Direct and reverse flotation solves the problem of fluorite beneficiation

The core challenge in fluorite separation lies in its efficient separation from calcium-containing gangue minerals such as calcite. Currently, this is primarily achieved through flotation processes, with the following specific methods:

I. Positive flotation process

Principle: Inhibiting gangue minerals such as calcite while selectively collecting fluorite is the most widely applied process currently.

1. Collector System

Anionic Collectors: Primarily based on oleic acid and its modified products (e.g., acidified oleic acid), these collectors enhance selective adsorption of fluorite by introducing functional groups (e.g., S=O groups) while reducing collection efficiency for calcite. For example, under specific conditions, acidified oleic acid can achieve a fluorite concentrate grade of 98.8% with a recovery rate exceeding 97%.

Combination collectors: Synergistic effects are achieved by blending anionic and cationic collectors (e.g., hexadecyl trimethyl bromide ammonium and styrene phosphonic acid), thereby amplifying the hydrophobicity difference between fluorite and calcite surfaces. For instance, a 1:1 molar ratio of combination collectors can increase the contact angle difference between the two to 26.7°, enhancing separation efficiency.

New collector: For example, bromine-containing carboxylic acid collectors like DCX-1 enhance chemical adsorption between the collector and fluorite surfaces through an induction effect. Under conventional inhibition conditions, this achieves a fluorite recovery rate of 98.37% and a calcite recovery rate of only 13.90%.

2. Inhibitor systems

Inorganic inhibitors: Acidified water glass is the most commonly used, with the silicate gel particles it generates selectively adsorbing onto the calcite surface to inhibit its flotation. For example, at pH=7 and modulus 2.4–2.7, acidified water glass reduces calcite recovery rate from 66.93% to 9.88%, while having no significant inhibitory effect on fluorite.

Organic inhibitors: Hydroxy-containing organic compounds such as tannins and gallic acid inhibit calcite through chemical adsorption. For example, gallic acid forms Ca-O chemical bonds with calcium on the calcite surface under weakly alkaline conditions, reducing CaCO₃ content in fluorite concentrate to 1.65%.

Combination inhibitors: Combinations such as acidified water glass with sodium humate (3:1 ratio) and water glass with sodium hexametaphosphate are suitable for complex, difficult-to-process ores. For example, combination inhibitors can achieve a fluorite concentrate grade of 98.07% and a recovery rate of 80.80% for high-calcium fluorite ore.

II. Flotation Process

Principle: Inhibit fluorite and collect calcite.

Inhibitors: New phosphonic acid-based reagents (such as DTPMP) preferentially adsorb onto the fluorite surface under neutral pH conditions, inhibiting its flotation through hydrogen bonding, thereby achieving reverse flotation separation. For example, when DTPMP is used at a dosage of 400 mg/L, it can selectively inhibit fluorite, with calcite recovery rates exceeding 80%.

Adjusting agents: Small-molecule carboxylic acids such as oxalic acid and citric acid synergistically inhibit calcite under acidic conditions and fluorite under alkaline conditions through the coordinated action of hydroxyl and carboxyl groups, achieving reverse separation.

Through the above methods, efficient separation of fluorite and calcite can be achieved for different ore properties. While positive flotation remains the mainstream method, reverse flotation and new reagent processes provide new pathways for the separation of complex ores.