Preparation And Properties Of Highmagnesium Nickel Slag-fly Ash Based Geopolymer Excited By Mixed Alkali Activator

High-magnesium nickel slag（HMNS）is an industrial waste produced in the production of ferronickel alloy,which has potential pozzolanic activity.Due to the low activity of HMNS,it is difficult to be used in alkali activated cementitious materials.In this thesis,the pozzolanic activity of HMNS is improved by adding CaO for molten water quenching and phase separation treatment.Different mixed alkali activators are selected and the optimum experimental process parameter of geopolymer is determined by orthogonal test.The geopolymer based on high-magnesium nickel slag（phase separation）-fly ash was prepared under the optimal experimental process parameter,and its reaction mechanism and process are analyzed.Finally,the raw material HMNS（phase separation and non phase separation）is partially replaced by Pb containing waste glass.The influence mechanism of silicon oxide in Pb containing waste glass as silicon source on geopolymer and the curing ability of geopolymer to Pb²⁺are studied.The crystal phase composition,network structure,micro morphology,mechanical properties,chemical corrosion resistance,thermal stability of geopolymer cementitious materials and the curing ability of geopolymer to Pb²⁺are studied by means of XRD,FTIR,SEM,DSC,heavy metal ion leaching dissolution and compressive test.The main research contents and conclusions are as follows:（1）The pozzolanic activity is improved by adding 20%wt CaO to the HMNS for molten water quenching and phase separation treatment.The dissolution of Si/Al element is the highest,the degree of vitrification is the highest,and the pozzolanic activity is the strongest.The bridging oxygen bonds（BOs）in the network of HMNS with CaO addition are interrupted to form non bridging oxygen bonds（Si–NBO and Si–2NBO）.The phase separation structure of rich silicon phase and rich magnesium phase is observed in HMNS20.The compressive strength of the prepared geopolymer increases with the increase of pozzolanic activity of the raw material.（2）The orthogonal test method is used to determine the optimal test scheme,that is,the mixed content of KOH is 7%,the curing method is standard curing,and the water cement ratio is 0.35.The compressive strength of geopolymer specimens cured for 28 days can reach34.6MPa,which is 56.6%higher than that of single Na₂Si O₃ activats.（3）Geopolymer is prepared by four phase separated raw materials.Tests show that geopolymer G-HMNS20 curing 28d has the highest compressive strength,up to 76.8MPa,forming more microcosmic morphology,adhesive and highly structured C（K）-A-S-H gel,forming Si-O-Si bond and Si-O-Al bond with stronger chemical bond energy,showing strong chemical resistance and thermal stability.（4）The compressive strength of geopolymer G-HMNS-W15 prepared by replacing one piece of raw material HMNS with Pb containing waste glass for 28 days is 51.86MPa.The compressive strength of geopolymer G-HMNS20-W15 prepared by replacing one piece of raw material HMNS20 with Pb containing waste glass for 28 days is is 30.95MPa.According to the leaching rate test of heavy metal ions,the low leaching concentration of Pb²⁺shows that the high degree of polymerization of geopolymer has good stability/curing performance for Pb²⁺.