logo 2004 best rev b

The reliable pH analyser system

Halland Instruments AS

Applications overview:

APPLICATION: Automatic pH control of the Neutral leaching process.

Process description:
Roasted zinc concentrate (calcine) is leached continuously in a string of five tanks.
The liquid flow into the first tank is a mixture of spent acid and overflow from the jarosite thickener. Oxygen is used for the oxidation of iron. This process is also a purification process. Accurate pH control is essential for a good result.
The first three tanks have screw feeders for adding calcine and the pH values are automatically controlled by three independent control loops.  The controller outputs goes to the variable frequency drives for the electric motors on the screw feeders.

pH range: 1-5 pH
Solid content: 30-50 g/l
Temperature: 75 - 85 C.
Flow: 250 m/h
Tanks: 5 tanks each with a capacity 200 m
Number of pH analysers: 7


NL-string, 5 tanks of 250 m3, the analysers are mounted in the container with the blue door.


The seven pH analysers are mounted indoors, in Norway we have cold winters with strong winds and heavy rain and snow.


Screw feeder with electric motor for adding calcine.

Trend picture:
7 pH analysers, last 8 hours. The calcine is added in tank 2 and 3, not in tank 1.


The analyser faceplate on the Delta V process computer system at the Boliden Odda zinc plant.