Pre-concentration and separation of heavy metal ions by chemically modified waste paper gel

Iminodiacetic acid was immobilized on waste paper by chemical modification in order to develop a new type of adsorption gel for heavy metal ions. Adsorption behavior of the gel was investigated for a number of metal ions, specifically Cu(II), Pb(II), Fe(III), Ni(II), Cd(II), and Co(II) at acidic pH. From batch adsorption tests, the order of selectivity was found to be as follows: Cu(II)  Fe(III) > Pb(II) > Ni(II)  Co(II) > Cd(II). Column tests were carried out for pairs of metal ions to understand the separation and pre-concentration behavior of the gel. It was found that mutual separation of Ni(II) from Co(II) and that of Pb(II) from Cd(II) can be achieved at pH 3. Similarly, selective separation of Cu(II) from Cu(II)–Fe(III) and Cu(II)–Pb(II) mixtures at pH 1.5 and 2, respectively, was observed by using this new adsorption gel. In all cases, almost complete recovery of the adsorbed metal was confirmed by elution tests with HCl.     

Sequential removal of heavy metals ions and organic pollutants using an algal-bacterial consortium

The residual algal-bacterial biomass from photosynthetically supported, organic pollutant biodegradation processes, in enclosed photobioreactors, was tested for its ability to accumulate Cu(II), Ni(II), Cd(II), and Zn(II). Salicylate was chosen as a model contaminant. The algal-bacterial biomass combined the high adsorption capacity of microalgae with the low cost of the residual biomass, which makes it an attractive biosorbent for environmental applications. Cu(II) was preferentially taken-up from the medium when the metals were present both separately and in combination. There was no observed competition for adsorption sites, which suggested that Cu(II), Ni(II), Cd(II), and Zn(II) bind to different sites and that active Ni(II), Cd(II) and Zn(II) binding groups were present at very low concentrations. Therefore, special focus was given to Cu(II) biosorption. Cu(II) biosorption by the algal-bacterial biomass was characterized by an initial fast cell surface adsorption followed by a slower metabolically driven uptake. pH, Cu(II), and algal-bacterial concentration significantly affected the biosorption capacity for Cu(II). Maximum Cu(II) adsorption capacities of 8.5+/-0.4 mg g-1 were achieved at an initial Cu(II) concentration of 20 mg l-1 and at pH 5 for the tested algal-bacterial biomass. These are consistent with values reported for other microbial sorbents under similar conditions. The desorption of Cu(II) from saturated biomass was feasible by elution with a 0.0125 M HCl solution. Simultaneous Cu(II) and salicylate removal in a continuous stirred tank photobioreactor was not feasible due to the high toxicity of Cu(II) towards the microbial culture. The introduction of an adsorption column, packed with the algal-bacterial biomass, prior to the photobioreactor reduced Cu(II) concentration, thereby allowing the subsequent salicylate biodegradation in the photobioreactor.     

Effect of biochars on adsorption of Cu(II), Pb(II) and Cd(II) by three variable charge soils from southern China

The purpose of this study is to compare the relative contribution of different mechanisms to the enhanced adsorption of Cu(II), Pb(II) and Cd(II) by variable charge soils due to incorporation of biochars derived from crop straws. The biochars were prepared from the straws of canola and peanut using an oxygen-limited pyrolysis method at 350 °C. The effect of biochars on adsorption and desorption of Cu(II), Pb(II) and Cd(II) by and from three variable charge soils from southern China was investigated with batch experiments. Based on the desorption of pre-adsorbed heavy metals, the electrostatic and non-electrostatic adsorptions were separated. EDTA was used to replace the heavy metals complexed with biochars and to evaluate the complexing ability of the biochars with the metals. The incorporation of biochars increased the adsorption of Cu(II), Pb(II) and Cd(II) by the soil; peanut straw char induced a greater increase in the adsorption of the three metals. The increased percentage of Cd(II) adsorption induced by biochars was much greater than that for the adsorption of Cu(II) and Pb(II). Cu(II) adsorption on three variable charge soils was enhanced by the two biochars mainly through a non-electrostatic mechanism, while both electrostatic and non-electrostatic mechanisms contributed to the enhanced adsorption of Pb(II) and Cd(II) due to the biochars. Peanut straw char had a greater specific adsorption capacity than canola straw char and thus induced more non-electrostatic adsorption of Cu(II), Pb(II) and Cd(II) by the soils than did the canola straw char. The complexing ability of the biochars with Cu(II) and Pb(II) was much stronger than that with Cd(II) and thus induced more specific adsorption of Cu(II) and Pb(II) by the soils than that of Cd(II). Biochars increased heavy metal adsorption by the variable charge soils through electrostatic and non-electrostatic mechanisms, and the relative contribution of the two mechanisms varied with metals and biochars.     

