Black sands assaying

Gold Refining Forum

Help Support Gold Refining Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

thesilverfox111

Active member
Joined
Nov 14, 2011
Messages
39
What is the best, most accurate method to assay the precious metals in black sands?

I super concentrate my sluice cons with a clean up sluice, then run the black sands on a miller table to get the very fine visible gold out down to -300 mesh.

My neighbors at their placer mine have had their black sands assayed and told me there is also platinum in our black sands in the area I am mining so I would like to also have samples of my black sands assayed.
 
Fire Assay is the best method. Do not send the sample to a small lab that will use atomic absorption (AA) for the Pt. It is amazing to me how many AA analysts still mistake Fe for Pt.
 
If I remember right, the AA is very insensitive when analyzing Pt. Takes a fairy strong solution to get decent readings.

That is correct. To get an idea of the difference, I prefer to run the following standards for the following metals;

Gold standards, 7.5, 15, 30 PPM
Palladium standards, 2.5, 5, 10 PPM
Platinum standards, 37.5, 75, 150 PPM

The reason I like these standards is they make for easy dilutions when preparing standards. But the Platinum does require higher concentrations to get to a good sensitivity on a standard curve, and in black sands, they may not be there.
 
We used to run acetylene and nitrous for the Pd and for Re analysis...

loss of sensitivity, but results were better.
 
I used acetylene/nitrous (good ol' laughing gas) for the Pt, if I recall, and air/acetylene for Au, Ag, and Pd. I'm probably nuts, but I prefer the old AA's, where all the adjustments were all manual and the absorbance/emission readout was on a meter. Easy to peak. The readouts on the standards were then plotted on log graph paper. I felt I was more in control than I was with the new, more automatic, digital ones. The first time I ran a digital AA, I felt as though I had lost an old friend. In about every place I worked in my first 20 years, I used an AA several times each day. I used it mainly for process control (like checking to see if all the gold had been zinced out of a cyanide solution) and rarely for buying or selling. I just didn't trust the AA enough for buying, even though I used techniques like the "method of additions" and MIBK solvent extraction. The trick was to make the matrix of the standards like that of the sample, but that wasn't that simple. I still remember the main gold line - 242.8. I experimented with membranes for a couple of years and the AA was great for seeing what the metal concentrations were in the various cells, after running current through them for a recorded amount of time.

Were I to have another refinery, I would look for an old used manual Varian, Tektron, or PE 303, with plenty of lamps.I still believe if you have a refinery, you MUST have an AA, preferably one with a furnace.
 
I got rid of my last 55 gal drum of MIBK in 1989. Never learned to like it - the smell.

If you own a refinery you need an ICP, they are very cheap (used) and fairly inexpensive to run.
 
I just bought my first AA. It took me months to get to grips with what I REALLY needed. When I finally realised that what I needed I went for an older model that was classed as ultra reliable. The benefits that it offers make it as essential as 4metals and western both say.
 
anachronism said:
I just bought my first AA. It took me months to get to grips with what I REALLY needed. When I finally realised that what I needed I went for an older model that was classed as ultra reliable. The benefits that it offers make it as essential as 4metals and western both say.
I think the 2 greatest money making equipment in a refinery are #1 = fire assay and #2 = an AA. In a negotiation, the person who knows most about the true value of the scrap in question, always wins
 
The first Atomic Absorption I used was an analog Perkin elmer 103, single beam, manual peaking and back then that was all the bells & whistles!

So when I got a job in a lab running electroplating solutions and waste treatment samples I spent a good amount of time manually plotting standard curves to get a result. Back then we had a cabinet made by Perkin Elmer which allowed us to plug in and power about 10 lamps, all with their own adjustable power. That saved time because all of the lamps I would need were all warmed up which saved time in switching elements.

We had a computer in the lab too, an HP 9830. The latest and the greatest! 88 led character display and a cassette to store programs on. It was programmable in Dartmouth Basic. Since none of the engineers knew Dartmouth Basic and I did, they hid the machine in the lab and I got to use it. It had a pen plotter and I programmed it to plot my standard curves and spit out concentrations in PPM from absorbances off the standard curve. I thought life couldn't get any sweeter!

