Soil quality of simulated landfill exposure to plastics in context of heavy metal analysis

Spatiotemporal distribution characteristics of physicochemical properties of waste plastics with different landfill age and depth

Plastics are widely used for their excellent properties, and the primary disposal method is sanitary landfilling. Waste plastics, persisting in landfills for long periods, change their surface physicochemical properties. However, research on the physicochemical changes of plastics after landfilling is scarce. This study analyzes the physicochemical characteristics of discarded plastics in landfills, focusing on depths (2-8 meters) and ages (0-30 years). The spatiotemporal distribution of waste plastics was studied using the 3D-Smoothe model. The results revealed that polypropylene (PP) and polyethylene (PE) were the predominant constituents of landfilled plastics. The carbonyl index (CI) and hydroxyl index (HI) accelerated with landfill age but increased and then decreased with landfill depth. Furthermore, the hydrophilicity of waste plastics increases with the landfill age, which is realized as 2 m > 5 m < 8 m in depth. The 3D model analysis indicates that PP displays a wavy downward trend in its spatiotemporal distribution, whereas PE exhibits a vortex-like downward trend. The toughness and strength of waste plastics rapidly decline in the early stages of landfilling and then stabilize. However, variations are noted at a depth of 5 m. The influence of landfill age on the mechanical properties of waste plastics is more significant than that of landfill depth by 3D model analysis. As the age and depth of landfills increase, there is a corresponding rise in the number of surface cracks and defects, a rise in surface roughness, and an increase in the abundance of surface elements. This study provides a scientific basis for understanding the environmental risks of landfilled waste plastics.

Eco-friendly strategy for preparation of high-purity silica from high-silica IOTs using S-HGMS coupling with ultrasound-assisted fluorine-free acid leaching technology

Iron ore tailings (IOTs), a typical hazardous solid waste, seriously threaten human health and the ecological environment. However, the abundance of quartz, particularly in high-silica IOTs, renders them useful. Yet, state-of-the-art technologies have rarely reported the preparation of high-purity silica from high-silicon IOTs. Thus, this study proposed an eco-friendly technology for producing high-purity silica from high-silica IOTs through the coupling of superconducting high gradient magnetic separation (S-HGMS) preconcentration with leaching followed by the use of ultrasound-assisted fluorine-free acid solution. Following an analysis of the separation index and chemical composition, the optimum conditions for the quartz preconcentration were determined as a magnetic flow ratio of 0.068 T s/m, a slurry flow velocity of 500 mL/min, and a pulp concentration of 40 g/L. Consequently, the SiO₂ grade increased from 69.32% in the raw sample to 93.12% in quartz concentrate following the application of S-HGMS, with the recovery reaching 45.24%. X-ray diffraction, vibrating sample magnetometer, and scanning electron microscope analyses indicated that quartz was effectively preconcentrated from the tailings by S-HGMS. Subsequently, employing the "ultrasound-assisted fluorine-free acid leaching process," impurity elements were removed and high-purity silica was produced. Under optimal leaching conditions, the SiO₂ purity of silica sand increased to 97.42%. Following a three-stage acid leaching process with 4 mol/LHCl +2 mol/LH₂C₂O₄, the removal efficiency of Al, Ca, Fe, and Mg exceeded 97% for all cases, and the SiO₂ purity in high-purity silica reached 99.93%. Thus, this study proposes a new strategy for the preparation of high-purity quartz from IOTs, which facilitated the effective realization of the high-value utility of the tailings. Furthermore, it provides a theoretical basis for the industrial application of IOTs, which is of great scientific significance and practical application value.

Soil Risk Assessment in the Surrounding Area of Hulene-B Waste Dump, Maputo (Mozambique)

Soil contamination in areas close to unplanned dumpsites represents an increasing risk to the ecosystems and human health. This study aimed to evaluate soil quality in the area surrounding the Hulene-B waste dump, Maputo, Mozambique, and to estimate potential ecological and human health risks. A total of 71 surface soil samples were collected in the surrounding area of the dump, along with 10 samples in areas considered not impacted by the dump. Chemical and mineralogical analyses were performed using XRF and XRD. Quartz was the most abundant mineral phase, followed by feldspars, carbonates, clay minerals, and Fe oxides/hydroxides. Results showed a significant contribution to ecological degradation by PTE enrichment, ranked as Zn >> Cu > Cr > Zr > Pb > Ni > Mn. Carcinogenic risk for both children and adults was significant due to Pb soil content. Soil sample concentrations of Cr, Cu, Mn, Ni, Pb, Zn, and Zr, posing a risk especially in children, suggested the need for continuous monitoring, as well as the definition and implementation of mitigation measures.