Lead (Pb) is an important pollutant and it is of significance to explore the Pb distribution, influencing factors and health risk. Pb concentration and mass load per unit area in 385 street dust samples collected from 19 cities in China were determined during 2011-2013. The results show that the Pb concentration are 68.8, 105.4, 41.7, 49.7, 75.6, 81.7, 131.9, 67.5, 109.3, 164.1, 74.8, 66.4, 99.8, 58.4, 114.0, 59.6, 103.7, 55.4 and 80.4 for Beijing, Chengdu, Daqing, Harbin, Jilin, Jinan, Kunming, Lanzhou, Luoyang, Panzhihua, Qingdao, Yinchuan, Guangzhou, Tangshan, Xi’an, Guangyuan, Nanjing, Taiyuan and Tianjin, respectively. The Pb pollution level of urban street dust varies among cities in the range of 1.72–5.56 times higher than soil background values. The allometric function can fit the change in Pb concentration with particle size well. The medium-sized (38–120 μm) particles contributed 60.2%–80.4% to the Pb load and should be highlighted when selecting street dust management techniques. Influenced by the distribution of Pb ore, the Pb concentration of urban street dust in China shows obvious regional differences, with value in the south 112% higher than that in the north. Among all kinds of mining types, metal-related mining activities discharge a large amount of Pb dust in the process of crushing and smelting, thus contributing most to the Pb load. The Pb load was also affected by transportation. The relationship between Pb load and gross domestic product (GDP) was described with the environmental Kuznets curve (EKC) model, which indicated that the Pb emissions of most cities were still increasing. Finally, the human health risk assessment model with adjusted parameters showed that the Pb risk of all cities was below the threshold. Despite all this, given the EKC law of Pb emission, long-term follow-up assessments are needed.

While the crushing of concrete gives rise to large quantities of coarse dust, it is not widely recognized that this process also emits significant quantities of ultrafine particles. These particles impact not just the environments within construction activities but those in entire urban areas. The origin of these ultrafine particles is uncertain, as existing theories do not support their production by mechanical processes. We propose a hypothesis for this observation based on the volatilisation of materials at the concrete fracture interface. The results from this study confirm that mechanical methods can produce ultrafine particles (UFP) from concrete, and that the particles are volatile. The ultrafine mode was only observed during concrete fracture, producing particle size distributions with average count median diameters of 27, 39 and 49 nm for the three tested concrete samples. Further volatility measurements found that the particles were highly volatile, showing between 60 and 95% reduction in the volume fraction remaining by 125 °C. An analysis of the volatile fraction remaining found that different volatile material is responsible for the production of particles between the samples.

The process of anaerobic digestion in food waste treatment plants generates a large amount of volatile organic compounds (VOCs). Long-term exposure to this exhaust gas can pose a threat to the health of workers and people living nearby. In this study, VOCs emitted from different working units in a food waste anaerobic digestion plant were monitored for a year. Variations in VOCs emitted from each unit were analyzed and a health risk assessment was conducted for each working unit. The results show that the concentration of VOCs in different units varied greatly. The highest cumulative concentration of VOCs appeared in the hydrothermal hydrolysis unit (3.49 × 10⁴ μg/m³), followed by the sorting/crushing room (8.97 × 10³ μg/m³), anaerobic digestion unit (6.21 × 10² μg/m³), and biogas production unit (2.01 × 10² μg/m³). Oxygenated compounds and terpenes were the major components of the emitted VOCs, accounting for more than 98% of total VOC emissions. The carcinogenic risk in the plant exceeded the safety threshold (ILCR<1 × 10⁻⁶), while the non-carcinogenic risk was within the acceptable range (HI < 1). The carcinogenic risk from the hydrothermal hydrolysis unit was the highest, reaching 4.4 × 10⁻⁵, and was labeled as “probable risk.” The carcinogenic risk at the plant boundary was 1.2 × 10⁻⁵, indicating exhaust gases can cause a health threat to neighbors. Therefore, management VOCs in anaerobic digestion plants should receive more attention, and employees should minimize the time they spend in the hydrothermal hydrolysis unit.

