very difficult level measurement because of material build-up and plugging that occurs on most types of level technologies. In addition, the harsh conditions necessitate the installation of a very robust device. 

In this application, Phelps Dodge uses the Probe ultrasonic level monitor from Siemens-Milltronics. This instrument combines sensor and electronics in a single package for effective liquid level measurement in open or closed vessels. It is easy to install and remove, and the non-contacting ultrasonic technology requires virtually no maintenance. The instrument does not touch the slurry. The Probe monitor features patented Sonic Intelligence®  echo-processing that filters out false echoes from acoustical or electrical noises and agitator blades in motion, giving superior measurement reliability.

Each flotation cell is equipped with a Probe to monitor the froth level. A second Probe measures the pulp level based on a metal target attached to a mechanical float assembly. The 4 — 20 mA analog output from the Probe is fed into the plant's control system to provide flotation cell level information.

The requirements for measurement are relatively narrow. The span for the pulp measurement (using the Probe with target and float assembly) is 10 inches and the froth level Probe uses a span of only two inches.

The Probes are very easy to program and they require no maintenance. The only set-up required is programming the span for the analog output. This is easily accomplished in the instrument shop or during installation. The Probes are proving to be a much better alternative to older bubbler technology. The company has Probes successfully installed at other properties as well.

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