KINETICS AND ISOTHERM OF Cu2+ ION SORPTION ON A NEW SORBENT OBTAINED ON THE BASIS OF VERMICULITE

ABSTRACT

This paper presents the results of the study of the sorption of Cu²⁺ ions in artificial solutions to the ion obtained on the basis of vermiculite at 293, 303 and 313 K, the duration of sorption to equilibrium (24 hours) and at different concentrations. The kinetics of the processes were studied, and Langmuir and Freundlix isothermal models were used to represent the adsorption mechanism at equilibrium. The isotherm parameters calculated on the basis of the obtained results are R²(0,998-0,9998). value was found to be consistent in all isothermal models. According to the Langmuir isotherm model, q_max = 40,161 mg / g, and according to the Freundlix isotherm model, n = 0,277. This indicates a high sorption of Cu²⁺ ions into the ionite based on vermiculite.

АННОТАЦИЯ

В данной работе представлены результаты исследования сорбции ионов Cu²⁺ в искусственных растворах ионита на основе вермикулита при 293, 303 и 313 К, продолжительности сорбции до равновесия (24 часов) и при различных концентрациях. Изучены механизмы сорбции процессов и использованы изотермические модели Ленгмюра и Фрейндлиха для представления механизма адсорбции в равновесии. Параметры изотермы, рассчитанные на основании полученных результатов, составляют R² 0,998-0,9998. Значение оказалось постоянным во всех изотермических моделях. По модели изотермы Ленгмюра q_max = 40,161 мг/г, а по модели изотермы Фрейндлиха n = 0,277. Это свидетельствует о высокой сорбции ионов Cu²⁺ в ионите на основе вермикулита.

Keywords: Vermiculite, copper ions (Cu²⁺), adsorbent, CEC, kinetics, Langmuir, Freundlich and isotherm.

Ключевые слова: Вермикулит, ионы меди (Cu²⁺), адсорбент, COE, кинетика, Ленгмюр, Фрейндлих и изотерма.

Introduction. It is clear that nowadays, the continuous development of industry in the world and the introduction of advanced technologies are causing the decline in water and air quality. The negative impact of an increase in the concentration of pollutants in the composition of water and air on the ecosystem and human life is steadily increasing. One of the risks from these effects is the presence of heavy metals in the composition of pollutants. These heavy metals pollute industrial wastewater and the environment. Due to their high concentration toxicity, carcinogenic effects occur on humans and animals. Based on the above, it is required to remove pollutants containing heavy metal ions such as Cu, Ag, Ni and Co from wastewater [1]. This is briefly mentioned in this research work.

The continuous development of industry and the introduction of advanced technologies in the world are causing the quality of water and air to decrease. The negative impact of the increase in the concentration of pollutants in water and air on the ecosystem and human life is increasing day by day. One of the most dangerous of these effects is the presence of heavy metals in pollutants. These heavy metals pollute industrial wastewater and the environment. Their high concentration has a carcinogenic effect on humans and animals due to their toxicity. Based on the above, it is required to remove pollutants containing heavy metal ions such as Cu, Ag, Ni and Co from waste water [1].

Traditional methods for removing heavy metals from aqueous solutions include ion exchange, ultrafiltration, and adsorption. The adsorption method from these methods is affordable, effective even when the concentration of heavy metals is low, is used in wastewater treatment due to its universal nature, sensitivity to toxic substances, the possibility of regeneration.

