In acidic medium, hazardous heavy metals of lead-zinc tailing (LZT) are easily leachable and mobilizable. Thus, the hazard, amount, form, and complexity of the leached heavy metals under acidic precipitation become a major environmental concern. This work investigates the gangue minerals, toxicity, speciation, leaching characteristics of heavy metals in LZT under simulated acid rain, as well as immobilization effects and mechanisms using a sustainable binder. In LZT, dolomite, quartz, calcite, and muscovite are the main gangue minerals, tiny hazardous metallic minerals were absorbed in the surface. The results revealed that Pb, Zn, Cr, and Cd were the predominant harmful elements, particularly Pb and Zn. Zn is leached completely and is the concerned hazardous element under simulated acid rain. In the acid rain neutralization ability test, the amount of leachable Pb, Cr, Ca, and Si maintained in equilibrium, leached Zn, Cd, Al, and Mg depended on the addition of acid. Pb and Ca were sedimented in residues. Immobilization of Pb, Zn, Cr, and Cd depended on the stability of Ca(OH)₂/C–S–H of hydrates, and 70% LZTHP after curing 7 days can be used for some practical engineering projects. This work opens up deeply understandings for the leached heavy metals under acidic precipitation and improves the sustainable and safe in the field of immobilization of heavy metals.

The present study was aimed at investigating the effects of different acids and pH neutralizers applied to dredged marine sediment for the treatment of heavy metals, and the resulting influence on the sediment quality as a plant growth medium. The inspection of barley germination in the dredged marine sediment revealed that residual salts are critical plant stressors whose adverse effects exceed those exhibited by high-level heavy metals and petroleum hydrocarbons present in the sediment. Acid washing and pH neutralization reduced not only the heavy metal contents but also the sediment salinity (by factors of 6.1–9.5), resulting in 100% germination of barley. For acid-washed and calcium-oxide-neutralized sediment, the barley growth was comparable to that observed in untreated and water washed sediment despite factors of 5.2–8.0 greater sediment salinity in the former. This result represents the protective effect of residual calcium against sodium and chloride toxicity. Water washing of acid-washed and pH-neutralized sediments further enhanced barley growth owing to the reduction in osmotic pressure. This study showed the effect of different sediment-washing reagents on the product quality. It also indicated the significance of balancing the enhancement of product quality and economic cost of further treatment requirements.

After the exploitation of coal mines in the 19th and 20th centuries in northern France, many mining slag heaps (SH) were left without any particular management or monitoring. Currently, the influence of these SHs on the quality of surrounding wetlands is hardly known.The purpose of this work is to determine the water quality in the neighbourhood of two SHs located near the city of Douai and its influence on the distribution of aquatic invertebrates in local wetlands. Our approach involves (1) the spatial and temporal characterization of the water composition (anions, major elements, sulphide, DOC and alkalinity) and of the biological diversity (aquatic invertebrates) and (2), based on this chemical and biological screening, the establishment of relationships between water quality and biodiversity distribution through multivariate data analysis. The results clearly indicate that substantial leaching from the slag heaps occurs, given the very high concentrations of dissolved sulphates (in the range of 2 g L⁻¹). While the pH remains weakly basic, indicating that the leaching water has been neutralized by the highly carbonated regional substratum, high levels of biodegradable organic matter and sulphate contents have been noticed. They sporadically cause significant drops in dissolved oxygen and the occurrence of dissolved sulphides that massively reduce biodiversity, qualitatively and quantitatively. In Summer, oxygen saturation is generally lower due to the higher rate of organic matter degradation, and the risk of anoxic episodes therefore increases. Finally, as wetlands are vulnerable environments, these preliminary results suggest that monitoring and management of these sites must be attempted quickly to avoid the degradation of those valuable habitats.

Cement-solidification and chelator-stabilisation of municipal solid waste incineration fly ash (MSWI-FA) are two main treatment techniques to immobilise heavy metals. Differences in the long-term stabilities of those two methods of heavy-metal immobilisation were explored to aid in determining the better MSWI-FA treatment. However, few comparative studies have been conducted on 6-year-old cement-solidified FA (Ce-6-FA) and chelator-stabilised FA (Ch-6-FA). In this study, we compared the physicochemical and heavy metal leaching characteristics of Ce-6-FA and Ch-6-FA. The chemical speciation of heavy metals was modelled using geochemical software to assess long-term stability. The results showed weaker long-term stability in Pb immobilisation under the chelating system. The leaching concentrations of target heavy metals, acetic acid leaching tests, acid neutralising capacity, and pH-dependent leaching results indicated that Ce-6-FA had higher long-term stability than Ch-6-FA. A column experiment indicated that the cumulative release rates of Pb in Ce-6-FA and Ch-6-FA were 2.49% and 4.72%, respectively. The phase-controlled leaching of Pb in Ce-6-FA mainly occurred through Pb2(OH)3Cl and chloropyromorphite (Pb5(PO4)3Cl), whereas that in Ch-6-FA mainly occurred through Pb5(PO4)3Cl. The decomposition of heavy metal chelates in Ch-6-FA and salt generation in this process led to the release of Pb via the inorganic complex.

