РОЛЬ ХИМИЧЕСКОГО СОСТАВА И СТРУКТУРЫ ПРИРОДНЫХ МИНЕРАЛОВ ПРИ ВОЗДЕЙСТВИИ ИМПУЛЬСНОГО МАГНИТНОГО ПОЛЯ НА СОРБЦИОННЫЕ ПРОЦЕССЫ

THE ROLE OF THE STRUCTURE AND THE CHEMICAL COMPOSITION

OF NATURAL MINERALS UNDER INFLUENCE OF THE PULSE MAGNETIC FIELD ON SORPTION PROCESSES кандидат химических наук, доцент кафедры химии Ходосова Н.А. доктор технических наук, профессор кафедры химии Бельчинская Л.И. кандидат химических наук, доцент кафедры химии Новикова Л.В.

ФГБОУ ВПО «Воронежская государственная лесотехническая академия» Khodosova N.A., Belchinskaya L.I., Novikova L.V.

FSBEIHPE «Voronezh State Academy of Forestry and Technologies» Этот адрес e-mail защищен от спам-ботов. Чтобы увидеть его, у Вас должен быть включен Java-Script

DOI: 10Л2737/3029

Abstract. The activating influence of pulse magnetic field treatment on formaldehyde adsorption on natural minerals enriched with clinoptilolite, montmorillonite and a mixed mineral was studied. The rise of adsorption and a relaxation effect were found.

Keywords: adsorption, clay minerals, pulse magnetic field treatment, formaldehyde.

Introduction

It is commonly known that the variety of aluminosilicates properties is caused by their composition, the structure and surface features. Active surface sites of aluminosilicates surface are represented by exchangeable cations K+, Na+, Ca2+, hydroxyl groups of acidic/basic character, as well as coordinately unsaturated ions of Al3+, Mg2+ and Fe3+. Owing to presence of these active sites alumosilicates exhibit significant ion-exchange, adsorption and catalytic properties already in natural form that continue attracting researcher to studying and searching of their new applications.

Adsorption processes, especially adsorption from the gaseous phase, are extremely sensitive to physical and chemical state of the real surface of solids, including natural sorbents. Traditionally, in order to enhance the adsorption and catalytic properties the aluminosilicates are activated by chemical and physical methods such as acid or alkaline, thermal, mechanical activations or their combinations. It worth mentioning that these means are highly energy intensive and have significant impact on the environment due to a high amount of wastes.

Recently it has been confirmed the significant effects of exposure of weak pulsed magnetic field (PMF) both on living systems, and on mechanical, physical, physic-chemical properties of metals and semiconductors. At the same time, there is a series of investigations of Belchinskaya L., et al. [1] confirming for the first time the effect of PMF on sorption capacity of natural nanoporous materials. Depending on the magnetic induction of the PMF the adsorption capacity of natural sorbents can be enhanced or inhibited.

The present paper is aimed at investigation of the adsorption-desorption processes on natural minerals having various structure and chemical composition under the influence of pulse magnetic field treatment.

Experimental

Objects of the study were represented by natural aluminosilicates having various structure types: clinoptilolite, 95% (C95) - hard-sphere framework structure, montmorillonite, 95% (M95) - layered structure, and a mixed mineral M45C2o containing montmorillonite (45%) and clinoptilolite (20%).

Samples in both natural and thermally treated (453 K, 493 K) forms were exposed of PMF with an amplitude B=0,011; 0,12; 0,2 T for 30 s and 120 s using the experimental unit developed in [1].

Adsorption ability of aluminosilicate sorbents was tested in relation of formaldehyde, which is an industrial toxicant of the atmosphere, working area and living quarters. Formaldehyde is a main component of urea-formaldehyde resins that are used as adhesives for manufacturing of furniture, lacquers, building paints, gluing materials, composites, etc. The release of formaldehyde from the adhesives or from goods and building materials is caused by presence of free formaldehyde or by destruction of the adhesive during the time.

Adsorption and desorption of formaldehyde by aluminosilicates samples were determined from gaseous phase by the gravimetric method at 293K.

