Study On The Preparation Of Carbon Modified Steel Slag Adsorbent And Its Adsorption Of Cr(Ⅵ) And Hg(Ⅱ) In Wastewater

As a by-product of steelmelting,steel slag has some characteristics including wide source,low cost and stable structure.At present,steel slag is mainly used as a substitute for roadbed or cement,and there are few researches on the high-value utilization.This thesis uses steel slag and sawdust as raw material to prepare adsorbent by hydrothermal and burning method.The new adsorbent was prepared to study the adsorption properties,influencing factors,adsorption kinetics,and isotherm theoretical basis for the treatment of chromium and mercury-contaminated wastewater.The SEM-EDS,BET,XRD and other characterization methods were used to further investigate the adsorption.The results show as follows:(1)This study prepared CSS(carbon-steelslag,CSS).The CSS was characterized to analyse its structural and physical composition.Selecting raw material ratio of 1:1,hydrothermal method,and calcining temperature of 400°C as preparation methods,CSS was prepared with a 2 to 3 times higher adsorption capacity than the original steel slag and a reduced amount of heavy metal leaching.(2)This study explored the adsorption selectivity of metal ions for CSS,and selected Cr(Ⅵ)and Hg(Ⅱ)to explore optimal reaction conditions,including: adsorbent dosage,pH,reaction time,reaction temperature,and initial metal ion concentration.The results show that: When pH=7,20°C,and the dosage of CSS is 1g/L,the reaction reaches the saturation point where the concentration of Cr(Ⅵ)solution is 900mg/L.The saturated adsorption capacity was 509.7 mg/L.Similarly,when the concentration of Hg(Ⅱ)was 700 mg/L the saturated adsorption capacity was 387.1 mg/L.(3)This thesis analyzed adsorption kinetics and adsorption isotherm model.The results show that the pseudo-second-order kinetic equation can accurately describe the adsorption process of Cr(Ⅵ)and Hg(Ⅱ)by CSS.The first stage of the reaction is based on physical adsorption,but the whole process is mainly chemical adsorption.Freundlich adsorption equation fitting shows that the adsorption process is heterogeneous adsorption of multiple layers,and there are many kinds of chemical adsorption such as ion exchange.(4)Adsorption mechanism of CSS on Cr(Ⅵ)and Hg(Ⅱ)shows that the whole adsorption process goes through three stages: outdiffusion stage,intragranular diffusion and complex reaction stage.It mainly includes pore adsorption,electrostatic adsorption,surface functional group complexation reaction,metal ion exchange reaction,adsorption of siliconoxygen bonds.The metal ion complex,the activated silicon oxygen structure and the surface functional groups play an important role in the adsorption.