The use of polyaluminum chloride in phosphorus removal is mainly reflected in:
1. After polyaluminum chloride is added into phosphorus containing waste water, it is hydrolyzed in the waste water to form trivalent aluminum metal ions. The trivalent aluminum ions can combine with the soluble phosphate in the waste water to form insoluble phosphate precipitation, so as to achieve the removal of phosphate ions in the waste water.
2. The flocculation of polyaluminum chloride can be compressed by the charge on the surface of phosphate ion after the decomposition of waste water, and the adsorption bridge can make phosphate and other organic pollutants in the waste water quickly flocculate into clusters and bond into flocs for precipitation.
3. For the fine particulate suspended matter produced after adding the phosphorus removal agent, the suspended matter grows and coarsens through the net catching mechanism of the sediment and the adsorption bridging function, and then coagulates, agglomerates and flocculates into larger particles and settles to the bottom layer. Then, the supernatant is discharged through solid-liquid separation to achieve the phosphorus removal effect.
Chemical agents are added to the sewage to make the phosphate ions in the water form insoluble salts, which form flocs and are separated from the water to remove the phosphorus contained in the water. In the specific reaction process, there are two main reaction processes. First, the trivalent aluminum ion reacts with phosphate to precipitate, and the precipitated compound is AlPO4.
Purpose: Flocculation
Polyaluminum chloride is mainly used for urban water supply and drainage purification: River water, reservoir water and groundwater; Industrial water supply purification, urban Sewage Treatment, recovery of useful substances in industrial wastewater and waste residue, promotion of coal dust deposition in coal washing waste water, and recovery of starch in starch manufacturing industry; Polyaluminum chloride can purify various industrial wastewater.
1. Treatment of river water, lake water and groundwater;
2. Treatment of industrial water and industrial circulating water;
3. Treatment of urban domestic water and urban sewage;
4. Recovery of coal mine scouring wastewater and porcelain industry wastewater;
5. Printing plants, printing and dyeing plants, leather plants, meat processing plants, pharmaceutical plants, paper mills, coal washing, metallurgy, mining areas, and the treatment of wastewater containing fluorine, oil and heavy metals;
6. Recovery of useful substances in industrial wastewater and waste residue, promotion of coal dust deposition in coal washing waste water and recovery of starch in starch manufacturing industry;
7. For some industrial wastewater with great difficulty in treatment, polyaluminum chloride is used as the parent and mixed with other chemicals to prepare composite polyaluminum chloride, which can achieve surprising results in treating wastewater;
8. Anti wrinkle of leather and cloth;
9. Cement setting and formwork casting;
10. Refining of glycerol and sugar, cosmetic raw materials;
11. It can be used as a good catalyst;
12. Adhesion of papermaking.
Factors affecting the use of flocculants
1. 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 and sedimentation effect of the selected flocculants. H + and oh - in water participate in the hydrolysis reaction of the flocculant. Therefore, pH value strongly affects the hydrolysis speed of the flocculant, the existing form and performance of the hydrolysate.
For example, when the pH value is less than 4, Al3 + can not be hydrolyzed into Al (OH) 3 in a large amount, mainly in the form of Al3 + ions, and the coagulation effect is extremely poor. When the pH value is between 6.5 and 7.5, Al3 + hydrolyzes and polymerizes to form a neutral colloid of Al (OH) 3 with high degree of polymerization, and the coagulation effect is good. When the pH value is > 8, Al3 + is hydrolyzed to AlO2 -, and the coagulation effect becomes very poor.
The alkalinity of water has a buffering effect on the pH value. When the alkalinity is insufficient, lime and other chemicals shall be added to supplement. When the pH value of water is high, it is necessary to add ACID to adjust the pH value to neutral. In contrast, the polymer flocculant is less affected by the pH value.
2. Water temperature affects the hydrolysis rate of flocculant and the formation rate and structure of alum. The hydrolysis of coagulation is mostly endothermic reaction. When the water temperature is low, the hydrolysis speed is slow and incomplete.
At low temperature, the viscosity of water is high, the Brownian motion is weakened, the collision times of flocculant colloidal particles and impurity particles in water are reduced, and the shear force of water is increased, which hinders the mutual adhesion of coagulated flocs; Therefore, although the dosage of flocculant is increased, the formation of flocs is still very slow, and the structure is loose and the particles are small, which is difficult to remove.
Low temperature has little effect on polymer flocculant. However, it should be noted that when using the organic polymer flocculant, the water temperature should not be too high. The high temperature will easily cause the organic polymer flocculant to age or even decompose into insoluble substances, thus reducing the coagulation effect.
3. Impurities in water
The uneven size of impurity particles in the water is beneficial to coagulation, and the fine and uniform particles will lead to poor coagulation effect. Too low concentration of impurity particles is often unfavorable to coagulation. At this time, reflux sediment or adding coagulant aid can improve the coagulation effect. When the impurity particles in the water contain a large amount of organic matter, the coagulation effect will be poor, and it is necessary to increase the dosage or add oxidant and other agents with coagulation effect. Calcium and magnesium ions, sulfides and phosphates in water are generally beneficial to coagulation, while some anions and surface active substances have adverse effects on coagulation.
4. Flocculant type
The choice of flocculant mainly depends on the nature and concentration of colloid and suspended solids in water. If the pollutants in the water are mainly in colloidal state, inorganic flocculants should be preferred to destabilize and coagulate them. If the flocs are small, polymer flocculants or activated silica gel and other coagulant aids should be added.
In many cases, the combination of inorganic flocculant and polymer flocculant can obviously improve the coagulation effect and expand the application range. For polymers, the larger the amount of charge carried on the chain molecules, the higher the charge density, the more the chain can be fully extended, the larger the scope of adsorption bridging, and the better the coagulation effect.
5. Flocculant dosage
In the treatment of any wastewater by coagulation method, there is the best flocculant and the best dosage, which are usually determined by experiments. If the dosage is too large, the colloid may be re stabilized. Generally, the dosage range of ordinary iron salt and aluminum salt is 10-100mg / L, the dosage of polymerized salt is 1 / 2-1 / 3 of the dosage of ordinary salt, and the dosage range of organic polymer flocculant is 1-5mg / L.
6. Flocculant dosing sequence
When a variety of flocculants are used, it is necessary to determine the optimal dosing sequence through experiments. Generally speaking, when inorganic flocculant and organic flocculant are used together, inorganic flocculant shall be added first, and then organic flocculant shall be added.
While the size of the treated impurity particles is in the range of 50 μ When it is above M, the organic flocculant is often added to absorb and bridge, and then the inorganic flocculant is 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 rapidly and evenly. In the reaction stage, it is necessary to create sufficient collision opportunities and good adsorption conditions to allow the flocs to have sufficient growth opportunities and prevent the small flocs from being broken. Therefore, the stirring intensity should be gradually reduced and the reaction time should be long enough.