Results and discussion

In order to find out the optimal conditions for PMF treatment we determined the amount of adsorbed formaldehyde on samples treated by PMF at various values of magnetic induction. The adsorption processes were started directly after the PMF treatment, duration of adsorption was 24 hours.

Fig. 1 shows influence of the duration of PMF treatment at B= 200 mT on the adsorption ability of C95 and M45C2o.

It is seen from fig.l that treatment of alumosilicates sorbents in PMF leads to decrease in formaldehyde adsorption by 9-23 % for C95 and by 24-43 % for montmorillonite containing sample. The inhibitory effect of PMF on adsorption ability increases at longer duration of PMF exposure.

Figure 1 - Adsorption capacity of natural aluminosilicates C95 and M45C20 before and after treatment in PMF (B=200 m T) for 30 and 120 s

Effect of a combined thermal and PMF treatment on adsorption ability of minerals towards formaldehyde is presented in figure 2.

Figure 2 - Adsorption of formaldehyde on C95 and M45C20 after thermal and PMF (200 mT) treatment

As it follows from figure2, application of thermal activation at 493 К raised adsorption ability of C95 and M45C2o by 81 % and 60 %, correspondingly. Nevertheless, subsequent application of PMF after thermal treatment of sorbents caused a decrease in formaldehyde adsorption as it was found in the absence of thermal treatment as well. In this case, the decrease of adsorption after 30 and 120 s of PMF exposure came to 60-75% for C95 and to 51-57 % for M45C20 respectively.

It is obvious that thermal and PMF treatment affect the aluminosilicate surface and the adsorption sites in a different manner. Upon heating, there is mainly desorption of water molecules or C02 takes place, increasing the surface area and giving free space for further adsorption of new molecules. In case of PMF exposure we meet another mechanism of action, which involves mainly orientation or disorientation of dipoles under the action of magnetic field. It is probable that PMF cause unfavorable orientation of surface hydroxyl dipoles and, as a results, lost of activity of adsorption sites.

One should take in to account that magnetic field cause changes which realize only after a definite time interval. For example, by treatment of metals and dielectrics in PMF there is a relaxation period. In further experiments the value of magnetic induction was decreased from 200 mT to 120 and 1 lmT and the time spent between the PMF treatment and the adsorption experiment was varied. The dependence of adsorption capacity of aluminosilicates sorbents on time spent after the PMF treatment is given in figure 3.

Figure 3- Kinetics of formaldehyde adsorption on aluminosilicates after exposure to PMF (B = 120 mT)

It can be distinguished from figure 3 that after the exposure of minerals to PMF there were two processes observed, namely, a period of activating the sorption ability and a period of activity decrease (so called “relaxation period”).

Adsorption of formaldehyde determined right after the PMF treatment was weak, probably due to a transfer of the sample in to a metastable state under the influence of magnetic field. In process of time, adsorption capacity of sorbent was increased by 3-5 times and reached its maximal values after 48 hours from the PMF exposure. By further increase of time spent between the PMF treatment and the adsorption process the adsorption ability of a mineral started to weaken and finally came to the values obtained right immediately after the PMF treatment. The former case one may attribute to the relaxation of sorbent, likewise behave metals and dielectrics treated by magnetic field. Experimental duration of relaxation in systems “clay mineral-formaldehyde” caused by PMF came to 72 h (figure 3).

The samples enriched in montmorillonite, M95 and M45C20, adsorbed higher amounts of formaldehyde than clinoptilolite C95. This fact indicates at more significant changes in physic-chemical properties of surface of minerals with layered structure, like montmorillonite, under the influence of PMF. Probably, it can be somewhat related to the higher content of iron ions Fe3+ and hydroxyl groups of basic character in the montmorillonite structure (table).

