Mackowski on Innovation and/or Revolutionary Rare Earths Technology (Part 3)
This article is Part 3 of a series of articles discussing new rare earths technologies as to whether they are innovative or revolutionary. Part 1 looked at an introduction to the definitions of innovation and revolutionary and Part 2, the technology based around discarding low value rare earth product (namely cerium) early in the flow sheet so as to reduce the scale and complexity of downstream processing, particularly separation.
The remaining two technologies to be discussed are:
- Heap leaching of rare earths ore and subsequent continuous ion exchange replacing the standard extraction and purification circuits, ie replacing sulphation/water leaching and impurity removal.
- Molecular Recognition Technology (MRT) that replaces the current operating standard for rare earths separation, ie replaces solvent extraction.
Before we can discuss the first technology in any detail or with any substance, an introduction to heap leaching and continuous ion exchange will be needed.
Heap leaching is a technology born out of the processing of low grade ores, typically, gold and copper, and more recently uranium. The driver for the development is low costs. The technology is mostly utilized on low grade ores that are not economic using more conventional technologies. The applicability of heap leaching is generally viewed as a trade-off between lower costs and lower recoveries. So a conventional plant is built and operated to manage the higher grade ore and heap leaching is used to tackle those lower grade ores. Simplistically, instead of grinding the ore and doing the hydrometallurgy in vessels, the ore needs only to be crushed, stacked and the hydrometallurgy is done on so-called leach pads.
To be successful, heap leaching requires a number of factors to align.
- The minerals need to be liberated at a coarse size or the rock is sufficiently porous to allow the leaching liquor to pass through.
- The reaction kinetics is such that local atmospheric conditions give acceptable leaching recovery at reasonable leaching times.
- The reaction chemistry is such that low reagent consumptions are needed.
- Local geography and climate must allow construction and operation of the pads.
Heap leaching, as is presented in today’s literature is different to the historic processing of the ionic clays in southern China, although there are superficial similarities. In China the ore is not made into heaps as such, but is for the most part in-situ. The reagents are distributed on the surface and the product liquors are collected “down-hill” so to speak. There is no management of the waste, un-dissolved rock. In heap leaching, the waste has to be managed. Typically, the heap is “washed” to recover all valuable liquor but also to neutralize any residual acid. Remember this rock has to be stored for all time, just as a tailings dam would need to be. In some smaller operations, the heaps are left as is, but in larger operations the leach pads are cleared of material, which is transported to long term storage, and the leach pads are rebuilt with new ore and the process re-commences. As such the proposed heap leach technology is an environmentally acceptable way to recover value.
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Comparison with other technology is difficult because each technology has been designed around different minerals. In a conventional plant, most of the CAPEX is required in the initial installation – the processing plant! In heap leaching, most of the CAPEX is sustaining capital for the continuous re-construction of new pads. This gives a key economic plus to heap leaching in that you can delay a lot of CAPEX. Using the Frontier Rare Earths (FRO) CAPEX extracted from their Preliminary Feasibility Study (PFS) detailed as Table 4 below, you can see that the Phase 1 start-up CAPEX is $906 million, all of which needs to be spent before production commences. Referencing the Texas Rare Earth Resources (TRER) PFS Section 21, where the start-up CAPEX is ~$300 million and the sustaining CAPEX over 20 years is ~$550 million. So similar total CAPEX but over a very different time line. This lower initial CAPEX could be seen as an advantage in financing during difficult times. By the way, I am not suggesting that FRO switch to heap leaching. The mineralogy is very different and therefore FRO ore is not amenable. I am just highlighting the CAPEX timing effect as a point to be aware of.
|Table 4: Zandkopsdrift Project Capital Expenditure Summary|
|PROJECT COMPONENT||PHASE 1 ($m)||PHASE 2 ($m) *||TOTAL ($m)|
|Upgrade of local district roads||11.8||–||11.8|
|Eskom bulk power||16.2||1.3||17.5|
|Desalination plant and pipe line||34.9||21.8||56.8|
|Mining equipment, surface infrastructure and pre-production||3.5||–||3.5|
|Hydrometallurgical plant (WorleyParsons)||205.2||193.2||398.4|
|Pyrometallurgical plant (Outotec)||228.9||206.1||435.0|
|Zandkopsdrift other (housing, land, capital contribution)||7.4||2.4||9.8|
|Tailings disposal facility||13.5||5.0||18.2|
|Social and labour plan contributions||0.4||–||0.4|
|Rehabilitation and closure||0.7||–||0.7|
|Total Zandkopsdrift Mine (excl. manganese sulphate plant)||522.6||429.8||952.1|
|Manganese sulphate plant (Veolia)||38.2||38.2||76.3|
|Total Zandkopsdrift Mine (incl. manganese sulphate plant)||560.8||467.9||1,028.4|
|Saldanha Separation Plant|
|Saldanha Separation Plant||237.7||176.6||414.3|
|Saldanha marine outfall pipeline, land purchase, Eskom||10.8||0.4||11.3|
|Total Saldanha Separation Plant||248.5||177.1||425.6|
|Total Zandkopsdrift Project|
|Total Zandkopsdrift Project (excl. contingency)||809.3||645.0||1,453.9|
|Total Zandkopsdrift Project (including contingency)||906.4||722.4||1,628.4|
The other issue to consider when looking at heap leaching CAPEX is the capacity. The FRO project is handling 0.5 million tonnes per year for it’s $900 mill of CAPEX, the TRER project is handling 7 million tonnes per year. TRER CAPEX through a process similar to FRO would be staggering!
So there are some pluses to heap leaching but there are potential negatives. Not the least of which is the long term management of the “used” heap materials.
Another difficult comparison is the OPEX. Because the hydrometallurgical conditions are so different, chemical comparison is meaningless. Cost per kilogram of output is really the only important metric. Does it make money? If so, good!
I need to also introduce ion exchange (IX) theory. IX can be simply seen as a particle of resin (inert) that has had a chemical impregnated into it’s surface. This chemical is special in that it is selective for particular chemical species. So when a liquor containing, rare earths for example, is passed by the resin the rare earths are held. They are later stripped by a different liquor. This technology is quite old and significantly pre-dates solvent extraction (SX). In fact, SX was developed to replace IX technology on cost benefit grounds. Remember the reagent impregnated in the resin (IX), can be the same reagent as used in SX. It is just the delivery method that is different. So in terms of today’s costs SX and IX can be seen as being reasonably comparable. What is different, however, in the TRER project is that the IX process is replacing other unit processes that are required in a more conventional rare earth plant. So the process flow sheet is a little simpler.
So is the use of heap leaching and IX innovative? Yes for TRER. Is the use of heap leaching and IX revolutionary? Well, I would say not for the rare earths industry as a whole since the technology is only applicable to very restricted ore types and local conditions. Ie Do not try to heap leach in the Artic! But it is important for TRER as their project economics would not be favorable using different technologies. But what is revolutionary at TRER and could be applicable across the rare earths space is their K Tech developed technology defined as Continuous Ion Chromatography (CIC). I say this because if successful and the economics are such, then CIC can displace the conventional SX process as a potential technology of choice for rare earths separation. To date there has been little published about CIC by TRER and so I am sorry to say that I can’t comment, even qualitatively. Jack Lifton has been associated with TRER during this development and has published comments previously. But for me, and hence you, we will all have to watch this space on whether CIC is a game-changer!
Next week brings my thoughts on MRT.
Mr Mackowski is a qualified engineer in mineral processing with over 30 years technical and operational experience in rare earths, uranium, industrial minerals, nickel, kaolin ... <Read more about Steve Mackowski>