A sedimentation process is to be used to separate pulverized coal from slate. A suspension of finely divided particles of galena (lead sulfide SG = 7.44) in water is prepared. The overall specific gravity of the suspension is 1.48.
(a) Four hundred kilograms of galena and a quantity of water are loaded into a tank and stirred to obtain a uniform suspension with the required specific gravity. Draw and label the flowchart (label both the masses and volumes of the galena and Water), do the degree-of-freedom analysis and calculate how much water (m3) must be fed to the tank.
(b) A mixture of coal and slate is placed in the suspension. The coal rises to the top and is skimmed off, and the slate sinks. What can you conclude about the specific gravities of coal and slate?
(c) The separation process works well for several hours but then a region of clear liquid begins to form at the top of the cloudy suspension and the coal sinks to the bottom of this region making skimming more difficult. What might be happening to cause this behavior and what corrective action might be taken? Now what can you say about the specific gravity of coal?