Potential reprocessing methods for tungsten recovery from tailings

1. Summary of previous reprocessing experiments

The tungsten ore beneficiation process usually includes pre-selection, roughing, cleaning and purification after crushing and grinding the ore. The final tungsten concentrate typically contains ≥65% WO 3. Wolframite ore is of good quality, high grade, easy to mine, easy to select, convenient for post-processing, and has little environmental harm. Gravity and magnetic separation are the most commonly used methods for enriching wolframite because it is a paramagnetic, heavy and dense mineral. But these methods are not suitable for the recovery of ultra-fine wolframite, especially the particle size below 20 μm. In contrast, scheelite is more suitable for flotation, which is a conventional method for scheelite beneficiation. To date, tungsten tailings are still viewed primarily as a waste rather than a resource, and experiments with tungsten tailings reprocessing have been limited.

A reprocessing experiment was conducted at the Panasqueira tungsten mine in Portugal to recover ultrafine wolframite from old and new tailings. The effects of froth flotation, magnetic separation and gravity separation on the reprocessing of old and new tailings were compared. The results show that froth flotation is the only feasible method for recovering wolframite in tailings post-processing, while magnetic separation has low recovery rates at different magnetic intensity levels. Three-stage gravity separation combined with intermediate sulfide flotation produces 50-55% WO3 wolframite concentrated from tungsten tailings with reasonable recovery rates. However, since the reprocessing of 1 ton of tungsten tailings only provides a few kilograms of tungsten concentrate, it is considered uneconomical.

2. Gravity separation

Gravity separation is an important method for beneficiation of wolframite ore. Compared with other mineral processing technologies, it has the advantages of high mineral processing efficiency, low investment and operating costs, no need for additional chemical reagents, and no potential pollution to the environment. But conventional gravity separation is inefficient for fine and ultrafine wolframite: it is reported to be less than 45%.

Due to the hard and brittle nature of wolframite, over-crushed wolframite will inevitably be produced during the grinding process. Therefore, most of the fine and ultrafine wolframite may remain in the tailings after gravity separation. However, in the same study, an enhanced gravity concentrator was successfully applied to fine tungsten ore beneficiation. Suspension and vibrating cone concentrators and Falcon concentrators are two very selective separators of fine-grained mineral particles (typically +10–75 μm) with very high mineral upgrading ratios (typically 20 to 1). Artificial samples composed of pure and fine minerals such as scheelite, wolframite, cassiterite, fluorite and calcite were prepared to test the recovery rate of fine tungsten minerals by the two enhanced gravity concentrators. Most of the minerals in the sample are distributed at the -74 μm level, and the ultrafine level (-19 μm) accounts for more than 30%. The results show that these two concentrators can achieve tungsten recovery rates of 83.15% and 76.38% respectively. However, it was also found that these separators were still ineffective in recovering ultrafine (-10 μm) wolframite particles.

3. Magnetic separation

In wolframite beneficiation, magnetic separation is usually carried out in a high-intensity magnetic separation system to obtain ideal wolframite recovery rate. In the traditional magnetic separation process, the particle size of wolframite plays an important role, similar to gravity separation. As the size of the wolframite particles decreases, the magnetic force acting on the wolframite particles rapidly decreases and becomes unable to resist hydrodynamic resistance. As a result, a small portion of the wolframite is lost as tailings. In addition, the feed stream and wash water can wash away ultrafine wolframite on the separation plate in a magnetic field. The recovery of wolframite through magnetic separation varies with different particle sizes and magnetic strengths. For particle sizes above 10 μm, the maximum recovery of wolframite can reach approximately 90% as the magnetic intensity increases to 1.3 Tesla (1.3 T). However, for wolframite particles below 10 μm, the maximum recovery is only about 60% even at magnetic strengths up to 1.5 T.

Wet high intensity magnetic separation (WHIMS) has been used as an effective enhanced method for the separation of low magnetic susceptibility minerals from tailings. The WHIMS model of tungsten tailings predicts good wolframite recovery: at a magnetic strength of 0.9 T (1.6 T), the recovery rate of new tailings is approximately 80% (90%) and the recovery rate of old tailings is approximately 65% (80%). Another study also found that WHIMS could successfully recover fine fractions of wolframite from tungsten sludge, achieving a recovery rate of 90% at a magnetic intensity of 1.15 T.