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Polymer

I. POLYMER: DEFINITIONS

Tramfloc flocculants consist of various molecular weight anionic, nonionic and cationic polymer. They are used to increase the efficiency of settling, clarification, filtration and centrifugation operations. Flocculation means a process in which individual particles of a suspension form aggregates.

In the water treatment industry, the terms coagulation and flocculation imply different mechanisms.

COAGULATION

The colloidal particles are normally less than one micron in size and undergo Brownian motion. The energy of this motion is sufficient to prevent the particles from settling under gravity and particles remain suspended for long periods of time. Colloidal suspensions can be stable or unstable.

COAGULATION is the process in which destabilization is achieved by the addition of salts which reduce, neutralize or invert the electrical repulsion between particles. Most common coagulants are mineral salts: aluminium sulfate, ferric chloride, lime, calcium chloride. magnesium chloride.

FLOCCULATION

FLOCCULATION is used to describe the action of polymeric materials which form bridges between individual particles. Bridging occurs when segments of a polymer chain adsorb on different particles and help particles aggregate. Flocculants carry active groups with a charge which will counterbalance the charge of the particles. Flocculants adsorb on particles and cause destabilization either by bridging or charge neutralization.

An anionic flocculant will usually react against a positively charged suspension (positive zeta potential). That is the case of salts and metallic hydroxides.

A cationic flocculant will react against a negatively charged suspension (negative zeta potential) like silica or organic substances.

However the rule is not general. For example, anionic flocculants agglomerate clays which are electronegative.

Three groups of flocculants are currently used

     1.1 – MINERAL FLOCCULANTS

They are colloidal substances. Adsorption and charge neutralization play some part in the flocculation mechanism. They are:

     1.2- NATURAL FLOCCULANTS

They are water soluble anionic, cationic or nonionic polymers. Nonionic polymers adsorb on the suspended particles. The most common natural flocculants are:

     1.3- SYNTHETIC FLOCCULANTS

Polyacrylamides

The most common polymers are those based on polyacrylamide, which is a nonionic polymer. Their effect is due to bridging between particles by polymer chains.

Polymers can be given anionic character by copolymerizing acrylamide with acrylic acid. Cationic polymers are prepared by copolymerizing acrylamide with a cationic monomer. All available acrylamide based polymers have a specific amount of ionic monomer giving a certain degree of ionic character.

They have a specific average molecular weight (i.e. chain length) and a given molecular distribution.

For each suspension, a certain degree of anionic, cationic or nonionic character is beneficial. Usually, the intrinsic flocculating power increases with the molecular weight.

Polyacrylamides have the highest molecular weight among the synthesized industrial chemicals in the range of 10-20 millions. Other polymers display specific properties and are used under specific conditions.

They are mostly:

II. POLYMER: LABORATORY EVALUATION

2.1- HOW TO DISSOLVE POLYACRYLAMIDE FLOCCULANTS

Flocculant solutions are highly viscous and it is difficult to prepare highly concentrated solutions. Flocculant solutions tend to degrade after a while.

In the laboratory, 0.5 % is the recommended concentration of stock solution which is then stable for two weeks. A 0.1 % solution is stable for six days. Polyacrylamides can be dispersed and dissolved in cold water. The water should be gently stirred using a magnetic or propeller stirrer. The powder is added at a rate which gives a good dispersion of the flocculant particles in the water.

Each flocculant particle should be wetted separately to prevent agglomeration increasing the normal dissolution time of under two hours. High shear can deteriorate the polymer chains so avoid the use of high speed mixers, disintegrators or centrifugal pumps.

     2.2 – SETTLING TESTS: HIGH SOLID SUSPENSION

In the case of such suspensions the boundary line between solid phase and liquid phase is clear cut. The settling speed can be measured in a cylinder by observing the rate of change of solid phase height with time.

