Gold Refining

Gold Refining Process

To present the essential points of all methods of gold refining commonly practised, as well as those of historic interest,” was the author’s purpose in this volume. The fifteen chapters of which the book consists deal with the Simpler Methods of Early Days;

  • Amalgamation Process;
  • Refining with Oxidising and Chloridising Agents;Gold Refining
  • Sulphur Refining;
  • Refining with Cementation Processes, and by means of Oxygen and Air;
  • Miller’s Process and that adopted at the Melbourne Mint;
  • Parting with Nitric Acid (two chapters);
  • Recovery of Silver from Nitrate Solutions;
  • Refining by Sulphuric Acid;
  • Parting by Electrolysis;
  • Electrolytic Refining of Gold;
  • Separation of Platinum from Gold;
  • Treatment of Cyanide Precipitates;
  • Refining of Gold Slimes by Nitric and Sulphuric Acid; the Nitre Cake Method of Purifying Slimes.
  • How Metallic Minerals Affect Silver and Gold Precipitation

Gold, as it occurs in Nature, is never pure. Occasionally the amount of alloying metal is less than 1%, hut as a general rule it is greater; the commonest alloy, in fact, the invariable one, being composed of gold and silver. Sometimes traces of ….Read more

Refining Gold with Oxidizing and Chlorinating Agents

Nitre Refining

When the molten gold is obviously impure nitre is added, and as a rule its main action is to eat the pot away, for as fast as metals are oxidised they are again reduced by the carbon of the pots. Where fireclay crucibles are used the nitre does effect a small amount of oxidation, but the action is very imperfect, unless the bullion is very low grade. If the nitre is added before the retorted cakes have commenced to melt, so that each honeycombed lump of gold is penetrated by the fused salt, the action is much more perfect than when it is thrown on the molten surface of gold. In some cases where the alloy is brittle after melting, the slags from the fluxes are thickened with bone-ash or other inert substance, and are lifted off by means of a flat spiral of iron wire. This is lowered on the surface of the slag, some slag is cooled, and adheres. This is lifted out and pressed against a cold surface; the slag now forms a circular cake adhering to the spiral; this is again dipped down, raised and flattened, and the process repeated until the molten metal surface becomes ….Read more

Simple Methods of Gold Purification

The purification of such alluvial gold alloys is a simple matter. The high specific gravity of the metal allows of separation from most admixed materials by some process of elutriation, or water concentration, or, in arid regions, by dry blowing. The coarser particles are readily picked out, but the finer are usually admixed with heavy sands, consisting of crushed zircons, garnets, cassiterite, wolfram, titanite, menaccanite, and in fact, almost any heavy oxidised compound or mineral. In a few cases platinum and osmiridium also occur. The separation of the sand is effected either by fluxing it when melting the gold, or amalgamating the gold, and thereby separating it from the admixed sands. By smelting the gold freed from sand in a graphite pot with borax glass, the gold is obtained free from any metal, excepting traces, save silver. Should there be any oxides of heavy metals, such as oxide of tin, present the gold should be smelted in fireclay pots, so that these oxides may not be reduced, and the gold be contaminated with base metals.

There is no process for removing silver except in very small quantities from ordinary alluvial gold. Solvents only remove a film. If the alluvial gold be ….Read more

Merrill Crowe Process & Equipment

Here is described the essential features of the Merrill Crowe Process and its equipment/apparatus used for the Simultaneous Clarification, De-aeration and Precipitation of cyanide solutions. Limited space has prevented a full description of all of the details involved but we have pointed out the application of the various types of equipment and the advantages to be expected, and where practical have included the essential operating features.

The Merrill-Crowe Precipitation Process, embodying the Simultaneous steps of Pre-Coat Clarification, De-aeration and Precipitation for the recovery of gold and silver from cyanide solutions is now almost universally used throughout the world. It appears in the flow sheets of all new mills and in addition has been adopted by most of the older plants effecting substantial savings in labor and reagent cost, and resulting in more efficient precipitation and higher grade bullion. The description which follows indicates how these results are obtained with the several different types of equipment.

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Enquiries and requests for quotations should specify the location of property, tMerrill-Crowe_Process_Flowsheethe nature and tonnage of the material to be cyanided, the tonnage of solution to be precipitated daily, and ….Read more

Gold Ore Chlorination

Experience has shown how difficult it is to obtain information regarding laboratory-tests in connection with the gold ore chlorination process for the extraction of gold from its ores, and I therefore present the following method, somewhat in detail, for the benefit of those who may desire to pursue research work in this field.

The ore chosen was a partly-decomposed porphyry, extremely siliceous and comparatively soft, and of an average value per ton of from $25 to $26 in gold and $0.68 in silver. The chemical analysis gave: Fe203, 3.35; FeS, 1.5; MnO, 0.75; ZnC03, 4; Al203, 3.20; H20, 0.7 ; Si02 and insol., 83.50 per cent.

The ore, first crushed to pass a 5-mesh screen, was coned and quartered until a 45-lb. sample was obtained. Samples for assay and analysis, taken from this lot by means of riffles, were crushed to pass a 100-mesh screen. The original sample was divided into 10-lb. lots, of which one was crushed to pass a 10- mesh screen; another through a 12-; the third through a 20-, and the last through a 30-mesh screen.

Because of the production of an excessive quantity of fine material it was deemed inexpedient to crush finer than 30-mesh size—a decision ….Read more

Gold Bromination & Gold Chlorination= F(Silver)

When dry chlorine gas is made to act in the cold upon finely-divided gold, it converts the latter with evolution of heat into auro-auric chloride, Au2Cl4, a hard, dark-red, hygroscopic salt. Moisture splits this salt into aurous and auric chloride, Au2Cl4 = AuCl + AuCl3 ; treatment with water converts it into auric chloride and gold, 3 Au2Cl4 = 4 AuCl3 + Au2. Aurous chloride, when stirred with water, undergoes a similar decomposition, 3 AuCl = AuCl3 + Au2. These decompositions of auro-auric chloride and of aurous chloride furnish the explanation for the practice of moistening an ore before it is treated by the Plattner chlorination-process; practical experience having shown that gaseous chlorine gave an unsatisfactory extraction with dry ore.

According to Rose, fine gold is acted upon more slowly by chlorine than gold containing some base metal, e.g., copper. He also says that small quantities of silver increase the rate of solution, but adds that the coating of silver chloride formed, checks, and finally stops, further action, if the percentage of silver be increased beyond a certain undetermined amount.

Bromine acts upon finely-divided gold in a manner similar to chlorine; the auro-auric bromide, Au2Br4, however, is not hygroscopic. Upon treatment ….Read more

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