Synthesis And Adsorption Passivation Effect For Cd²⁺ In Water And Soil Of Carbon/doped Carbon Hydroxyapatite From Eggshell

Heavy metal pollutant Cd can accumulate in organisms and cause chronic poisoning through the food chain.Cd pollution in water and soil mainly comes from surface runoff,industrial wastewater,industrial waste residue,etc.,in situ adsorption fixation or biological activity passivation is a widely used repair method.Hydroxyapatite（HAP）is a kind of effective pollution passivating agent,but its cost is high,and its preparation process may have secondary environmental pollution risk so that it’s difficult to popularise the application.If the preparation of hydroxyapatite with biological materials such as animal bone,egg shell,shell and so on,the raw materials are cheap,the preparation process is environmentally friendly,and it has good economy and practicability.In this paper,carbon hydroxyapatite（CHAP）was prepared by using eggshell,and doped hydroxyapatite was prepared by modified CHAP with doping ammonium bicarbonate,the physical and chemical characteristics of CHAP,DCHAP were analyzed by X ray fluorescence spectrometer（XPS）,infrared spectrometer（FTIR）,and so on,through the analysis of the isothermal adsorption and adsorption kinetics of Cd pollution in water,the good effect of carbon/doped carbon hydroxyapatite（CHAP/DCHAP）was selected to as adsorbent materials for soil,by soil culture experiment to study on passivation effect of Cd contaminated soil,thus,the purpose of the experiment is to provide theoretical basis and technical support for using low-price CHAP materials for adsorption and reduction of soil cadmium.The following are main outcomes:（1）Using abandoned eggshell and the method of sol-gel,the carbon hydroxyapatite（CHAP）was prepared under the condition of 30℃,75℃and 120℃,the doped carbon hydroxyapatite（DCHAP）was prepared by this modification doping producyion on the basic,the CHAP and DCHAP all had excellent physical and chemical properties.The functional group structure of synthetic materials was basically the same as that of the ordinary hydroxyapatite（HAP）,and ppeared asymmetric stretching vibration split peak of CO₃^2-in functional group structure of synthetic materials;the CEC content(15.23cmol·kg^-1),specific surface area（28.86 m²/g）,CO₃^2-content（5.19%）and Cd²⁺adsorption(44.21 mg·L^-1)of synthetic carbon hydroxyapatite under 75℃（MC）were biggest,the grain of MC had low crystallinity and had microporous pore diameter,and the granule was flocculated like sponge;the the CEC content(22.12 cmol·kg^-1),specific surface area（94.04 m²/g）,the CO₃^2-content（7.33%）and Cd²⁺adsorption is largest of doped carbon hydroxyapatite with doping 8 g NH₄HCO₃ under 30℃（LC-4）,and it has micropores,and the surface of granule was covered with flocculent spherical particles.（2）The results of isothermal adsorption and adsorption kinetics of Cd²⁺in water showed that the adsorption of Cd²⁺in water by CHAP and DCHAP were consistent with Langmuir and Freundlich isothermal adsorption,and second order kinetics equation with the adsorption of electrostatic adsorption,ion exchange adsorption and coprecipitation were the main method.The adsorption performance was best of synthetic CHAP from shell and phosphoric acid under 75℃（MC）with the saturated adsorption amount of Cd²⁺of44.21 mg·L^-1;Under certain temperature conditions,adsorption amount of Cd²⁺of DCHAP in the water increased as the doping amount of NH₄HCO₃ increased,the adsorption performance was best of DCHAP which doping 8 g NH₄HCO₃ under 75℃（LC-4）,for the saturated adsorption amount of Cd²⁺was 61.69 mg·L^-1.（3）Compared with common abandoned eggshell（ES）and hydroxyapatite（HAP）,selecting the carbon hydroxyapatite（synthesized under the condition of 75℃）,doped carbon hydroxyapatite（30℃under mixed 8 g NH₄HCO₃ synthesis）which had excellent effect material of Cd²⁺adsorption as soil Cd pollution repair materials,repair agent adsorption desorption test results were shown that the maximum Cd adsorption（Qmax）of CHAP,HAP,and ES treated by low concentration restorer（1.5%）was not very different,between 6.07⁸.92 mg·g^-1,but the Qmax of DCHAP reached 12.50 mg·g^-1,which was1.40².06 times that of CHAP,HAP and ES.The effect of CHAP and DCHAP on soil Cd adsorption and desorption was relatively small,and DCHAP treatment has a significantly higher adsorption capacity than CHAP.The results of 30 days of soil passivation were shown that CHAP and DCHAP can effectively reduce the effective state of cadmium content in the soil,all with high concentration（5%and 7.5%）treatment effect was significantly greater than the low concentration（1.5%and 3%）,and with optimal treatment effect of DCHAP,CHAP with no obvious difference between HAP and ES.In addition,CHAP and DCHAP treatment significantly improved soil pH,effective phosphorus,effective potassium and alkali-soluble nitrogen,and improved soil nutrient supply.In conclusion,synthetic carbon hydroxyapatite by using abandoned eggshell（synthesized under the condition of 75℃）and on the basis of modified doped carbon hydroxyapatite by doping producyion（30℃under mixed 8 g NH4HCO3 synthesis）which had low grain crystallinity,developed microporous,and flocculent particles that were together like a sponge or surface was full of flocculent spherical particles,which had good physical and chemical properties,not only have good adsorption and stable effect for Cd²⁺in water and soil,can also be as passivation restorative materials for Cd contaminated soil,and the preparation process of CHAP and DCHAP were simple,and had no secondary pollution,and realizing the comprehensive utilization of shell resource.