Air-quenching High Titanium Blast Furnace Slag And Its Application Exploration

High titanium blast furnace slag is a bulk solid waste emitted during the process of smelting pig iron from vanadium and titanium magnetite.Its composition and characteristics significantly differ from conventional blast furnace slag.The Ti O2 content of high titanium blast furnace slag is generally above 15%,with lower levels of calcium,silicon,aluminum,and magnesium oxides compared to blast furnace slag.It exhibits a relatively strong ability for Ti O2 nucleation and crystallization growth.Despite the use of water quenching and rapid cooling processes,a considerable amount of physicochemically stable perovskite and diopside remain,and its glass phase content is lower than that of traditional blast furnace slag.Therefore,high titanium blast furnace slag has minimal hydration and low activity,making it unsuitable as a cementitious material for cement or concrete with poor usability and economic value.Moreover,the environmental conditions of the naturally cooling or water quenching and rapid cooling process slag pretreatment sites are harsh,and the wastewater,dust,and slag contain a significant amount of heat that cannot be recycled.This is incompatible with the industry’s environmental development goals.The air quenching process,on the other hand,is relatively simple,with high cooling granulation efficiency and heat recovery,and has been successfully employed in the field of molten steel slag pretreatment.In this thesis,air-quenched high-titanium blast furnace slag(ATS)was obtained by applying the remelting-air-quenching process as a modification pretreatment of blast furnace slag.The air-quenched modification process technology and physicochemical properties of ATS were studied,and the application of ATS was discussed based on these findings.The main conclusions of this research are as follows:(1)Air-quenching modification effectively achieves the cooling granulation,mineral reconstruction,and particle reshaping of high-titanium blast furnace slag.The particles of ATS are mainly distributed below 4.75 mm,exhibiting high sphericity and a compact and smooth surface.It has low crushing value and low bulk porosity.The mineral composition of ATS is mainly glassy,with the major elements uniformly and continuously distributed in the glassy matrix.The Ti-O groups enter the glass network of ATS,enhancing the glass network framework and improving the stability of ATS in strong acid(p H=2.36)and strong alkali(p H=13.2)environments.(2)ATS has high density,low bulk porosity,high sphericity and roundness,low crushing value,good strength,and low water absorption,making it suitable as a functional aggregate.Cementitious grout materials prepared with ATS aggregates meet the requirements of Class III cementitious grout materials in terms of flowability,mechanical properties,and vertical expansion when the modified fineness modulus is2.5,the sand-to-binder ratio is ≥ 0.9,and the water-to-binder ratio is 0.24-0.27.When the sand-to-binder ratio is 1.1,the grout material exhibits optimal mechanical properties,with compressive strength and flexural strength reaching 73.6 MPa and14.2 MPa,respectively.(3)The ATS aggregates,densely packed with a maximum particle size of 2.36 mm and 1.18 mm,exhibit remarkably low void ratios of only 33.55% and 32.57%,respectively.The resulting ultra-high performance concrete(ATS-UHPC)demonstrates excellent workability and mechanical properties.The introduction of water-quenched high titanium slag(WTS)as a porous lightweight aggregate effectively reduces the apparent density of ATS-UHPC and suppresses system self-shrinkage and drying shrinkage.It is important to note that this addition leads to a significant decrease in compressive strength.(4)ATS has the potential to be used as a petroleum fracturing proppant,but it faces challenges such as low crushing value and high acid solubility.After being heat-treated at 1000°C for 3 hours,ATS proppants with specifications of 16-30 mesh,40-70 mesh,and 70-140 mesh exhibit sphericity and roundness >0.9,with respective crush rates of 12.8%,9.15%,and 4.97%,and acid solubilities of 12.8%,10.1%,and9.0%.The heat treatment introduces crystals such as calcium titanate,pyroxene,and clinopyroxene,while eliminating the internal stresses generated during the air-quenching process,significantly improving the anti-crushing ability and acid resistance of ATS.