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Litharge Replacement Lead Oxide PbO (14 replies)
Teach your assayers how to be clean. Monitor the Pb in blood monthly. Bismuth has been used but without much success.
It will be very difficult to replace litharge because of its unique properties. The litharge is easy to reduce to lead metal in the form of fine droplets that can collect all the precious metals in the sample. Not many other metal oxides will act the same as litharge on a cupel. You are right good ventilation and housekeeping can make lead safe to use.
Use an assay bench that is directly connected to your dust collection system.
Agreed with all above!
Have a separate storage and flux mixing area, practice good laboratory housekeeping (separate litharge area lab coats, sticky floor mats, etc).
The classical “Lead collection” for Au and Ag has attributes including the use of large amount of collector relative to sample mass and the convenience of subsequent lead removal and not to mention, reproducibility and accuracy. One may take a cue from the PGM industry that has a more complex assay requirement with 5-7 metals of interest. A nickel sulphide based pyrometallurgical collector system is routinely used in conjunction with instrumental methods such as ICP.
Bismuth but you will not get the assay quality out of it and it’s expensive. Bismuth results in a low assay bias. I design, audit and train at several labs per year and have been doing so since 1992. Prior to that I worked in mining and commercial labs! Lead contamination is always blamed for problems when in fact it is poor ventilation that should be the focus. Stopping the use of lead only means that your personnel are no longer exposed to lead and it does not reduce their exposure to silica and other airborne chemicals. I also find that most high level lead issues that are not related to ventilation are simply poor lab practice. Most common is removal of slag from the buttons. The lead that is present in this slag is highly soluble and if the buttons are handled with bare hands or there is dust exposure on the skin blood lead levels will spike quickly.
It should also be pointed out that even if you go with Bismuth you still have to dispose of used crucibles, slag and cupels the same way you dispose of your present lead waste. Fix your ventilation. Labs and ventilation systems I design only require that personnel use respirators at their preference they do not require them avoid personnel lead contamination.
Nickel sulphide is not an option for normal gold assays. Messy and difficult to use even by the most experienced assayer. In my opinion it’s over rated for recovery and analysis of Pt group metals and could never be justified for a gold fire assay.
You have a lot of experience. People with no idea of fire assay requirements always come up with the idea to remove lead. Safe operation is possible with clean work habits and good ventilation. OR you can remove lead and then try and figure out what happened to the material balance.
Your "OR" really does sum it up and is a scenario I've dealt with a several times in the past 20 years since bismuth made its debut. Bi does work better than any of the other substitutes but at the present PM prices who can afford a random low bias.
The analysis of Gold by Fire Assay for collection in Bismuth as analysis is interesting, in some cases the results are comparable between both methods, but sometimes the results show a great dispersion, indicating that the quality of the results depends of very good controlled factors to give good results and this made doubt on the robustness of the method.
I'm completely agree with, fixing ventilation systems only require your personnel use respirators at their preference they do not require them avoid lead contamination personnel. The attached link is Patent US5279644 1994
The whole idea of assaying for Au is a "chasing" technique. One compound chases the next depending on its properties. Then eliminate the chaser to end up with that beautiful little gold bead that spells and smells money.
I think the question in your mind is the issue of safety and health in the work environment. As stated by the others above, meticulous work habits once instilled in the operators can provide safe environments. Initial costs of these set ups can be capital intensive, but with the price of gold at this time, easily mitigated. General upkeep will maintain safety and promote a healthy environment.
You can also use AA if you have the equipment for Au Ag analysis but you have to "polish" your methodology because this method has some variation with respect fire assay.
Atomic absorption has its place. This is the final stage of analysis. The first being collection and separation. Generally speaking when using AA, it is associated with an aqua regia digestion and solvent extraction.
This technique is used extensively in geochemical analysis; however there are cases where labs are set up for rapid turnaround in fire assay geochemistry Au. I believe that the chemist makes the choice of technique based on level of accuracy and precision as well. This does not withstand the sample treatment/preparation and aliquot stage of the analysis of Au. A very fundamental step in the entire analysis! Once again because of the nature of Au one has to take all the above into account. I have faced years and years of this "elusive" metal and a challenge it certainly has been.
Agree with all the above. One more thing is to ensure that you do not use the weighing materials on any other tests to avoid contaminating the flux. And thus translating into GLP and housekeeping.
Anyone knows another way to do the fire assay for the determination of Au and Ag, replacement on the use of lead oxide. Another element that can be used to prevent lead contamination!