Study On The Characteristics Of Spirulina Adsorbing Rare Earth Ions (Er³⁺, Pr³⁺, Yb³⁺)

Rare earth is an indispensable key element in transforming traditional industries,developing emerging industries and national defense science and technology industries,but it is also an important strategic resource that cannot be regenerated.Biosorption technology is a rapidly developing wastewater treatment technology in the environmental field in recent years.It highlights important research value in the process of treating low concentration rare earth ion wastewater and is an effective way to treat rare earth wastewater.Biosorbents can be broadly divided into three types:bacteria,yeast and algae.The traditional process uses these three biosorbents to treat heavy metal ions.In this paper,Spirulina maxima cultured from algae species is innovatively used as biosorbent,and Er³⁺,Pr³⁺and Yb³⁺are used as target ions to systematically explore and study the biosorption mechanism where solve the problem of low-concentration wastewater discharge.Spirulina maxima is a kind of high quality material with mature cultivation technology,low cultivation cost and repeatable cultivation.Based on the basic research on the material properties and adsorption properties of spirulina platensis,a recycling and treatment technology for rare earth mine ion wastewater is designed,which can be processed in batches,is simple to operate and has low cost.The biological adsorbent Spirulina was analyzed and characterized by scanning electron microscope（SEM）,energy dispersive X-ray spectroscopy（EDX）,Fourier transform infrared spectroscopy（FT-IR）,X-ray photoelectron spectroscopy（XPS）,etc.In the experiment,the effects of initial pH value of solution,dosage of biosorbent Spirulina platensis,initial target ion concentration,adsorption time,mixed coexistence of various target ions and other factors on the adsorption process in simulated mine wastewater were studied.Finally,the application of acid in desorption after adsorption of rare earth ions by Spirulina platensis was investigated.The experimental data were fitted by Freundlich,Langmuir,Redlich-Peterson and Dubinin-Radushkevich isothermal adsorption models,pseudo first-order,pseudo second-order,Elovich equations and intraparticle diffusion kinetic models.Base on the adsorption experiments on spirulina,it was found that the optimal pH value for spirulina to adsorb Er³⁺,Pr³⁺and Yb³⁺was 5.0.The optimal dosage of spirulina is 2.0 g/L（50 mL）,and spirulina has high adsorption efficiency for Er³⁺,Pr³⁺and Yb³⁺.The adsorption process of Spirulina takes place in a fast adsorption process.In the adsorption process of rate is fast in the first 30 min,reaching more than 75%of the total adsorption amount,then the adsorption rate increases slowly,the adsorption rate curve tends to be stable after 30 min,and the curve remains basically unchanged after 60 min of reaction.The experimental results show that the adsorption process of Spirulina on Er³⁺,Pr³⁺and Yb³⁺meets the Freundlich,Langmuir,Redlich-Peterson and Dubinin-Radushkevich isothermal adsorption models.According to the correlation coefficient,Langmuir equation（R²>0.9）can be obtained,which can well fit the experimental data.The adsorption capacity is Er³⁺>Yb³⁺>Pr³⁺.The free energy of adsorption platensis is Pr³⁺>Yb³⁺>Er³⁺,which is greater than 8 kJ/mol,indicating that the adsorption process is chemical adsorption.According to the thermodynamic parameters of adsorption,the process of adsorption of rare earth ions by spirulina platensis is spontaneous,and the spontaneous degree is Yb³⁺>Pr³⁺>Er³⁺,and the adsorption process is endothermic.Through scanning electron microscopy（SEM）and energy dispersive X-ray spectroscopy（EDX）analysis of spirulina,it can be concluded that the element content changes during the adsorption of Er³⁺,Pr³⁺,Yb³⁺,thus it can be known that cation exchange adsorption occurs during the biosorption process.Comparing the Fourier infrared spectra（FT-IR）before and after adsorption by Spirulina platensis,it can be found that the change of peak shape indicates that functional groups participate in the adsorption process.Through X-ray photoelectron spectroscopy（XPS）analysis of the changes of various elements,it can be further found that functional groups participate in the reaction during the adsorption process.Desorption experiments show that rare earth ions can be recovered by HNO₃.The above results show that spirulina is an efficient,high-quality,simple and low-cost biosorption material,in which the adsorption removal rate of Er³⁺can reach90.73%,and the adsorption efficiency of Pr³⁺and Yb³⁺is above 75%,which can effectively treat and recover Er³⁺,Pr³⁺,Yb³⁺in mine wastewater.