Experimental Study On The Manganese Removal From Groundwater By Modiifed River Sand Filter Material

Groundwater is the most widespread and important drinking water resource forpeople. Especially in the Northeast China, even90%of daily water comes fromgroundwater. However, high levels of soluble Mn2+are often detected in groundwaterin that area. The excessive manganese in water could cause adverse effects on humanhealth, daily life and industrial manufacture. This study was supported by the NationalKey Technology R and D Program. In view of the safety of drinking water in thebackward remote villages/towns in Northeast areas, the removal of manganese fromgroundwater was investigated in this paper. In this paper, river sand was used as rawmaterials, and the optimal modification method, modification parameters andmanganese removal conditions were investigated. The scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectronspectroscopy (XPS) analysis methods were employed to investigate the surfaceproperties of the raw sand and modified river sand, and the results preliminarilyrevealed the manganese removal mechanism by modified river sand filter material.Filter column experiment, single factor alternative experiment andcharacterization analysis were carried out in this paper to investigate the river sandmodification method and mechanism. The main results were as follows:(1) KMnO4soaking method, KMnO4soaking-calcination method and alkalipretreatment-KMnO4soaking-calcination method were used to making three kind ofmodified river sand filter material. Filter column experiment was used to evaluatingthe manganese removal capacity of them. The results showed that, the three kind ofmodified river sand filter material could remove Mn2+from water, and the filtermaterial made by alkali pretreatment-KMnO4soaking-calcination method had thebest manganese removal capacity. The color of the modified river sand became darker than the raw sand and shined black-brown metallic luster.(2) N2-BET analysis was performed to evaluate the influence of factors in alkalipretreatment on the specific surface area of filter material. Acid digestion method wasused to evaluate the influence of factors in KMnO4soaking and calcination treatmenton the ratio of manganese coated to the sand. The results showed that the optimalconditions for river sand modification were as follows: base activation of sand with9%mass percent NaOH for24h when the solid-liquid ratio was1:1; KMnO4soakingof base activated sand with7%mass percent KMnO4for24h when the solid-liquidratio was1:0.5, and finally calcination at250℃for4h. The specific surface area ofthe base-activated river sand prepared under the optimal conditions was1.449m2/g,and the ratio of manganese coated to the sand of the modified river sand was1.43Mn/g sand.(3) The manganese removal capacity of the modified river sand filter materialprepared under the optimal conditions was investigated in the filter columnexperiment. In this experiment, pH, DO and hydraulic retention time were selected asthe important factors during the filtration process. And then the optimal conditions forthe filtration process were determined to be neutral pH, DO>5.5mg/L and the shortesthydraulic retention time of12min to ensure the effluent quality. There was nosignificant difference before and after backwash in the manganese removal capacityof the filter column.(4) The scanning electron microscopy, energy dispersive X-ray spectroscopy andX-ray photoelectron spectroscopy analysis methods were employed to investigate themicroscopic surface properties of the raw sand and modified sand. The raw sand had afairly uniform surface. On the contrary, the base-activated river sand had asignificantly rougher surface and larger specific surface area. The surface of the finalmodified river sand was apparently occupied by newly formed clusters of crystallinemanganese oxide with mixed manganese oxidation state (Mn (III) and Mn (IV)).Moreover, the surface of the filter material after filtration experiment was occupied bymany newborn flocculent manganese hydrous oxides, and the layer was thicker andevener. Before and after filtration, Mn and O on the modified river sand surface had the similar oxidation state. This indicated that the newly formed manganese oxidelayer could in turn catalytically facilitated the adsorption of Mn2+and oxidation withoxygen, and could ensure the manganese removal capacity continue. The modifiedriver sand filter material in this study has potential as a catalytic adsorbent formanganese removal in small waterworks in country sites.