METSO Barmac B-Series VSI Crushers Metallic minerals

Barmac VSI: Economical, High Tonnage Fine Reduction for Mining Applications

The Barmac VSI, with its high capacity and ability to produce finely graded products such as mill feed, sinter feed or material for heap leach operations, is an ideal machine to replace high cost, inefficient crushing and milling equipment.

The addition of a Barmac VSI to an existing crushing circuit can save considerable capital funds when increased production is required from an existing milling circuit.

Critical size control

A Barmac VSI can improve the productivity of an autogenous and semi-autogenous circuit which requires reduction of critical size generated in the mill.

The Barmac VSIs unique autogenous crushing and grinding action has been successful in reducing critical size pebbles from the mill, either as the critical size crusher itself or by relieving the existing critical size crusher.

Advantages of using the Barmac VSI include gaining increases in capacity, low cost modifications, ease of maintenance, reduced power consumption, peak load control and maximised operational efficiency.

Critical size control in SAG & AG milling circuits

A problem associated with autogenous and semi-autogenous grinding is the production of critical size material. These are the particles that are too small to efficiently grind other particles, but too large to be ground themselves.

Critical size particles tend to accumulate in the mill, which reduces capacity and increases the required specific power draw causing mill capacity increases in the order of 12% to 25%. They have to be removed and crushed separately by traditional crushing equipment.

The critical size particles for each milling circuit are different, depending on the viscosity of the pulp, configuration of the plant, seasonal variations and a whole host of raw feed and plant considerations.

The best method of determining the critical size particles is to pilot scale laboratory tests or testing in an existing mill. The means of identifying critical sized particles is to compare particle size fraction/s that shows least change in the amount of material before and after test.

For best mill performance, this material should be taken out of the circulating load and processed by communition means. For optimal performance, however, the crushed recirculating critical sized material should be crushed as finely as possible. This results in even less mill work required and finer mill product.

Barmac VSI as a means of treating critical sized material

The Barmac VSI rock-on-rock crushing action uses attrition and abrasion crushing mechanisms as well as cleavage and shatter to crush material. The attrition and abrasion crushing mechanisms of the crushing action produce micro fines and fines in the crusher product.

The ability of the Barmac VSI to produce product with a high proportion of fine material improves milling circuit performance by reducing energy requirement.

This is achieved by allowing the mill to do less work due to the addition of extra fines in the feed. This also leads to an increase plant capacity. Furthermore, the improved shape of the mill feed can produce increased grinding media and wear plate life.

The Barmac VSI performs best in this application when operating in a closed circuit. The critical sized material is screened and then reports to the Barmac VSI. The crusher product is then sent back to the screen, with the non-critical particle sizes re-circulated back to the mill.

Pregrinding

Pregrinding with a Barmac VSI =
Increased Mill Capacity + Reduced Mill Power Draw

The unique crushing action of the Barmac VSI makes it ideally suited to the role of pregrinding or oversize reduction in any mill circuit.

Depending on the present system, mill capacity can be increased by up to 25% and specific power savings of around 15% can readily be achieved, often without the need to replace any other equipment.

The Barmac VSI utilises a high energy rock-on-rock crushing action that produces a crushed product high in fines and protects the machine from rock-on-metal wear.

Designed to achieve low operating costs and high availability, the Barmac VSI will readily fit into any processing environment.

Replacement of fine crushing equipment

The Barmac VSI is a crushing machine which combines impact crushing, high intensity grinding, and inter-particle pulverising. It is best suited in the last crushing stage or as the first stage of the milling process.

Over the last few years there has been an increasing trend towards reducing the number of downstream communition machines. The traditional technology utilised in mining has not changed much in the past 25 years or so. To improve mining circuits new practices and machines must be adopted.

Since the development and use of rock-on-rock crushers in mining circuits, the one area where it has outperformed traditional crushing equipment is in fine crushing duties.

There are various crushers in the industry which perform fine crushing duties, however in many of these applications operators experience difficulties due to the crushing technique employed.

Problems associated with other types of crushers and mills do not occur with the Barmac VSI. Problems with wet and sticky feeds, high wear costs, generation to little fine and ultra fine material, capacity problems, ‘caking’ and the shape of crusher product can all be mitigated by installing a Barmac VSI.

Heap leaching

The Barmac VSI crushing mechanism exploits natural flaws within the ore. The Barmac VSI is utilised to expose the target mineral for more efficient liberation.

Some ore bodies will not withstand the cost of milling down to micron sizes, or the ore may be disseminated in such a way that its unnecessary to reduce it to very fine sizes for satisfactory recovery.

To obtain optimum results from the leaching process the ore must be carefully reduced to a particle size that ensures the maximum liberation of target mineral/s. An example of this technique is leaching.

Reduction of the grain size allows more rapid dissolution of the target mineral/s. Cost aspects of fine crushing and/or grinding must be weighed up against the extra recovery that may be expected. Also, consumption of the reagent due to finer gangue particles is higher.