Polyaluminum chloride, referred to as polyaluminum, abbreviated as PAC in English, has a structure between AlCl3 and Al(OH)3 and is a water-soluble inorganic polymer. The appearance form is divided into two types: liquid and solid. The solid form has different appearance colors due to different contents, and is generally white or yellow powder.

Polyaluminum chloride has adsorption, coagulation, precipitation and other properties. Polyaluminum chloride can be applied to raw water of various turbidities and has a wide pH range. It is one of the most widely used water treatment agents in the fields of drinking water and industrial sewage. .
Polyaluminum chloride (PAC) is an emerging water purification material and inorganic polymer coagulant, referred to as polyaluminum. It is a water-soluble inorganic polymer between AlCl3 and Al(OH)3. Polyaluminum chloride has a high charge polymer ring chain, which has a high degree of electrical neutralization and bridging effect on colloids and particles in water. , and can powerfully remove slightly toxic substances and heavy metal ions, with stable properties. Due to the bridging effect of hydroxide ions and the polymerization of multivalent anions, polyaluminum chloride is an inorganic polymer water treatment agent with a larger relative molecular weight and higher charge.
Physical and chemical properties Polyaluminum chloride has properties such as adsorption, cohesion, and precipitation, but its stability is poor. Polyaluminum chloride has good spray drying stability, adapts to wide waters, has fast hydrolysis speed, and has strong adsorption capacity, forming large alum flowers and dense mass. It has the advantages of fast precipitation, low effluent turbidity, and good dehydration performance. Spray drying products can ensure safety, reduce water accidents, and is very safe and reliable for residents' drinking water. Therefore, polyaluminum chloride is also referred to as high-efficiency polyaluminum chloride, high-efficiency PAC or high-efficiency grade spray-drying polyaluminum chloride. Polyaluminum chloride is suitable for raw water of various turbidities and has a wide pH range.
Concentration ratio method: When solid polyaluminum chloride is diluted into liquid, first of all, according to the raw water conditions, a small test should be done before use to obtain the optimal dosage. When using polyaluminum chloride in production, just mix and dissolve according to the mass ratio of polyaluminum chloride solid:water = 1:9-1:15. Solutions with an alumina content of less than 1% are easy to hydrolyze, which will reduce the use effect. If the concentration is too high, it will be difficult to add evenly. After the agent is put into use, if there are few alum flowers and large residual turbidity in the sedimentation tank, the dosage is too small; if there are large alum flowers and turned up in the sedimentation tank, the dosage is too large and should be adjusted appropriately.
Color type Polyaluminum chloride generally has white, yellow, and tan colors. Polyaluminium chloride of different colors also has great differences in application and production technology. Solid polyaluminum chloride with an aluminum trioxide content within the standard range of 27% to 30% is mostly khaki, to yellow, or light yellow solid powder. These types of polyaluminum chloride have relatively good water solubility. During the dissolution process, they are accompanied by physical and chemical changes such as electrochemistry, coagulation, adsorption, and precipitation. The flocs form quickly and thickly, with high activity, rapid precipitation, and resistance to high turbidity water. The purification effect is obvious.
White polyaluminum chloride is called high-purity iron-free white polyaluminum chloride, or food-grade white polyaluminum chloride. Compared with other polyaluminum chlorides, it is the highest quality product. The main raw material is high-quality hydroxide. Aluminum powder, hydrochloric acid, the production process used is the most advanced technology spray drying method. White polyaluminum chloride is used in drinking water treatment, papermaking sizing agent, sugar decolorizing and clarifying agent, tanning, medicine, cosmetics, precision casting and water treatment and other fields.
The raw materials of yellow polyaluminum chloride are calcium aluminate powder, hydrochloric acid, and bauxite. It is mainly used in sewage treatment and drinking water treatment. The raw materials used in drinking water treatment are aluminum hydroxide powder, hydrochloric acid, and a small amount of aluminum. Calcium acid powder adopts plate and frame filter press process or spray drying process. Yellow polyaluminium chloride is generally produced by drum drying or spray tower drying, and is available in two solid forms: flakes and powder.
The raw materials of brown polyaluminum chloride are calcium aluminate powder, hydrochloric acid, bauxite and iron powder. The production process uses a drum drying method, which is generally used in sewage treatment. Because iron powder is added to it, the color is tan. The more iron powder is added, the darker the color. If the iron powder exceeds a certain amount, the color will be darker at some point. Known as polyaluminum ferric chloride, it has excellent results in sewage treatment.

