The production rate of industrial and agricultural waste is increasing due to population growth. Soil is the most important receiver of industrial and agricultural waste. Contaminants such as heavy metals in various waste after reception by the soil, immediately become part of the cycle that has different impacts on the environment. Geopolymer, as a chemical stabilizer has the potential to stabilize heavy metals in the soil. In this research, several geopolymers for the stabilization of heavy metals in soil were synthesized. Silicon dioxide (SiO2) and aluminosilicate (Al2SiO4) must be used to produce the geopolymers. Rice husk ash was used as the SiO2 source. Also, Iranian zeolite and sepiolite, and red clay soil were utilized as the source of Al2SiO4. The synthesized geopolymers were investigated for the adsorption of nickel and cadmium. Also, batch and column studies of using geopolymers for the chemical stabilization of heavy metals in soil were conducted. The results revealed a high adsorption capacity of the geopolymers. The zeolite, sepiolite, and red clay geopolymer-soil samples adsorbed 100% of the heavy metals (i.e., Ni and Cd) at a concentration of 100 ppm. The zeolite geopolymer adsorbent adsorbed 57% and 96% of Ni and Cd at a concentration of 1000 ppm, respectively. In general, it was concluded that the use of geopolymer compounds in soils with high heavy metal adsorption capacity could be an efficient approach to prevent groundwater resource pollution.

Microplastic pollution is emerging as a global environmental issue, and its potential for transferring hazardous chemicals to aquatic organisms is gaining attention. Studies have investigated the transfer of chemicals, mainly sorbed chemicals, through ingestion of microplastics by organisms, but limited information is available regarding chemical additives and uptake via the aqueous route through plastic leaching. In this study, we compared two bioaccumulation pathways of the additive hexabromocyclododecane (HBCD) by exposing mussels (Mytilus galloprovincialis) to two different sizes of expanded polystyrene (EPS): inedible size (4.2–5.5 mm) for leachate uptake and edible size (20–770 μm) for particle ingestion and leachate uptake. Over 10 days, the HBCD concentration increased significantly in mussels in the EPS exposure groups, indicating that EPS microplastic acts as a source of HBCD to mussels. The concentration and isomeric profiles of HBCD in mussels show that uptake through the aqueous phase is a more significant pathway for bioaccumulation of HBCD from EPS to mussels than particle ingestion. HBCD levels measured in EPS, leachate and exposed mussels from this study are environmentally relevant concentration. The fate and effects of chemical additives leached from plastic debris in ecosystem requires further investigation, as it may affect numerous environments and organisms through the aqueous phase.

Intentional or incidental thermal changes inevitably occur during the lifecycle of plastics. High temperatures accelerate the aging of plastics and promote their fragmentation to microplastics (MPs). However, there is little information available on the release of MPs after fires. In this study, an atomic force microscope combined with nanoscale infrared analysis was used to demonstrate the physicochemical properties of polypropylene (PP) plastics under simulated fire scenarios. Results showed that the chemical composition and relative stiffness of heat-treated plastic surfaces changed, significantly enhancing the generation of MPs under external forces; over (2.1 ± 0.2) × 10⁵ items/kg abundance of MPs released from PP which were burned at 250 °C in air and trampled by a person. The leaching of antimony (Sb) from MPs in different solutions first increased and then decreased with increasing temperature, reaching a maximum at 250 °C. Higher concentrations of humic acid (10 vs 1 mg/L) caused a greater release of Sb. Furthermore, the tap water leachates of PP burned at 250 °C had the greatest effect on the growth and photosynthetic activity of Microcystis aeruginosa. Our results suggest fires as a potential source of MPs and calls for increased focus on burning plastics in future research.

Size and magnetic separation of incineration bottom ash (IBA) are common for ferrous metals recovery, however, their influences on the mineral phase and the element redistribution, and subsequently the induced variation of metal leaching potential herein remain limited understanding. The lack of research in this field may misunderstand IBA performances, cause confused results for comparison among various studies, and potentially lead to biased conclusions. We herein quantitatively investigate the effects of size and magnetic separation on the IBA based on element distribution, leaching behavior, morphology, and mineralogy with statistical analysis. For preparation, sieving was performed with the original IBA (to obtain 7 size-fractions termed as OR1-7, respectively), followed by magnetic separation of each, to further yield magnetic fractions (MF1-7) to discriminate nonmagnetic fractions (NF1-7). In this study, we show that size and magnetic separation may pose significant yet different impacts on different fractions, which would affect their leaching potential concerning their respective downstream applications.

Biochar amendments could enhance retention of nutrients such as ammonium (NH4+), nitrate (NO3-), and phosphate (PO43-) in soils. However, the situation for sulphate (SO42-), which is an indispensable nutrient element for crop growth, is unclear. In this paper, the effects of biochar derived from rape (Brassica campesstris L.) straw at 600°C on the sorption and leaching of SO42- in light sierozem (Calcids) was studied in columns, where biochar amendment rate, column soil height, solution pH value and initial sulphate concentration were selected as factors. It is shown that the transport of sulphate was a significant non-equilibrium process and the sorption and leaching curves (SLCs) of sulphate were asymmetrical. The breakthrough time would be increased by increasing biochar amendment and soil column height, and by decreasing solution pH value and initial sulphate concentration. The SLCs of bromide trace were fitted to determine dispersion coefficient (D) using equilibrium convection dispersion equation (CDEeq). The non-equilibrium (two-site) model (CDEnon-eq) with the results from CDEeq was used to simulate the transport processes of sulphate in the soil column, with good fitness, using software CXTFIT 2.1 fitting. The results could supply an implication for biochar application in loess areas.

Although magnesium phosphate cement (MPC) is conventionally deemed effective in heavy metal-contaminated soil remediation, the variations of its mechanical and leaching characteristics under the action of dry-wet cycles remain unclear as yet. This paper primarily addressed the effect of dry-wet cycles and fly ash on MPC-solidified zinc-contaminated soil via a disparate group of experiments. In this study, solidified cylindrical samples were subjected to different drying-wetting cycles ranging in times from 0 to 10 with varying content of fly ash. We then measured the mass loss, the unconfined compressive strength, and the Zn²⁺ leaching concentration of the leachate for the samples undergoing specified cycles. In addition, X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests were conducted to explore the mechanism of MPC-solidified zinc-contaminated soil with fly ash. The results indicate that the Zn²⁺ concentration in the leaching solution increases rapidly with the number of cycles for 0–3 cycles and then tends to flatten out. Moreover, the unconfined compressive strength of the samples without fly ash decreases with an increasing dry-wet cycles. For the samples with various fly ash contents, in contrast, their unconfined compressive strength experiences an initial rise and a subsequent decline owing to the development of dry-wet cycles. With the purpose of facilitating practical applications, the appropriate fly ash content (approximately 20%) was estimated in terms of the enhanced dry-wet cycles durability of the solidified soil and unconfined compressive strength, according to the limited experimental measurements undertaken (for the Zn²⁺ concentration of 0.5). The role of dry-wet cycles in the physical and leaching properties of MPC-solidified soil may be of major practical significance.