The responsibilities of a flotation plant operator include maintaining the normal operation of equipment, adjusting reagents and equipment based on flotation phenomena to ensure stable and optimal flotation indices. Therefore, accurate judgment of flotation phenomena is crucial for achieving good indices. Common methods for judging the quality of flotation products include observing the foam and washing the products.

1. Observing the Foam

Flotation operators adjust the amount of flotation reagents, the quantity of concentrate scraped out, and the amount of middling circulated based on their judgment of the flotation foam’s appearance. The main aspects of observing flotation foam include:

(1) Solid vs. Hollow  

Foam is described as “solid” when the mineralization degree on the mineral surface is high, resulting in firm, substantial foam, typically seen in roughing and cleaning operations. In scavenging operations, because useful minerals have been largely floated in roughing, the foam tends to be “hollow.” Reagent addition directly affects flotation foam characteristics. If reagent dosage is appropriate, the foam in the first roughing cell will be “solid.” Excessive depressant or insufficient collector will result in “hollow” foam.

(2) Large vs. Small  

The size of bubbles on the foam layer surface varies with ore properties, reagent regime, and flotation operation. In general sulfide ore flotation, bubbles with a diameter of 8-10 cm are considered large, 3-5 cm as medium, and 1-2 cm as small. Well-mineralized bubbles are usually medium-sized, commonly seen in roughing and cleaning operations. During bubble coalescence, some large bubbles may appear to increase concentrate grade. Poorly mineralized bubbles are often large (hollow bubbles), commonly seen at the tail end of scavenging operations. In oxidized ore flotation, small and numerous bubbles might indicate low-grade rough concentrate with high recovery, whereas small, numerous, and hollow bubbles suggest both low-grade and low recovery. Hence, observing bubble size and solidity is crucial for judging flotation indices.

The size of bubbles on the foam layer surface varies with ore properties, reagent regime, and flotation operation.

(3) Color  

Foam color is determined by the attached minerals and the water film color. For instance, in hematite flotation, the foam is brick red. Scavenging tail foam is often white (water film color). The deeper the floating mineral color in scavenging, the greater the metal loss. Conversely, the deeper the color in roughing and cleaning, the better the concentrate quality. A common but not absolute standard for clean flotation in scavenging operations is whether the foam appears white, though specific situations need detailed analysis.

(4) Luster  

Foam luster is influenced by the mineral’s luster and the water film’s sheen. The coarseness of flotation mineral particles also affects foam surface luster.

(5) Outline  

Mineralized bubbles in flotation often appear nearly round or elliptical due to the influences of slurry flow, bubble interaction, and the gravitational pull of surface-layer mineral particles. Freshly formed mineralized bubbles have distinct outlines, whereas bubbles on the slurry surface for extended periods have blurred outlines.

Mineralized bubbles in flotation often appear nearly round or elliptical due to the influences of slurry flow, bubble interaction, and the gravitational pull of surface-layer mineral particles.

(6) Thickness  

The thickness of the foam layer is related to the amount of frother used and the degree of bubble mineralization. More frother, high ore grade, high concentration, and good mineralization result in a thicker foam layer, and vice versa. However, overly coarse flotation mineral particles make it challenging to form a thick foam layer. Different ore properties require varying foam layer thicknesses.

(7) Brittleness vs. Stickiness  

Brittle foam has poor stability and breaks easily, whereas overly sticky foam may cause “froth overflows,” resulting in poor concentrate grade and transportation difficulties. Excessive frother, oil contamination, or substantial slime content in the ore can make foam sticky.

(8) Sound  

The sound of foam being scraped off by a scraper indicates mineral properties. Heavy minerals with coarse particles and solid foam make a “sizzling” sound when falling into the foam trough.

2. Washing Products

Washing foam products or tailings with a spoon, bowl, or washing pan helps assess concentrate quality and metal loss.

3. Washing Requirements

Choose appropriate washing locations and products based on the washing purpose. Determine suitable sample amounts and washing extent based on mineral content and type.

For accurate washing inspections, ensure consistency in sampling locations, sample amounts, and washing extent each time.

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