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Slag from steel production as a versatile fertilizer: Evaluation of ladle furnace slag in sandy soils and hydroponics
Soil quality is one of the main limiting factor in the development of the food sector in arid areas, mainly due to its poor mechanics and lack of water retention. Soil’s organic carbon is nearly absent in arid soils, though it is important for water and nutrient transport, to soil mechanics, to prevent erosion, and as a long-term carbon sink. In this study, we evaluate the potential benefits that are brought to inert sand by the incorporation of a range of, mainly, cellulosic networks in their polymeric or structured (fiber) forms, analogously to those found in healthy soils. We explore the impact of a wide range of nonfood polysaccharide-based amendments, including pulp fibers, nanocellulose, cellulose derivatives, and other readily available polysaccharide structures derived from arthropods (chitosan) or fruit peels (pectin) residues. A practical methodology is presented to form sand–polymer composites, which are evaluated for their soil mechanics as a function of humidity and the dynamics of their response to water. The mechanics are correlated to the network of polymers formed within the pores of the sandy soil, as observed by electron microscopy. The response to water is correlated to both the features of the network and the individual polysaccharides’ physicochemical features. We expect this work to provide a rapid and reproducible methodology to benchmark sustainable organic amendments for arid soils.
This study characterizes seedling exudates of peas, tomatoes, and cucumbers at the level of chemical composition and functionality. A plant experiment confirmed that Rhizobium leguminosarum bv. viciae 3841 enhanced growth of pea shoots, while Azospirillum brasilense Sp7 supported growth of pea, tomato, and cucumber roots. Chemical analysis of exudates after 1 day of seedling incubation in water yielded differences between the exudates of the three plants. Most remarkably, cucumber seedling exudate did not contain detectable sugars. All exudates contained amino acids, nucleobases/nucleosides, and organic acids, among other compounds. Cucumber seedling exudate contained reduced glutathione. Migration on semi solid agar plates containing individual exudate compounds as putative chemoattractants revealed that R. leguminosarum bv. viciae was more selective than A. brasilense, which migrated towards any of the compounds tested. Migration on semi solid agar plates containing 1:1 dilutions of seedling exudate was observed for each of the combinations of bacteria and exudates tested. Likewise, R. leguminosarum bv. viciae and A. brasilense grew on each of the three seedling exudates, though at varying growth rates. We conclude that the seedling exudates of peas, tomatoes, and cucumbers contain everything that is needed for their symbiotic bacteria to migrate and grow on.
Ladle slag is a byproduct formed during the ladle refining stage of steel making. It is a dusty material that has been considered industrial waste. Technical advancements towards a sustainable industry led to the development of different applications for ladle slag. Depending on the processing methods during the steel slag production and the weathering of the slag post‐production, the elemental composition of the steel slag largely varies. Owing to this, its characteristics cannot be generalized and specific applications depending on the sources are developed. It is generally used in construction materials, soil rejuvenation, and CO2 capture. This paper reviews the production process, the mineralogical and morphological properties, stabilization techniques, and the applications of ladle furnace (LF) slag. One of the prime focuses of waste remediation and sustainable industry is to find meaningful ways to turn waste into products. In this respect, a comprehensive review of the properties of LF slag and its current application will help provide a framework for the development of future sustainability goals. With increased slag usage, the ladle refining process of steelmaking can be turned into a more carbon‐neutral process.
Plant phenotyping involves the quantitative determination of complex plant traits using image analysis. One important parameter is how green plant tissues appear to the observer, which is indicative of their health and developmental stage. Various formulas have been developed to quantify this by calculating leaf greenness scores. We have developed a revised formula called "Green Index" (GI) devised out of the need to quantitatively assess how the apparent greenness of seedlings changes during de-etiolation. The GI calculation is simple, uses widely available RGB values of pixels in images as input, and does not require commercial software platforms or advanced computational skills. In this study we describe the conception of the GI formula, compare it with other widely used greenness formulas, and test its wider application in plant phenotyping using the open source free software platform RawTherapee. We demonstrate the utility of the GI in addressing common issues encountered in assessing plant biology experiments, underscoring its potential as a reliable and accessible tool. Finally, we explore the correlation between GI and chlorophyll content, assess its reliance on different types of photography, and summarizes the key steps for its effective utilization.
Biosystems and bioprocesses are typically not connected to arid areas, where the produced biomass and its availability are low. There is however a large potential for arid areas to become major bioeconomical actors via more localized biomass generation strategies. Indoor farming, bioengineering, and aquaculture have a great potential to be at the center of this transition. They are expected to address important challenges associated with food and (bio)materials supply and, ultimately, to climate and environment. Specifically, the utilization of the by- and coproducts deriving from these strategies could synergistically connect into a range of circular processes toward sustainable bioproducts’ supply and the greening of arid areas. These topics are at the center of this perspective, where emerging biomass generation and management strategies in arid areas are introduced. The potential positive feedback loops between their coproducts are then put in relation with the development of more diverse and thriving biosystems as well as the generation of a range of bioproducts. These approaches are contextualized with the current and alternative energy sectors and water treatments processes, which have well-established economical portfolios across most arid areas. The mapping of innovative bioeconomical actors in arid areas and their synergistic interactions, as put forward herein aims to intensify research efforts toward a fully integrated and global sustainable bioeconomy.
