Химия и Химические Технологии/

Фундаментальные проблемы

создания новых материалов и технологий

Yu.A.Shilina, S.V. Nechipurenko, M.K.Nauryzbaev

al-Farabi Kazakh National University, Karasai Batyr Str., 95-a, Almaty, 050012, Republic of Kazakhstan, tel.: +7(727) 2921374, fax: +7(727) 2923731

E-mail: yushilina@mail.ru, nauryzbaev@cfhma.kz

Developing novel sorbents from raw materials of Kazakhstan

One of the important problems facing the mankind is the general aggravation of an ecological situation and, as a consequence, an increase in toxic loading of living organisms. Therefore, it is of great importance to develop novel technologies allowing reducing levels of toxic substances, without breaking the balance of vital compounds in a human body, i.e. to use natural sorbents as enterosorbents. Nowadays, the application of enterosorbents is a separate branch of a medical science. There are a number of the preparations intended for eliminating toxicants from an organism. The application of carbon-based materials for toxin elimination from a human body is widely recognized. However, the relatively high costs of these materials limits their application. Lignin can be considered as a promising material for manufacturing active charcoals.

Wood is a unique constantly renewed source of raw materials which importance continuously increases in complex chemical processing. The most important branch of chemical and chemical-mechanical processing of wood is a manufacture of technical cellulose, lignin and fibers.

Elemental composition

The elemental composition of lignin-containing materials was determined by burning method and the data are presented in table 1.

Table 1 – Elemental composition of lignin-containing materials

Type of material	Sample weight	Weight СО2	Weight Н2О	С, %	Н, %	Ash, %
AC	4,91	14,39	1,54	78,12	2,71	8,35
Lignin	4,48	10,76	2,56	64,79	5,19	-

It is clearly seen that lignin-based materials contain 78,12-64,79 % of carbon and yield small percentage of ashes.

Scanning electron microscopy

SEM images of hydrolytic lignin and activated charcoal samples are shown in Figure 1.

a) Hydrolytic lignin b) Activated charcoal

Figure 1 – Scanning electron microscopy images of hydrolytic lignin and activated charcoal

Both sorbents have a highly developed porous structure includes macro -, mezo- and -micro pores.

The ultra structure of natural lignin is a structural level which describes a spatial structure of lignin’s cellular covers, consisting of supramolecular microparticles. Ultra structural level covers, basically, spatial scale from 10 nanometers to 104 nanometers. In ultra structure of lignin as a material print, the information on the processes of dynamic self-organizing proceeding in a course lignification is ciphered. The basic part of hydrolytic lignin structure according to these microphotographs includes highly developed mesh structure with the sizes of cells of 1-10 microns. The microphotographs of the activated charcoals show cross-section cuts of carbonized skeletons with clearly identifiable fibrous trachea forms.

Lignin skeletons maintain the morphological structure of saxaul cells. Lignin in mesh structure, as a whole, represents a rather friable system with chaotically alternating spatial multifocal uptake – globular particles and their units of various densities and sizes (10-500 nanometers).

IR-spectroscopic studies.

The most typical absorption bands for lignin-containing materials are 1510 and 1600 cm^-1 (aromatic rings vibrations). The first can be used as a proof of lignin as there are practically no other bands in this area. The typical bands for guayacyl and seringyl rings are around 1270 and 1330 cm^-1, respectively. The intensive bands at 1660-1715 cm^-1 related to carbonyl groups, allow concluding about their presence in the structure of these materials. In all spectra the band of valent vibrations of hydroxyl groups is observed at 3400 cm^-1 which, however, cannot be used for estimating the structure of these complex structures . The same concerns the bands of valent vibrations of С-Н at 2800-3000 cm^-1 (partially also caused by vibrations of OH groups) and to the bands at1000-1400 cm^-1, arising from a combination of С-О and some deformation vibrations. The width and intensity of the bands at 1000-1100 cm^-1 characterizes the presence of sugars or polysaccharides impurities [4,5].

Determination of sorption capacities of hydrolytic lignin and activated charcoals with respect to heavy and non-ferrous metal ions

Sorption of zinc (II).

The sorption data of zinc ions from solution containing 8,00 mg/l of Zn^{2 + at} рН=5,48 is presented in Table 2. The experiments were performed by passing solutions through a column packed with a sorbent during 5 minutes.

Table 2 - Adsorption of zinc (II) in a dynamic mode with initial concentration of 8,00 mg/l

Entry	Time of sampling, min	Equilibrium concentration Zn^2+, mg/l
		Lignin	Activated charcoal
1	5	6,16	0,29
2	10	6,25	0,31
3	15	6,25	0,75
4	20	6,34	1,26
5	25	6,43	1,96
6	30	6,43	2,59
7	35	6,43	3,04
8	40	6,43	3,75
9	45	6,43	4,02
10	50	6,43	4,93
11	55	6,52	5,45
12	60	6,61	5,71
13	65	6,61	5,71
14	70	6,88	5,80
15	75	6,91	5,80
16	80	6,92	5,80
17	85	6,94	5,89

It can be seen from Table 1 that the activated charcoal absorbs Zn^{2 +}ions better than the hydrolytic lignin, without losing its sorption activity during the experiments.

Sorption of chrome (III).

The sorption data of chrome ions from solutions containing 5,00 mg/l of ions Cr^{3 +} at рН=5,48 is presented in table 3. Sampling was made by passing solutions through a column packed with a sorbent.

Table 3- Adsorption of chrome (III) in a dynamic mode with initial concentration of 5,00 mg/l

Entry	Time of sampling, min	Equilibrium concentration Cr^3+, mg/l
		Lignin	Activated charcoal
1	5	3,93	0,02
2	10	3,96	0,03
3	15	4,02	0,04
4	20	4,04	0,04
5	25	4,06	0,04
6	30	4,09	0,05
7	35	4,10	0,06
8	40	4,25	0,06
9	45	4,27	0,06
10	50	4,30	0,07
11	55	4,30	0,08
12	60	4,32	0,08
13	65	4,33	0,10
14	70	4,36	0,11
15	75	4,63	0,11
16	80	4,86	0,37
17	85	4,88	0,42

From table 3 it is clear that the activated charcoal takes ions Cr^{3 +} better (extraction of 97-99 %) than the hydrolytic lignin (extraction of 2-22 %), without losing sorption activity during these experiments.