Experimental Study on Mechanism of Adsorption of Mn2+by In-situ Generated Nano-MnO2 Colloids
Nano MnO2 colloids were in-situ generated at laboratory scale by means of the reaction of Mn2+ions with KMnO4 in solution,which were used to adsorb Mn2+ions in water.The MnO2 colloids in-situ produced was then characterized by opti-cal microscopy(OM),energy dispersive spectroscopy(EDS),Fourier transform infrared spectroscopy(FTIR),and particle-size/zeta-potential analyzers to explore the adsorption mechanism.The effect of the concentration of MnO2 colloids,adsorp-tion temperature,adsorption time,and pH value on the adsorption capacity was investigated.The results obtained showed that the adsorption of Mn2+ions onto the MnO2 colloids fit the Freundlich adsorption model(R2＞0.97),indicating that multi-level adsorption had occurred,the optimal adsorption process took about 30 minutes,so it conformed to the pseudo second-order ki-netic equation(R2＞0.98)as well;the adsorption capacity of MnO2 colloids generated in situ in low Mn2+concentration was greater than that in high concentrations,and the adsorption capacity of the MnO2 colloids in Mn2+concentration of 1 mg/L could be as high as 2 022.19 mg/g at 25 ℃;low temperature was conducive to the physical adsorption of Mn2+ions by the MnO2 colloids,while high temperature was conducive to the complexation of surface hydroxyl groups with Mn2+ions;and at a pH of 8.03 the adsorption capacity of the MnO2 was approx.four times that at a pH of 4.56,in addition the surface Mn-OH and hydroxyl groups grew,and the adsorption capacity of MnO2 colloid concentration of 45 mg/L could reache 1 647.13 mg/g.Furthermore,after Mn2+ions having been adsorpted on MnO2 colloids the zeta potential value was equal to-12.6 mV at pH of 4.56,and-1.10 mV at pH of 8.03.Generally speaking,the adsorption of Mn2+ions in water by in-situ generated nano MnO2 colloids is actually a combination of physical adsorption,electrostatic attraction and surface coordination.
in-situ generatednano MnO2adsorption and removal of Mn2+influencing factorsadsorption mechanism
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