Preparation And Adsorption Performance Of Biochar-based Adsorbent For Pb²⁺ And Cu²⁺ Removal

In this study,peanut shell biochar is selected as the basic material for adsorbing Pb²⁺ and Cu²⁺ and its adsorption performance is researched.In order to obtain a stronger adsorption capacity,potassium permanganate is used to modify the peanut shell biochar adsorbent.In view of the fact that the original and modified biochar which has adsorbed heavy metals is difficult to be separated from water.This study also focuses on the research of biochar immobilization adsorbent.The peanut shell biochar powder is immobilized by sodium alginate?SA?gel embedding method using Ca²⁺ as the crosslinking agent.Firstly,the suitable sodium alginate concentration,calcium chloride mass fraction,stirring crosslinking time and particle size are selected to study the sphericity of the gel ball,the effect of embedding carbon powder and the mechanical properties.Secondly,the optimum biochar embedment and rhamnolipid dosage are selected by the research of adsorbing Pb²⁺ and Cu²⁺.Under the optimum conditions,the double modified gel beads of immobilizing potassium permanganate modification biochar with excellent adsorption performances are prepared.In this study,scanning electron microscopy?SEM?,fourier transform infrared spectroscopy?FTIR?and X-ray powder diffraction?XRD?are utilized to characterize the surface morphology,functional groups and structure of peanut shell biochar-based adsorbents.In order to research their adsorption properties for Pb²⁺ and Cu²⁺,the effects of solution p H value,dosage of adsorbents,initial mass concentration of Pb²⁺ and Cu²⁺,adsorption time on the adsorption of Pb²⁺ and Cu²⁺ are studied by batch experiments.To analyze the adsorption mechanisms and evaluate the adsorption effect,the Langmuir and Freundlich isothermal adsorption models,the pseudo-first-order and pseudo-second-order adsorption kinetics models are utilized to analyze the processes of isothermal and kinetic adsorption,respectively.Moreover,the desorption and regeneration properties of the double modified gel beads are also investigated.The aim of the study is to provide theoretical basis and technical support for further development of high-efficiency adsorbents and large-scale application of adsorption technology in heavy metal pollution treatment.The main results are as follows:?1?The adsorption of peanut shell biochar to Pb²⁺ and Cu²⁺,which is suitable for the solution p H from 4.5 to 5.5 and from 5.0 to 6.0 respectively,when the initial mass concentration of Pb²⁺ and Cu²⁺ are 100 mg/L and 75 mg/L,and the biochar dosages are 2 g/L and 6.25 g/L,whose equilibration time is 480 min and 900 min,and adsorption capacities are49.32 mg/g and 11.35 mg/g,respectively.?2?The adsorption of Pb²⁺ by potassium permanganate modification peanut shell biochar reaches equilibrium at 720 min at the condition of initial mass concentration of 100 mg/L and dosage of modification biochar of 0.50 g/L,and the theoretical equilibrium adsorption capacity is 195.37 mg/g;the adsorption of Cu²⁺ by potassium permanganate modification peanut shell biochar reaches equilibrium at 960 min at the condition of initial mass concentration of 100 mg/L and dosage of modification biochar of 2.00 g/L,and the theoretical equilibrium adsorption capacity is 49.19 mg/g.?3?The optimum preparation conditions of immobilized biochar gel bead adsorbent are as follows: sodium alginate concentration of 13 g/L,calcium chloride mass fraction of 3.5%,stirring crosslinking time of 50 min,gel bead diameter of 1.8 mm,rhamnolipid volume ratio of 1%,potassium permanganate modification biochar powder mass fraction of 0.5%;and the adsorption of Pb²⁺ and Cu²⁺ by double modified gel beads reaches equilibrium at 720 min and840 min at the condition of initial mass concentration of 100 mg/L Pb²⁺ and 50 mg/L Cu²⁺ and dosage of double modified gel beads of 12 g/L and 16 g/L,and the theoretical equilibrium adsorption capacities are 210.25 mg/g and 70.69 mg/g,respectively.It is also found that the double modified gel beads have good regeneration and utilization ability.?4?The adsorption processes of peanut shell biochar-based adsorbents are fitted well with the Langmuir isothermal adsorption model and the pseudo-second-order adsorption kinetics model,i.e.,adsorption is cushy to carry out and the chemical adsorption is the main adsorption process.