Arsenic Removal from Mining Effluents Using Plant-Mediated, Green-Synthesized Iron Nanoparticles

Abstract

Arsenic contamination in industrial and mining effluents has always been a serious concern. Recently, nano-sized iron particles have been proven effective in sorptive removal of arsenic, because of their unique surface characteristics. In this study, green synthesis of iron nanoparticles was performed using a mixed extract of two plant species, namely Prangos ferulacea and Teucrium polium, for the specific purpose of arsenic (III) removal from the aqueous environment. Results of UV-visible spectrometry, X-ray powder diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) analyses confirmed the formation of iron nanoparticles from Prangos ferulacea (Pf) and Teucrium polium (Tp) extracts. The synthesized Fe nanoparticles morphology was studied via microscopy imaging. The particle size was 42 nm, as assessed by dynamic light scattering (DLS) analysis. Adsorption experiments were also designed and performed, which indicated 93.8% arsenic removal from the aqueous solution at 200 rpm agitation rate, 20 min agitation time, pH 6, initial concentration of 0.1 g/L, and adsorbent dosage of 2 g/L. Adsorption isotherm models were investigated, and the maximum uptake capacity was determined to be about 61.7 mg/g. The kinetic data were best represented by the pseudo-second kinetic model (R 2 = 0.99). The negative value of Gibbs free energy, the enthalpy (−7.20 kJ/mol), and the entropy (−57 J/mol·K) revealed the spontaneous and exothermic nature of the adsorption process. Moreover, the small quantity of the activation energy confirmed the physical mechanism of arsenic adsorption onto iron nanoparticles and that the process is not temperature sensitive.toxic than arsenate, more mobile in aqueous environments, and more hazardous to the environment. Long-term consumption of arsenic-contaminated water is a threat to human health [3]. Among the chronic effects of exposure to arsenic are the spread of cancers, skin diseases, and infertility. According to World Health Organization (WHO) and United States Environmental Protection Agency (USEPA), the maximum arsenic concentration limit in drinking water is 10 µg/L [4].Several methods have been proposed for removal of arsenic from aqueous solutions, each having their unique limitations and benefits. The available strategies generally include the oxidation-based [5,6], coagulation, settlement, and filtration methods [7,8]; and membrane [9], ion-exchange [10], and adsorption processes [11,12]. Most arsenic removal methodologies are non-effective for arsenite ions, which are predominantly non-charged at pH < 9.2 [5]. The precipitation, adsorption, and ion-exchange methods are, therefore, less applicable for removal of trivalent arsenic. Accordingly, the optimum arsenic removal methods are usually composed of two individual stages: initial oxidation of arsenite to arsenate, and subsequent removal of arsenate [13].In spite of the availability of biological and chemical methods (chemical oxidation, electrochemical acidification) to remove arsenic from the aqueous solutions, the ef...

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