Pilot scale electric pulse processing of tin ore.
Keywords: Energy Efficiency, comminution, European resources, Tin
This article published in Minerals Engineering as part of the FAME project, compareselectric pulse fragmentation (EPF) and traditional crushing of a tin (Sn) ore – In this case a cassiterite bearing schist. Cassiterite is brittle, risking potential overgrinding and losses of tin in later stages of mineral processing, so alternative methods of processing that can potentially reduce overgrinding and losses of Sn to fines are attractive.
Our previous post on W processing contains the background to the FAME project. This article is a companion article to the first, focussing on tin (Sn) ore. This article is also the first published study using a Selfrag fully continuous electric pulse fragmentation system – the Scoria (Figure 5).
Method
Two tests were conducted using the Scoria EPF system:
1) processing at 6.5kWh/t to weaken and/or concentrate the Sn. In this test, material was passed once through the process zone, then collected.
2) Repeated processing at 6.5kWh/t to reduce material to below 5mm. In this test, material was passed through the process zone then sieved at 5 mm after exiting the system. Oversize was returned to the process zone with fresh feed and this repeated twice, then all material recombined, with an estimated total energy input of ~12.5kWh/t.
Weakening assessment
Bond rod mill (BRM) and Bond Ball Mill (BBM) tests – these are small scale tests designed to simulate the conditions within a full-size rod mill or ball mill. The EPF treated sample was milled in both systems and compared to conventionally crushed material.
Concentration
Concentration tests were performed on a Mozely laboratory separator, a large table which rocks back and forth. The sample is added at one end under a flow of water. The water transports the light particles further than the heavy, in the same way a gold pan works, and the heavy minerals get concentrated at the start of the table.
Results and Discussion
Size reduction
A comparison of mechanical crushing showed that conventional crushing both produced an overall coarser product (Figure 8), but also one higher in fines than EPF (Figure 9). The combination of coarse size reduction combined with reduced ability to crush at lower size ranged has been observed before[1] and suggests EPF has utility in comminution and liberation without excessive size reduction or production of fines.
Weakening
While the rod mill tests showed that EPF treated materials required less energy to grind, the ball mill showed an increase in abrasivity. This phenomenon has been observed before (SELFRAG, pers. comm 2016) and is likely due to the separation of the rock into discrete, single minerals such as quartz, which are more resistant to milling. Complementary mineral liberation analysis should be used to indicate the % of monomineralic/already liberated particles that make up the feed for this test. In any processing environment, resistant gangue such as quartz should be rejected before entering the mill.
Concentration
Mozley table tests showed that while EPF treatment can lead to a higher-grade concentrate, there is no conclusive evidence that it can improve overall Sn recovery – mineral liberation analysis is required to support this.
Conclusions
EPF has been shown to weaken ores improve concentrate grade in some circumstances. In these small pilot tests, overall recovery of Sn was unaffected and total energy consumption of each process was not calculated. EPF process conditions were based on laboratory scale tests and were not optimised for fully continuous processing. Ideally any EPF/Liberation treatment stage should be coupled with a sorting stage directly afterwards to reject gangue and improve downstream processes.
Summary
+ Schist showed weakening in rod mill tests.
+ Potential to increase Sn grade of concentrate.
- No overall improvement recovery of Sn.
- Increase in abrasivity in ball mill tests
Testwork shows potential for weakening and concentration of Sn, but benefits are inconclusive in this study. The increase in abrasivity likely linked to presence of liberated quartz gangue visibly observed in EPF product, reinforcing that any EPF treatment stage should be followed by a gangue removal/separation stage to maximise EPF’s effect. Knowing mineral liberation at each stage is key to optimising a processing plant and highlights the importance of strong geometallurgical knowledge in modern processing.
[1] Bru, K., Touzé, S., Auger, P., Dobrusky, S., Tierrie, J., Parvaz, D.B., 2018. Investigation of lab and pilot scale electric-pulse fragmentation systems for the recycling of ultra-high performance fibre-reinforced concrete. Miner. Eng. 128, 187–194. https://doi.org/10.1016/j.mineng.2018.08.040