| In the treatment processes of groundwater polluted by iron, manganese and ammonia nitrogen, the catalytic oxidation film would be gradually produced on the surface of quartz sand and thickened in long-term operation, which resulted in declining the filter filtration properties, interception abilities and shortening the backwashing interval. To solve this problem, it’s essential to carry out experiments of peeling off the catalytic oxidation film from the surface of quartz sands. The removal abilities of Fe, Mn and NH4+ and the recovery of backwashing interval were studied by peeling oxide film off the surface of mature quartz sand with different oxidants, acids and reductants. Combined with the physical structure and morphology of the filters, chemical constituents, specific surface area, pore volume and average pore diameter, characterized by SEM, BET, XRD, XRF and XPS, the peeling effect with different agents was clarified. The main results are as follows:(1) The oxide films were peeled effectively by impregnating in 0.6% HCl solution with about 80% removing rate, and the single peeling effect was superior to multiple peeling effect.(2) In the long term, after the film peeled by 0.6% HCl solution,the removing rate of Fe, Mn and NH4+ were above 80% and the effluent of water quality met the standards for drinking water. At the same time, the backwashing interval was recoveried and increased from 48 h to 68 h. The oxide film of quartz sand filter after peeled still have the abilities on removing iron, manganese and ammonia nitrogen simultaneously, and recoverying backwashing interval. So 0.6% HCl can be used for the film peeling.(3) The specific surface area and pore volume of mature quartz sand were about 40 times than those of quartz sand, and greatly than the diameter of Fe, Mn, NH4+, which inproved the adsorption performances of ammonia, iron and manganese.(4) The surface of quartz sand was dense and rarely porous, while the surface o f the mature quartz sand was coarse and porous and there are a lot of oxide particles in 1-6 μm on the surface. The particles are composed of iron-manganese oxides which are amorphous structures. The main substances are K0.27 Mn O2·0.54H2O(δ-Mn O2). After peeled by chlorine dioxide, nitric acid and sodium nitrite, the surface of the oxide particles were damaged to become smooth, and the oxidation active sites were destroyed. Meanwhile, after peeled by hydrochloric acid and other chemical agents, the changes of the oxide film suface morphologic were unconspicuous. After peeling the thickness of the oxide film could reduce from 100~110 μm to 25~40 μm, which are benefit for the increase of voidage and lengthen the backwash intervals.(5) Comprehensive analysis, in the peeling process, the acids, ozone and hydrogen peroxide had no pollution to water. While chlorine dioxide, sodium sulfite, sodium nitrite and ascorbic could decompose to generate ions which competitively adsorb on the surface film to reduce the adsorption of ammonia and manganese ions. This phenomenon declined the removal efficiencies, worsened water quality result in further disposing processes for water. In practical production, through considering peeling results, saving reagents, water quality treatments after peeling and other factors, 0.6% hydrochloric acid was chosen as a suitable choice for peeling off filter film. |
PDF Full Text Request