Table - Elemental composition of natural alumosilicates

Sample

Content, atomic %

SSA

(H20)

,m2/g

SiCb

C

0

Na

Mg

A1

Si

К

Ca

Fe

Cu

Ti

АЕОз+БегОз+М

go

C95

5,69

54,81

0,19

0,61

5,16

  • 26,9
  • 0

2,46

1,76

0,99

1,42

-

117,02

4,7

M45C

20

6,62

52,79

0,63

1,54

5,85

  • 22,0
  • 5

1Д4

4,18

3,63

1,14

0,43

149,54

2,5

M95

8,25

49,01

053

1,08

7,63

  • 22,9
  • 3

m

0,71

5,79

1,94

0,51

14628

2,15

Note: SSA - Specific surface area.

As follows from table 1, the values of Si/Al ratio for M95 and M45C2o is about two times lower than for C95. This fact testifies to presence of basic OH groups in the layered structures of montmorillonite, which can be sensitive towards action of PMF treatment causing either polarizing or orientating effect on them. Alumosilicates having zeolitic structure, i.e. clinoptilolite C95, have typically acidic surface sites owing to bridge hydroxyls SiO(H+)Al and higher Si/Al ratio, which are less sensitive to exposure of PMF. Weakening of the PMF to magnetic inductions of 11 mT keeps the observed effect of enhanced adsorption ability by 6-8 times after 48 h followed by the relaxation period during next 72 h.

At present moment, we can explain such phenomenon using the approaches of Buchachenko [2], Bingi and Savin [3] and Salikhov [4]. Taking into consideration that the PMF causes activation of molecular systems at the level of a spin subsystem, it is most likely a spin disordering in A10H, FeOH, MgOH groups, hydroxylated cations, etc., and as a result, formation of radical pairs, acting as active sites, to a greater extent at a relatively hydroxylated surface of montmorillonite comparing to clinop- tilolite. The rotational electric field induced by the alternating pulsed magnetic field, probably contributed to dipole polarization of active sorption sites and reflected on their orientation.

It worth mentioning that PMF affects also the desorption processes on natural minerals. For sorbents in natural form the desorption processes were sufficiently marked providing desorption of 37-69 % of adsorbed formaldehyde. Application of thermal treatment (T= 453 K) observed lower formaldehyde desorption (21-53 %).

Application of the PMF with a higher magnetic induction (B = 200 mT) revealed higher rate of desorption. In case of clinoptilolite C95, about 50% of adsorbed formaldehyde was desorbed both after the single PMF and a combined thermal and PMF treatment. On the contrary, for mixed M45C20 sample single PMF treatment provided 60% of formaldehyde desorption whereas combined thermal and PMF treatment spotted only 25-30% of formaldehyde desorbed.

By transition to PMF of lower magnetic induction there was observed a stronger inhibition of desorption (9-14%) for B=120 mT, and even full absence of desorption processes for all type of minerals for B=ll mT. The reason for suppression of desorption could be formation of solid complexes by adsorption of formaldehyde. At this, the exchangeable cations, water molecules and formaldehyde molecules are involved in hydrogen bonding of formaldehyde molecules by polarized water molecules in the interlayer space of the minerals.

Acknowledgments

The researches were carried out within the ECONANOSORB Europeanproject under the frames of Marie Curie Actions FP7-PEOPLE-IRSES-295260.

References

  • 1. Belchinskaya L.I., Khodosova N.A., Bitiutskaya L.A. Adsorption of formaldehyde on mineral nanoporous sorbents treated by pulse magnetic field // Physico-chemistry of surface and protection of materials. - 2009. - V45. №2. - P.218-221.
  • 2. Buchachenko A.L., Sagdeev R.Z., Salikhov K.M. Magnetic and spin effects in chemical reactions. - Novosibirsk: Nauka, 1978.
  • 3. Bingi V.N., Savin A.V. Physical problems of action of weak magnetic fields on biological systems // Advances of physical science. - 2003. - V.173.- №3. - P.265-300.
  • 4. Salikhov K.M., Molin Yu.N., Sagdeev R.Z. Buchachenko A.L. Spin polarization and magnetic field effects in radical reactions, edited by Yu.N. Molin, 1984, Elsevier, Amsterdam.

УДК 674.093.26

 
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