For further resource utilization of solid waste steel slag and the reduction in biodiesel production costs, this study used steel slag as a carrier to synthesize a CaO-CeO2/slag solid base catalyst for the effective transesterification of palm oil into fatty acid methyl esters (FAMEs). The synthesis involved a two-step impregnation of steel slag with nitrate of calcium and cerium and thermal activation at 800 °C for 180 min. Then, the catalysts’ textural, chemical, and CO2 temperature-programmed desorption properties were characterized. The catalytic activity depended highly on the ratio of Ca-Ce to steel slag mass; the CaO-CeO2/slag-0.8 catalyst showed outstanding performance. Characterization showed that the surface area and total basicity of the Ca-Ce/slag-0.8 catalyst were 3.66 m²/g and 1.289 mmol/g, respectively. The reactivity results showed that FAMEs obtained using 7 wt.% catalyst, 9:1 of methanol-to-palm-oil molar ratio, 180 min reaction duration, and 70 °C reaction temperature was optimum (i.e., 95.3% yield). In addition, the CaO-CeO2/slag-0.8 catalyst could be reused for at least three cycles, retaining 91.2% of FAMEs yield after n-hexane washing. Hence, the catalyst exhibits an excellent potential for cost-effective and environmentally friendly biodiesel production.
Metal-phenolic networks (MPN) foams are prepared using colloidal suspensions of tannin-containing cellulose nanofibers (CNF) that are ice-templated and thawed in ethanolic media in the presence of metal nitrates. The MPN facilitates the formation of solid foams by air-drying, given the strength and self-supporting nature of the obtained tannin-cellulose nanohybrid structures. The porous characteristics and (dry and wet) compression strength of the foams are rationalized by the development of secondary, cohesive layers combined with a hydrogen bonding network involving the CNF. The shrinkage of the MPN foams is as low as 6% for samples prepared with 2.5-10% tannic acid (or condensed tannin at 2.5%) with respect to CNF content. The strength of the MPN foams reaches a maximum at 10% tannic acid (using Fe(III) ions), equivalent to a compressive strength 70% higher than that produced with tannin-free CNF foams. Overall, a straightforward framework is introduced to synthesize MPN foams whose physical and mechanical properties are tailored by the presence of tannins as well as the metal ion species that enable the metal-phenolic networking. Depending on the metal ion, the foams are amenable to modification according to the desired application This article is protected by copyright. All rights reserved.
Root exudates are an essential carrier for material cycling, energy exchange, and information transfer between the belowground parts of plants and the soil. We synthesize current properties and regulators of root exudates and their role in the belowground ecosystem as substances cycle and signal regulation. We discussed the composition and amount of root exudates and their production mechanism, indicating that plant species, growth stage, environmental factors, and microorganisms are primary influence factors. The specific mechanisms by which root secretions mobilize the soil nutrients were summarized. First, plants improve the nutrient status of the soil by releasing organic acids for acidification and chelation. Then, root exudates accelerated the SOC turnover due to their dual impacts, forming and destabilizing aggregates and MASOC. Eventually, root exudates mediate the plant–plant interaction and plant–microbe interaction. Additionally, a summary of the current collection methods of root exudates is presented.
The recycling of steel plant side streams through cold-bonded briquettes has become quite common. However, Portland cement is mainly used as a binder in the briquettes, contributing significantly to the energy consumption, costs, and carbon footprint associated with the production of cold-bonded briquettes. This paper reports on a more sustainable method for side stream recycling that involves replacing cement with an ettringite-based binder. Ettringite binders develop early high strength and mainly consist of ladle slag, another side stream of the industry. Here, the ettringite-based binder is assessed in terms of its mechanical and thermal properties against a reference briquette made using the conventional technique. Three different briquette types are produced using several side stream materials and varying ettringite-based binder content. Briquettes produced using 15% and higher ettringite-based binder content exhibited excellent mechanical properties within a shorter curing period compared to conventional used binder. Moreover, the ettringite-based binder briquettes exhibited a better swelling behavior to conventional cement briquettes under conditions simulating a blast furnace.
