Introduction to application technology of organic polymer flocculant
The company's flocculants are high molecular weight anionic, nonionic and cationic polymers. They are used to increase the efficiency of processes such as settling, clarification, filtration, and centrifugation. The flocculation process is the process by which many individual particles in the suspension form aggregates. In water treatment, coagulation and flocculation represent two different mechanisms.
Colloidal particles typically have a particle size of less than 1 micron and are constantly subjected to Brownian motion. The energy of the Brownian motion is sufficient to prevent the particles from settling under gravity, keeping them in suspension for a long time. The colloidal suspension can be either stable or unstable.
The coagulation process is to reduce, neutralize or reverse the electrical repulsion between the particles by adding salts. The most commonly used coagulants are inorganic salts such as aluminum sulfate, ferric chloride, lime, calcium chloride and magnesium chloride.
Flocculation is the process by which a polymer bridges between individual particles. "Bridge" means that polymer segments are adsorbed on different particles to promote particle aggregation. The charge of the active group band of the flocculant is offset by the charge of the particles. The flocculant is adsorbed on the particles and the particles are destabilized by bridging or electrical neutralization.
Anionic flocculants typically act with a positively charged suspension (positively moving electrical potential), such as certain salts and metal hydroxide suspensions.
Cationic flocculants typically function with a negatively charged suspension such as silica or an organic material.
But this rule is not entirely true, such as anionic flocculants can aggregate clay, while clay is negatively charged. There are three types of flocculants currently in use:
1.1 Inorganic flocculant
They are colloidal substances, and adsorption and electrical neutralization play a role in the flocculation process. They have:
* Active silica
* Some colloidal clays (such as bentonite)
* Some metal hydroxides with a polymer structure (aluminum hydroxide, iron hydroxide)
1.2 Natural flocculant
They are water soluble anionic, cationic or nonionic polymers. The nonionic polymer is adsorbed on the suspended particles. The most commonly used natural flocculants are:
* Starch derivatives: Most are pre-formed water-soluble gels. They are corn or potato starch. They may be natural starches, anionic oxidized starches, or amine treated cationic starches. The use of such materials in water treatment has been reduced, but it is still important in the paper industry.
* Glycans: Guar gum is usually used, and most of it is used in acidic media.
* Seaweed: It is an anionic type used to treat drinking water.
1.3 synthetic flocculant
The most commonly used is a polyacrylamide-based polymer which is anionic and acts by bridging between the particles through the polymer chain.
Such polymers can be negatively charged by copolymerization of acrylamide with acrylic acid. With acrylamide and a cationic monomer polymer, a cationic polymer can be produced.
An acrylamide-based polymer, such as containing a certain amount of ionic monomer, exhibits a certain amount of ionic character.
Moreover, these polymers have a certain average molecular weight (i.e., chain length) and a certain molecular weight distribution.
For each suspension, an anionic, cationic or nonionic polymer is most suitable as a flocculant.
Generally, the flocculation ability increases as the molecular weight increases.
Polyacrylamide has the highest molecular weight in synthetic industrial chemicals, ranging from 10 million to 20 million. Other polymers have their special properties and are used as flocculants under certain special conditions. Most of them are:
* Polyethylene polyamine
2. Indoor evaluation
2.1 How to dissolve organic polymer flocculant
The flocculant solution has a high viscosity, so it is difficult to formulate a solution having a high concentration. The flocculant solution degrades over time.
It is recommended in the laboratory to formulate a 0.5% solution for storage with a stabilization period of about two weeks. The 0.1% solution has a shelf life of 6 days. The organic polymer flocculant can be dispersed and dissolved in cold water. The water is moderately agitated with a magnetic or blade agitator and the flocculant powder is added. The rate of addition is controlled so that the powder particles are well dispersed in the water and each particle should be wetted with water to avoid agglomeration. If there is agglomeration, it will increase the dissolution time. The dissolution time is usually within 2 hours. High-speed shearing degrades the polymer chain, so high-speed mixers, shredders, or centrifugal pumps should be avoided.
2.2 Settlement test: high solids suspension
The boundary between the solid phase and the liquid phase in this suspension is clear, so the rate of change of the solid phase height with time can be observed in the measuring cylinder to determine the sedimentation velocity.
* Inject a suspension into a one liter cylinder.
* From the 1g/L flocculant solution, pipet the required amount of flocculant and add it to the suspension cylinder.
