[Passivation of Simulated Pb-and Cd-Contaminated Soil by Applying Combined Treatment of Phosphate, Humic Acid, and Fly Ash].

In this study, three kinds of amendments including superphosphate, humic acid, and fly ash and their complex combination were adopted to passivate the artificially simulated Pb-and Cd-containing soils. The passivation efficiency evaluation was performed via the CaCl2 and triethylenetriaminepentaacetic acid (DTPA) extraction method as well as a BCR morphological classification experiment. The microstructures and structures of the soil were explored further via X-ray diffraction (XRD) and scanning electron microscopy with X-ray energy dispersive spectroscopy (SEM-EDS) to elaborate the passivation mechanism. The results demonstrated that all passivation processes, excluding single humic acid addition, could reduce the CaCl2 and DTPA extraction contents of Pb and Cd in soils, where the optimal efficiency could be achieved by the sequential addition of superphosphate and humic acid, followed by fly ash. There was a weakly positive correlation between soil pH and CaCl2/DTPA extraction content of Pb, a negative correlation between soil pH and CaCl2/DTPA extraction content of Cd, and a significantly negative correlation between available phosphorous content and CaCl2/DTPA extraction contents of Pb and Cd, suggesting the crucial role of available phosphorous contents to control the activities of Pb and Cd. In the presence of phosphate, humic acid, and fly ash, the Pb and Cd could convert from active weak acid extraction to low-activity residual speciation, resulting in effectively reducing Pb and Cd transferability. Throughout the XRD and SEM-EDS analyses, it was found that ion exchange was the predominant mechanism in heavy metal passivation by single superphosphate, wherein the heavy metals were transformed into an insoluble Ca-containing phosphate mixture. The dissolving/precipitation or surface adsorption could be concluded as the main mechanism in the combination of the three passivation agents that converted heavy metals to lead phosphate precipitate[(Pb3(PO4)2] or mixed heavy metal mineral[PbFe3(SO4)(PO4)(OH)6], so as to obtain superior heavy metal passivation achievement.

[Mixture Leaching Remediation Technology of Arsenic Contaminated Soil].

Soil contamination of arsenic pollution has become a severely environmental issue, while soil leaching is an efficient method for remediation of arsenic-contaminated soil. In this study, batch tests were primarily conducted to select optimal mixture leaching combination. Firstly, five conventional reagents were selected and combined with each other. Secondly, the fractions were analyzed before and after the tests. Finally, to explore the feasibility of mixed leaching, three soils with different arsenic pollution levels were used to compare the leaching effect. Comparing with one-step washing, the two-step sequential washing with different reagents increased the arsenic removal efficiency. These results showed that the mixture of 4 h 0.5 mol · L⁻¹ NaOH + 4 h 0.1 mol · L⁻¹ EDTA was found to be practicable, which could enhance the removal rate of arsenic from 66.67% to 91.83%, and the concentration of arsenic in soil was decreased from 186 mg · kg⁻¹ to 15.2 mg · kg⁻¹. Furthermore, the results indicated that the distribution of fractions of arsenic in soil changed apparently after mixture leaching. Leaching process could significantly reduce the available contents of arsenic in soil. Moreover, the mixture of 0.5 mol · L⁻¹ NaOH + 0.1 mol L⁻¹ EDTA could well decrease the arsenic concentration in aluminum-type soils, while the mixture of 0.5 mol · L⁻¹ OX + 0.5 mol · L⁻¹ NaOH could well decrease the arsenic concentration in iron-type soils.

[Preparation of Visible-light-induced g-C3N4/Bi2S3 Photocatalysts for the Efficient Degradation of Methyl Orange].

Visible light responsive heterojunctions of graphitic carbon nitride (g-C3N4) and Bi2S3 were successfully designed and constructed by a simple solvothermal process. The as-prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and UV-vis diffuse reflectance spectroscopy (DRS). Under visible light irradiation, the as-prepared g-C3N4/Bi2S3 photocatalysts exhibited highly enhanced photochemical efficiency in the degradation of methyl orange (MO) compared with pure g-C3N4 and Bi2S3. On the basis of the calculated energy bands, the excellent enhancement was attributed to the efficient separation of photoinduced electron-hole pairs. In addition, a detailed degradation pathway of MO degradation by g-C3N4/Bi2S3 composites was proposed to further elucidate the inner photodegradation mechanism. This research may provide a cost-effective and easy-scaling up approach to develop visible-light-driven photocatalysts, which could be applied in wastewater treatment.

[Stabilization Treatment of Pb and Zn in Contaminated Soils and Mechanism Studies].

In the present work, the combined application of potassium dihydrogen phosphate, quick lime and potassium chloride was used to immobilize the Pb and Zn in contaminated soils. The efficiency of the process was evaluated through leaching tests and Tessier sequential extraction procedure. The mechanism of stabilization was analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM) to reveal the mechanism of stabilization. The results showed that the stabilizing efficiency of Pb contaminated soils was above 80% and the leaching concentrations of Pb, Zn were far below the threshold when the ratio of exogenous P and soil (mol · mol⁻¹) was 2:1-4: 1, the dosing ratio of CaO was 0.1%-0.5% ( mass fraction) and the dosage of potassium chloride was 0.02-0. 04 mol. Meanwhile, Pb and Zn in soil were transformed from the exchangeable fraction into residual fraction, which implied that the migration of Pb, Zn in soil could be confined by the stabilization treatment. XRD and SEM analysis revealed that Ca-P-Pb precipitation, lead orthophosphate [PbHP04, Pb3 (PO4)2], pyromorphite (Pb-PO4-Cl/OH) and mixed heavy metal deposits (Fe-PO4- Ca-Pb-Zn-OH) could be formed after solidification/stabilization in which Pb and Zn could be wrapped up to form a solidified composition and to prevent leaching.