Graphical Abstract
The construction industry needs to reduce greenhouse gases, in which cement production is currently responsible for generating between 4% and 6% of the total CO2 released into the atmosphere. Similarly, many industries produce large amounts of solid waste, which often have low value-added applications or are directly taken to landfills, with consequent negative environmental impacts. One of these industries is the steel industry, which in 2016 generated 18.4 Mt of slag (melting and refining slag) among all European Union countries. In terms of refining steel slag (ladle or white slag), it is estimated that for each ton of steel, between 20 and 30 kg of slag is produced; that is, in 2016, more than 700,000 tons of white slag were generated. It is also known that this material has cementitious properties and can be used as a precursor in alkaline activation processes. Depending on the concentrations used of the activating agent, a higher or lower mechanical performance of the developed materials can be obtained. This work studied the alkali activation of a ladle slag used to manufacture mortars, subjecting them to an initial curing of 24 h at different temperatures (20, 40, and 70 °C). Sodium silicate and sodium hydroxide were used as activating agents, using percentages of Na2O between 5% and 10% to obtain an optimal dosage of the activator. The physical and mechanical properties of the mortars were evaluated at different ages of curing. In addition, monitoring was undertaken of linear shrinkage due to drying and the mineralogical changes due to activation and curing time.
On acid soils, the trivalent aluminium ion (Al³⁺) predominates and is very rhizotoxic to most plant species. For some native plant species adapted to acid soils including tea (Camellia sinensis), Al³⁺ has been regarded as a beneficial mineral element. In this study, we discovered that Al³⁺ is actually essential for tea root growth and development in all the tested varieties. Aluminum ion promoted new root growth in five representative tea varieties with dose‐dependent responses to Al³⁺ availability. In the absence of Al³⁺, the tea plants failed to generate new roots, and the root tips were damaged within 1 d of Al deprivation. Structural analysis of root tips demonstrated that Al was required for root meristem development and activity. In situ morin staining of Al³⁺ in roots revealed that Al mainly localized to nuclei in root meristem cells, but then gradually moved to the cytosol when Al³⁺ was subsequently withdrawn. This movement of Al³⁺ from nuclei to cytosols was accompanied by exacerbated DNA damage, which suggests that the nuclear‐targeted Al primarily acts to maintain DNA integrity. Taken together, these results provide novel evidence that Al³⁺ is essential for root growth in tea plants through maintenance of DNA integrity in meristematic cells.
The paper presents the results obtained in pHstat leaching test and assesses the influence of pH changes and occurring processes on the release of heavy metals (Cd, Ni, Crtotal, Pb, Cu and Zn) from metallurgical slag in a zinc smelter. Additionally, the analysis of the potential maximum amount of element available for leaching and releasing in the batch leaching test was carried out. All the results of the leaching tests were compared with the total content of heavy metals in the material. In order to evaluate the chemical forms of elements, a sequential extraction study was also carried out. On the basis of test results obtained in pHstat test, a strong dependence of heavy metals leaching on the pH was found. The highest concentrations of the analysed elements were observed in acidic environment. For most metals, except for lead, an increase in the pH of the solution caused a decrease in their concentration. Lead showed an upward trend of release under alkaline conditions. A sharp increase of copper leaching at pH 10.5 was also observed. Based on the results of the study, cadmium can be considered the most mobile element from metallurgical slag. Chromium indicated the lowest degree of release.
The effective utilization of slag fertilizer in agriculture to neutralize soil acidity, improve crop productivity, mitigate greenhouse gas emissions, and stabilize heavy metals in contaminated soils turns it into a high value added product in sustainable agriculture. These effects could be due to the shift in microbial metabolism and/or modification of microbial habitats. At the system level, soil microorganisms play an integral role in virtually all ecosystem processes. There is a growing interest to reveal the underlying mechanisms of slag-microbe interactions and the contribution of soil biota to ecosystem functioning. In this perspective, we discuss the possible driving mechanisms of slag-microbe interactions in soil and how these slag-microbe interactions can affect crop yield, greenhouse gas emissions, soil carbon sequestration, and heavy metal stabilization in contaminated soils. In addition, we discuss the problems and environmental concerns in using slag in agriculture. Emphasis has been given for further research to validate the proposed mechanisms associated with slag-microbe interactions for increasing soil quality, crop productivity, and mitigating environmental consequences. While evaluating the slag amendment, effects on agriculture and environment, the potential risks, socio-economics, techno-economics, and ethics should be assessed.
Soil organic matter (SOM) represents the biggest pool of carbon within the biosphere and influences the flux of greenhouse gases between land surface and atmosphere. In this regard, conservation tillage systems have been adopted to reduce negative impacts of conventional tillage practices on greenhouse gases (GHG) emissions. However, the role of these techniques to increase carbon sequestration also depends upon soil features and climatic conditions, which is studied and managed by precision agriculture (PA) principles and technologies. Simulation models have shown to be useful tools to understand the interaction between soil, climate, genotypes and management practices to simulate the long-term effects of management approaches of different soils on crop yield, soil organic carbon (SOC) storage, and GHG emissions. The research goals of this study are (1) to examine the mid-term (15 years) trajectory of SOC in the upper 0.4 m of the soil profile under different tillage systems using the SALUS model; (2) determine the impact of PA on the inputs to the crop and CO2 emissions; (3) identify the strategies, derived from the synergy between conservation agriculture and PA, so as to decrease the CO2 emissions of agricultural systems. The validated SALUS simulation showed a significant reduction in SOC losses in minimum tillage (MT) and no-tillage (NT), 17% and 63% respectively, compared to conventional tillage (CT). Furthermore, the adoption of conservation tillage techniques decreased carbon emissions related to farming operations, while PA technologies led to an optimization of the exhaustible sources such as fossil fuels and fertilizers. Finally, the synergy between conservation tillage systems, especially NT, and PA strategies represents a useful tool in terms of carbon emissions mitigation with a reduction of 56% of total CO2 as compared to CT.
