Study Of The Performance And Mechanism Of Phosphorus Adsorption With Solid Waste

Oyster shell, eggshell, fly ash, lava, slag were used as adsorbents to remove phosphorus from wastewater. Phosphorus adsorption kinetics, adsorption isotherms, thermodynamics were examined to investigate the adsorption characteristics and mechanisms of these materials. The influences of initial phosphorus concentrations, initial pH, adsorbent dosage and particle size of materials on phosphorus removal were studied. The adsorption mechanisms of these five materials were discussed.Pseudo-second order kinetics were fitted to describe the process of phosphorus adsorption by the materials tested. With the decrease of initial phosphorus concentration and increase of temperature, the adsorption equilibrium time became short. The adsorption characteristics of oyster shell and fly ash were fitted to Langmuir, Freundlich and D-R isotherms. Phosphorus adsorption onto eggshell can be described by Freundlich and D-R isotherms. The Freundlich isotherm was suitable to describe the phosphorus adsorption onto the slag. The highest adsorption capacity was:oyster shell> fly ash> lava> slag. The phosphorus adsorption (by oyster shell, eggshell, fly ash and slag) processes were spontaneous endothermic reaction, Phosphorus adsorption by lava was exothermic reaction under lower temperature (<25℃), endothermic reaction under higher temperature (>25℃).With the increase of initial pH, phosphorus adsorption efficiencies (by oyster shell, eggshell, lava and slag) decreased. Phosphorus removal efficiencies increased with the decrease of particle size for lava and slag. The equilibrium adsorption capacities (Xe) of oyster shell, eggshell and lava decreased with the increase of material dosages, meanwhile, whereas increased at the beginning and then decreased for fly ash and slag.The mechanisms of phosphorus adsorption can be concluded:(1) For oyster shell and eggshell, precipitation was the dominating reaction. (2) For fly ash, with lower phosphorus concentration, the adsorption was mainly precipitation reaction between Ca and phosphorus, whereas, with higher phosphorus concentration, physical adsorption was the main process. (3) Phosphorus was removed with lava mainly through physical adsorption at lower temperature, while under higher temperature, the chemical adsorption was dominated reaction.(4) Phosphorus adsorption by slag was mainly physical adsorption.