Soot nanoparticles (SNPs) produced from incomplete combustion have strong impacts on aquatic environments as they eventually reach surface water, where their environmental fate and transport are largely controlled by aggregation. This study investigated the aggregation kinetics of SNPs in the presence of macromolecules including fulvic acid (FA), humic acid (HA), alginate polysaccharide, and bovine serum albumin (BSA, protein) under various environmentally relevant solution conditions. Our results showed that increasing salt concentrations induced SNP aggregation by suppressing electrostatic repulsion and that CaCl2 exhibited stronger effect than NaCl in charge neutralization, which is in agreement with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The aggregation rates of SNPs were variously reduced by macromolecules, and such stabilization effect was the greatest by BSA, followed by HA, alginate, and FA. Steric repulsion resulting from macromolecules adsorbed on SNP surfaces was mainly responsible for enhancing SNP stability. Such steric repulsion appeared to be affected by macromolecular structure, as BSA having a more compact globular structure on SNP surfaces imparted long-range steric repulsive forces and retarded the SNP aggregation rate by 10–100 times. In addition, alginate was shown to enhance SNP aggregation by ∼10 times at high CaCl2 concentrations due to alginate gel formation via calcium bridging. The results may bear strong significance for the fate and transport of SNPs in both natural and controlled environmental systems.

Acid mine drainage (AMD) is a global environmental issue. Conventionally, a number of active and passive remediation approaches are applied to treat and manage AMD. Case studies on remediation approaches applied in actual mining sites such as lime neutralization, bioremediation, wetlands and permeable reactive barriers provide an outlook on actual long-term implications of AMD remediation. Hence, in spite of available remediation approaches, AMD treatment remains a challenge. The need for sustainable AMD treatment approaches has led to much focus on water reuse and resource recovery. This review underscores (i) characteristics and implication of AMD, (ii) remediation approaches in mining sites, (iii) alternative treatment technologies for water reuse, and (iv) resource recovery. Specifically, the role of membrane processes and alternative treatment technologies to produce water for reuse from AMD is highlighted. Although membrane processes are favorable for water reuse, they cannot achieve resource recovery, specifically selective valuable metal recovery. The approach of integrated membrane and conventional treatment processes are especially promising for attaining both water reuse and recovery of resources such as sulfuric acid, metals and rare earth elements. Overall, this review provides insights in establishing reuse and resource recovery as the holistic approach towards sustainable AMD treatment. Finally, integrated technologies that deserve in depth future exploration is highlighted.

Size-segregated particulate pollutants (PM<0.95, PM0.95–1.5, PM1.5–3.0, PM3.0–7.2 and PM>7.2) were collected over Patiala (30.33°N, 76.40°E; 250 m amsl), a semi-urban city located in northwestern Indo-Gangetic Plain (IGP), during October, 2012 to September, 2013. Mass concentration of total suspended particulates (TSP), derived by summation of particulate (aerosol) mass in different size range, varied from 88 to 387 μg m−3 with highest mass concentration (∼55% of total mass) in submicron size (PM<0.95) during the entire study period, which broadly reflects relative higher contribution of various anthropogenic sources (emissions from biomass and bio-fuel burning, vehicles, thermal power plants, etc) to ambient particles. Concentration of SO42−, NO3−, NH4+, K+ and Ca2+ exhibited large variability ranging from 0.52 to 40, 0.20 to 19, 0.14 to 12, 0.06 to 5.3 and 0.08 to 5.6 μg m−3, respectively, in different size ranges with varying size distribution for most of the species, except NH4+. A strong linear correlation (r = 0.97) between (SO42− + NO3−) and (K+ + NH4+) concentrations has been observed in submicron particles collected in different seasons, suggesting the formation of secondary inorganic salts. However, relatively poor correlation is observed in higher size ranges where significant correlation between (SO42− + NO3−) and (Ca2+ + Mg2+) has been observed. These observations indicate the acid neutralization by dust in coarser modes of particles. Chemical composition of submicron particulates (PM<0.95) in different seasons as well as for whole year was used to identify PM sources through the application of Positive Matrix Factorization (PMF, version 5.0) model. Based on annual data, PMF analyses suggests that six source factors namely biomass burning emission (24%), vehicular emission (22%), secondary organic aerosols (20%), power plant emission (13%), secondary inorganic aerosols (12%) and mineral dust (9%) contribute to PM<0.95 loading over the study region. Such studies are important in dispersion modeling, health impact assessment, and planning of pollution mitigation strategies.

