In the selection of gold extraction processes, the cyanide method has become the widely applied method, dominating the gold ore beneficiation industry. According to statistics, the annual discharge of cyanide tailings in China has exceeded 20 million tons.
Cyanide tailings can be classified based on different leaching processes, including heap leaching tailings, full mud cyanide tailings, fine cyanide tailings, and oxidative roasting-cyanide tailings. Sulfur-containing cyanide tailings come from the tailings discharged after gold-bearing sulfide ores undergo flotation and cyanide leaching in the gold extraction process.
The sulfur content in cyanide tailings is often above 0.8%, mainly present in the form of sulfides. When the sulfur content is less than 40%, the economic feasibility of resource utilization of sulfur-containing cyanide tailings to prepare sulfuric acid is no longer viable. Instead, they can only be treated as waste and stored or disposed of. In China, such cyanide tailings are a major solid waste in the gold industry, with an accumulated storage exceeding 100 million tons. So, how should high-sulfur cyanide tailings be handled?
Research indicates that the reduction roasting-magnetic separation technology is an effective method for recovering iron from cyanide tailings. Depending on the reduction degree of iron minerals, magnetic separation products can be divided into iron concentrates and reduced iron. Researchers using the reduction roasting-magnetic separation process for cyanide tailings obtained iron concentrates with a high iron grade under suitable conditions.
The reduction roasting-magnetic separation steps for cyanide tailings include mixing, reduction roasting, grinding and magnetic separation, and washing. The specific operational methods are as follows:
1.Mixing:
Select bituminous coal as a reducing agent and mix it thoroughly with cyanide tailings.
2.Reduction Roasting:
Load the sample into a crucible and perform reduction roasting in a vertical furnace. When the furnace temperature reaches the preset reduction temperature of 1150 ℃, introduce N2 at a flow rate of 5 L·min -1 to remove air from the vertical furnace. When the gas analyzer shows O2 in the furnace is zero, suspend the crucible in the vertical furnace. Then, reduce the N2 flow rate to 3 L·min -1. Once the set reduction time is reached, take out the suspended crucible and cool the roasted product to room temperature.
3.Grinding and Magnetic Separation:
The grinding and magnetic separation process involves two stages of grinding and two stages of magnetic separation. The first-stage grinding fineness is -0.074 mm 85%, and the magnetic field strength is 112 kA·m -1. The second-stage grinding fineness is -0.043 mm 80%, and the magnetic field strength is 96 kA·m -1. Rod mill and magnetic separator are the main grinding and magnetic separation equipment used. The obtained magnetic product is called powdered direct reduced iron product or simply "reduced iron."
4.Washing of Cyanide Tailings:
The treated cyanide tailings need to undergo washing to meet environmental requirements. During washing, specialized washing equipment and washing agents are used. The washing equipment must be thoroughly cleaned and disinfected to ensure that the treated cyanide tailings do not re-contaminate the environment.
In conclusion, the handling of high-sulfur cyanide tailings involves an effective reduction roasting-magnetic separation process. The treated tailings should be properly disposed of, including methods such as sealing, burial, incineration, etc., depending on the regulations of different regions, to ensure that the treated cyanide tailings no longer pose a threat to the environment and human life and property.
