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This study investigated the competitive sorption of black soil to adsorb Pb(II) and methylene blue (MB) from multi-contaminated soils. According to the experimental data, the process of adsorption can be clearly explained by pseudo-second-order kinetic equation. Both single and binary systems of the adsorption isotherms had a good fit with Langmuir models. The maximal adsorption abilities of Pb(II) and MB acquired from binary systems sorption were attenuated compared to those from the single system (Pb(II): 77.70 > 65.96 mg g -1 ; MB: 242.31 > 222.36 mg g -1 ). Pb(II) and MB can inhibit each other's sorption ability. A combination of three-dimensional excitation-emission matrix (3D-EEM), synchronous fluorescence spectra as well as two-dimensional correlation spectroscopy (2D-COS) were employed to determine the binding of dissolved organic matter (DOM) for Pb(II) and MB during soil sorption process. As a result, 3D-EEM implicated that the two main composes of DOM were humic acid-like substances and the fluorescence of DOM specimens were gradually diminished with increasing concentrations of Pb(II) and MB. According to synchronous fluorescence spectra, static quenching of Pb(II) and MB mainly led to fluorescence quenching. Specifically, fluorescence-2D-COS implicated that Pb(II) and MB bound to fluorescence in the following sequence: the earlier occurrence of the humic-like fraction compared to that of protein-like fraction. FTIR-2D-COS results concluded that the structural change sequence of DOM by Pb(II) binding followed the order: 1700＞863＞1332＞1529＞1200＞1086 cm -1 and the sequence of the MB binding affinities followed the order: 1520＞1399＞1345＞1152＞1602＞993＞881 cm -1 . These findings would be beneficial to understand the mechanism of adsorb multi-component systems and have the potential to contribute significance to the interaction mechanism of multi-component with soil DOM at the molecular level., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Biochar is being widely considered as a promising amendment agent for immobilizing heavy metals in contaminated acidic soils, where plenty of soluble Al(III) ions exist. In view of uncertain significance of the effects of coexisting Al(III) on Pb(II) sorption by biochars, this study used kenaf core biochar (KB550; high carbon, low ash) and sewage sludge biochar (SB550; low carbon, high ash) pyrolyzed at 550 °C to elucidate the influence of coexisting Al(III) species and biochars' mineral components on Pb(II) immobilization conducted in aqueous solution with initial pHs of 3.0-4.5. Results showed that Al(III) reduced Pb(II) sorption on KB550 primarily via pH buffering against biochar alkalinity, thus inhibiting lead carbonate formation. In contrast, the reduction on SB550 mainly resulted from direct competition for sorption sites, especially on Fe-rich phengite 2M1 and metakaolinite. Because of Pb-P precipitation and Pb-K interlayer exchange, the residual Pb(II) adsorption capacity resistant to coexisting Al(III) was 3-5 times higher on SB550 than on KB550. The Pb-K interlayer exchange was enhanced by lower pH and coexisting Al(III), while Pb-P precipitation was the dominant Pb(II) sorption mechanism on SB550 resistant to Al(III) buffering and competition at higher pH. Application of these two biochars as amendments confirmed that the mineral-rich SB550 was more suitable for Pb(II) immobilization in acidic soils with high levels of extractable Al(III)., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Competitive sorption and resulting nonequilibrium transport of Cu and Pb were investigated using slag as a primary sorbent. A series of estimation models were applied based on the equilibrium, and nonequilibrium sorption respectively, and finally calibrated by incorporating the experimentally determined batch kinetic data. When applied individually, the behavior of metals in slag-sand column were well predicted by both equilibrium and nonequilibrium models in CXTFIT code. However, coexisting Cu and Pb exhibited competition for sorption sites, generating an irregular breakthrough curves such as overshoot (higher concentration in effluent than the feed concentration) of Cu and corresponding earlier peak of Pb followed by gradual re-rising. Although two-site nonequilibrium model further considers coupled hydrochemical process, desorption of the Cu from competition