Halogen and its compound method

The mid-19th century, people began to use chlorine leaching of gold, due to the emergence of cyanide and stop using. This process has been re-emphasized since the 1970s, and has developed high-temperature chlorination roasting and electrochlorination leaching methods. The chemical reaction of gold extraction by chlorination is: due to the high activity of chlorine, there is no problem that the surface of gold particles is passivated. Therefore, under the given conditions, the leaching speed of gold is very fast, generally only 1~2h. This method is more suitable for treating carbonaceous gold, gold-bearing ore was acid-washed, concentrates containing arsenic and the like.

The Jerrit Canyon gold selection plant of Freerport Mining Company of the United States uses air oxidation and chlorination immersion gold to treat arsenic-containing carbonaceous gold ore. The chlorination time is 18h, the pulp concentration is about 55%, and the temperature is 49-54°C. The average chlorine consumption is 17.5kg / t, gold leaching rate of 94%.

Newmont converted to a flash chlorination system in 1988, increasing the gold extraction rate by 6% and reducing chlorine consumption by 25%.

Recently, Peru and France reported a new gold salt leaching process that uses high concentrations of NaCl as an oxidant to produce elemental chlorine in solution. The latter dissolves gold quickly under the action of an aqueous solution.

The method of carbon leaching in the United States is to stir coarse-grained activated carbon with a carbon-impermeable refractory gold ore. Chlorine reacts with the slurry under acidic conditions. The gold dissolves into a gold-chloride complex and is then reduced to metal gold on the surface of the carbon particles. After the leaching is completed, the gold-loaded charcoal is sieved out of the finely ground slurry for gold recovery treatment. The method is characterized in that the pretreatment, leaching and recovery of the refractory ore are carried out in the same system. The United States has also invented a similar method, using chloride leaching, ion exchange resin gold extraction, suitable for the treatment of carbonaceous ore or mixed ore of carbonaceous ore and oxidized ore.

South Africa has commissioned a large-scale water chlorination treatment of re-election gold concentrate test plant. The concentrate is oxidized and calcined at 800 °C for desulfurization. The calcination is leached in a ventilated hydrochloric acid solution, and the gold leaching rate is as high as 99%.

The Beijing Research Institute of Mining and Metallurgy obtained a flotation gold concentrate containing 65 g/t of Au obtained from the fine-grained gold ore with high arsenic, antimony , sulfur and carbon content in Miaolong , Guizhou, after roasting to remove impurities. The calcination was leached by water chlorination, the gold leaching rate was 91.48%, and the leaching time was only 5% at the time of cyanide leaching.

The use of bromine and its compounds as gold leaching reagents is the same as chlorine, because the oxidation potential is high enough to dissolve gold when halogen is changed to halide, and the halide ion (x ^- ) is a strong ligand of Au ⁺ and Au ³⁺ from thermodynamics. In general, it is conducive to the occurrence of immersion gold reaction.

As early as 1881, Shaff published a patent for the bromine gold extraction process, but it was not until the past 10 years that due to changes in environmental protection and ore properties, it began to re-examine seriously.

Around 1990, countries such as Canada and Australia have published many articles, claiming that the bromination leaching method such as bioleaching-D method and K-method should compete with cyanide leaching method, emphasizing that these new methods have the advantage of not polluting the environment.

In the bioleaching-D method, a leaching agent called Bio-D is used, which is a leaching agent composed of sodium bromide and an oxidizing agent, which can be used to leach precious metals, and has a greater affinity for denser metals than For the less dense metal, it can be used in weakly acidic to neutral solution. The dilute solution is non-toxic, the reagent is easy to regenerate, and it has biodegradation effect. The leaching rate of most ore leaching can reach 90% at 2.5 h. However, since a considerable amount of bromine vapor escapes from the solution during the reaction, this not only increases the consumption of the reagent, but also causes serious corrosion and health problems, and is still in the laboratory and semi-industrial test stage.

The K-leaching method was invented by Kalias, Australia. It essentially uses a new process using bromide as a leaching agent. It can be immersed in gold from ore under neutral conditions, but it is still in the development stage and is industrially popularized. There are still some difficulties in using it.

According to another report, Arizona Bahamian refining company developed a new method for leaching gold and silver ore in 1987 as an alternative to cyanidation. The leaching agent used is essentially sodium bromide and halogen. In addition to its fast leaching speed, it also leaches at lower temperatures.

The advantages of the bromination gold extraction process can be summarized as follows: high leaching speed, non-toxicity, strong adaptability to pH changes, and low cost of environmental protection facilities. When refractory gold ore is treated, since bromine can dissolve gold in an acidic medium, bromine can be directly added to the slurry after pressurized oxidation, and the pre-neutralization treatment process is omitted.

VELVET LAMINATION FILMS

FEATURES: