The Method of Processing Low-Grade Gravity Concentrates and Tailings of Placer Gold-Concentrating Sites
One of the solutions of the problem of reducing losses in alluvial and hardrock gold processing by gravity methods (various equipment, jigs, centrifugal concentrators) is a more frequent concentrate removal. Low-grade concentrate produced in this process, has to be reduced (reprocessed) before final processing, as equipment at placer gold-concentrating sites or gold recovery plants in general consists only of a jig unit and a shaking table, and at best – of additional magnetic and magnetic fluid separators, and because of its poor efficiency cannot process such amount of concentrate at the reprocessing stage. Hence, it is made to operate at almost maximum capacity, which leads to considerable losses of precious metal, primarily, of plate and flake particles of fine and fine-dispersed grain size classes whose content reaches from tens to hundreds grams per 1 tonne.
To solve the problem of raising gravity concentrates grade and of concentrate amount reduction, the authors of industrial centrifugal concentrators put forward the idea of reprocessing low-grade concentrates at small-sized models of equipment similar in their design to the industrial ones. For instance, the Canadian companies «Knelson» and «Falcon» for these purposes recommend 7.5 and 6-inch models, correspondingly, and the Russian company “Itomak” – the KN-1; KG-2; KG-5 concentrators.
However, as experience confirms, the centrifugal method of processing low-grade precious metals concentrates with the use of the above-mentioned devices does not yield the desired result in precious metals concentration and extraction. Losses of fine, plate and flake particles of precious metals are especially high. The reasson for this is that in reprocessing low-grade concentrates having rough granulometric characteristics in relation to feed sample, fine and plate (flake) mineral particles are washed out from mineral bed settled down in the catching grooves of the concentrator cup by counter current of liquefying pressure water used for loosening mineral bed formed in the grooves.
The research carried out by the “Pugachev and Partners” company on processing low-grade concentrates produced at equipment sluices and industrial concentrators “Knelson” and “Itomak” used at various gold-mining enterprises, demostrate that best results are obtained when centrifugal concentrators based on separation principle are operated at 30-50% of their maximum capacity. (for low-grade concentrate amount below 100 kg — the CKP-0.2M concentrator; for concnetrate amount over 100 rg – the CVKP-3).
For example, gravity concentrate produced at the OAO “Norilsk Industrial Complex” ОАО with the use of “Knelson-30” (7.5 inches) had average precious metals content of 590g/t (grain size – 0.7 mm). After one stage of processing at the centrifugal oscillation concentrator CVKP-3 the precious metals content amounted to 24 kg/t and 84% of valuable components were extracted. After reprocessing of tailings down to grain size 0.05 mm and further reprocessing at CVKP-3, additional 10% were extracted (more than 6 kg/t of precious metals in addition). The CVKP-3 capacity was 1000…1200 kg/hour, and the pulp density – solid to liquid ratio=1:10.
The introduction of centrifugal oscillation concentrators CKP-0.2М and CVKP-3 based on separation enrichment principle, not only solves the problem of processing low-grade gravity concnetrates but reduces losses at the reprocessing stage by recleaning tailings of jigging machines, concentration tables and magnetic liquid separators. They make it possible to recover precious metals losses from old tailings of placer gold-concentrating sites.