Adsorption Of Heavy Metal On Different Temperature Derived Biochars From Coconut

Use the coconut fibre and coconut shell to preparate of biochar at300℃.500and700℃. Research the effects and mechanism of the biochars adsorb pb(Ⅱ) to compare the differences between each other, providing a basis for product high adsorption properties biochar. Using the TG-DTG, BET, FTIR, SEM, EDS method to analysis physical and chemical characteristics of biochars, using isothermal adsorption experiment to analysis the consequences of the biochar adsorb of lead. Aimed at screening highly efficient heavy metal absorbent, three coconut fiber-derived biochars (YA300, YA500and YA700) were prepared by pyrolysis of coconut shell fiber at different temperatures (300,500and700℃) under a limited oxygen condition to investigate their capacities and mechanisms in absorption of metals including Cd(Ⅱ),As(Ⅱ),Cr(Ⅲ) and Cr(Ⅵ). Langmuir and Freundlich Sorption Isotherm Models were applied to study the metal absorption differences of these biochars. Granite Latosol from Hainan Province of China were incubated with three coconut fiber-derived biochars pyrolysed at300,500and700℃(refer to YA300, YA500and YA700). To provide the theoretical basis for the research on remediation of heavy metal contaminated soil by adding biochars, the effect of biochars pyrolysed at different temperatures on soil for Pb(Ⅱ) adsorption and mechanism were investigated by finishing batch isothermal adsorption and desorption experiments. The Langmuir and Freundlich sorption isotherms were used to model the adsorption datas of Pb(Ⅱ), and calculation method of adsorption and desorption was used to investigate the difference of electrostatic and non-electrostatic adsorption of treatment soils to Pb(Ⅱ). Results showed that:1. At the same pyrolysis temperature, the adsorption amount of coconut fibre-derived biochar are greater than coconut shell-derived biochar. With the same material preparation of biochar, the higher the temperature, the better adsorption effect; In the preparation of the two materials under different pyrolysis temperature, results of biochar on the adsorption Pb(Ⅱ) fit the Langmuir isothermal adsorption curve regression better; Coconut fibre-derived biochar has better adsorption performance than coconut shell-derived; the adsorption of coconut shell-derived biochar is more stable; Biochar preparated of high temperature has more Pb(Ⅱ) adsorption capacitythan then low temperature preparated of biocha.2. The Langmuir and Freudlich Sorption Isotherm Model well fit the metal absorption curves of these biochars. The maximum absorption capacities of biochars onto Cd (Ⅱ) and Cr (Ⅲ) were increased, while the maximum absorption capacities onto As (Ⅲ) and Cr (Ⅵ) decreased, with the pyrolysis temperature increasing from300℃to500and700℃. And it was suggested that the main factors leading to the increase in Cd(Ⅱ)and Cr(Ⅲ) absorption were the increase in C and ash content, pH, CEC and surface area of biochar, that increased with the pyrolysis temperature increased. And the reasons causing the decrease in As(Ⅲ) and Cr(Ⅵ) absorption were the increase in base functional groups that increases with the decrease of O and H content, the decrease in hydroxyl and phenolic hydroxyl functional groups with the increase of pyrolysis temperature.3.The incorporation of coconut fiber-derived biochars induced a significant increase in soil pH value and cation exchange capacity after30d of incubation, the improvement order is YA700>YA500>YA300; the incorporation of biochars also increased Pb(Ⅱ) adsorption capacity of soils, while increased the non-electrostatic adsorption of soils to Pb(Ⅱ), the improvement order also present to be YA700>YA500>YA300; The Langmuir model was a better fit for isothermal adsorption of treatment soils to Pb(Ⅱ). The maximum adsorption capacity of subsoil to Pb (Ⅱ) is4.89mg/g, while it increased to8.04,9.35and17.5mg/g when incorporate with YA300, YA500and YA700after incubation. For low pH value and cation exchange capacity of subsoil, the incorporation of coconut fiber-derived biochars majorly increased the pH value, cation exchange capacity and negative surface charge, induced an increase Pb (Ⅱ) adsorption capacity and non-electrostatic adsorption of soils, therefore, decreased the activity of Pb (Ⅱ) in soils.