To choose an adsorbent, the following criteria must be taken into account [3]:

• sorption ability of adsorbent;
• sensitivity, efficiency, mechanical strength and chemical stability;
• biological decay;
• recyclable or reuse;
• impact on the environment;
• price;
• chemical stability and environmental resistance

In recent years, the use of “slyuda” and composite compounds made from them as adsorbents has been giving effective results in order to prevent and eliminate pollution of the environment with organic and inorganic pollutants. Therefore, interest in the use of non-chemical and cheap adsorbents is growing, an example of which is the vermiculite-clay mineral, to which the group of aluminosilicate belongs.[4]

There is a classification of origin and distribution of vermiculite, which divides Mica minerals into three main groups: the kaolinite group, the illite group and the smectite-vermiculite group. Smectite-vermiculite belonging to the vermiculite groups is formed mainly as a result of purification from potassium biotite, phlogopite. Vermiculite has several advantages of high hardness, easy processing, low adsorbent and selectivity compared to other solids. It was first discovered in 1824 by the American XXXob. Vermiculites appear naturally, they are formed primarily as a result of changes in minerals (alternating mixtures of various minerals such as vermiculite, hydrobiotite and phlogopite) caused by weather, hydrothermal action, percolation of groundwater or a combination of these three factors[5].

Vermiculite is an environmentally friendly product that does not contain heavy metals. It is a 100% natural material and is neutral in relation to alkalis and acids that do not pose a danger to humans, the environment. Vermiculite is not prone to rotting and oxidation organic solvents and is insoluble in water and therefore does not lose its properties over time and has significant relief (0.065–0.130 g/cm³) as well as being a very abundant and much cheaper raw material in nature. It can be modified in many ways, resulting in inorganic-organic hybrid materials [6]. One of the unique properties of vermiculite is its delamination at high temperatures due to the loss of water inside the layers. It has a high resistance to chemicals and heat, the interchangeability of cations, the ability to maintain temperature and adsorb water. Vermiculite was also used as a reinforcing material for the production of polymer composites. Vermiculite has a cation exchange capacity, being a type 2:1 layered aluminum silicate mineral that has water molecules and exchange cations in its inter-layer cavity [7].

It will have a relatively high constant negative charge due to the exchange of Al³⁺ in octahedral areas of vermiculite to Mg²⁺/ Fe²⁺, and Si⁴⁺ in tetrahedral areas to Al³⁺. Its constant negative charge is mainly balanced by Mg²⁺ and Ca²⁺ cations within the inter-layered and basal region, and ion Exchange and external sphere complexes are usually formed. In vermiculite crystals (edge nodes), surface hydroxyl groups formed by hydrolysis of Al and Si atoms can interact with metal cations through internal spherical complexes and also through the outer sphere. Because vermiculite has a specific surface area, ion exchange capacity and surface activity, it is widely used in many fields such as agriculture, chemical industry and environmental protection. Vermiculite treatment results in an improvement in a specific surface area, ion exchange capacity, surfactant groups, and hydrophilic/hydrophobic properties of the surface, allowing the use of vermiculite in both hydrophilic and hydrophobic environments or in appropriate substrates [8].

The inter-layer areas of vermiculite, which are characterized by exchange of ions, adsorption, etc., are considered favorable for chemical reactions. Organic or inorganic species can be introduced into the inter-vermiculite space by physicochemical method, such as ion exchange, adsorption, and intercalation resulting in changes in vermiculite properties [9].

The ability of cation exchange in vermiculites is the result of surface and inter-layer ion exchange processes as well as isomorphic exchange. Such properties associated with high surface areas have been studied as adsorbent materials to remove heavy metal ions from industrial and household waste. The level of the ability of cation exchange of vermiculite will depend on the amount of exchange cations present in the layer and the outer surface. It has a constant negative charge, characteristics of large surface areas, and the sorption ability of cations, such as high cation exchange ability (120-140 mmol/mg) [10].

Normal vermiculite was also found to have a cation exchange capacity of 89 smol (+)/kg, which is lower than typical for vermiculites (actually 100-200 smol (+)/kg). However, it is known that Palabora vermiculite exhibits variability both in its composition and in its central locations. Palabora vermiculite is not pure vermiculite, but rather a mixed-layered vermiculite-biotite formed by percolation of aqueous hydration of phlogopite biotite. Unlike K⁺ cations fixed in the interlayer phase of biotite, hydrated interlayer ions in vermiculites are relatively easily exchanged [11].