Then during a vacation shutdown, there was a fire that destroyed most of the lab. My AA was toast as was the HP. Well the newest Perkin Elmer on the market (the number of which escapes me) replaced it and it was digital with an onboard computer. The digital instruments have much greater control than the old analog instruments, you can program in parameters for maximum drift of standards and it won't just spit out data if your curve is off,it will tell you the error in your curve exceeds parameters and the result is suspect.

Sorry to say I got over manually plotting standards rather quickly!!!!
 
4metals said:
The first Atomic Absorption I used was an analog Perkin elmer 103, single beam, manual peaking and back then that was all the bells & whistles!

So when I got a job in a lab running electroplating solutions and waste treatment samples I spent a good amount of time manually plotting standard curves to get a result. Back then we had a cabinet made by Perkin Elmer which allowed us to plug in and power about 10 lamps, all with their own adjustable power. That saved time because all of the lamps I would need were all warmed up which saved time in switching elements.

We had a computer in the lab too, an HP 9830. The latest and the greatest! 88 led character display and a cassette to store programs on. It was programmable in Dartmouth Basic. Since none of the engineers knew Dartmouth Basic and I did, they hid the machine in the lab and I got to use it. It had a pen plotter and I programmed it to plot my standard curves and spit out concentrations in PPM from absorbances off the standard curve. I thought life couldn't get any sweeter!

Then during a vacation shutdown, there was a fire that destroyed most of the lab. My AA was toast as was the HP. Well the newest Perkin Elmer on the market (the number of which escapes me) replaced it and it was digital with an onboard computer. The digital instruments have much greater control than the old analog instruments, you can program in parameters for maximum drift of standards and it won't just spit out data if your curve is off,it will tell you the error in your curve exceeds parameters and the result is suspect.

Sorry to say I got over manually plotting standards rather quickly!!!!
What I hated was diluting samples for the AA with pipets and vol flasks. I got an automatic dilutor real quick. Saved hours.

I never analyzed plating solutions with an AA and in the refinery, there wasn't that much plotting. Usually I ran gold samples on the AA

Right after the Air Force, I moved from Missouri to L.A. My first job was as an analytical chemist in the Udylite customer service lab. At that time, Udy was the largest seller of base metal plating systems in the world, mainly copper, nickel, and chrome. There were 4 other chemists in the lab and we analyzed the plating solutions for free from Udy's 5000, or so, customers. Most analyses were by titration and my guess is that I averaged 50 titrations per day, by assembly line. I also did a lot of gravimetric analysis, wet ashing. hull cell testing, pilot plating, etc. Great job but not much money. My wife convinced me (she had her ways) to change jobs, which I did after about a year (and 13,000 titrations).
 
If you own a refinery you need an ICP, they are very cheap (used) and fairly inexpensive to run.

I never have seen an ICP being as functional in a refinery as an AA. Sure they are great to run a lot of elements at once but not if they are in high concentrations. I do see ICP as necessary if your product purity must be verified routinely as the ICP can measure 20 impurities at once to do a purity by difference run. Plus the carrier gas in a Dewar will off gas and need refilling whether or not you run samples.
I do believe the higher plasma temperatures does eliminate some of the interference you can experience in concentrated samples.

An AA has the disadvantage of only running 1 element at a time. But in refining it is often tasked to analyze concentrates in much greater excesses than an ICP can handle, plus if it really gets concentrated you can turn the burner head 90 degrees. Plus when you shut off the Acetylene tank, it is off and not gassing off and losing gas. Plus they are cheaper (not cheap, but cheaper) to have serviced.
Interference from concentrated samples can be dealt with (or negated slightly) with matrix matching.

For its versatility and durability if I could only have one, it would be an AA. But I am always open to other opinions.
 
4metals said:
I got rid of my last 55 gal drum of MIBK in 1989. Never learned to like it - the smell.

The smell I could never get over was Pyridine.
The worst. At Udylite, there was some sort of a pyridine brightener that we ran in its own tiny fume hood at the back of the lab. The hood had one of those tiny oval sinks inside it where we dumped the solutions after the analysis. Everything was designed so it stayed in that hood. We only had 2 or 3 customers using that brightener and, luckily, there were only a coupe of samples each month and whoever's turn it was to be in the barrel got them. It's been 50 years and I can still smell it. I remember looking pyridine up in the encyclopedia (remember those?) and it said that the smell of pyridine produced depression. No s___?
 
