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12CHEMICAL SCIENCES
RGULARITIES OF SORPTION CU (II) IONS BY NATURAL AND ACTIVATED BENTONITE
CLAYS
Fedenko Yu.
Ph.D., assistant, The Department of Technology of Inorganic Substances, Water Purification and General Chemical Technology, Igor Sikorsky Kyiv Polytechnic Institute
Abstract
The phase and chemical composition of native samples of bentonite clay was determined. The acid activation of bentonites was carried out. The regularities of Cu2+ sorption by native and activated bentonite clays of Ukrainian origin (sorption isotherms, kinetic curves) are studied. The rational conditions for the sorption of Cu (II) ions by bentonites are determined.
Keywords: activation, sorption, bentonite, copper (II) ions, isotherm, kinetics.
Introduction
Bentonite clay got its name from Fort Benton, located in the state of Wyoming (USA), where their first commercial production was begun at the end of the XIX century. In world practice, it is customary to attribute finely dispersed clays to bentonites, consisting of not less than 70% of the minerals of the smectite group (montmorillonite, beidellite, nontronite, saponite and hectorite), which have a high binding ability, thermal stability, as well as adsorption and catalytic activity [1, p. 17].
In the form of impurities, bentonites contain quartz, calcite, cristobalite, feldspar, hydromica, mixed-layer minerals, zeolites, palygorskite, halloysite, kaolinite, etc.
The most widely used bentonite clay is traditionally used in the metallurgical industry, as a binder for pelletizing iron ore concentrates; drilling, for the preparation of drilling fluids; foundry industry, as a binder in the manufacture of foundry molds; chemical, rubber, paper, pharmaceutical industries, construction, agriculture, etc. There are more than 200 directions of use of bentonite. Relatively new and very promising areas include the production of organoclay of different quality and destination. This group includes various types of layered-silicate nanocomposites, anhydrous foundry mixtures, sealants, and hydrocarbon-based drilling fluids.
Currently, there has been a significant increase in interest in the creation of new environmentally friendly sorbents based on natural clay materials and alumino-silicates [2, p. 24]. Compared with other inexpensive adsorbents, clay and composite materials based on them have a higher adsorption capacity. Bentonites, montmorillonites, kaolinites, chlorites and other clay minerals widely used due to their high specific surface, chemical and mechanical stability, variation of surface and structural characteristics and low cost [3, p. 117; 4, p. 48]. Of particular interest are materials with layered column structure derived from natural clay by modifying it inorganic polyhydroxocations [5, p. 235].
The purpose of this work is to study the structural and sorption properties of a material of natural origin -bentonite clay Dashukivsky deposit of Cherkassy region (natural and activated) on the example of cation Cu2+.
Materials and methods
The XRF analysis of bentonite samples was conducted by x-ray diffractometer DRON-3M (Cu-radia-tion).
The chemical analysis was conducted by X-ray fluorescence spectrometer (Rigaku Corp.).
Acid activation of bentonite clays was conducted by heating of samples in water solution of 2 M hydrochloric acid at the temperature 90 °C during 2 hours.
The following reagents were used as materials: copper (II) 5-water sulfate (h.ch.) (1 g / dm3 solution), complexone (III) (0.05 N solution), ammonia buffer mixture (pH 10), murexide indicator (dry mixture with NaCl in the ratio 1: 100).
The analysis of residual amounts of Cu2+ was carried out using the standard copper determination method with complexometric titration
To construct an isotherm of adsorption in 5 conical flasks, weighing bentonite weighing 1 g was added. Each of the flasks was poured into 100 cc of solutions with concentrations of Cu2+ 25, 50, 100, 250, 500 mg / dm3. The flasks were sealed and placed on shaking for 20 minutes. Experiments were performed without adjusting the pH.
To construct kinetic curves in 5 conical flasks, weighing bentonite weighing 1 g was added. Each of the flasks was poured into 100 cubic centimeters of solutions of copper (II) at a concentration of 100 mg / dm3. The flasks were sealed and placed on shaking over different time intervals, min: 5, 10, 15, 20, 30. The experiments were performed without adjusting the pH.
Experimental
Figure 1 shows XRF-diffractogram of natural sample of the bentonite, used in investigations.
Fig. 2. XRF-diffractogram of natural sample of the bentonite
Data, presented in fig. 1, shows, that the sample of of describing its properties it is appropriate to make an
natural bentonite consists of following phases: mont-moriUonite (angle 20 = 7 deg.) and also quartz, feldspar ad hematite (angles 20 = 20, 22,5 and double peak 35, 37 deg. respectively). Thus, the natural sample of bentonite has heterogeneous structure. For simplification
assumption, that the sample of bentonite has a structure of montmorillonite.
The chemical composition of bentonite clay is presented in table 2.
The chemical composition of bentonite clay.
Table 2.
Mineral Quantitative analysis, mass %
SiO2 AhO3 TiO2 Fe2O3 MgO K2O Annealing losses
Bentonite (montmorillonite) 63 14 0,34 3 2 0,5 19
According to the data in table 2, it can be seen, that the structure of bentonite includes metal oxides (mainly, 14 mass %) and the main part - SiO2 (as quartz).
Fig. 2 shows the adsorption isotherm of Cu2+ on the bentonite surface.
35 ^30
M
s 25
it
1 20 a
s 15 c o
U 10
!-h
o
™ 5
100 200 300 400
Equilibrium concentration, mg/L
0
Fig. 2. Sorption isotherm of Cu (II) ions on the bentonite (1 - activated bentonite, 2 - native bentonite)
As can be seen from fig. 2, the sorption capacity of bentonite increases with an increase in the initial concentration of Cu (II) ions in solution and reaches a maximum value of 15 mg / g at an initial concentration of copper in a model solution of 200 mg / dm3 (for native sample) and 32 mg / g at an initial concentration of copper in a model solution of 200 mg / dm3 (for activated sample). With further growth of the initial concentration of copper, the sorption capacity does not
100
change. Consequently, starting from the concentration of Cu2+ 200 mg / dm3, the bentonite-based sorbent completely exhausted its sorption capacity (Zn2+ filled all available functional groups on the bentonite surface). The isothermal appearance of adsorption shows its flow through the Langmuir model.
Figure 3 shows the kinetic curve for the extraction of Cu2+ ions on the surface of bentonite (native and activated).
90
80
<u
g? 70
й <u о
!-н
<u CP
60 50 40 30
53 20 10
> о
10
15
20
25
30
Duration, min
0
0
5
Fig. 3. Kinetic curve of Cu (II) ions removing by the bentonite (1 - activated bentonite, 2 - native bentonite)
According to the data, presented in figure 3, maximal removal percentage of copper (II) is reached at 20 minutes. In the case of non-activated bentonite, the removal percentage reaches 77 % (for activated one - 92 %). The dependence for non-activated bentonite differs from one for activated by presence the bend in the case of activated bentonite. On our opinion, it is connected with different models of sorption in the case of activated bentonite. Firstly, copper is sorbed by natural bentonite's active centers; then, active centers formed by acid activation.
Conclusions
The studies conducted in this paper allow us to make the following conclusions:
- bentonite clays (especially, activated) are effective sorbents of cations Cu (II) from model aqueous solutions;
- the maximum sorption capacity for copper (II) reaches 32 mg/g (activated bentonite).
- the maximum possible degree of copper extraction is 92 % and the dose of sorbent 1 g / 100 ml of
solution at a concentration of 200 mg / dm3, the duration of sorption for 20 minutes (activated bentonite);
- the evidence shows that activated bentonite is much better sorbent, than native one.
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