Phosphogypsum (PG) is disposed worldwide in large stacks usually placed in coastal zones, as in the case of Huelva (SW of Spain), where around 100 Mt of PG are stored on the salt marshes of the Tinto River estuary covering a surface of about 1000 ha. This management generates the weathering of PG, and due to its high acidity (pH ≈ 2) and pollutant load can provoke significant emissions into their surroundings. In this work were evaluated by laboratory experiments the effects of pH increase in the behaviour of heavy metals and natural radionuclides during the mixing of phosphogypsum leachates with seawater.The acidic phosphogypsum leachates showed concentrations of heavy metals from two to three orders of magnitude higher than natural continental waters, and natural radionuclides (U-isotopes and ²¹⁰Po) from four to five orders of magnitude higher than unperturbed aquatic systems. Major elements and some heavy metals as Mn, Ni, Cd, As, Sb and Co showed a conservative behaviour during the neutralisation of the leachates with seawater, remaining in the liquid phase, while other ones as Al, Fe, Cr, Zn, Cu, Pb precipitated and/or were adsorbed onto the solid phase. The U-isotopes and ²¹⁰Po showed a clear non-conservative behaviour probably due to coprecipitation/adsorption processes onto the formed precipitates, but while ²¹⁰Po reached a total removal at pH ≈ 7, U- isotopes after a total removal at pH ≈ 5 returned into the liquid phase due to redissolution/desorption processes at near neutral pH.The formed precipitates, mainly composed by iron phosphates particles, showed heavy metal and natural radionuclide concentrations from one to three orders of magnitude higher than unperturbed soils. All these facts demonstrate the serious environmental impact produced by the PG stacks into their surroundings and the urgency of effective restoration measures.

Atmospheric wet deposition of base cations (BCs) plays a significant role in providing plant nutrients and buffering acidification. However, the temporal dynamic of wet BC deposition in China during the past two decades remain unclear. Here, we used long-term monitoring and literature data since 2000 to assess the temporal dynamics (seasonal and inter-annual variation), spatial patterns, main influencing factors, source apportionment, and capacity to neutralize the acidity of wet BC depositions at site, regional, and national scales. The results showed that total wet deposition of BCs was, on average, 2.12 keq ha⁻¹ yr⁻¹, where Ca²⁺ accounted for 65.57% of the total deposition, followed by Na⁺ (13.21%), Mg²⁺ (13.68%), and K⁺ (7.55%). Qinghai-Tibet had significantly lower BC deposition fluxes than northern, southern, and central China, as well as Inner Mongolia. Exchangeable BCs in soil, PM₁₀ in the atmosphere, energy consumption, and cement production are significantly related to wet BC deposition, which account for 79.17% of the variation in the spatial deposition of BC. Influenced by the strategies to control acid rain and particulate matter in China, interannual variations showed a stabilization trend after a continuous decline from 2000 to 2017, which can be explained by inter-annual changes in PM₁₀, energy consumption and cement production. Statistical methods confirmed that 45.95% of wet BC deposition was derived from crustal contributions, 27.78% from sea salt sources, and 26.27% from anthropogenic sources. Furthermore, we found that wet deposition of BCs neutralized 84.85% of the acidity due to NO₃⁻ and SO₄²⁻ depositions. Under the emissions reduction strategy, there has been a decrease in the deposition of BC. However, SO₄²⁻ and NO₃⁻ depositions decreased faster than BC deposition, which buffered a higher proportion of acidic depositions. Our findings contribute to an improved understanding of wet BC deposition in China, an evaluation of their capacity to neutralize acidity, and important parameters for acidification models.

A laboratory bioassay was conducted to investigate the ecotoxicity of a chromium-enriched superfood, Spirulina platensis, on the meiofauna collected from the Ghar El Melh lagoon, Tunisia. After 1 month of exposure, the abundances of meiobenthic taxa and the taxonomic and morpho-functional diversity of nematodes showed significant differences between the Spirulina and Spirulina + chromium groups. The nematodes were more tolerant of all types of stressors compared to harpacticoids, polychaetes, and oligochaetes, and the lowest taxonomic and morpho-functional diversity of nematodes was observed in the highest sedimentary concentration of S. platensis (50% DW). The mixed treatments may have been richer in micro-habitats and subject to low selective pressure, thereby hosting nematodes with a wide range of adaptations. The responses of the nematode species differed depending on their functional traits. Spirulina enriched with chromium induced two responses for the same feeding group: high toxicity for Daptonema fallax and low toxicity for two Theristus species (T. flevensis and T. modicus). The ecotoxicity of the Spirulina/chromium mixtures were lower than that of Spirulina alone, suggesting mutual neutralization between these two elements. The association between functional traits and taxonomic diversity showed that the effects of the mixtures were not additive and that one of the stressors camouflaged the effect of the other. Our findings should encourage the commercialization of chromium-enriched S. platensis owing to its lower ecotoxicity than Spirulina alone.