Original Research Paper
Application of oak powder/Fe3O4 magnetic composite in toxic metals removal from aqueous solutions

https://doi.org/10.1016/j.apt.2018.12.006Get rights and content

Highlights

  • The powdered biochar of oak fruit shell was combined with Fe3O4 (=OP/Fe3O4).

  • Physical-chemical properties of OP/Fe3O4 magnetic composite were fully assessed.

  • The optimal pH to absorb Co, Ni, and Pb by the powdered OP/Fe3O4 was found to be 6.

  • Heterogeneous surface was more effective than a homogeneous one in adsorbing metals.

  • Based on thermodynamic study, the metals adsorption was spontaneous and exothermic.

Abstract

In this study, the capability of a magnetic composite of oak powder/Fe3O4 (OP/Fe3O4) for the adsorption of lead, cobalt, and nickel ions from aqueous solutions was examined. Characteristics and structure of oak powder (OP) and OP/Fe3O4 magnetic composite were explored by FTIR, SEM, TGA-DTG, VSM, and XRD analysis. The XRD results showed that OP/Fe3O4 magnetic composite and OP were in crystalline form. Kinetic behavior of adsorption process was studied using pseudo-first-order, pseudo-second-order, and Elovich models. Results indicated that the pseudo-second-order model (R2 > 0.999) can better describe the kinetic behavior of the metal adsorption process. Equilibrium behavior of the adsorption process was also tested using Langmuir, Freundlich, Dubinin–Radushkevich (D–R), and Scatchard isotherm models. The results revealed that the adsorption equilibrium data for three metals match with the Freundlich isotherm model (R2 > 0.99). This indicates the effectiveness of heterogeneous surfaces in comparison with homogeneous ones in the adsorption process of metal ions. Moreover, the results showed that the adsorption process of metal ions with the OP/Fe3O4 magnetic composite is physical. Finally, negative values of enthalpy and entropy indicated that the process of the metal ion adsorption is spontaneous and exothermic.

Introduction

Nowadays, the contamination of natural water resources by heavy metal ions is a serious concern. One of the major reasons for such contamination is the release of heavy metals into wastewaters due to the rapid industrialization and unorganized cities growth [1]. Presence of heavy metal ions in the environment is harmful to human health and other creatures and affects their bodies through drinking water and foods routs [2], [3]. These pollutants are toxic and non-biodegradable and can be accumulated inside living cells [4]. Therefore, an even very low concentration of heavy metals ions can be harmful to marine and living organisms [4]. In the body of living beings, the unmetabolized metal ions cannot be accumulated in soft organs and thus caused toxic effects [5]. In general, there are three groups of heavy metal ions causing serious concerns. These groups are categorized as toxic metals (Hg, Cr, Sn, Co, As, Cd, Ni, Cu, Zn, Pb), valuable and worthy metals (Pd, Ru, Au, Ag, Pt), and radioactive metals (Am, Ra, Th, U) [6]. According to the list of World Health Organization (WHO) and International Program on Chemical Safety (IPCS), aluminum, chrome, cobalt, nickel, copper, cadmium, zinc, mercury, and lead are also considered as toxic metals [7]. Lead is one of the four major toxic metals which causes very serious harm to the human health. This metal is widely used in industries like battery production, pigments, metalwork, soldering materials, ceramic, and glass industries as well as in steel production units [8]. It can be discharged into the environment through the wastewaters of such industries [8]. This metal ion can be inhaled, digested or transported to the body by skin contact and orally, and can result various illnesses like encephalopathy, hepatitis [9], severe damage to kidney, reproduction system, liver, brain [10], barrenness, blood pressure diseases, abortion, low intelligence, and maybe death [11]. Cobalt is discharged into the environment through the wastewaters of a nuclear power plant, power generation with coal, mining, metallurgy, plating, painting, petroleum industries, and electronics [12]. This cation is a natural element which is essential for the body at very low concentrations and plays an important role in the production of B12 vitamin [13]. However, high concentrations of Co(II) ions can be dangerous for respiratory and cardiovascular systems leading to unconsciousness or even death [14]. Nickel is the most common toxic contaminants and its poisoning causes headache, vertigo, nausea, aching in the thorax, asthma, dry coughs, cyanosis, and severe weakness [15]. Therefore, heavy metal ions removal from aqueous solutions and industrial wastewaters before entering into the environment and water bodies is very essential and mandatory.

