ORE REDUCTION: THE USE OF THE AVS IN MINING
The features of the ferromagnetic vortex layer allow for efficient use of the AVS to intensify several mining chemical processes, including mineral and ore reduction, solution and leaching, metal cementation etc.
Ore reduction mills
Ore and concentrate grinding. Milling fineness in ball and bar mills used for the purpose is limited by several hundred micron, making it impossible to fully refine finely disseminated ores. Most minerals can be ground to several microns in the AVS. This opens a range of new possibilities for better extraction of many materials. However, it should be noted that such fine grinding of especially hard minerals incur up to 100 kWh per one ton of ore, with insignificant processing capacity of the equipment. The conclusion is that the viability of AVS application must be determined on a case by case basis. Some of the processes where the AVS is efficient are grinding of precious or rare metal ores, as well as low strength minerals, such as sulfides, chalk, kaolin, talcum etc.
AVS-100 ore grinding mill
SOLUTION AND LEACHING
Changing the solubility of substances in the vortex layer can be used to accelerate the process of solution and leaching to increase the rate of product extraction from ore. One example is the halurgic method of potassium chloride production, based on the different solubility of chlorine salts of potassium and sodium in water. Sylvinite ore usually solves in alkali and screw dissolvers at 80-90°C. In this method, much of the potassium chlorine cannot be extracted from the ore, being a part of poorly soluble minerals, and is usually disposed of (halitic waste).
Dissolution of ore in the vortex layer allows for a significant potassium extraction rate increase. Table 1 shows some data in the contents of Na+, K+, Mg2+, Cl–, SO21 ions in the solution after processing the ore in screw dissolvers and in the vortex layer (80°С temperature).
As seen in the table, the content of potassium in the solution increased by 20-30%. Beside potassium, the concentrations of other products have also increase: +20-70% magnesium, +90% chlorine. At the same time, the content of sodium decreased, which is very valuable for this process. The increase of potassium and magnesium concentrations in the solution, as demonstrated by the analysis, is due to almost complete dissolution of halite.
Sodium leaching is common in hydrometallurgy to refine ore; these involve mixing and baking ore and sodium to make certain components soluble. This process, for instance, is the base of dephosphorization of manganese concentrates. It is know that some manganese ores from the Nikopol basin are highly phosphorous (0.2—0.25%), which prevents melting of low phosphorous ferromanganese and silicomanganese. The sodium method of refining manganese ore involves baking of manganese concentrate with soda at 850—900°С, to make phosphorous and siliceous minerals interact with sodium carbonate, forming water-soluble sodium silicates and phosphates, which can then be extracted by leaching.
Research demonstrates that the vortex layer technology can be used in such processes for various effects. First, beside intensification of mixing soda with ore, the mixing already causes some formation of water soluble compounds and material activation, which leads to accelerated and more efficient chemical interactions during baking. Second, intensive mechanical and chemical interactions occur during the processing of ore in a water soda solution, including the process of phosphorus transitioning into the solution. Dephosphorization of the concentrate by leaching without baking becomes possible. Third, the AVS allows to replace expensive soda with less expensive sodium-containing materials, such as sylvinite, sodium chloride, sodium sulfate etc.
Table 2 lists comparative data on dephosphorization and desiliсation of ore using different processes. The data is for manganese concentrate, containing 38.9% Mn, 0.201% P, 23.4% SiO2, 2.35% Fe, 1.9% CaO, 1.26% MgO, 1.37% Al2O3. The iron ore sample contained up to 40% iron and 1% phosphorus.
METAL cementation
Cementation, which is an electrochemical process, requires potential difference between various parts of the metal surface. As was already determined, the difference of potentials on the metal particles in the vortex layer due to collisions and friction is sufficient not only for cementation, but also for electrolysis. This phenomenon is used in new methods of metal cementation, based on the vortex layer. Cementation with iron, nickel or cobalt if copper, gold, silver, arsenic, platinum and other metals can be very efficient in the AVS, especially when the concentration of these metals in solutions is low.
Table 3 lists data on cementation of platinum, palladium, iridium and rhodium with iron in AVS-100 units with 10 mg/liter concentration of each metal
As can be observed from the table, using the AVS for this process is quite viable, since metals are extremely difficult to extract at such low concentrations and are disposed of with waste water.