During soil development, bacteria and fungi can be differentially affected by changes in soil biogeochemistry. Since the chemistry of parent material affects soil pH , nutrient availability, and indirectly litter quality, we hypothesize that parent material has an important influence on microbial community patterns during long‐term soil development.
In this paper, we tested for the effect of parent material, as well as, soil and litter properties upon microbial community patterns in three c. 20 000‐year‐old semi‐arid chronosequences developed on sedimentary and volcanic (i.e. Andesitic and Dacitic) soils in the Dry Puna of Bolivia. We evaluated microbial patterns by analysing the terminal restriction fragment length polymorphism from amplified bacterial 16S rRNA genes, and the fungal internal transcribed spacer region, and quantitative real‐time polymerase chain reaction.
Soil and litter characteristics differed significantly between the Sedimentary and volcanic chronosequences. In particular, soil pH was alkaline in all stages of the Sedimentary chronosequence; whereas it changed from alkaline to near neutral across stages in both volcanic chronosequences. Composition of bacterial communities changed across volcanic chronosequences, and this change was associated with a reduction in soil pH and increases in litter quality, whereas no differences were found in the Sedimentary chronosequence. Fungal community composition, in contrast, did not change across any chronosequence.
Relative microbial abundance, expressed as the fungal:bacterial ratio, declined across stages of the Sedimentary chronosequence in association with decreases in TC and TP , whereas in the Andesitic chronosequence decreases in fungal:bacterial ratios were related with increases in litter quality and declines in soil pH .
Synthesis . Our results show the importance of parent material in affecting bacterial and fungal communities during soil development. Further, in semi‐arid chronosequences, fungal:bacterial ratios tend to decline given that soil pH in young soils is rather alkaline. Our results also are consistent with the general framework that highlights the importance of above‐ground (i.e. litter quality) and below‐ground (i.e. soil properties) in affecting microbial relative abundance and community composition during soil development.
Strongly supersaturated homogeneous calcium citrate solutions are formed spontaneously when solid sodium citrate and solid calcium hydroxycarboxylates are dissolved simultaneously in water or when solid sodium citrate is dissolved in an already saturated aqueous solution of the calcium hydroxycarboxylate at ambient conditions. Maximal supersaturation of calcium citrate was found to decrease for an increasing value of the stability constant for calcium binding: L-lactate < D-gluconate < citrate, indicating citrate assisted dissolution through competitive complex formation as a thermodynamic factor controlling spontaneous supersaturation for up to a factor of more than twenty. Time elapsing prior to initiation of precipitation of calcium citrate was found to be shorter for a higher degree of supersaturation and lasted between hours and days. During subsequent precipitation equilibrium solubility of calcium citrate was approached with a simultaneous increase in water activity. Both thermodynamic and kinetic factors are suggested to be important for the spontaneous supersaturation, which seems to explain the paradoxal but well-stablished high bioavailability of calcium from the sparingly soluble calcium citrate and the high mobility of calcium in the presence of citrate during biomineralization.
Slag-based silicate fertilizer has been widely used to improve soil silicon- availability and crop productivity. A consecutive early rice-late rice rotation experiment was conducted to test the impacts of steel slag on soil pH, silicon availability, rice growth and metals-immobilization in paddy soil. Our results show that application of slag at a rate above higher or equal to 1 600 mg plant-available SiO2 per kg soil increased soil pH, dry weight of rice straw and grain, plant-available Si concentration and Si concentration in rice shoots compared with the control treatment. No significant accumulation of total cadmium (Cd) and lead (Pb) was noted in soil; rather, the exchangeable fraction of Cd significantly decreased. The cadmium concentrations in rice grains decreased significantly compared with the control treatment. In conclusion, application of steel slag reduced soil acidity, increased plant–availability of silicon, promoted rice growth and inhibited Cd transport to rice grain in the soil-plant system.
