Hi Lou. Thanks for input.
I'm particularly interested in the specifics for this section of Hoke's book, page 205:
In this new system, in the words of the authors, "Precipitation with
ammonium chloride, fusion with pyrosulfate and extraction of metallic
residues with acids are avoided entirely. The separation of platinum
from palladium, rhodium and iridium is accomplished by controlled
hydrolytic precipitation. When a boiling solution containing these four
metals as chlorides, and in addition sodium bromate, is neutralized to
approximately pH 7, the hydrated dioxides of palladium, rhodium, and
iridium precipitate quantitatively, leaving platinum in solution. A second
precipitation of the dioxides suffices to effect complete removal of platinum.
. . Palladium is separated from iridium and rhodium, in chloride
solution, by precipitation with dimethyl glyoxime. . . Rhodium is
separated from iridium by reducing it to metal with titanous chloride in
a boiling solution of the sulfates in diluted sulfuric acid. The metallic
rhodium is dissolved in hot sulfuric acid and precipitated a second time,
to remove iridium completely.
"When this new procedure is applied to the separation of all six of
the platinum metals from one another, osmium is the first metal to be
isolated. This is accomplished by distilling its volatile tetroxide from
a nitric acid solution. Ruthenium is next isolated by distilling its tetroxide
from a solution of the sulfates in diluted sulfuric acid to which sodium
bromate is added. A very suitable reagent for the absorption of osmium
tetroxide, and also of ruthenium tetroxide, is 6N hydrochloric acid
saturated with sulfur dioxide. . .
"In the recovery and determination of each of the six metals, the new
features of the procedure consist in the precipitation of osmium, of
ruthenium, and of iridium, as hydrated oxides, with final ignition to
metal. Rhodium, and also platinum, are recovered as sulfides, and
ignited to metal. Palladium is recovered as the glyoxime compound, in
which form it may be weighed, or it may be determined as metal after
ignition of the glyoxime precipitate. . . The procedure is designed for
the analysis of the platinum group, in the absence of other metals."
I believe that all published papers are deemed public material, and hence not protected by copyright.
Here ìs a more recent paper on solvent extraction of gold and the platinum group to high purity employed by Johnson Matthey, but the techniques seem more suitable for a large shop with a continuous flow of material to be refined, and I believe Wichers and Gilchrist are more suitable to the assay and small shop that works with one-off batches.
Cheers.