Until now, the properties of vermiculite sorption, its application in wastewater treatment have been widely studied, and the results of the experiment have been studied to make it a suitable adsorbent for the treatment of heavy metals such as Pb(II), Cd(II), Cu(II) and others from wastewater. Vermiculite has been used in aqueous solution as an effective adsorbent for simultaneous adsorption of Cd²⁺ and Pb²⁺ ions, for which it has been modified with the surface active ingredient octylamine and adsorption has been studied. The effectiveness of adsorption has increased due to the ion exchange and complexing properties of the surfactant. Modified vermiculite with octylamine increased maximum adsorption efficiency for Cd(II) 69,595 mg/g and Pb(II) 121,986 mg/g, respectively. This means that it has good and stable regeneration properties as an effective adsorbent for cleaning water contaminated with heavy metals. [12].

Research materials and methods

In particular, in this article, the kinetics and isotherm of the sorption of Cu²⁺ ions of vermiculite-based ion exchangers in the study of artificial solutions were obtained from ion exchangers with a static exchange capacity of 2.5 mg•eq/g on HCl in an amount of 4 g/l. ions. Solutions of different concentrations, which contained Cu²⁺ and were 0.1, 0.05 0.025 and 0.0125 mol•l^-1, were prepared. Sorption of 100 ml of solution at temperatures of 293, 303 and 313 K until reaching equilibrium (up to 24 hours) was studied (with the help of  EMC-30PC-UV Spectrophotometer) (Cu²⁺ at 800 nm wavelength).

The CEC value of an ion exchange was calculated as follows:

k₁ ― 0,1×V ( alkali)/ V (acid) = 0,1 theoretical, k₂ ― 0,1×V (primary acid)/V (spent alkali)

а ― amount of alkali consumed per sorbed HCl, g ― sorbent mass

СEС unit mg •eq/g

The amount of sorption was calculated using the following formula:

In order to study the mechanism of adsorption of vermiculite-based ion exchange based on the balance of the sorption process, it was studied whether it fits the Langmuir and Freundlich models:

The Langmuir isotherm model is used to find the q_max and K_L values from the Ce/qe dependence graph by the angle value of the slope of the intersection using the following linear representation [9].

Using the linear representation given below, the Langmuir isotherm model finds the q_max and K_L values through the angular value of the intersection slope from C_e dependence graph of C_e/q_e[9].

The linear equation of the Freundlich isotherm model can be expressed in the following formula [13].

Results and discussion

Research

The figure below shows the duration of absorption of copper (II) ions at different times and to the ion exchange obtained on the basis of vermiculite.

Figure 2. Graph of the time dependence of the absorption of Cu²⁺ ions into an ion exchange obtained on the basis of vermiculite 

Figure 3. SEM images of vermiculite-based ionite (a) and (b) before Cu (II) adsorption

SEM morphologies of vermiculite-based ionite before and after Cu(II) adsorption are shown (Figure 3). It can be concluded that copper(II) ions were absorbed into the vermiculite-based ionite.

The results of the study of the isotherm of equilibrium state in adsorption processes are presented in the following (a and b ) graphs:

Figure 4 Graphs of Langmuir (a) and Freundlich (b) isotherm models of sorption of Cu2+ ions on vermiculite-based ion exchange

Table 1.

Absorption isotherm constants of Cu²⁺ ion

In summary, in Figure 2 above it can be seen that with an increase in time and concentration, the sorption amount of Cu (II) metal ions to the ion exchange increases. This indicates the absorption of Cu (II) ions into the ion exchange obtained on the basis of vermiculite.

The above table (Table 1) shows that the amount of sorption of Cu(II) metal ions to ion exchange is R²(0.998-0.9998). According to the Langmuir isotherm model =40,161mg/g, and the RL value is 0.131 in all studied concentrations, which indicates that the sorption process is favorable. According to Freundlich isotherm model n=0.277 absorption was convenient. This means that Cu²⁺ ions are absorbed into the new ion exchange by chemisorption. This shows the sorption of Cu²⁺ ions to the new ion exchange.

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