According to their chemical composition, flocculants can be generally divided into two categories: inorganic flocculants and organic flocculants. Inorganic flocculants include inorganic flocculants and inorganic polymer flocculants, while organic flocculants include synthetic organic polymer flocculants, natural organic polymer flocculants, and microbial flocculants.
Inorganic flocculants include aluminum sulfate, aluminum chloride, ferric sulfate, ferric chloride, etc. Of these, aluminum sulfate was first developed by the United States and has been used to date as an important inorganic flocculant. Commonly used aluminum salts are aluminum sulfate AL2(SO4)3.18H2O and alum AL2(SO4)3.K2SO4.24H2O. The other category is iron salts are ferric trichloride hydrate FeCL3.6H2O. Ferrous sulfate hydrate FeSO4.7H2O and iron sulfate. Simple inorganic polymer flocculant, this type of inorganic polymer flocculant is mainly a polymer of aluminum and iron salts, such as polymeric aluminum chloride (PAC), polymeric aluminum sulfate (PAS), polymeric ferric chloride (PFC), and polymeric ferric sulfate (PFS). The fundamental reason why inorganic polymer flocculants are more effective than other inorganic flocculants is that they provide a large number of complexions and can strongly adsorb colloidal particles through adsorption, bridging, and cross-linking, thus causing the colloids to coalesce. It also undergoes physicochemical changes, neutralizes the charge on the surface of colloidal particles and suspended matter, reduces the δ potential, changes the colloidal particles from being repulsive to being absorbent, destroys the stability of the colloidal mass, causes the colloidal particles to collide with each other, thus forming a flocculent coagulation precipitate, the surface area of the precipitate can reach (200 to 1000) m2/g, with great adsorption capacity.
Extremely soluble in water, aluminum sulfate cannot be dissolved in pure sulphuric acid (only coexist), in sulphuric acid solution, and sulphuric acid co-dissolve in water, so the solubility of aluminum sulfate in sulphuric acid is the solubility of aluminum sulfate in water.
The precipitation at room temperature contains 18 molecules of crystalline water: aluminum sulfate 18 water and is mostly produced as aluminum sulfate 18 water. Containing 51.3% anhydrous aluminum sulfate does not autolyze (dissolve in its own crystalline water) even at 100°C. It is not easily weathered and loses its crystalline water, is relatively stable, loses water when heated, and decomposes at high temperatures into aluminum oxide and sulfur oxides. Decomposition to aluminum oxide, sulfur trioxide, sulfur dioxide, and water vapor begins at 770°C. Soluble in water, acids, and bases, insoluble in ethanol. The aqueous solution is acidic. Hydrolysis produces aluminum hydroxide. Aqueous solution boiling for a long time can produce basic aluminum sulfate. The industrial product is off-white in flakes, granules, or lumps, with a light greenish tinge due to the low iron salt content and a yellowish surface due to the low iron salt's oxidation. The coarse product is off-white with a fine crystalline structure and porous. Non-toxic, the dust can irritate the eyes.
1. Used as a paper sizing agent in the paper industry to enhance paper's water-resistance and impermeability.
2. Dissolved in water can make the fine particles and natural gum particles in water coalesce into large flocs, which can be removed from the water, so it is used as a coagulant for water supply and wastewater.
3. Used as turbid water purifying agent, also used as precipitating agent, color fixing agent, filling agent, etc. In cosmetics, it is used as a raw material for anti-sweat cosmetics (astringent).
4. in the fire-fighting industry, baking soda and foaming agents form a foam fire extinguishing agent.
5. Analytical reagent, mordant, tanning agent, oil decolorizer, wood preservative.
6. stabilizer for albumen's pasteurization (including liquid or frozen whole eggs, egg whites, or egg yolks).
7. as a raw material for the manufacture of artificial stones and high-grade ammonium alum, other aluminates
8. In the fuel industry, it is used as a precipitant in the production of chrome yellow and color precipitating dyes and as a color fixing and filling agent.
1. Polysilicate flocculant (PSAA) is a new type of inorganic polymer flocculant with more robust oil removal capability for the treatment of thick oil produced water in oil fields due to its easy preparation method, comprehensive source of raw materials, and low cost, so it has excellent development value and broad application prospects.
