Mechanical Operations

431. With increase in the capacity of screens, the screen effectiveness

1. Remains unchanged
2. Increases
3. Decreases
4. Decreases exponentially

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432. With increase in the pressure drop across the cake, the specific cake resistance for the compressible sludge

1. Increases
2. Decreases
3. Remains constant
4. Increases linearly

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433. Work index is defined as the

1. Gross energy (kWh/ton of feed) needed to reduce very large feed to such a size that 80% of the product passes through a 100 micron screen
2. Energy needed to crush one tonne of feed to 200 microns
3. Energy (kWh/ton of feed) needed to crush small feed to such a size that 80% of the product passes a 200 mesh screen
4. Energy needed to crush one ton of feed to 100 microns

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434. Work index is the gross energy (kWh/tonne of feed) necessary to reduce a very large feed to such a size that 80% of product particles will pass through a 0.1 mm screen. The value of work index determined for wet grinding should be multiplied with _________ to get the same for dry grinding.

1. 1
2. 0.5
3. 1.34
4. 4.34

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435. Xanthates are used in the froth floatation process as a/an

1. Conditioner
2. Frother
3. Collector
4. Activator

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