Platinum Group/Iron Assaying

Isn't Rhodium a platinum group element?

Are you trying to find a way to determine concentrations of each? Presence of each/any? Or concentration of combined group?

You are correct- Rhodium is a PGE group element but apparently in many ores, particularly Magnetic Iron, the Rhodium binds with other PGE group metals and masks them and also causes problems is separating- I as to the other questions I am trying to start by finding if any are present, then how much of each, then how to get them out- sort of a progression of knowledge- since they do not show in fire assays nor with any Spectrography we have tried, the Mining industry as a whole says " If these methods don't show it, it aint there" and while we have been able to separate with the Nuclear process, this is both costly, needs a facility with capabilities (reactor) so is no good for exploration in the field- I am looking for a shortcut and I believe there are enough Gurus out there that are off the wall like me, and may have an answer

Just to be clear; you are describing 'magnetic' ores (so a good percent magnetite, or elemental iron, nickel...etc) and not necessarily 'magmatic' ores. I just what to make sure as it is an easy typing or reading error to make.

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I think the easy thing to use will be reactivity.

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If the ore is first reduced to a metallic state, (which can be cheaply done with a thermitic reaction;igniting mixture of fine powdered ore and aluminum or magnesium), any of a number of various dilute acids can be used to remove the non PGE metals.

Excess aluminum or magnesium will likely react with some PGE metals. I think these intermetallics are generally not affected by most dilute acids, but I am not certain about specifics, so do a little research. It might not be a bad idea to verify with an experiment first.

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I do know those intermetalics are generally more easily dissolved by aqua regia, so it may make refining what is left after (the more reactive metals are removed by dilute acids), easier.

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I also think you can get a decent idea about the possibility of PGE metals by checking density of the reduced metal....

it won't be conclusive, but after reducing to metal, a higher than otherwise expected density would be a good indicator that PGE metals are present.

An X-ray Fluorescence Spectrometer will determine what elements you have present (from sodium upwards) regardless of what chemical or physical state they are in. There is no such thing as "masking" in this technique. They are not particularly cheap, but there are various manufacturers of benchtop XRF instruments that can solve your problem. Suggest you check out Spectro, Shimadzu, Rigaku, Niton, Horiba, Bruker and others and perhaps find one within your budget. Used instruments are also available.

'...There is no such thing as "masking" in this technique....'

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There use to be significant effects that could cause inaccuracy related to surface roughness, other elements present, particle size, or variations in chemical composition, that could enhance or diminish characteristic signals.

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The effects of other element having peaks overlapping or nearly overlapping the element of interest use to present significant hurdles and could certainly might reasonably be described as 'masking'. So there certainly used to be a phenomena of artifact creation that could reasonably be described as 'masking'.....

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I don't claim to be an expert or even up on the very latest technology, so if changes have come about eliminating these problems, I would be interested in an explanation or link to such....

Much work has been done to minimize inter-element effects ["ZAF" programs to account for atomic number (Z), absorption (A), and fluorescence (Z) effects] and surface roughness. As regards peak overlaps, this has been addressed by "peak deconvolution" software for many years for energy dispersive XRF, where the energy resolution of the detector is around 140 eV (Si/Li) to 500 eV (proportional counter). Whether you want to call these effects as "masking" is more an issue of semantics. I have never heard them called as such.

For WD-XRF peak overlap is very rarely an issue since detector energy resolution is approx. 10 times better.

I am out of of touch with the newest developments also, but understand that quantitative accuracy and minimum detectable limits have all improved.

Thank you.

Your comment are valuable and while the semantics may be out of whack, ( I sometime have to search for the correct word or phrase) the term masking was used by a PhD (chemistry/Geology) friend who is far more technically savvy than I- sadly as he is getting older and while his subject knowledge is flawless he does have some delusional periods that detract from my using his knowledge- his was the term "masking" which I took to mean the Rhodium presence prevented the other elements from being detected or extracted easily. All of our experience with this situation is within the last 8 months so the Spectro and Nuclear technology is up to date according to the Bruker and Niton technologists. My problem personally is that I have been away from the Mining and Geological fields since 1973 so am trying to catch up as that past came back to haunt me last september- so please bear with my semantics and also possible jumps into uncharted waters- your comments and input is appreciated.

I note that a response I wrote must have fallen by the wayside and does not appear here-and I do not recall it totally- but here is the Gist- we have had the material tested by both Bruker and Niton spectrographs which indicated no PGE elements- the same sample was assayed using the Nuclear absorbsion and did show Gold and some PGE minerals- One Sprectro did also show Rhodium present. The samples were black Sands??? extracted from the raw ore using a magnet or shaking table (gravity,- as they were heavier) and also some black mud from Volcanic venting areas- we have obtained a material using acid extraction, both H2SO4 and Aqua Regia, but as yet due to the need for temperature and pH control not finalized a result- (my little lab is not heated and it is too cold for the lab to work (no water) here in Canada. sorry about the lost page- hope this helps your understanding, and thanks for your input

I'm curious about what your extraction yields....

it needs to hurry up and realize its not winter up there anymore.

This was on E bay

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In a real world sample, particularly a magnetic sample, The most prolific element is iron. Coincidentally, iron exhibits emission peaks at more different wavelengths across the UV-Visible-NIR spectrum than any other single element. Because of this, the sparser and weaker emission lines of elements usually found only at the trace level in ores are obscured or overlapped by the prolific Fe lines. And so, the first order of business is to separate the PGE from the Fe matrix - nickel sulfide fire assay is useful for this step. The next step would be to prepare the fire assay PGE residue for analysis. X-ray methods and arc/spark methods can be used for solids. Flame atomic absorption and plasma emission methods require a dissolved sample.

Of the instrumental methods, atomic absorption is the least expensive, but the temperature of an air/acetylene flame(~2300°C) is not adequate to fully excite the platinum group elements. At 2900°C, the nitrous oxide/acetylene flame produces adequate excitation energy, but it uses a shorter absorption path and introduces considerable signal noise which will adversely affect detection limits. Atomic absorption(AA) can be used to determine the PGE, but a better choice would be ICP/MS(Inductively Coupled Plasma/Mass Spectrometry).

Copper mines generally produce significant amounts of the platinum group elements as a byproduct of copper recovery. They use arc, spark or plasma emission to identify and quantitate the PGE.

Time for a dicyanoacetylene/oxygen flame? I've looking for a good reason for one to be required....

Speaking of cyanides, the most commonly used extraction of the PGEs on a commercial scale is alkaline cyanide extraction. The big companies will (after extensive exploration accompanied core sampling) demolish a mountain with explosives, remove all of the loose material, line the hole with clay followed by a plastic liner and install a sump in the bottom. They then crush the material which has been removed and put it back in the hole. At this point, they erect a plastic sprinkler system and pump alkaline cyanide (sodium cyanide plus sodium hydroxide) into the sprinklers. This wets the crushed ore and percolates slowly down to the sump, carrying with it the extracted PGEs. The sump is pumped into large tanks into which they dump scrap zinc which reduces the PGEs to a metallic sludge. After a time, the sludge is removed, melted and cast into bars which are sent out for refining. The spent cyanide solution is refortified and sent back to be pumped over the ore again. The process continues until the recovery percentage is too low to justify the process. Then starts reclamation.