2. Polyferric Silicate Sulphate (PFSS) flocculant, it is found that highly polymerized silicic acid together with metal ions can produce a good coagulation effect. The metal ions are introduced into the polysilicicic acid, and the coagulant obtained has an average molecular mass of up to 2×10, which may partially replace organic synthetic polymer flocculants in water treatment.
3. Polyphosphoric ferric chloride (PPFC) in the high-valent anion and Fe3+ has a strong affinity for the hydrolysis solution of Fe3+, and can participate in the complexation reaction of Fe3+ and can bridge between iron atoms to form a multinuclear complex; the electric neutralization and adsorption bridging effect of the negatively charged diatomaceous earth colloid in water is enhanced, while the volume and density of alumina increase due to the participation of the impact of flocculation Improve.
4. Polyphosphoric aluminum chloride (PPAC) is also based on the substantial agglomeration effect of phosphate on polymeric aluminum (PAC), the introduction of an appropriate amount of phosphate in polymeric aluminum, through the agglomeration effect of phosphate, making PPAC produces a new class of highly charged multinuclear intermediate complexes with phosphate.
5. Polysilicate iron (PSF) is not only suitable for low temperature and low turbidity water. Then the flocculation effect of iron sulfate has obvious superiority, such as less dosage, feeding a wide range, but alum formation time is also short and coarse form easy to settle, can shorten the residence time of water samples in the treatment system, etc., thus improving the processing capacity of the system, the pH value of the treated water does not affect.
Inorganic flocculants' advantages are that they are economical and straightforward to use; however, the dosage is large, the flocculation effect is low, and there are disadvantages of high cost and corrosiveness. Organic polymer flocculants are a new type of wastewater treatment agent developed in the late 1960s. Compared with traditional flocculants, it can increase efficiency exponentially, and the price is lower, so it has gradually become the mainstream of the trend of pharmaceuticals. Together with the stable quality of products, organic polymeric flocculants' production has accounted for 30% to 60% of the total output of flocculants. Variety classification
1. The most widely used flocculant in domestic water treatment is the synthetic polyacrylamide series, mainly divided into anionic, cationic, non-ionic, and amphoteric types. Polyacrylamide, often abbreviated as PAM (also abbreviated as PHP in the past), is essentially a polymer product produced by the copolymerization of a certain proportion of acrylamide sodium acrylate and is available in a range of products. Polyacrylamide can be divided into ultra-high relative molecular weight polyacrylamide, high relative molecular weight polyacrylamide, medium relative molecular weight polyacrylamide, and low relative molecular weight polyacrylamide according to the size of the molecular weight. Ultra-high relative molecular weight polyacrylamide is mainly used in oilfield tertiary oil recovery. High relative molecular weight polyacrylamide is primarily used as a flocculant; medium relative molecular weight polyacrylamide is mainly used as a dry strength agent for paper; low relative molecular weight polyacrylamide is used mainly as a dispersant. Polyacrylamide is a high molecular polymer. They specialize in the treatment of complex wastewater and sludge dewatering. (Cationic polyacrylamide is generally used for sludge dewatering.) It is widely used to treat sludge in municipal wastewater and the paper printing and dyeing industry. The molecular formula of acrylamide is CH2 = CH-CONH2 The molecular formula of sodium acrylate is CH2 = CH-COONa.
2. Non-ionic organic polymer flocculants Non-ionic organic polymer flocculants are mainly polyacrylamides. The polymerization of acrylamide obtains it.
3. Anionic organic polymer flocculants Polymers such as polyacrylic acid, sodium polyacrylate, calcium polyacrylate, and alkali-hydrolysates of polyacrylamide. Copolymers such as styrene sulfonates, lignosulfonates, acrylic acid, and methacrylic acid.
4. Cationic organic polymer flocculants Quaternised polyacrylamide cations are all obtained by hydroxymethylation and quaternization of -NH2, divided into polyacrylamide cationic and cationic acrylamide polymerization. Polyacrylamide (PAM) first reacts with an aqueous formaldehyde solution. The amide group is partially hydroxymethylated, followed by a reaction with secondary amines for alkylation and hydrochloric acid or amination reagents to make tertiary amine quaternization. Under alkaline conditions, the acrylamide is first reacted with formaldehyde in an aqueous solution, then with dimethylamine, cooled, and quaternities with hydrochloric acid. The product is concentrated by evaporation and filtered to give the quaternity acrylamide monomer.
