EDITOR: | May 20th, 2014 | 10 Comments

Separation of Rare Earths – Art vs. Science (Part II)

| May 20, 2014 | 10 Comments
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Steve MackowskiIn my last article I was anxiously awaiting my first site visit to a fully-fledged Chinese REO separation plant. Since my previous extensive experience with uranium separation solvent extraction plants and my exposure to REO processing at Mary Kathleen, I was very keen to see how technology had advanced, process design improved, control systems enhanced, particularly on separation circuits producing multiple product streams, exceptional quality, with modern plants. These first visits were to the JAMR and ZAMR plants that became part of Neo Materials and now Molycorp. What did I see? Well to be quite truthful – nothing. Yes, there was the expected 10’s and 100’s of stages of solvent extraction mixer settlers formed into banks of primary extraction and stripping, similar progressive systems for the less dominant REOs, very manual feed preparation and product finishing and handling , but where was the control system with it’s new age instrumentation supported by thorough process logic, detailed observation and monitoring? Where was it? I recall discussing this with Dudley Kingsnorth (also on the visit). The question was how can something (REO separation) that is stated as being so difficult to do, appear to be so easy? The process just ran! There were no control instruments. There were no variable speed drives. There was no readily apparent method of checking for phase continuity, no apparent ability to adjust phase ratios. The only process measurement I could see was a packet of litmus papers (used to measure pH), and from the readings chalked on a blackboard every hour there was not a great deal of variation occurring. I was gob-smacked! I was deflated! I had come here to learn but could see nothing to learn from. How can this separation that I have been told is so difficult, be so easy? So easy that it does not need the degree of control that I would have expected.

Standing in one of the world’s leading separation plants I had a Confucian moment! I had come here looking to take away answers! I had not come here armed with the right questions! So, I have spent the last few years working out the questions and hopefully developing the answers. I have also spent a lot of time developing friendships. Back in the mid-2000’s I was seen as a stranger, almost certainly a competitor, a little arrogant and certainly quite ignorant. Why should the Chinese REO separation gurus give up their secrets? I was determined to do whatever was necessary to not be seen as a stranger, to become a colleague in REO, to learn humility and to be open to learning. I now have many friends and colleagues in REO separation and we collaborate. I will share with you our philosophy and thoughts, but not just yet. First, you need to understand what the current term “separation” that is banded about in the investment literature is not.

Scientifically speaking, separation is just that. Separating one from another. In the REO scenario, again scientifically speaking it is the taking of a liquor based solution of a mixture of REO and impurities, and getting the various elements or compounds separate. Just imagine a cup of coffee. You want to treat this mixture to get the coffee back, the water back, the sugar and the milk (or cream!), all in nice clean separate piles. In REO, the process used is solvent extraction where a specialized and very specific organic compound (in liquid form) is used to target the elements of interest. However in the REO industry there are a number of solvent extraction steps that are not included in the accepted term REO “separation”. For example one, in the processing of REO in Niobium/Zirconium hosted ores, after baking and water leaching, a sulphuric acid based liquor is formed that contains the dissolved REE, Nb, Zr, co-extracted aluminium and many other impurities. The Nb/Zr is separated from the REE and impurities by solvent extraction, then the REE is separated from the impurities  by solvent extraction. These solvent extraction stages are not part of the current term “separation” as they are part of the extraction circuit. For example two, in the processing of REO in conventional uranium circuits, a solvent extraction stage is used on the liquor tailings from the uranium circuit. Again, this is not part of the current term “separation”, as it is also part of the extraction circuit. And again, for example three, in the processing of REO from phosphate based fertilizer circuits, solvent extraction is used to concentrate the REO away from carried through phosphate. Again, an extraction circuit function. So what is the current term “separation”?

In almost every case I can think of, the final product from the REO extraction circuit is an REO compound in solid form. It is either a rare earth carbonate, oxalate or oxide and is a mixture of all of the individual rare earths that were present in the ore, and very importantly plus some impurities. There used to be a market for concentrated liquids but I am not aware of this practice any more. I have heard Jack Lifton reference the term here as PLS. This is an incorrect term here. PLS is pregnant leach solution and in reference to the current term “separation” is the liquor after the solid REO compound has been re-dissolved. So for overall coverage, the solid rare earths mixed carbonate or oxide is the feed to the separation plant. This is not to be confused with mineral concentrates, these are the feed to the extraction stage prior to the separation stage. So mining, mineral processing to produce a mineral concentrate, extraction to produce a mixed rare earths carbonate or oxide, then separation. Just as “oils aint oils”! Separation is not just separation. A separation circuit for LREO is different to a MREO circuit and is different to a HREO circuit. The circuit that you design (or visit) has been specifically built based on the spectrum of REO in the feed, the range of impurities in that feed, the products that are desired to be produced and very importantly the quality of each product to be produced.

