Study On Functional Reconstruction Of Active Components Of Steel Slag And Removal Of Heavy Metals

How to combine the resource utilization of steel slag with the“carbon peaking and carbon neutrality”goal of our country,and“transform waste into treasure”,it is very important to find and design sustainable,green and low carbon disposal new strategy and resource utilization processes.This requires us to transform it into valuable active functional materials based on the concept of industrial ecology.The main core challenges are the adoption of harmless technologies and the improvement of the comprehensive utilization rate of steel slag.In view of the existing problems in the utilization of steel slag,this thesis systematically studied the resource utilization of steel slag,and obtained a variety of heavy metal purification materials.The main research results are as follows:Aiming at Ca,the main metal element in steel slag,calcium silicate hydrate with high adsorption capacity is synthesized from calcium components in steel slag to remove common metal ions.The spent CSH adsorbent is also used as a resource.Sparked by natural carbonation‘weathering’,the decalcification reactions of metal-bearing CSH results in recovery of noble metals（Ag,Au,Pd）.Moreover,after‘weathering’decalcification,the surface fractions of the AM^x+-CSH-CO₂can be converted into metal（Au⁰,Ag⁰,Pd⁰,Fe⁰,Co⁰,Ni⁰,Cu⁰,Zn⁰）,oxide（Ce O₂,Gd₂O₃ and Y₂O₃）nanoparticles,and diverse hybrid materials（Cu⁰-Ag⁰,Cu⁰-Ce O₂,and Cu⁰-Ag⁰-Ce O2）for construction of Si O₂-based nanocomposites,by exposing them in H2/Ar（5vol%H₂）mixed airflow.Notably,M⁰（M=Ag,Cu,Ni）@Si O₂,especially100Cu⁰@Si O₂,exhibits remarkable catalytic activity and high selectivity for（p-,m-,o-）nitrophenol→（p-,m-,o-）aminophenol reduction reactions.The performance of nanomaterials is often deteriorated due to the aggregation of nanoparticles.A hydroxyapatite（Hap）functionalized hierarchical porous biochar（HB）composite is fabricated using a filtrate rich in Ca²⁺ions after steel slag reuse and spent Hami melon peel as raw materials.Microstructural analyses indicate that Hap nanoparticles are loaded on HB with hierarchical pores.A series of HB-Hap materials by tuning HB addition amount（0.5,1,and 2 g）can be obtained through a coprecipitation process.As a case study,HB-0.5Hap exhibits high specific surface area of 66.92 m²/g and the maximum adsorption capacities of HB-0.5Hap are 134.4（Pb（II））and 60.4（Cd（II））mg/g,which are 1.77 and 1.23 times higher than that of pure HB,respectively.It is attributed to a synergistic mechanism involving ion exchange,chemical precipitation,surface complexation,and cation-πinteraction.According to a semi-quantitative calculation,ion exchange plays a major role in the removal of Pb（II）（78.61%,the relative contribution of ion exchange mechanism）and Cd（II）（77.77%）.Aiming at Fe and Mg,the main metal elements in steel slag,an innovative method is created for transforming RO phase(Mg O_0.239Fe O_0.761)on steel slag surface into nanostructured Mg_0.04Fe_2.96O₄ layer.It is found that salicylic acid modification and alkaline roasting procedures remarkably increase the specific surface area from 0.46m²/g（raw steel slag）to 69.5 m²/g(Mg_0.04Fe_2.96O₄),and the generation of Mg_0.04Fe_2.96O₄enhances the absorption of visible light and Cr（VI）conversion with 2-times increasement than raw steel slag.Surface complexation between H₂C₂O₄ ligands and Fe metal moiety on Mg_0.04Fe_2.96O₄ induces the intramolecular electron transfer under visible light irradiation based on a ligand-to-metal charge transfer mechanism,thus resulting in Cr（VI）photoreduction.Moreover,recyclability tests based on magnetic separation show that the photoreactivity is closely related to Mg content of Mg_0.04Fe_2.96O₄ layer where Mg leaching occurs and finally generates cubic spinel configuration Fe₃O₄.Based on the concept of multi-component utilization of steel slag,this work adopts a“branch”and“regroup”method to tailor steel slag and construct two current Cr（VI）removal nanomaterials:A filtrate rich in Fe（III）,Mg（II）,and Al（III）metal ions is applied as raw materials to synthesize 2D intercalated Mg/Al-layered double hydroxide-supported iron sulfide nanocomposites via carboxylate anion（Fe S-LDH-RCOO）.The acetate intercalated Fe S-LDH,Fe S-LDH-CH₃COO,shows a Cr（VI）adsorption capacity of 36.1 mg/g via synergistic effect of electrostatic interactions,hydrogen bonding and anion exchange.Moreover,the Ca-containing whewellite precipitation is collected for the crystallization of 1D hydroxyapatite（Hap）nanorod,which then is loaded by Fe（III）ions via cation exchange to construct Fe（III）-bearing Fe@Hap(x Fe@Hap,x represents the initial concentrations of Fe³⁺ion).60Fe@Hap shows 100%Cr（VI）photoreduction（60 m L,40 mg/L Cr（VI））with the assistance of oxalic acid based on intramolecular charge transfer from oxalic acid to Fe（III）in[Fe^III（C₂O₄）_n]^3-2n complex under visible light irradiation.