Question

This is from the chapter principles of metallurgy

what processes are used to extract low reactivity silver, platinum and gold?
please explain the processes briefly.

Answer 1

SILVER: Silver is extracted from the ore-argentite (Ag2SAg2S). The process of extraction of silver is called as cyanide process as sodium cyanide solution is used. The ore is crushed, concentrated and then treated with sodium cyanide solution. This reaction forms sodium argento cyanide Na[Ag(CN)2]Na[Ag(CN)2].
AgS+4NaCN⇌2Na[Ag(CN)2]+Na2SAgS+4NaCN⇌2Na[Ag(CN)2]+Na2S
The solution of sodium argento cyanide combines with zinc dust and forms sodium tetra cyanozicate and precipitated silver. This precipitated silver is called spongy silver.

Zn+2Na[Ag(CN)2]→Na2[Zn(CN)4]+2AgZn+2Na[Ag(CN)2]→Na2[Zn(CN)4]+2Ag
The spongy silver is fused with potassium nitrate to obtain pure silver. Then the silver obtained is purified by electrolytic process.

GOLD:Gold extraction or recovery from its ores may require a combination of comminution, mineral processing,hydrometallurgical, and pyrometallurgical processes to be performed on the ore.[1]

Gold mining from alluvium ores was once achieved by techniques associated with placer mining such as simple gold panning and sluicing, resulting in direct recovery of small gold nuggets and flakes. Placer mining techniques since the mid to late 20th century have generally only been the practice of artisan miners. Hydraulic mining was used widely in the Californian gold rush, and involved breaking down alluvial deposits with high-pressure jets of water. Hard rock ores have formed the basis of the majority of commercial gold recovery operations since the middle of the 20th century where open pit and or sub-surface mining techniques are used.

Once the ore is mined it can be treated as a whole ore using a dump leaching or heap leaching processes. This is typical of low-grade, oxide deposits. Normally, the ore is crushed and agglomerated prior to heap leaching. High grade ores and ores resistant to cyanide leaching at coarse particle sizes, require further processing in order to recover the gold values. The processing techniques can include grinding, concentration, roasting, and pressure oxidation prior to cyanidation.

PLATINUM:Platinum is an incredibly rare metal that is mined and extracted in a variety of different ways depending on the technological sophistication of the miners attempting to extract it. It is incredibly difficult to find in large pure quantities, so it needs to be extracted from the ore in a very specific way. Platinum ore can be obtained through controlled explosions or by advanced mining techniques. Once it has been mined, the platinum is extracted from the ore in the same way.

The platinum ore is not pure, so it is first crushed. This produces many tiny particles that can be treated. Air particles then bubble through an aeration tank and adhere to the platinum particles. This brings the platinum particles, with the air particles, up to the top of the tank. The layer of particles that ultimately forms can be skimmed off and refined into platinum.