Performance And Mechanism On The Phosphorus Adsorption By Iron Modified Peanut Shell Biochar

Eutrophication and phosphorus-contaminated wastewater have become one of tough environmental issues around the world.Among numerous technologies removing phosphorus from aqueous solution,the adsorption method has attracted people's extensive attention due to its high phosphorus removal efficiency,fast adsorption rate,simple operation,low cost and friendly environment.In this study,biochar was derived from waste peanut shells and then impregnated with ferrous sulfate?FeSO₄·7H₂O?and ferric nitrate?Fe?NO₃?₃·9H₂O?,and was obtained iron-modified biochar adsorption materials?FS-BC and FN-BC?respectively.Investigating phosphate adsorption performance,regularity and interaction mechanism of FS-BC and FN-BC under static and dynamic operating conditions were investigated.Batch experiments were carried out to investigate the impacts of adsorbent dosage,pH,initial phosphorus concentration,and co-existing ions on the adsorption of phosphorus by FS-BC and FN-BC.These showed maximum adsorption capacity in the initial pH range of 3.0¹0.0,and the adsorption capacity was basically constant and the environmental adaptability was strong.The influence of coexisting ions CO₃^2-and HCO₃^-on phosphorus adsorption was significant.Adsorption kinetics studies have demonstrated that the pseudo-second order kinetics models could be more suitable for adsorption process on FS-BC and FN-BC,indicating that the chemisorption process was the main rate-control step.The adsorption isotherm data of FS-BC were fitted well by the Langmuir isotherm model,while the data of FN-BC were fitted well with the Langmuir and Freundlich models,hinting the results of homogeneous and heterogeneous interactions for FN-BC.Thermodynamic tests indicated the spontaneous and endothermic adsorption process for both of the FS-BC and FN-BC.Column experiments were performed to explore the impacts of adsorbent fill height,influent phosphorus concentration,and influent flow rate on the adsorption of phosphorus.The results showed the filling height of adsorbents with FS-BC and FN-BC was positively correlated with breakthrough time,exhausted time and adsorption capacity.The increase of the influent phosphorus concentration will lead to a decrease in the time of penetration and depletion,and the adsorption capacity will increase significantly.The influent flow rate had an effect on the dynamic adsorption of FN-BC,yet it rarely affected on FS-BC.Both of the Thomas and Yoon-Nelson models were successful to illustrate the dynamic phosphorus adsorption on FS-BC and FN-BC.The results of SEM,FTIR and XPS characterization analysis showed that Fe²⁺was oxidized to be Fe³⁺during the FS-BC preparation process,and FS-BC was mainly removed phosphorus by the coordination exchange(Fe³⁺and phosphate)and surface chemical precipitation processes in aqueous solution.While the phosphorus adsorption by FN-BC was mainly achieved by the exchange of Fe-OH with phosphate ions and the surface chemical precipitation of Fe₃O₄ with phosphate.