Toxic effect of metal cation binary mixtures to the seaweed Gracilaria domingensis (Gracilariales,Rhodophyta)

The macroalga Gracilaria domingensis is an important resource for the food, pharmaceutical, cosmetic, and biotechnology industries. G. domingensis is at a part of the food web foundation, providing nutrients and microelements to upper levels. As seaweed storage metals in the vacuoles, they are considered the main vectors to magnify these toxic elements. This work describes the evaluation of the toxicity of binary mixtures of available metal cations based on the growth rates of G. domingensis over a 48-h exposure. The interactive effects of each binary mixture were determined using a toxic unit (TU) concept that was the sum of the relative contribution of each toxicant and calculated using the ratio between the toxicant concentration and its endpoint. Mixtures of Cd(II)/Cu(II) and Zn(II)/Ca(II) demonstrated to be additive; Cu(II)/Zn(II), Cu(II)/Mg(II), Cu(II)/Ca(II), Zn(II)/Mg(II), and Ca(II)/Mg(II) mixtures were synergistic, and all interactions studied with Cd(II) were antagonistic. Hypotheses that explain the toxicity of binary mixtures at the molecular level are also suggested. These results represent the first effort to characterize the combined effect of available metal cations, based on the TU concept on seaweed in a total controlled medium. The results presented here are invaluable to the understanding of seaweed metal cation toxicity in the marine environment, the mechanism of toxicity action and how the tolerance of the organism.     

Patterns of metals and arsenic poisoning in Vibrio fischeri bacteria

The Microtox bioassay was used to establish dose-response curves for some toxic elements in aqueous solutions, namely, Zn(II), Pb(II), Cu(II), Hg(II), Ag(I), Co(II), Cd(II), Cr(VI), As(V) and As(III). Experiments were carried out at either pH 6.0 or pH 7.0 to indicate that pH may influence the measured toxicity of some elements due to pH-related changes of their chemical speciation. EC20 values, which represent a measurable threshold of toxicity, were determined for each element and were found to rank as Pb(II)>Ag(I)>Hg(II) approximately Cu(II)>Zn(II)>As(V)>Cd(II) approximately Co(II)>As(III)>Cr(VI). These values were compared to the limit concentrations allowed in industrial wastewater according to the official regulations in Catalonia (Spain). It appears that the Microtox test is sensitive enough for detecting some of the tested elements with respect to official regulations of Catalonia (Spain) dealing with pollution control, with the exception of cadmium, mercury, arsenate, arsenite and chromate.     

Biosorption characteristics of copper (II), chromium (III), nickel (II), and lead (II) from aqueous solutions by Chara sp. and Cladophora sp.

The aim of this research was to expose individual removals of copper, chromium, nickel, and lead from aqueous solutions via biosorption using nonliving algae species, Chara sp. and Cladophora sp. Optimum pH values for biosorption of copper (II), chromium (III), nickel (II), and lead (II) from aqueous solutions were determined to be 6, 7, 7, and 3 for Cladophora sp. and 5, 3, 5, and 4 for Chara sp. respectively. Maximum adsorption capacities of Chara sp. [10.54 for chromium (III) and 61.72 for lead (II)] and Cladophora sp. [6.59 for chromium (III) and 16.75 and 23.25 for lead (II)] for chromium (III) and lead (II) are similar. On the other hand, copper (II) and nickel (II) biosorption capacity of Cladophora sp. [14.28 for copper (II) and 16.75 for nickel (II)] is greater than Chara sp. [6.506 for copper (II) and 11.76 for nickel (II)]. Significantly high correlation coefficients indicated for the Langmuir adsorption isotherm models can be used to describe the equilibrium behavior of copper, chromium, nickel, and lead adsorption onto Cladophora sp. and Chara sp.     

