MINERAL PROCESSING KNOWLEDGE · TIN ORE PROCESSING
Wolframite and cassiterite overlap in density, so a shared gravity front end and a magnetic split recover both metals better than either process alone.
Technical overview. Actual process selection depends on representative ore samples, mineralogy, testwork and site conditions.
Tin and tungsten commonly occur together, and the question plant designers ask is a direct one: can a single circuit produce both concentrates? The answer is yes, but never by gravity alone. Density brings the two minerals together into one product; magnetism is what pulls them apart.
Technical note: The mineral properties and field strengths quoted here describe typical behaviour of tin–tungsten ores and are intended for orientation only. Your flowsheet must be confirmed by representative sampling, mineralogical examination and magnetic separation testwork on the actual concentrate.
1. A Density Difference Too Small to Exploit
Cassiterite has a specific gravity of 6.8–7.1 g/cm³. Wolframite, (Fe,Mn)WO4, is only slightly heavier at 7.1–7.5 g/cm³. The ranges overlap, and within a single ore the two minerals are usually so close in density that no gravity unit, whether jig, spiral or table, can produce a clean split between them. A difference of this size is buried in the natural variation of the minerals themselves, in particle shape and in the hydraulic conditions of the machine.
This is not a failure of the flowsheet. Gravity still does the most valuable work in the plant: it rejects the bulk of the gangue at low cost and high capacity, and reduces run-of-mine feed to a small, high-grade tungsten–tin mixed concentrate. That concentrate is a legitimate intermediate product, and it is far cheaper to treat further than the original ore.
2. The Difference the Magnets See
Where density cannot help, mineral chemistry can. Wolframite contains iron and manganese within its crystal lattice, which makes it a weakly magnetic mineral. Cassiterite is essentially pure tin dioxide; it carries no iron and is non-magnetic. Two minerals that are nearly identical in weight therefore differ clearly in magnetic susceptibility, and that difference can be exploited at industrial scale.
- Density controls the front end. Gravity recovers both minerals together and discards most of the gangue.
- Magnetism controls the split. A magnetic field holds the weakly magnetic wolframite and releases the non-magnetic cassiterite.
- Liberation controls both. Composite particles containing both minerals respond as a mixture of the two properties and will always blur the separation.
3. Dry Versus Wet High-Intensity Magnetic Separation
The mixed concentrate is treated at a field strength of 1.0–1.4 T. Two equipment routes are common. In dry processing the concentrate is dried and fed to a high-gradient dry disc magnetic separator, where weakly magnetic wolframite is attracted to the magnetic poles and carried into the tungsten product while non-magnetic cassiterite passes to the tailings as a tin concentrate. In wet processing the same duty is performed by a wet high-intensity magnetic separator on a slurry feed. Both routes work in the same field range, and both can achieve separation efficiency above 95% when the feed is properly prepared and liberated.
| Aspect | Dry disc separation | Wet high-intensity separation |
|---|---|---|
| Feed condition | Dried mixed concentrate | Slurry of mixed concentrate |
| Field strength | 1.0–1.4 T | 1.0–1.4 T |
| Drying requirement | Essential; adds fuel and handling cost | None |
| Water and tailings | Minimal water; dry tailings | Requires water balance and slurry handling |
| Dust control | Important, especially on fine concentrate | Not an issue |
| Main constraint | Feed moisture and dust | Matrix cleaning and water recovery |
Selection usually comes down to site conditions: water availability, the cost of drying, climate, and the size distribution of the concentrate. A dry route suits sites where drying is cheap and water is scarce; a wet route suits sites where drying would be a significant operating cost or where the concentrate is fine.
4. Building the Shared Circuit
The shared front end should be designed as a conventional tin gravity circuit, because it must recover the whole of the heavy fraction rather than an optimized tin product. Coarse fractions are treated in jigs, fine fractions on shaking tables, and bulk pre-concentration, where capacity and liberation permit, in spiral chutes. Classification ahead of each gravity stage keeps the feed within the size range where that unit works, and desliming prevents fines from short-circuiting the tables.
Before the magnetic stage, the mixed concentrate should be clean, well liberated and consistent in moisture. Composite particles that still contain both minerals will report partly to each product, which is why regrinding and cleaning of the gravity concentrate is often justified before magnetic separation. After the split, the two products must be kept strictly apart; a small cross-contamination can push a tungsten concentrate below specification as easily as it can contaminate tin.
Monitor the mass balance across the magnetic stage, not only the assay. A falling magnetic yield at a stable feed grade usually indicates a mechanical issue in the matrix or the disc, whereas a rising non-magnetic yield with falling tin grade points to entrainment or insufficient liberation.
Conclusion
Tin and tungsten can share a circuit, provided the circuit is divided into two clearly different duties. Gravity, driven by density, is unmatched for rejecting gangue and producing a small mixed concentrate. Magnetic separation, driven by the iron and manganese in wolframite, is unmatched for splitting that concentrate into a tungsten product and a tin product. Neither process can do the work of the other, and a flowsheet that respects the division can recover both metals from a single ore without compromising either concentrate.
How LiCheng Tech can help
LiCheng Tech supplies gravity and magnetic separation equipment for polymetallic ores, including jigs, shaking tables, spiral chutes and both dry and wet high-intensity magnetic separators. We can help you evaluate whether a shared circuit suits your ore, review liberation and concentrate preparation, and specify magnetic separation equipment for the products you need to make. The wider circuit context is described on our tin ore processing page.
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