Adsorption Of Malachite Green From Aqueous Solutions Onto Organic Sepiolite

Malachite green has been prohibited to be used as veterinary drug for its hightoxicity, high residue and potential hazardous effects to the aquatic animals. However,it is still widely used in printing and dyeing industry such as leather and ceramic.Therefore, it is extremely urgent to find a economic and effective technology to treatthe dyeing wastewater containning malachite green. Sepiolite is a natural nonmetalmineral of good physicochemical properties and low price. It has been widely used inthe field of various wastewater treatment as an adsorbent. The modified sepiolitewhich retained its original crystal structure shows a better adsorbability to the organiccompounds.In this paper, the sepiolite which is from Hunan LiuYang was modified by theorganic surface sodium dodecyl benzene sulfonate (SDBS). And it had been used inthe adsorption of malachite green. The effect of initial pH, oscillation rate, dosage ofthe adsorbent, initial concentration, contact time and temperature had beeninvestigated. The adsorption mechanism of modified malachite green was studiedbased on the standpoint of thermodynamics and kinetics. In addition, the further studyof adsorption mechanism was investigated by the analisis of the structure and surfacechemical composition of organic sepiolite, which was characterized by means ofBET,SEM,XRD and FT-IR. The main experimental conclusions were summarized asfollows.20g sepiolite which purified by precipitation method,200mL distilled water and3.55g SDBS which equaled to100%CEC of sepiolite had been added in a500mLbeaker, and Adjusting pH value to9. The mixed liquid stratified after an hour’sstirring at the room temperature, then the supernatant was discarded and theprecipitate was eluted by distilled water several times. By the above means could theorganic sepiolite be prepared. It was dried in a blast dryer at75℃for12h and wasground to pass through75μm sieve. The decolorization ratio of malachite green,whose concentration is100mg/l, achieved98%by the organic sepiolite.The static experimental results showed that the decolorization rate of malachitegreen whose mass concentration ranged from100mg/L to500mg/L could be90%atleast and the adsorption capacity could be (49.67~251.41)mg/g under the condition of25℃, pH3.5±0.15, oscillation rate170r/min, dosage of organic sepiolite2g/L and adsorption time2h.The adsorption isotherm date of malachite green on organic sepiolite fitted theLangmuir isotherm better than the Freundlich isotherm at the temperature rangedfrom25℃to55℃.The thermodynamic analysis indicated that H>0, G<0, S>0,when the organic sepiolite adsorbed malachite green, showing a spontaneousendothermic process. Granged from-37.46kJ/mol to-42.24kJ/mol demonstratedthe process was not just a physical or chemical absorption process but both of themexisted in the adsorption process and made the system even more disordered. Theadsorption kinetics results illustrated it was better fit for the pseudo-second orderequation. Well adsorption capability was regained after four cycles of hydrochloricacid regeneration. organic sepiolite used as an adsorbent was more economic thanactivated carbon.Microstructural tests showed that sodium dodecyl benzene sulfonate(SDBS)entered the the interlayer structure of sepiolite successfully. It expanded the space oflayers and improved the hydrophobicity of sepiolite, which may be the reason for theimprovement of adsorption perforemance.