Since the 20th century, gold has been principally extracted in a cyanide process by leaching the ore with cyanide solution.
Cyanide-based processing is widely used by modern gold mining operations to extract gold from very low-grade ores because cyanide (applied in moderate concentrations as 'free' or uncomplexed sodium or potassium cyanide) forms a very strong aqueous complex with gold.
A process called “Cyanidation”, or cyanide leaching, has been the dominant gold extraction technology since the 1970s. In this process sodium cyanide, in a dilute solution of ranging from 100 ppm to 500 ppm or 0.01% to 0.05% cyanide, is used to selectively dissolve gold from ore.
Various methods are Leaching , amalgamation, Froth Floatation, . Leaching method is most commonly used. Electrolytic refining is used to purify gold.
The chemistry of gold extraction from alkaline cyanide solution by solvating extractants, particularly TBP and DBBP, is described. Undiluted TBP is an effective extractant for gold at high ionic strengths, whereas undiluted DBBP needs little ionic strength adjustment in order to extract gold.
But, the most efficient method for gold extraction is froth flotation. Along with mechanized mining, froth flotation allowed the best recovery of gold from much lower grade ore than before – making it perhaps the most important mining industry innovation of the 20th century.
The most useful and important vehicle for dissolving gold is aqua regia, (royal water), composed of two parts of hydrochloric (muriatic) acid, and one part of nitric (aquafortis).
Traditionally, once gold ore is mined from the ground, it's crushed to a powder and passed through a series of tanks in a process called leaching. Cyanide is then used to separate the gold from the ore into the leached solution.
In another container, mix two parts hydrochloric acid and one part weak hydrogen peroxide (a concentration of three per cent). Pour this mixture over the circuit boards so they are completely submerged. Wait for a week, giving the vessel a stir every day with a glass or plastic rod.
Most gold and silver are parted electrolytically after being recovered in the slimes left over from copper refining or as a metallic by-product of lead or zinc smelting. The bullion is cast into anodes, which are placed into an electrolytic cell and subjected to an electric current.
The solution replaces cyanide with a safe, alternative reagent known as thiosulphate. Thiosulphate dissolves the fine gold out of ores (the gold that has not recovered by gravity) at similar rates to conventional techniques.
Cyanide use in mining
Gold is one of the noble metals and as such it is not soluble in water. Cyanide, which stabilizes the gold species in solution, and an oxidant such as oxygen are required to dissolve gold. The first step in the process is to prepare the ore by crushing and grinding.
Gold, like most minerals, can be 'dissolved' in mercury to form what's called an amalgam. An amalgam is a physical mixture, a type of alloy. This is a comparatively straightforward way of separating the gold from the rock, as the rock remains untouched by the mercury.
Among all home devices, computers and televisions typically contain the most gold. Gold is also found in the circuit boards of earlier generations of cameras, radios, and media players.
Despite these challenges, the extraction of gold from electronics can be worth it for individuals looking to recover valuable metals and reduce e-waste. Additionally, gold prices are constantly increasing, making it an attractive investment for those looking to extract gold from electronics.
Bleach can permanently damage gold jewelry. It can't tell you if your gold is fake, since most gold jewelry has other metals mixed in to give it strength. For alternative testing methods, try holding a magnet to your jewelry or dropping your gold in vinegar. Pure gold won't stick to a magnet or react with vinegar.
The effect of hydrochloric acid, organic phase and metals initial concentration were examined at ambient temperature. It was found that 0.25 mol/L TBP in the presence of 2.5 mol/L hydrochloric acid can cause high extraction of gold. Meanwhile, in these conditions the extraction of other impurities is negligible.
Gold is not soluble in sulphuric acid except when nitric acid or some other oxidising agent is present. In this case it is again precipitated on dilution with water. Neither platinum nor palladium are dissolved when these are present in a silver alloy.
Pour nitric acid into the glass container over the circuit boards. Stir the mixture with the glass or metal rod until the contents become a uniform fluid. Once the gold has separated from the plates — it may take some time — strain the nitric acid from the mix using the filter. Take out the pieces that aren't melted.
A refractory ore generally contains sulphide minerals, organic carbon, or both. Sulphide minerals are impermeable minerals that occlude gold particles, making it difficult for the leach solution to form a complex with the gold.