Microwave-treated bentonite for removal of lead from wastewater

Abstract

Clay-based materials are promising adsorbents for removal of various pollutants from wastewater. This work is aimed to study the changes in structure and adsorption capacity of microwave-treated bentonite after adsorption of lead(II) ions. The structural investigation of the microwave-treated sample reveals that a partial destruction of silica skeleton takes place, and new surface nucleation centers are formed during microwave processing. The adsorption of Pb 2+ on natural bentonite occurs on heterogeneous adsorption sites, whereas the removal of lead on microwave-treated sample is accompanied by the formation of plumbophyllite microcrystals. The natural and microwave-treated adsorbents were tested for lead adsorption in batch experiments. The results were fitted according to Langmuir, Freundlich, Toth, Redlich-Peterson, and Langmuir-Freundlich isotherms of adsorption. The microwave-treated samples revealed substantially higher efficiency towards the removal of lead, their maximal adsorption capacity was 114.7 mg g-1 , whereas natural samples showed only 31 mg g-1 .

Adsorption of Copper Ions by Microwave Treated Bentonite

“…The detailed description of the procedure of analytical processing of adsorption curves has been presented in our previous publications [23,24].…”

“…The adsorption on MTB sample takes place not only in pores or in monomolecular layer on the bentonite surface, but the prevalent mechanism is surface-induced co-precipitation of copper as microcrystals of individual copper compound. 23 ) on the surface of MTB (ser. DIR) after adsorption from concentrated aqueous solutions is described in our previous works [20,22,23].…”

“…Two methods of sorbent microwave treatment without adding acids or other activators were described earlier [19][20][21][22][23][24]. In so called STIM-method [19,21,23,24] natural bentonite is washed by bidistilled water and simultaneously irradiated with microwaves, later the sorbent is exposed to contact with salt solutionsa twostep procedure for activating the sorbent (i.e. "stimulation").…”

“…In the DIR-method (direct irradiation) [20,22,23] samples of natural bentonite contacted with aqueous salt solutions under the microwaves irradiation. It is proved [19][20][21][22][23][24] that both methods of bentonite microwave treatment lead to a significant increase in its maximum adsorption capacity of heavy metal ions Ni [19,20], Zn [21,22], Pb [23], Cu [24]. The advantage of DIR-method is the intense spontaneous crystallization of a new phase on the surface of the sorbent [20,22,23].…”

“…It is proved [19][20][21][22][23][24] that both methods of bentonite microwave treatment lead to a significant increase in its maximum adsorption capacity of heavy metal ions Ni [19,20], Zn [21,22], Pb [23], Cu [24]. The advantage of DIR-method is the intense spontaneous crystallization of a new phase on the surface of the sorbent [20,22,23]. It is believed that the reason for this phenomenon is formation of new crystallization centers due to the redistribution of micropores on the surface of the sorbent under the influence of microwaves.…”