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Sifting Precious Metals From Dental Lab Scraps 90% Faster

Atlantic Precious Metals Resources reduced sifting time by 90% when it went from hand sifting of scrap and sweepings from dental laboratories to screening with a 24 in. (610 mm) diameter circular vibratory separator.

The time savings helped the four-person foundry accommodate a recent doubling of business. The VIBROSCREEN® separator from Kason Corporation paid for itself in less than nine months out of labor savings.

APM recovers and refines particles of silver, gold, platinum and palladium from scraps and sweepings purchased from dental laboratories and offices. The scraps come from workbenches, suction unit filters, floor sweepings, vacuum cleaner bags. After screening, the particles are smelted in APM's four furnaces, and sold as bars or ingots to precious metal processors.


Sifting Dental Laboratory Scraps

About 20% of incoming batches must be sifted since they arrive mixed with large pieces of paper towel shreds, straw from brooms, paper clips, plaster pieces, and plastics from impression trays. Batches containing fewer foreign pieces are not sifted prior to smelting.

Previously, APM operators took three hours to sift a typical 50 to 100-lb (22.7 – 45.4 kg) batch manually using kitchen-type strainers. Now, one operator, in 30 minutes, separates equivalent batch sizes by emptying the contents of 5-gal (18.9 l) buckets onto the top screen deck of the VIBROSCREEN circular screener. The unit is positioned adjacent to a DCE dust collector, which evacuates dust during operation. "We leapfrogged from Gold Rush days into the 21st Century with the new equipment," owner Don Mappin, Jr. jokes.

The circular vibratory screener is equipped with an imbalanced-weight gyratory motor positioned beneath the screening chamber. The motor imparts multi-plane inertial vibration to the two spring-mounted screening decks, causing oversize particles to vibrate across the screen surface in controlled pathways to the screen periphery where they are discharged. Screening efficiency improves by forcing material to pass over a maximum amount of screen surface. Undersized particles pass rapidly through the screen to a feed tray that directs them to the screen beneath.

The top 10-mesh screen separates the large pieces, which exit the top frame discharge, and are sent out for incineration.


From Screener to Smelter

The material falling through the 10-mesh upper screen and retained by the 40-mesh lower screen exits through the middle frame discharge port into 5-gal (18.9 l) containers for smelting. The below-40-mesh precious metal dust exits the bottom frame discharge port in similar fashion.

Batches of the 10-to-40-mesh particles and the below-40-mesh dust are then blended with flux and smelted in one of four 18 in. (460 mm) diameter gas-fired furnaces. The melt is poured from the crucible into a cone mold. After cooling, the metal (mostly gold and palladium) is capped off, assayed and sold as bars or ingots.

Kason's representative Solid Solutions, Inc., McMurray, PA, specified and installed the separator and dust collector.

As APM's business grows, its next goal will be to add furnaces. "We could quadruple in volume before having to add another circular vibratory screener," Mappin says.

Sifting Precious Metals From Dental Lab Scraps 90% Faster
 

Dental laboratory scraps are unloaded into top 10-mesh screen of 24 in. (610 mm) diameter Kason VIBROSCREEN circular vibratory separator.


Sifting Precious Metals From Dental Lab Scraps 90% Faster
 

Circular screener separates scraps and sweepings for smelting. Top 10-mesh screen separates large, unusable pieces. Middle frame port (right) discharges below-10 mesh to 40-mesh precious metal particles. Bottom frame port (rear of unit) discharges below-40-mesh precious metal dust.

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