     METHOD

Repeat the procedure with all the flocculants under tests and select the best one. Repeat the procedure with different dosages of this flocculant and thus determine the optimum dose rate. The flocculation of concentrated suspensions is very sensitive to stirring and it is therefore vital to employ uniform stirring throughout.

     2.3- SETTLING TESTS: LOW SOLID SUSPENSION

In the case of low solid suspensions, we observe low settling speeds. The flocs are dispersed and it is necessary to induce a velocity to the suspended solids in order to obtain bigger flocs.

The obtained results are compared in terms of floc size and clarity of the supernatant.

The most practical device for such evaluations is a jar test. One proceeds as follows:

Then compare the different flocculants and the various dosages in terms of floc size supernatant clarification and settling speeds.

     2.4- FLOCCULATION TESTS AFTER COAGULATION

All suspensions which contain a high proportion of colloidal organic substances cannot be directly flocculated. They first have to be destabilized through addition of a di or trivalent metallic salt: lime, ferrous sulphate, ferric chloride, aluminum sulphate or sodium aluminate.

The use of synthetic flocculants makes coagulation less pH sensitive and makes possible the use of:

With each suspension, there is an optimum pH which has to be found in order to reach the optimum results. Evaluations are made with a jar test.

Firstly, the amount of coagulant necessary to destabilize the suspension has to be determined:

The beaker which gives first a clear supernatant contains the optimum amount of coagulant sufficient to destabilize the colloidal suspension. More than 200 ppm of coagulant may be required for optimum destabilization.

Secondly, the amount of flocculant necessary in order to obtain the desired settling speed is determined:

In many cases, the best result is obtained with a combination of lime and iron salts, especially in effluent treatment, when the optimum pH lies between 7 and 9.5.

     2.5- FILTRATION TESTS

          2.5.1- Buchner test

           2.5.2- Tests with test filter leaf

A leaf is mounted on a funnel which is connected to a vacuum pump with a pipe. The funnel is immersed in the suspension for a known time after which the thickness of the filter cake, the moisture content of the cake, the quality of the filtrate and the washing speed can be measured.

     2.6- CENTRIFUGING TESTS

The test on a laboratory centrifuge has only relative significance:

III. POLYMER: DOSAGE RATES

In most applications, the amount of flocculant necessary to obtain a good solid/liquid separation is very small. The average range of dosage is:

IV. POLYMER: PLANT APPLICATION TECHNIQUES

Industrial scale dissolution of flocculants requires a procedure which has to be adapted to the flocculant specifications:

A dissolution plant has the following components:

It is recommended that the flocculant is dissolved at the highest possible concentration and diluted after the metering pump.

     4.1- THE DISPERSER SYSTEMS

          4.1 .1 – Disperser for flocculant

The disperser operates on an aspiration principle. It facilitates dissolving powder flocculants.

Up to an amount of 5 kg per batch, water projections on the disperser can clog the inlet tube.

          4.1.2- Direct addition into the vortex of the dissolution tank

The flocculant is poured in the vortex of the dissolving tank either directly or through a funnel or through a vibrating device. This method is adapted to low concentrations of the flocculant solution. Above a certain concentration, the viscosity increase of the solution tends to prevent the dispersion of the powder when it reaches the solution.

          4.1.3- Addition of the powder in a fresh water cyclone

As above, an optimal dispersion is obtained with this process.

     4.2- DISSOLVING TANK

Flocculant solutions are non-corrosive. It is impossible to use mild steel or plastic equipment (polyester, glass fiber, polyethylene, polypropylene, PVC).

Agitation must be sufficient to keep the flocculant particles in suspension and not too violent in order to prevent mechanical degradation of the polymer.

     4.3- TRANSFER PUMPS

Positive displacement pumps can be used or low pressure centrifugal pumps. The dissolving tank can be put above the stock tank. The transfer pump can then be omitted.

     4.4- THE STOCK TANK

The stock tank will have a higher capacity than the make up tank. The solution in the tank need not be agitated.

