In froth flotation, a depressant keeps unwanted minerals from floating so the valuable mineral reports to the concentrate cleanly. Lignosulfonates are studied and used as low-cost organic depressants in several sulfide and gangue separations. This page summarises the published evidence, the variables that decide whether it works, and a bench test plan. For general mineral-processing uses, see lignosulfonate in ore flotation.
How Lignosulfonate Acts as a Depressant
Lignosulfonate is an anionic polymer. It adsorbs on some mineral surfaces, through metal sites such as calcium or through hydrophobic interaction, and covers them with a hydrophilic layer. Collector adsorption on those surfaces is reduced, so the mineral stays in the pulp. Selectivity comes from the difference in adsorption between minerals under the chosen pH, water chemistry and collector.
Published Separations
| Separation | Mineral depressed | Reported findings |
|---|---|---|
| Chalcopyrite–molybdenite | Molybdenite | Depression increased with pH, linked to calcium sites on the molybdenite surface. Chalcopyrite depression seen with sodium isopropyl xanthate was suppressed with potassium amyl xanthate, which enabled separation. A seawater study reported molybdenite depression above 60% with chalcopyrite recovery over 95% at pH 9 and high lignosulfonate concentration. |
| Chalcopyrite–talc | Talc | Calcium ions combined with calcium lignosulfonate depressed talc effectively across pH 6–12 (Metals, 2021). |
| Chalcopyrite–galena | Galena | Ferric chromium lignosulfonate reduced lead in the copper concentrate to 4.73%, against 10.71% with a dichromate depressant (2018 study). |
These are laboratory results on specific ores and conditions. They show where lignosulfonate is worth testing, not what it will do in your circuit.
Variables That Decide the Result
- Ore mineralogy, liberation size and slime content.
- pH and dissolved ions, especially calcium, magnesium and salinity (seawater or recycled water).
- Collector type and chain length, frother and conditioning sequence.
- Lignosulfonate type: cation (calcium or sodium), molecular-size distribution, sugar content, and modified forms such as metal-complexed lignosulfonates.
Bench Test Plan
- Characterise the ore: assay, mineralogy and size distribution.
- Use plant or synthetic plant water; record pH, calcium and conductivity.
- Run a baseline without depressant, then a dosage series of lignosulfonate added at the conditioning stage.
- Keep collector, frother, pH and conditioning times fixed while screening dosage; then optimise pH.
- Plot grade against recovery for each condition, and repeat the best two conditions.
- Check downstream effects: settling, filtration and water recycling.
Grades for Testing
| Grade | Key values (TDS) | Why test it |
|---|---|---|
| Calcium lignosulfonate | Grade One: 55% min lignosulfonate content (dry basis); insolubles 1.5% max | Used in the published talc depression work |
| Sodium lignosulfonate | Grade One: Ca + Mg 0.5% max | Low calcium, for comparing the effect of added calcium |
Packaging and Documents
- Powder: 20 kg or 25 kg woven bags with polyethylene liner, or 500 kg / 600 kg jumbo bags (FIBC).
- Liquid grades: IBC totes, drums or flexitanks.
- Documents: TDS, SDS and batch COA; samples for laboratory work.
Request a Test Sample
Send the ore type, separation target, current depressant, pH and water type to info@greenagrochem.com or use the contact form.
Frequently Asked Questions
What does lignosulfonate do in flotation?
It is mainly used as a depressant: it adsorbs on selected mineral surfaces and makes them less floatable, so the target mineral can be floated away from them. It is not a collector.
Which separations has it been studied for?
Published work includes chalcopyrite–molybdenite separation, depression of talc in chalcopyrite flotation, and chalcopyrite–galena separation with a ferric chromium lignosulfonate.
Does water chemistry matter?
Yes. Studies on molybdenite show that depression depends on pH and on calcium at the mineral surface, and seawater flotation behaves differently from fresh water. Test with plant water.
How should I start testing?
Run bench flotation tests on representative ore with plant water, a no-depressant baseline and a dosage series, and judge by grade–recovery curves rather than one test.