Advantages Polyaluminum chloride (PAC) has the advantages of good spray drying stability, adaptability to wide water areas, fast hydrolysis speed, strong adsorption capacity, large alum flowers, fast precipitation with dense mass, low effluent turbidity, and good dehydration performance. Under the same water quality, the dosage of spray-drying polyaluminum chloride is reduced. Especially when the water quality is poor, the dosage of spray-drying products can be reduced by half compared with drum-drying polyaluminum chloride, which not only reduces workers' fatigue Labor intensity, and more importantly, reducing water production costs for users. In addition, spray drying products can ensure safety, reduce water accidents, and is very safe and reliable for residents' drinking water. Polyaluminum chloride is processed through a spray drying process. Therefore, it can also be called high-efficiency spray-drying polyaluminum chloride.

Principle of water purification: The structure of the double electric layer of compressed double electric layer micelles determines the maximum concentration of counter ions on the surface of the colloidal particles. The greater the distance outward from the surface of the colloidal particles, the lower the concentration of counter ions, which ultimately matches the ions in the solution. Concentrations are equal. When an electrolyte is added to the solution to increase the ion concentration in the solution, the thickness of the diffusion layer decreases.
When two colloidal particles approach each other, since the thickness of the diffusion layer decreases and the ξ potential decreases, their mutual repulsive force decreases. That is, the repulsive force between colloidal particles with a high ion concentration in the solution is smaller than that with a low ion concentration. The suction between colloidal particles is not affected by the composition of the water phase, but due to diffusion thinning, the distance between them when they collide is reduced, so the suction between them becomes greater. It can be seen that the combined force of repulsion and attraction changes from repulsion to suction (repulsion potential energy disappears), and the colloidal particles can quickly condense. This mechanism can better explain the sedimentation phenomenon in harbors. When fresh water enters seawater, salts increase, the ion concentration increases, and the stability of colloidal particles carried by fresh water decreases. Therefore, clay and other colloidal particles are easy to deposit in harbors.
According to this mechanism, when the external electrolyte in the solution exceeds the critical condensation concentration for condensation by a large amount, no more excess counterions will enter the diffusion layer, and it is impossible for the colloidal particles to change their sign and re-stabilize the colloidal particles. This mechanism uses simple electrostatic phenomena to explain the effect of electrolytes on the destabilization of colloidal particles, but it does not consider the effects of other properties (such as adsorption) in the destabilization process, so it cannot explain other complex destabilization phenomena, such as trivalent If the amount of aluminum salt and iron salt used as coagulant is too much, the coagulation effect will decrease or even stabilize again. For example, polymers or high-molecular organic matter with the same electric number as the colloidal particles may have good coagulation effect: the isoelectric state should It has the best coagulation effect, but in production practice, when the potential is greater than zero, the coagulation effect is often the least.

In fact, the phenomenon of destabilizing colloidal particles by adding coagulant in an aqueous solution involves the interaction between colloidal particles and coagulant, colloidal particles and aqueous solution, and coagulant and aqueous solution. It is a comprehensive phenomenon.

Adsorption and charge neutralization means that the particle surface has a strong adsorption effect on the parts with opposite signs of ions, colloidal particles or chain ion molecules with different charges, because this adsorption neutralizes part of its charge. , reducing the electrostatic repulsion, so it is easy to get close to other particles and adsorb each other. At this time, electrostatic attraction is often the main aspect of these effects, but in many cases, other effects exceed electrostatic attraction.

For example, Na and dodecyl ammonium ions (C12H25NH) were used to remove the turbidity caused by the negatively charged silver iodide solution. It was found that the destabilizing ability of the same monovalent organic amine ion was much greater than that of Na. Excessive addition of Na Adding water will not cause the colloidal particles to restabilize, but this is not the case for organic amine ions. When the addition exceeds a certain amount, the colloidal particles can restabilize, indicating that the colloidal particles have absorbed too many counter ions, causing the original negative charge to change into a negative charge. positive charge. When the dosage of aluminum salt and iron salt is high, re-stabilization phenomenon will also occur and the charge will change. The above phenomenon is very suitable to be explained by the mechanism of adsorption and electroneutralization.

