Classification and Mechanisms of Flotation Reagents

Whether a mineral floats depends not on the equipment but on the flotation reagents. Most minerals in nature have poor natural floatability. By precisely modifying the surface wettability of minerals with different reagents, we can efficiently separate valuable minerals from gangue minerals that are intergrown together. Flotation reagents are the most flexible and controllable core tool in the entire mineral processing flow. This article systematically breaks down the three major categories of flotation reagents—collectors, frothers, and modifiers—covering their mechanisms and commonly used models in practice.

Collectors – The Core Driving Force of Flotation

Mechanism of action
Collectors are organic reagents that selectively adsorb onto the surface of target minerals and enhance their hydrophobicity. Their molecules have a dual‑group structure:

• A polar hydrophilic group (mineral‑affinity end) that firmly attaches to the mineral surface via chemical or molecular bonds;
• A non‑polar hydrophobic hydrocarbon group (air‑affinity end) that extends outward, forming a hydrophobic film that renders the originally hydrophilic mineral surface water‑repellent, allowing it to adhere stably to air bubbles and rise with them.

Based on their dissociation behaviour in water, collectors are divided into two main types:

① Non‑ionic collectors: kerosene, diesel oil and other hydrocarbon oils, which are uncharged. They are mainly used for separating naturally hydrophobic minerals such as coal and graphite, and can also serve as auxiliary collectors.

② Ionic collectors: the most widely used in mineral processing, further divided into anionic and cationic types. Anionic collectors suit the majority of sulphide metal ores; cationic amine collectors are mostly used for reverse flotation of oxide gangue minerals like quartz and feldspar.

Commonly used collectors in the market

① Xanthates (xanthogenates)
The leading anionic collectors, they are the most universal reagents for sulphide ores (lead‑zinc, copper, gold ores) with good selectivity. Depending on the hydrocarbon chain length, they include ethyl xanthate, butyl xanthate, and isoamyl xanthate—longer chains give stronger collecting power but lower selectivity.

② Dithiophosphates (black agents)
Compared with xanthates, they have stronger oxidation resistance and inherently better depression of iron sulphide minerals (pyrite), making them suitable for selective flotation of high‑sulphur polymetallic ores.

③ Fatty acids (oleic acid, oxidized paraffin soap)
Specialised collectors for oxide ores, used in flotation of fluorite, hematite, and phosphate ores. Their performance is strongly affected by pulp pH and calcium ions, and they have poor solubility at low temperatures.

④ Amine cationic collectors
Dodecylamine and lauryl amine are mostly used for reverse flotation of quartz and flotation of potash ores, performing best in alkaline pulp conditions.

Frothers – The Dedicated Transporters for Mineral Particles

Molecular structure and core mechanism
Frothers are heteropolar surfactants with one polar hydrophilic end and one non‑polar hydrophobic end. They orient at the gas‑liquid interface and:

• During agitation and aeration, they break large air bubbles into numerous fine, uniform small bubbles;
• Coat the bubble film to prevent bubble coalescence and rupture, enhancing foam layer stability;
• Moderately control foam toughness to ensure smooth scraping while avoiding excessive stickiness or dewatering difficulties.

The performance is determined by both groups:

• Non‑polar hydrocarbon chain: longer chains increase frothing ability but reduce water solubility; the preferred chain length in mineral processing is 6–8 carbon atoms.
• Polar hydrophilic group: water solubility order – –O– < –COOH < –OH < –SO₃H, which directly determines the applicable pulp environment.

Mainstream frother types and common models

① Natural frothers (forestry extracts)

• Pine oil: the earliest industrial natural frother, mainly α‑terpineol, a pale yellow liquid with strong frothing power and almost no collecting ability. Dosage is generally 10–60 g/t of raw ore, with moderate cost.
• No. 2 oil (pine alcohol oil): the most widely used classic frother in Chinese concentrators. Produced by hydration of pine oil, containing 40%–60% terpene alcohols. It produces crisp foam with good selectivity, suitable for most sulphide ores, with dosage 20–100 g/t and strong versatility.
• Camphor oil and eucalyptus oil: forestry by‑products. Eucalyptus oil has weaker frothing but excellent selectivity; blue camphor oil has both frothing and weak collecting properties, and can be used in combination.

② Industrial by‑product frothers (coal chemical / petrochemical by‑products – cost‑effective choice)

• Fusel oil: a by‑product of alcohol plants, a mixture of propanol and butanol, producing brittle foam suitable for coal washing and high‑sulphur ores, dosage 200–300 g/t.
• Sec‑octyl alcohol: a by‑product of castor processing, with better frothing performance than fusel oil, widely used in Chinese coal preparation plants, dosage about 100 g/t.
• Mixed alcohols and ester oils: processed from residual liquids of butyl‑octyl alcohol production, producing large foam volume without sticking and good dewatering properties, making them a popular low‑cost alternative to pine oil.

③ Synthetic frothers (high‑end refined reagents)

• MIBC (methyl isobutyl carbinol): a globally used high‑end frother, producing fine, dense foam with rapid defoaming and strong selectivity, friendly to fine particle flotation. Its higher unit cost limits it to precious metal and high‑precision processing lines.
• Ether alcohol frothers: allow customisation of carbon chain structure, controllable frothing ability, dense foam without stickiness, and very low dosage (10–80 g/t). They are mainstream in overseas metal mines, suitable for stringent separation criteria.

Modifiers – Determining the Upper Limit of Separation

Modifiers generally do not directly float minerals themselves; instead, they regulate the pulp environment and reagent adsorption states to optimise the performance of collectors and frothers. They fall into four categories:

1. Activators – “Awakening” difficult‑to‑float minerals
Mechanism: they generate new active sites on the target mineral surface, enabling minerals that previously could not adsorb collectors to become floatable.
Common reagents:

• Copper sulphate: the classic activator for sphalerite, used with xanthate to float zinc minerals.
• Sodium sulphide: activates oxidised copper and lead ores, but can also act as a depressant for some sulphides—different dosages produce completely opposite effects.

2. Depressants – “Locking” gangue minerals to prevent unwanted flotation
Mechanism: they form a hydrophilic film on gangue mineral surfaces, blocking collector adsorption, suppressing waste rock from floating, and greatly improving concentrate grade.
Common reagents:

• Lime (quicklime): an alkaline regulator, most commonly used in sulphide flotation, simultaneously depresses pyrite, with excellent cost‑effectiveness.
• Sulphuric acid and soda ash: acidic / weak alkaline regulators for oxide and fluorite ores.

4. Dispersants and Flocculants
For ores with high slime content and severe slime coating:

• Dispersants (polyphosphates, water glass): break down fine particle agglomerates, eliminating interference from slime coating on target minerals.
• Flocculants (polyacrylamide, PAM): used in reverse mode to make fine slimes coagulate and settle, improving froth quality.