FLEXICONE processing technology of refractory ores and concentrates
For the processing of refractory gold-bearing refractory and sulfide ores, Flexicone has developed a unique enrichment technology.
The technology includes the processes of ultrafine grinding and oxidation of sulphides, extraction of released gold and platinum group metals by centrifugal concentrators and leaching of gold, silver and palladium.The possibility of using our iodine-iodide technology at negative ambient temperatures makes it unique for the regions of the Extreme North and areas with permafrost
Flexicone Oxidation Process
The Flexicone Oxidation technology is a combination of ultrafine grinding and the oxidation of sulphides with air. The process of atmospheric oxidation of sulphides occurs without the use of high temperatures (up to 100 ° C), at normal atmospheric pressure (open apparatus) and at an acidity of the medium close to neutral. Unlike other existing technologies for processing sulphide concentrates, the Flexicone Oxidation technology has several advantages:
1. no need for pure oxygen, the oxidation process is air
2. the process of ultrafine grinding and oxidation combined
3. the possibility of using only gravity extraction and complete or partial abandonment of the leaching process.
The grinding and oxidation of sulfides is carried out in a Vortex ultrasonic reactor to a particle size of the order of -10 microns. Due to the use of the combined ultrafine grinding and oxidation process, the amount of released free gold particles for gravitational extraction significantly increases, the surface area of minerals is increased and the mechanochemical activation of sulfides occurs, which ensures a high rate of oxidation. The physical process of grinding minerals in an ultrasonic reactor is of a resonant-explosive nature, the effect of friction of gold particles decreases and in comparison with other methods, it requires several times less energy expended on grinding. Due to the active course of chemical reactions, spontaneous heating of the pulp to a temperature of more than 80 ° C occurs, but below the boiling point of water, i.e. the process is autothermal. The oxidation process of sulfide minerals can be described by the following reaction equations: 2FeS2 7.5О2 H2O = Fe2 (SO4) 3 H2SO4 (1)
2FeAsS 5.5O2 H2O = 2HAsO2 2FeSO4 (2)
2FeSO4 0.5O2 H2SO4 = Fe2 (SO4) 3 H2O (3)
HAsO2 Fe2 (SO4) 3 2H2O = H3AsO4 2FeSO4 H2SO4 (4).
If further leaching of gold by cyanidation or the chloride-hypochlorite method is assumed, then the process is carried out in a relatively neutral medium: at a pulp pH above 4.0. For the neutralization resulting from the oxidation of the reactions (1) and (4) of sulfuric acid, the cheapest reagent is used — limestone and / or soda. Thus, in general, the oxidation of sulfides in the process can be described by the following reaction equations:
2FeS2 7.5O2 9H2O 4CaCO3 = 2FeOHON 4CaSO4 2H2O 4CO2 (5)
FeAsS 3.5O2 2H2O CaCO3 = FeAsO4 CaSO4 2H2O CO2 (6)
Flexicone Leaching Technology
Technology leaching of gold and silver by cyanidation.
The advantage of the process over a number of other traditional decomposition processes of sulfide minerals is the relative inertness of oxidation products in relation to cyanide and their environmental safety. Due to the fact that the process is carried out in a relatively neutral environment, almost all of the sulfur that passes into the solution during the oxidation of sulphides is precipitated in the form of gypsum. As a result, there is no accumulation of sulfur in the solution (the concentration of sulfur in the solution during oxidation is maintained at less than 2 g / l). Under these conditions, the oxidation of sulfides proceeds with the formation of sulfates, and not elemental sulfur, as in the processes proceeding at a lower pH level (bacterial oxidation, acid-oxygen oxidation, etc.). During the subsequent cyanidation of the oxidation product, elemental sulfur (if present in the material) actively interacts with cyanide ion to form thiocyanates, leading to an increased consumption of sodium cyanide. Thus, the application of the technology allows not only to reveal finely disseminated gold for gravitational extraction, but also to ensure a relatively low consumption of reagents if the cyanidation process of the oxidized material is used. Due to the fact that the application of technology occurs at elevated temperatures (more than 80 ° C), the precipitation of iron and arsenic from solutions proceeds with the formation of goethite and scorodite, which have a crystalline structure. These forms of compounds are the most inert with respect to sodium cyanide. In addition, crystalline skorodite is the most stable and environmentally safe form of storage of arsenic waste. In the oxidation processes occurring at lower temperatures compared with the Flexicone process, iron and arsenic can precipitate in the form of iron hydroxides and skorodite of an amorphous structure, as well as jarosite, complex sulfates. The presence of these compounds in the oxidized material leads to an increased consumption of sodium cyanide when leaching gold. The presence of amorphous skorodite leads to partial dissolution of arsenic during storage of tailings leaching, which has a negative impact on the environment.
