| Nickel-iron slag is the solid waste produced during the nickel-iron smelting process.As the demand for ferronickel products expands,the corresponding amount of ferronickel slag also increases.Due to the complex composition of nickel-iron slag and the inclusion of heavy metals such as Ni and Cr,it is difficult to use,and the storage process not only takes up a lot of land,but also causes serious environmental pollution.In order to make better use of nickel-iron slag,it is necessary to study the crystallization behavior of chromium and nickel slag during quenching,and the crystallization characteristics of quenched glass under heat treatment.Therefore,based on the nickel-iron slag system Si O2-MgO-Al2O3-NiO-（Cr2O3）,the corresponding simulated slag system was prepared by chemical reagent preparation and high-temperature melting-quenching method.The analysis and detection methods were conducted in-depth research on its crystallization behavior and leaching characteristics,and the following research results were obtained.（1）The crystallization behavior of glass with different NiO/MgO molar ratios and different Cr2O3dosages was studied.The chemical reagents 4Mg CO3·Mg（OH）2·4H2O,Al（NO3）3·9H2O,Ni Cl2·6H2O,Si O2,Cr2O3,H3BO3were used,different NiO/MgO molar ratio（H=0.3/0.7,0.4/0.6,0.5/0.5,0.6/0.4,0.7/0.3）were chosen.The raw materials were weighed,mixed in water bath,dried,primarily calcined,and then melted at 1550°C for 1 h.At the end of holding,the molten slag were casted into copper mold and quenched.When the content of Cr2O3is 0.5%and 1%,repectively,all the slag samples with different R have crystals precipitated under quenching conditions;and when the dosage of Cr2O3is 0%and 0.25%,repectively,glass were formed for H=0.3/0.7,0.4/0.6,0.5/0.5,but glass cannot be formed for H=0.7/0.3 and H=0.6/0.4（0.25%Cr2O3）.The thermal stability parametersΔT and S decrease with increasing H（0.3/0.7,0.4/0.6,0.5/0.5）,indicating that the glass forming ability decreases.However,the glass forming ability of R=0.6/0.4 system is improved.In H=0.3/0.7 and 0.4/0.6 systems,the addition of Cr2O3slightly reduced the glass-forming ability;while in H=0.5/0.5 system,the glass-forming ability increased.（2）The as-obtained glasses with different contents of Cr2O3and different R were heat-treated at 950°C,1000°C,1150°C and 1250°C.The results showed that cordierite is formed as the main crystalline phase by XRD.FTIR and SEM+EDS also verified the existence of cordierite phase.The introduction of 0.25%Cr2O3will suppress the crystallization of cordierite,and the spinel solid solution will be precipitated at the same time.（3）Based on the above experiment,Fe2O3was used to replace the（NiO+MgO）content with different molar ratios to study the effect of different W=（NiO+MgO）/Fe2O3molar ratio on the crystallization behavior of the slag system.H=0.3/0.7 and W=0.95/0.05,0.90/0.10,0.80/0.20 were chosen.In the system without Cr2O3,all samples is amorphous even under quenching.However,when the Cr2O3content is 0.5%,only the system of W=0.90/0.10 and 0.80/0.20 is glassy.The as-quenched glassy samples are heat treated at 1000°C,1150°C and 1250°C,respectively,for 2 h.We found that cordierite is the main crystal phase.When 0.5%Cr2O3is added in W=0.90/0.10 and 0.80/0.20,spinel is formed as the main crystal phase.At the same time,as iron oxide increases,the peak intensity of the spinel phase gradually increases,indicating that the addition of Fe2O3is favorable for the spinel formation.（4）The Kissinger method was used to study the crystallization kinetics of glass formed from different ferronickel slag systems.For H=0.3/0.7,0.4/0.6 and 0.5/0.5,the introduction of Cr2O3leads to an increase in crystallization activation energy,reducing the crystallization ability.For W=0.90/0.10,Cr2O3increases the crystallization activation energy and lowers crystallization ability.While for W=0.80/0.20,Cr2O3decreases crystallization activation energy and promotes the crystallization.（5）The slag system with H=0.5/0.5 and 1.0%Cr2O3（marked as No.2 sample）and the slag system explored by the research team（marked as No.1 sample）were selected for the comparative leaching experiment using TCLP method.Liquid-to-solid ratio of 20∶1 and particles of 325 mesh were set.Using the leaching agent of A and B,we conducted the experiments on glass（before heat treatment）and glass-ceramics（after heat treatment）in order to study the leaching behavior of Cr and Ni under room temperature and leaching times of 20 h,7 d,15 d,30 d,and 60 d.The results show that,for the glass,leaching amount of Cr and Ni ions is larger under agent B,and Ni-leaching of both samples exceed the standard.However,Cr-leaching in No.2 is lower than that in No.1 and the standard.As for glass-ceramics,Cr-and Ni-leaching in No.2 was lower than that that in No.1.Cr-leaching does not exceed the standard,while Ni-leaching in No.1 is higher than standard,indicating that glass-ceramics is favor for stablizing Cr and Ni in ferronickel slag. |
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