Preparation Of MgO-loaded Biochar And Its Adsorption Performance For Bimetallic Systems Of Pb(?) And Cd(?)

In recent years,with the continuous development of global industry and economy and excessive environmental damage,water pollution has become increasingly serious,especially heavy metal pollution.Adsorption is a low-cost and widely used treatment method for heavy metals.Biochar,as a new adsorbent,has a broad development prospect in the treatment of heavy metal pollution in water,with the characteristics of safety,no pollution and wide range of raw materials.At present,the research mainly focuses on the removal of single heavy metal ions.While,in the industry wastewater,the components are complex,including a variety of heavy metals and other pollutants.Therefore,how to obtain highly selective biochar is the main research direction at present.In this study,MgO-loaded biochar was prepared by maceration-pyrolysis method,and its isothermal adsorption characteristics,adsorption kinetics,acid resistance,competitive adsorption and dynamic adsorption were analyzed.The adsorption mechanism is analyzed through experiments and characterization results,while the dynamic adsorption was simulated and evaluated by Comsol Multiphysics software.Origin biochar AM-400 was prepared from xylose residue as raw material,and biochar MgO-ABC was prepared by maceration-pyrolysis method.MgO-ABC exhibits a Pb?II?adsorption capacity of 880.1mg/g and a Cd?II?adsorption capacity of 425.3 mg/g.Pb?II?and Cd?II?were better fitted with the Langmuir adsorption model,indicating that the adsorption of Pb?II?and Cd?II?was monolayer adsorption.While the kinetics of Pb?II?was more in line with the pseudo-second-order kinetics,the adsorption process of Cd?II?was better fitted by the first-order kinetic model.The initial p H affects the adsorption capacity of heavy metals mainly by consuming the MgO on the biochar surface through the concentration of H+ in the solution,and occupying a large number of adsorption sites on the biochar surface in the competition between H+and heavy metal ions.The main mechanism of adsorption of Pb?II?and Cd?II?by MgO-ABC is ion exchange and precipitation reaction.The products of precipitation reaction are Pb3?OH?2?CO3?2 and CdCO₃,respectively.Besides,carbon dioxide is conducive to the formation of Pb3?OH?2?CO3?2 by providing carbonate,and the complexation reaction of cationic-?also promotes Cd?II?adsorption.The adsorption capacity of MgO-ABC was studied in the system with the coexistence of multiple heavy metals.In the system of Pb?II?and Cd?II?,there is inhibition between Pb?II?and Cd?II?adsorption.When the addition amount of Cd?II?was 1.5mmol and p H was 4.0,Kr reached the peak,showing MgO-ABC had the best selective adsorption for Pb?II?.In the complex system,the main reason for the inhibition of Cd?II?adsorption by Pb?II?may be that lead is more likely to react with oxygen-containing functional groups,and the stability of Pb3?OH?2?CO3?2 formed by Pb?II?adsorption is higher than the stability of CdCO₃.While the cationic-? bond complexation reaction increases the adsorption capacity of Cd?II?,which is not the main reaction mechanism to Cd?II?adsorption and has little effect on competitive adsorption.Finally,the adsorption model was established by Comsol Multiphysics to evaluate the adsorption performance of adsorption beda nd predict the service life of the adsorption column.The bed height,entrance velocity and entrance concentration affect the breakthrough time by increasing the active site,the solution retention time,the mass transfer rate and the mass transfer driving force,respectively.With faster entrance velocity,higher bed height,higher initial Pb?II?concentration,the breakthrough time was shorter.The change of bed height and entrance velocity will not affect the adsorption balance and capacity of Pb?II?,and only change the time to reach the maximum adsorption capacity.However,the change of initial influent concentration will not only affect the time required to reach the maximum adsorption capacity,but also affect the maximum adsorption capacity of biochar.The breakturongh curve of dynamic adsorption of Pb?II?on MgO-ABC was well described by Thomas model,with the theoretical equilibrium adsorption quantity Qe of 780.4mg/g.