Research On Adsorption Efficiency Of Nickle Ion By Synthetic Manganese Oxides

Heavy metal nickel is a kind of carcinogen. When waste water with nickel is discharged directly into the water, not only threatening the aquatic organisms, but also destroying the ecological environment and endangering the human body health through the way of adsorption, precipitation and chain of food. The current main methods of treating heavy metals in solution includes adsorption technology, precipitation technology, ion exchange technology, biological technology and so on. Due to the wide application, simple operation and easy for mass production, the adsorption technology is considered to be an effective way to removal the heavy metals in the water. The metal oxide and hydroxide of iron, aluminum and manganese have porous structure, large specific surface area and be with a great amount of negative charge. Because of these characters, they have strong ability of adsorption for heavy metals and organic matters,using metal oxides as adsorbent to remove the pollutants in the water also arouse people’s interests.Manganese oxide are used as adsorbent. There are four different kinds of synthetic manganese oxides prepared and then screened out according to their adsorption performance for nickel in the water. The manganese oxides which are screened out are analyzed by X-ray diffraction(XRD) and Fourier Transform infrared spectroscopy(FTIR), and measure their point of zero charge(PZC). In the static adsorption experiments, through the way of controlling single factors to analyze their influences for adsorption. The main factors include the dosage of manganese oxides, p H values, ion concentration, temperature and initial concentration of nickel, adsorption time and so on.Meanwhile, analyzing the process of adsorption by the adsorption thermodynamics and adsorption kinetics. Conclusions are as follows:Four different kinds of chemosynthetic manganese oxides are prepared, they areα-Mn O2, β-Mn O2, γ-Mn O2, δ-Mn O2. Determining to use α-Mn O2 and β-Mn O2 as adsorbent in this experiment through adsorption test. Both of α-Mn O2 and β-Mn O2 are black solid particles and their surfaces are with metallic luster after washing and drying.The manganese oxides powder after grinding is brown and black. The X-ray diffraction(XRD) test shows that the two manganese oxides are poorly crystalline and amorphous structure. Fourier Transform infrared spectroscopy(FTIR) test shows that both two manganese oxides have the adsorption peaks of characteristics for M―O key, M―OH surface hydroxyl and bound water. Murray’s basic reference titration of manganeseoxides shows that PZC of α-Mn O2 and β-Mn O2 are 1.22, 1.46, respectively.When the dosage of two manganese oxides added in the experiment are more than10 mmol, the adsorption efficiency of 100 m L, 2mmol/L nickel solution is nearly 100%.The p H value has strong influence on the adsorption efficiency of manganese oxides, as the p H value of reaction system(range:2~8) rises, the adsorption efficiency of α-Mn O2 and β-Mn O2 for nickel are from 20.8% and 8.3% to 62.6% and 45.9%, respectively. In the ion concentration experiment, adding different amount of Na NO3 to the reaction system, the coexistence of sodium ions has effect on adsorption. As the concentration of Na NO3 rises from 1mmol/L to 50mmol/L, the adsorption efficiency of α-Mn O2 andβ-Mn O2 for nickel are from 49% and 31.4% to 41.6% and 24.6%, respectively. The adsorption of two manganese oxides for nickel are specific adsorption and nonspecific adsorption working together. When the initial concentration of nickel is high, the adsorption efficiency is low, but adsorption unit improves significantly. Due to the adsorption of manganese oxides tend to be saturated at the same time, the effect of temperature is relatively small. When the initial concentration of nickel is low, the adsorption efficiency improves, but the adsorption unit reduces and does not reach adsorption saturation state. The temperature rises is beneficial to adsorb at this situation.The adsorption process of α-Mn O2 and β-Mn O2 mainly happens in the period of0~30min, belongs to the rapid adsorption phrase, the adsorption rate is fast. In the period of 30~150min, the adsorption rate slows down, belongs to the slow adsorption phrase. After 150 min, nearly stops and reaching the adsorption equilibrium.By comparing three linear adsorption isotherm, we can learn that the adsorption of two kinds manganese oxides fit the Langmuir adsorption isotherm best, the value of correlation coefficient R is bigger than 0.996. Meanwhile, we can know from the qm calculated that saturated adsorption amount of α-Mn O2 is larger than β-Mn O2, the adsorption capacity is stronger. Analyzing the adsorption kinetics, the adsorption process of two kinds manganese oxides fit the Lagergren pseudo-second-order kinetics best, the value of correlation coefficient R is bigger than 0.999. The qe calculated are28.77mg/g and 18.93mg/g, be nearly consistent with the experimental values. The adsorption process belongs to chemical adsorption. In addition, from intraparticle diffusion equation, we can learn that the intraparticle diffusion is not the only control step, the adsorption is controlled by film diffusion and intraparticle diffusion.