Char-based adsorbents (char-FeCl3, char-FeCl2, and char-FeCit) derived from cotton textile waste (CTW) were synthesized by one-step low-temperature pyrolysis approach with different iron salts. The properties of the samples were conducted by BET, SEM, EDS, XRD, XPS, TEM, and FTIR. The results suggested that the surface areas of char-FeCl3 and char-FeCl2 were higher than those of char-FeCit. The presence of Fe2O3 as well as pyrolysis gas (HCl (g) and H2O (g)) could catalyze the formation of porosity. Meanwhile, FeCl3 showed the strongest catalysis effect to decompose cellulose to produce char. The pyrolysis process analysis was investigated by means of thermogravimetry-DSC. FeCl3 and FeCl2 could accelerate the breakage of cellulose structure whereas FeC6H5O7 was not beneficial to form char at low temperature as the incomplete decomposition of citrate. The adsorption property of Cr(VI) for the chars was evaluated. Adsorption processes were fitted well with the Freundlich model, and char-FeCl3 presented the best adsorptive capacity (70.39 mg/g). Thus, this low-temperature pyrolysis method was economical and technologically simplified as well as efficient adsorption capacity of Cr(VI) removal.
Graphical abstract
Several industrial waste from metal industries in the UAE have been identified to be recycled as low-cost materials for high-temperature thermal energy storage (TES) systems development. Electric arc furnace (EAF) slag, ladle furnace (LF) slag, aluminum pot skimming (APS) and aluminum white dross (AWD) have been chemically and thermally characterized. Chemical analysis showed that these materials contain relatively inert components and are non-hazardous in general (neglected amount of heavy metals). In addition, except for APS, these wastes were in general stable at high temperatures up to 1100°C after performing one or two thermal cycles.
The target of the current metallurgical industry is to recycle and utilize all their by-products, so as
to close the sustainable production loop. Slags are the important wastes and by-products of
metallurgical industry, which have been treated, recycled and used worldwide. The present paper
summarizes the current status of utilization of the various slags from ferrous and non-ferrous
metal production, as well as waste incineration, and recycling of salt fluxes in secondary metal
production. In addition, the environmental issues of the metallurgical slags are addressed. The
metallurgical oxide slags have stone-like properties and, thus, their major applications are in civil
engineering field. The slags should be recycled, modified and processed in a proper way, by
taking the environmental impact into consideration. With the treatment of salt slags for melting
aluminium scraps, as an example, the recycling and elution properties of the salt slags are
discussed. Our research indicates that the viscosity of the salt flux is increased with addition of
non-metallic components, that a certain percentage of fines remain in suspension, which
determines the viscosity, affecting the settling of heavier materials. High slag viscosity will lead
to more fine aluminium metal entrapped in the salt slag (may also be seen as a high temperature
slurry), and thus increase the load of salt slag recycling.
Keywords: recycling, environment, metallurgy, slags, fluxes, salts.
Haloalkaliphiles are polyextremophiles adapted to grow at high salt concentrations and alkaline pH values. In this work, we isolated 122 haloalkaliphilic bacteria upon enrichments of 23 samples from 5 distinct saline systems of southern Tunisia, growing optimally in media with 10% salt and at pH 10. The collection was classified into 44 groups based on the amplification of the 16S-23S rRNA internal transcribed spacers (ITS-PCR). Phylogenetic analysis and sequencing of the 16S rRNA genes allowed the identification of 13 genera and 20 distinct species. Three gram-positive isolates showing between 95 and 96% of 16S rRNA sequence homology with Bacillus saliphilus could represent new species or genus. Beside the difference in bacterial diversity between the studied sites, several species ecological niches correlations were demonstrated such as Oceanobacillus in salt crust, Nesterenkonia in sand, and Salinicoccus in the rhizosphere of the desert plant Salicornia. The collection was further evaluated for the production of extracellular enzymes. Activity tests showed that gram-positive bacteria were mostly active, particularly for protease, lipase, DNase, and amylase production. Our overall results demonstrate the huge phenotypic and phylogenetic diversity of haloalkaliphiles in saline systems of southern Tunisia which represent a valuable source of new lineages and metabolites.
A promising type of steel slag for applications is the ladle furnace (LF) slag, which is also known as the basic slag, the reducing slag, the white slag, and the secondary refining slag. The LF slag is a byproduct from further refining molten steel after coming out of a basic oxygen furnace (BOF) or an electric arc furnace (EAF). The use of the LF slag in further applications requires knowledge of its characteristics. The LF slag characterization in this paper has been performed using the following analytical methods: chemical analysis by energy dispersive spectrometry (EDS), mineralogical composition by X-ray diffraction (XRD), surface area properties by the Brunauer-Emmett-Teller (BET) and the Barrett-Joyner-Halenda (BJH) methods, surface chemistry by infrared absorption (FTIR) spectroscopy, and morphological analysis by scanning electron microscopy (SEM). The results showed that the main compounds are calcium, silicon, magnesium, and aluminium oxides, and calcium silicates under their various allotropic forms are the major compounds in the LF slag. Surface area properties have shown that the LF slag is a mesoporous material with relatively great BET surface area. The ladle furnace slag is a nonhazardous industrial waste because the ecotoxicity evaluation by its eluate has shown that the LF slag does not contain constituents which might in any way affect the environment harmfully.
