Adsorption Characteristics Of Micro-nano Crab Shell Particles For Copper And Phosphorus In Wastewater

Crab shells with low added value have long been regarded as waste and discarded,resulting in great waste of biological resources and environmental pollution in coastal areas.The recycling of discarded crab shells is the only way to solve this dilemma.In our study,the effects of different influencing factors?including reaction time,temperature,amount of adsorbent,initial concentration of solution and pH?on the adsorption properties of copper and phosphorus in wastewater were investigated by orthogonal test.On the basis of experiments,adsorption kinetics and thermodynamics studies were carried out,and explored the adsorption mechanism of discarded crab shells.The results of adsorption of copper from waste crab shells showed that:1)The removal rate of copper ions increased with the increase of reaction temperature,increasing from 78.90%at 20? to 97.50%at 50?.The acidic environment is not conducive to the adsorption of copper ions.Through single factor and orthogonal test analysis,the copper ion removal rate was as high as 98.20%when the initial concentration of copper ion was 100 mg/L,temperature at 50?,pH=8 and adsorption time was 180 min.2)The Langmuir adsorption isotherm equation well describes the adsorption of copper ions by the discarded crab shell,and its maximum saturated adsorption capacity is 64.94 mg/g.The calculation of kinetic parameters shows that the quasi-secondary kinetic model can better describe the kinetic behavior of the adsorption of copper ions by discarded crab shells.The thermodynamic equilibrium constant Kc increased from 53.37 to 665.55 as the reaction temperature increased,further confirming that the high temperature is favorable for the adsorption of copper ions.3)XRD,FTIR and XPS analysis of the discarded crab shell before and after adsorption showed that the adsorption of copper ions may be a chemical adsorption process,in which the amino and hydroxyl groups in the crab shell reacted with copper.The results of adsorption of phosphorus from waste crab shells showed that:1)Acidic?pH 2.0-5.0?and alkaline?pH 7.5?11.0?environment are not conducive to the adsorption of phosphorus by discarded crab shells.The amount of phosphate adsorbed increased with the increase of reaction temperature,from 0.98 mg/g at 15? to 1.37 mg/g at 50?.2)The Freundlich adsorption isotherm equation can better describe the adsorption of phosphorus on the waste crab shell,and the maximum saturated adsorption capacity is 4.60mg/g.The quasi-secondary kinetic model is more suitable for describing the kinetic behavior of phosphorus adsorption by discarded crab shells.On the thermodynamic analysis surface,?H0 and ?S0 were 11.270 kJ/mol and 0.114 kJ/mol/K,respectively,and ?G0 was varied between-22.27 and-26.19 kJ/mol.3)EDS analysis showed that the content of calcium and carbon in the discarded crab shell decreased and the oxygen content increased after adsorption of phosphorus.The XPS analysis observed changes in the binding energy of Ols,and Ca2p and P2p showed new peaks with binding energies of 134 and 347.9 eV.The removal of phosphorus from the discarded crab shell is mainly caused by the hydrolysis of phosphate ions to produce precipitation of H₂PO₄^-and HPO₄^2-with Ca²⁺ in the adsorbent.