Preparation and adsorption characteristics for heavy metals of active silicon adsorbent from leaching residue of lead-zinc tailings.

To comprehensively reuse the leaching residue obtained from lead-zinc tailings, an active silicon adsorbent (ASA) was prepared from leaching residue and studied as an adsorbent for copper(II), lead(II), zinc(II), and cadmium(II) in this paper. The ASA was prepared by roasting the leaching residue with either a Na2CO3/residue ratio of 0.6:1 at 700 °C for 1 h or a CaCO3/residue ratio of 0.8:1 at 800 °C for 1 h. Under these conditions, the available SiO2 content of the ASA was more than 20%. The adsorption behaviors of the metal ions onto the ASA were investigated and the Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models were used to analyze the adsorption isotherm. The result showed that the maximum adsorption capacities of copper(II), lead(II), cadmium(II), and zinc(II) calculated by the Langmuir model were 3.40, 2.83, 0.66, and 0.62 mmol g-1, respectively. The FT-IR spectra of the ASA and the mean free adsorption energies indicated that ion exchange was the mechanism of copper(II), lead(II), and cadmium(II) adsorption and that chemical reaction was the mechanism of zinc(II) adsorption. These results provide a method for reusing the leaching residue obtained from lead-zinc tailings and show that the ASA is an effective adsorbent for heavy metal pollution remediation.

Contaminant characteristics and environmental risk assessment of heavy metals in the paddy soils from lead (Pb)-zinc (Zn) mining areas in Guangdong Province, South China.

In November 2016, the total metal concentrations in nine representative locations in lead (Pb)-zinc (Zn) mining areas, located in Guangdong Province, South China, were determined experimentally by flame atomic absorption spectrometer. The results indicated that the paddy soils were heavily contaminated with Cd (20.25 mg kg-1), Pb (1093.03 mg kg-1), and Zn (867.0 mg kg-1), exceeding their corresponding soil quality standard values and background values. According to the results, the mean enrichment factor levels of the studied metals decreased in the following order: Cd > Zn > Pb > Cu > Ni > Mn > Cr. Among these metals, Cd, Pb, and Zn were predominantly influenced by widespread anthropogenic activities. The highest concentrations of the studied metal pollutants were distributed in the areas surrounding the mining activity district. Multivariate statistical analysis indicated that the major contributing sources of the studied metals were metal ore mining, smelting, and processing activities. However, the composition of soil background was another potential source. Moreover, the assessment results of environment risks showed that the potential ecological risks, in decreasing order, were Cd > Pb > Zn > Cu > Ni > Cr > Mn. Additionally, the non-carcinogenic risk represented the trend of HI Pb > HI Mn > HI Zn > HI Cu , and the carcinogenic risk ranked as CR Cr > CR Cd > CR Ni . Among the environmental risk substances, Cd and Pb were the main contributors that pose ecological harm and health hazards through their serious pollution. Consequently, greater attention should be paid to this situation.

Efficient Determination of Specific Surface Area of Shale Samples Using a Tracer-Based Headspace Gas Chromatographic Technique.

This paper reports on a novel method for determining the specific surface area (SSA) of shale via headspace gas chromatography (HS-GC). The method is based on the water adsorption on the surface of shale sample after achieving phase equilibrium at an elevated temperature (i.e., heating at 125 °C for 48 h). A mathematical model shows that the SSA can be determined from the signal of the vapor water released during HS-GC analysis. The results obtained by this method correlated well (R2 = 0.992) with data obtained by the reference BET method. Because the phase equilibrium step for multiple samples can be conducted simultaneously, and because the phase re-equilibrium step is much faster in the HS-GC measurement, the present method is more efficient for batch sample testing.

Determination of Porosity in Shale by Double Headspace Extraction GC Analysis.

This paper reports on a novel method for the rapid determination of the shale porosity by double headspace extraction gas chromatography (DHE-GC). Ground core samples of shale were placed into headspace vials and DHE-GC measurements of released methane gas were performed at a given time interval. A linear correlation between shale porosity and the ratio of consecutive GC signals was established both theoretically and experimentally by comparing with the results from the standard helium pycnometry method. The results showed that (a) the porosity of ground core samples of shale can be measured within 30 min; (b) the new method is not significantly affected by particle size of the sample; (c) the uncertainties of measured porosities of nine shale samples by the present method range from 0.31 to 0.46 p.u.; and (d) the results obtained by the DHE-GC method are in a good agreement with those from the standard helium pycnometry method. In short, the new DHE-GC method is simple, rapid, and accurate, making it a valuable tool for shale gas-related research and applications.

Spatial distribution of heavy metal contamination in soils near a primitive e-waste recycling site.

