Adsorption Characteristics And Mechanism Of Copper Ions From Aqueous Solutions By Acidosasa Edulis Shoot Shell

Heavy metal wastewater has become one of the most urgent environmental problems because of its high toxic,non-biodegradable and persistent nature.Due to the fascinating features of biosorption,such as low-cost,eco-friendly,and high efficiency in treating low concentration wastewater,it received huge expectations in academic,research,and industries.In the present study,acidosasa edulis shoot shell?AESS?was used as a biosorbent to remove copper ions from water.The effects of process conditions were studied by static adsorption method.The "particle concentration effect?Cs-effect?" phenomenon was investigated.The biosorption experimental data were analyzed by several isotherm models,kinetic models and thermodynamic parameters to better understand the biosorption characteristics and the biosorption mechanism which was further conformed by several characterization methods.The consecutive biosorption-desorption cycles were conducted to examine the stability and reusability of the biosorbent.In order to enhance the copper ions adsorption capacity,the feasibility of alkali treatment of acidosasa edulis shoot shell was explored,the modification and biosorption mechanism was confirmed by functional groups determination,point zero charge determination,SEM,FTIR and XRD.The main conclusions were as follows.?1?The acidosasa edulis shoot shell could be used as an alternative biosorbent for copper ions removal from aqueous solution.?2?There was obvious Cs-effect in the Cu2+-AESS biosorption process,and the solid-liquid adsorption system was in "metastable-equilibrium adsorption state".?3?The biosorption of copper ions mainly occurred in the amorphous region of acidosasa edulis shoot shell.The carboxyl and hydorxyl groups were mainly responsible for the biosorption.Carboxyl groups exchanged H+ with copper ions by ion-exchange mechanism,while hydroxyl groups formed complex with copper ions.?4?The optimum pH was founded to be 5.The adsorption capacity increased first and then decreased with the increasing temperature?in the range 25-55 ??.The adsorption capacity increased with the initial copper ions concentration?in the range 10-100 mg·L-1?.The removal rate of copper ions increased first and then remained at a certain level with the increasing biosorbent concentration?in the range 2-20 g·L-1?.The adsorption was rapid,the adsorption capacity is eighty percent of the saturated adsorption capacity in the first 5 min,and the equilibrium was obtained in the first 30 min.?5?Compared to Langmuir and Freundlich isotherm models?two-parameter model?,Redlich-Peterson model?three-parameter model?could describe the equilibrium data better.The kinetics data were best described by the pseudo-second-order model,and the pseudo-second-order rate constant increased with the increasing temperature and initial copper ions concentration.Both the film diffusion and intra-particle diffusion were the rate-controlling steps of the whole biosorption process.?6?Negative value of ?G⁰ and positive value of ?H⁰ indicated the biosorption process was spontaneous and endothermic.The positive value of ?S⁰ indicated the increased randomness at the solid/solution interface after copper ions adsorption.?7?0.05 mol·L-1H₂SO₄could be used as suitable eluent,the desorption rate was more than 80 percent after four adsorption-desorption cycles.?8?The modification of acidosasa edulis shoot shell by NaOH to improve its adsorption capacity was feasible.