Preparation Of Alkali-lignin Biochar And Application In Heavy Metal Adsorption

With the rapid development of industry and agriculture,a large number of heavy metals pollutants are discharged into ocean and rivers,Resulted in far more than the river’s self-purification ability,The treatment of heavy metal in pollution water has become a hot topic in the world.Adsorption is a promising treatment method in recent years because of the difficulty in biodegradation and transformation of heavy metals.Biochar is a kind of adsorbent material with low cost and sustainable development.It has a broad application prospect and has attracted extensive attention in recent years.In this paper,biochar was prepared from alkali lignin,and subsequentiy used to investigate the adsorption properties of Cd²⁺,Cu²⁺,Zn²⁺ and Ni²⁺ in single ion system,binary system,ternary system and quaternion system,furthermore,it was used to research the adsorption mechanism of heavy metals by alkali lignin-based biochar.This paper is mainly as follows:1.Biochar has been prepared by the pyrolysis of alkali lignin under different temperatures.,and used to research the physical and chemical properties of biochar.The results show that alkali lignin-based biochar shows alkalinity,small specifics surface area,abundant functional groups,and a large number of white crystals on the surface（sodium carbonate,sodium chloride）.2.The single ion static adsorption experiment showed that the adsorption of alkali lignin-based biochar on Cd²⁺,Cu²⁺,Zn²⁺ and Ni²⁺ was dominated by chemical adsorption and supplemented by physical adsorption,which could be well fitted with Freundlich adsorption model and Langumuir adsorption model.Under optimal adsorption conditions,the adsorption capacity of lkali lignin-based biochar is Cd²⁺（812.33 mg/g）>Cu²⁺（462.96mg/g）>Zn²⁺（398.73 mg/g）>Ni²⁺（325.92mg/g）obtained bythermodynamic fitting in a single system.Precipitation（more than 50%）and complexation（M-πcomplexation and functional group complexation）are the main adsorption mechanisms.There are some inorganic salts in biochar,which leads to dominance.If remove the effect of inorganic salts,the largest contribution of the mechanism is M-πcomplexation.There are vacant orbitals in heavy metal ions,which can be complexed with the electron donor system of biochar.Therefore,this kind of biochar has excellent adsorption property to all heavy metals.3.Multiple competitive static adsorption experiments showed that when there are multiple ions in the solution,the adsorption amount of Cu²⁺ by alkali lignin-based biochar is much higher than that of Cd²⁺,Ni²⁺ and Zn²⁺,and its adsorption capacity is even higher than that of single adsorption,indicating that it can promote the adsorption of Cu²⁺ when the competitive ions in the solution For Ni²⁺ and Zn²⁺,the presence of Cu²⁺ greatly inhibited the adsorption of biochar on them,while for Cd²⁺,the presence of Cu²⁺ had little inhibition.The adsorption competitiveness of Cu²⁺ is the strongest,follow by Cd²⁺,Zn²⁺ and Ni²⁺.