Very important possibilities in metal cementations are due to the fact that any metal can be cemented in the vortex layer by any other metal (with the exception of the alkaline metals), regardless of their mutual positions in the galvanic series. Perhaps, cementation is not the correct term in this case, since during AVS cementation of a metal to the right in the series by one to the left in the series, the former may precipitate as hydroxide.
Aluminum, for instance, is extracted only as Аl(ОН)3 in case of cementation with copper.
Since the electromagnetic field only moves ferromagnetic particles in the vortex layer, cementation with non-magnetic metals requires mixing ferromagnetic and non-magnetic particles. It is necessary to employ one significant feature of the vortex layer: in water solutions of metal salts, predominantly one of the metals present in the vortex layer in solid particles transits into the solution, pushing out the solved metal. E.g. if the vortex layer is created of nickel and iron particles, only iron ions transit into a zinc sulfide solution, pushing zinc out.
Table 4 lists some data on the content of metals after cementation of zinc from water solutions of zinc sulfide in the vortex layer using particles of two metals (initial zinc content 1 g/liter).
It is possible to develop such composition of the vortex layer for practically any solution, that only the metal that is desired in the solution enters the solution.
The next important feature of the cortex layer cementation is the fact that different metals in the processed solution have different cementation affinity. The ability to be pushed out by iron from the solution can be ranged for some metals as follows: Са < Мg < Мn < Ni < Zn < Аl. This means that only the “contaminant” metals can be extracted from complex solutions selectively. They may be instead replaced by the metals of choice. The above examples vividly demonstrate that the vortex layer has many promising applications in hydrometallurgy.
EXTRACTION
Extraction is one of the main methods of rare earth metal production and separation. Changing the coefficient of material in triple systems by treating them with magnetic fields and in the vortex layer, as well as changing the extraction selectivity coefficient opwn many possibilities of applying the AVS and the extraction method not only in rare earth metal production, but also in such processes, where extraction was previously inefficient.
FLOTATION
In refining ore by flotation, the important operations are attritioning of clay slime from flotation materials, mineral surface activation and even distribution of flotation agents in the pulp. In potassium salt production, for instance, attritioning is performed in horizontal attritioning units for 10—15 minutes. However, due to the large size of the equipment, about 30% of the product is under the influence of laminar liquid flow. As a result, the product supplied to flotation contains large amounts of slime. The clay slime, finely dispersed in the pulp, have a well-developed surface and can adsorb a significant amount of flotation agents, causing excessive consumption of chemicals, process complication and concentrate contamination.
Reliable attritioning of clay mineral occurs in the vortex layer in fractions of a second. Currently, facilities disperse reagents in the pulp in contact vats or in double shaft mixers. With this method, the amines introduced into the pulp, are distributed in the form of large micelles, which causes excessive amine consumption (no more than 25% is actually used). Foam flotation of water-soluble potassium salts (sylvinite) is performed in solutions, saturated with KCl and NaCl. This requires emulsification of flotation agents, such as heavy oil, in saturated solutions. Current equipment does not allow the production of such emulsions, therefore regular heavy oil is used as flotation agent, contaminating the product and hindering the consequent drying process.
Emulsification of heavy oil in the solution and even distribution of amines in the pulp is easily achieved by the AVS.
Selective ore milling and grinding
Selective milling and grinding in the vortex layer can be used in the refining process. Experiments showed that it is possible to select such mode of vortex layer operation when kimberlite would be intensively ground, while the natural diamond grains will remain undamaged. Fine grinding of kimberlite ore in the AVS is accelerated by tens of times in the AVS, compared to ball mills. Besides, it allows to extract diamonds smaller than 0.2 mm. Using the vortex layer for selective mineral grinding can be very efficient.
Production of dispersed hydroxides and carbonates
A range of mining chemical processes involves production of hydroxides, carbonates and other insoluble compounds as intermediate or final products. The solid materials formed in the vortex layer as the result of the chemical reactions, is dispersed one order of magnitude finer than the same material produced in a mechanical agitator. Hydroxides, carbonates etc may have increased or decreased solubility, different magnetic, electric or optical properties and chemical activity. Their sedimentation in the vortex layer may be performed with pH different from the pH under normal conditions. All of these factors make the vortex layer very promising for a range of chemical ore refining processes.
The processes listed in the article are only a fraction of all capabilities of the vortex layer.
Ms. Anna Morynets
GlobeCore GmbH
Edewechter Landstra?e 173,
Oldenburg-Eversten,
Germany,
26131
e-mail: [email protected]
phone: +17134893755
www.fuelcleaning.globecore.com
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