Underflow Pump Requirements

Another factor was the inability of the thickener underflow pumps (inappropriately sized for the service) to handle slurries containing much more than 15% solids. This required the dilution of the thickener underflow before being pumped to the filter. A much higher demand was then placed on the already limited capabilities of the filter. The slurry had to be dewatered from 15% solids to 55% instead of from 25 to 55% thus, more than doubling the amount of filtrate to be removed from the same amount of insoluble solids. 

Mechanical classifiers are expensive to install but in some apphcations they are selected for high-density valuable minerals as they assist in their immediate recovery without requiring further complicated flotation circuits. In some respects, flotation circuits use some of the principles of mechanical classifiers by using a circular internal weir, a mixer, an underflow pump, and a separate froth pump. 

The feed rate is manually set as required for either pH or reactant stoichiometry control. Soda ash is added to the fourth reactor as sodium makeup. Reactor effluent slurry flows by gravity to the thickener centerwell. Clarified liquor overflows from the thickener to the forward feed hold tank from which it is pumped to the tray tower. A horizontal belt filter is used for further dewatering of the thickener underflow solids. 

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