Many types of physical and chemical methods can remove heavy metal ions from aqueous solutions including filtration, evaporation, chemical sedimentation, oxidation/reduction, electrochemical methods, ion change, reverse osmosis, adsorption, electrolyte or extraction with liquid, and electrodialysis [16], [17], [18]. Among these, the adsorption method is very important because of economic reasons, simplicity, effectiveness, reusability, low- or no- cost of precursor materials, and high operational rate [19]. The adsorption process could be more economical and environmentally friendly if the adsorbent is produced from wastes like fishery-, agriculture- and horticulture-wasted biomass. In this regards, many wastes such as Malva sylvestris biomass [20], corn stalk and sewage sludge [21], and local forest [22] have been examined for production of sorbents to remove heavy metals. The process of adsorption can be more effective if the adsorbent material is recycled and used several times. Removing adsorbents to reuse is difficult and costly. One of the approaches to solving this problem is the magnetization of adsorbents for its easy separation. Magnetic adsorbents such as Fe@MgO nanocomposite [23], magnetically modified zeolite [24], and agricultural biomass-derived magnetic adsorbent [25] were successfully tested to remove heavy metals ions. According to the latest scientific researches, the biochar derived from the oak fruit shell has not been used in a magnetism form to remove pollutants. Therefore, the test results of such adsorbent can be valuable and significant.

As a large amount of oak fruit is annually produced at no- or low- cost, so in this study, the biochar of oak fruit shell was mixed with Fe3O4 nanoparticles to produce a magnetic adsorbent to remove metal ions of lead, cobalt, and nickel. Characteristics of the oak powder/Fe3O4 (OP/Fe3O4) were determined using Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), thermal gravimetric analysis- differential thermal gravimetric (TGA-DTG), and vibrating sample magnetometer (VSM). Moreover, the effects of operational parameters on the adsorption efficiency were investigated. The kinetic, isotherm, and thermodynamics of the metals adsorption were also tested.

Section snippets

Materials and solution

The stock solutions of Pb(II), Co(II), and Ni(II) with concentration of 1000 mg/L were prepared after dissolving a definite amount of lead nitrate (Pb(NO3)2), nickel chloride (NiCl2·6H2O), and cobalt nitrate (Co(NO3)2·6H2O) in one liter of double-distilled water, respectively. Then, the stock solution was diluted with double-distilled water to prepare solutions with certain concentrations of nickel, cobalt, and lead ions. Sodium hydroxide (NaOH) and hydrochloric acid (HCl) were used for pH

Adsorbent properties

Chemical properties of OP and OP/Fe3O4 were analyzed with FTIR and the results are shown in Fig. 1a. According to this analysis, there are different peaks in various regions. These peaks in the range of 3448 cm−1 and 3437 cm−1 are corresponding to the vibrations of single bondOH functional group in OP and OP/Fe3O4 composite. In the range of 2926 cm−1 and 2922 cm−1, there is another peak related to the vibrations of single bondCH functional group within the structure of adsorbents [27]. Adsorption peaks in the range

Conclusion

In the present study, the magnetic composite of OP/Fe3O4 was synthesized and used to adsorb lead, cobalt, and nickel ions from aqueous solutions. The OP/Fe3O4 composite was fully characterized using FTIR, SEM, XRD, TGA-DTG, and VSM techniques to prove the surface properties and structural features. The FTIR analysis showed that different functional groups like single bondOH, Csingle bondO, and Fesingle bondO were present in the composite structure. At the conditions of pH 6, OP/Fe3O4 composite dose of 3 g/L, and contact time

Declarations of interest

None.

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