In order to improve the quality of Hunyuan inferior Ca-based bentonite(Ca-Bent),semidry process was used to modify Ca-Bent into superior Na-based bentonite(Na-Bent).The factors affecting sodium-modification were investigated.The optimized experimental parameters are obtained as follows:Na2CO3 dosage 4.0%,ageing time 25 d,briquetting pressure 25 MPa and briquetting moisture 20%.Under the optimization conditions,the modified Na-Bent has a colloid value of 73.6 mL/(3g),dilation of 38 mL/g and water absorption in 2 h(2HWA) of 465%,respectively.The balling results indicate that the modified Na-Bent pellets have higher drop strength and compression strength than the Ca-Bent pellets.
A modified humic acid(MHA) binder was tested as a substitute for bentonite to prepare qualified specularite pellets. The results show that there is stronger chemisorption between organic functional groups in MHA binder molecular and specularite particles, improving the green pellet strength. MHA binder has obvious effect on the strength and microstructure of preheated pellets due to the thermal decomposition of organic matters in MHA binder. Appropriately increasing preheating temperature or time can eliminate the adverse impact of organic matters on the preheated pellet strength. Compared with the bentonite pellets, the roasted pellets with MHA binder have a more compact microstructure, and the recrystallization of the Fe2O3 crystal grains is better.Consequently, under optimal conditions, 0.75%(mass fraction) MHA binder pellets have equal or better pellet strengths and contain1.06% more total iron than 2 % bentonite pellets. The testing results indicate that MHA binder is a promising and effective alternative to bentonite for the specularite pellets.
By means of isothermal oxidation and chemical analysis,great importance was attached to the parameters that made effects on the oxidation degree of vanadium,titanium-bearing magnetite pellet in high-temperature processing(1073-1323 K).Based on the experimental data,oxidation kinetics of pellet was analyzed according to shrinking unreacted-core model subsequently.Experiment results display that the oxidation degree of pellet increases with increasing of oxidation time,oxidation temperature and oxygen content,as well as shrinking of pellet diameter.Under the condition of oxidation time 20 min,oxidation temperature 1223 K,oxygen content 15%,and pellet diameter 12 mm,oxidation degree of pellet reaches 92.92%.The analysis of oxidation kinetics indicates that oxidation process of pellet is controlled by chemical reaction with activation energy 68.64 kJ/mol at a relatively lower temperature(1073-1173 K).Oxidation process of pellet is mixed-controlled by chemistry reaction and diffusion with activation energy 39.66 kJ/mol in the temperature range of 1173-1273 K.When oxidation temperature is higher than 1273 K,the limited link of oxidation reaction is the diffusion control with the activation energy 20.85 kJ/mol.These results can serve as a reference to the production of vanadium,titanium-bearing magnetite pellet.
HAN Gui-hong JIANG Tao ZHANG Yuan-bo HUANG Yan-fang LI Guang-hui
Based on the characteristics of the lignite sample,effects of assistant anthraquinone(AQ) on extraction yield of humic substances(HS) and the action mechanisms of AQ in alkaline condition were studied by Fouvier transform infrared(FT-IR) spectroscopy.The results indicate that assistant AQ can not only increase the extraction yield of HS but also reduce the alkali dosage(NaOH) as well as the extraction temperature and extraction time.Under the optimal conditions of alkali dosage of 9%,AQ dosage of 0.75%,extraction temperature of 80 oC,extraction time of 30 min,stirring speed of 600 r/min and solid-to-liquid ratio of 1:3,the extraction yield of HS reaches 80.08%,which is increased by more than 20% compared with the conventional extraction.FT-IR spectra show that AQ is able to prevent dissolved HS from being destroyed into undissolved substance by alkali and HS obtained in the presence of AQ possesses more groups of -COOR and -COOH than that obtained without AQ.
Modified humic acid (MHA) binder based on lignite humic substances is a novel sort of promising organic binder for iron ore pellets.Humic acid (HA) is one of the main ingredients of MHA binder.Pure HA was firstly isolated from lignite and then adsorption of HA onto magnetite particle surface was investigated.The final results indicate that the adsorption of HA onto magnetite surface accords with Langmuir model well,and it is evidently influenced by the initial HA concentration and solution pH value.Adsorption depends on chemical interaction at pH values above the PZC (the pH where the Zeta potentials of minerals are zero) of magnetite,while electrostatic attraction and chemical interaction both contribute to the adsorption at pH values below the PZC.
The structure characteristics and adhesive property of humic substance(HS) extracted with different methods were mainly studied by terms of elementary analysis,visible spectrum,FT-IR spectroscopy,viscosity,adsorption and pelletizing experiments.The results show that HSs extracted with new method(HS-a) own higher degree of aromatization and polymerization,larger relative molecular mass and more polar functional groups than HS extracted with usual method(HS-b).The viscosity of HS-b is about 30-40 mPa·s lower than that of HS-a.The maximum adsorption amounts of HS-a and HS-b onto iron concentrates are 9.11 mg/g and 8.08 mg/g,respectively.Meanwhile,HS-a has a better performance than HS-b in the practical application for pelletizing of iron concentrates.The difference in agglomeration behaviors with iron concentrates lies in the differences of the structure characteristics of HSs.With higher content of polar functional groups,larger relative molecular mass and viscosity of HSs,the agglomeration behavior is improved.
