My first failed process in attempting to recover values from such materials was the furnace. I managed to fill the neighborhood with heavy SO2 fumes, and achieved no results. The concept of burning up sulfides equates to the liberation of considerable sulfur dioxide. The volume from a few grams sample may not be much, but when you heat huge volumes, that quickly changes.
For the record, I grew up in a smelter town----Midvale, Utah. They closed the doors on the smelter in 1958. It was very common to breath air heavily contaminated with SO2, in spite of the more than 400' tall stack that was a part of the smelter. This was long before the days of EPA and emissions being controlled.
I have mentioned in other posts that in many cases, you must abandon assay procedures in order to achieve success. They often do not scale up well, as was the case with the material I processed. I'm not arguing that it doesn't work, I'm simply suggesting that while it works well for small samples, when it is scaled up, it generally becomes unworkable and cost prohibitive. Crucible life, for one, is cut drastically short when fluxes are introduced. Unless the material involved is high in values, costs of the process would easily overrun the value of the material.
I think the point that should be remembered is that an assay is not intended to be a recovery process for the sake of recovery, but to prove content of any given lot of materials. The value of the recovered material is generally not enough to pay for the process------so it makes sense that the same procedures, unless performed on exceedingly high values, would not be cost effective, in spite of the fact that they may work well. Readers should keep that in mind before attempting to process by furnace.
Harold