Study On Adsorption Of Red Mud For Heavy Metal Cr⁶⁺ In Water

Red mud is a sort of residue in the process of alumina production, when bauxite was lixiviated by the alkali. This paper study the phase composition, chemical composition, structural characteristics,properties of red mud and the removal rate of chromium(Ⅵ) by red mud adsorption.The paper makes a microscopic analysis on red mud and calcination red mud by scanning electron microscopy (SEM). Red mud is mainly porous frame structure, connected by tiny particles, scattered and no definite shape.Calcined red mud red has the rough surface in comparison with raw red mud.Calcined Bayer red mud treated at 200℃is more dense than the red mud, showing some adhesion. Combined red mud structure is more porous and loose in comparison with raw red mud.As the increases of calcination temperature, the red mud surface is more rougher, more compact and more cemented.The X-ray diffraction (XRD) of red mud analyse that Bayer red mud phase is mainly composed of hematite, hydrate garnet, boehmite, ilmenite and calcite; Combined red mud phase is mainly composed of quartz and calcium aluminum melilite, followed by albite, andradite garnet, and perovskite garnet.Standing for the raw red mud, the paper researchs some factors for chromium ion removal rate based on dosage, pH and adsorption time. PH has obvious affection among many factors. Adding Bayer red Mud 1g and combined red mud 0.5g apparently into 100ml analog static water which contains 0.08ug/ml Cr6+ion. On experimental adsorption time 2h, it concludes that the removal efficiency of Bayer red mud increased significantly in the pH=4 and the removal rate is 100% in the pH=2;the removal efficiency of combined red mud has a significant increase in the pH=2 and the removal rate is 100%in the pH=1 or so.Studying the chromium ion removal rate by modified red mud via high-temperature calcination, HCl, NH3·H2O, FeCl3 and H2O2 modification. To 100ml analog static water containing 0.08ug/ml Cr6+ion, the removal efficiency of Bayer red mud by HC1 is 73.38%and by FeCl3 is 87.64%; the removal efficiency of combined red mud by HC1 is 59.12% and by FeCl3 is 78.13%; the chromium ion removal rate is zero above 200℃calcination temperature.The paper draw adsorption isotherms for Bayer red mud and combined red mud on different chromium ion concentrations and Langmuir and Freundlich isotherm curve. It indicates that the chromium ion adsorption by red mud is completed through physical adsorption and chemical adsorption synergy.