Biomass-derived materials in the remediation of heavy-metal contaminated water: removal of Cadmium(II) and copper(II) from aqueous solutions

Manganese-coated activated carbon (MCAC) and activated carbon were used in batch experiments for the removal of cadmium(II) and copper(II). Results showed that uptake of Cd(II) and Cu(II) was unaffected by increases in pH (3.0 to 8.5) or concentration (1 to 20 mg/L). Increased ionic strength (from 0.001 to 1 M NaNO3), however, significantly affected the uptake of Cd(II); adsorption of Cu(II) was not affected. Freundlich adsorption isotherm results indicated that MCAC possessed higher sorption capacity than activated carbon. Second-order rate constants were found to be 0.0386 for activated carbon and 0.0633 g/mg x min for MCAC for Cd(II) and 0.0774 for AC and 0.1223 g/mg x min for MCAC for Cu(II). Column experiments showed that maximum sorption capacity of MCAC was 39.48 mg/g for Cu(II) and 12.21 mg/g for Cd(II).     

Selective removal of the heavy metal ions from waters and industrial wastewaters by ion-exchange method

By ion exchange undesirable ions are replaced by others which don't contribute to contamination of the environment. The method is technologically simple and enables efficient removal of even traces of impurities from solutions. Examples of selective removal of heavy metal ions by ion-exchange are presented. They include removal of Pb(II), Hg(II), Cd(II), Ni(II), V(IV,V), Cr(III,VI), Cu(II) and Zn(II) from water and industrial wastewaters by means various modern types of ion exchangers.     

Effect of arsenate on adsorption of Cd(II) by two variable charge soils

The effect of arsenate on Cd(II) adsorption in two variable charge soils and the desorption of Cd(II) pre-adsorbed in the presence of arsenate were studied. The batch type experiments showed, the presence of arsenate led to increase in Cd(II) adsorption and the desorption of pre-adsorbed Cd(II). Further it was observed that the extent of adsorption and desorption of Cd(II) was greatly influenced by the initial concentrations of arsenate and Cd(II), the solution pH, and the nature of the soils. In general the increase in arsenate concentration and pH favored the uptake of Cd(II). Moreover, the arsenate concentration influenced more in Hyper-Rhodic Ferralsol than Rhodic Ferralsol at least for the Cd(II) adsorption/desorption. This may be due to the content of Fe/Al oxides in these soils. The larger the content of Fe/Al oxides, the more the adsorption of arsenate by the soil, hence greater the uptake of Cd(II). It can be assumed that the enhanced Cd(II) adsorption was mainly due to the increase in net negative surface charge of the soil induced by the adsorption of arsenate, because the presence of arsenate led to the decrease in zeta potential of these soil suspensions. The increase of electrostatically adsorbed Cd(II) was responsible for the increase in the desorption of Cd(II) pre-adsorbed in the presence of arsenate.     

Removal of bisphenol A and some heavy metal ions by polydivinylbenzene magnetic latex particles

In this study, magnetic polydivinylbenzene latex particles MP_DVB with a core-shell structure were tested for the removal of bisphenol A (BPA), copper Cu(II), lead Pb(II), and zinc Zn(II) from aqueous solutions by a batch-adsorption technique. The effect of different parameters, such as initial concentration of pollutant, contact time, adsorbent dose, and initial pH solution on the adsorption of the different adsorbates considered was investigated. The adsorption of BPA, Cu(II), Pb(II), and Zn(II) was found to be fast, and the equilibrium was achieved within 30 min. The pH 5–5.5 was found to be the most suitable pH for metal removal. The presence of electrolytes and their increasing concentration reduced the metal adsorption capacity of the adsorbent. Whereas, the optimal pH for BPA adsorption was found 7, both hydrogen bonds and π–π interaction were thought responsible for the adsorption of BPA on MP_DVB. The adsorption kinetics of BPA, Cu(II), Pb(II), and Zn(II) were found to follow a pseudo-second-order kinetic model. Equilibrium data for BPA, Cu(II), Pb(II), and Zn(II) adsorption were fitted well by the Langmuir isotherm model. Furthermore, the desorption and regeneration studies have proven that MP_DVB can be employed repeatedly without impacting its adsorption capacity.     

The influence of iron and sulfur mineral fractions on carbon tetrachloride transformation in model anaerobic soils and sediments

