Heavy metals (Cd²⁺, Cu²⁺ and Pb²⁺) removal mechanisms of nZVI from aqueous solution.

There has been an increasing challenge from the emission of methylene blue (MB) dye-containing wastewater and its management methods in industry. The sorption process is one conventionally used method. In this study, nanoclay, nano zero valent iron (nZVI), and iron impregnated nanoclay were prepared and studied for the removal of MB dye in batch mode. The effects of operating parameters like pH, dye concentration, sorbent dosage, and contact time were investigated and optimized. The nZVI, nanoclay, and iron impregnated nanoclay sorbents showed zeta potentials of −32.1, −53.4, and −40.7 mV, respectively. All the nano adsorbents were crystalline. The nanoclay was characterized by an average surface area, pore volume and pore diameter of 43.49 m² g⁻¹, 0.104 cm³ g⁻¹ and 2.806 nm, respectively. nZVI showed a surface area of 47.125 m² g⁻¹, pore volume of 0.119 cm³ g⁻¹, and pore diameter of 3.291 nm. And iron impregnated nanoclay showed a surface area of 73.110 m² g⁻¹ with a pore volume of 15 cm³ g⁻¹ and a pore diameter size of 3.83 nm. A Langmuir EXT nitrogen gas adsorption isotherm (R² ∼ 0.99) was the best fit. The thermodynamics parameters, such as ΔG° (−12.64 to −0.63 kJ mol⁻¹), ΔH° (+0.1 to +62.15 kJ mol⁻¹) and ΔS° (+0.10 to +0.22 kJ mol⁻¹), confirmed that a spontaneous and endothermic adsorption process took place at a high rate of disorder. Iron impregnated nanoclay showed higher negative Gibbs free energy (−12.64 kJ mol⁻¹), higher enthalpy change (+62.5 kJ mol⁻¹) and entropy (+0.22 kJ mol⁻¹) and gave a better MB removal performance. In addition, the lower negative heat of enthalpy for all adsorptions proved the dominance of physisorption. The methylene blue adsorption isotherm on nZVI and nanoclay showed the best fit with the Freundlich isotherm model with correlation coefficients (R²) ∼0.98 and 0.99, respectively. Whereas the Langmuir adsorption isotherm was the best fit for iron impregnated nanoclay (R² ∼ 0.98). The adsorption activities of nZVI, nanoclay and iron impregnated nanoclay were fitted to a pseudo-second-order kinetic model with correlation coefficients (R²) of 0.999, 0.997 and 0.983, respectively. The optimal pH 7.0 (RE: 99.1 ± 0.73%), initial MB concentration 40 ppm (RE: 99.9 ± 0.03%), contact time 120 min (RE: 99.9 ± 0.9%), and adsorbent dose 80 (99.9 ± 0.03%) were obtained for iron impregnated nanoclay. The optimal operational parameters of nanoclay and nZVI, respectively, were pH 11.0 and 13.0, initial MB concentration 20 and 20 ppm, adsorbent dose 100 and 140 mg, and contact time 120 and 140 min. In general, iron impregnated nanoclay has shown promising cationic dye adsorbance for industrial applications; but a recyclability test is suggested before scale-up.

Correction for ‘Nano zero valent iron (nZVI) particles for the removal of heavy metals (Cd ²⁺ , Cu ²⁺ and Pb ²⁺ ) from aqueous solutions’ by Mekonnen Maschal Tarekegn et al. , RSC Adv. , 2021, 11 , 18539–18551. DOI: 10.1039/D1RA01427G.