The total concentrations of 12 heavy metals in surface soils (SS, 0-20 cm), middle soils (MS, 30-50 cm) and deep soils (DS, 60-80 cm) from an acid-leaching area, a deserted paddy field and a deserted area of Guiyu were measured. The results showed that the acid-leaching area was heavily contaminated with heavy metals, especially in SS. The mean concentrations of Ni, Cu, Zn, Cd, Sn, Sb and Pb in SS from the acid-leaching area were 278.4, 684.1, 572.8, 1.36, 3,472, 1,706 and 222.8 mg/kg, respectively. Heavy metal pollution in the deserted paddy field was mainly concentrated in SS and MS. The average values of Sb in SS and MS from the deserted paddy field were 16.3 and 20.2 mg/kg, respectively. However, heavy metal contamination of the deserted area was principally found in the DS. Extremely high concentrations of heavy metals were also observed at some special research sites, further confirming that the level of heavy metal pollution was very serious. The geoaccumulation index (Igeo) values revealed that the acid-leaching area was severely polluted with heavy metals in the order of Sb > Sn > Cu > Cd > Ni > Zn > Pb, while deserted paddy field was contaminated predominately by metals in the order of Sb > Sn > Cu. It was obvious that the concentrations of some uncommon contaminants, such as Sb and Sn, were higher than principal contaminants, such as Ni, Cu, Zn and Pb, suggesting that particular attention should be directed to Sn and Sb contamination in the future research of heavy metals in soils from e-waste-processing areas. Correlation analysis suggested that Li and Be in soils from the acid-leaching area and its surrounding environment might have originated from other industrial activities and from batteries, whereas Ni, Cu, Zn, Cd, Pb, Sn and Sb contamination was most likely caused by uncontrolled electronic waste (e-waste) processing. These results indicate the significant need for optimisation of e-waste-dismantling technologies and remediation of polluted soil environment.

Distribution of heavy metal pollution in sediments from an acid leaching site of e-waste.

The spatial distribution, bioavailability, potential risks and emission sources of 12 heavy metals in sediments from an acid leaching site of e-waste were investigated. The results showed that the sediments from the acid leaching site were significantly contaminated with Cu, Zn, Cd, Sn, Sb and Pb, especially in the middle sediments (30-50 cm), with average concentrations of 4820, 1260, 10.7, 2660, 5690 and 2570 mg/kg, respectively. Cu, Cd and Pb were mainly present in the non-residual fractions, suggesting that the sediments from the acid leaching site may exert considerable risks. Mn, Ni, Zn, Sn and Sb were predominantly associated with the residual fraction. Despite their low reactivity and bioavailability, uncommon pollutants, such as Sn and Sb, may exert environmental risks due to their extremely elevated total concentrations. All of these results indicate that there is an urgent need to control the sources of heavy metal emission and to remediate contaminated sediments. CAPTURE ABSTRACT: In addition to Ni, Cu, Zn, Cd and Pb, the sediments from an acid leaching site in Guiyu were heavily polluted with uncommon heavy metal pollutants, such as Sn and Sb.

Determination of maximal amount of minor gases adsorbed in a shale sample by headspace gas chromatography.

In this paper, we present a novel method for determining the maximal amount of ethane, a minor gas species, adsorbed in a shale sample. The method is based on the time-dependent release of ethane from shale samples measured by headspace gas chromatography (HS-GC). The study includes a mathematical model for fitting the experimental data, calculating the maximal amount gas adsorbed, and predicting results at other temperatures. The method is a more efficient alternative to the isothermal adsorption method that is in widespread use today.

A novel method for the determination of adsorption partition coefficients of minor gases in a shale sample by headspace gas chromatography.

A novel method has been developed for the determination of adsorption partition coefficient (Kd) of minor gases in shale. The method uses samples of two different sizes (masses) of the same material, from which the partition coefficient of the gas can be determined from two independent headspace gas chromatographic (HS-GC) measurements. The equilibrium for the model gas (ethane) was achieved in 5h at 120°C. The method also involves establishing an equation based on the Kd at higher equilibrium temperature, from which the Kd at lower temperature can be calculated. Although the HS-GC method requires some time and effort, it is simpler and quicker than the isothermal adsorption method that is in widespread use today. As a result, the method is simple and practical and can be a valuable tool for shale gas-related research and applications.

Advanced oxidation degradation of dichlorobenzene in water by the UV/H2O2 process.

Through UV/H2O2 photocatalytic advanced oxidation technique the performance, kinetics, pathway, and mechanism of ortho-dichlorobenzene (O-DCB) in water and the effect parameters of degradating reaction were studied systematically. The results showed that the reaction of photocatalytic degradation of O-DCB was fast and accorded well with the pseudo-first-order kinetics. The roles of some parameters, such as the pH, the initial concentrations of O-DCB, H2O2, and some anions in reaction solution, were examined in detail. It was found that weak acidic or neutral environment was favorable to the degradation reaction and some anions slowed down the photocatalytic degradation rate. Input amount of H2O2 possessed the best value under specified condition. The intermediates of O-DCB degradation were also tentatively identified 2,3-dichlorophenol, 3,4-dichlorophenol, formic acid, acetic acid, and oxalic acid mainly adopting GC/MS and ion chromatogram (IC) techniques. According to this, the pathway and mechanism of UV/H2O2 photocatalytic degradation of O-DCB were deduced and led.

Photochemical degradation performance of quinoline aqueous solution in the presence of hydrogen peroxide.

Photochemical degradation performance of quinoline aqueous solution in the presence of H2O2 was carried out, and some intermediates produced during quinoline degradation were also identified tentatively. The experimental results showed that the advanced oxidation of quinoline by UV/H2O2 process accorded well with the pseudo first order kinetics, and the dependence of concentrations of H2O2 and quinoline, and pH value on the photodegradation kinetics has been investigated in detail. It is found that the concentrations of hydrogen peroxide and quinoline have opposite effect on photodegradation kinetics. That means the photodegradation rate of quinoline increased significantly as the hydrogen peroxide concentration increasing, while the photodegradation rate decreased critically as the initial concentration of quinoline increasing. It also concluded that the photodegradation of quinoline by H2O2/UV process is more favorable under alkali solution than acid solution.