Arsenic and heavy-metal-contaminated environments are a major concern due to their negative impacts on exposed people and ecosystems. In this study, sludge from an iron-ore processing area was used as an adsorbent to remove As, Mn, Zn, Cd, and Pb from aqueous solutions. The adsorption capacity of target adsorbates was investigated in batch experiments of both single- and mixed-metal solutions. The batch studies show that the maximum Langmuir adsorption capacities of the heavy metals onto the adsorbent occurred in the order Pb > As > Cd > Zn > Mn, and ranged from 0.710 mg/g to 1.113 mg/g in the single-metal solutions and from 0.370 mg/g to 1.059 mg/g in the mixed-metal solutions. The results of the kinetic experiments are consistent with pseudo-first-order and pseudo-second-order models, with a slightly better fit to the latter. Adsorption performances indicate that iron-ore sludge can simultaneously adsorb multiple metal ions and is a promising adsorbent for the removal of toxic pollutants from water.

This study was conducted to assess the removal of arsenic (As) and heavy metals from mining wastewater by the combination of adsorption, using modified iron-ore drainage sludge, and horizontal-subsurface-flow constructed wetland with common reed (Phragmites australis). The pilot-scale experiment with a constant flow rate of 5 m³/day was operated for four months using real wastewater from a Pb–Zn mine in northern Vietnam. Atomic absorption spectroscopy was used for elemental analysis in wastewater and plant. X-ray diffraction (XRD), surface charge measurements (by a particle charge detector (PCD)), Fourier-transform infrared (FTIR), and surface area Brunauer–Emmet–Teller (BET) measurements were performed to determine the characteristics of the adsorbent. The results showed that the average removals of As, Mn, Cd, Zn, and Pb by the combined system with limestone substrate during four months were 80.3%, 96.9%, 79.6%, 52.9%, and 38.7%, respectively. The use of another constructed wetland substrate, laterite, demonstrated better removal efficiency of As than limestone. The concentrations of As and heavy metals in the effluent were lower than the limits established by the QCVN 40:2011/BTNMT for industrial wastewater, which indicated the feasibility of combining adsorption and constructed wetland for the treatment of mining wastewater.

This study was conducted to determine the soil contamination and the accumulation of arsenic (As) and heavy metals including chromium (Cr), copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) in 15 native and cultivated plant species in a Pb recycling area of Dong Mai village, Hung Yen Province, Vietnam. The analysis of 32 soil samples collected from seven different sites in the study area revealed that the contents of Al, Fe, As, Cr, Cu, Zn, Cd, and Pb in the soils ranged from 6200–32,600, 11,300–55,500, 5.4–26.8, 24.9–290, 66.0–252, 143–455, 0.71–1.67, and 370–47,400 mg/kg, respectively. The contents of As, Cr, Cu, Zn, Cd, and Pb in rice grains and the shoots of 15 plant species ranged from 0.14–10.2, 1.00–10.2, 5.19–23.8, 34.7–165, 0.06–0.99, and 2.83–1160 mg/kg-dry weight (DW), respectively. Hymenachne acutigluma (Steud.) Gilliland, a potential hyperaccumulator of Pb (1160 mg/kg-DW), is considered the best candidate for phytoremediation of Pb-contaminated soil. The cultivation of rice and vegetables, and the use of some native plants for food for humans, pigs, and cattle should be managed with consideration of the accumulation of Pb in their aboveground biomass.

Groundwater contamination by arsenic (As) is a serious issue in many countries, particularly in middle- and low-income nations. High concentrations of As in drinking water and groundwater cause serious health problems. Numerous technologies, such as ion exchange, oxidation, coagulation–flocculation, phytoremediation, membrane filtration, and adsorption, have been applied to remove As from the water environment. Among these technologies, adsorption is the preferred method in low- and middle-income countries due to its affordability, high efficiency, and ease of design, operation, and maintenance. Along with this technology, a variety of materials have been developed and investigated for their ability to remove As from water environments, though iron-based adsorbents have been reported to be the most effective. Thus, the aim of this paper is to briefly review the sources of As and the prevalence of As species in water bodies, as well as the currently available technologies for As removal. A detailed analysis of recent studies on iron-based adsorbents used to remove As from aqueous solutions in both laboratory conditions and field conditions is presented.

This study was conducted to assess the removal of heavy metals from solutions by the combination of modified iron mine drainage sludge (sorbent column) and surface and subsurface flow constructed wetlands using the common reed (Phragmites australis) during 30 days of experiment. The results of this study demonstrated that the average removal rates of Zn, Pb, Mn, and As by sorbent column were 59.0, 55.1, 38.7, and 42.4%, respectively. The decreasing trend of removal rates of metals by sorbent column was obtained during the experiment. The average removal rates of Zn, Pb, Mn, and As by sorbent column-surface constructed wetland were 78.9, 73.5, 91.2, and 80.5%, respectively; those by sorbent column-subsurface flow constructed wetland were 81.7, 81.1, 94.1, and 83.1% which reflected that subsurface flow constructed wetland showed higher removal rate than the surface system. Concentrations of heavy metals in the outlet water were lower than the Vietnamese standard limits regulated for industrial wastewater. The results indicate the feasibility of integration of iron mine drainage sludge and constructed wetlands for wastewater treatment.

Mangrove forests are important in providing habitats for complex communities of terrestrial and marine fauna. Moreover, they are recognized as highly productive ecosystems in providing nutrients to mangrove food webs or exporting them to nearby coastal waters. In the present study, stable isotopes of carbon and nitrogen were applied to examine the changes in the diets of benthic invertebrate communities following mangrove restoration. The isotope signature of invertebrate tissues varied among the forest ages and locations and ranged from 3.7 ± 1.0 to 13.9 ± 1.1‰ and −26.6 ± 0.5 to −15.0 ± 0.4‰ for δ¹⁵N and δ¹³C, respectively. The results showed that the food source assimilation of macro-invertebrates is slightly altered from a mixture of benthic microalgae and marine phytoplankton in the mudflat to a combination of benthic microalgae and sediment organic matter in the Sonneratia caseolaris and the Kandelia obovata forests. Therefore, the diets of macro-invertebrates varied following forest ages and the position of the forest in the intertidal zone. These insights from the present study are useful for the effective conservation and restoration of mangrove forests in Vietnam and worldwide.