The objective of this research was to identify the dissolved species or solid phase mineral fraction(s) best correlated with rates of carbon tetrachloride (CT) reductive transformation in systems modeling sulfate-reducing and iron oxide-rich soils and sediments. We used sulfide (S(-II))-treated goethite as our model system, but also studied Fe(II) and S(-II)-treated goethite, Fe(II)-treated goethite, pure FeS, and Fe(II)-treated FeS in order to isolate and evaluate the influence of different mineral fractions on reaction rates. Initial rates of CT transformation were measured for different pH values and concentrations of added Fe(II), as well as different aging times and conditions. The following dissolved species and iron and sulfur mineral fractions were quantified and compared with CT transformation rates: aqueous Fe(2+) and S(-II), surface associated Fe(II) (including weakly and strongly bound Fe(II)), FeS(s), and Cr(II) reducible solid phase S. Over the pH range of 6-10, CT transformation rates were correlated with surface associated Fe(II), while at pH 8, rates were correlated with weakly bound Fe(II). Aging of S(-II)-treated goethite led to oxidation of surface sulfur and a change in the concentration of weakly bound Fe(II), but did not change the relationship between initial rates and weakly bound Fe(II). The results of this research suggest that surface associated Fe(II) and weakly bound Fe(II) could serve as indicators of the potential for abiotic CT dechlorination in natural soils under sulfate-reducing conditions.     

Accumulation and fraction distribution of Ni(II) in activated sludge treating Ni-laden wastewater

The accumulation and fraction distribution of Ni(II) in sludge was determined, and their effect on the performance of sequencing batch reactor (SBR) systems was evaluated at laboratory scale. The results showed that the removal efficiencies of substrates decreased significantly with increasing feeding concentration of Ni(II) into SBRs. The concentration of Ni(II) fed into the SBRs was significantly positively correlated with the Ni(II) contents accumulated in the sludge, while it was negatively correlated with the biomass in the SBRs. The accumulated Ni(II) in the sludge was distributed mainly in the available fraction, accounting for 75.8–90.0 % of the total Ni(II) content. The accumulated content of Ni(II) in each sludge fraction could be predicted satisfactorily by the feeding Ni(II) concentrations in the solutions. As compared with the total contents and other chemical fractions, Ni(II) in the oxidizable fraction in sludge exhibited more important inhibition effects on sludge microorganisms in the SBRs.     

Comparison of hematite/Fe(II) systems with cement/Fe(II) systems in reductively dechlorinating trichloroethylene

Reactive reductants of cement/Fe(II) systems in dechlorinating chlorinated hydrocarbons are unknown. This study initially evaluated reactivities of potential reactive agents of cement/Fe(II) systems such as hematite (alpha-Fe(2)O(3)), goethite (alpha-FeOOH), lepidocrocite (gamma-FeOOH), akaganeite (beta-FeOOH), ettringite (Ca(6)Al(2)(SO(4))(3)(OH)(12)), Friedel's salt (Ca(4)Al(2)Cl(2)(OH)(12)), and hydrocalumite (Ca(2)Al(OH)(6)(OH).3H(2)O) in reductively dechlorinating trichloroethylene (TCE) in the presence of Fe(II). It was found that a hematite/Fe(II) system shows TCE degradation characteristics similar to those of cement/Fe(II) systems in terms of degradation kinetics, Fe(II) dose dependence, and final products distribution. It was therefore suspected that Fe(III)-containing phases of cement hydrates in cement/Fe(II) systems behaved similarly to the hematite. CaO, which was initially introduced as a pH buffer, was observed to participate in or catalyze the formation of reactive reductants in the hematite/Fe(II) system, because its addition enhanced the reactivities of hematite/Fe(II) systems. From the SEM (scanning electron microscope) and XRD (X-ray diffraction) analyses that were carried out on the solids from hematite/Fe(II) suspensions, it was discovered that a sulfate green rust with a hexagonal-plate structure was probably a reactive reductant for TCE. However, SEM analyses conducted on a cement/Fe(II) system showed that hexagonal-plate crystals, which were presumed to be sulfate green rusts, were much less abundant in the cement/Fe(II) than in the hematite/Fe(II) systems. It was not possible to identify any crystalline minerals in the cement/Fe(II) system by using XRD analysis, probably because of the complexity of the cement hydrates. These observations suggest that major reactive reductants of cement/Fe(II) systems may differ from those of hematite/Fe(II) systems.     

Industrial wastewater pre-treatment for heavy metal reduction by employing a sorbent-assisted ultrafiltration system