V. POLYMER: INDUSTRIAL TREATMENT WITH FLOCCULANTS

The flocculant has to be used properly to ensure maximum efficiency. Its use depends on numerous physico-chemical factors which can alter the obtained result.

At the industrial stage, efficiency lies at 60 to 120 per cent of laboratory efficiency.

Most factors which will influence the final result are:

On most settling units, it is possible to check efficiency through sample observation at the inlet part of the unit.

In the case of low solid suspensions, sludge recirculation to the inlet of the settling unit improves the settling rate and the clarity of the supernatant.

When flocculant and coagulant are used together the following equipment improves the efficiency:

VI. POLYMER: AREAS OF APPLICATION

The tendency to use compact liquid solid separation equipment corresponds to the use of high efficiency polymers.

     6.1 – In the mineral industry

     6.2- In the chemical industry

At the clarification stage of the following processes: phosphoric acid, dicalcium phosphate, brine electrolysis, magnesia production, titanium dioxide.

     6.3- Industrial waste treatment

     6.4- Sewage and municipal waste

     6.5- Paper industries

Other applications are found in most water consuming industries:

AREAS OF APPLICATION FOR TRAMFLOC POLYMER

Adhesives
  • replacement of animal glues
  • gummed paper tapes and labels
anionic
anionic
Aluminum anodization
and surface treatment
  • chemical treatment of effluent
  • sludge treatment
anionic
anionic
Aluminum smelters
  • water recycling
anionic
Aluminum sulphate
  • impurity removal during process
anionic
Asbestos plate
  • improvement of filtration rates
anionic
nonionic
Borax production
  • process
anionic
or other
Brewing industry
  • effluent
cationic
Brine clarification
  • Ca and Mg removal
anionic
Centrifugation aid
Ceramic industry
  • effluent treatment
Chemical industry effluent
  • organic chemicals and inorganics
  • biological treatment sludge handling
  • physico-chemical treatment
cationic
anionic
Clay, china clay production
  • concentration
  • recycling of water
anionic
nonionic
Coagulant
  • under certain circumstances polymers replace or partially replace inorganic coagulants
cationic
nonionic
anionic
Coagulant aid
  • i.e. flocculant allowing reduction of alum use by half
slightly anionic or cationic
Coal washing
  • settling of coal slurries
  • settling of tailings
  • filtration of coal
  • filtration of concentrated tailings
  • centrifugation of tailings
anionic
anionic
anionic
anionic
nonionic
anionic
Copper mining
  • settling of fines in counter current decantation
  • thickening of concentrate
  • acid leaching
nonionicanionic
cationic
Cyanidation
  • gold mining
cationic
nonionic
anionic
Dairy and milk industry
  • biological treatment of effluent
  • sludge handling
cationic
Dicalcium phosphate
  • wet process
anionic
Dredging and land reclamation
  • hopper dredges (silt settling)
  • soil stabilization
all
Electroplating industry
  • treatment of hydroxides
anionic
Drying beds
  • reduction of drying time
cationic
Filter aid
  • sludge conditioning prior to filtration
all
Flotation aid
  • improvement of particle size prior to flotation
Food processing industry
  • wastewater
all
Hydraulic back-fill
  • in mining operations
Industrial raw water treatment
  • as a coagulant aid during treatment of river or underground water
  • dewatering of settled sludge
all
Iron ore
  • settling
  • filtration of fines
anionic
nonionic
Iron and steel industry
  • steel works blast furnace gas washing
  • clarification in steel rolling mills
  • clarification of pickling water
anionic
Latex and synthetic rubber effluent treatment
  • effluent treatment
all
Leaching
  • uranium mining
  • copper mining
  • other mineral processing
nonionic
anionic
cationic
Magnesia from seawater
  • sedimentation of magnesium hydroxide
anionic
Meat processing
  • wastewater treatment
all
Motor/automotive
  • wastewater treatment
anionic
Municipal sewage
  • primary sludge treatment
  • digested sludge treatment
  • drying beds
  • sieve belt presses
  • physico-chemical treatment
  • phosphate removal
cationic
Oil production
  • treatment of drilling water
  • secondary oil recovery
all
Petroleum refineries
  • effluent treatment
all
Pharmaceutical industry
  • effluent treatment
cationic
Phosphate ore
  • water recycling
anionic
Phosphoric acid wet process
  • acid clarification
  • filtration rate
  • reduction of P2O5 losses in gypsum
anionic
Potato industry
  • effluent treatment
Potable water
  • improvement of process efficiency
  • reduction of alum consumption
  • treatment of hydroxide sludges
anionic
cationic
nonionic
Potash mining
  • impurity removal in salt cold and hot process
Pulp and paper
  • treatment of incoming water
  • filler fiber retention aid
  • drainage aid
  • flotation aid on save-all
  • effluent treatment
Sand and gravel
  • recycling of water
  • clay removal
anionic
cationic
Settling aid
  • improvement of settling rates through use of flocculant
  • design of compact units
Sugar processing ·
  • cane or beet sugar juice clarification
  • recycling of water in beet sugar industry
Tailing disposal
  • in mining for environmental purposes or water economy
Tannery
  • effluent treatment
Textile industry
  • effluent treatment
Titanium dioxide manufacture
  • clarification of “Black liquors”
  • processing of titanium dioxide slurries
Zinc electrolysis
  • acid leach
  • neutral leach

