Study On The Gelling Activity Of Copper-Nickel Slag By Different Activators

As the largest consumer of copper-nickel metal mines in the world,China's average output has reached 1 million tons every year.However,the problem of copper-nickel slag discharge and large-area accumulation in the production process had become an increasingly concern in the metallurgical industry and society.The use of copper-nickel slag to make cementitious materials can not only alleviate the large area stacking problem of copper-nickel smelting slag,but also transform the waste residue after smelting into useful materials by alkali-activated method,which has significant economic and environmental benefits.In this paper,the physical and chemical properties of the copper-nickel slag of the Kalatongke ore in Xinjiang were analyzed.The dissolution rate of silicon,aluminum and calcium in copper-nickel slag was studied by the method of alkali dissolution,and the potential activity was stimulated by different kinds of activators.Cementitious materials blended with fly ash and slag were prepared,which will be the foundation for the further study of mine filling in the future.At the same time,the mechanism of compressive strength growth of copper-nickel slag cementitious materials and modified samples were further explored by means of XRD,TG,infrared spectroscopy,SEM and other microscopic testing methods.The main research contents include:?1?The dissolution rate of silicon,aluminum and calcium in copper-nickel slag was studied by boiling method and the NaOH concentration,reaction temperature and reaction time were be used as variables.The results showed that the relationship between the dissolution rate of silicon,aluminum and calcium and NaOH concentrations was much complicated.When the NaOH concentration increased to 0.5 mol/L,the dissolution rates of silicon,aluminum and calcium reach the lowest,at 41.1mg/L,0.4mg/L and 21.5mg/L,respectively.The dissolution rates of silicon,aluminum and calcium all increased when reaction temperature and reaction time increased.The TG,FTIR and SEM were used to observe the microscopic morphology of the samples of copper-nickel slag dissolved by different NaOH concentrations.It was found that most of the dense fayalite of copper-nickel slag has been eroded to become a broken structure after the dissolution reaction.With the increase in NaOH concentration,gel-like and needle-like substances can be found on the surface of the fayalite structure,which indicated that the silicon,aluminum and calcium elements eluted in the early stage began to hydrate and form a precipitate on the surface of the copper-nickel slag.?2?The copper-nickel slag was activated by water glass,NaOH and both of them.The optimum dosage of each activator was selected by testing the compressive strength,and various microscopic test methods were used to study the hydration process and the formation of hydration products.The results showed that when using water glass as the activator,the compressive strength of copper-nickel slag cementitous materials at different ages increased before decreasing with the increase in the content of water glass,and the best content was8%,which can reach 17 MPa at 28d.When NaOH was used as the activator to activate copper-nickel slag,the compressive strength of the specimens was lower than that of water glass as the activator.However,the compressive strength of the specimens also showed a rise trend before decreasing compared with the every ratio of NaOH.When the NaOH dosage was7%,the compressive strength of the specimens reached the maximum at each age,and compressive strength reached 7.9 MPa at 28d.The main cause of deterioration in compressive strength may be the occurrence of efflorescence.Gelling activity of copper-nickel slag was activated by adding water glass and NaOH,the effect was better than that of the single-mixing.The 28d compressive strength can reach 18.3 MPa.From the point of view of NaOH dosage,the compressive strength of the specimens showed a increase trend before decreasing with the increase in the amount of NaOH.Microscopic test analysis showed that the main mineral components of copper-nickel slag,fayalite and ferrisite,provided a silicon source during alkali-activated reaction,and a small amount of C-S-H gel was formed under the action of the activator.At the same time,another hydration product in the system was Fe?OH?₂ or Fe?OH?₃gel material,and this two gel-like materials adhered the partially inert components tightly and firmly,thus resulting in improving compressive strength.?3?The copper-nickel slag cementitious material was modified by fly ash and slag,and compressive strength was tested.The mechanism of growth of compressive strength was discussed by various microscopic testing methods.The conclusions were as follows:,the compressive strength of the modified copper-nickel slag cementitious material increased through the addition of fly ash,and the more the content of fly ash,the higher compressive strength.This is because addition of fly ash filled the gap of insufficient calcium source.Under the action of alkaline activator,the two materials provided the silicon source and aluminum source needed for alkali-activated polymerization,which improved the reaction rate of alkali-activated reaction and thus improved the compressive strength of the specimens.At the same time,when the fly ash was used as the mineral admixture to modify the copper-nickel slag cementitious material,the compressive strength also increased with the increase in curing temperature and high-temperature curing time,especially for the early strength which increased by more than 60%.When the slag was used as a mineral admixture and added to the copper-nickel slag cementitious material,the compressive strength of the specimens was obviously improved.The content of slag had a great influence on the compressive strength,and the highest strength was showed when 50%of the slag was added,which almost can replace ordinary portland cement.The products and microstructure of the modified copper-nickel slag cementitious materials were analyzed by means of XRD,FTIR and SEM.The reaction products were determined to be amorphous C-S-H gel and calcium carbonate.