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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.

In this study, manganese dioxide (MnO2) derived from groundwater treatment sludge was used in the adsorption of nickel (Ni(II)) ions from aqueous solutions. The synthetic MnO2 was prepared via permanganate reduction using manganese extracted from the sludge by reductive acid leaching and hydroxide precipitation. Scanning electron microscopy images showed aggregated micron-sized MnO2 particles. Fourier transform infrared analysis of MnO2 revealed functional groups at 3,396 cm−1, 1,630 cm−1, 1,427 cm−1 and 468 cm−1 bands. Zeta potential measurements at the pH range of 2–8 confirmed the net negative surface charge of MnO2 particles. Moreover, Ni(II) adsorption by MnO2 was best described by the Langmuir isotherm model, as indicated by the high values for the coefficients of determination (R2> 0.9703). The separation factor (RL) for the range of pH values and initial Ni(II) concentrations considered in this study indicated that Ni(II) adsorption by MnO2 was favorable. The kinetic data of Ni(II) adsorption by MnO2 at pH 6.5 and initial Ni(II) concentrations from 10 to 200 mg L−1 conformed to the pseudo-second order adsorption kinetic model, with R2 > 0.9997. Chemisorption occurred through the complexation of Ni(II) ions with available MnO2 functional groups. The thermodynamic study at temperatures of 298.15, 308.15 and 318.15 K revealed that Ni(II) adsorption by MnO2 was spontaneous and thermodynamically favorable for initial Ni(II) concentrations ranging from 50 to 200 mg L−1. Overall, Ni(II) adsorption by MnO2 was endothermic, as indicated by the positive ΔH° values. In addition, MnO2 had good affinity towards the Ni(II) ions, as shown by the positive ΔS° values at all Ni(II) concentrations. Simple cost analysis revealed that the MnO2 production from groundwater sludge was economically viable and may be scaled up for commercial applications.

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 cleaning of membranes fouled by natural organic matter (NOM) generates secondary pollution. In this study, the effect of ultrasonic cleaning of polytetrafluoroethylene (PTFE) membrane fouled by pre-coagulated humic acid-bentonite mixture was investigated. Results show that chemical coagulation prior to microfiltration improved turbidity and TSS removals by 9.5% and 11.4%, respectively. Experimental data fitted to constant pressure filtration models determined the sequence of dominant fouling mechanism as follows: (i) membrane resistance-limited, (ii) pore blocking resistance-limited, and (iii) cake formation resistance-limited. Relative membrane permeability of 53 and flux recovery of 45% were achieved when continuous ultrasonic cleaning was done at a 2.0 cm probe distance, 25 min total cleaning time, 15 mg/L coagulant dose, and 15 W ultrasonic power. Ultrasonic cleaning was found to be more effective than hydraulic cleaning in terms of flux recovery. Compared to chemical cleaning, it is a competitive and safer alternative in mitigating NOM-induced fouling.

In this study, the removal of Cu(II), Ni(II), Pb(II), and Zn(II) from aqueous solution in single and multi-metal system using chitosan-coated montmorillonite (ChiMC) beads was investigated. The non-crosslinked and crosslinked ChiMC beads were characterized using SEM–EDX, Fourier transform infrared, and Brunauer, Emmett, and Teller analysis. The effect of ionic strength and pH on the adsorption capacity and percent (%) removal of ChiMC was examined. Kinetic studies revealed that adsorption using ChiMC follows the pseudo-second-order equation with high correlation coefficient values (R2 > 0.95). The equilibrium data were correlated with Langmuir and Freundlich isotherm models, where crosslinked ChiMC provided higher maximum adsorption capacity over ChiMC. The calculated Langmuir adsorption capacities for Cu(II), Ni(II), Pb(II), and Zn(II) using ChiMC in single-metal system are 13.04, 12.18, 29.85, and 13.50 mg/g, respectively. An increase in the calculated adsorption capacities derived from Langmuir...

In this study, Cu(II) removal using non-crosslinked and cross-linked chitosan-coated sand (CCS) from aqueous solution was investigated. To improve the mechanical and chemical stability, chitosan was coated onto sand (CCS) and cross-linked using epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE). The effect of pH (2.0–5.0) on the adsorption capacity was examined. The maximum adsorption capacity of CCS, CCS–ECH, and CCS–EGDE occurred at an initial pH of 5.0, 4.0, and 5.0, respectively. The kinetic experimental data agreed well with pseudo-second order equation (R 2 > 0.988), which implies that chemisorption is the rate controlling step. Langmuir, Freundlich and Dubinin–Radushkevich were used to analyze the equilibrium data, where the Langmuir model provided the best fit for the isotherm data obtained using CCS, CCS–ECH, and CCS–EDGE (R 2 > 0.990). Adsorption-desorption was carried out using HCl solution (pH 1.0 and 3.0) and tap water (pH 7.0), where HCl solution (pH 1.0) provided t...

The removal of Mn2+ and Fe2+ from synthetic groundwater via oxidation using potassium permanganate was investigated. Batch jar tests were carried out under a constant pH of 8.0, where the effect of parameters such as the oxidant dose, presence of co-ions (Ca2+, Mg2+) and alum addition on the removal of Mn2+ and Fe2+ was examined. The partial removal of Mn2+ using aeration in single and dual metal system was 30.6% and 37.2%, respectively. The oxidant dose of 0.603 mg/L KMnO4 was the minimum amount needed to reduce Mn2+ below its maximum contaminant level. The presence of Fe2+ improved the removal of Mn2+ due to the autocatalytic effect of hydrous manganese-iron oxide, where its presence was confirmed by digital microscopy and EDX. The presence of Ca2+ and Mg2+ as well as the alum addition after oxidation has a negative effect on the removal of Mn2+. The removal mechanism of Mn2+ and Fe2+ was a combination of oxidation and adsorption or co-precipitation between the hydrous oxide and the dissolved me...

The aim of this study is to investigate the conditions for the removal of manganese ions from synthetic groundwater by oxidation using KMnO(4) to keep the concentration below the allowed level (0.05 mg/L). The process includes low-level aeration and addition of KMnO(4) in a Jar test system with Mn(2 + ) concentration of 0.50 mg/L, similar to that of natural groundwater in Taiwan. Different parameters such us aeration-pH, oxidant dose, and stirring speed were studied. Aeration alone was not sufficient to remove Mn(2 + ) ions completely even when the pH was increased. When a stoichiometric amount of KMnO(4) (0.96 mg/L) was used, a complete Mn(2 + ) removal was achieved within 15 min at an optimum pH of 8.0. As the amount of KMnO(4) was doubled, lower removal efficiency was obtained because the oxidant also generated manganese ions. The removal of Mn(2 + ) ions could be completed at pH 9.0 using an oxidant dose of 0.48 mg/L because Mn(2 + ) could be sorbed onto the MnO(2) particles. Finally, The MnO(2) particles were characterized using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX).