| The arsenic pollution is seriously harmful to human health and the normal metabolism of animals and plants,so the pollution of arsenic has been paid more and more attention.At present,arsenic compounds have been found in some Tibet salt lakes and produced minerals.In consideration of the utilization of these salt lakes amd minerals,the adsorption performance of arsenic by manganese oxide adsorbents was studied in two kinds of water systems: NaAsO2 solution and the high concentration salts system.Manganese oxide nanomaterials were successfully synthesized viaa hydrothermal method and explored the influences of reaction time on the morphology of products.The crystalline,morphologies,and pore structural characters of manganese oxide nanomaterials were investigated by X-ray diffraction（XRD）,scanning electron microscope（SEM）,Fourier transform infrared spectroscopy（FT-IR）and N2 adsorptiondesorption.With the prolongation of hydrothermal reaction time,the morphologies of products changed from flower-like（30 min）to sea-urchin-like（4 h）,and the corresponding crystal form of products was δ-MnO2 and α-MnO2,respectively.The specific surface areas of the flower-like MnO2 and the sea-urchin-like MnO2 were 107.3 m2·g-1 and 43.4 m2·g-1.The adsorption performance and mechanism of the flower-like MnO2 and the seaurchin-like MnO2 for the arsenic adsorption in NaAsO2 solution system were studied systematically.The experimental results showed that the flower-like MnO2 and the seaurchin-like MnO2 adsorbents have a wide arsenic adsorption range of p H（p H=48）.Sea-urchin-like MnO2 can basically reach the adsorption equilibrium at 120 min,while the adsorption equilibrium time of the flower-like MnO2 is 720 min,and the equilibrium adsorption capacity is 3.86 mg·g-1 and 4.20 mg·g-1,respectively.The arsenic adsorption process conforms to the pseudo-second-order kinetic equation.The adsorption isotherm conforms to the Freundlich isotherm model,which indicated this is a chemical adsorption process.The high concentration of Na2SO4,KCl,Na Cl and Li Cl have no effect on the adsorption of arsenic（III）while the increase of the concentration of the inorganic salts.After five cycles of regeneration,the arsenic adsorption performance of the sea-urchin-like MnO2 was much better than that of the flower-like MnO2.The arsenic adsorption mechanism was mainly chemisorption,which is the synergistic effect of oxidation-adsorption.The adsorption performance of the flower-like MnO2 and the sea-urchin-like MnO2 for arsenic（III）adsorption in the high concentration salts system was also studied.The experimental results show that when the initial p H value ranges from 4 to 10,p H factors has no effect on the equilibrium adsorption capacity of these two MnO2 adsorbents.Both of the adsorbents possess a wide range of temperation application.When the adsorbent dosage reaches to 0.25 g·L-1,the arsenic（III）equilibrium adsorption capacity reaches the maximum value,which is 20.16 mg·g-1 and 10.38 mg·g-1,respectively;while the adsorbent dosage increases to 5 g·L-1,the arsenic（III）removal rate of these two adsorbents is more than 95%.The arsenic（III）adsorption process of the flower-like MnO2 and the sea-urchin-like MnO2 reaches the state of adsorption equilibrium at 720 min and 600 min,respectively.The adsorption process is more consistent with the pseudo-second-order kinetic model.The Freundlich adsorption isotherm model is in accordance to the arsenic（III）adsorption of the flower-like MnO2 and the sea-urchin-like MnO2 adsorbents in the high concentration salts system,which suggests that the arsenic（III）adsorption process is chemisorption.In addition,these two adsorbents has been applied to the arsenic removal in the Tibet Baqiancuo Brine.The experimental results reveal that the arsenic removal rate can be reached to 97.60% and 96.06%,when the absorbent dosage is 30 g·L-1.Therefore,the flower-like MnO2 and the sea-urchin-like MnO2 have great potential for the adsorption of high concentration arsenic in the salt lake brine systems. |
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