5. Cationic derivatives of polyacrylamide These products are obtained mainly by co-polymerization of acrylamide with cationic monomers.
6. Amphoteric polyacrylamide polymers Amphoteric polyacrylamide flocculants with carboxyl and amine methyl groups are synthesized by Mannitz reaction using partially hydrolyzed polyacrylamide with appropriate formaldehyde amounts dimethylamine.
7. Acrylamide graft copolymers Because starch is cheap and plentiful, it is also a polymer compound with hydrophilic rigid chains used as a skeleton and grafted with flexible polyacrylamide branched chains.
The flocculation and precipitation method uses inorganic flocculants (e.g., aluminum sulfate) and organic anionic flocculants, ammonium polyacrylate (PAM), to prepare an aqueous solution to be added to the wastewater, which produces a compressed double electric layer, causing the suspended particles in the wastewater to lose their stability and the particles to increase in size as the colloidal particles merge, forming flocs and alum flowers. The flocs grow to a particular volume and then precipitate out of the aqueous phase under gravity, thus removing a large amount of suspended matter from the wastewater and thus achieving the effect of water treatment. To improve the separation effect, coagulants can be added at the right time and in the right amount. The treated effluent can meet the discharge standard in terms of color, chromium content, and suspended matter content and can be discharged or used as re-injection water for artificial water injection oil recovery. Flocculant is currently the most widely used agent in sewage treatment; the flocculation process is an indispensable key link in the sewage treatment process. Its chemical composition can be divided into inorganic salt flocculants, organic polymer flocculants, and microbial flocculants. Users can make a reasonable choice according to the nature of the wastewater. Combining flocculants and wastewater treatment equipment makes wastewater treatment more effective and solves wastewater treatment problems effectively. The application of flocculants in wastewater treatment effectively enhances the wastewater treatment rate and makes wastewater treatment effective. At present, the agent is widely used in the wastewater treatment of various industries to ensure that the water quality after treatment by large wastewater treatment equipment can meet the national discharge standards, effectively preventing the deterioration of the current state of water pollution and ensuring the sustainable development of the ecological environment. Organic polymer flocculant in the treatment of oil refinery wastewater to join the flocculant makes the water and impurities quickly and more thoroughly separated from each other.
The choice of flocculant in wastewater treatment depends on the characteristics of the wastewater in the specific industry and where the flocculant is added, and its purpose. Generally, when choosing an inorganic flocculant, the composition and PH of the wastewater are taken into consideration, and the most suitable one is selected (iron, aluminum or iron-aluminum salt, silicon-aluminum salt, silicon-iron salt, etc.).
When choosing an organic flocculant (e.g., polyacrylamide PAM), it depends mainly on whether anionic, cationic, or non-ionic polyacrylamide is used. Anionic polyacrylamides are generally divided into weak, medium, and robust anions depending on hydrolysis. Cationic polyacrylamide selection is generally used in municipal wastewater treatment plants for medium and strong cationic polyacrylamide, paper and dyeing plants for sludge dewatering, and pharmaceutical wastewater for strong cationic polyacrylamide. Non-ionic polyacrylamides are mainly used under weakly acidic conditions, while printing and dyeing plants use more non-ionic PAM. The selection of all these flocculants is based on tests to determine the approximate dosage, observe the flocculation and sedimentation rate, calculate the cost of treatment and select an economical and suitable flocculating agent. From the charged type of flocculant, charge density, molecular weight, molecular structure analysis about the classification of flocculants, to understand its profile, a clearer understanding of the application of various flocculants, the choice of sewage flocculants have a clearer understanding.