* Close the measuring cylinder mouth and back and forth the measuring cylinder four times; or use a metal rod with a holed hole (the diameter of the circular sheet is similar to the inner diameter of the measuring cylinder), and move the circular sheet up and down four times from the top of the measuring cylinder to the bottom to Stir the suspension in the cylinder.
* Measure the solid phase height at regular intervals.
* Draw the sedimentation curve of the solid phase height as a function of time.
All the flocculants to be tested were tested according to the above procedure, and the best one was selected. Repeat the above steps for the selected flocculant for different dosing amounts to determine the optimum dosing amount. The flocculation process of the concentrated suspension is extremely sensitive to agitation, so it is critical to use a uniform mixing method from start to finish.
2.3 Settlement test: low solids suspension
In the case of low solids suspensions, we only observed very slow settling rates. The floc is dispersed, so it is necessary to give the suspended solid a rate of induction, making it a larger floc. The test results were compared by the size of the floc and the clarity of the supernatant.
The most practical instrument for doing this evaluation is a jar-test. The practice is as follows:
* Take 5 beakers and add 1 liter of suspension to each beaker.
* The flocculant was added at a high speed rotation of the blade (100 rpm) and stirred for 10 seconds to allow the flocculant to be sufficiently dispersed in the suspension.
* Stir for another 3 minutes at 40 rpm. Then, the floc size, the clarity of the supernatant and the sedimentation speed were compared to compare different flocculants and different dosages.
2.4 Flocculation test after adding coagulant
Suspens containing a high percentage of colloidal organic matter cannot be directly flocculated, and it is necessary to first add a divalent or trivalent metal salt such as lime, ferrous sulfate, ferric chloride, aluminum sulfate or sodium aluminate to destabilize the colloidal particles. The use of synthetic flocculants makes the coagulation process less sensitive to pH, which allows:
* Calcium salt for pH 4 to 14
* Iron salt for pH 4 to 13
* Aluminum salt for pH 4.5 to 10
However, it is necessary to find the optimum pH for each suspension in order to achieve the best results. The pH can be selected with a multi-head mixer.
First, it is necessary to determine the amount of coagulant used to destabilize the suspension:
* Prepare a 1% coagulant solution and add 10, 30, 50, 100, 200 ppm coagulant.
* When the acidity is too high, it is necessary to add alkali to adjust the pH back to 6.
* Stir at 200 rpm for 1 minute.
* Usually add 2 PPM of an anionic degree of synthetic flocculant and stir at 50 rpm for 2 minutes.
The beaker of the supernatant is first present and contains the optimum amount of coagulant to destabilize the colloidal suspension. For best instability, a coagulant of more than 200 PPM may be required.
Then determine the amount of flocculant required to achieve the desired settling velocity:
* Fill the suspension in 5 beakers. The coagulant was added in the amount of the coagulant previously determined and stirred at 100 rpm for 2 minutes.
* Compare flocculant efficiency with floc size, supernatant clarity and settling velocity.
In many cases, the combination of lime and iron salts gives the best results, especially when the pH of the discharged wastewater is in the optimum range of 7 to 9.5.
2.5 Filtration test
2.5.1 Brinell funnel test
* Mix the flocculant into the suspension with a glass rod.
* Pour the flocculant-containing suspension into a Buchner funnel and filter at a certain pressure.
* Determine the amount of filtrate at regular intervals (30 seconds or 1 minute).
* At this point, a clean water rinse test can be performed to measure the amount of clean water passing through the filter cake over a certain period of time (30 seconds or 60 seconds).
2.5.2 Filter membrane test
The filter membrane was placed in a funnel that was connected to a vacuum pump using a tube. The funnel was immersed in the suspension for a known period of time and then the filter cake thickness, filter cake moisture, filtrate quality and rinsing rate were measured.
2.6 Centrifugal test
Laboratory centrifuge tests can only be used as a relative reference.
* Put a flocculant-containing suspension in the centrifuge tube of the centrifuge. The flocculant has various dosages.
* Centrifuge at 1000g for 2 minutes.
* Determine the amount of sediment in each tube and the clarity of the supernatant.
3. Dosing amount
In most cases, the amount of flocculation required to achieve good solid/liquid separation is small. The average range of dosing is:
* 0.5 - 3 grams per cubic meter of diluted inorganic suspension,
* Concentrated inorganic suspension per cubic meter, 2 - 20 grams,
* Filtration or centrifugation of inorganic slurry: 25 - 300 grams of flocculant per ton of dry solids.
