Modification Of Carbon Black And Its Efficiency And Mechanisms Of Adsorbing Ammonia Nitrogen And Phosphate In Water

Ammonia nitrogen and phosphate are important nutrient elements in nature, but also the main pollutants causing eutrophication of water body and other environmental problems. Exceeding of ammonia nitrogen and phosphate in drinking water source will seriously affect water treatment efficiency and the quality of effluent water. So, it’s necessary to find an efficient way of ammonia nitrogen and phosphate removal to ensure the safety of drinking water. As a new, cheap and clean absorbent, carbon black has great research value and broad application prospect. In this study, carbon black is used for absorbing ammonia nitrogen and phosphate from water, and modification is performed to improve its absorbing efficiency.After selection and optimization of modification method, Fenton was used to modify carbon black. Results of characterization show the modified carbon black was improved in polarity and hydrophilicity, quantities of oxygen containing functional groups like carboxyl and phenolic hydroxyl increased significantly. A complete carbon skeleton and honeycomb structure was found, and the specific surface area and porosity were improved. Particles with different sizes were covered inside and outside the pores. Surface morphology structure conforms natrojarosite and iron sulfate hydroxide. The iron content was 114.16mg/g and had higher load intensity in alkaline condition.Efficiency of carbon black on absorbing ammonia nitrogen and phosphate was studied. Results shows that removal of ammonia nitrogen is suitable for an alkaline condition, and removal of phosphate is more suitable for an acid condition. Removal of phosphate is less reflected by p H. Increasing of modified carbon black dosing and temperature can contribute to ammonia nitrogen and phosphate removal efficiency. Adding the initial concentration of ammonia nitrogen and phosphate can promote the adsorption capacity of modified carbon black. The removal rates of ammonia nitrogen and phosphate can all over 90% with the initial concentration of ammonia nitrogen below 7mg/L and phosphate below 15mg/L. Among common co-existing ions, divalent and trivalent cations have strong inhibition on ammonia nitrogen removal, whereas carbonate and sulfate can inhibit the removal of phosphate. In addition, the desorption and regeneration performance of modified carbon black were studied, results shows that using hydrochloric acid after adsorbing ammonia nitrogen and using sodium carbonate and sodium hydroxide after absorbing phosphate can get higher regeneration efficiency.Dynamic and thermodynamic models were invested to analyze adsorption mechanisms of modified carbon black. Fitting results showed that adsorption of ammonia nitrogen and phosphate with carbon black conform to pseudo second-order equation and intra-particle diffusion model in kinetics. In thermodynamics, adsorption of ammonia nitrogen could be well described by Langmuir model, and adsorption of phosphate fitted Langmuir model as well as Frendlich model. Adsorption of two pollutants are all endothermic and spontaneous processes. The maximum ammonia nitrogen and phosphate adsorption capacity can reach 10.28mg/g and 14.39mg/g. Adsorbing ammonia nitrogen onto modified carbon black are chemical process, which contains electrostatic adsorption and hydrogen bonding. While phosphate adsorption by modified carbon black involves physical and chemical processes, the main mechanisms are surface complex, electrostatic adsorption, chemical precipitation and hydrogen bonding.