Adsorption and bridging The mechanism of adsorption and bridging mainly refers to the adsorption and bridging of polymer substances and colloidal particles. It can also be understood that two large colloid particles of the same size are connected together because there is a colloid particle of different sizes in the middle. Polymer flocculants have a linear structure, and they have chemical groups that can interact with certain parts of the colloidal particle surface. When the polymer comes into contact with the colloidal particles, the groups can produce special reactions with the colloidal particle surface and adsorb each other. The rest of the polymer molecule stretches in the solution and can adsorb to another colloid with vacancies on its surface, so that the polymer acts as a bridge connection. If there are few colloidal particles and the stretched part of the polymer cannot adhere to the second colloidal particle, then sooner or later this extended part will be adsorbed to other parts by the original colloidal particles, and the polymer will not be able to play a bridging role, and the colloidal particles will In a stable state again. When the dosage of polymer flocculant is too large, the surface of the colloidal particles will be saturated and cause re-stabilization. If the colloidal particles that have been bridged and flocculated are subjected to vigorous and long-term stirring, the bridging polymer may detach from the surface of another colloidal particle and roll back to the original surface of the colloidal particle, resulting in a restabilized state.

The adsorption of polymers on the surface of colloidal particles comes from various physical and chemical effects, such as van der Waals attraction, electrostatic attraction, hydrogen bonds, coordination bonds, etc., and depends on the characteristics of the chemical structures of the polymer and the surface of the colloidal particles. This mechanism can explain the phenomenon that non-ionic or ionic polymer flocculants with the same electric signal can achieve good flocculation effects.

Sediment trapping mechanism

When metal salts (such as aluminum sulfate or ferric chloride) or metal oxides and hydroxides (such as lime) are used as coagulants, when the dosage is large enough to rapidly precipitate metal hydroxides (such as Al(OH)3, Fe(OH)3, Mg(OH)2] or metal carbonates (such as CaCO3), the colloidal particles in the water can be trapped by these precipitates when they are formed. When the precipitate is positively charged (Al(OH)3 and Fe(OH)3 in the neutral and acidic pH range), the precipitation rate can be accelerated by the presence of anions in the solution, such as sulfate ions. In addition, the colloidal particles in the water themselves can serve as the core for the formation of these metal oxyoxide precipitates, so the optimal dosage of coagulant is inversely proportional to the concentration of the substance to be removed, that is, the more colloidal particles, the less the dosage of metal coagulant.

Salinity

The basicity of polyaluminum chloride is a relatively important indicator in polyaluminum, especially for drinking water grade polyaluminum products. This standard is one of the important indicators for controlling the production of polyaluminum production lines. The lower the salinity, the higher the price. Each buyer can operate according to the actual situation of the factory. In addition, polyaluminum chloride products produced with different raw materials and processed by different processes also have different salt bases, which requires manufacturers to make adjustments. Improving the salt base of polyaluminum chloride products can greatly improve the economic benefits of production and use. The salinity is increased from 65% to 92%, the cost of production raw materials can be reduced by 20%, and the use cost can be reduced by 40%.

The flocculation effect of poly (poly) aluminum chloride is as follows:
a. Strong electrical neutralization of colloidal substances in water.
b. The hydrolyzate has excellent bridging adsorption effect on suspended solids in water.
c. Selective adsorption of dissolved substances.

Polyaluminum chloride is an inorganic polymer coagulant. It is an inorganic polymer water treatment agent with larger molecular weight and higher charge produced due to the bridging effect of hydroxide ions and the polymerization of multivalent anions.) It is mainly determined by the working principle of the pressure atomizer.

performance
a. The purified water quality is better than aluminum sulfate flocculant, and the water purification cost is 15-30% lower than it.
b. The flocs form quickly and settle quickly, and have greater processing capacity than traditional products such as aluminum sulfate.
c. The alkalinity of the consumed water is lower than that of various inorganic flocculants, so no or less alkali agent can be added.
d. It can condense if the source water pH range is 5.0-9.0.
e. Low corrosiveness and good operating conditions.
f. Solubility is better than aluminum sulfate.
g. The salt content in the treated water increases less, which is beneficial to ion exchange treatment and high-purity water production.

h. Its adaptability to source water temperature is better than inorganic flocculants such as aluminum sulfate.

Form classification Polyaluminum chloride forms are divided into two types
a. Liquid polyaluminium chloride is in an undried form, does not need to be diluted, is easy to load and unload, and is relatively cheap. The disadvantage is that transportation requires the use of ton barrels or tankers, and the unit transportation cost increases (each ton of solid is equivalent to 2-3 tons of liquid), more suitable for users at close range.
b. Solid polyaluminum chloride is the dried form of liquid polyaluminum chloride. It has the advantage of convenient transportation. The disadvantage is that it needs to be diluted when used, which increases the working intensity.

Process classification
a. Drum-type poly(aluminum chloride) has a general aluminum content and high water-insoluble matter, and is mostly used for sewage treatment.
b. Plate and frame type poly(poly)aluminum chloride has high aluminum content and low water-insoluble matter, and is used for municipal sewage treatment and domestic sewage treatment.

c. Spray-drying poly(poly)aluminum chloride has high aluminum content, low water-insoluble matter, and fast dissolution speed. It is used for drinking water and higher standard water treatment.