1、The charged type of flocculant The type of flocculant charged is selected according to the type of particles in the sewage. In general, the choice of flocculant chargeability should follow the following. Principle. Use negatively charged flocculants to capture inorganic particles Use of positively charged flocculants to capture organic particles Usually, it is only through experimental methods that what can compare the exact type of flocculant charged
2、Density of charge distribution of flocculants (ionicity) The density of the charged charge distribution of a flocculant indicates the amount of positive or negative charge required to obtain the best flocculation effect with the least amount of flocculant used. The charge distribution density of municipal sludge is usually a function of the sludge's organic content, which is usually related to the volatile content. The higher the volatile content, the higher the charge of the flocculant required.
3. Molecular weight The choice of molecular weight depends on the type of equipment used for the dewatering process, while the molecular weight also indicates the length of the polymer chain. For centrifuge type dewatering equipment: the higher the molecular weight of the polymer, the better, as the flocs will be subjected to a large shear force during the centrifugal dewatering process. For filtered dewatering equipment: a flocculant with a low to medium molecular weight can meet the requirements and at the same time provide a good water consideration function.
4、Molecular structure The choice of the molecular structure of the flocculant depends on the required dewatering performance. The molecular structure of cationic flocculants is divided into the linear structure, branched structure, cross-linked network structure. From the above aspects, we can easily find that there is a great regularity in selecting flocculants. As long as we observe the rules with care summarizers in our daily applications, we will find that each type of wastewater has its own specific flocculant or flocculants that can meet the flocculant dewatering conditions of sewage treatment. If you have any other questions, please contact us for professional answers!
The optimum set-up program is as follows. 1.first laboratory analysis, if the suspended material solid-liquid phase potential is negative (generally negative), you can use PAC + CPAM program. 2.Determine the dosage of PAC: It is also necessary to do a dosage test in the test chamber to determine the dosage and turbidity removal effect curve when PAC is used alone. 3.If the amount of PAC added under the best effect when used alone is A, the actual amount used could be set at 1/4 - 1/3 of the A value, while the remaining work is left to CPAM to complete. 4. the laboratory to determine the proportion of PAC and CPAM additions: is PAC's use in the case of 1/3 of the value of A, to determine how much CPAM is needed to bridge the cohesive effect of PAC the most appropriate. Through the experiment, determine the ratio of PAC and CPAM added to use.
There are many factors affecting the flocculation effect, mainly the type of flocculant, concentration, dosage, mixing condition during coagulation treatment, ph value, temperature and its changes, etc. Different countermeasures should be adopted according to the specific situation.
1. Type and dosage of flocculant: Different flocculants should be used for different wastewater. The amount of flocculant affects the flocculation effect to a large extent. Excess or deficiency will lead to the dispersion and stabilisation of the soluble particles, so the optimum dosage should be determined by experiment.
2. Influence of mixing and reaction time: After a certain amount of flocculant has been added to the wastewater, the flocculant must first be diffused rapidly and evenly into the water. After the flocculant is fully dissolved, the resulting colloid will form many tiny alum flowers in contact with the original colloid and suspended matter in the water, a process also known as mixing. This process is also known as mixing. The mixing process requires intense turbulence in the water flow, so that the agent is fully mixed with the water within a relatively short period of time, generally requiring a few seconds to 2 minutes of mixing time.
3. ph, alkalinity impact: ph has a great impact on flocculant operation, so when wastewater is flocculated, full attention must be paid to its effective ph range. Organic polymer flocculants have less strict restrictions on the ph value, but when the ph value is small, it has a greater impact on the flocculation effect of flocculants. Inorganic flocculants are more sensitive to the ph value of the wastewater, and as the hydrolysis reaction of flocculants continuously produces hydrogen ions, the hydrolysis reaction should be kept fully carried out.
4 Influence of temperature: The water temperature also has an influence on the flocculation effect, the hydrolysis reaction of inorganic flocculants is a heat absorption reaction, the low water temperature is not conducive to the hydrolysis of flocculants, the viscosity of water is also related to the water temperature, if the water temperature is low, the viscosity of water is large, resulting in the weakening of the Brownian motion of water molecules, which is not conducive to the destabilization and flocculation of pollutant colloids in water, and thus the formation of flocculants is not easy. Therefore, the amount of flocculant used in winter is more than in summer. The increase in temperature is conducive to the collision between colloids and coalescence, but temperatures above 90 degrees Celsius tend to cause the flocculant to age or decompose to produce insoluble substances, which in turn reduces the flocculation effect.