Fire assays

Like the refining of the PGMs, the analysis is compHcated by the chemical similarity of the metals. The techniques used depend on the elements present and their concentration in the sample. For some low grade samples, analysis is preceded by a concentration stage using fire assay with collection into a lead or nickel sulfide button. The individual metals can then be determined. 

Nitric acid dissolves silver at all concentrations. This is the principal chemical reaction for the dissolution of silver into the soluble nitrate, which is the chemical intermediate for the production of electroplated ware, catalysts, battery plates, pharmaceuticals, mirrors, and silver haUdes for photographic materials. Nitric acid removes silver from the residual pellet in the gold fire assay. 

The fire assay, the antecedents of which date to ancient Egypt, remains the most rehable method for the accurate quantitative determination of precious metals ia any mixture for concentrations from 5 ppm to 100%. A sample is folded iato silver-free lead foil cones, which are placed ia bone-ash cupels (cups) and heated to between 1000 and 1200°C to oxidize the noimoble metals. The oxides are then absorbed iato a bone-ash cupel (ca 99%) and a shiny, uniformly metaUic-colored bead remains. The bead is bmshed clean, roUed fiat, and treated with CP grade nitric acid to dissolve the silver. The presence of trace metals ia that solution is then determined by iastmmental techniques and the purity of the silver determined by difference. 

The tin content of ores, concentrates, ingot metal, and other products is determined by fire assay, fusion method, and volumetric wet analysis. 

In a fire-assay method used at the smelters, a weighed quantity of concentrate is mixed with sodium cyanide in a clay or porcelain cmcible and heated in a muffle furnace at red heat for 20—25 min. The tin oxide is reduced to metal, which is cleaned and weighed. Preliminary digestion of the concentrate with hydrochloric and nitric acids to remove impurities normally precedes the sodium cyanide fusion. 

PIROMETALLURGICAL PROCESSES OF FIRE ASSAY PRECONCENTRATION OF NOBLE METALS UNDER AN OPERATION OF ULTRASONIC... 

Our researches of a method fire assay (FA) of ores have shown that the losses of noble metals (NM) in scoria s FA hardly depend on composition of used fusion mixture. Usage of ultrasonic (US) oscillations of low frequency allows lowering on 50-100° temperature FA, to reduce time in 3-4 times. Even under unfavorable conditions thus the extent of extraction NM is conserved at FA on NiS (Ni S ) or Sn and is augmented at usage as a collector Pb or Cu. 

Brenn-. burning, of combustion, calorific distilling (Optica, etc.) focal, -achse, /. (Opt.) focal axis, -apparat, m. distilling apparatus, still branding machine, -arbeit, /. fire assaying, -atzverfahren, n. pyrography. 

Torres, Marcos Martinon- and Thilo Rehren. Alchemy, chemistry or metallurgy all of them, fire assay in Renaissance Europe. Der Anschnitt. 

Analytical Methods Whole rock and LA-ICPMS analyses were carried our at Universite du Quebec a Chicoutimi (UQAC). Sulfur was determined by combustion and IR analysis. Ni and Cu were determined by atomic absorption spectrophotometry after aqua regia digestion. Gold and PGE were determined by Ni-sulfide fire assay followed by Te co-precipitation followed by ICPMS. 

Whole rock Cr, Al, Mg, Fe, Co, Ni, Mn, V, Zn, and Sc of chromitites were determined by INAA whole rock Ti and Ga were determined by XRF, and whole rock PGE were determined by Ni-sulfide fire assay followed by Te co-precipitation with ICP-MS finish. 

Rock samples collected from archived core, mine workings and outcrop were pulverized, homogenized, then analyzed using four-acid dissolution (SGS Lab, Toronto) to determine the near-total lithogeochemical composition (cassiterite, rutile, monazite, zircon, sphene, gahnite, chromite and barite are partially dissolved). Gold analyses were done by Fire Assay with Atomic Absorption finish on 30g samples and have a detection limit of 5 ppb. 

Analytical and quality control details are summarised in Arne et al (2008). Gold was determined by fire assay, and major elements by ICP-OES following a four-acid digestion, with the exception of fresh drill core samples from Wildwood, which were analysed by lithium borate fusion and XRF. Trace elements were determined by ICP-MS. Refractory elements (W, Zr, Ba and Ti) were analysed by pressed powder XRF. 

All the samples should be analyzed for 40 elements (by ICP-MS) as well as gold (Fire assay) and the results should be cross checked by several methods. 

The French chemist Jean Hellot noticed that the tin smelters in Cornwall added natural bismuth, instead of the ingredients recommended m die pharmacopoeias, to make the tin haid and brilliant, and in 1737 he obtained bv fire assay of a cobalt-bismuth ore a button of the latter metal... 

Martindn-Torres, Marcos, and Thilo Rehren. "Alchemy, Chemistry and Metallurgy in Renaissance Europe A Wider Context for Fire-Assay Remains." Historical Metallurgy 39, no. 1 (2005) 14-28. 

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