A toxic legacy from years of gold mining in Africa, cyanide-laced mine wastewater is a byproduct of gold extraction that has become one of the continent’s biggest environmental problems.
Leaching gold process
According to different leaching gold equipments, there are different ways for gold extraction. Let’s see more about it.
Full flotation process
Through the interaction of various chemical agents and tailing minerals, the difference in chemical properties of the surface between ores is used to effectively separate the minerals.
Gold cyanide leaching
The cyanidation leaching process, that is, the gold ore is first finely ground into pulp, and then the ore is recovered through secondary treatment such as cyanide leaching and activated carbon adsorption.
The process of extracting gold from ore can be very hazardous. Cyanide is used in the extraction process to dissolve the gold from the ore. The cyanide solution is then sent to a chemical plant where it is recovered and reused.
The above two methods are very beneficial to the output of gold ore, but the pollution in the wastewater discharge is relatively large.
What is cyanide?
Cyanide is any substance that contains a specific type of carbonitride anion group. This may include the free cyanide anion (CN–), as well as many different compounds such as potassium cyanide (KCN), cyanogen chloride (CNCl) and many others.
Hazards of cyanide wastewater
People who work with cyanide may develop health problems from long-term exposure to the chemical. They could also be harmed by short-term exposure if they do not use proper safety equipment and follow all safety regulations while working with cyanides.
Cyanide removal method
There are many wastewater treatment technologies available for cyanide removal, and as with any separation or treatment solution, choosing the best cyanide removal technology comes down to meeting your facility’s specific needs. One of the most important factors to consider is which cyanide species are present in the waste stream.
Aeration with acid
In the past, aeration was used to remove cyanide from the atmosphere. Now it is improved by adding acid first to maximize the acidification of sewage, then aerating it—this method can remove cyanide more effectively. The cyanide remains in its original state, but this method is only applicable to very limited areas. We can also use alkali to recover the gasified cyanide.
Ozone, a form of oxygen with three atoms instead of two, can release atomic oxygen to participate in the reaction in aqueous solution and has strong oxidizing properties. The main feature of ozone treatment is that no other pollutants are added during the whole process, and the amount of mud produced is small. We can use ozone treatment method to treat cyanide in wastewater; only need an ozone generator, simple and convenient, no secondary pollution, no need for further treatment.
Alkaline chlorination treatment
Alkaline cyanidation treatment is a mature method. Chlorination treatment can decompose cyanide at the same time, and hydrogen chloride produced in the middle can be converted into cyanate. It is a new way of destroying cyanide.
Activated carbon treatment
What is activated carbon?
Activated carbon is made from different types of carbonaceous materials, such as wood, coal, fruit shells and fruit stones. It is made by chemical activation or physical activation under high temperature and certain pressure.
How does activated carbon work?
When activated carbon comes into contact with wastewater containing oxygen and cyanide, it produces hydrogen peroxide (H2O2). Under the influence of copper salt, the H2O2 oxidizes the cyanide in the wastewater and decomposes it into oxygen gas (O2) and other compounds. If there is insufficient H2O2 in the wastewater, a hydrolysis reaction occurs on the surface of the activated carbon: HCN+H20=HCONH2. At this point, gold and silver in the wastewater are recovered by absorbing Au(CN)2 onto or inside activated carbon.
For years, Zhulin has become a trusted and reliable activated carbon factory. The activated carbon we produce is widely used in water treatment, air filters, decolorization and other areas. We provide customers with the most economical solution for thousands of applications. We cooperate with top professors in many industries to conduct in-depth cooperation and solve technical problems in various fields.
When it comes to mine wastewater treatment, we’re the best in the business.