FLOCCULANTSانواع الفلوكات

Flocculants

INTRODUCTION
The agent named flocculant is used to purify water by gathering and adhering suspensions and impurities in the process of water treatment
Flocculation includes coagulation and coacervation

It’s basic principle includes electric double layer compression and theory of
absorption. Flocculation technology is a high efficient, economical and simple treatment technology.

Choosing suitable flocculant is the key. According to difference of chemical
components, flocculants can be divided into inorganic, organic and microorganism.

INORGANIC FLOCCULANTS
Inorganic flocculants fall into inorganic small molecular flocculants and inorganic high molecular flocculants by different molecular weight.
Inorganic small molecular flocculants were used less and less in recent years because of much consumption, and waste and poor effect

But
inorganic small molecular flocculants are used in certain ratio due to low price, abundant supply of goods and convenient transportation and reservation.
On the contrary,
inorganic high molecular flocculants are used more and more due to its excellence of high molecular weight, multi-nuclus complex ion structure, strong ability of adheresion, flocculation and charge neutralization, immediate sedimentation and short consumption compared with inorganic small molecular flocculants

Inorganic small molecular flocculants
Inorganic small molecular flocculants include aluminum sulphate, aluminum chloride, ferric sulphate, ferric chloride and so on..
They are directly put in establishment of water treatment by dry method or wet method.

Hydrolyzing polymerization takes place after being put in establishment of water treatment

Aluminum sulphate was developed firstly by America.
It has been one of the most important inorganic flocculants up to now. But when small molecular flocculants were used in water treatment, there are many shortcoming such as:-

expensive cost
slow speed of congregation
small floc
relatively serious causticity,
and poor effect in some occasions and so on.

Inorganic high molecular flocculants
Traditionally inorganic high molecular flocculants include poly aluminum, poly iron, polysilisic acid and compound inorganic high molecular flocculants.
But according to
what kind of charge colloid has, inorganic high molecular flocculants can fall into cation type, anion type and some compound series

. In the past ten or more years, kinds of inorganic high molecular flocculants have gradually developed into series

There are scores of patent about inorganic high molecular flocculants; some of them still are produced

There are many kinds of inorganic high molecular flocculants:-
Cation type includes PAC, PAS, PAP, PFS and PFP.
Anion type include AS, PS. Inorganic compound type include PAFC, PFSS, PASS, PFSC, PFCS PASI, PFSI, PAFSI, PAFP, SCPAFC

Cationic inorganic high molecular flocculants
This kind of flocculants mainly include polymer of aluminum salt and iron salt. Multihydroxyl complex ion exists in these flocculants.

In inorganic high molecular flocculants, polyaluminium chloride is much produced and used widely Compared with aluminum sulphate, ferrous sulfate, ferric chloride and etc.,

polyaluminium chloride has less dosage, higher efficiency, bigger flocculating constituent quicker subsiding and better purifying effect,.
Variety of PH is small before treatment and aftertreatment. Causticity is also less to device
. Therefore,
polyaluminium chloride used widely. It is used in high turbid water, low temperature and turbid water, colored water and industrial waste water

. What is noteworthiness is poison of aluminum, especially positive aluminum
. At the same time, not perfect method of prepare polyaluminium leads to mote of hydrolyzed aluminum existing in water, which limits usage of polyaluminium

. By improving condition of coagulating and prolonging time of low speed
coagulating, content of aluminum in water can be reduced.

basicity is higher, polymerization degree is higher, charge and surface area of forming hydroxyl complex are more, effect of flocculating is also better

. So controlling basicity is a key when polyiron is prepared
synthesized PFCS by using (KIO3+KI) as catalyzer, Cl2 and O2
oxidation FeSO4. 5mg/L PFCS was used to treat water from (pH 7.9, turbidity 52.1, whole iron 0.20 mg/L)
,
turbidity of treat water was up to drinking standard(<5mg/L),
whole iron in treated water is less than 0.3mg/L.
pH reduced not too.
Secondary pollution did not take place.

