Methylene Blue Removal From Water By Modified Sawdust And Adsorption Performance

Dye wastewater is the focus of our wastewater treatment, because of its complex components, high color, high toxicity, high amount of water, etc., is one of the typical refractory industrial wastewater. Sawdust has a wide variety of sources, is a natural adsorbent material.In this paper, different kinds of modification were used to modify sawdust, and two modifications were chosen to study. Firstly, take different methods to analysis the modified sawdust and natural sawdust, such as BET、 IR、SEM、FTIR. And in the bath experiment, the effects such as pH of solution, particle diameter, initial MB concentration, adsorption time, adsorbent dosage, adsorption temperature on adsorption were studied, and set up the models of adsorption thermodynamics and adsorption dynamics. We came to conclusions as follows:1. It was founded the N-sawdust adsorbent obtained by using 4g·L-1 NaOH solution to immerse for 3h was the optimal modified sawdust. The results of characterization showed that the specific surface area became bigger, surface became smoother, and few holes could be observed, the amount of OH in the N-sawdust became larger.The study of adsorption isotherms indicated the calculated monolayer maximum adsorption capacity by Langmuir model of N-sawdust was 108.696 mg·g-1, which was 3.2 times larger of natural sawdust; The KF and 1/n values implying the adsorption capacity of N-sawdust was higher and the affinity of N-sawdust with methylene blue was stronger and the adsorption of N-sawdust was more favorable. The batch adsorption experiment of adsorption rate indicated the adsorption of N-sawdust was fitted with pseudo-second-order kinetics.The effect of reaction conditions (adsorbent dosage, particle diameter, pH and initial concentration) on adsorption were studied in the paper. The results showed that pH was an important factor affect adsorption, pH value enlarged as the adsorption rate raised, when the initial concentration was 50ppm、 100ppm、150ppm, and the best dosage of adsorbent was 2 g·L-1、4 g-L-1 and 6 g·L-1, respectively.2. It was founded natural sawdust was first pyrolysis at 240℃ for 1h and then immerse in 0.4mol·L-1 NaOH solution for 3h, then obtained PN-sawdust which was the optimal modified sawdust. The results of characterization showed that the specific surface area became bigger, surface became smoother, and a lot of holes could be observed, the amount of OH in the PN-sawdust became larger.The study of adsorption isotherms indicated the calculated monolayer maximum adsorption capacity by Langmuir model of PN-sawdust was 322.58mg·g-1, which was 2.77 times larger of activated carbon; The KL, KF and 1/n values implying the adsorption capacity of PN-sawdust was higher and the affinity of PN-sawdust with methylene blue was stronger and the adsorption of PN-sawdust was more favorable. The batch adsorption experiment of adsorption rate indicated the adsorption of PN-sawdust was fitted with pseudo-second-order kinetics. The results of thermodynamic indicated methylene blue removal by PN-sawdust was spontaneous, endothermic and the degree of freedom increased during adsorption.The effect of reaction conditions (adsorbent dosage, pH of solution, particle diameter, initial concentration and adsorption temperature) on adsorption were studied in this paper. The results showed that pH value enlarges as the adsorption rate raises, when the initial concentration was 200ppm> 300ppm, and the best dosage of adsorbent was 0.8 g-L-1、1.2 g-L-1, respectively. Particle size made little influence on the PN-sawdust compared with activated carbon; and the higher temperature is beneficial for adsorption of methylene blue.The paper provides two methods to modify sawdust, N-sawdust could not attain same adsorption capacity with PN-sawdust, but N-sawdust had the advantages of simple preparation process, and the adsorption capacity had been incrased a lot compared with natural sawdust; PN-sawdust could adsorb more methylene blue compared with activated carbon, but the preparation process was relatively complex, on the other hand, PN-sawdust need less energy to consume at the papreation process compared with activated carbon.