made the model prediction inaccurate. However, the parameter estimation could be improved by incorporating the experimentally determined mass transfer rate, ωexp from batch kinetics. Based on the calibrated model, the fraction of instantaneous retardation, βexp of Pb decreased from 0.41 in the single system to 0.30 in the binary system, indicating the shift from equilibrium to nonequilibrium state, where which of Cu increased from 0.39 to 0.94, representing the shift towards equilibrium. The modified results were also compared with five-step sequential extraction data, confirming that the shift of particular metal fractions from the competition triggered the nonequilibrium transport., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The uptake of Cd(2+) and Pb(2+) ions by a soybean hull (SH) biosorbent in single and binary systems has been investigated. Sorption tests regarding SH in natura and chemically treated were carried out testing a suitable value range of solution pH, sorption temperature and shaking velocity. Sorption capacity is improved at pH 4, 30 °C temperature and 100 rpm. When a strong base is applied, a related-to-untreated SH increasing of 20% in the sorption capacity of Pb(2+) ions was observed, but with poor results for Cd(2+) uptake. Additionally, a relatively strong decreasing in both sorption capacities of Pb(2+) and Cd(2+) ions was evidenced for all acidic treatments. Regarding untreated SH, kinetic sorption data of both metals were well-interpreted by a pseudo second-order model and a rate-limiting step on the basis of an intra-particle diffusion model was suggested to occur. An inhibitory effect of Pb(2+) diffusion over Cd(2+) one was observed, limiting to reach the obtained maximum sorption capacity in single system. Maximum adsorption capacities of 0.49 and 0.67mequivg(-1) for Cd(2+) and Pb(2+), respectively, were predicted by the Langmuir isotherm model that reproduced well the equilibrium sorption data for single systems. The inhibitory effect of one metal over the other one was verified in equilibrium sorption data for binary systems interpreted on the basis of a modified extended Langmuir isotherm model, predicting changes in metal affinity onto the SH surface. Finally, SH is an alternative biosorbent with a great potential for the wastewater treatment containing cadmium and lead ions., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Abstract The scavenging properties of MnO 2 are largely attributed to sorption on layer vacancy sites. However, co-occurrence of Mn(II, III) with MnO 2 can change mineral reactivity by modifying its Mn(III) content or number of free vacancy sites. These processes are critical in biogenic MnO 2 because nascent precipitates are in contact with aqueous Mn(II) and redox processes involving the biomass can modify the Mn(III) content of the oxide. Here we studied the mechanism of Zn(II) and Pb(II) sorption by the biogenic MnO 2 precipitated by Pseudomonas putida GB-1. Sorption isotherms on biogenic MnO 2 at pH 5.2 ± 0.3 showed considerably higher loadings for Pb(II) (0.49 mol Pb mol−1 Mn) than for Zn(II) (0.12 mol Zn mol−1 Mn). For loadings above 0.1 mol mol−1 Mn, Zn(II) and Pb(II) sorption was concomitant, albeit to different extents, with Mn(II) accumulation in solution. Wet chemical measurements and analysis of Zn K–edge and Pb L 3 -edge EXAFS spectra showed that the difference in metal loadings on the oxide and extent of Mn(II) release to solution originates from the ability of the cations to displace interlayer Mn(III), which then undergoes disproportionation and accumulates as Mn(II) in solution. In addition, the formation of nanoscale precipitates rich in Pb-P-Cl in the biomass matrix, as shown by energy dispersive X-ray analysis, leads to greater accumulation of Pb than Zn on the biomass. Our findings show how the reactivity of biogenic MnO 2 towards co-occurring trace or contaminant metals in natural systems depends directly on the mineral Mn(III) content and competitive sorption processes. Highlights • Metal sorption by biogenic MnO 2 was studied using EXAFS spectroscopy and STEM-EDX imaging. • Zn partitions to biomass and MnO 2 at all loadings at pH 5. • Pb can access four times as many reactive sites compared to Zn. • Pb but not Zn can dislodge Mn(III) adsorbed on vacancy sites. • Initial Mn(III) content and competitive sorption control contaminant uptake by biogenic MnO 2. [ABSTRACT FROM AUTHOR]