Lignite fly ash (FA) and waste rocks (WRs) were mixed in three different ratios (1:1, 1:3 and 1:5) and studied to compare the effects of adding FA on acid mine drainage generation from coal mining WRs, leachability of elements and the potential occurrence of the secondary minerals. FA mixed with WRs showed significant differences in pH levels compared to previous research. The 1:1 mixture performed best of all the three mixtures in terms of pH and leachability of elements, mainly due to the higher proportion of FA in the mixture. The pH in the 1:1 mixtures varied between 3.3 and 5.1 compared to other mixtures (2.3–3.5). Iron and SO₄²⁻ leached considerably less from the 1:1 mixture compared to the others, indicating that the oxidation of sulphides was weaker in this mixture. Aluminium leached to a high degree from all mixtures, with concentrations varying from mg L⁻¹ to g L⁻¹. The reason behind this increase is probably the addition of FA which, due to acidic conditions and the composition of the FA, increases the availability of Al. For the same reason, high concentrations of Mn and Zn were also measured. Geochemical modelling indicates that the 1:1 mixture performs better in terms of precipitation of Al³⁺ minerals, whereas Fe³⁺ minerals precipitated more in mixtures containing less FA. These results suggest that, with time, the pores could possibly be filled with these secondary minerals and sulphate salts (followed by a decrease in sulphide oxidation), improving the pore water pH and decreasing the leachability of elements. Since grain size plays a crucial role in the reactivity of sulphides, there is a risk that the results from the leaching tests may have been influenced by crushing and milling of the WR samples.

Physicochemical and morphological characteristics of atmospheric particles in new urban centers of fast-developing megacities are not well understood. In this study, atmospheric coarse particles (PM₂.₅–₁₀) were simultaneously collected in multiple stations (10) in new urban centers, namely Beylikduzu, Buyukcekmece, and Esenyurt, of Istanbul using a modified passive particulate sampling method. Scanning electron microscope and energy dispersive X-photon spectroscopy (SEM-EDS) was used to investigate the size distribution characteristics, chemical composition and their weight percent abundances, and morphological properties of the collected particles. The particle clusters were mainly dominated by Ca-rich Al silicates, Ca dominant, Ca- and S-rich, and NaCl particles, respectively. Their potential sources were assigned to the natural sources (e.g., wind erosion, soil resuspension, and sea sprays) and anthropogenic activities (construction, transportation, mining and crushing, and cement production). In addition to the major contributions (up to 47% of particle number abundance), the minor contribution clusters (less than 1%) with transitional metals rich particles (Fe, Zn, and Cu rich) mainly from anthropogenic sources (combustion, traffic, and vehicular emissions) were identified. The typical size range (> 0.65 to < 11.00 μm) distribution of the major particle clusters fits a left-skewed modal distribution with a peak at 1.10–2.30-μm size range. However, the number of particles decreases significantly with increasing distance to the source, and this justification is stronger for larger size fractions (> 2.3 μm). Particle numbers and varieties indicated significant spatial variations depending upon the identified sources, meteorological factors, and temporal conditions. In general, the results of this study suggest that the passive sampling of PM₂.₅–₁₀ coupled with SEM/EDS based single-particle analysis is an effective tool to understand the physicochemical characterization and spatial and temporal variations of atmospheric particles in urban environments.

Laboratory and greenhouse experiments were carried out to investigate the chemical, physical, and microbial properties of seawater-neutralized bauxite residues and the effects of additional leaching (1 pore volume of deionized water versus an additional 6 pore volumes) and amendment with gypsum (5%) and/or cattle manure (6%) on its properties and on the growth of Rhodes grass (Chloris gayana). Additional leaching resulted in a decrease in EC, exchangeable Na, SAR, and ESP. For unamended control treatments, additional leaching induced a rise in pHSE from 8.5 to 9.6 and pH₁:₅ from 9.1 to 10.1 due to dissolution of residual alkalinity. Addition of gypsum arrested this pH increase resulting in a final pHSE of 7.5 and pH₁:₅ of 8.8. In control treatments, additional leaching resulted in a pronounced decrease in Rhodes grass yields. However, in gypsum and cattle manure-amended treatments, it led to substantial yield increases and decreases in tissue Al and Na concentrations and increased K/Na ratios. Upon drying for the first time, bauxite residue was shown to contract and form a solid massive structure. The aggregates formed from crushing this material were water stable (as measured by wet sieving). Additions of cattle manure or gypsum to residue aggregates did not affect pore size distribution. Addition of cattle manure increased organic C and microbial biomass C content and basal respiration rate while additional leaching increased basal respiration and metabolic quotient. It was concluded that a combination of drying and crushing the residue, amending it with gypsum and organic manure followed by extensive leaching results in the formation of a medium that supports plant growth.