 

POLYMER: EMULSIONS OF POLYACRYLAMIDES

I. POLYMER: POLYACRYLAMIDES

Polyacrylamides are high molecular weight water soluble polymers, being flocculants their main use. When mixed with water, they dissolve slowly giving a viscous solution, generally through a 60-120 minute process.

To increase the speed of dissolution it is possible to grind the polymer to a size of over 750 µm, particles of under 750 µm tend to agglomerate together when added to water, resulting in “fish eyes”. For quick dissolution time and “fish eyes” free solutions, it is possible to use polyacrylamides in emulsion form.

To produce these emulsions the manufacturing process is given below:

This emulsion, when mixed with water, will not disperse/dissolve.

Therefore, it is necessary to:

Tramfloc produces “self inverting” emulsions only. However, in certain cases as mentioned below, it is necessary to add some surfactant to the water.

II. POLYMER: CONCENTRATIONS OF INVERSION EMULSIONS IN WATER

To obtain a good inversion of the emulsion it is necessary for the surfactant to be present at its minimum effective concentration.

In water of standard hardness, the level has been determined to be 5 g/l to give a good inversion.

Standard emulsions contain between 28 and 46 % active content. Optimum dilution is between 50 and100 fold.

If this concentration is not achieved:

III. POLYMER: SHEAR DURING INVERSION

To obtain a good inversion it is necessary for each polymer particle to be dispersed separately in water, otherwise the particles will agglomerate.

To ensure efficient dispersion it is necessary to use high shear mixing at the point of emulsion water contact.

     Equipment used:

If the emulsion is efficiently dispersed, there is no need for further agitation to obtain dissolution, only a contact time of 3-15 minutes is imperative. In practice if the inversions are not perfect, a stirrer is necessary in the storage tank mixing for 3-15 minutes.

IV. POLYMER: FACTORS AFFECTING THE DISSOLUTION

Water quality affects inversion seriously.

Hard water : 30-40 grains of hardness gives poor dispersion with severe difficulties over 50 grains.

Calcium is reducing the efficiency of the surfactant, i.e., sea water and brines 30 g/l are at the limit of acceptance.

In such cases it is possible:

For cationic emulsions it is necessary to select a nonionic surfactant to avoid precipitation with the polymer.

V. POLYMER: STORAGE AND STORAGE TEMPERATURE

By nature, the emulsion is an unstable compound. The continuous phase, oil having a specific gravity of 0.85 and the water over 1.05. Over extended periods of time, this water phase has tendency to settle to the bottom.

