How to Choose Polyaluminum Chloride in water Treatment?What are the most important quality indicators of PAC (polyaluminum chloride)?

How to Choose Polyaluminum Chloride in water Treatment?What are the most important quality indicators of PAC (polyaluminum chloride)?

The production of polyaluminium chloride in the Chinese market has formed industrial norms, and the industry has formulated unified quality standards.What are the quality evaluation criteria for purchasing polyaluminum chloride from China? In the following article from Zoomri company you will get the answer.

PAC (polyaluminium chloride) is a highly efficient flocculant, water purifier and phosphorus removal agent. Due to its outstanding characteristics and advantages and wide application range, the dosage can be reduced by more than 30% compared with traditional water purifiers, and the cost can be saved by more than 40%. It has become a recognized excellent water purifier. In addition, polyaluminium chloride can also be used to purify drinking water and tap water supply and other special water quality treatments, such as iron removal, cadmium removal, fluoride removal, radioactive pollutant removal, floating oil removal, etc.

• Characteristics and uses of PAC

1. PAC (polyaluminum chloride) features:

Polyaluminum chloride is between ALCL3 and ALNCL6-NLm] where m represents the degree of polymerization and n represents the neutrality of the PAC product. Polyaluminum chloride, abbreviated as PAC, is also commonly known as polyaluminum chloride or coagulant. Its color is yellow or light yellow, dark brown, or dark gray resinous solid. This product has strong bridging adsorption properties. During the hydrolysis process, physical and chemical processes such as aggregation, adsorption and precipitation occur.

2. PAC (polyaluminium chloride) applications:

(1) flocculation

Polyaluminum chloride is mainly used for urban water supply and drainage purification: river water, reservoir water, groundwater; industrial water supply purification, urban sewage treatment, recovery of useful substances in industrial wastewater and waste residues, promotion of sedimentation of coal powder in coal washing wastewater, starch manufacturing industry Recycling of medium starch; Polyaluminum chloride can purify various industrial wastewaters, such as: 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, etc.; Polyaluminium chloride for wastewater treatment: paper sizing, sugar liquid refining, casting molding, cloth anti-wrinkle, catalyst carrier, pharmaceutical refined cement rapid setting, cosmetic raw materials.

(2) Phosphorus removal

Chemical agents are added to the sewage to cause phosphate ions in the water to generate insoluble salts, which form flocs and then separate from the water, thereby removing the phosphorus contained in the water. In the specific reaction process, there are two main reaction processes. First, trivalent aluminum ions react with phosphate to precipitate, and the precipitated compound is AlPO4.

Al3++PO43-→AlPO4 ↓

Secondly, trivalent aluminum ions can undergo a hydrolysis reaction. In this process, there will be positive charges and the presence of mononuclear hydroxyl complexes and polynuclear hydroxyl complexes. After a series of effects such as van der Waals forces and net trapping, A relatively ideal precipitation effect can be achieved, thus meeting the requirements for chemical phosphorus removal.

• Quality indicators of PAC

The quality indicators of PAC (polyaluminum chloride) produced in China are mainly divided into two categories, for industrial water treatment (GB/T 22627-2022) and for drinking water treatment (GB 15892-2020). Please see the below table for specific indicator differences.

• What are the three most important quality indicators of PAC (polyaluminum chloride)?

The basicity, PH value, and alumina content that determine the quality of polyaluminum chloride are the three most important quality indicators of polyaluminum chloride.

1. Salinity.

The degree of hydroxylation or alkalization of a certain form in PAC (polyaluminum chloride) is called the degree of salinity or alkalization. Generally expressed by the molar ratio of aluminum hydroxyl B=[OH]/[Al] percentage. The salinity is one of the most important indicators of polyaluminum chloride and is closely related to the flocculation effect. The higher the concentration of raw water and the higher the salinity, the better the flocculation effect. To sum up, in the range of raw water turbidity of 86~10000 mg/L, the optimal basicity of polyaluminum chloride is 409~853, and many other characteristics of polyaluminum chloride are related to the basicity.

2. pH value.