This work examined the adoption of a sorbent-assisted ultrafiltration (UF) system for the reduction of Pb(II), Cu(II), Zn(II) and Ni(II) from industrial wastewater. In such a system metals were removed via several processes which included precipitation through the formation of hydroxides, formation of precipitates/complexes among the metal ions and the wastewater compounds, adsorption of metals onto minerals (bentonite, zeolite, vermiculite) and retention of insoluble metal species by the UF membranes. At pH = 6 the metal removal sequence obtained by the UF system was Pb(II) > Cu(II) > Zn(II) > Ni(II) in mg g⁻¹ with significant amount of lead and copper being removed due to chemical precipitation and formation of precipitates/complexes with wastewater compounds. At this pH, zinc and nickel adsorption onto minerals was significant, particularly when bentonite and vermiculite were employed as adsorbents. Metal adsorption onto zeolite and bentonite followed the sequence Zn(II) > Ni(II) > Cu(II) > Pb(II), while for vermiculite the sequence was Ni(II) > Zn(II) > Cu(II) > Pb(II) in mg g⁻¹. The low amount of Pb(II) and Cu(II) adsorbed by minerals was attributed to the low available lead and copper concentration. At pH = 9 the adoption of UF could effectively reduce heavy metals to very low levels. The same was observed at pH = 8, provided that minerals were added. The prevailing metal removal process was the formation of precipitates/complexes with wastewater compounds.     

Estimated validity and reliability of on-board diagnostics for older vehicles: comparison with remote sensing observations

Based on requirements under the Clean Air Act Amendments of 1990, most state vehicle inspection and maintenance (I/M) programs have, since 2002, replaced the tailpipe emission testing with the on-board diagnostic (OBD) II testing for 1996 model and newer vehicles. This test relies on the OBD II system to give the pass or fail result, depending on certain conditions that might cause the vehicle to emit pollution 1.5 times higher than the regulated standard. The OBD II system is a computer and sensors installed in the vehicle to monitor the emission control units and signal if there is any malfunction. As a vehicle ages, its engine, pollution control units, and OBD II system deteriorate. Because the OBD II system's durability directly influences the test outcome, it is important to examine the fleetwide trend in the OBD II test results in comparison with an alternative measure of identifying high emitting vehicles. This study investigates whether the validity and reliability of the OBD II test is related to the age of the OBD II system installed in the fleet. Using Atlanta's I/M testing records and remote sensing device (RSD) data collected during 2002-2005, this research establishes the convergent validity and interobserver reliability criteria for the OBD II test based on on-road emissions measured by RSDs. The study results show that older vehicles exhibit significantly lower RSD-OBD II outcome agreement than newer vehicles. This suggests that the validity and reliability of the OBD II test may decline in the older vehicle fleets. Explanations and possible confounding factors for these findings are discussed.     

Dechlorination of trichloroethylene by a steel converter slag amended with Fe(II)

This study aims to assess the feasibility of using slag, byproduct from iron and steel making industries, as a new reactive material for dechlorination reactions and to investigate dechlorination chemistries of the systems containing the slag and Fe(II). Initially, screening experiments were conducted to evaluate various systems containing slags with or without Fe(II). A combination of the steel converter slag and Fe(II) showed a potential to be developed as a reactive material to treat chlorinated organics. Further kinetic studies with the steel converter slag/Fe(II) systems revealed that the dechlorination capacity of the slag/Fe(II) system is comparable to that of zero-valent iron and generally higher than the cement/Fe(II) system. The slag/Fe(II) system can substantially dechlorinate trichloroethylene (TCE) in the neutral pH region, although the dechlorination rate was greatest in the pH region between 12 and 13. TCE reductions in the slag/Fe(II) system were observed to occur through reductive beta-elimination pathways that produce primarily acetylene and no chlorinated intermediates such as vinyl chloride. These results demonstrate that the steel converter slag with Fe(II) has sound characteristics for an alternative reactive medium for subsurface remediation.     

Detection of copper(II) and zinc(II) binding to humic acids from pig slurry and amended soils by fluorescence spectroscopy

The effect of the consecutive annual additions of pig slurry at rates of 0 (control), 90 and 150 m3 ha(-1) yr(-1) after a 7-year period on the Cu(II) and Zn(II) binding behavior of soil HAs was investigated in a field experiment. A fluorescence titration method and a single site model were used for determining metal ion complexing capacities and stability constants of metal ion complexes of HAs isolated from pig slurry and unamended and amended soils. With respect to control soil HA, pig-slurry HA featured much smaller Cu(II) and Zn(II) binding capacities and stability constants. Pig-slurry application to soil decreased Cu(II) and Zn(II) complexing capacities and binding affinities of soil HA. These effects increased with increasing the rate per year of PS application to soil, and are expected to have a large impact on bioavailability, mobilization, and transport of Cu(II) and Zn(II) ions in pig slurry-amended soils.     

