The Study Of The Phosphate Adsorption Using Steel Slag In The Decentralized Sewage Treatment

In this paper, the dynamic、isotherm、influencing factors(temperature、pH、coexisting ions、 humic acid) of phosphorus adsorption by steel slag powder were studied and the modification of steel slag and its performance on phosphorus removal were investigated. The mechanisms of phosphate adsorption on steel slag and modified steel slag were analyzed by XRF、FITR、 SEM-EDS、BET and the morphological structure of phosphate in saturated steel slag. And the adsorption of phosphorus from actual wastewater by dynamic adsorption column experiments and biological contact oxidation/steel slag combined process were studied. The results were as follows:The change of phosphorus concentration with time could be described by the pseudo second-order kinetics. Langmuir isotherm model can simulate the adsorption processes better than other models, with the theoretical saturated capacity of94.61mgP/g. The optimal pH for the adsorption was3～5. Higher temperature was more effective for the adsorption process. Cl-、NO3-and SO42-had no effects on the adsorption. Due to the inhibition of the Ca-P generation by F-and HCO3-, they reduced the adsorption effects of phosphate by steel slag. The existence of humic acid significantly inhibited the generation of Ca-P and O-P.Modified granular steel slag were prepared by several methods, e.g. acid, alkali, salt, water, and heat modification. The results showed that after the slags(0.9-2mm)were immersed in3mol/L NaOH for24h, and then heated at800℃for1h, the maximum adsorption capacities could reach13.39mg/g, increased60.75%compared to the unmodified steel slag.A fixed bed, which was used to examine the dynamic adsorption of phosphorus. The results showed that:The filled way、the particle size、the way and the flow rate of influent were all affected the dynamic adsorption of phosphorus. When the weight of the modified steel slag particles were99.Og, the particle size of the steel slag were5mesh, the way of influent was upflow, the influent flow rate was7.2ml/min, the penetration time of the steel slag adsorption was73.73h. The main forms of phosphorus were Ca10-P、Ca8-P and Fe-P.The combined process of biological contact oxidation/steel slag was used to treat actual sewage. The results showed that:the removal rates of COD、TN、TP、NH4+-N were90%,35%、90%and90%, respectively. The combined process were penetrated after158days(TP>0.5mg/L was considered penetration).