The pH of PAC (polyaluminium chloride) solution is also an important indicator. It represents the number of free OH- in the solution. The pH value of polyaluminum chloride generally increases with the increase in salinity, but for liquids of different compositions, there is no corresponding relationship between the pH value and the salinity. Liquids with the same salinity concentration have different pH values when their concentrations are different.

3. Alumina content.

The alumina content in PAC (polyaluminium chloride) is a measure of the active ingredients of the product. It has a certain relationship with the relative density of the solution. Generally speaking, the greater the relative density, the higher the alumina content. The viscosity of polyaluminum chloride is related to the alumina content, and the viscosity increases as the alumina content increases. Under the same conditions and the same concentration of alumina, the viscosity of polyaluminum chloride is lower than that of aluminum sulfate, which is more convenient for transportation and use.

• The difference between PAC colors

Due to different production processes and raw materials, the color of the produced PAC is also somewhat different. Generally, there are six colors of polyaluminum chloride: white, light yellow, golden yellow, brown.

1. White polyaluminum chloride

The latest research and development of a new type of water purification material, professionally used in food, drinking water, urban water supply, precision manufacturing water purification, paper industry, medicine, sugar liquid refining, cosmetic additives, daily chemical industry, etc. It has a very wide range of applications , the purity is very high, and the price is also the highest.

2. Light yellow polyaluminum chloride

The mid-to-high series products, second only to white polyaluminum chloride, are mainly used for drinking water treatment. The content restrictions on heavy metals are relatively strict, especially the drinking water grade polyaluminum chloride products we produce. The water treated with it is clarified. There is no precipitation, the AL2O3 content is around 30 (±0.5), the powder is fine, the particles are uniform, the flocculation effect is good, the purification is efficient and stable, the dosage is small, and the cost is low. It is a dedicated water treatment flocculant for major water plants with long-term cooperation.

3. Golden yellow polyaluminum chloride

It is currently the most widely used polyaluminum chloride on the market. It is an efficient flocculant used for sewage treatment and has good flocculation effect. Therefore, it is the best choice for industrial water supply, industrial wastewater, industrial water circulation and urban sewage treatment.

4. Brown polyaluminium chloride

It is a water treatment product produced according to the special requirements of individual customers for water treatment. The iron content is higher than other polyaluminum chloride product series, so the color is darker than golden yellow. It is highly effective in sewage with low temperature, low turbidity and high algae, and is mainly used for the treatment of drinking water, urban water supply, industrial water supply purification, etc.

• Dissolution Guidelines for Polyaluminium Chloride

1. Depending on the quality of the raw water, a small test should be done before use to determine the optimal dosage. Before use, dissolve the solid polyaluminum chloride PAC to a concentration of 5~10% so that it can take effect quickly. When dissolved, First use tap water at room temperature to dissolve PAC. Increasing the temperature can slightly promote dissolution. However, the water temperature should not exceed 50 degrees. Too high water temperature will cause thermal degradation of PAC, thus affecting the use effect. Add water to half the volume of the dissolution tank. Turn on the stirrer to stir. While stirring the water in the dissolving tank, slowly add the solids to make them evenly dispersed in the water. Do not let them form lumps, which can easily block the pipes and cause waste.

2. PAC requires sufficient stirring time to fully dissolve the powder. Insufficient mixing or agglomeration of PAC may affect other performance, and may even cause sedimentation, block pipelines and dosing pumps. Add water to the designated location and adjust to a specific concentration. Continue stirring until PAM is completely dissolved. Since strong stirring for a long time will reduce its performance, it is recommended that the mixer be dissolved at a speed of about 20-200 rpm. If the prepared aqueous solution is left for a long time, its performance will gradually decrease depending on the water quality. Therefore, after the aqueous solution is prepared, please use it within two days.

• Factors affecting the use of PAC

1. pH value of water

The pH value of water has a great influence on the use effect of inorganic flocculants. The pH value is related to the type, dosage and coagulation sedimentation effect of flocculants. H+ and OH- in the water participate in the hydrolysis reaction of the flocculant. Therefore, the pH value strongly affects the hydrolysis rate of the flocculant, the existence form and performance of the hydrolyzate.