Purpose ⒈City water supply and drainage purification: river water, reservoir water, groundwater.
⒉Industrial water purification.
⒊Urban sewage treatment.
⒋The recovery of useful substances in industrial wastewater and waste residues, the promotion of sedimentation of coal powder in coal washing wastewater, and the recovery of starch in the starch manufacturing industry.
⒌Various industrial wastewater treatment: printing and dyeing wastewater, leather wastewater, fluorine-containing wastewater, heavy metal wastewater, oily wastewater, papermaking wastewater, coal washing wastewater, mining wastewater, brewing wastewater, metallurgical wastewater, meat processing wastewater, sewage treatment.
⒍Paper sizing.
⒎Refining sugar liquid.
⒏Casting.
⒐The cloth is anti-wrinkle.
⒑Catalyst carrier.
⒒Pharmaceutical refining ⒓Cement rapid setting.

⒔Cosmetic raw materials.

Instructions for use: Dissolve the solid product into liquid by adding water at a ratio of 1:3, then add 10-30 times of water to dilute it to the required concentration before use. The optimal pH value for adding is 3.5-5.0. Choosing the optimal pH value for adding can maximize the benefits of coagulation. The dosage can be determined according to the different turbidity of the raw water. Generally, when the turbidity of the raw water is 100-500mg/L, the dosage per thousand tons is 10-20kg. When the turbidity of the raw water is high, the dosage can be appropriately increased; when the turbidity is low, the dosage can be appropriately reduced.
For rural use, the agent can be put into a water tank, stir evenly, let it stand, and the supernatant can be used. Add about 1 gram of this agent per 50 kilograms. If this agent is used in combination with the polymer flocculant produced by the company, the effect will be even better. For dosing, the anionic polyacrylamide or cationic polyacrylamide produced by the company can be dissolved together with PAC to form a composite flocculant before use, or PAC can be added to the treated water first to form an agglomerate, and then the anionic polyacrylamide produced by the company can be added to adsorb and bridge. form large flocs.
The dosage of polyaluminum chloride in different water qualities:
1. In low turbidity water, dilute the solid polyaluminum chloride product with tap water in a ratio of 1:3 (weight ratio) and stir until completely dissolved.
2. In domestic and production sewage, add about 30g of polyaluminum chloride product per ton of sewage first. Then add the diluted polyacrylamide product. (If the effect is not obvious, please reduce or increase the product dosage as appropriate.)
3. In the wastewater treatment of paper mills, the proportion of low turbidity water should be used. If the effect is not obvious, it can be added as appropriate.
4. When the turbidity of raw water is 100-500mg/L, the dosage is 5-10mg, that is, the dosage per thousand tons of water is 5-10kg. Before use, it is best to conduct a small test based on the water quality characteristics to select the best value, and then Put into use.


Packaging of polyaluminum chloride and precautions: ⒈ Solid polyaluminum chloride, external plastic woven bag, with plastic film set inside, net weight of each bag is 25kg, can also be modified according to user requirements; liquid polyaluminum chloride uses ton barrels and liquid bag container.
2. It is prohibited to mix, transport and store this product with toxic substances. The product should be stored indoors in a dry, ventilated and cool place and protected from moisture.
⒊Be careful when loading and unloading. The storage period of solid products is one year.
Application areas ⒈Water purification treatment: domestic water, industrial water;
⒉Urban sewage treatment;
⒊The treatment of industrial wastewater, sewage, sludge and the recovery of certain residues in sewage, etc.;
⒋For some industrial sewage that is difficult to treat, PAC can be used as the matrix, mixed with other agents, and formulated into a composite PAC, which can achieve surprising results in treating sewage.


