Abstract
The continued decrease in water quality requires new advances in the treatment of wastewater, including the preparation of novel, effective, environmentally friendly, and affordable sorbents of toxic pollutants. We introduce a simple non-conventional mechanochemical synthesis of magnetically responsive materials. Magnetic lignite and magnetic char were prepared by high-energy ball co-milling from either raw Slovak lignite or coal-based char together with a ferrofluid. The products were characterised by X-ray diffraction, electron microscopy, 57Fe Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS), volumetric magnetic susceptibility, and low-temperature nitrogen adsorption, and both magnetic carbons were comparatively tested as potential sorbents of As(V) oxyanions and Cd(II) cations in aqueous solutions. The magnetic char was an excellent sorbent of As(V) oxyanions (Qm = 19.9 mg/g at pH 3.9), whereas the magnetic lignite was less effective. The different sorption properties towards arsenic anions may have been due to different oxidation states of iron on the surfaces of the two magnetic composites (determined by XPS), although the overall state of iron monitored by Mössbauer spectroscopy was similar for both samples. Both magnetic composites were effective sorbents for removing Cd(II) cations (Qm (magnetic lignite) = 70.4 mg/g at pH 6.5; Qm (magnetic char) = 58.8 mg/g at pH 6.8).
Highlights
High-quality water is essential for living organisms
The carbon content decreased in the samples of magnetic sorbents after the coal/char was mixed with FF and the subsequent mechanical treatment
Iron content was similar in the two magnetic sorbents (7.7% for magnetic lignite and 8.4% for magnetic char)
Summary
High-quality water is essential for living organisms. Rapid industrialisation has produced hazardous secondary products on a large scale, polluting water especially in developing countries. Biodegradation, electrochemical oxidation, and adsorption have been established for eliminating toxic substances either in organic (e.g., pharmaceuticals, personal-care products, and reactive dyes) or inorganic (heavy metals) forms. New environmentally friendly and regenerable materials are still being developed for improving sorption properties and minimizing the cost. Adsorption on carbonaceous materials offers low-energy consumption, lack of by-products, simplicity, reliability, and low cost. These materials are very effective, but separating them and effectively from wastewater in a continuous-flow system remains a challenge [10]. Iron-based magnetic sorbents are very beneficial for removing highly toxic arsenic oxyanionic species, which are one of the major environmental health hazards in contaminated groundwater [10,11,12]. Magnetic adsorbents can be divided into three main groups based on the type of material:
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