Study On The Characteristic Of Chicken Eggshells For Removing Heavy Metals In Acid Wastewater

Recently,industrial wastewaters have become one of the most serious problems for surrounding environment and human health,especially the acid mine drainage(AMD)from the exploitation of mineral resources,which bring about widespread concern.The low-cost chicken eggshells can be used in restoration of AMD.It not only can solve heavy metals pollution and acid pollution in aqueous solution,but also provide a new approach for the multipurpose utilization of chicken eggshells.In this study,the adsorption characteristics and removal mechanisms of heavy metal ions on eggshells were analyzed by characterizing technologies and adsorption experiments.A continuous fixed bed study was carried out by using eggshells for the removal of heavy metals from AMD.The adsorption characteristics in the fixed bed were studied,which provide theoretical basis for the industrial application in-situ of rivers.The main results are as follows:1.The eggshells were mainly composed of calcite.The presence of(Ca,Cd)CO3 crystals after experiment has been demonstrated by scanning electron microscope with element mapping.What's more,the reducing pH values as Cd2+ concentration increasing,which corroborated that the adsorption process was dominated by co-precipitation at low concentrations and cation exchange at high concentrations.The removal efficiency of Cd2+ ions had reached above 90% in 0.45-1 mm diameter of eggshells at pH 4.5.In binary metal competitive experiment of Cd2+-Cu2+ and Cd2+-Pb2+,the adsorption capacity of eggshells at lower concentrations was found to decrease according to Cu2+ > Cd2+ > Pb2+,while at higher concentrations the selective order was Pb2+ > Cu2+ > Cd2+.2.The adsorption isotherms,kinetics and binary metal competition were further studied.The results indicated that the Langmuir model fitted to the equilibrium data.The maximum uptake was 2.4,6.4 and 3.3 mg g-1 for Cd2+,Pb2+ and Cu2+ at 25°C,respectively.The adsorption process better followed pseudo-second-order kinetics and the activation energy was 23.67 kJ mol-1,both showed the chemical sorption being the rate-controlling step.3.In the simulated study of eggshells fixed-bed to remove heavy metals in AMD,the obtained breakthrough curves showed that the breakthrough time increased with increasing bed heights,whilst decreased with increasing flow rates and increasing particle sizes.The Pb2+ ions had the highest removal efficiency and best adsorption potential.4.The Thomas model and Bed Depth/Service Time model could predict the bed dynamic behavior accurately.At 10 cm bed height,10 ml min-1 flow rate and 0.18-0.425 mm particle sizes,for the multi-component heavy metals solution containing Cd2+,Pb2+ and Cu2+,the capacities of ES were found to be 1.57,146.44 and 387.51 mg g-1,respectively.5.The acidity of AMD effluent reduced obviously.Because of the excessive concentration of Fe2+ and Fe3+ in AMD,iron flocs easily formed which obstructed the bed to develop the overall effectiveness.