Synthesis Of Phosphate Adsorbents From Anodes Of Li-ion Batteries And Its Mathematical Modeling Study

Eutrophication is becoming more and more serious in China,even in the whole world,it's quite necessary to solve the problem of eutrophication.Adsorption method has drawn much attentions in the fields of removing nitrogen and phosphorus in waste water,due to its easy operation,less limiting factors and the advantage of not drawing other ions into the water.Besides,the usage amount of Li-ion Batteries?LIBs?are increasing more and more quickly in the current circumstances.If they can be recycled reasonably to synthesize phosphate adsorbents,it will not only contribute to alleviating pollution of eutrophication,but also help to recycle the waste sources and lower the production cost.Under such a background,this study used five carbon anodes of Li-ion batteries as matrixes to synthesize phosphate adsorbents with the method of Mg-modification.After measuring the phosphate removal rate of each material with and without modification,it can be found that the raw materials all had no phosphate adsorption ability,while after modification,the removal rate of each one had improved 60%at least.This result confirmed that the synthesis method could generally increase the phosphate adsorption ability of anodes of LIBs.To learn how pyrolysis temperature would affect the phosphate removal rate of products,MCMB was specifically used as feedstock to be pyrolysed under different temperatures.The result of phosphate removal test showed that the phosphate removal rate would keep above 90%,if the pyrolysis temperature was higher than 600?.Four kinds of advanced techniques including X-ray diffraction?XRD?,scanning electron microscope?SEM?,energy dispersive X-ray spectroscopy?EDX?and X-ray photoelectron spectroscopy?XPS?were used to characterize the physicochemical property of the synthesized product obtained from MCMB?MCMB-Mg?.The analytical results showed:before phosphate adsorption,XRD,SEM and other techniques all determined MgO crystals of nano-scale existed on MCMB-Mg;while after phosphate adsorption,they also demonstrated that Mg₃?PO₄?₂ crystals existed on the MCMB-Mg.Adsorption kinetics and isotherm studies of phosphate onto MCMB-Mg were conducted.The results showed that the law of dynamics here was controlled by first-order model,and the maximal adsorption capacity could reach 475.5 mg·g^-1 according to the Langmuir model,which reflected the great advantage of MCMB-Mg in phosphate adsorption.pH is a critical factor to affect the phosphate adsorption efficiency.To quantitatively analyse this influence,here for the first time,mathematical model based on thermodynamic theories was established to strictly deduce the function relationship between these two variables.The calculated results showed that if the final phosphate removal rate was higher than 60%,the corresponding initial pH should be kept in the range from 1.56?7.63.The relevant experiment result was consistent with the theoretical result,which confirmed the correctness of deduction.