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. (3) 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?
Problem 4.19:A sedimentation process is to be used to separate pulverized coal from slate. A suspensionof finely divided particles of galena ( lead sulfide, SG=7.44) in water is prepared. Theoverall specific gravity of the suspension is 1.48.a) 400 kg of galena and a quantity of water are loaded into a tank and stirred to obtain auniform suspension with the required specific gravity. Draw and label the flowchart , dothe degree of freedom analysis, and calculate how much water (m^3) must be fed into thetank.b) A mixture of coal and slate is placed in the suspension. The coal rises to the top and isskimmed off, and the slate sinks. What can you conclude about the specific gravities of thecoal and slatec) The separation process works well for several hours, but then a region of clear liquidbegins to form at the top of the cloudy suspension and the coal sinks to the bottom of thisregion, making skimming difficult. What might be happening to cause this behavior andwhat corrective action can be taken Now what can you say about the specific gravity ofcoalSolution 4.19:Step-1 (a) Here we have to draw and label the flowchart for the sedimentation process and have to calculate the volume of water fed into the tank.The flow chart is given below,Let us consider the total mass balance = m +400 = m ----------------(1) 1 3Assume volume additivity we can write, -----------(2)Now, solving equation (1) and (2) simultaneously m = 668 Kg 1 O and m = 1062Kg 3suspension.\n M 3 3V1 668 Kg × 1000 Kg = 0.668 m water fed to tankThus the volume of water is found to be 0.668 m . 3Step-2(b) A mixture of coal and slate is placed in the suspension. The coal rises to the top and isskimmed off, and the slate sinks. Here we have to explain what can we conclude about thespecific gravities of the coal and slate.In this question it has been given that, when the coal skimmed off the slate sinks. That means thespecific gravity of coal is less than 1.48 and the specific gravity of slate is greater than 1.48.Thus the specific gravity of coal < 1.48 < specific gravity of slate.Step-3(c) The separation process works well for several hours, but then a region of clear liquid beginsto form at the top of the cloudy suspension and the coal sinks to the bottom of this region,making skimming difficult. Here we have to find out what might be happening to cause thisbehavior and what corrective action can be taken Now what can you say about the specificgravity of coalFrom the given data, it has been found that the reason of this behaviour is ‘ suspension begins tosettle’. In order to get rid of this behaviour, we have to stir the suspension. The specific gravityof coal is greater than 1.00 and less than 1.48 i.e,1.0 < specific gravity of coal < 1.48.
