Process automation worth its weight in gold

Agnico Eagle was founded in 1957 and is today one of the largest gold mining companies in the world. The Kittilä mine in northern Finland is the largest primary gold producer in Europe. The mine extracts and processes about 4000 tonnes of ore per day, which results in the production of approximately 200,000 ounces (or 6000 kg) of gold per year.

The ore at the Kittilä mine goes through a treatment process of grinding, flotation, pressure oxidation and treatment in carbon-in-leach circuits. A pressure oxidation circuit (autoclave) is required because of the ore’s refractory nature. Gold from the leach circuit is stripped from the carbon and recovered from the solution using electrowinning.

The primary chemical used in the separation process is cyanide, which due to its highly toxic nature places strict reliability and accuracy demands on pH measurements. An inaccurate or incorrect reading could result in a potentially hazardous situation. At the very least such an occurrence would result in difficulties, delays and higher costs.

Agnico Eagle was not fully satisfied with the functionality and reliability of its existing instruments at the time. Inaccuracies in pH measurements resulted in diminished safety and process efficiency. Also, the calibration of instruments was taking up a considerable amount of time and resources. Therefore, the company wanted to significantly boost process control with measurements and at the same time improve the maintenance of the measurement devices.

Agnico Eagle carried out an extensive year-long field trial with various manufacturers. Endress+Hauser came up on top, largely thanks to its high-performance instruments and its know-how, as well as the friendly and competent service that accompanies the products. The process in the Kittilä mine is not an easy one for measurement and analysis devices, and there are no simple solutions. Technical issues have been solved through close cooperation between the Agnico Eagle and Endress+Hauser teams.

All in all, Endress+Hauser supplied around 320 instruments, including flow meters (Coriolis, electromagnetic, thermal and ultrasonic); level transmitters (microwave and capacitance); level limit switches; pressure transmitters; temperature transmitters; and various types of analytical instruments for pH ORP and turbidity.

It was the pH measurement technology that provided the significant improvements that the mine was seeking. Endress+Hauser supplied its Memosens and Liquiline platforms to be used as a solution for the challenges of pH measurement. The Memosens sensors are able to perform reliable measurements even in extreme conditions and in demanding applications. The non-contact digital signal between the sensor and the transmitter is very reliable and is not disturbed by any external factors, such as moisture. Calibration can already be performed outside of harsh field conditions, and the devices facilitate preventive maintenance. The effort required in calibrating the pH loops was reduced drastically.

Correct calibration is the basis for reliable measurements and analysis. With the Memosens technology, calibration no longer needed to be carried out in difficult and hazardous field conditions.

For grab sample measurements, Agnico Eagle decided to use Liquiline To Go. The handheld instrument makes it possible to use the same sensor types for grab sample measurement as those used in the process. This eliminates deviations resulting from the use of different sensor technologies.

The cleaning of devices positioned outdoors was difficult, time consuming and inconvenient, especially during the -40°C winter months. The automatic cleaning feature of the instruments provided Agnico Eagle measurable improvements in terms of both efficiency and staff satisfaction.

“In the past, pH calibration took us 2200 hours each year,” said Reijo Mämmioja, senior instrumentation engineer at Agnico Eagle. “With Memosens technology we were able to decrease the time needed to 240 hours per year. This means over 2000 hours less work. With Memosens there is no need to stay in the field for the pH electrode calibration. This is a huge improvement in safety.”

Using the same measuring technology for manual and inline measurements also led to complete data consistency, and thus to more confidence in the measuring results. The consumption of chemicals such as the expensive sodium metabisulfite was also reduced by up to 50% due to the more accurate pH measurements.

“Reliable pH measurement allows us more precise dosing of chemicals and therefore substantial cost savings,” said Annika Niiranen, a metallurgist at Agnico Eagle.