Properties and Mechanisms of Humic Acid Adsorption by Hematite at Different Temperatures
The effects of temperature on the adsorption of organic matter by soil minerals were investigated by studying the adsorption of humic acid on hematite at different temperatures.Adsorption kinetic tests were performed and the mechanisms of humic acid adsorption on hematite at different temperatures were clarified by using a combination of scanning electron microscopy,energy-dispersive spectroscopy,Fourier-transform infrared(FTIR)spectroscopy,X-ray diffraction,and zeta-potential measurements.The experimental results show that the equilibrium amounts of humic acid adsorbed on hematite at 25,30,35,and 40℃were 28.52,28.99,29.74,and 30.69 mg·g-1,respectively indicating that the higher the tem-peratures,the higher the adsorption of humic acid on hematite.The adsorption kinetics of humic acid on hematite at differ-ent temperatures were better described by a quasi-secondary kinetic model than by a quasi-primary kinetic model.This in-dicates that the adsorption rate is mainly determined by a chemisorption mechanism.With increasing temperature,the C/Fe ratio on the hematite surface gradually increased,the single-particle size gradually increased,the crystallinity decreased continuously,and the zeta potential initially increased and then decreased.The FTIR spectra showed that the trends in the amounts of various functional groups present differed.In conclusion,increasing the temperature promotes the adsorption of organic matter by soil minerals.
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