Microwave - Activated Granular Red Mud And Its Application In Wastewater Purification

Red mud, which is produced from alumina industry, nowadays has been the largest nonferrous residue pilled up around the global. But because of some difficulty in activation, separation, circulation and indistinction of principle, the process is still cannot be applicated in large-scale. This research preferred to adopt microwave pore-making and activation process (MPA) to produce new type adsorbent with red mud. The principle of MPA process lies in that microwave energy can selectively and quickly act with water, organics and the high-microwave-adsorption solids existing in wet granular red mud(GRM), which can explosively make tiny pore and channel generated because of water vaporation and organics volatilization. Thus the process can activate the adsorption characteristics and increase the intensity of the GRM, and it can become a porous adsorbent with high strength, and be used in purifying the waste water containing pollutants of organics deeply.Using XRD, SEM, FTIR to represent activated GRM. The results shows that surface area and strength of microwae activated GRM is better than normal activated GRM. GRM formate mcropore, the size of mcropore is 2mm,0.2mm and 0.05mm. The pore channel is distinct. It’s good for waste water into the GRM.The microwave condition is 500℃,2.6kw, keep warm 30min. The GRM has been became better absorbent after microwave microwave activation.In batch mode, the effects of shaking time, adsorbent dosage, initial concentration, pH and solution temperature on the methylene blue removal ratio were studied, and we obtained the optimal process parameters. The thermodynamic parameters of adsorption were calculated by Van’t Hoff equation, and the equilibrium data were analyzed by Langmuir and Freundlich isotherms at different temperatures. The experimental data were analyzed by the pseudo first order kinetics model, pseudo second order kinetics model and the intraparticle diffusion model, obtaining the initial sorption rate and rate constants. The results showed that adsorption isotherm fits with Freundlich equation. The maximum adsorption capacities of MB per gram GRM were calculated as 7.3670 mg (293K),9.0975 mg (303K) and 9.9771 mg (313K), respectively. Thermodynamic research suggested that the adsorption of MB onto GRM was spontaneous and chemical reaction. The pseudo second order kinetics model fits the experimental data well and adsorption rate limiting step was film diffusion.In column mode, the effects of important parameters on breakthrough curve, such as the filler height, the flow rate and the initial mass concentration of MB, were studied. The BDST and Thomas models were applied to simulate column adsorption data and to gain the characteristic parameters of two models using linear regression. At the same time, the regeneration of saturated GRM was researched. The results showed that GRM, as an adsorbent to remove MB from solution, was efficient. When the filler height increasing, the breakthrough point in the breakthrough curves moved to right; this fact suggested the extension of breakthrough time. But by the increase of the flow rate and the initial concentration of MB, the breakthrough point moved to left, which implied the decrease of breakthrough time. The breakthrough time at different flow rate and initial concentration was forecasted accurately by the BDST model (error<5%). Thomas model was found suitable for describing the column adsorption kinetics at initial concentration of MB 100, 150 and 200 mg/L; the balance adsorption capacity was respectively 5.0117,4.4915 and 3.5357 mg/g. After adsorption, the adsorption column desorpted by dilute nitric acid solution (pH=3) and regenerated has high adsorption efficiency, which indicates that the granular red mud adsorbent can be reused. The method of segmented circular elution is superior to continuous recycling elution to save the quantity of nitric acid.