Study On The Preparation And Mechanization Of Geopolymer From Vanadium Tailings By Mechanical Activation

Geopolymer is a new kind of inorganic material consisting of tetrahedral SiO₄and AlO₄ units polycondensed into three-dimensional structure under the reaction between aluminosilicate materials and alkaline activator.Geopolymer exhibits good chemical and thermal stabilities,high compressive strength and anti-permeability.Also,the preparation of geopolymer needs less cost and energy,and emits 80%CO₂less than that of Portland cement,which is environmentally friendly.Thus as a promising alternative cementitious product,it has attracted more attention in recent years.In general,many materials that are rich in silica and alumina can be used to prepare geopolymer including kaolin,fly ash,even waste materials such as slag.In China,large amount of vanadium tailings has been accumulated due to the rapid development of vanadium extraction from stone coal,which occupied vast land and post treat to environment.Thus,it is urgent to pay more attention to the utilization of vanadium tailing.Vanadium tailing is a potential material for geopolymer preparation,thanks to the presence of silica and alumina oxides as the main components.However,it has seldom received the attention on geopolymer preparation due to its low reactivity,which can result in the poor performance of geopolymers.Thus further investigations to improve the reactivity of the tailing and make it possible as the raw material for geopolymer preparation are needed.The main contents and results are as follows:?1?After mechanical activation,the particle size of tailing is reduced with the increasing specific surface area,and the content of active component and the surface activity are improved.The reactivity of mechanical activated tailing is improved significantly,which promotes the polymerization reaction.The activation efficiency of agitated milling is better than vibratory milling and planetary milling.?2?The mechanical activated tailing is used as the main material for geopolymer and the optimum conditions for geopolymer preparation are as follows:the Si/Al of the material with 2.5,the ratio of cement to sand with 1:1,the amount Na₂SiO₃ with21%,the ratio of liquid to solid with 0.34.The amount of Na₂SiO₃ and curing conditions have an great important influence on decreasing the efflorescence behavior of geopolymer.It can decrease the efflorescence behavior of geopolymer by control the amount of Na₂SiO₃ in an appropriate range and increasing the curing temperature properly?>40°C?.Appropriate introduction of additional calcium source can increase the early compressive strength of the polymer sample.?3?The results of XRD,FTIR and SEM-EDS analysis show that there is a small amount of crystalline phase in the product expect for the amorphous aluminosilicate.In the low calcium system,the main crystalline phase in the product is mainly zeolite-like phase,and in the high calcium system,the main crystalline phase contains the C-S-H phase expect for zeolite-like phase.Under the alkaline conditions,Si-O bond and Al-O bond are broken,and partly tetrahedral AlO₄ replaces part of SiO₄,which leads to the structural reorganization.The early product of the polymer sample is PSS type and later is PSDS type.?4?The formation of the geopolymer is as follows:firstly,the sodium silicate hydrolyze to OH-and silicic acid,and then the aluminosilicate materials dissolve and depolymerize as oligomers in the high alkaline conditions.The oligomers,silicic acid,alkali metal ions and OH-polycondense to Si-O-Al multimers.Finally,amorphous aluminosilicate gel and zeolite phase are formed.