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Cement is the most important binding agent used in soil stabilization and significantly improves the strength and compressibility of soils. However, owing to the significant environmental and socio-economic impact of cement production, alternative, low-carbon binders are increasingly being sought. Among them, waste-based inorganic additives used in construction provide sustainable soil treatment materials and reduce the need for landfills. Effective mud stabilization depends on the type of stabilizers and their mineralogical setup, as well as an understanding of their water absorption capacity. Therefore, this study investigated the factors influencing the water absorption characteristics of waste-based additives, including paper sludge ash (PSA), palm kernel shell ash (PKSA), rice husk ash (RHA), coal fly ash, hemihydrate gypsum, limestone powder, and basalt rock powder (BRP). The water absorption capacity (W ab) of each additive represents the amount of water absorbed per gram evaluated via the suction filtration method. The long-term water absorption capacities of the waste additives were compared with a conventional additive, blast furnace cement class B (BFCB). Although PSA, PKSA, and RHA absorbed more water than BFCB under short-term curing, BFCB exhibited the highest W ab under long-term curing. PSA, PKSA, and RHA had a water absorption capacity at 4 h (W ab) t = 4h of 74.5%, 107.3%, and 62.9%, respectively, whereas that of BFCB was 37.4%. In contrast, after 168 h, the water absorption capacity of BFCB increased to 126.1%. These evaluated water absorption capacities were categorized into immediate and time-dependent stages. Mercury intrusion porosimetry, X-ray diffraction (XRD), and scanning electron microscopy investigations were conducted to investigate the influence of factors such as porosity and hydration of the different additives on water absorption capacity. The results showed that porosity characteristics affect the immediate water absorption capacity, and hydrate formation contributes to increased water absorption during curing. The waste additives PSA, PKSA, and RHA with irregular surfaces and pores were highly porous and exhibited a high immediate water absorption capacity (W ab) t = 4h , unlike the additives with flat surfaces and less irregularities with lower (W ab) t = 4h. The XRD investigation revealed that the presence of ettringite and calcite contributed to increased water absorption during curing for PSA, PKSA, and BFCB. The generation of needle-like ettringite could promote a denser microstructure in PSA, PKSA, and BFCB, thus further improving W ab during curing. Finally, using cone index strength, we explored the effective application of waste-based additives as soil stabilizers, attempting to predict the effect of water absorption capacity on the properties of treated soil. The stabilizer addition ratio (A) and W ab of the waste additives were found to be essential indicators for predicting the strength development of treated clays. A clear correlation was observed between the cone index (q c) and parameter β (t), which is derived from W ab and A , of the treated clays. [ABSTRACT FROM AUTHOR]

• Paper sludge ash-based stabilizer (PSAS) is a new type of soil stabilizer. • The W ab and PSD of PSAS influence the change in consistency PSAS-treated soil. • The q c of PSAS-treated soil can be estimated based on its liquidity index I L. • Required PSAS amount for a specific q c of PSAS-treated soil can be estimated. Paper sludge ash-based stabilizers (PSASs) have recently been developed in Japan as sustainable construction materials for soil stabilization. PSASs are produced by the in-solubilization of heavy metals in paper sludge (PS), which is generated as a by-product of the de-inking and re-pulping of paper. PSASs can improve the stability of high-water-content clays immediately after mixing owing to their good water absorption and retention performance. However, mixture design methods that consider time variations of the water absorption and retention performance of a PSAS are lacking. Therefore, in this study, the effects of a PSAS on the physical and mechanical properties of the treated clay were experimentally investigated, considering the change in the water absorption and retention performance of the PSAS with curing time. The water absorption and retention rate, W ab , of the PSAS, is defined as the ratio of the mass of water absorbed and retained by the PSAS to its dry mass. Physical tests and cone index tests were conducted on different types of clays treated with different types of PSASs. The test results showed that different W ab values were obtained depending on the type of the PSAS and that the W ab value increased with curing time. From the experiments, it was found that the liquid limits, w L , and plastic limits, w P , of the PSAS-treated clays with different curing times could be evaluated from the W ab values of the PSAS and the particle sizes of the PSAS and untreated clays. A clear correlation was also found between the cone index, q c , and liquidity index, I L , of the treated and untreated clays. Based on the results, a new approach for mixture design was proposed. The applicability of the proposed method was investigated, and the results showed that the measured q c value of the PSAS-treated clay was close to the target q c value. The average measured q c was approximately 1.1 times the corresponding target q c. The maximum error between the measured q c and target q c values was approximately 30%. [ABSTRACT FROM AUTHOR]

