Polymer Systems

Clarifiers

Fines Recovery

Frequently Asked Questions

1) What are polymers or flocculants?

2) Are flocculants safe to put in my process water?

3) Are flocculants necessary in Aggregate Operations?

4) Why would I want to add flocculants to my dirty water going to my settling ponds?

5) What is the cost of using flocculants?

6) Are all flocculants the same or similar?

7) I've heard of liquid and dry flocculants, what is the difference?

8) Why would an operator buy a water clarifier?

9) How do clarifier designs differ?

10) Which clarifier design will yield the thickest, most concentrated mud?

11) What do cyclones do for Aggregate Plants?

12) Is there a down side to installing cyclones?

13) Why do some people install Belt Presses?

14) How do I see what flocculants will do for me?

 

1) What are polymers or flocculants?
Polymer is a generic term that applies to large man made molecules that are built out of a repetitive chain of atoms. Flocculants are a type of polymer. The best performing flocculants in the aggregate industry is generally "Anionic Polyacrylamides". These flocculants employ an ionic attraction to form a bridge of many tiny clay particles into a large "snowflake" of clay that rapidly settles.

2) Are flocculants safe to put in my process water?
Yes, the dry Polyacrylamides are very safe. The EPA and local environmental officials will not prohibit their use. Some emulsion (liquid) flocculants are not as environmentally safe inasmuch as they contain surfactants and hydrocarbons. In potable water applications, a GRAS flocculant is used which contains very few free monomers.

3) Are flocculants necessary in Aggregate Operations?
No, but they are extremely useful. People have been discharging their dirty water into settling ponds for years and allowing the fines to settle naturally. Flocculants are necessary in thickeners, clarifiers, and belt presses.

4) Why would I want to add flocculants to my dirty water going to my settling ponds?
Flocculants cause all of the fine suspended material in your dirty water to immediately fall to the bottom of the first pond. This will generally happen within 30 feet of the pipe going to the pond. Only clean water will leave the first pond, hence you can shut down your second and third ponds. When you clean the pond with a backhoe or dragline, you will get a larger bucket of material with each scoop, and the mud you cast on the side of the pond will dry out more quickly, unlike un-flocculated mud.

5) What is the cost of using flocculants?
A good rule of thumb is that the flocculant cost is $0.06 per ton of material that you wash and sell. Hence if your plant washes 200 tph of sand and rock, you will spend $12.00 per hour on the chemical costs.

6) Are all flocculants the same or similar?
No. The only way to find a flocculant that will work well in your plant is by testing a good number of them against your dirty water. If a company manufactures 30 different flocculants (of different charges and different molecular weights), generally, only two or three of them will work well at your plant. Therefore, it is imperative to have a competent company test your water. They should test your dirty water against all of the flocculants manufactured by 3 or 4 different manufacturers to discover the best flocculant for your plant.

7) I've heard of liquid and dry flocculants, what is the difference?
The dry flocculants are made in a bead or powder form. They come in 50-pound bags or very large bags. The dry flocculants are white in color and look like "Dry Laundry Detergent". These flocculants are 99% active and need to be properly mixed with water to become active. It is best to mix them to a 1/4% solution to a 1/10 of 1% solution. In other words, a flocculant system would mix up about 6 pounds of the dry flocculant into a 300-gallon container of water. The liquid polymers are generally polyacrylamide emulsions. These flocculants are manufactured in a water/oil emulsion. This is necessary so that the flocculant does not "uncoil" or break apart before it is needed. The emulsion will not disperse or dissolve when mixed with water. Therefore the manufacture adds a hydrophilic surfactant (similar to dish soap) that inverts the emulsion. When you are ready to use the flocculant, you mix this emulsion at a 1% to 2% solution. The emulsions are 28% to 46% active, depending upon the product. Emulsions generally cost more to use. To pay $1.00 per pound for a 33% active emulsion is equivalent of paying $3.00 per pound for a 99% active dry flocculant.

8) Why would an operator buy a water clarifier?
A water clarifier eliminates the cleaning of a pond altogether. The dirty process water is pumped into the clarifier as flocculant is added. Very clean water overflows the top of the clarifier and can go right back to the wash plant for reuse. The underflow, or thickened mud is then pumped to a final resting place or an internment area where it remains as landfill. Therefore, no men or equipment is used to handle or re-handle the mud.

9) How do clarifier designs differ?
The older designs employed sloped plates to aid in settling. With the advent of flocculants sloped plates have been rendered obsolete. Some clarifiers use underwater drag chains to scrape the mud to one end, some use rakes to pull the mud to the center of the bottom of the tank. The design that removes the mud in the thickest consistency is generally the best.

10) Which clarifier design will yield the thickest, most concentrated mud?
Large circular thickeners will produce an underflow in the 20% to 25% solids range. Rectangular clarifiers will get the mud in the 25% to 35% range. A deep clarifier with a slow moving, high torque rake can remove the mud from 35% to 50% solids by weight.

11) What do cyclones do for Aggregate Plants?
Cyclones take the dirty water and spin the larger particles out. The larger the cyclone, the larger particles size it takes out. A 24" cone will take out plus 170 mesh material, a 9" cone will take out plus 325 mesh material. Cyclones require no chemicals, have low operating costs, and are generally good for producers. These are especially good devices if the producer can sell the product the flows from the bottom of the cyclones.

12) Is there a down side to installing cyclones?
Yes. If the cyclone removes all of the plus 325 mesh material, then the ponds will receive only minus 325 mesh material. The ponds now get only the finest of the slimes. The pond is now very difficult to clean without using flocculants.

13) Why do some people install Belt Presses?
Belt presses are expensive to buy, and very expensive to operate. There are producers who must, because of limited plant size, or severe environmental constraints, have their wash water fines pressed into a stackable consistency. Belt presses do perform well, but the cost again can be prohibitive. In 1999 one producer in the Seattle area spent $3.80 per ton of mud discharged from his two belt presses.

14) How do I see what flocculants will do for me?
You can contact Clearwater Industries or any reputable company and ask them to test your water. The Company's representative will run tests and should show you how the Chemical they selected performs against your dirty water.