* Clarification of organic wastewater: 10 - 200ppm coagulant, plus 0.25 - 2 ppm flocculant,
* After adding coagulant, filter or centrifuge organic flesh: add 1-5 kg per ton of dry solids.
* Paper machine to increase retention rate: 50-250 grams per ton of finished paper,
* Increase solution viscosity: add 4 - 10 grams per liter.
4. Field application technology
When industrializing a scale flocculant, a method suitable for the characteristics of the flocculant is required:
* Concentration: The flocculant solution is still very thick when it is thinner
* Avoid severe cutting when mixing
* If the flocculant particles are not well dispersed, they will agglomerate, which will not dissolve easily.
* If the flocculant is scattered on the ground and encounters water, it will be very slippery.
The dissolution device consists of the following components:
* Dispersion system to ensure that the powder is fully wetted without agglomeration
* Dissolving tank
* Transfer pump
* Storage tank
* Metering pump and dilution system
It is recommended to use the highest possible concentration when dissolving the flocculant, and then dilute it by metering the pump.
4.1 Decentralized system
4.1.1 Disperser for flocculant
The disperser uses a pumping principle that facilitates the dissolution of the powdered flocculant.
Disperse up to 5 kg each time. Water splashing onto the disperser blocks the flocculant suction tube.
4.1.2 Add directly to the stirring vortex of the dissolution tank. Or add it with a funnel or with a vibrating device.
This method is suitable for low concentration flocculant solutions. Above a certain concentration, the increase in viscosity of the solution does not allow the powder to disperse well when it contacts the solution.
4.1.3 Add powder to the vortex formed by clean water
As with the above method, this method can achieve the best dispersion effect.
4.2 Dissolving tank
The flocculant solution is not corrosive and does not require the use of low carbon steel or plastic equipment (polyester, fiberglass, polyethylene, polypropylene, polyvinyl chloride).
Stirring is sufficient to keep the flocculant particles in suspension; at the same time not too intense to avoid mechanical degradation of the polymer.
4.3 Transfer pump
A positive displacement pump or a low pressure centrifugal pump can be used. If the dissolving tank is placed on the tank, the transfer pump can be omitted.
4.4 storage tank
The tank is larger than the tank. The solution in the tank does not need to be stirred.
5. Flocculant for industrial treatment
Flocculants must be used reasonably to ensure maximum efficiency. It depends on many physico-chemical factors that change the effect of use.
The efficiency of industrial applications is between 60% and 120% of the experimental efficiency.
Most of the factors that affect the final effect are:
* The position of the injection point must have vortex to fully disperse the flocculant, but not to break the floc;
* Multi-point dosing often improves the contact of the flocculant with the suspension system;
* Dilute solutions often make the effect better.
Most settling devices can be sampled at the inlet of the device and the flocculation efficiency is checked by observing the sample.
In the case of a low solids suspension, the recirculation of the deposit into the inlet of the settling device improves the settling velocity and the clarity of the supernatant.
When using flocculants and coagulants at the same time, the following devices can improve their efficiency:
* A coagulating tank with medium speed stirring, the residence time in the tank is about 5 minutes;
* A flocculation tank that can be used as part of a settling tank as a place where chemical reactions take place. When a vacuum filtration or centrifuge is used, the flocculant is added from the inlet line.
6. Application areas
The current trend is to use a compact solid-liquid separation device that requires a highly efficient polymer.
6.1 In the mining industry
* Ore leaching (uranium, zinc, gold, bauxite, copper, etc.)
* Processing after flotation
* Dispose of tailings to prevent pollution and reuse water resources
6.2 Chemical Industry
A clarification process used in the following production processes: phosphoric acid, dicalcium phosphate, electrolytic brine, magnesium oxide, titanium dioxide.
6.3 Industrial wastewater treatment
* Blast furnace gas washing
* Surface treatment
* Refinery wastewater
6.4 Urban domestic sewage and waste
* Perform physico-chemical treatment
* Before sludge dewatering
6.5 Paper Industry
* Retain solid particles and fillers
* Increase the water filtration rate
In most industries that use water, there are also the following uses:
* Treatment of unpurified water
* Drinking water treatment
* Remove carbonate
* Sugar industry
* tertiary oil recovery
Municipal sewage treatment