Yong Ke

Quantitative evaluation of environmental risks of flotation tailings from hydrothermal sulfidation–flotation process

Floatation tailings (FT) are the main by-products of the hydrothermal sulfidation–flotation process. FT (FT1 and FT2) were obtained by treating two different neutralization sludges (NS) (NS1 and NS2). This paper quantitatively evaluated the environmental risks of heavy metals (Zn, Cd, Cu, Pb, and As) in FT versus NS. The total concentration and leaching rates (R2) of heavy metals in FT were much lower than those in NS, demonstrating that the hydrothermal sulfidation–flotation process was able to effectively suppress the mobility and leachability of heavy metals. The BCR-three sequence leaching procedure of FT confirmed that all metals were transformed into more stable forms (residue and oxidizable forms) than were found that in NS. The potential ecological risk index indicated that the overall risks caused by heavy metals decreased significantly from 6627.59 and 7229.67 (very serious risk) in NS1 and NS2, respectively, to 80.26 and 76.27 (low risk) in FT1 and FT2, respectively. According to the risk assessment code, none of the heavy metals in FT posed significant risk to the natural environment except Zn (with low risk). In general, the risk of heavy metals in FT had been well controlled.

Hydrothermal sulfidation and floatation treatment of heavy-metal-containing sludge for recovery and stabilization

This study focuses on the application of hydrothermal sulfidation and floatation to treat the heavy-metal-containing sludge for recovery and stabilization. After the hydrothermal sulfidation, the sulfidation percentage of zinc and lead reach up to 85.0% and 75.4%, respectively. 33.3% of Zn, 58.9% of Pb and 68.8% of Cu can be recovered from the sludge by floatation. The lower recovery of ZnS attributes to its surface and structural characteristics. To compare these characteristics, three types of synthetic metal sulfide (ZnS, PbS and CuS) were prepared and examined with XRD, SEM and TEM. The poor floatability of the finely dispersed, round shape of ZnS can be improved by crystal modification in hydrothermal condition. With increasing the temperature and reaction time, the grain size of the ZnS increased from 7.95 nm to 44.28 nm and the recovery of Zn increased to from 33.3% to 72.8%. The TCLP results indicate that all the leached heavy metal concentrations of floatation tailings are under the allowable limit. No obvious increase of heavy metal concentration was observed in continuous leaching procedure. The presence of alkaline compounds after hydrothermal sulfidation might act as mineralogical scavengers of dissolved heavy metal released by sulfide oxidation to avoid the heavy metal pollution.

Health and ecological risk assessment of heavy metals pollution in an antimony mining region: a case study from South China.

In recent years, international research on the toxicity of the heavy metal, antimony, has gradually changed focus from early medical and pharmacological toxicology to environmental toxicology and ecotoxicology. However, little research has been conducted for sources identification and risk management of heavy metals pollution by long-term antimony mining activities. In this study, a large number of investigations were conducted on the temporal and spatial distribution of antimony and related heavy metal contaminants (lead, zinc, and arsenic), as well as on the exposure risks for the population for the Yuxi river basin in the Hunan province, China. The scope of the investigations included mine water, waste rock, tailings, agricultural soil, surface water, river sediments, and groundwater sources of drinking water. Health and ecological risks from exposure to heavy metal pollution were evaluated. The main pollution sources of heavy metals in the Yuxi River basin were analyzed. Remediation programs and risk management strategies for heavy metal pollution were consequently proposed. This article provides a scientific basis for the risk assessment and management of heavy metal pollution caused by antimony basin ore mining.

Fe-FeS2 adsorbent prepared with iron powder and pyrite by facile ball milling and its application for arsenic removal

Arsenic is one of the major pollutants and a worldwide concern because of its toxicity and chronic effects on human health. An adsorbent of Fe-FeS2 mixture for effective arsenic removal was successfully prepared by mechanical ball milling. The products before and after arsenic adsorption were characterized with scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The adsorbent shows high arsenic removal efficiency when molar ratio of iron to pyrite is 5:5. The experimental data of As(III) adsorption are fitted well with the Langmuir isotherm model with a maximal adsorption capacity of 101.123 mg/g. And As(V) data were described perfectly by the Freundlich model with a maximal adsorption capacity of 58.341 L/mg. As(III) is partial oxidized to As(V) during the adsorption process. High arsenic uptake capability and cost-effectiveness of waste make it potentially attractive for arsenic removal.

Utilization of red mud and Pb/Zn smelter waste for the synthesis of a red mud-based cementitious material

A new method in which Pb/Zn smelter waste containing arsenic and heavy metals (arsenic sludge), red mud and lime are utilized to prepare red mud-based cementitious material (RCM) is proposed in this study. XRD, SEM, FTIR and unconfined compressive strength (UCS) tests were employed to assess the physicochemical properties of RCM. In addition, ettringite and iron oxide-containing ettringite were used to study the hydration mechanism of RCM. The results show that the UCS of the RCM (red mud+arsenic sludge+lime) was higher than that of the binder (red mud+arsenic sludge). When the mass ratio of m (binder): m (lime) was 94:6 and then maintained 28days at ambient temperature, the UCS reached 12.05MPa. The red mud has potential cementitious characteristics, and the major source of those characteristics was the aluminium oxide. In the red mud-arsenic sludge-lime system, aluminium oxide was effectively activated by lime and gypsum to form complex hydration products. Some of the aluminium in ettringite was replaced by iron to form calcium sulfoferrite hydrate. The BCR and leaching toxicity results show that the leaching concentration was strongly dependent on the chemical speciation of arsenic and the hydration products. Therefore, the investigated red mud and arsenic sludge can be successfully utilized in cement composites to create a red mud-based cementitious material.

Aromatic organoarsenic compounds (AOCs) occurrence and remediation methods

Many researchers at home and abroad have made a body of researches and have gained great achievements on the environmental occurrence, fate, and toxicity of inorganic arsenic. But there is less research on the use of aromatic organoarsenic compounds (AOCs), which are common feed additives for livestock in the poultry industry. In this review, we outline the current state of knowledge acquired on the occurrence and remediation of AOCs, respectively. We also identify knowledge gaps and research needs, including the elucidation of the environmental fate of AOCs, metabolic pathway, the impact of metabolic modification on toxicity, and advanced analytical or repaired methods that allows for monitoring, identification or removal of the degradation products.

Hydrothermal Treatment of Arsenic Sulfide Residues from Arsenic-Bearing Acid Wastewater

Arsenic sulfide residue (ASR), a by-product from the treatment of arsenic-bearing acidic wastewater, is abundantly generated but not properly disposed of in China. The utilization of such high-content arsenic waste residue is limited by the market. The traditional methods of stabilization/solidification (S/S) by lime cement or iron salt have a large mass/volume addition, high dumping cost and secondary pollution risk. In this paper, hydrothermal technology was used to treat three kinds of ASRs obtained from different smelters to minimize waste. The leaching toxicity and chemical speciation of the generated products was also evaluated by TCLP and BCR analyses. It was found that the hydrothermal treatment could greatly reduce the volume and moisture content of the ASRs. TCLP tests showed that the leachability of arsenic and heavy metals significantly decreased after the treatment. According to the BCR analysis, most of the unstable As, Cd and Cr transformed into a residual fraction. Finally, XRD, SEM, Raman and XPS techniques were carried out to reveal the mechanism. As a result, hydrothermal treatment can efficiently achieve the dehydration, volume reduction and stabilization/solidification of ASRs.