Foam color is a prominent visual characteristic of flotation. Flotation workers can judge whether flotation is proceeding normally and the quality of the froth products by observing changes in froth color in different operations and areas.
The color of the froth product is determined by the color of the minerals adhering to the froth surface. In froth, chalcocite appears lead-gray, chalcopyrite appears golden-yellow with a greenish tinge, malachite appears dark green with a blackish tinge, galena appears lead-gray (with a slightly darker tinge when the froth is hollow), sphalerite appears pale brownish-yellow, and hematite appears brick-red. The froth in the scavenging tail is often the color of a white water film. If the froth in the scavenging zone becomes darker, showing the color of the useful minerals, it indicates increased metal loss in the tailings. In the cleaning zone, the darker the color of the floated minerals, the better the concentrate quality.
The luster of the froth is also determined by the luster of the attached minerals and the luster of the water film. Sulfide minerals often exhibit a strong metallic luster, while oxide minerals mostly exhibit a submetallic or earthy luster. In the scavenging zone, the foam exhibits poor mineralization, displaying a glassy luster resembling a water film. If the scavenged foam shows a semi-metallic luster, it indicates increased metal loss. Coarse mineral particles result in a rough foam surface with weak luster, giving it a wrinkled appearance; fine mineral particles result in a smooth foam surface.