When I first got seriously involved in the REO space, I looked at research done on the value adding chain of REO and the companies involved. Obviously China was pre-dominant in the early part of the value add chain. I was amazed at the vast number of quite small operators there was. There were many producers of neodymium for example, each producing a few tonnes, sold to the next in line and onto the final end user. The point that I finally realized here was that the reason the supply chain looked so wide and dis-jointed was because it needed to be, because each end user had a different quality specification. So what this means to a separation plant is that you don’t simply have a market for cerium oxide, for example. There are many products called cerium oxide, and they are all different. Different depending on where the product is going and what it is used for. Different quality. Different impurities. Maybe different size distribution. Wait for it – certainly different packaging. If we follow the cerium oxide example, if it is used for glass polishing, or as part of a catalyst recipe, or as an additive to automotive glass (Lexus), it will have a different specification. Where am I going with? Well, as I try to take you on the separation journey, you need to understand that the design and operation of a separation plant is as much about where the products are going, as to where the feed stock came from. So there is no one design suits all, no generic design. Each design is a very specific statement about the feed material and the products to be produced and their destination. Next week, I will relate a few examples to give you some insight into what types of plants are out there and what and why there are differences.


Steve Mackowski

Editor:

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>


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Comments

  • Tim Ainsworth

    Great article Steve, many thnx. The logical extension is the ability to add value thru manufacturing to LT contract specification. A point that appears to escape most of the superficial commentary.

    May 20, 2014 - 10:11 AM

  • Jack Lifton

    Steve,

    I use the term, PLS, to mean “process leach solution,” by which I mean the solution resulting from the extraction of the elements (i.e., dissolving them or solubilizing them reactively by making an insoluble oxide, for example, into a soluble sulphate or other ionic salt or species) using any “solvent.” If it is not the term of the chemical engineer’s art used in a specific situation I apologize for any confusion I may have caused anyone.
    I think your main point, that the separation of the rare earths from each other and from other chemical elements by solvent extraction is complex and the details of which must be calibrated to the feed stock, is well taken. I have been trying to say for many years that the oversimplification of these processes by junior miners led to their being unprepared for the time, effort, and cost required to build and operate downstream processing.
    I look forward to your continuing saga of the true nature of SX as it is applied to the separation of the rare earths.

    Jack Lifton

    May 20, 2014 - 3:54 PM

  • Steve Mackowski

    Thanks Jack. The point I was trying to make was that all REO extraction circuits produce a solid intermediate, mixed REO carbonate or others. Even if the subsequent separation process is on the same property. I will expand in my next article.

    May 20, 2014 - 6:07 PM

  • pva1

    Excellent and helpful article. Thanks!

    A good timing for me as it helped me better understand the recently completed GW’s DFS hydro-metallurgy process which will produce solid LRE and HRE carbonates to be shipped to toll separation facility.

    Re: The circuit that you design (or visit) has been specifically built based on the spectrum of REO in the feed, the range of impurities in that feed, the products that are desired to be produced and very importantly the quality of each product to be produced.

    According to GW’s DFS, the bulk of the separated REOs produced by the toll separation facility will be
    used internally at LCM. That means GW has a clear path to work with the toll separation facility to design the separation process to produce the desired product of the desired quality for their own internal needs. It seems really important to me and as a big advantage as everything will be purpose-built for GW. It sounds like competitors in the similar situation would not be able to design and build the SX circuits without the MoUs and offtakes with the future customers first.

    May 20, 2014 - 9:08 PM

  • Steve Mackowski

    I have no commercial knowledge of GW and even if I did I could not answer your specific questions due to commercial-in-confidence. What I can do however is look at the logic of your question to see if it makes sense.
    It was always the GW slogan to go “Mine to Market”. There are two ways to do this. One is develop a mine and then integrate vertically to market. The other is to develop the market then move downstream to mining. These developments can evolve or be by purchase. GW purchased Less Common Metals to get the market part right. Good logic? One would think so. Good business, good cash flow I presume, poor REO supply situation however. The SmCo magnets needed samarium. Other than Frank Tusk’s new US refinery 🙂 the Sm comes from China. Solution? Develop SSK. Process the REO to get the Sm for LCM and develop a sales model for the remaining REO. Sound logic? You bet! Mine’s output matching Market’s input. The other REO will go some where. Watch GW announcements for updates. Good question. Thanks for it. I will try to provide more examples (based on logic) as I go through my weekly articles.

    May 21, 2014 - 12:34 AM

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  • oscar trincado

    steve.}muchas gracias por su informacion,
    me agradaria conocer su mail para hacer consultas
    o su skype
    el mio es
    otrin1000
    gracias
    oscar trincado
    otrin1@gmail.com
    engineer senior chile

    June 8, 2014 - 1:31 AM

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