An ICP can be used for just about any concentration of any element, simply dilute.

As for Argon, if you run enough samples, a dewar is necessary, if you don't, use compressed argon cylinders and shut them off after use.

For a "true refinery", the need for ICP runs:

1. Impurity determination in incoming feedstock for better control of refining cells and better control of foundry operations to make sure you stay in compliance with OSHA PEL's for personnel exposure
2. Process control of refining cells, both electrolyte and Ag crystal
3. Waste water analysis for permit limit compliance
4. Trace impurity analysis on final product for ASTM, COMEX and customer specifications compliance
5. Alloy component and trace impurity analysis on finished alloy product
6. Failure analysis for finished returned product

Of course, if your feedstock is always the same you can eliminate #1 and #2. For refineries where the feedstock varies from Ag content as low as 35% and Sn as high as 10% with varying other alloy elements, almost every lot needs to be analyzed and separated for best process management.

If you are simply a melt shop, an AA is ok and you probably don't even need that.

Added to initial post - This is my opinion based on my particular experiences, others will have other experiences and opinions.

I have used both AA (TJA's 4 lamp AA) and ICP, and I stopped using AA in my lab long ago.
 
AA just doesn't have the heat to do the elements we analyze but FAAS is just fine for Au/Ag/Cu/Zn etc. Marginal for Pt and Pd w/ C2H2/N2O. Virtually worthless Re or Rh or Ta and W and a ROYAL pain if you had to analyze the chalcogenides/hydride formers. We had an 8 lamp turret so we'd have Ag/Cu/Pd/Zn/Ni as our nitrate suite when we would do all HNO3-containing sample days. Then for Au/PGMs we'd do in 3% HCl. The AA was convenient...just walk up, aspirate your sample and then you could get your readings and crunch them easily. I think for people doing cyanide work or silver cell work, an AA, a good analytical balance, 1 fume hood, and a burette and dispensette are ample.

Alas, that AA's still sitting in storage waiting for a home :/

I do enjoy being able to prep 200 different samples/dilutions (we bracket our concentrations) and let the robot do the work. Prep takes the longest amount of time, as you have to take the temperature of the room, weigh the aliquot from the pipette, enter it into the spreadsheet and program and go down the list. You select a method, let's say you wanted to know Pd--then you do a Pd method specific to the XRF trace of the impurity profile. If it's high purity Pd where matrix/impurities effects are minimal and IECs/models aren't needed, then you use a method by difference.

Of course, and what no one tells you when they sell you one, and what hasn't been mentioned here: anyone who does this for a living knows (or darn well better) that you don't go straight to ICP for settlement results--you go straight to gravimetric pre concentration THEN ICP. This means fire assay (gold or NiS collector for the PGMs), dimethylglyoxime, certain analytical resins, etc. ICP is good for house keeping solutions but it does not compare to tried and true protocols. Marry them both, like fire assay for Au, impurities by difference, silver by titration/Pd by DMG...then you have something.

Unfortunately, as my business seems to process really oddball/difficult matrices that either the big refiners won't do or can't, often times I'm spending effort and lots of time on method development where I'm figuring out which elements interfere with which others and correcting for that. In some instances, ICP-OES, even with a 150K instrument is nigh on worthless for Pt so a different technique needs picked out. Nice thing about ICP-MS for Pt is no barometric interferences; not nice thing is the stupid dilution factors which throw in absurd error bars, so you're stuck doing it on a Cahn microbalance if you want to keep RSD down. I'm a big fan of mass/mass make up for samples and standards.
 
Very true Lou about settlement results.

We don't use ICP results for settlement except Au <0.5%, Pd and Pt <~2%. Otherwise it is all gravimetric work.

Also true about the oddball work. Large refineries don't have the time or desire to deal with difficult refining work unless there is a very large amount of it. And then, it is under extended settlement times and surcharges.
 
DylanDownright84 said:
I hardly understood anything you gentlemen were talking about, but dang, was it interesting as heck to read! I need to take a tour of some refineries. :)


I used to be that way with almost every thread I read. :lol:

Mark this one and come back in a year and read it again. It can be amazing the things you pick up on just reading threads that may not even pertain to what your looking for sometimes.
 
Back
Top