Preparation Of Nano-iron Loaded Peanut Hull And Its Performance On The Removal Of Phosphate From Water

It is reported when the concentration of phosphorus in lakes and oceans is more than 0.03 mg/L can lead to blooms of algae or red tide. For this reason, the effluent phosphorus limits have been decreased from 0.5-1.0 mg/L to 0.1 mg/L in some developed countries. In recent years, the eutrophication of our country is getting more and more serious, and the phosphorus is the controlling nutrient in rivers and lakes, thus decreasing the effluent phosphorus limits is the trend. At present, chemical precipitation and enhanced biological phosphorus removal (EBPR) or a combination of both are the most popular phosphorus removal technologies applied at home and abroad. The effluent total phosphorus concentrations could be controlled at 0.5 mg/L or below by combined process of EBPR and chemical precirition in municipal wastewater treatment plant, but it is difficult to control it below 0.1 mg/LThe phosphate in aqueous solutions can be effectly removed by the nano-sized adsorbent and the effluent phosphorus concentration of adsorption unit can be reached 0.1 mg/L or less, but it is difficult to separate the nano-sized absorbent from aqueous solutions. The peanut hull was used as a support to prepare the nano-iron immobilization adsorbent, and the absorbent’s microstructure and morphology were investigated by SEM, XRD and BET respectively. At the same time, the adsorption and desorption performances of nano-iron loaded peanut hull were also studied, the phosphorus in desorption reagent could be recycled and the adsorbent has showed a good application prospect.The results showed that the optimal preparation conditions for the nano-iron loaded peanut hull were that the impregnation solution contained 3 mol/L FeCl3 and 5 mol/L NaCl, the impregnation temperature was 298 K for 8 h, and the heat treatment temperature was 328 K for 12 h. The iron oxides loaded on peanut hull are spherical and the particle diameters are between 30 and 100 nm; the mass fraction of iron, the specific surface area and the phosphate absorption capacity were improved with the increasing of iron concentration.The suitable pH values for phosphorus adsorption by nano-iron loaded peanut hulls were between 6.0 and 7.0. The absorption capacity per gram of adsorbent could reach 1.89 mg P/g in 10 mg P/L aqueous solutions. The adsorption process could be present by Freundlich adsorption isotherm model and the adsorption kinetics conformed to the pseudo second order kinetic. Thermodynamic analysis showed both AGθ and △Hθ<0, △Sθ>0, indicating that the adsorption process was spontaneous, exothermic and entropy increase process. Common coexisting anions in wastewater such as Cl-、SO42- and NO3 can reduce the phosphorus removal efficiency of adsorption process by the nano-iron loaded peanut hull, and the order showed as SO42->NO3->Cr-.Desorption of used nano-iron loaded peanut hull could be easily carried out with 0.3 mol/L NaOH, and the desorption reagent could be reused in order to raise the concentration of phosphorus in it. After two cycles of adsorption and desorption, the processes becomed stable.During the continuous adsorption process, the optimum adsorption conditions of nano-iron loaded peanut hulls (K-3) were the wastewater flowrate= 2 BV/h and ratio of height to diameter=7.39. As the simulated wastewater contains 10 mg P/L pass through the adsorption column under the above-mentioned conditions, the penetration volume was about 72 BV. Then, the desorption reagent (0.3 mol/L NaOH solution) was pass through the column in 2 BV/h flowrate for 7.5 hours, the desorption efficiency was about 86.7%.