| Pyrophyllite is a relatively rare mineral that is often used as a raw material in many industrial applications,particularly in ceramics and refractories.However,the dioctahedral structure has revealed a potential use of this pyrophyllite clay in the removal of heavy metals and dye molecules.Therefore,the application of pyrophyllite on wastewater treatment has become of great interest in China because of its abundance in local reserves as well as its stable adsorbent structural properties.In this work,raw pyrophyllite powders were modified by pickling, grinding and pickling-grinding treatments in advance and a comparative study of raw and modified powders was carried out.Thechemical analysis of pickling powders showed an obvious decrease of Al3+,Fe2+ and Ti2+.The SEM micrographs are evident that the pickling process not only caused the surface erosion,but also the destruction of Van der Waals forces between two layers.The result of particle sizes analysis showed that the D50 of raw particles was 21.42μm,while the D50 of grinding powders was decreased to be 5.55μm after a milling treatment. The kinetics of the removal of methylene blue(MB) from aqueous was studied in order to find an understanding of the dynamics of the adsorption reactions on raw and modified pyrophyllite powders.The results showed that the adsorption kinetics of pyrophyllite Powders agreed well with the pseudo-second-order model and that grinding and pickling facilitated the adsorption reaction.Within the initial 5 min, adsorption capacity was found to be 4.24 mg/g for pickling-grinding powders whereas it was only 3.71 mg/g for raw powders.All of the adsorption capacities of sample powders increased sharply as the pH increased.Especially,the rate of absorption achieved 99%within the first 30 min at pH 11 on pickling-grinding powders.The effect of temperature was discussed in this study and the result indicated that the adsorption capacity of the rapid stage increased with increased temperature.In addition,surface modification with OP emulsion was extraordinary useful.The thermodynamics of MB adsorption on raw and modified pyrophyllite powders showed that all of the samples have a high adsorptive capacity for dyes.Isotherm analysis and thermodynamic calculations were carried out,which indicated that the adsorption capabilities agreed with the Langmuir isotherm with the△G,△S,△H all being negative values.Thus,the mode of MB adsorption on pyrophyllite particles was found to be a monolayer adsorption,in which the translation freedom energy of the adsorbate was reduced and the adsorption process was observed to be spontaneous and exothermic.The pickling-grinding pyrophyllite powders formed a uniform surface and larger maximal adsorption capacity.Then,the adsorption of Cr(Ⅵ) on pyrophyllite powders from aqueous solution was studied.The relation between removal rate and the influencing factors such as reaction time,amount of adsorbate and initial pH value was investigated.The results indicated that the process of the adsorption of Cr(Ⅵ) on raw and modified powders surface also can be separated into two stages and the adsoption rate was decreased with a higher amount of adsorbate.The optimal initial pH value was at the range of 1.5 to 2.Finally,the process of the removal of Cr(Ⅵ) from aqueous solution by pyrophyllite can be considered as a chemical adsorption with negative ion exchange.
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