Study On Sludge Activated Carbon Preparation And Its Adsorption Properties Of Phenol And Nitrobenzene

To reusing the sewage sludge as a resource, sludge was used to prepare the sludge activated carbon and its physiochemical properties and removal efficiencies for phenol and nitrobenzene were studied in this paper.The optimal operating conditions were obtained through orthogonal experiment. Iodine value, BET surface area, pore size distribution, SEM photography and surface functional groups were analyzed. Phenol and nitrobenzene were selected as the target pollutants to be adsorbed and their removal efficiency and adsorption mechanisms were investigated and compared, in every case, with a market activated carbon made from wood (MAC).Results indicate that the optimal operating conditions are:concentration of ZnCl2 30%, weight ratio of dried materials to ZnCl2 1:0.8, heating temperature 600℃, activation time 60min. corn cob to sludge mixing ratio of 1:1. The maximal iodine value of activated carbon obtained under such conditions is 678 mg/g, BET surface area is 712.8 m2/g. Activated carbon made from the sludge only (SAC) is poor in surface area. Surface functional groups of SAC are mainly acid groups.Kinetic data of phenol and nitrobenzene adsorption on the SAC and MAC fit to the pseudo second-order model best. Compared with MAC, the mesoporous character of SAC leads to a quicker diffusion of phenol because the molecular diameter of phenol is a little bigger than the micropore diameter of activated carbon. While the nitrobenzene molecular diameter is smaller than the micropore diameter of activated carbon, its diffusion related to the quantities of the micropore of activated carbon, so the adsorption rate of nitrobenzene on SAC was much slower than that on MAC.Surface area of the SAC is much smaller than that of the MAC, so the phenol and nitrobenzene adsorption capacity of SAC is lower than that of MAC. Phenol and nitrobenzene adsorption isotherm on SAC is S type and L type respectively, indicating that the water molecular competitive adsorption is strong for phenol but weak for nitrobenzene. Based on the physiochemical properties of the two organic pollutants and the activated carbons, it can be inferred preliminarily that phenol adsorption is mainly affected by surface area but nitrobenzene adsorption is affected by both surface area and surface functional groups. This inference can be verified by the corresponding relations between SAC and MAC's surface areas and their adsorption capacities. Where SAC's surface area of is 1/4 of MAC's, SAC's phenol adsorption capacity is also 1/4 of MAC's but the nitrobenzene adsorption capacity is 1/3 of MAC's. In organic phase, SAC's phenol adsorption capacity is higher and nitrobenzene adsorption capacity is lower than that in water. However, MAC's phenol adsorption capacity doesn't change much but nitrobenzene adsorption capacity decrease a lot compared that in water. The results furtherly indicate that the hydrophobicity and the polarity of the organic pollutants can greatly affect their adsorption in water. Nitrobenzene is more hydrophobic and polar than phenol, the hydrophobicity leads to a weaker competitive adsorption from water molecular. And the polarity leads to a stronger orientation force between nitrobenzene and SAC. So, nitrobenzene adsorption capacity of SAC was bigger than phenol adsorption capacity.