The feasibility of steel slag used as an iron fertilizer was studied in a pot experiment with corn. Slag alone or acidified slag was added to two Fe-deficient calcareous soils at different rates. Results showed that moderate rates (10 and 20 g kg−1) of slag or acidified slag substantially increased corn dry matter yield and Fe uptake. Application of steel slag increased the residual concentration of ammonium bicarbonate-diethylenetriamine pentaacetic acid (AB-DTPA) extractable Fe in the soils. The increase of extractable Fe was usually proportional to the application rate, and enhanced by the acidification of slag. Steel slag appeared to be a promising and inexpensive source of Fe to alleviate crop Fe chlorosis in Fe-deficient calcareous soils.
The steel-making slag (SMS), a by-product of steel manufacturing process with an alkaline pH (11–12) and high amount of iron
(Fe) and calcium (Ca) oxides, was used to reduce arsenic (As) phytoextractability. The by-product was selected as an alternative
to commercial Fe oxides, which can decrease plant uptake, but they are expensive if used as amendments of contaminated arable
soils. SMS was applied at rates 0, 2, 4, and 8Mgha−1 to an As (1N HCl-extractable As 25mgkg−1) contaminated soil prepared by mixing non-contaminated soil and mine tailings and cropped to radish (Raphanus sativa L.) seeding. Calcium hydroxide (Ca(OH)2), a common liming material in Korea, was applied at the same rates for comparison. Steel-making slag more effectively suppressed
radish As uptake and increased yield than Ca(OH)2 due to stronger As immobilization because it significantly increased extractable Fe concentration and decreased extractable
As. The SMS-treated soil showed an apparent increase in As chemisorbed by Fe and Al oxides and hydroxides of surface soil,
As associated at the Fe and Al oxides and hydroxides of internal surfaces of soil aggregates, and Ca-associated As. The steel-making
slag can be a good soil amendment to suppress As phytoextractability and improve nutrient balance in As-contaminated soil.
KeywordsArsenic-As immobilization-Plant As uptake-Steel-making slag (SMS)
Calcareous soils are frequently characterized by the low bioavailability of plant nutrients. Consequently, many vascular plant species are unable to successfully colonize calcareous sites and the floristic composition of calcareous and acid silicate soils has been shown to differ markedly. The root exudation of oxalate and citrate has been suggested to play a pivotal role in same nutrient acquisition mechanisms operating in calcareous soils. The aim of this study was therefore to investigate the nutrient extraction efficiency of three individual organic acids commonly identified in root exudates, i.e. citric, malic and oxalic acid. Our results clearly demonstrate the context dependent nature of nutrient release by organic acids. The degree of P extraction was highly dependent on which organic acid was added, their concentration and pH, and their contact time with the soil. P is generally more efficiently extracted by organic acids at a high pH and follows the series oxalate>citrate>malate. The opposite relationship between pH and extraction efficiency was apparent for most other cations examined (e.g. Zn, Fe), which are more efficiently extracted by organic acids at low pH. A serious constraint to the ecological importance of organic acid exudation in response to P deficiency is, however, their very low P mobilization efficiency. For every mol of soil P mobilized, 1000 mol of organic acid has to be added. It can, however, be speculated that in a calcareous soil with extremely low P concentrations it is still beneficial to the plants to exude organic acids in spite of the seemingly high costs in terms of carbon.
Plant mineral nutrition has immense significance for crop productivity and human well-being. Soil acidity plays a major role in determining the nutrient availability that influences plant growth. The importance of calcium (Ca) in biological processes, such as signaling, metabolism, and cell growth, underlines its critical role in plant growth and development. This review focuses on soil acidification, a gradual process resulting from cation leaching, fertilizer utilization, and drainage issues. Soil acidification significantly hampers global crop production by modifying nutrient accessibility. In acidic soils, essential nutrients, such as nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), and Ca become less accessible, establishing a correlation between soil pH and plant nutrition. Cutting-edge Ca nutrition technologies, including nanotechnology, genetic engineering, and genome sequencing, offer the potential to deliver Ca and reduce the reliance on conventional soluble fertilizers. These fertilizers not only contribute to environmental contamination but also impose economic burdens on farmers. Nanotechnology can enhance nutrient uptake, and Ca nanoparticles improve nutrient absorption and release. Genetic engineering enables the cultivation of acid-tolerant crop varieties by manipulating Ca-related genes. High-throughput technologies such as next-generation sequencing and microarrays aid in identifying the microbial structures, functions, and biosynthetic pathways involved in managing plant nutritional stress. The ultimate goal is to shed light on the importance of Ca, problems associated with soil acidity, and potential of emerging technologies to enhance crop production while minimizing the environmental impact and economic burden on farmers.