Poly(methyl methacrylate)-grafted montmorillonite (PMMAgMMT) clay and sodium-exchanged montmorillonite (NaMMT) clay were prepared through in situ graft polymerisation and used to remove Cd2+ and Pb2+ from synthetic wastewater. The modification of adsorbent materials was confirmed by fourier transform infra-red spectroscopy (FTIR), thermogravimetric analysis (TGA) and X-ray powder diffraction (XRD) techniques. BET surface area measurements showed NaMMT had a higher surface area than PMMAgMMT. Batch experiments were used to assess the simultaneous uptake of Cd2+ and Pb2+ from a synthetic binary solution. Pb2+ was preferentially sorbed, exhibiting greater affinity for the sorbents compared to Cd2+ as shown by its relatively higher uptake onto the sorbents than Cd2+. The maximum sorption capacities for NaMMT and PMMAgMMT were 18.73 and 19.27 mg/ g for Cd2+, and 30.03 and 34.25 mg/g for Pb2+, respectively. The sorption data obeyed the Langmuir model and the pseudo-second order kinetic model with R2 of at least 0.9800 for both models. The sorbents could also be regenerated up to three cycles without a significant loss in the sorption capacity. FTIR measurements showed the presence of metal-oxygen bonds after sorption, confirming the occurrence of adsorption as one of the heavy metal removal processes. The work demonstrated the potential of using low-cost nanoscale composite material for the removal of Cd2+ and Pb2+ from aqueous solution. [ABSTRACT FROM AUTHOR]

To assess the competitive sorption and desorption of cadmium (Cd) and lead (Pb), batch equilibrium experiments were performed using single- and binary-metal solutions in surface samples of three paddy soils from eastern China. Sorption isotherms were well fitted with one-metal and competitive Langmuir equation for single- and binary-metal system, respectively. The distribution coefficient ( K) values were K (Pb) > K (Pb) > K (Cd) > K (Cd), indicating that Pb was stronger sorbed by these soils than Cd in binary metal system. Soils with high pH and clay content had the greatest sorption capacity as estimated by the maximum sorption parameter ( Q). The co-existence of both metals reduces their tendency of sorption, whereas Cd sorption was affected to a greater extent than that of Pb. The Langmuir binding strength parameter ( b) in binary sorption system was greater than that in single sorption system for all soils ( b < b), indicating that competition for sorption sites promote the retention of both metals into more specific sorption sites. Sorption of Cd and Pb decreased soil pH by 1.61 U for YRS, 1.39 U for PCS, and 0.91 U for SLS. The decreases of pH in binary metal system were greater than in single-metal system for three soils. Cadmium and Pb desorption increased with increasing Cd and Pb sorption saturation for all soils; however, Cd desorption ratio in binary metal system ( d*) was much greater than Pb ( d*), indicating that under the competitive sorption conditions, the sorbed Cd was more readily desorbed from the soils than the sorbed Pb. [ABSTRACT FROM AUTHOR]

Competitive biosorption of Pb2+, Cu2+ and Zn2+ on valonia tannin resin (VTR) present in binary and ternary mixture were compared with the single metal solution. The effects of the presence of one metal ion on the biosorption of the other metal ion were investigated in terms of equilibrium isotherm and biosorption yield. Experimental results indicated that the uptake capacity and biosorption yield of one metal ion were reduced by the presence of the other metal ion. The extent of adsorption capacity of the binary and ternary metal ions tested on VTR was low (18–80%) as compared to single metal ions. Comparisons between biosorption of Pb2+, Cu2+ and Zn2+ ions by the biomass of VTR in the binary and ternary solution could lead to the conclusion that biosorption of Pb2+ ions was preferential to that of Cu2+ and Zn2+ ions. VTR removed the target metal ions in the selectivity order of Pb2+ >Cu2+ >Zn2+. The biosorption equilibrium data for the single metal solutions fitted the Langmuir model well. Results show that the pseudo-second-order equation provides the best correlation for the biosorption process in the single-ion system. [Copyright &y& Elsevier]

