Contamination of heavy metals is one of important role in water pollution .This paper summarizes the source , toxicity, chemic behavior , transformation and recent treatment methods of heavy metals. What's more , considering with literature reported, it is likely to use the natural cryptomelane to treat with the heavy metal ions existing in water.The natural manganese mineral from Hunan was charactered by XRD and EPMA . The results showed that the main phase is cryptomelane besides a small quality of illinite, dolomite and quartz . The zero point of pH value for the natural crytomelane was also measured by Zeta potential instrument, and the results showed pHpzc is near to 6.3 .The equilibrium time had been determined after investigating the kinetics of the adsorption for heavy metal ions such as Hg2+,Pb2+,Cd2+ . All of them need 20 hours to reach the equilibrium at least. But after the first hour ,the percentage of the adsorption is above 60% , and after 15 hours is above 90 %.Through a series of experiments for the factors that influence the adsorbing capacity , the pH value of the solution was verified being the most important role . The most suitable acid-base conditions are near neutral or alkaline slightly .The alien electrolytes also affect the disposal effect . The depression of the disposal by the alien electrolytes is due to the ligands ,which coordinate heavy metal ions strongly , especially when the concentration of the ligands is high . Moreover, the diameter of mineral grain also influence the quantities of disposal . The smaller the diameter is, the higher the quantity of the adsorption . The pH values are somewhat different in the solution before and after the reaction .In addition, isothermal adsorption experiments of natural cryptomelane indicate that the disposal of the three kinds of metal ions are all complied with Langmuir adsorption isotherms. For Sample A Maximal quantity of adsorbed Hg2+ is 27.6mg/g and maximal quantity of adsorbed Cd2+ is 5.54mg/g. While for Sample B maximal quantity of adsorbed Pb2+is 7.12mg/g . When the ratio of the mineral's mass(g) vs the solution's volume(mL) is appropriate, the percentages of disposal are more than 90% in low concentration solutions.As to the desorption experiments following adsorption of heavy metal , the quantity ofdesorption is fluctuant with the conditions of desorption solutions .They are basically corresponding to the adsorption experiments, that is, the conditions of maximal adsorption are the same as those of minimal desorption . Especially, the adsorbed Pb2+ ion is rather stable, so ,after leaching and parching processes , the desorption of the adsorbing slags is impossible unless the pH value is very low.During the course of heavy metal ions being adsorbed on the cryptomelane's surface , the quantities of Mn2+ and K+ separating out of cryptomelane's structure increase . From this , The conclusion can be drawn that heavy metal ions , besides surface coordination, replace the Mn2+ in the structure of crypto melane and exchange with K+ in the hole .The order of sample B's disposal quantity is: Pb2+>Hg2+>Cd2+ .In a word , those experiments have verified that natural cryptomelane is a good kind of environmental mineral material for dealing with contaminated water by heavy metals ions . |