Vanadium production at Vametco - an overview

Ophidian

30 December 2018

A High Level View of the Mining and Plant operations at Vametco

We can broadly speaking break the process down into the following very high level steps:

  • Prospect the whole area so we know where to dig 

  • Dig out the rocks 
  • Process the Rocks (broken down into)
    • Crush up the rocks 
    • Separate out the magnetite fraction we want
    • Chemically remove the Vanadium from the Magnatite
  • Dispose of the waste

So picking them off one by one:

Prospecting the whole Area so we know where to dig: 

Typically, there will have been Diamond drill cores cut down through the rock from the surface to about (probably) 200m down. These cores will have been dotted about all over the whole site and will have been drilled in representative areas crossing the geologies of interest that will have been initially determined by soil testing, Davies tube work and potentially smaller drill campaigns and on site geology observations. The cores are then cut into representative lengths (usually 5m or 10m) and chemically tested for their elemental content and thereby inferred geological make up. Whilst it is Vanadium we are interested in of course, the other key elements are also of interest as they tell you what the rocks are and can be critical in later decision making. For this reason they will in all probability have data for Iron, Phosphorous, Titanium, Sulphur, Aluminium, Copper, Manganese, Nickel and possibly some other idiosyncratic to local lithology. All of that chemical knowledge is then combined into a block model which is a representation of the whole of the mineable area of interest detailing the relative areas of concentrations, this looks a little like one of those wire cage 3D computer models.

Dig out the Rocks

Our mine is a large open Pit. It is being mined in “shelves”. This means it looks like a massive inverted version of a Paddy field. Basically mining down in steps. In an open cast mining operation like Vametco, with an on- site processing plant, the two operations of “Digging it out” and “Processing it” are quite separate. 

What is important, broadly speaking, is that the Plant will work best when nothing much is changing, so “Digging it out” can directly impact “Processing it”. This means:

  • The input grade is broadly similar to always

  • The particle size distribution is broadly the same as always
  • The feed rates are stable and the output volumes of concentrate are broadly similar

In short nothing much changes.

To help ensure that this is the case, before random rocks are thrown in at the front end they need to be characterised. This is where the ROM pad comes in. – ROM (Run of Mine) pad is simply a (sometimes very large) area where the rocks being dug out are embargoed prior to being fed in to the Plant. Hence “Run of Mine material.

So how do the rocks get out of the ground and onto the ROM pad? Typically, a set of holes are drilled at known spacings, explosives are dropped down the holes, the rock is blown up and then very big diggers and even bigger dumper trucks move the liberated material to a designated place on the ROM pad. Now, between the hole being drilled and the rock being blown up, a little guy collects the material that has come out of each of the drilled holes, bags them up carefully using a notation system that allows him to map a sample to a location and then delivers the bags of chippings to the lab. The lab analyses the chippings getting a complete mineralogical profile of the chippings hole by hole thereby enabling the area being dug out to be mapped and described in terms of the input head grade concentration(s) of each element of interest. When the Material is delivered to the ROM pad, the pile is effectively then of a “known” concentration in our case of Vanadium but also of the other elements that are important within the Process. Now, because the input profile that the plant knows and loves is already established, the Plant manager or someone can pick and choose how much of each pile of rocks to feed in together to “blend” the input concentrations to most closely meet the Plants operational specification.

Why you might think is this important – well this is why I think we have been having a few recent issues in Q2 and into Q3 perhaps. Remember, the Vanadium isn’t equally spread out through the rocks, it is concentrated in the Magnetite portion. Now the Magnetite portion can be maybe between 22% and 33% of the total ore body. Similarly, the Vanadium content of the Magnetite can be let’s say between 0.6% and 2.0 %. So, if on one particular day we took 1 Tonne of Ore that had a magnetite content of 25% and a Vanadium content in Magnetite of 0.75%, then we would produce 1.05Kg of Vanadium. If however we took 1 Tonne of Ore that had 33% Magnetite and a vanadium content of 2.0% then we would produce 3.73Kg of Vanadium – clearly this would be problematic in the Plant.

Crush up the Rocks

The rocks are first put through a primary crusher, this is typically either a jaw crusher or rollers – I’m not sure which they use on site but basically it just crushes the rocks down from the “Mined” size down to something more uniform – probably in the range of about up to 15cm across the longest axis. At this stage that crushed material might itself be stored for later use.

The next step, the secondary crusher takes the primary material and crushes it down even smaller typically about 3.5cm to 5cm. Finally the Tertiary crushers will grind it down to about 13mm. Between each of these crushing steps, the racks are circulated through “screens”  which are basically big sieves (see image of one of the screens at Vametco above). At each screen, the oversize material is circulated back for another go whilst the target size material passes on to the next step.

After crushing up the rock, the 13mm fraction is them milled down using wet ball milling to form a slurry with a particle size of around 150 micrometers.

Separate out the Magnetite portion

The slurry is fed over very strong magnets where the magnetic Magnetite fraction (hence the name) is pulled off by the magnets whilst the non-magnetic portion (the rest of the rock) is just passed through. The Magnetite slurry is then fed through the kiln and dried to produce a “concentrate”, the non-magnetite portion will have the water reclaimed and then sent to the waste circuit for disposal.

Chemically remove the Vanadium

The Concentrate is mixed with Sodium sulphate and sodium carbonate and Roasted (hence Salt Roast Process – SRP) to produce Sodium metavanadate (NaVO3). This is then pH adjusted with sulphuric acid (H2SO4), it is a soluble form of Vanadium salt.

Next the solution is precipitated out with Ammonium sulphate forming Ammonia metavanadate (AMV) NH4VO3 – this is a white solid. The AMV is then further heated which drives off water and Ammonia leaving behind oxides of Vanadium including our old friend V2O5. This is what Bushveld refer to as their MVO (mixed Vanadium Oxides).

View of Vametco showing the long rotary kiln in which the salt roast process is undertaken.

Dispose of the Waste

The non-magnetite fractions that went into the waste circuit will find their way onto huge waste piles which will eventually backfill the hole in the ground from which they were originally dug out. The waste chemicals will go through various reclamation cycles to remove what can be recycled. That which cant (the Calcine waste) is what we talked about before must be stored in a manner that prevents it from getting into the ground water. This has been a problem in the past for Vametco in a time before BMN and they have had environmental warnings about it – my guess is that is why BMN are on it now and investing in appropriate disposal.

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