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Cyanide tailings are the major hazardous wastes generated in the production process of the gold industry, which not only contain highly toxic cyanide, but also contain heavy metals with recycling value and other substances suitable for building materials or filling. These tailings are in urgent need of purification treatment and safe utilization. In this study, the impacts of treatment methods, types and combinations of reagents on decyanation effect were researched. Gold in cyanide tailings was recovered by flotation, and flotation tailings were used for filling after identifying the properties of solid waste. Results are as follows: (1) INCO method and 5 reagents (sodium sulfite, sodium persulfate, copper sulfate, ferrous sulfate and zinc sulfate) were selected for synergistic decyanation treatment, and cyanide concents in slurry and leaching solution were decreased to the minimum. (2) The gold recovery rate of the tailings through flotation was increased by 27.8% than without detoxification. (3) Flotation tailings were identified as general industrial solid wastes by leaching toxicity and toxic substance content analysis. (4) As filling aggregate, under the conditions of slurry concentration of 63% and cement-sand ratio of 1:6, the strength filling body of flotation tailings reached 1.32 Mpa after 28 days of maintenance. (5) This process and combined reagents were applied to engineering. The cyanide content in the leaching solution and the flotation recovery rate of gold were kept below 0.2 mg/L and above 60% respectively, and the strength of the filling body was stable to meet the requirements of underground filling. [Display omitted] • Different decyanation methods and reagents of cyanide tailings were researched. • Five reagents were screened for decyanation and their interaction mechanism was expounded. • Gold was extracted by flotation after detoxification and the gold recovery rate was much higher than that of non-detoxification. • Flotation tailings were identified as general industrial solid wastes for filling, and filling parameters were explored. • Efficient detoxification and full resource utilization of cyanide tailings were realized and applied to industry. [ABSTRACT FROM AUTHOR]

Oxalic acid is the most abundant low molecular weight organic acid (LMWOA) in many environments and offers enormous prospects for treating Cr(VI) contamination. In this study, laboratory batch experiments were conducted to estimate the roles of oxalic acid in Cr(VI) removal by Penicillium oxalicum SL2. Oxalic acid changed the initial pH and provided a suitable condition for the growth of strain SL2 when the penicillium was applied to bioremediation of Cr(VI) contamination in alkaline soil. Gompertz model analysis indicated that initial pH affected the lag time of the growth curve of strain SL2. Scanning electron microscopy and scanning transmission X-ray microscopy analysis showed strain SL2 sufficiently contacted with contaminated soil and reduced Cr(VI) to Cr(III) in the hyphae. The results suggested that oxalic acid could enhance the bioremediation efficiency of strain SL2 though improving chromium bioleaching from the contaminated soil and strengthening Cr(VI) removal in the leaching solution. This study provided oxalic acid as a green reagent for stimulating Cr(VI) removal by strain SL2 and would expand knowledge on the roles of LMWOA in Cr(VI) bioremediation. [Display omitted] • Gompertz model could simulate the growth curve of strain SL2 under initial pH5 to pH9. • Growth of strain SL2 had a strong correlation with Cr(VI) removal. • Oxalic acid improved chromium bioleaching by strain SL2 from contaminated soil. • Oxalic acid enhanced Cr(VI) removal by strain SL2 in the leaching solution. [ABSTRACT FROM AUTHOR]

The toxic chemical element cadmium (Cd) in paddy fields triggered increasing problems of growth inhibition and food security in rice consistently. In this study, we found Metarhizium robertsii , which is widely used as a bioinsecticide and biofertilizer in agriculture and recently found to be resistant to Cd, developed intraradical and extraradical symbiotic hyphae in rice seedlings, and successfully colonized in the rice rhizosphere soil to more than 103 CFUs g−1 soil at harvesting. M. robertsii colonization significantly reduced Cd accumulations in both hydroponically cultured seedlings and the matured rice cultured in Cd contaminated potting soil (2 ppm). Notably, Cd accumulation reduction of the roots, stems, leaves, husks and grains of the matured rice induced by the fungus were 44.3%, 32.1%, 35.3%, 31.9% and 24.7%, respectively. It was caused by the M. robertsii -induced suppression of Cd intake transporter gene osNramp5 in the rice roots, and the chemical stabilizing of Cd to the residual fraction in the rhizosphere soil. In addition, the colonization of M. robertsii significantly promoted the growth characters and the photosynthesis of the rice plants. This is achieved by the increase of endogenous hormone levels of indole-3-acetic, gibberellin A 3 and brassinolide induced by M. robertsii. Furthermore, the fungus enhanced the antioxidative capacities via increasing enzyme activities of catalase, peroxidase and the production of glutathione, ascorbic acid, proline in the rice plants. Our work provides theoretical basis for expanding the use of M. robertsii as in situ Cd accumulation reduction and detoxification agents for rice in contaminated paddy fields. [Display omitted] • M. robertsii colonized well in the rice roots and the rhizosphere soil. • M. robertsii reduced Cd accumulation and promoted plant growth of rice. • Rice osNramp5 was suppressed and soil Cd ions were stabilized by the fungus. • Endogenous phytohormones IAA, GA 3 and BL were elevated by the fungus. • M. robertsii stimulated antioxidative capacities of rice. [ABSTRACT FROM AUTHOR]

