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 .
The adsorption isotherms of nickel ions from aqueous solutions on bentonite, a natural argillaceous material, previously prepared using ultrahigh-frequency electromagnetic waves ("microwaves") were researched in the article. The phase composition of the sorbent was studied by applying the X-ray powder method. Bentonite sample being pre-wetted and irradiated by microwaves shows 2.7 times better sorption properties than the untreated (native) sample, which was shown on the example of the adsorption process of nickel ions from model solutions in static conditions. The sorption parameters prepared by using the "microwaved" and the native samples of bentonite were calculated according to the Langmuir adsorption equations. The barrier density of nickel in the irradiated sorbent is 16.4 mg/g (0.28 mmol/g), whereas for native bentonite the value of the analogous parameter is 6.0 mg/g (0.10 mmol/g). The reason for such an increase in sorption properties may be the change in the crystalline structure and distribution of micropores on the surface of the sorbent under the action of "microwaves" in the aqueous medium. The determinants in the pre-preparation of sorbent by "microwaves" are the ultimate power and time of irradiation.
Наведено результати вивчення сорбційних характеристик, мікроструктури та фазового складу природного глинистого сорбенту бентоніту у процесах очистки ним водних розчинів з високими концентраціями іонів Цинку. Робота є продовженням попередньої серії аналогічних досліджень авторів з використанням модельних розчинів солей Цинку з малими концентраціями. Активація сорбенту проводилась у 2 способи: а) попередня промивка його чистою водою з одночасним опроміненням мікрохвилями, а потім контакт з розчином солі Цинку; б) пряме опромінення мікрохвилями під час контакту з розчином солі. Показано, що в обох варіантах є помітне зростання сорбційної ємності бентоніту за іоном Цинку. Особливістю даного дослідження є той факт, що у другому випадку («пряме опромінення») спостерігається інтенсивна спонтанна кристалізація нової фази на поверхні сорбенту. Методами скануючої електронної мікроскопії, енергодисперсійного та рентгенофазового аналізу встановлено, що цією новою фазою є гідроксосилікат Цинку. Причиною такого явища може бути виникнення нових центрів кристалізації внаслідок перерозподілу мікропор на поверхні сорбенту під дією мікрохвиль у водному середовищі. Другий варіант підготовки сорбенту («пряме опромінення») є простішим у технічному виконанні, тому його можна ефективно використовувати у процесах очистки стічних вод.
The physicochemical parameters of the process of sorption water purification from compounds of Nickelwith clay sorbent in static conditions are studied. The absorption isotherm of ions of this metal from concentratedaqueous solutions on samples of bentonite using ultrahigh-frequency irradiation (microwave) is analyzed. Mostcorrectly, it is described by the linear equation of Langmuir. It is shown that irradiation of this sorbent bymicrowaves in the process of nickel ion sorting almost 2 times increases the value of the marginal sorptioncapacity for this metal (in comparison with the method of "stimulation" - preliminary washing of bentonite withpure water under the action of microwaves). The results of the study of spent bentonite by scanning electronmicroscopy, energy dispersion and X-ray diffraction analysis indicate that the metal under action of themicrowave is deposited on the surface of the bentonite not only in the form of an adsorbed monolayer of ions, butalso in the form of a separate crystalline phase, nickel silicate. Changes in the acidity of the medium duringsorption purification under the action of microwave are observed: from pH ≈ 5.7 ... 6.5 (before exposure) to pH ≈6.7 ... 7.1 (after irradiation). Confirmed assumption about that under the action of microwaves in the aqueousmedium there is a partial destruction of the silicate framework of clay sorbents with the release of silicon ionsSiO32-. These ions undergo hydrolysis, as a result of which the pH of the solution increases. Also, the directdiscontinuity of the Si-O bonds in the near-surface groups ≡Si-OH is not excluded, which leads to an increase inthe number of "free" hydroxyl groups.
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