Removal Of Cadmium And Arsenic From Water And Soil By Bio-based Carbon Materials

With the development of industrial production and the improvement of people's living standards,heavy metal pollution has become increasingly serious.Heavy metals cause water and soil pollution,and then enter the body through the food chain,which has a serious impact on human health.Among them,cadmium and arsenic are the most typical and serious heavy metal pollution.At present,the methods for treating cadmium and arsenic pollution in water and soil include flocculation precipitation method,membrane filtration method,ion exchange method,and electrochemical method.However,these methods have problems such as high cost,complicated steps,and easy to cause secondary pollution.Adsorption method has become the main method for removing heavy metals due to its simple operation and high removal efficiency.At present,common adsorbents include metal oxides,graphene,biochar,kaolin,etc.These adsorbents have the problems of relatively poor adsorption effect or high production cost.Therefore,the preparation of an efficient and low-cost adsorbent has become a research hotspot.Biomass materials have a wide range of sources and low cost.We have combined biomass materials with other materials such as metal oxides and kaolin to overcome the defects of the original materials and give play to the advantages of a single material.It is mainly divided into the following three parts :(1)In this study,a novel carbon aerogels(CGs)is prepared from persimmon fruit via hydrothermal treatment at 140?,product freeze-drying and finally carbonization at 550? for 4 h under an inert atmosphere.A further carbon aerogels material containing magnetite nanoparticles(denoted as MCAs)is also prepared from persimmon by introducing a microwave-assisted step into the CGs synthesis.Characterization of the CGs and MCAs materials reveals that both materials have high specific surface areas and very porous structures,with the Fe3O4 nanoparticles in MCAs possessing a yolk-shell structure.The adsorption experiment also been performed to investigate the adsorption performance of prepared CGs and MCAs.The results suggest that 100% of As(V)in water and 98.3% of As(V)in mud can be removed with MCAs as the absorbent.(2)Currently there is enormous interest in the discovery of efficient and low cost adsorbents for the removal of heavy metals from water and soils.Herein we describe the successful fabrication of a novel biochar-porous geopolymer(BC/PGP)composite whose physical properties were tailored for heavy metal adsorption.The BC/PGP composite was prepared in a facile two-step process.Firstly,hemp straw powder was introduced into a conventional alkaline activator-assisted synthesis of a geopolymer from metakaolin.The resulting composite was then heated at 600? for 4 h under an N2 atmosphere.The hemp powder served as both a biochar source and porogen in the synthesis of BC/PGP.The BC/PGP composite possessed a high specific surface area and greatly improved mass transfer efficiency relative to its individual components(BC or GP),resulting in an improved adsorption capacity for Cd(II)ions.The BC/PGP adsorbent was effective in removing Cd(II)ions from water at a low concentration,and could efficiently remove Cd(II)from sand-soil mixtures.Results suggest that the low cost BC/PGP adsorbent developed in this work was good potential for waste water treatment and detoxification of soils contaminated by heavy metals.(3)In this study,calcium carbonate and sodium hydroxide in discarded crab shells were used to prepare alkaline activators,and diatomite was used to prepare chitosan-doped single geopolymers.And change the ratio of alkaline activator to diatomite to optimize material properties.The adsorption performance of crab shell(CS),diatomaceous earth(DM),and a single geopolymer(CPG)made with different proportions of activator on Cd(?)in aqueous solution was compared.CGP(4:1)prepared at 4:1 has the best adsorption effect.The adsorption process of Cd(?)in aqueous solution by this adsorbent conforms to the quasi-second-order kinetics model and Langmuir adsorption isotherm model.The maximum adsorption amount can reach 123 mg / g,indicating that the material is chemically adsorbed to Cd(?).It is an autonomous adsorption process and single-layer adsorption,and the adsorbent also has a good adsorption effect on Cd(?)in soil,which makes the adsorbent have a good application prospect.