Take the aluminum salt that achieves coagulation by generating Al(OH)3 charged colloid as an example. When the pH value is <4, Al3+ cannot be hydrolyzed into Al(OH)3 in large amounts and mainly exists in the form of Al3+ ions. The coagulation effect is extremely good. Difference. When the pH value is between 6.5 and 7.5, Al3+ hydrolyzes and polymerizes into Al(OH)3 neutral colloid with a high degree of polymerization, and the coagulation effect is better. After the pH value exceeds 8, Al3+ is hydrolyzed into AlO2-, and the coagulation effect becomes very poor again.

The alkalinity of water has a buffering effect on the pH value. When the alkalinity is insufficient, lime and other chemicals should be added to supplement it. When the pH of the water is high, acid needs to be added to adjust the pH to neutral. In contrast, polymer flocculants are less affected by pH value.

2. Water temperature

Water temperature affects the hydrolysis rate of flocculant and the rate and structure of alum flower formation. The hydrolysis of coagulation is mostly an endothermic reaction. When the water temperature is low, the hydrolysis rate is slow and incomplete.

At low temperatures, the viscosity of water is high, Brownian motion is weakened, and the number of collisions between colloid particles of the flocculant and impurity particles in the water is reduced. At the same time, the shear force of the water increases, hindering the mutual adhesion of the coagulated flocs; therefore, despite the increase Regardless of the amount of flocculant added, the formation of floc is still very slow, and the structure is loose and the particles are fine, making it difficult to remove.

Low temperature has little effect on polymer flocculants. However, it should be noted that when using organic polymer flocculants, the water temperature should not be too high. High temperatures can easily cause the organic polymer flocculants to age or even decompose into insoluble substances, thereby reducing the coagulation effect.

3. Impurities in water

The uneven size of impurity particles in water is beneficial to coagulation, while small and uniform impurity particles will lead to poor coagulation effect. Too low concentration of impurity particles is often detrimental to coagulation. At this time, refluxing sediment or adding coagulant aids can improve the coagulation effect. When the impurity particles in the water contain a large amount of organic matter, the coagulation effect will become worse, and it is necessary to increase the dosage or add agents such as oxidants to aid coagulation. Calcium and magnesium ions, sulfide and phosphide in water are generally beneficial to coagulation, while certain anions and surface active substances have adverse effects on coagulation.

4. Types of flocculants

The choice of flocculant mainly depends on the nature and concentration of colloids and suspended solids in the water. If the pollutants in the water are mainly in a colloidal state, inorganic flocculants should be preferred to destabilize and coagulate them. If the flocs are small, polymer flocculants or coagulants such as activated silica gel need to be used in conjunction.

In many cases, the combined use of inorganic flocculants and polymer flocculants can significantly improve the coagulation effect and expand the scope of application. For polymers, the greater the charge on the chain molecules, the higher the charge density, the more fully the chain can stretch, the wider the scope of adsorption and bridging, and the better the coagulation effect will be.

5. Dosage of flocculant

When using coagulation to treat any wastewater, there is an optimal flocculant and optimal dosage, which are usually determined through experiments. Excessive dosage may cause colloid re-stabilization. Generally, the dosage range of ordinary iron salt and aluminum salt is 10~100mg/L, the dosage range of polymer salt is 1/2~1/3 of ordinary salt, and the dosage range of organic polymer flocculant is 1~5mg/L. .

6. Flocculant dosage sequence

When using multiple flocculants, the best dosage sequence needs to be determined through experiments. Generally speaking, when inorganic flocculants and organic flocculants are used together, the inorganic flocculants should be added first, and then the organic flocculants.

When dealing with impurity particle sizes above 50 μm, organic flocculants are often added first to adsorb and bridge, and then inorganic flocculants are added to compress the electric double layer to destabilize the colloid.

7. Hydraulic conditions

In the mixing stage, the flocculant and water are required to be mixed quickly and evenly. In the reaction stage, it is necessary to create enough collision opportunities and good adsorption conditions to allow the flocs to have sufficient growth opportunities, and to prevent the generated small flocs from being absorbed. Break into pieces, so the stirring intensity should be gradually reduced and the reaction time should be long enough.