Coagulation process ⒈Condensation stage: It is a process in which the chemical liquid is injected into the coagulation tank and the raw water quickly coagulates to form fine alum flowers in a very short time. At this time, the water body becomes more turbid, which requires the water flow to produce intense turbulence. In the beaker experiment, it is advisable to stir quickly (250-300 rpm) for 10-30 seconds, generally no more than 2 minutes.
⒉Flocculation stage: It is the process in which alum flowers grow and become thicker. It requires an appropriate degree of turbulence and sufficient residence time (10-15 minutes). In the later stage, a large number of alum flowers can be observed to gather and sink slowly, forming a clear layer on the surface. In the beaker experiment, stir at 150 rpm for about 6 minutes and then at 60 rpm for about 4 minutes until it becomes suspended.
⒊Settling stage: It is a floc settling process carried out in a settling tank, which requires slow water flow. In order to improve efficiency, an inclined tube (plate) settling tank is generally used (it is best to use air flotation to separate flocs), and a large number of thick alum flowers are used. Blocked by the inclined tube (plate) wall and deposited at the bottom of the pool, the water in the upper layer is clear water. The remaining alum flowers with small particle size and low density slowly descend while continuing to collide with each other and form a large amount. In the later stage, the residual turbidity is basically gone. Change. For the beaker experiment, it is recommended to stir slowly at 20-30 rpm for 5 minutes, then let it sit for 10 minutes, and measure the residual turbidity.
⒋Strengthening filtration mainly involves the rational selection of filter layer structure and filter aids to improve the removal rate of the filter. It is an important measure to improve water quality.
⒌This product is used in the treatment of environmental protection and industrial wastewater. The usage method is roughly the same as that in water production plants. It is very effective in treating raw water with high color, high COD and BOD, supplemented by auxiliaries.
⒍Enterprises that use chemical coagulation method do not need to make major modifications to the original equipment. They only need to add a dissolved alum tank to use this product.
⒎This product must be stored in a dry, moisture-proof, and heat-proof place.

⒏This product must be dissolved before use. Dissolution equipment and dosing facilities should be made of corrosion-resistant materials.

Sewage treatment Sewage contains colloidal particles (colloidal particles formed by dust, humus, cellulose, etc. and water in the water), which cannot be removed by natural precipitation. Some chemicals (flocculants) must be added to decoagulate, aggregate, and flocculate the colloidal particles that are difficult to precipitate into larger particles in the water to precipitate.
In order to determine the process parameters of the water flocculation process, such as the type and dosage of flocculant, the pH value of water, temperature and the order of adding various chemicals, simulation experiments are generally done. Under the conditions of a certain water temperature and controlling the appropriate stirring intensity and time, different flocculants and dosages are used to adjust the pH value of water of different colors to see the flocculation effect.
ASTM "Water Flocculation, Flocculation Cup and Jar Test Method" is an advanced water treatment method, which includes three steps: rapid stirring, slow stirring and static settling. The added flocculant is quickly dispersed through rapid stirring and comes into contact with the colloidal particles in the water, and the colloidal particles begin to aggregate to form flocs. Through slow stirring, the microflocs further contact each other and grow into larger particles. After stopping stirring, the formed colloidal aggregates naturally settle to the bottom by gravity.
This method is suitable for determining the process parameters of the water flocculation process, including: flocculant type, dosage, water pH, temperature, and the order of adding various chemicals.

By measuring the turbidity and color of the water sample in the beaker experiment, the degree of colloid dehydration and aggregation can be known.

process
1) The rotation speed of the multi-position mixer can be infinitely adjusted between 20-150r/min. The stirring blade is made of lightweight corrosion-resistant material, the size of the blade is 60mm*40mm*2mm, and the shape is rectangular. There should be a lighting device at the base or inside of the multi-position mixer through which the formation of flakes can be observed. The size of the multi-position stirrer and stirring blade should be 3/4 of the beaker when immersed in water.
2) The size of the beaker and the beaker are the same in appearance and the volume is not less than 1500mL.
Steps
1) According to the number of beakers set on the multi-position stirrer, measure 100mL of each water sample into the beaker, and position the beaker. Then put the stirring paddle into the water. The axis of the paddle should be offset from the center of the beaker, and there should be at least a 6.4mm gap between the paddle and the wall of the beaker. Record the temperature at which the experiment begins.
2) Put the flocculant into the test tube of the reagent rack. When administering the medicine, dilute the medicine in each test tube to 10 mL with water. If the dosage of one of the drugs is greater than 10mL. The other test tubes should also be filled with water until the volume is the same as the amount used. When adding suspension chemicals, shake the chemicals well before adding.
3) Start the multi-position stirrer, stir quickly at 120r/min, add the medicine to each beaker at the same time according to the predetermined dosage, and stir for 1 minute.
4) Reduce the speed to 20-40r/min to keep the particles in the beaker evenly suspended. Stir slowly for about 20 minutes. Record the time of initial flake formation.
5) After completing the slow stirring, lift the stirring blade out of the water, observe the settlement of the floc, and record the time it takes for most of the floc to settle. However, in special cases where sedimentation is affected by convection, the recorded sedimentation time should be approximately the same time when the number of unsettled flocs moving upward and downward is approximately the same.
6) After 15 minutes of sedimentation, record the thickness of the flakes at the bottom of the beaker. Use a pipette to absorb the water sample from 1/2 of the clear water in the beaker, and measure the burning degree, color and pH value of the water sample.