Inoculation with plant growth-promoting bacteria (PGPBs) has remarkably increased yield and nutrient uptake of crop plants. The objective of this study was to evaluate the effect of bacterial inoculation with Azospirillum brasilense, Bacillus subtilis and Pseudomonas fluorescens on growth, accumulation of nutrients as well as N-NH 4 + and N-NO 3 − in hydroponic arugula plants. The research was carried out in a nutrient film technique (NFT) system and designed in randomized blocks with 5 replications. The treatments consisted of inoculation with A. brasilense, B. subtilis and P. fluorescens via nutrient solution at a dose of 0.1 mL L − 1 and without inoculation treatment. Inoculation with P. fluorescens promoted N-NH 4 + accumulation in shoots and roots by 311% and 119% respectively as compared to non-inoculated plants. Inoculations with A. brasilense, B. subtilis and P. fluorescens reduced N-NO 3 − accumulation in shoots and roots by18 and 14% as compared to without inoculation treatments. Fresh and dry mass of roots, root volume and leaf chlorophyll index were increased with inoculation of P. fluorescens and being considered the most suitable inoculant for hydroponic arugula cultivation. Inoculation with A. brasilense, P. fluorescens and B. subtilis reduced shoot N-NO 3 − accumulation, thus benefiting human health.
Alkali-activated slag Rheological behavior Mineral admixture Surface free energy Interparticle force A B S T R A C T This study investigates the effect of low surface free energy mineral admixtures (CaF 2-dominated fluorite (FL) and fluorine-containing lithium slag (LS)) on the rheological behavior of alkali-activated slag (AAS) pastes. The fluidity, rheological behavior, surface charge properties and surface free energy properties were tested. The interparticle forces based on extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory were calculated to understand the mechanism for the rheological behavior improvement. The results revealed that both FL and LS could improve the fluidity and decrease the yield stress and plastic viscosity of AAS pastes. Furthermore, the attraction is manifested by the sum of electrostatic, van der Waals, and Lewis acid-base forces, and this value decreases with increasing LF or LS content, implying that the particle dispersion in AAS pastes is improved. Furthermore, observing flocculent structures captured by the metallographic microscope proves the better dispersion of AAS pastes after adding FL and LS. Moreover, incorporating LS or FL decreases the flexural and compressive strengths of AAS mortars.
Incorporating amendments of industrial waste such as biochar and steel slag in cropland has been used to enhance the storage of soil organic carbon (SOC) while sustaining crop production. Short-term laboratory and field studies have identified important influences of biochar on active SOC fractions associated with soil microbial activity in paddy soils, but the long-term effects remain poorly understood. To address these knowledge gaps, we examined the effects of slag, biochar, and slag+biochar treatments on total SOC concentration, active SOC fractions and soil microbial communities in a paddy field two years after incorporation. Across both two seasons, the addition of slag, biochar, slag+biochar increased soil salinity by 26–80%, 1.3–37% and 42–79%, and also increased soil pH by 0.8–5.7%, 2.1–2.4% and 4.0–6.3%, respectively, relative to the control. SOC concentration was higher in the slag, biochar, and slag+biochar treatments across both rice seasons by 4.3–5%, 0.5–17% and 4.3–7%, respectively. Soil C-pool activity and C-pool management indices in the late paddy season were significantly lower in the slag+biochar treatment than the control by 26.3 and 21.3%, respectively, indicating that the amendments contributed to the stability of SOC. The C concentrations of the biochar and slag amendments affected bacterial abundance more than fungal abundance and affected C cycling. Our study suggests that combined slag and biochar amendments may increase bacterial abundance that may maintain SOC storage and reduce the abundances of potential SOC decomposers in key functional genera, indicating strong coupling relationships with changes of soil properties such as salinity, pH, and SOC concentration. These outcomes due to the amendments (e.g. slag+biochar) may increase microbial C-use efficiency and support the stability of active SOC fractions, with opportunities for long-term C sequestration.
Slags are a co-product produced by the steel manufacturing industry and have mainly been utilised for aggregates in concreting and road construction. The increased utilisation of slag can increase economic growth and sustainability for future generations by creating a closed-loop system, circular economy within the metallurgical industries. Slags can be used as a soil amendment, and slag characteristics may reduce leachate potential of heavy metals, reduce greenhouse gas emissions, as well as contain essential nutrients required for agricultural use and environmental remediation. This review aims to examine various slag generation processes in steel plants, their physicochemical characteristics in relation to beneficial utilisation as a soil amendment, and environmental implications and risk assessment of their utilisation in agricultural soils. In relation to enhancing recycling of these resources, current and emerging techniques to separate iron and phosphorus slag compositions are also outlined in this review. Although there are no known immediate direct threats posed by slag on human health, the associated risks include potential heavy metal contamination, leachate contamination, and bioaccumulation of heavy metals in plants, thereby reaching the food chain. Further research in this area is required to assess the long-term effects of slag in agricultural soils on animal and human health.
