Adsorption Of Hg²⁺ From Aqueous Solution By Modified Eichhornia Crassipes Powder

Heavy metal wastewater refers to the mining and metallurgy, machinery manufacturing, chemical, electronics, instrumentation and other industrial production process in the discharge of heavy metal containing wastewater. Heavy metal waste water is serious to the environment pollution, and is harmful to human beings. Mercury is a common heavy metal ion in wastewater, which has a great negative impact on the natural environment and human production and life. At present, the removal methods of mercury in wastewater include chemical precipitation, ion exchange, activated carbon adsorption, electrolysis and membrane separation. These methods have their own advantages in the treatment of mercury containing wastewater. However, these methods have the defects of slow reaction rate, high cost energy consumption, low removal rate, large amount of chemical reagent, and easy to be polluted by two times. Adsorption is an efficient and low consumption water remediation purification method and received the attention of people. E. crassipes widely and easily obtained the biosorbent, plants contain large amounts of cellulose, hemicellulose and lignin material contains abundant active groups, can absorb a lot of metal ions and anionic substances, but the adsorption effect is poor. At the same time, the active groups contained in the E. crassipes are easy to be chemically modified to prepare the cellulose adsorbent, and the adsorption effect can be improved. This study used CS₂ modified E. crassipes powder, in order to improve its adsorption capacity. Because the powder adsorbent is not easy to separate and recycle, using PVA-SA gel immobilized E. crassipes powder, preparation of immobilized particles, investigate the adsorption capacity and the actual use value. By studying the modified and un-modified E. crassipes powder structural changes, static adsorption and desorption processes of E. crassipes powder adsorption of Hg²⁺, and adsorption mechanism of Hg²⁺, for E. crassipes powder and immobilized E. crassipes powder used in practice and provide a scientific basis. The main results of this study are as follows:（1） Compared with the unmodified E. crassipes powder, modified E. crassipes powder surface structure, crystal structure, molecular structure group had obvious changes. Modified E. crassipes powder surface is uneven, fold increase, irregular distributed a large number of pores, more rough and loose, the structure is more conducive to the adsorption process. FTIR analysis found that modified E. crassipes powder in 1101cm^-1 appeared new absorption peaks, which marks the modified successfully, CS₂ modified successfully to the water hyacinth powder. The content of S in modified E. crassipes powder was 2.05%.（2） The adsorption effect of modified E. crassipes on Hg²⁺ in wastewater was greatly improved. The equilibrium adsorption amount of modified E. crassipes powder on Hg²⁺ was 961.70μg/g, the maximum adsorption capacity of Hg²⁺ was 31.05 mg/g. The adsorption processes of Hg²⁺ on modified and unmodified E. crassipes are better fit to the pseudo two order kinetics model, chemical adsorption is an important rate limiting step during the whole adsorption process. At the same time, Dynamic boundary model fitting found that liquid film spreading is also an important step in the adsorption of Hg²⁺. The adsorption process of Hg²⁺ can be well consistent with the Langmuir model, and the adsorption of Hg²⁺ is mainly based on the pore or surface adsorption. Physical adsorption exists in the whole process of adsorption, the adsorption process can be carried out spontaneously at the test temperature, the adsorption process is endothermic, and the temperature rising is beneficial to the adsorption process.（3） The optimum conditions of E. crassipes powder adsorbed Hg²⁺ are obtained through single factor and orthogonal experiment, it is test temperature of 30℃, pH 7.0, 2.5 g/L of E. crassipes powder dosage, E. crassipes powder particle < 0.25 mm and Hg²⁺ initial concentration of 1mg/L, adsorption time 3.5h. Under these conditions, the removal rate of Hg²⁺ was 99%.（4） The best immobilized condition of the modified E. crassipes powder were as follows: the concentration of PVA was 5%, the concentration of SA was 0.5%, the concentration of CaCl2 was 5%, and the concentration of modified water was 8%. The equilibrium time of adsorption of Hg²⁺ was 300 min, which was increased compared with modified E. crassipes powder（180min）. The equilibrium adsorption capacity was reduced to 167.80 μg/g. The adsorption process of immobilized E. crassipes powder on Hg²⁺ was in accordance with the pseudo two order kinetics model. The Freundlich linear equation can describe the isothermal adsorption process of Hg²⁺, and the adsorption process is spontaneous, and the adsorption process is endothermic process.（5） For modified E. crassipes powder, the desorption ability of different desorption: H₂ O < NaNO₃< EDTA < HCl; For unmodified E. crassipes powder, the desorption ability of different desorption: H₂ O < NaNO₃< HCl < EDTA. For immobilized E. crassipes powder, the desorption ability of different desorption: EDTA ≈ HC l> NaNO₃ > H₂ O. In the regeneration process, Four kinds of regeneration fluid all have the ability of regeneration. Both the E. crassipes powder and the immobilized E. crassipes powder has a good adsorption capacity after times of regeneration.