Over a 6 month period at an average temperature of 200C, this settled phase is composed of agglomerates which are easily redispersed using mechanical or air agitation.

At higher temperatures, 350C, the effect is accelerated and becomes more difficult to redisperse. The shelf life is reduced to 3 months.

A similar effect is observed if the product is frozen, the emulsion remains pourable down to -100C, below this temperature the product becomes immobile, due to increased viscosity of the oil.

If the emulsion has been frozen

VI. POLYMER: EQUIPMENT FOR THE STORAGE AND DISSOLUTION OF EMULSIONS

     6.1 – Compatibility

The carrier oil is an aliphatic hydrocarbon containing less than 0.1 % aromatic.

Plastics, rubber and metal compatibility:

 

Natural Rubber Poor
Nitrile Good
Butyl Poor
Chloroprene Medium
Viton / Hyplon Good
Hard PVC Good
Plasticized PVC Poor
Above for fuel oil Good
High density Polyethylene Good
Low density Polyethylene Medium
Polypropylene Good
A B S Medium
Polyester Fiber Glass Good
Poly carbonate Good
Plexiglass Good
Polyamide Medium
Stainless Steel Good

 

Avoid the use of copper, cast iron, galvanized iron.

Polyethylene is used for the transport of emulsions but the oil has a tendency to dissolve in low density polyethylene decreasing the drum strength.

     6.2 – Emulsion Storage

Emulsion storage tanks are normally stainless steel (304), fiberglass or high density polyethylene.

To inhibit layering:

This method imports high shear which reduces emulsion stability

The tank has to be vertical with a conical bottom to help redispersion, it should also be fitted with an inspection cover to facilitate cleaning using high pressure water, once per year.

     6.3 – Pumps and filters

The emulsion if not properly mixed may contain some agglomerates which can plug filters and pumps. These agglomerates being water soluble can be pumped to the dissolution tank, except in paper applications.

Pump types

     6.4 – Filtration and storage of the finished products

When the dissolved emulsion is used in paper production it is normally filtered at 50 microns. The dissolved emulsion can be stored in polyethylene, polypropylene, PVC, fiberglass, stainless steel and coated steel. Iron and galvanized iron should be avoided, and all pipes should be plastic, copper or stainless steel.

Problems arising with the oil

VII. POLYMER: USE OF EMULSIONS IN LAB TRIALS

It is very difficult to weigh small amounts of emulsion. The use of a syringe is more general. The specific gravity of emulsions is between 1.02 /1.05. Glass syringes are used due to the incompatibility of plastics.

Following its use, it should be washed with mineral spirits or hot water.

As for polyacrylamide powders, the solutions are more stable at high concentrations, preferably 5 g/l active content and also preferably inverted at this concentration. This solution is diluted before use.

 

Polymer: Stability 5 g/liter

ANIONICS About 15 days
CATIONICS
> 1%
0.1%
3-4days
1day

 

VIII. POLYMER: DIFFERENCES BETWEEN POWDERS AND EMULSIONS

Given the same initial composition, powders and emulsions have varying efficiency differences depending on the application.

Generally:

IX. POLYMER: HEALTH AND SAFETY INFORMATION

The polymer contained in the emulsions has the same toxicity (very low) as powders.

The free acrylamide content of industrial emulsions is around 1,000 ppm (0.1 %).

For special uses it is possible to produce products with less than 500 ppm (0.05 %) of free acrylamide.

The oil is a dearomatized aliphatic hydrocarbon.

The flash point of the solvent, alone, is over 1050C, the emulsion has a flash point of over 1000C but when settled it decreases to 1000C.

The surfactants used have very low toxicity, obtained from esters of sorbitol and oxyethylated nonyl phenol.

The cationic emulsions are eye irritants. Emulsion spills should be absorbed with saw dust and burned. Any remaining should be washed with high pressure water.

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