2 Equipment and materials•Balance.•pH meter and buffer solutions (pH 7 & 10).•Magnetic stirrer and stir bar.•Stopwatches.•100 ml measuring cylinders.•500 ml beaker.•Glass rods.•Pasteur pipette.•Copper chloride dihydrate.•Sodium chloride.•Solution of sodium chloride (30 g/L,•pH 11).•Solution of sodium hydroxide (1 M, 0.5 M).•Hydrochloric acid solution (~1 M).3 Methods3.1 Preparation of suspension Sedimentation is carried out in the 100 ml measuring cylinder, using a solution of copper hydroxide which is precipitated out of a soluble salt of copper (copper chloride dihydrate; 15 g/L) in an alkalineenvironment (pH 11) with the ionic strength of the solution buffered by sodium chloride (30 g/L).To prepare the suspension:1. Calibrate the pH meter using the buffers at pH 7 and pH 10.2. Weigh the appropriatequantities of copper and sodium salts (to create a final volume ofsuspension of 400 mL) and transfer the salts to a 500 mL beaker.
3. Add distilled water (up to a volume less than the final) and set it to agitate on the magneticstirrer.4. Dissolution of the salts will occur. Insert the pH meter and begin to slowly add the solution ofsodium hydroxide already prepared under continuous mixing.5. Bring to pH 11 and take the time to ensure that the pH has stabilised.3.2 Transference and dilution of the suspensionSedimentation will be tested at several dilutions: (suspension:final) 100:100, 75:100, 50:100, and30:100. In each case you will be studying 100 mL of diluted suspension, so these values indicate thevolume of suspension you will need to dilute to 100 mL.The dilution will be carried out directly within the cylinders used for the test after the transfer ofthe appropriate quantity of suspension. The transfer of suspension must be made in such a waythat it is ensured that each cylinder receives the
Page 2of 4same initial concentration suspension. Therefore,this transfer must happen as quickly as possible after the beaker is removed from the magneticstirrer. You should proceed as follows:1. Directly pour the suspension from the beaker, quickly, and in a single movement withoutworrying about getting the exact required volume for the dilution. You should record theactual volume transferred.2. You should pour the suspension into each cylinder in order from highest dilution to lowest(just in case you pour too much and need to try to pour a smaller amount again). Shake orreturn your beaker to the magnetic stirrer between each pour to ensure it is well agitated.You are trying to avoid sedimentation during the pouring as each beaker should receivethesame initial concentration suspension.
3. Dilute each cylinder up to 100 mL using the sodium chloride solution.
4. Redisperse the solution using the glass rods provided before any sedimentation tests areconducted.
3.3 Measurement of sedimentation You may perform these tests in parallel, provided you offset each test by a few minutes and start with the “slowest” (highest concentration) sedimentation first. For each test, follow this procedure:1. Maintain a dispersed suspension by stirring slowly with a glass rod.
2. Stop stirring, remove the rod, and record the start time.
3. Observe the suspension top to identify exactly when a clear separation between thesuspension and the clarified supernatant appears. Record the time and the correspondingvolume at which it appears.
4. Continue observing the downward movement of the interface andnote the time it reaches aset of volume marks (your choice).
5. End the test once the sedimentation slows sufficiently.
6. Redisperse the suspension and pour it into the disposal container.3.4 Processing of resultsFor each of the tests:
1. Convert the volume data to height (remember to measure the heights of the graduations onyour measuring cylinders).
2. Plot the height versus time.
3. Calculate the speed of sedimentation using the “straight” sections of sedimentation.
4. Calculate the initial concentration of suspended solids at time zero (considering theprecipitation of Cu(OH)2).
You must then plot the rate of sedimentation as a function of the concentration of solids. Youshould then fit an appropriate function to the velocity/concentration data. Finally,you shouldcalculate the minimum area required for a thickener to treat the following feedstream:•10 m3/hr.•1 kg/m3Cu(OH)2suspension.•Exit concentration 5 kg/m3•Supernatant concentration negligible.
5. Now calculate the minimum area required for a thickener using Kynch theory and compare itwith the result obtained previously using 𝑢𝑐and c data (or fitted function). Note that Kynchtheory is used when settling experiment data are available for only one initial concentration.
