Raw Material Processing at FZTSO (Full-Cycle Processing Plant)
The mined ore is transported to the plant by road. The volume of the ore arriving is measured at the weighing station, where every vehicle is weighed on a weighbridge. The weight of every vehicle is registered. The weight information is transferred to the QC department. A sample is taken from the batch of ore to be processed in order to establish water content. The ore from every shaft is stored separately and then, as it accumulates, is separately milled.
During milling, a sample is taken to establish precious metal content. A sample from the batch of 50 tons is handled as per the approved instruction and handed over to be analyzed at the Fire Assay Lab. The results of the analysis are transferred, on a daily basis, to the QC specialist. According to the results of the precious metals analysis (their content in the ore) and the weight of the processed ore, the imbedded precious metals are calculated.
After milling, the ore is then ground, concentrated and cyanided. After cyanidation in pachucas (vertical tanks for mixing pulp with the air), the pulp (ground ore with water) is filtrated. After water washing the filter cake (solid phase separated from water) is delivered to the agitator tank and pumped to the tailings storage (water works for waste storage). Every shift registers the processed pulp and takes the cumulative shift sample of tailings.
After the thickeners, the filtrate (liquid phase after filtration) and pregnant solutions pass on to clarification and then to precious metals precipitation. Precious metals precipitation takes place in a mixer tank with radial filter membrane frames. Together with the clarified solutions to be precipitated, metal zink powder is supplied. The dust is precipitated on the membrane and reprecipitates the precious metals from the solution, while the lean solutions pass through the filter membrane. The zink precipitations are removed, as necessary. The zink precipitations removed from the precipitator are drained and then acetified and heat-treated. By melting zinc precipitations in the furnace, a rich alloy is obtained (gold and silver alloy), which is packed and delivered to the gold reception desk. From each alloy batch a sample is taken for chemical analysis of precious metals content.
Ore Processing at ZIF
The mined ore is stored at the platform near the plant loading hoppers and then, with the help of a bulldozer and a conveyor system, delivered for grinding. Each shift, a sampler from the QC department takes the sample from the coming ore for water content.
The ground ore goes to the thickener, and the thickened product is pumped to the leaching pachucas. Before entering a leaching pachuca the pulp is sampled for solid phase precious metals content. On each shift and on a daily basis, the weight of the arriving ore is registered. According to the results of the precious metals analysis (their content in the ore) and the weight of the processed ore the imbedded precious metals are calculated.
After thickening and primary leaching, the pulp goes to sorption pachucas, where the dissoluted precious metals come into contact with the sorbents and the gold from the solution is absorbed by the activated carbon (the sorbent). The sorption pachucas are cascade-type tanks with drain piping. The pulp comes to the first pachuca and comes out of the last one, while the carbon is delivered to the last pachuca and comes out of the first one saturated. The waste (tailings) from the last pachuca goes through the cleaner screen on to disposal and is pumped to the tailings storage. A cumulative sample is collected from the waste to measure precious metals content.
Activated carbon from the first pachuca goes to stripping. The stripping results in two products:
- Carbon – poor in precious metals.
- Eluates – rich in precious metals.
After reactivation, the carbon is returned to sorption, while the eluates are electrolyzed, with precious metals precipitating from the solution as cathode deposit. The accumulated cathode deposit is removed 3 or 4 times per month, and baked and melted into rich alloy bullion. The bullion is sampled as per approved technology, and the sample goes to the Fire Assay Lab for determination of the precious metals content. The bullions are then weighed, packed and delivered to the gold reception desk. After the sample is read, the chemically pure precious metals content is determined.
Similar to FZTSO, a monthly metal balance is drawn, but such balance takes into account the non-finished production, i.e. the metals contained in the sorbent. The non-finished production value may vary and be either positive or negative at the end of the month.
Heap Leaching Processing
Heap leaching ore preparation includes two separate milling lines with milling in the jaw and rotary crushers with intermediate screening (- 40 mm). The milled ore is palletized with cement in the drum pelletizer, moved by conveyors and then put on a waterproof base by a telescopic stacker to form an ore stock pile 6-8 m high.
This pile is further sprinkled with the water cyanide-containing solution through a dropper system. The pregnant solution flows through the drains to the gold solution pond and is then pumped to sorption. The gold solution is processed by the carbon sorption in two parallel lines with three sorption columns each. Stripping and regeneration of the activated carbon takes place at ZIF.
The main technical tools are electrode boilers where the alkali solutions are heated, the strippers where the gold is stripped from the coal and the electrolyzers used for precipitation from the rich stripping solutions. Lean stripping solutions and reduction solution tailings are forwarded to the sorption column for final stripping. Gold cathode deposits are baked and melted into rich alloys.
Open Dredge Method
The open dredge method of production includes the following stages:
• stripping operations
• mining operations
• concentrating at the placer gold-concentrating site
• delivery of the gold placerstream to the refinery
During the entire season (250 days from the beginning of April until mid December) gold mining is a continuous cycle and includes the following sequence of operations:
- early development works – all year around;
- recovery and concentration in the dredge – during the season;
- complete upgrading of the metal content at the placer gold-concentrating site – daily during the season;
- mined-land reclamation.
Development work is undertaken with the help of heavy bulldozers and excavators. During development and mining the following is done:
1.Removal of snow, tree stumps, bushes and top soil is undertaken in winter by heavy bulldozers in order to create an efficient environment for the dredges and performance of other work, i.e. the relocation of delays, cable, power lines, fuel supply, etc. Average transportation distance is 40-80 m.
2. Removal and storage of the potentially fertile soil is also done by bulldozers. The soil is moved to the ground walls and further used for land reclamation.
3. While drifting catchwater moves both bulldozers and excavators are used.
Stripping is done to comply with the environmental requirements and to upgrade sand, decrease the freeboard and improve the operating conditions of concentrating equipment.
Waste dumps are protected from wash-out by catchwater and drain ditches. To ensure timely preparation of the deposits for recovery and due to water-logged areas, part of the work is done in the winter time (40%), with prior ripping of frozen formations, and the remaining part (60%) is done in summer.
The stripped ground is metal deposits ready for dredging. The prepared ground is further dredge-treated with the use of the following mining methods:
- Development of narrow placer areas – single longitudinal system with one stopping;
- Development of wide placer areas – single lateral system with one stopping;
- Development of placer areas wider than the maximum. stopping width – adjacent longitudinal system with two stoppings. Dredged sand is concentrated on the dredge, the processing scheme including the following stages: disintegration and screening in the dredge tank, sluicing and upgrading metal content.
The gold containing concentrate is collected from all dredges on a daily basis and delivered to the gold reception desk. During the following day it is treated at the placer gold-concentrating site as per the magnet gravitation scheme. The final product is gold placerstream, which will be sent to refinery for further treatment (recovery of 999 fine bullions).
The mine lands are reclaimed by flattening of the dredge and overburden dumps and restoration of the stored fertile soil.