Microbial remediation is preferred as a clean and cost-effective method for restoring environments polluted by organics. But the biodegradation rates of hydrophobic organic contaminants (HOCs) are usually extremely restricted by their low bioavailability, especially in soil. Here, a physical method (mechanical mixing) and a chemical method (randomly methylated- β -cyclodextrins, RAMEB) were adopted to improve the bioavailability and biodegradation of polychlorinated biphenyls (PCBs) of an aged soil. The bioavailability of tri-CBs was increased by adding RAMEB in soil/slurry or assisting mechanical mixing in slurry, but these methods had no effects on the bioavailability of tetra-CBs and high chlorinated PCBs (Cl > 4). The degradation rate of tri-CBs could be obviously enhanced by adding RAMEB in soil or assisting mechanical mixing in slurry. The highest removal amount of tri-CBs reached 43.8% in 100 d with a first-order decay kinetics constant of 0.0059 d −1 . But the removal of tetra-CBs and high chlorinated PCBs (Cl > 4) were not significant in all mesocosms, possibly due to the lack or weakness of the native degrading microflora. Based on the analysis of the richness and diversity of bacterial communities, the characteristics of the heatmap and the variation of bphC copy numbers in the soil/slurry mesocosms, it could be inferred that there was no obvious corresponding relationship between the variation of the bacterial communities and the physical/chemical measures. [ABSTRACT FROM AUTHOR]

Using manure-derived-biochar as an alternative phosphorus (P) source has bright future prospects to improve soil P status. A 98-day microcosm incubation experiment was set up for two soils which were amended with manure biochar at proportions of 0, 0.5% and 1.5%. Swine manure samples were air-dried and manure biochar was prepared by pyrolysis at 400 °C for 4 h. As determined by P-31 nuclear magnetic resonance ( 31 P NMR) spectroscopy, manure biochar mainly increased the contents and fractions of orthophosphate and pyrophosphate in two soils, while decreased those of monoesters ( P < 0.05). At the end of incubation, 1.5% of manure biochar raised soil pH by 0.5 and 0.6 units, cation exchange capacity by 16.9% and 32.2%, and soil total P by 82.1% and 81.1% for silt loam and clay loam soils, respectively, as compared with those soils without biochar. Simultaneously, 1.5% of manure biochar decreased acid phosphomonoesterase activities by 18.6% and 34.0% for clay loam and silt loam, respectively; while it increased alkaline phosphomonoesterase activities by 28.5% and 95.1% for clay loam and silt loam, respectively. The enhancement of soil P availability after manure biochar addition was firstly due to the orthophosphate and pyrophosphate as the major P species in manure biochar which directly increased contents of soil inorganic P, and also attributed to the decomposition of some organic P like monoesters by enhanced alkaline phosphomonoesterase activities from manure biochar addition. [ABSTRACT FROM AUTHOR]

Lead (Pb) and arsenic (As) exist in soil with different ionic forms, and it is difficult to immobilize simultaneously Pb and As in soil. The objective of this study is to determine the effects of water management including flooding (FL), alternate wetting and drying (AWD) and dry farming (DF) combined with addition of phosphate (P) on the accumulation of Pb and As in rice. Our results showed that Pb accumulated in root during vegetative stage, and most of As in root was transported to the above ground parts during the reproductive stage. Pb was evenly distributed in grains, and As was mostly accumulated in bran and aleurone layer. Water management had a reverse effect on the accumulation of Pb and As in rice. However, the effects of P on arid soil environment and Pb, As accumulation in rice were stronger than that in flooded soil. Application of P under AWD treatment could maintain a similar quantity of Fe plaque with flooding, decrease the availability of Pb in rhizosphere soil, reduce Pb and As accumulation in root, and result in the reduction of Pb and As accumulation in grains by 86% and 66% respectively. Besides, our study also found that flooding or AWD during vegetative stage facilitated the formation of iron plaque. In conclusion, AWD combined with P application could maintain a relatively lower concentrations of Pb and As in grains. [Display omitted] • Lead accumulated in root primarily during the vegetative stage. • Arsenic in root was transported to aboveground parts during the reproductive stage. • Flooding or AWD during the vegetative stage in soil would help to form iron plaque. • AWD combined with application of P could decrease simultaneously lead and arsenic in grains. • Lead was distributed evenly in grains, and arsenic was mostly accumulated in bran and aleurone layer. [ABSTRACT FROM AUTHOR]

Bioremediation of Cr(VI) contamination using microorganisms is a promising method for reducing its environmental risks. The objective of this study was to clarify Cr(VI) removal by Penicillium oxalicum SL2 in terms of indirect Cr(VI) reduction by metabolites, interaction sites, and form transformation of chromium. Strain SL2 could sequentially remove Cr(VI) in the bioreactor. Oxalic acid produced by the fungus contributed to Cr(VI) reduction. Scanning transmissiony X-ray microscop (STXM) analysis suggested strain SL2 could partly reduce Cr(VI) to Cr(III) in the cell. Amine, carboxyl, and phosphate groups were related to Cr(VI) removal. Chromium K-edge X-ray absorption near edge structure (XANES) analysis implied Cr(III)-Cys potentially acted as an intermediate for the formation of chromium oxalate complexes during the process of treatment. This study would support the application of strain SL2 in Cr(VI) bioremediation and expand knowledge on the interaction of chromium with fungus., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)