Chloride-hypochlorite technology of leaching of gold from ores and concentrates.
We have developed a chloride-hypochlorite technology for leaching gold in an alkaline medium with a pH of 8-8.5. This technology makes it possible to operate the system under less corrosive conditions with a lower chloride concentration and can be used as an alternative to cyanide. To activate the process of dissolving gold and reduce the consumption of reagents in our technology, ultrasonic reactors are used. Unlike existing chloride-hypochlorite technologies, in our technology the leaching system contains an additive of an activator and a stabilizer and consists of 2-5% NaCl (or another source of chloride), 0.1% sodium hypochlorite. The stabilizer is a compound with which chlorine is still active, but is in a more stable form. At high pH, sodium hypochlorite is itself a very weak oxidizing agent in order to cause any significant dissolution of gold. However, in the presence of an activator, this weak oxidizer becomes very effective. For the complete extraction of gold from solution and cake, we developed the FE150 two-chamber electrolyzers with a capacity of 150 kg per load and FE 2500 with a capacity of 2500 kg per load.
Advantages of Flexicone Leaching chloride-hypochlorite technology:
possibility of leaching gold from refractory ores
speeding up the leaching process by 2-4 times
leaching of gold in an alkaline medium with a pH of 8-8.5
perfect compatibility with the Flexicone Oxidation process
low cost of equipment and reagents
Iodine-iodide technology leaching of gold, silver and palladium from ores and concentrates.
We have developed iodine-iodide gold leaching technology in an environment with a pH of 4-9. This technology is universal and makes it possible to operate the system under less corrosive conditions with a lower concentration of iodine. To activate the process of dissolving gold and reduce the consumption of reagents in our technology, ultrasonic reactors and additives are used to activate the process. For the complete extraction of gold from solution and cake, as well as the regeneration of iodine-iodide, we developed the four-cell electrolysers FEI150 and FEI 2500.
Advantages of Flexicone Leaching iodine-iodide technology:
universality of use for most types of ores
possibility of leaching with gold silver and palladium
speeding up the leaching process
leaching in an environment with a pH from 4 to 9
perfect compatibility with the Flexicone Oxidation process
low cost of equipment
low consumption of reagents (from 0.1 kg iodine per ton of ore)
The possibility of using our iodine-iodide technology at negative ambient temperatures makes it unique for the regions of the Extreme North and areas with permafrost
The research results showed that the Flexicone technology makes it possible to efficiently process poor sulphide ores, tailings of processing plants and concentrates with finely disseminated gold at lower operating costs. The Flexicone technology allows for the processing of refractory products with significantly smaller capital investments. Unlike real competitors — autoclave and bacterial oxidation — it does not require the participation of highly qualified specialists; there is no need to create a high concentrate enterprise or a portal for processing concentrates from several objects. Consequently, it is possible to organize local production of small capacity, which will allow to involve in processing medium and small deposits of refined gold, processing of tailings with low gold content. We offer the possibility of using environmentally friendly gravity gold extraction using Flexicone centrifugal concentrators and complete or partial abandonment of the leaching process.