In general terms, plant managers of sites producing construction wastes assess materials according to concise, legally recommended leaching tests that do not consider the compaction stage of the materials when they are applied on-site. Thus, the tests do not account for the real on-site physical conditions of the recycled aggregates used in civil works (e.g., roads or embankments). This leads to errors in estimating the pollutant potential of these materials. For that reason, in the present research, an experimental procedure is designed as a leaching test for construction materials under compaction. The aim of this laboratory test (designed specifically for the granular materials used in civil engineering infrastructures) is to evaluate the release of pollutant elements when the recycled aggregate is tested at its commercial grain-size distribution and when the material is compacted under on-site conditions. Two recycled aggregates with different gypsum contents (0.95 and 2.57%) were used in this study. In addition to the designed leaching laboratory test, the conventional compliance leaching test and the Dutch percolation test were performed. The results of the new leaching method were compared with the conventional leaching test results. After analysis, the chromium and sulphate levels obtained from the newly designed test were lower than those obtained from the conventional leaching test, and these were considered more seriously pollutant elements. This result confirms that when the leaching behaviour is evaluated for construction aggregates without density alteration, crushing the aggregate and using only the finest fraction, as is done in the conventional test (which is an unrealistic situation for aggregates that are applied under on-site conditions), the leaching behaviour is not accurately assessed.

Preparation of the value-added products from e-waste resources is an important step in the recycling process. The present paper aims to propose a methodology for the recovery of In from scrap LCD panel via preparation of InBO₃ nanostructure. Discarded LCD panel was subjected to a recycling process through crushing, milling, and oxalic acid leaching to prepare In₂(C₂O₄)₃·6H₂O. Through the leaching process, B(OH)₃ from glass part (alumina borosilicate) has been leached out along with indium oxalate hydrated. Further thermal treatment on these extracted materials at 600 °C could result in the formation of InBO₃ nanostructures with an average particle size of 20 nm. A multistep mechanism based on thermodynamic calculations for the recycling of the InBO₃ form extracted precursors was proposed. Graphical abstract

Crushed waste rocks can be used as materials for backfilling goafs, so as to achieve the simultaneous goals of processing solid waste and controlling surface subsidence; however, particle size distribution directly affects the compaction of crushed waste rocks. Therefore, by employing a self-designed bidirectional loading test system for granular materials, this study tested compaction characteristics of crushed waste rocks with four different particle size distributions. Moreover, this research tested the changes of parameters in lateral and axial loading of crushed waste rocks and analysed the influence of particle size distribution on lateral strain, axial strain, porosity, lateral stress, and lateral pressure coefficient during compaction. The test results show that (1) particle size distribution affects porosity, strain, and lateral pressure coefficient of crushed waste rocks under lateral and axial loading. (2) For the samples under particle size distribution ranging from 0 to 10 mm, the initial porosity is low and deformations are small under axial loading, so that particles can make contact and bear effective stress in grain-grain contact. Therefore, more stress is transferred to the lateral direction. (3) After compaction, the curves of the samples of crushed waste rocks under four particle size distributions all shift upwards in comparison with those before compaction, indicating that particles are crushed and the proportion of small particles constantly increases. (4) A reasonable particle size distribution can significantly improve stress characteristics, reduce crushing of particles in the samples, and increase the stiffness of the samples, so as to achieve better compaction effects.