Combined Flotation of Phosphate Ore

For mixed phosphate ores with relatively high silicon and magnesium impurity content, single positive (or negative) flotation struggles to produce high-quality phosphate concentrate. Combined flotation—integrating positive and negative flotation—is required. By tailoring the process to ore characteristics and removing impurities in stages, qualified phosphate concentrate is achieved. Currently, primary combination flotation methods include: positive-negative, negative-positive, and double-negative flotation. The sequence depends on the relative content of carbonate and silicate impurities.

Direct-Reverse Flotation: Primarily suited for phosphate ores with high silicate impurity content. The typical process involves: 1.  Direct Flotation: Under weakly alkaline conditions (pH=9~10), silicate inhibitors (mainly water glass) suppress quartz and other silicate gangue minerals from floating. 2.  Reverse Flotation: Fatty acid collectors are then used to enrich apatite and carbonate impurities, yielding a direct flotation concentrate. Subsequently, the pulp environment is adjusted to acidic conditions (pH=4–5). Apatite suppressants (primarily phosphoric acid or phosphoric acid derivatives) are added to the positive flotation concentrate to perform reverse flotation of carbonate impurities.

Reverse-Positive Flotation: This process reverses the sequence of positive-reverse flotation, first performing reverse flotation to remove carbonates from phosphate ore, followed by reverse flotation to remove silicates. It is primarily suitable for phosphate ores with high carbonate content.

Double Reverse Flotation: Suitable for phosphate ores with high levels of both carbonate and silicate impurities. The primary process involves reverse flotation to remove magnesium from apatite, followed by adjusting the pulp to weakly alkaline conditions. Silicate collectors (primarily polyamine ethers) are then used to reverse-flotate the magnesium-depleted concentrate to remove silica.