A technology for polishing feed solutions for solvent-extraction plants.
The Bateman Pinned-Bed Clarifier is a unique process for hydrometallurgical plants where solution clarity is important. Offering very low suspended-solids counts in the overflows, the clarifier regularly achieves clarities of less than 30 ppm solids, and even as low as 20 ppm.
Each clarifier comprises a cone and cylinder outer body similar to a pachuca. A fine screen is fitted across the top of the cylinder. A feed pipe is inserted through the centre of the screen down to the level of the top of the cone. When liquor containing low-density beads is injected into the clarifier, the beads rise and are trapped against the screen by the upflow of the liquor and form a 'pinned bed'. Any fine flocculated solids in the liquor soon aggregate as a further layer below the pinned bed which is extremely effective in trapping the fine solids rising with the liquor in the clarifier.
Most of the flocculated solids suspended in the feed are withdrawn through the base of the cone while the rest are filtered by the pinned bed. The flocculated bed is flushed without interruption to the feed and results in an expansion of the pinned bed of beads and flocculated solids.
Overflow clarities are re-established quickly as the clarifier is returned to service by re-establishing the pinned bed.
The BATEMAN Pinned-Bed Clarifier offers
- Robust and stable performance
- An auto regulatory process capable of handling wide ranges of flows and solids in the feed liquor without close supervision
- Within the design range, a clarity of product not affected by the amount of solids in the feed or fluctuations in the feed flow rate.
- Many and varied operating benefits
- Extremely low crud formation in solvent-extraction circuits fitted with the clarifier
- Low solids-residence times, minimising
slimes build-up
- Optimal usage of chemicals, such as flocculants
- On line backwashing.
- Simple, yet effective clarifier design
- Small footprint
- Low comparative capital expenditure
- Ease of enclosure in existing plants
- No moving parts, virtually eliminating the need for maintenance.
Development
The Bateman Pinned-Bed Clarifier was originally developed as a result of the poor clarification performance of conventional clarification systems which failed to meet the requirement of less than 40ppm of suspended solids in the pregnant-liquor solution (PLS) fed to a solvent-extraction (SX) plant.
The technology is based on the concept of buoyant-media filtration and utilises the configuration of the Bateman Ultrasep. This allows substantially higher rise rates inside the Pinned-Bed Clarifier than would be practical in a standard clarifier, substantially reducing the clarification area and producing a far more cost-effective solution.
Test work at several sites confirmed the operating parameters and solution clarities achievable and a reliable model for design and performance prediction has been developed.
While in most cases the clarifier alone is sufficient, when used in combination with downstream sand filters, the clarifier provides good output clarity at far lower capital and operating cost than pressure filters alone.