Several physicochemical techniques have been widely studied for heavy metals removal despite most of them are associated with challenges of higher cost, accessibility, and complex technical feasibility. In this study, nano-sorbent materials were developed from a naturally available clay matrices and its heavy metals (Cu ²⁺ and Pb ²⁺ ) removal capacity was tested at its pristine and iron impregnated form. Both top to down and borohydride reduction methods were used to produce the nano-sorbents. The nano-sorbents were characterized by XRD, XRF, SEM, FTIR, BET, and TGA/DGA. The sorption was studied in batch experiments. The surface area, pore-volume, and pore diameter of nano-clay were found 43.49 m ² /g, 0.104 cm3/g, and 2.81 nm, respectively while iron impregnated nano-clay has shown a surface area (73.11 m ² /g), pore-volume (0.153 m ³ /g), and pore diameter (3.83 nm). Both nanoparticles have shown a mesoporous nature. The highest Cu ²⁺ and Pb ²⁺ removal capacity of nano-clay was 99.2% (~11.9 mg/g) and 99.6% (~11.95 mg/g), respectively. Whereas, the iron impregnated nano-clay has achieved the highest Cu ²⁺ and Pb ²⁺ removal efficiency 99.8% (~11.97 mg/g) and 99.7% (11.96 mg/g), respectively. The highest Cu ²⁺ adsorption efficiency of iron impregnated nanoclay was achieved at pH 5.0, adsorbent dose 0.83 g/L, contact time 150 minutes, and Cu ²⁺ initial concentration 4 ppm while its highest Pb ²⁺ adsorption activity was achieved at pH 5.0, contact time (90 minutes), Pb ²⁺ initial concentration (6 ppm), and the adsorbent dose (0.67 g/L). Whereas, the Cu ²⁺ adsorption using nano-clay was highest at pH 5.0, contact time (180 minutes), adsorbent dose (1.0 g/L), and Cu ²⁺ initial concentration (2 ppm). While, pH 5.0, contact time (90 minutes), adsorbent dose (0.83 g/L), and Pb ²⁺ initial concentration (4 ppm) was found to the conditions of highest Pb ²⁺ removal. In all cases, the pseudo-second-order kinetics indicated the presence of chemisorption. Langmuir adsorption characteristics has been reflected on Pb ²⁺ and Cu ²⁺ removal activities of the nanoclay and iron impregnated nanoclay, respectively. Whereas, Freundlich isotherm model was better fitted for Cu ²⁺ adsorption activity of the nanoclay. The −ΔG (<−20 KJ/mol), + ΔH°, and + ΔS° have shown a spontaneous and endothermic adsorption activity with a high level of adsorbents disorder. In general, the result of iron impregnated nano-clay has shown a promising result for the removal of Cu ²⁺ and Pb ²⁺ aqueous solution.

Introduction. An increase in population and related increased demand for health services, expansion of industries, and increasing transportation demands have increased the emission of dioxin and furan persistent organic pollutants (POPs) in Addis Ababa, Ethiopia. Objective. This study aimed to identify sources of dioxin and furan emissions, quantify their release into various environmental medias and assess related management practices. Methods. The standard United Nations Environmental Programme (UNEP) (2005) toolkit guide and default emission factor were used to identify the main anthropogenic sources and to quantify the amount of released dioxin and furan. Stratified random sampling techniques were applied to assess current management practices. Results. Nine main groups of dioxin and furan emission sources were identified. The emission of each source group was calculated by the activity rate data multiplied by an emission factor. The results found that about 138.85 g toxic equivalent(TEQ)/a(TEQ/year)o...

Lake Ziway, located in the Ethiopian Rift Valley, faces significant environmental pressure due to intensive agricultural and floriculture practices that heavily utilize pesticides. This study examined the concentrations, bioaccumulation, and health risks associated with 22 selected pesticides in four fish species: Oreochromis niloticus, Cyprinus carpio, Carassius carrasius, and Clarias gariepinus. A total of 48 fish, grouped by size into three sets for each species, were sourced from local fisheries and analyzed in duplicate. The dorsal muscle samples were extracted using a speed extractor, purified with florisil, and quantified using gas chromatography coupled with mass spectrometry (GC–MS/MS). Most compounds showed mean recoveries between 60 and 120%, except for dieldrin (51.33%) and bendiocarb (121.86%). Detection limits ranged from 0.01 to 2.6 μg kg⁻¹. Positive pesticide residues, including Σ HCH, Σ DDTs, HCB, Σ heptachlor, chlorpyrifos, propoxur, and diazinon, were detected at concentrations between 0.010 and 66.44 μg kg⁻¹. However, levels of β-HCH, γ-HCH, aldrin, dieldrin, endosulfan I, endosulfan sulfate, bendiocarb, profenofos, chlordane-trans, chlordane-cis, methoxychlor, and chlorpyrifos-methyl were below the detection limit. DDTs were the most prevalent contaminants, with concentrations ranging from 5.08 to 213.61 μg kg⁻¹, likely due to historical contamination from past practice. The detection of newer pesticides points to ongoing agricultural pressure and inadequate pesticide management practices in the lake’s catchment area. These challenges underline the urgent need for integrated policy responses that combine stricter enforcement of existing bans on legacy POPs, strengthened monitoring systems to include emerging contaminants like carbamates, and improved farmer training and awareness programs to promote sustainable pesticide use. Prolonged consumption of pesticide-contaminated fish poses carcinogenic risks, also highlighting the need for enforcement of pesticide regulations.