• Factors affecting the use of PAC as a phosphorus removal agent

1. Wastewater mixing time

After the phosphorus removal agent is added into the wastewater, it adsorbs the phosphorus in the wastewater through precipitation and flocculation reactions, a coagulation process of phosphorus removal of metal ions and phosphates. Therefore, high-intensity phosphorus removal must be carried out immediately after the phosphorus removal agent is added. Mix and stir, otherwise the mixing intensity will be insufficient, which will hinder the precipitation reaction of phosphate. On the contrary, if the slow stirring time is too long, it will also affect the growth of floc.

2. Wastewater alkalinity

In the process of chemical phosphorus removal, whether aluminum salt or iron salt is added to remove phosphorus, a large amount of calcium carbonate alkalinity in the wastewater must be consumed. When too much alkalinity is consumed and the alkalinity of the wastewater is too low, it will affect the reaction effect of the phosphorus removal agent, so once this happens, alkali needs to be added immediately.

3. Wastewater PH value range

Regardless of whether aluminum salt or iron salt is used as a phosphorus removal agent, the pH value range required for the best phosphorus removal effect is 6.5--7.0. Within this pH value range, aluminum salts and iron salts can exert the greatest precipitation and phosphorus removal effects. The enhanced phosphorus removal agent developed by Chimelong Technology has a pH value ranging from 4 to 6. A good phosphorus removal effect can still be achieved within this range. However, if it is lower than this range, it will have an unfair impact on the effect. It will also cause deviations in the solubility of some aluminum salt phosphorus removal agents, thus affecting the phosphorus removal effect.

4. Suspended solids (ss) and dissolved solids (TDS) in wastewater

The function of the phosphorus removal agent in chemical phosphorus removal is to condense solid particles in the wastewater. Therefore, if there is too much SS in the wastewater, a large amount of phosphorus removal flocculant will be consumed. Therefore, many chemical phosphorus removal processes occur at low temperatures. In the case of SS and low DS.

5. How much phosphorus removal agent should be added?

The amount of phosphorus removal agent added during the process of chemical precipitation phosphorus removal has a reverse parabolic shape on the phosphorus removal effect. When we test through experiments, the amount of phosphorus removal agent is the best when the phosphorus removal effect is the best. Sometimes, adding more or less will cause the phosphorus removal effect to decline. In addition, the different dosage points of phosphorus removal agent directly affect the dosage of phosphorus removal agent.

• Precautions for PAC operation and storage

1. In terms of operation, the water purification process of polyaluminum chloride is generally divided into three stages. These three stages are the coagulation stage, the flocculation stage and the settling stage. In the coagulation stage, when the chemical liquid is injected into the coagulation container and the raw water is rapidly coagulated, fine alum flowers will be formed in a very short time. At this time, the water body becomes more turbid, which requires the water flow to produce intense turbulence. Then polyaluminum chloride enters the flocculation stage. The flocculation stage is the process in which alum flowers grow and become thicker. It requires an appropriate degree of turbulence and sufficient residence time (10 to 15 minutes). In the later stage, a large number of alum flowers can be observed to gather and slowly sink. Form a clear layer on the surface.

When the flocculant is in the settling stage, it is a floc settling process carried out in the settling tank, which requires slow water flow. In order to improve efficiency, an inclined tube or plate settler is generally used. A large number of thick alum flowers are blocked by the inclined tube (plate) wall. When deposited at the bottom of the pool, the upper water is clear water, and the remaining alum flowers with small particle size and low density continue to collide with each other and grow larger while slowly falling, and the residual turbidity remains basically unchanged in the later stage.

2. Polyaluminium chloride must be stored in a dry, moisture-proof, and heat-proof place (<80°C, do not damage the packaging, the product can be stored for a long time).

3. Polyaluminum chloride products must be dissolved before they can be used. Dissolution equipment and dosing facilities should be made of corrosion-resistant materials.

4. The effective storage period of polyaluminium chloride liquid products is half a year, and the effective storage period of solid products is two years. The solid products can still be used after getting damp.