Simplified method of determing silver, gold and platinum in ores and wastes

Dr Novikov Oleg N., Kudriavtsev  Yuri A.
 1.    Simplified method of determing silver in ores and wastes

Previously grinded piece 20,2 g of sample with silver content up to 0,5 – 60 g/t accordingly has been dissolved in mixture 10-15 ml HF and 5 ml HNO3, to this substance 5 ml H2SO4 (1:1) has been added and, finally, solution has been evaporated for SO2 steam. After that 5 ml water has been added and again evaporated until white steam. The rest has been processed by 2 530 ml H2SO4 at concentration  0,5 N, sediment has been out-filtered. Filtrate has been dissolved by H2SO4 at 0,5 N up to 50 ml solution, after what silver has been extracted by 10 ml of 0,01% ditizon in benzole solution for 1 minute. Then silver has been re-extracted by solution of 4,5 ml H2SO4 at 1,1 N and 0,5 ml Kbr at 2 N, being shaken during 1 minute. To the water phase 0,5 ml of 0,1 %  butylrodamine C and 5 ml H2SO4 at 15 N have been added consequently, after what (silver) has been extracted by 5 ml benzole during 30 seconds. After phases have been highlighted, benzole layer shall be mesured by fluorometry using light-filters with crossing extreme significance 580 nm. Failure of silver determination is less than 18%.

 2.    Simplified method of determing gold in ores and wastes

Variant A. The ore has been pounded in an iron cast pot to obtain powder from it. Then to small portion of this powder solution of pharmacy iodine tincture (iodine) has been poured to it, after what resulted liquid shall be shaken several times. After mixture is infused, striped bandwidth (filter) paper, which  absorbs liquid. After the paper is air-dried and its dip into the solution repeated several times, it shall be burned. In the case, if gold is present in quartz, after paper is burned its ash shall be colored in purple. If quartz, which is suspected to contain gold, contains also pyrites, so before testing ore by iodine quartz shall be previously annealed in the fire. 

Variant B. Method of gold determing is procedure of dissolving of ore powder by “chclorazotic acid”(aqua regia) (mixture of nitric and hydrochloric acids). If solution of gold put previously into leaching chloride solution, then nitric acid simply shall be added, after what solution has been evaporated up to the bottom in porcelain cup. The rest of evaporated substance shall be dissolved by water, after what solution of iron vitriol shall  be added to resulted substance. Gold, if contained, falls to the sediment as a brown powder. It's possible also (after eveporation of “chlorazotic acid”to the bottom) to add tin dichloride. Method results as purple colored liquid (so called “Cassius purple”), but if gold is in overall mass, then sediment of the same purple color has been arised.

3.    Simplified method of determing platinum in ores and wastes

On to platinum alloy beyond the 950th sample of purity "potassium iodide" reagent doesn't act. While testing platinum alloy on the assay stone by mentioned reagent (KJ with N 1,0; 7,5 ml HCl; 2,5 ml HNO3) assay stone has been heated up to 70-80 oC on electric hot plate or gas burner through asbestos grate. Then on to stripe, discovered on assay stone by alloy, a few drops of "potassium iodide" has been applied by glass rod for drops interconnection. "Chlorazotic acid", contained in reagent, dissolves platinum on the stripe, reflected on assay stone, with platinum-hydrochloric acid (H2PtCl6 ) as sediment, that creates yellow colored potassium chlorineplatinate (K2PtCl3) in reaction with potassium ions, which is practically unsoluble at high concentrations of potassium ions. If alloy contains iridium, colored spots with brown shade have been created. Colored spots have been caused by on the way precipetated potassium chlorineiridate (K2IrCl6) of black color, what changes color of potassium chlorineplatinate. If platinum alloy contains rhodium, "dirty" green spots have been built up on stripes (due to arise of hydrate of rhodium dioxide). It's recommended to escape overheating of assay stone to avoid change of spot's color. The most intensively colored spots have been formed on the well dried strips. Specialists have to remember: it isn't advised to delete reagent with filter paper (to avoid change of spot's color). Accordingly, adding potassium reagent as a salt to platinum solution, if available, results with yellow precipetate. With iridium reaction results as a black precipetate. With rhodium – as a green sediment.

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