Multivariate Image Analysis in Mineral Processing - Advanced Control and Supervision of Mineral Processing Plants - page 111

A (44%) B (49%)

C (52%) D (54%)

Figure 3.12 Froth images of increasing sphalerite grade (elemental Zn %) collected at the zinc
flotation plant of Agnico-Eagle/Laronde (Abitibi, Quebec, Canada)

not float well without pre-conditioning with an activator agent. The activator agent
is therefore crucial for maintaining a high collector selectivity. The collector agent
(potassium xanthate or KAX) is then added into the second tank. The last tank is
used for mixing only ( i.e. additional residence time for conditioning). Finally, an air
stream is mixed with the conditioned feed stream before entering the first rougher
cell, called a contact cell ( i.e. , a hybrid between conventional flotation cells and
columns). This rougher cell was selected for the test since it was known to be diffi-
cult to stabilize. A digital RGB camera as well as a lighting system were installed
above the cell as shown in Figure 3.14, close to the junction of the center and periph-
erical downcomers. Each image had a resolution of 640 × 480 pixels, and captured a

froth surface approximately 10 15 cm in size.

To span a wide range of operating conditions, froth color and texture, and con-
centrate grade, three tests of about 2-4 h each were performed. Step changes were
implemented on the flow rates of collector (KAX), air, and activator agent (CuSO 4 ).
Froth images were collected every 30 s (except 15 s for the air flow test). A total
of 2050 froth images were captured: 643, 872, and 535 during the KAX, air, and
activator tests, respectively. Since the contact cell was not equipped with an OSA, a
froth sampling strategy was used to make representative composite samples for con-
centrate grade assays. The 12-points sampling strategy, also shown in Figure 3.14,
was designed to obtain a representative sample of the concentrate overflowing the
downcomers lips all around the cell and in the center, at least the regions that were
physically accessible. This also minimized the dead-time between the concentrate

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