Estimated Validity and Reliability of On-Board Diagnostics for Older Vehicles: Comparison with Remote Sensing Observations

ABSTRACT

Based on requirements under the Clean Air Act Amendments of 1990, most state vehicle inspection and maintenance (I/M) programs have, since 2002, replaced the tailpipe emission testing with the on-board diagnostic (OBD) II testing for 1996 model and newer vehicles. This test relies on the OBD II system to give the pass or fail result, depending on certain conditions that might cause the vehicle to emit pollution 1.5 times higher than the regulated standard. The OBD II system is a computer and sensors installed in the vehicle to monitor the emission control units and signal if there is any malfunction. As a vehicle ages, its engine, pollution control units, and OBD II system deteriorate. Because the OBD II system's durability directly influences the test outcome, it is important to examine the fleetwide trend in the OBD II test results in comparison with an alternative measure of identifying high emitting vehicles. This study investigates whether the validity and reliability of the OBD II test is related to the age of the OBD II system installed in the fleet. Using Atlanta's I/M testing records and remote sensing device (RSD) data collected during 2002–2005, this research establishes the convergent validity and interobserver reliability criteria for the OBD II test based on on-road emissions measured by RSDs. The study results show that older vehicles exhibit significantly lower RSD–OBD II outcome agreement than newer vehicles. This suggests that the validity and reliability of the OBD II test may decline in the older vehicle fleets. Explanations and possible confounding factors for these findings are discussed.

IMPLICATIONS This research demonstrates the potential worsening validity and reliability of the on-board diagnostic (OBD) II test in old vehicles. If the main source of low validity and reliability comes from the OBD II system malfunction, we expect this malfunctioning OBD II fleet will continue to grow in the future. If unchecked, the deterioration of OBD II system may impair the effort of the inspection and maintenance (I/M) program to identify high-emitting vehicles and the ultimate objective of reducing the air pollution from automobiles. This result is especially important in a regulatory context where technological and emissions standards dominate environmental policy and yet little attention is paid to the possible degradation of environmental monitors themselves.     

Removal of Ni(II) and Cu(II) ions using native and acid treated Ni-hyperaccumulator plant Alyssum discolor from Turkish serpentine soil

Alyssum discolor biomass was collected from serpentine soil and was used for removal of metal ions. The plant species grown on serpentine soils are known to be rich with metals ions and thus have more capability for accumulating heavy metals. Native and acid-treated biomass of A. discolor (A. discolor) were utilized for the removal of Ni(II) and Cu(II) ions from aqueous solutions. The effects of contact time, initial concentration, and pH on the biosorption of Ni(II) and Cu(II) ions were investigated. Biosorption equilibrium was established in about 60 min. The surface properties of the biomass preparations were varied with pH, and the maximum amounts of Ni(II) and Cu(II) ions on both A. discolor biomass preparations were adsorbed at pH 5.0. The maximum biosorption capacities of the native, and acid-treated biomass preparations for Ni(II) were 13.1 and 34.7 mg g⁻¹ and for Cu(II) 6.15 and 17.8 mg g⁻¹ dry biomass, respectively. The biosorption of Ni(II) and Cu(II) ions from single and binary component systems can be successfully described by Langmuir and Freundlich isotherms. When the heavy metal ions were in competition, the amounts of biosorbed metal ions on the acid treated plant biomass were found to be 0.542 mmol g⁻¹ for Ni(II) and 0.162 mmol g⁻¹ for Cu(II), the A. discolor biomass was significantly selective for Ni(II) ions. The information gained from these studies was expected to indicate whether the native, and acid-treated forms can have the potential to be used for the removal and recovery of Ni(II) ions from wastewaters.     

Adsorption of Pb(II) on variable charge soils amended with rice-straw derived biochar

Two Ultisols and one Oxisol from tropical regions of southern China were incubated with rice straw biochar to investigate the effect of biochar on their surface charge and Pb(II) adsorption using batch methods. The incorporation of biochar induced a remarkable increase in soil cation exchange capacity after 30 d of incubation. The incorporation of biochar significantly increased the adsorption of Pb(II) by these variable charge soils; the enhancement of adsorption of Pb(II) by these soils increased with the addition level of biochar. Adsorption of Pb(II) involved both electrostatic and non-electrostatic mechanisms; however, biochar mainly increased Pb(II) adsorption through the non-electrostatic mechanism via the formation of surface complexes between Pb²⁺ and functional groups on biochar. There was greater enhancement of biochar on the non-electrostatic adsorption of Pb(II) by the variable charge soils at relatively low pH. Therefore, the incorporation of biochar decreased the activity and availability of Pb(II) to plants through increased non-electrostatic adsorption of Pb(II) by acidic variable charge soils.