Abstract: The aim of this work is to compare the simultaneous sorption of copper and lead ions from a binary aqueous solution in the presence and in the absence of ultrasound. The experiments under sonication were carried out by 20-kHz apparatus. Results indicated that the removal of copper and lead ions from a binary aqueous solution was greater in the presence of ultrasound than in control method. The removal of these ions was examined by varying experimental conditions such as the amount of sorbent, contact time, and temperature. In addition, the competitive sorption of ions was considered with different concentrations of each ion under the constant total concentration. The Langmuir isotherm model fits adequately the experimental data. In point of kinetics, the second-order kinetic model describes the sorption process for both ions. It was found that more than 90% of the lead and 60% of the copper ions was removed in less than 2min from the solution under sonication. The thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were determined for the sorption of Cu2+ and Pb2+ from the temperature dependence of the sorption process. [Copyright &y& Elsevier]

Abstract: Immobilized Microcystis aeruginosa in a flow-through sorption column was evaluated for the potential to remove Pb2+, Cd2+ and Hg2+ from aqueous solutions. M. aeruginosa showed high affinity for the three heavy metals with removal efficiency of 90% for Cd2+ and Hg2+, and 80% for Pb2+ at saturation conditions. Competitive sorption experiments conducted in paired and ternary systems indicated that Pb2+ was sequestered preferentially over Cd2+ and Hg2+. The presence of Cd2+ interfered only slightly with the uptake of Hg2+, as Pb2+ and Hg2+ did with Cd2+. In contrast, Hg2+ sorption was affected by Pb2+ to a great extent. Desorption with 1M HCl was completed within 25min with high efficiency and effectiveness for the three metals. The results of this study indicate that M. aeruginosa is to be a potential biosorbent material except when Hg2+ and Pb2+ are in the same contaminated solution. [Copyright &y& Elsevier]

The bioavailability and ultimate fate of heavy metals in the environment are controlled by chemical sorption. To assess competitive sorption of Pb and Cd, batch equilibrium experiments (generating sorption isotherms) and kinetics sorption studies were performed using single and binary metal solutions in surface samples of four soils from central Spain. For comparisons between soils, as well as, single and binary metal solutions, soil chemical processes were characterized using the Langmuir equation, ionic strength, and an empirical power function for kinetic sorption. In addition, soil pH and clay mineralogy were used to explain observed sorption processes. Sorption isotherms were well described by the Langmuir equation and the sorption kinetics were well described by an empirical power function within the reaction times in this study. Soils with higher pH and clay content (characterized by having smectite) had the greatest sorption capacity as estimated by the maximum sorption parameter (Q) of the Langmuir equation. All soils exhibited greater sorption capacity for Pb than Cd and the presence of both metals reduced the tendency for either to be sorbed although Cd sorption was affected to a greater extent than that of Pb. The Langmuir binding strength parameter (k) was always greater for Pb than for Cd. However, these k values tended to increase as a result of the simultaneous presence of both metals that may indicate competition for sorption sites promoting the retention of both metals on more specific sorption sites. The kinetic experiments showed that Pb sorption is initially faster than Cd sorption from both single and binary solutions although the simultaneous presence of both metals affected the sorption of Cd at short times while only a minor effect was observed on Pb. The estimated exponents of the kinetic function were in all cases smaller for Pb than for Cd, likely due to diffusion processes into micropores or interlayer space of the clay minerals which occurs more readily for Cd than Pb. Finally, the overall sorption processes of Pb and Cd in the smectitic soil with the highest sorption capacity of the studied soils are slower than in the rest of the soils with a clay mineralogy dominated by kaolinite and illite, exhibiting these soils similar sorption rates. These results demonstrate a significant interaction between Pb and Cd sorption when both metals are present that depends on important soil properties such as the clay mineralogy. [Copyright &y& Elsevier]