Preparation Of Biochar Modified With Phoshoric Acid And Its Adsorption Properties For Rare Earth Scandium

Scandium（Sc）and its compounds have been widely used in aerospace,energy,laser,nuclear technology,medical and other fields due to their excellent physical and chemical properties.With the increasing development of science and technology,the market demand for scandium resources grows rapidly.However,limited by the lack of independent deposits,the extraction of scandium from secondary resources is difficult,and the process is complex and costly,leading to a high price of scandium and its compounds.Therefore,it has greatly practical significance to develop a low-cost but environmentally friendly way to achieve efficient extraction of scandium resources.Biochar,a cost-effective green adsorbent,has been widely used for the adsorption of heavy metal ions in the environment.In this study,phosphoric acid pretreated biochar was prepared by slow pyrolysi with pitaya peel used as the raw material.P40-750,which had the best performance,was further compounded with bis-（2-ethylhexyl）phosphate（P204）to achieve secondary modification,and a new adsorbent DP-X（DP and X represents composite material and the weight ratio of P204/P40-750,respectivily）was synthesized.The adsorption behavior and selectivity of raw DP-X for Sc（Ⅲ）were investigated through static adsorption experiments and its practicability was evaluated in actual red mud leaching solution.The adsorption mechanism of Sc（Ⅲ）on the adsorbent was revealed by combining the characterization means such as SEM,BET,FTIR,XPS and elemental analysis.The main conclusions are as follows:（1）The specific surface area and pore structure of biochar can be effectively expanded by phosphoric acid pretreatment modification.The surface pore structure,hydrophilicity,aromaticity and surface polar functional group content of the modified biochar are positively correlated with the pyrolysis temperature.The phosphorus-containing functional group is successfully introduced into the biochar adsorbent.Besides,the static adsorption experimental data were analyzed.The results showed that the phosphoric acid pretreated biochar（P40-750）prepared by pyrolysis at 750℃had the optimal adsorption performance for Sc（Ⅲ）.The maximum adsorption capacity was 20.77 mg/g at p H 3.The quasi-two-stage kinetic model and Freundlich isothermal line were in good agreement with the experimental data.The adsorption process for Sc（Ⅲ）was multi-layer chemical adsorption.Exhibits excellent selective adsorption and reuse properties at p H 3.The adsorption mechanism of P40-750 for Sc（Ⅲ）is complex,which is determined by the electrostatic attraction on the surface of biochar,the chelation of phosphorus-containing functional groups with Sc（Ⅲ）and the cation-πbond interaction.（2）A novel adsorbent called DP-X was successfully prepared by compounding P204 with P40-750 through the microporous and mesoporous structure of biochar.At p H 1,DP-0.25 exhibited the best adsorption performance for Sc（Ⅲ）.The whole adsorption process followed the quasi-second-order kinetics and Langmuir isothermal model,and belonged to single-layer chemisorption.The saturated adsorption capacity was 15.31 mg/g,which achieved the purpose of adsorbing Sc（Ⅲ）in a low p H environment.At p H 1,the selectivity for Sc（Ⅲ）was significantly stronger than that of P40-750,and excellent reusability was observed.In aqueous solution at p H 1,the cation exchange between H⁺and Sc³⁺on DP-0.25 surface-OH and the chelation of P=O functional group with Sc（Ⅲ）are the mechanisms by which Sc（Ⅲ）is adsorbed.Both P40-750 and DP-0.25 prepared in this work show strong utility.The extraction rate of Sc（Ⅲ）in the actual application of red mud leaching solution is83%and 90.83%respectively,Adsorbents are expected to be applied in the extraction of scandium.