Vanadium (V) is a redox-sensitive trace metal that typically exists in one of three oxidation states (+3, +4 and +5) in natural waters; a feature increasingly used in paleoredox studies of ancient marine sediments. However, our knowledge of V geochemistry in low-oxygen marine environments is still limited, especially regarding interactions of V with reduced iron minerals such as green rust. Carbonate green rusts (GR CO3) are mixed FeII/FeIII-phases found in some modern ferruginous settings, such as Lake Matano (Indonesia), and were likely abundant in ancient ferruginous marine systems where they may have played an essential role in authigenic V enrichments in sediments. Here, we present an abiotic pathway of V removal from seawater via reduction and adsorption onto amorphous GR CO3. Suspensions of the freshly precipitated GR CO3 (1 g L−1) were added to vanadate (1 mg VV L−1 initial concentration) in anoxic synthetic seawater solutions. Vanadium removal by GR CO3 was rapid and efficient, with 92 – 99% of V removed in under 20 seconds. Synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy showed that VV adsorbed by GR CO3 was partially reduced to a mixture of VV and VIV, with the average oxidation state of adsorbed V increasing (+4.3 to +4.7) with increasing solution pH (7.5 to 8.5). Upon subsequent exposure to aerated seawater, V-bearing GR CO3 oxidized to lepidocrocite [γ–FeO(OH)] within 24 h, with concomitant reduction of all solid-phase VV to VIV. During oxidation, V was not released back into solution; rather, extended X-ray absorption fine structure (EXAFS) modeling revealed that VIV was structurally incorporated into lepidocrocite as octahedral vanadyl (VO2+). Our work further constrains the aqueous geochemistry of V, which has implications for understanding V cycling and removal mechanisms in both modern and ancient marine systems. [ABSTRACT FROM AUTHOR]

Engineered zinc oxide (ZnO) and silver (Ag) nanoparticles (NPs) used in consumer products are largely released into the environment through the wastewater stream. Limited information is available regarding the transformations they undergo during their transit through sewerage systems before reaching wastewater treatment plants. To address this knowledge gap, laboratory-scale systems fed with raw wastewater were used to evaluate the transformation of ZnO- and Ag-NPs within sewerage transfer networks. Two experimental systems were established and spiked with either Ag- and ZnO-NPs or with their dissolved salts, and the wastewater influent and effluent samples from both systems were thoroughly characterised. X-ray absorption spectroscopy (XAS) was used to assess the extent of the chemical transformation of both forms of Zn and Ag during transport through the model systems. The results indicated that both ZnO- and Ag-NPs underwent significant transformation during their transport through the sewerage network. Reduced sulphur species represented the most important endpoint for these NPs in the sewer with slight differences in terms of speciation; ZnO converted largely to Zn sulfide, while Ag was also sorbed to cysteine and histidine. Importantly, both ionic Ag and Ag-NPs formed secondary Ag sulfide nanoparticles in the sewerage network as revealed by TEM analysis. Ag-cysteine was also shown to be a major species in biofilms. These results were verified in the field using recently developed nanoparticle in situ deployment devices (nIDDs) which were exposed directly to sewerage network conditions by immersing them into a municipal wastewater network trunk sewer and then retrieving them for XAS analysis. [ABSTRACT FROM AUTHOR]

The use of nanoscale Ag in textiles is one the most often mentioned uses of nano-Ag. It has previously been shown that significant amounts of the Ag in the textiles are released upon washing. However, the form of Ag present in the textiles remains largely unknown as product labelling is insufficient. The aim of this study was therefore to investigate the solid phase speciation of Ag in original and washed silver textiles using XANES. The original Ag speciation in the textiles was found to vary greatly between different materials with Ag(0), AgCl, Ag2S, Ag-phosphate, ionic Ag and other species identified. Furthermore, within the same textile a number of different species were found to coexist. This is likely due to a combination of factors such as the synthesis processes at industrial scale and the possible reaction of Ag with atmospheric gases. Washing with two different detergents resulted in marked changes in Ag-speciation. For some textiles the two detergents induced similar transformation, in other textiles they resulted in very different Ag species. This study demonstrates that in functional Ag textiles a variety of different Ag species coexist before and after washing. These results have important implications for the risk assessment of Ag textiles because they show that the metallic Ag is only one of the many silver species that need to be considered. [ABSTRACT FROM AUTHOR]