Outotec is the leading supplier of copper slag concentrators. Production of copper concentrate out of copper slag at the smelter site offers a compact and cost-effective means to recover copper.
Outotec® Slag Concentrator concept provides several advantages:
- high copper recovery
- low operation costs
- proven technology
- ease of operation and maintenance
Various types of smelter slags can be treated at the slag concentrator for copper recovery.
The process is based on slow cooling of the molten slag, crushing and wet-grinding of the cooled slag and recovery of copper by flotation to produce a concentrate.
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Outotec® Slag Concentrator |
Slow cooling of the slag prior to flotation facilitates crystallization of copper and copper sulfides to form large, separate crystals, which is a precondition for their separation from gangue minerals in the subsequent grinding and flotation processes.
The slag cooling process has an essential effect on concentrator performance. The slag is tapped for cooling into ladles where the process can be controlled and the rate of crystallization is slow enough, first by air and then with water sprays. The objective is to form large liberated crystals from copper sulfides.
After cooling, the ladles are emptied by a hydraulic hammer. Possible copper lenses can be removed.
The grinding method is typically autogenous (Outotec® AG Mills or Outotec® SAG Mills) and only single-stage crushing is needed.
The typical grinding process is two-stage grinding where the first step is an AG/SAG mill and the second a ball or pebble mill. The primary mill can be in open or closed circuit depending on the secondary stage. In the closed circuit process, the classifier can be screen, spiral or cyclone. The secondary stage is always in closed circuit with cyclones.
If the grinding concept is such that the transfer size from the primary to secondary mill is fine enough, there can be a rougher stage before secondary grinding. Flash flotation can also be utilized in the grinding circuit.
Secondary grinding overflow is followed by flotation that typically comprises a rougher/scavenger and two cleaning stages. Scavenger concentrates and 1st cleaner tails are circulated back to rougher. Flotation is done in natural pH with a xanthate collector and frother only.
The most important control parameter of flotation is the grinding fineness. If the fineness is optimized, a recovery of 85-95 % can be reached with a concentrate grade of 20-30 % copper. Tails copper assay is seldom below 0.35 % copper.
Copper concentrate is dewatered conventionally with thickener and vacuum filter. Filter cake goes into the concentrate pile and is transported back to the copper smelter.