Research Of Porous Ceramics By Nickel Smelting Slag

Nickel smelting slag?referred to as nickel slag?is a by-product in the production process of ferronickel.With the development of ferronickel industry,the discharge of nickel slag is increasing year by year,and may become the second largest industrial metallurgical slag after steel slag.However,the low content of precious metals,the low gelation activity and the poor stability of nickel slag limit the recovery and utilization of nickel slag.A large number of nickel slag are treated by stacking,landfill and other ways,not only occupying the land resources,but also the leaching of Ni,Fe,Co and other metal elements from nickel slag will pollute the soil and groundwater,which will cause harm to the environment and human health.At present,the preparation of porous ceramics with solid waste as raw material has become a research hotspot in recent years.The content of Si and Mg in nickel metallurgical waste residue is relatively high.More than 85%of them are in the form of Mg₂SiO₄ and MgSiO₃,which are good substitutes for ceramic raw materials.Therefore,using nickel slag as ceramic raw material can not only save industrial cost,but also reuse solid waste resources and reduce production cost.The porous ceramics with high porosity and low density were successfully prepared by using the magnetic separation technology.The phase composition and pore morphology of porous ceramics were analyzed by XRD,stereomicroscope and SEM.The main results are as follows:The porous ceramic with nickel slag was prepared by physical foaming method.The effects of raw material ratio,sintering temperature and the content of foaming agent on the bulk density,mechanical strength and pore structure of the samples were investigated.The results showed that porous ceramics with bulk density 200kg/m³,compressive strength 0.4 MPa and thermal conductivity 0.05 W/?m·K?could be prepared by EPS.When the sintering temperature was 1160?C,the crystal structure of the sample changed and MgAl₂O₄ spinel was formed.With the increase of the sintering temperature,the peak of MgAl₂O₄ became sharp.The crystal began to grow at this time,which was about 2?m in size.At this time,the pore structure of the sample was relatively complete,and the pore size was about 600-700?m.When the mass ratio of fly ash to nickel slag was 3:7 and the mass ratio of EPS to slurry was 1:10,a lightweight porous ceramic with a density of 199.5 kg/m³ was obtained.The compressive strength was 0.4 MPa,the flexural strength was 0.28 MPa,the volume shrinkage was 4.21%,and the thermal conductivity was 0.024 W/?m·K?.In this paper,nickel slag porous ceramics were prepared by chemical foaming.The effects of the ratio of raw materials,the type of foaming agent and the content of foaming agent on the bulk density,porosity,flexural strength and pore structure of the samples were studied.The results showed that a certain amount of nickel slag could reduce the temperature of the eutectic point,produce more liquid phase,and promote the foaming of porous ceramics in the sintering process,but the content of nickel slag should not be too high.When the content of nickel slag exceeded 60%,the bulk density of the sample began to increase.With the increase of the content of SiC,the porosity and bulk density could be increased and decreased.But when the content of SiC exceeded 1.0%,the bubbles began to grow unevenly and form pore structures with different sizes of 1 mm² mm.The bulk density of the samples increased slightly and the bending strength decreased.When the content of nickel slag was 50%,the foaming agent was silicon carbide,and the addition amount was0.8%,the sample sintered at 1100?C for 30 min had the best performance,compact bubble and similar size.At this time,the bulk density was 241 kg/m³,and the porosity was 87%.The effect of magnetic separation on the properties of nickel slag and porous ceramics was studied.The roller magnetic separator with adjustable magnetic field intensity?2000 Oe¹2000 Oe?was used to separate the magnetic nickel slag and the non-magnetic nickel slag.The results showed that magnetic separation does not affect the comprehensive utilization of nickel slag,and the main crystal structures of non-magnetic nickel slag were Forsterite,Enstatite,Clinoenstatite.According to EDS of non-magnetic nickel slag after magnetic separation with different magnetic field intensity,with the increase of magnetic field intensity,the distribution of iron elements in the region became more and more sparse.Magnetic separation can remove the mechanical iron and iron oxide existing in nickel slag,so as to reduce the powder density of nickel slag.After magnetic separation,the density of the non-magnetic nickel slag powder milled for 60 min?N2?decreased most obviously,as low as 2.956 g/cm³.Therefore,N2 was selected as the raw material to prepare light porous ceramics on the basis of the optimal formula.From the XRD of porous ceramic samples,the phase composition of the samples did not change due to magnetic separation,and with the increase of magnetic field intensity,the peak of Forsterite gradually increased and became sharp.At this time,the mechanical strength and porosity of the samples increased,and the volume density decreased.Obviously,magnetic separation can optimize the properties of porous ceramics,and the most suitable magnetic separation intensity of nickel slag is 8000-10000 Oe.