Anion inorganic high molecular flocculants
Positive silicic acid is used widely all over the world as a kind of anion inorganic high
molecular flocculants. It was often prepared with sodium silicate and acid. Due to uneasy
controlling of gelating time and PH, production is not stored for long time. Therefore, it was
not researched and used in China. In recent years, many people in China have done much
research, positive silicic acid and modified products (PSAM and PSAA). Shortcoming of
positive silicic acid was got over. Specific method [9] is to add certain bivalent or trivalent
metallic ion to control polymerization degree of positive silcic acid, density of charge and
enhance effect of flocculating when positive silicic acid was prepared.
Positive poly silicic acid is a kind of anion inorganic high molecular flocculants.
Because poly silicic acid is easily gelled, its stability is too poor to be used widely. Song Lǚ
etc[10] used composite copolymerization process to prepare PFSS. Orthogonal test was used to
research effect of Fe3+ /SiO2 mole ratio, pH, content of addition on coagulating. Compared
with PAC, PFSS has better effect of purification.

Complex flocculants
Because others ion, especially high charge ion, was add in inorganic complex high molecular flocculants, its polymerization degree and ability of electrical
neutralization increased much.

Its ability of flocculating is better than poly silicic acid or alone poly metallic
ion. Compare with poly silicic acid, it has better stability and ability of electrical
neutralization. Its shortcoming is to need good skill in preparation and high cost.

For example,
PAFCS [11] has multi-nucleus polyiron, polyaluminium, chlorion, and sulfate radical. It has ability of polyaluminium and polyiron.
Its effective content of aluminum (Al2O3+Fe2O3) is more than 22%, degree of alkalization 65%-85%. Hygroscopicity of product is small

PAFCS
has better effect in oily wastewater and dyeing waste water than PAC. It has strong ability of decolor and is suitable to industrial water treatment.

Strictly speaking, inorganic and organic complex flocculants should be used multiply. It is different from above inorganic complex high molecular flocculants

Real complex inorganic and organic high molecular flocculants seldom were reported
Used inorganic high molecular flocculants include aluminum, iron, poly silicic acid and etc..
Used inorganic high molecular flocculants include PAM, PDMDAAC and etc.

These material are combined to chose four typical organic high molecular flocculants and researched possibility of combined using between polyaluminium, cation and anion organic high molecular flocculants

Reciprocity between polyaluminium and organic high molecular flocculants was researched. The results showed that effect of flocculating can be improved only when added content of polyaluminium and cation organic high molecular flocculants was up to a certain value

But addition of anion organic high molecular flocculants improved
highly absorptive ability of polyaluminium.

ORGANIC HIGH MOLECULAR FLOCCULANTS
Organic high molecular flocculants include natural organic high molecular and
synthesized organic high molecular.

Natural organic high molecular flocculants include starch, alga and etc.. Synthesized organic high molecular flocculants are all water-soluble polymer

Group with charge exist in polymer. Therefore it was also called polyelctronic
medium. Polyelctronic medium include anion type, cation type, amphoterism type and nonion type.

Addition quantity in water of organic high molecular flocculants is few. Its flocculating speed is quick, and a little affected by concomitant salt, medium and environmental temperature

Hydrophile groups, such as -COO-，-NH-，-SO3-，-OH-, exist in polymer.
Polymer has chain, ring and much structure, which are beneficial to flocculating effect.

Compared with PAM, it has stronger flocculating ability, more stable molecular chain, wider using field and easier cation reaction triethylamine, formaldehyde and hydrochloric acid were added to graft copolymerization

. A kind of cation high molecular flocculant FNQE, was produced.
, This flocculant has special molecular structure and relatively high molecular weight
. Its effect on kaoline turbid liquid was quite good
. For city waste water, good effect was got when addition quantity was up to 10mg/L.
Additionally, removal ratio of turbidity and chroma was above 90%.
Because most organic high molecular flocculants themselves or their hydrolysate
degradation products are toxic and high cost, their development and using are limited and flocculants
are
(1) High efficiency,
(2) Easier to be degraded, no poison,
(3) No secondary pollution,
(4) Wide serviceable range, and
(5) Better ability of removing turbidity and decoloring.

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