Researchers are in continuous search of better strategies to minimize, if not prevent, the anthropogenic release of toxic heavy metals, such as Cu(II) and Pb(II), into drinking water resources and the natural environment. Herein, we report for the first time the low-temperature combustion synthesis of magnetic chitosan-manganese ferrite in the absence of toxic cross-linking agents and its removal of Cu(II) and Pb(II) from single-component metal solutions. The nonlinear Langmuir model best described the isotherm data, while the nonlinear pseudo-second order model best described the kinetic data, signifying monolayer Cu(II) or Pb(II) adsorption and chemisorption as the rate-determining step, respectively. Adsorption capacities by magnetic chitosan-manganese ferrite obtained for both metals were consistently higher than those by manganese ferrite, indicating that chitosan enhanced the performance of the magnetic adsorbent. The maximum adsorption capacities of magnetic chitosan-manganese ferrite for Cu(II) and Pb(II) were 14.86 and 15.36 mg g⁻¹, while that of manganese ferrite were 2.59 and 13.52 mg g⁻¹, respectively. Moreover, the adsorbents showed superior binding affinity and sorption for Pb(II) than Cu(II) owing to the stronger ability of the former to form inner-sphere complexes with manganese ferrite and magnetic chitosan-manganese ferrite. Finally, thermodynamic studies revealed that the uptake of either Pb(II) or Cu(II) by magnetic chitosan-manganese ferrite was spontaneous and endothermic. The as-prepared adsorbent was characterized for morphology, elemental composition, surface functional sites, and particle size using scanning electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, and dynamic light scattering technique, respectively.

The ubiquitous occurrence of heavy metals in the aquatic environment remains a serious environmental and health issue. The recovery of metals from wastes and their use for the abatement of toxic heavy metals from contaminated waters appear to be practical approaches. In this study, manganese was recovered from groundwater treatment sludge via reductive acid leaching and converted into spherical aggregates of high-purity MnO₂. The as-synthesized MnO₂ was used to adsorb Cu(II) and Pb(II) from single-component metal solutions. High metal uptake of 119.90 mg g⁻¹ for Cu(II) and 177.89 mg g⁻¹ for Pb(II) was attained at initial metal ion concentration, solution pH, and temperature of 200 mg L⁻¹, 5.0, and 25 °C, respectively. The Langmuir isotherm model best described the equilibrium metal adsorption, indicating that a single layer of Cu(II) or Pb(II) was formed on the surface of the MnO₂ adsorbent. The pseudo-second-order model adequately fit the Cu(II) and Pb(II) kinetic data confirming that chemisorption was the rate-limiting step. Thermodynamic studies revealed that Cu(II) or Pb(II) adsorption onto MnO₂ was spontaneous, endothermic, and had increased randomness. Overall, the use of MnO₂ prepared from groundwater treatment sludge is an effective, economical, and environmentally sustainable substitute to expensive reagents for toxic metal ion removal from water matrices.

Chemical disinfection of surface waters has been proven effective in minimizing the risk of contamination by water-borne pathogens. However, surface waters contain natural organic matter (NOM) which, upon chemical disinfection, is readily converted into hazardous disinfection-by-products. Hence, NOM removal from these waters is critical. Chemical coagulation is a readily implementable technology to minimize these undesired side-effects by NOM removal. Herein, capabilities of ferric chloride (FeCl₃) and polyaluminum chloride (PACl) as pre-treatment for NOM abatement from natural raw surface water have been benchmarked. Excitation-emission fluorescence matrix (EEM) spectroscopy characterization of NOM fractions demonstrated high removal efficiency. A two-level full factorial design was employed to analyze the effects of coagulant dosage and initial pH on the removal of turbidity, humic acid-like substances and fulvic acid-like substances from the raw water. Higher removal of ~77% NOM was attained with PACl than with FeCl₃ (~72%). Optimization through response surface methodology showed that the initial pH—coagulant dosage interaction was significant in removing NOM and turbidity for both PACl and FeCl₃. These results identify the opportunity for coagulation technologies to prevent and minimize disinfection-by-products formation through NOM removal.

We investigated the reducing rate of manganese oxides (MnOs) and organic matter in water by using pre-oxidation and coagulation/sedimentation methods with different chemicals. The reduction rate using NaOCl for organic matter was about 11%, while that of manganese was 12%. The reduction rate using chlorine dioxide (ClO₂) was only 7% for organic matter. However, the rate of manganese was 29% when using ClO₂. Potassium permanganate (KMnO₄) removed organic matter and MnOs more effectively, with a rate of 18 and 71%. Moreover, aluminum sulfate (Al₂(SO₄)₃), ferric chloride (FeCl₃), and polysilicate iron (PSI) worked more effectively, with a reduction rate of 99% and 55% for turbidity and organic matter.