Fine, Fine-Dispersed and Dust Gold Extraction from
Alluvial Sands in Conditions of Fresh Water Deficit
At present in the practice of concentration of ores and alluvial sands containing precious metals, a wide range of foreign and Russian concentrators of various design are used for the extraction of fine and fine-dispersed gold, platinum and silver. In this process, extraction effectiveness primarily depends on the degree of loosening of mineral bed formed in trapping circular grooves at the interior surface of the concentrating cup, as due to significant centrifugal force caused by the cup rotation, processed material is rapidly pressed into the grooves impeding the replacement of light fraction by the heavy one, which lowers concentration quality.
There exist a wide range of technological solutions of this problem used in Russian and foreign centrufugal concentrators of various design, the most popular and widespread in gold mining being concentrators using similar loosening principle: by pure water supply under pressure via multiple small-diameter openings of small diameter in the walls of the cup grooves through the consolidated bed. Such concentrators are reffered to as the classifying type of equipment.
The principal disagvantage of these concentrators are high requirements to purity of water supplied to the concentrator inner jacket, that should be free of suspended particles and salts, for them not to fill the cup openings through which water is supplied from the inner water jacket to loose the bed. The lack of effective water filtration systmes is a major reason preventing the introduction of such concentrators in most of prospetors’ teams mining deposits in areas located far away from pure water sources. Such problems are commongly faced by many prospectors’ teams developing precious metals deposits in Africa where water is literally worth its weight in gold.
Another disadvanrage of such concentrators design related to their operating principle, is the fact that they are not able to simultaneously recover heavy minerals grains of various grain and form classes, as pressure at inner water jacket of water loosening the bed should be adjusted for each class individually. Experience of operating such concentrators and tests to compare them with other concentrators types carried at the ZAO “Mekhanobr Engineering” (Saint-Petersburg) (see “Ore Concentration”, 2001) and OAO “Irgirmet” (Irkutsk) (see IRB “Gold Mining”, 2005, № 76) have demonstrated that equipment of classifying type is by far less effective (by 10-20%) in extracting fine particles of high density, as well as plate and flake particles than concentrators based on separation principle – CVK and CKPP. The reason for this is that the bed in the grooves of such equipment is coarsened under the effect of loosening counter water flows and its granulometric size composition is gradually changed at the cost of washing out of fine, fine-dispersed and flat gold particles.
OOO “Group of Companies ‘Pugachev&Partners” offer a totally innovative model of the centrifugal oscillation concentrator CVKP-5 (design is protected by the RF Patent №2220772) based on separation principle , that operates on circulating water and effectively recovers fine, fine-dispersed and dust gold, as well as plate and flake gold.
Operating principle of the new concentrator is based on forced separation of processed material supplied as pulp, into two fractions: heavy fraction settled down in catching circular riffles of the concentration cup rotating about its vertical axis, and light fraction carried away by rising pupl flow over the cup edge to a tailings receptacle and further, through a discharge sleeve, out of the the concentrator.
Forced gravitational differentiation of solid phase accumulated in the cup grooves, is caused by combined effect on each particle of centrafugal forces of rotating pulp and of high-frequency oscillations of the cup, whose frequency and oscillation amplitude are correspondingly adjusted, thus causing jigging effect. which adjusted the inter and forming mineral bed. Such interaction of forces creating the modes of compression and loosening of material and its intensive shaking, ensures the most effective concentration through segregation, as it facilitates the penetration of fine and fine-dispersed heavy particles trough gaps between large light particles and forcing the latter out from the cup grooves.
The concentration Diagram below for illustration purposes is presented in the form of an enlarged catching circular riffle of the concentrator cup with mineral bed formed at the initial stage of concentration primarily of light fraction consisting mainly of sand grains of 2 mm size (for alluvial sands) or enclosing ore rock grains ground down to 22 mm size, at the first stage of concentration.
The Diagram demonstrates that gaps between sand or large heavy minerals grains in their size exceed fine, fine-dispersed and dust gold, which fascilitates the penetration of such gold inside the bed under the oscillation effect. Due to such operating principle the new concentrator has a great advantage in its major characteristic – the possibility to extract small-size heavy grains in the conditions of pure water deficit.