Dewatering: Thickening, Filtering, CCD, Water Treatment & Tailings Disposal

Dewatering: Thickening, Filtering, CCD, Water Treatment & Tailings Disposal2017-04-04T06:57:46-04:00
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Settling Test Procedure (2 replies and 1 comment)

3 years ago
Boyd 3 years ago

hi all,

i need help with the settling test procedure and calculation of how many millilitres of flocculant needed to be added to 1 litre pulp. we have 3 types of flocculant on site and i need to know the effectiveness of each.

i want to make 0.05 and 0.1 concentrations of each during the test.

i appreciate you for taking time to read my need and valuable contributions you will make. 

3 years ago
Obergruppenfuhrer 3 years ago

Boyd, the capacities of thickeners and tailings dams are inherently related to the settling rates of the 'material to be thickened. Since both units are inclined to be very expensive items, it well behooves the research staff to test the settling characteristics extensively. Initial tests should be done on the material as it comes from the process. They may be done in 1000 C.C. graduated cylinders where the interface may be visible and measured so that a rate per hour and an area can be calculated. A safety factor of 33% should be used for these results for. scale-up. Confirmatory tests should be done in a 7 to 10 cm (3 to 4 inch) diameter pipe which is 2 to 3 meters (6 to 9 feet) long, capped at one, end and tapped at regular intervals for sample extraction. The results of these tests should be multiplied by 120% for safety.

Confirmatory tests should be done at various feed dilutions because the settling characteristics can be appreciably different. Also, since temperatures have a pronounced affect on settling rates, routine tests should be conducted at the temperature expected in practice. Previously heated pulps after cooling frequently settle faster than unheated pulps and, therefore, if heat is involved in the process, the researcher may want to take particular note of that fact. Normally, the settling tests will be done without settling aids. Hence, if the results are average or reasonable,,a measure of safety is available when operations begin, upsets are encountered and the operator finds that settling aids have to be used. However, some materials such as clays or fine precipitates are very difficult, if not impossible, to settle without flocculants and, under these circumstances, the next step must be conducted using the aids available. Although reasonable rates may be demonstrated in the laboratory, using these aids, it would be wise to use an additional safety factor of 20%. There are,recorded instances where it would appear that settling or flocculating in tailings dams is extremely slow so that large basins and/or long period of time are required to get satisfactory effluents. Due to the high volumes which must be handled, it is doubtful that it would be economic to add flocculants to speed up the tailing settling rates.

  1. Add slurry or solids (approximately 200-300 g dry weight) to the measuring cylinders, and make up to 1000 ml with water.
  2. Add flocculents and pH modifiers, if required.
  3. Agitate the pulp by inverting the cylinder 10 times.
  4. Cease agitation and start the timer, taking readings at regular intervals, of the pulp/water interface. It is critical that sufficient readings are taken to accurately draw the settling versus time curve. Record on the Thickener Testing Form.
  5. Take the final reading after 24 hours; take the final interface level. Dry and weigh the solids.
  6. Determine the specific gravity of the dry solids.
  7. If required, calculate the thickener area using the appropriate procedure. (Review SME Handbook.)
  8. Record all testing parameters on the Thickener Testing Form.
3 years ago

hi, kindly receive by appreciation for this in-depth knowledge you have passed to me

3 years ago
Romain CADENAT 3 years ago
1 like by David

Dear Boyd

Ober post is right. I would just add that you have to do the test with several quantities of floculant in order to check what is the best between Settling Speed and floculant consumption. 

Also I would do the test with 50g of solid per liter instead of 200g/l. But in fact in depends of what is the solid concentration of the pulp in your  plant. 

Usually I do settling test in 1 liter or 2 liters test tube and I record the time each 100ml or less depending on the settling speed. 

As Ober said you need a safety factor of 1.3. 

An average floculant consumption is between 50 and 200g of floculant per ton of dry solid. 

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