Magnetic coagulation and precipitation technology for the treatment of white carbon black production wastewater
A large amount of waste water produced in the process of white carbon black production will cause serious pollution to the environment, and the treatment of this kind of waste water is urgent. At present, this kind of wastewater is often treated by coagulation and precipitation, but the ordinary coagulation process is more complex, prone to interference by a variety of factors, and the treatment effect is unstable. In view of the shortcomings of ordinary coagulation, magnetic coagulation process, as a new high-efficiency solid-liquid separation technology, has emerged in recent years. Through strict control of relevant parameters of coagulation process and based on contact flocculation, efficient solid-liquid separation of wastewater is realized. The main principle of this technology is to use magnetic particles such as magnetic particles to aggregate with colloidal particles suspended in wastewater and other fine particles in the process of wastewater coagulation treatment to form high-density dense flocs. The mass of the aggregated solid phase material increases and the settlement is accelerated, so as to achieve efficient solid-liquid separation. After the reaction, the added magnetic materials such as magnetic species can be recycled and reused, and the method can be used to remove pollutants such as solid suspended matter (SS), total phosphorus (TP) and partial chemical oxygen demand (COD). The use of magnetic coagulation treatment technology can complete the effective separation of solid and liquid in a few seconds, and the hydraulic residence time of the reaction is fully reduced, which greatly reduces the geotechnical facilities, saves the land area, and is widely used in water treatment.
1. Materials and methods
In this experiment, the production wastewater of a carbon black industrial park was treated, and the water quality characteristics were shown in Table 1.
As shown in Table 1, the pH of the water is neutral, in which the COD content is low, about 10 ~ 30mg/L, SS and TP content is high, and the TP concentration is about 5mg/L. According to the characteristics of the wastewater, five coagulants, polyaluminum chloride PAC, calcium oxide CaO, ferrous sulfate FeSO4, ferric sulfate and aluminum sulfate, are selected in this experiment. Magnetic coagulation tests were carried out in combination with negative and cationic PAM to treat this kind of wastewater. The treated water amount was 10L, the experimental concentration of five coagulants was 100mg/L, the addition amount of negative and cationic PAM was 2mg/L, and the magnetic powder was ferric oxide powder. All of them were treated with 200 mesh and the addition amount was 300mg/L.
2. Results and discussion
2.1 Comparison test between magnetic coagulation method and ordinary coagulation method
The comparative test results of magnetic coagulation method and ordinary coagulation method are shown in Figure 1. As can be seen from Figure 1, after the reaction of ordinary coagulant, a large number of white floc was suspended in the solution, which was not easy to settle, resulting in high SS of the solution and unable to meet the discharge standard. Compared with ordinary coagulation method, magnetic coagulation method can significantly improve the SS removal efficiency in wastewater. The SS removal effect of five coagulants added with magnetic powder is in the order of PAC > ferric sulfate > CaO > aluminum sulfate > ferrous sulfate. The treatment effect of SS < 10mg/L can be obtained directly in PAC magnetic coagulation group, and the treatment effect of SS < 20mg/L can also be obtained by CaO, ferric sulfate and aluminum sulfate magnetic coagulation tests. In conclusion, magnetic coagulation can be used to treat SS of this white carbon black wastewater with excellent results.
2.2 Contrast test of negative and cationic PAM
As shown in Figure 2, different types of PAM have little influence on the pH of solution in different reagent experiments, and the pH of solution is all less than 10. Meanwhile, the COD degradation effect in this wastewater is not good, and the COD is about 15mg/L, which may be due to the fact that the coagulation process can mainly remove colloid and suspended organic matter in wastewater. Although more floc is formed in this experiment, it should be inorganic components. And the floc did not remove the COD in the wastewater through the effects of encapsulation and adsorption, so the COD in the wastewater should be dissolved COD.
The reduction of TP concentration in wastewater has little correlation with PAM type, which is restricted by the type of coagulant. The order of TP removal effect is aluminum sulfate > iron sulfate > ferrous sulfate > CaO > PAC. The removal rate of TP in aluminum sulfate group is above 95%, and the effluent TP is stable less than 0.3mg/L. This is mainly because TP in the white carbon black wastewater mainly exists in the form of phosphate, and the removal of TP is mainly a chemical precipitation reaction of phosphate. In this experiment, aluminum salt has the best phosphorus removal effect. Anionic PAM has better removal effect on wastewater SS, with a removal rate of more than 92%, while cationic PAM has better removal effect on wastewater SiO2. It is found that SiO2 colloidal particles are electronegative, so the compression double layer and electroneutralization of cationic PAM have better treatment effect. The results of the treatment of SS by anionic PAM show that there are positively charged suspended particles in the wastewater, and better treatment effect can be obtained by using anionic PAM. In summary, when anionic PAM is used for treatment, aluminum sulfate group can obtain better SS and TP treatment effects at the same time, so it is recommended to use this agent for treatment.
2.3 Change of silica concentration in solution after magnetic coagulation
In order to monitor the change in the concentration of SiO2 in the solution after magnetic coagulation and check whether SiO2 solid substances are precipitated and then deposited in the structure over a long period of time (a large amount of silicon powder is deposited in the hydrolysis acidification pool and oxidation ditch of the sewage treatment plant), this experiment is designed to observe the change in the concentration of silica in the solution after magnetic coagulation. The experimental results are shown in Figure 3. In this experiment, 10L waste water was taken and aluminum sulfate was selected for magnetic coagulation test. The addition amount of aluminum sulfate was 100mg/L, the addition amount of anionic PAM was 2mg/L, and the magnetic powder was selected with high purity 300 mesh ferric oxide powder and the addition amount was controlled to 300mg/L. After the magnetic coagulation test, the concentration of dissolved SiO2 is basically stable at 75mg/L, and the 45d observation test shows that after coagulation, SiO2 can exist in the solution in the form of silicate, and will not be precipitated in solid phase form, nor deposited in the reactor.
3. Conclusion
(1) The SS treatment effect of white carbon black wastewater under the addition of magnetic powder is better than that of ordinary coagulation test.
(2) Combined with the change law of the concentration of SiO2 in the solution after magnetic coagulation, the concentration of SiO2 in the white carbon black wastewater can be stable for a long time and will not be precipitated in the form of solid phase. The removal of SS in the wastewater is more critical, so the anionic PAM which is more conducive to the removal of SS is more suitable for this kind of wastewater.
(3) Considering the removal effect of SS and TP, it is suggested that aluminum sulfate combined with anionic PAM should be used as the additive for magnetic coagulation in the treatment of waste water from the production of white carbon black.