A large volume of slag is generated as a by-product during steel manufacturing. In order to ensure environmental and economic sustainability, it is imperative to find innovative solutions for the efficient recycling of slag. This review broadly and critically explores the available information concerning the effective recycling of slag in agriculture and its potentials in crop yield, soil conditioning, greenhouse gas (GHG) emissions, soil carbon sequestration, and heavy metal stabilization in contaminated soils. An agronomic assessment of GHG emissions and environmental concerns related to potential contamination of heavy metals in the food chain have also been evaluated. Existing literatures documents a range of impacts that slag fertilization can be effective in increasing crop yield, mitigating GHG emissions, and decreasing yield-scaled global warming potential. Heavy metal accumulation in soil and their uptake by the plant are not consistent with the application of slag, mostly accumulated in roots, and very low translocation level in grains/fruits. In order to secure the reliability of recycling slag in agriculture, regulatory compliance related to environmental problems, novel technological solutions to improve the quality of slag, and strategic planning to expand its market value need great attention.
Ladle furnace slag (LFS) has great potential as a new type of cementitious material, but the important value has not been effectively used at present. One of the main reasons is that the over-burned free MgO (f-MgO) and free CaO (f-CaO) in LFS would cause the volume expansion of material. In this study, the f-MgO and f-CaO phases in LFS are optimized by air quenching treatment. It was found that the size of f-MgO is reduced from 30-45μm to 2.5-3.5μm, which is about an order of magnitude lower. The f-CaO is distributed in the leaf-like morphology with smaller size in the range of 15-20μm. The f-MgO and f-CaO in air-quenched modified LFS (MLFS) can be dispelled in the early hydration stage. Compared with LFS, the volume expansion of blended cement with 20% MLFS is reduced by more than 10%, showing an obvious improvement effect on volume stability.
Waste amendments, such as steel slag and biochar, have been reported as a strategy for improving soil fertility, crop productivity, and carbon (C) sequestration in agricultural lands. However, information regarding the subsequent effects of steel slag and biochar on C cycling and the underlying microbial mechanisms in paddy soils remains limited. Hence, this study aimed to examine the effect of these waste amendments (applied in 2015–2017) on total soil CO2 emissions, total and active soil organic C (SOC) contents, and microbial communities in the early and late seasons in a subtropical paddy field. The results showed that despite the exogenous C input from these waste amendments (steel slag, biochar and slag + biochar), they significantly (P < 0.05) decreased total CO2 emissions (e.g., by 41.9–59.6% at the early season), compared to the control soil. These amendments also significantly (P < 0.001) increased soil salinity and pH. The increased soil pH had a negative effect (r = −0.37, P < 0.05) on microbial biomass C (MBC). The biochar and slag + biochar treatments (cf. control) significantly (P < 0.001) increased SOC contents in the both seasons. The amendments altered the soil microbial community structure that associated with soil C cycling: (1) all three amendments increased the relative abundance of Agromyces and Streptomyces, which was associated with higher soil pH (cf. control); and (2) biochar and slag + biochar treatments caused a higher relative abundance of Sphingomonas, which was supported by high SOC contents under those amendments. Overall, this study demonstrated that the steel slag and biochar amendments altered microbial community composition due to changes in key soil properties, such as salinity, pH and SOC contents, with implications for increasing soil C stocks while mitigating CO2 emissions in the paddy field.
Steel slag, in particular, basic oxygen furnace slag (BOF-S)-a by-product in the steelmaking industry-is an environmental challenge due both to the large volume of the material that is produced annually and its potentially detrimental environmental impacts. Globally, waste generation and management has become a critical issue with waste prevention and recycling rates reportedly too low to keep up with the growing rate of production. In this regard, considerable research has been done to improve traditional applications as well as explore possible reuse options of BOF-S. Multiple, innovative, new technologies and uses have emerged, including BOF-S reuse as a cement binder, a neutralizing agent, an anti-microbial additive or as a carbon se-questration material. Many applications involve the treatment or processing of other waste products such as wastewater, contaminated soils or thin film transistor liquid crystal display waste. Even so, much still needs to be done for sizeable implementations and noticeable differences to be made in the BOF-S reuse field. Large slag dumps continue to exist and grow in many parts of the world as the global steel production rate increases on an annual basis. This paper presents an overview of BOF-S characteristics and composition and discusses how these qualities contribute to the range of possible applications of the by-product. The applications for use of BOF-S presented herein, range from novel, small-scale applications and extends to well-established, large-scale uses.
Steel slags can be used in agriculture, as they are composed of CaO, MgO, SiO2, and compounds such as P2O5, FeO, and MnO. The solubility of slag may be higher than that of lime, which can make this residue an excellent source for soil acidity correction in no-till systems. However, there are few studies reporting their benefits when applied to the soil surface. This study evaluated slag amendment effects on soil chemical attributes and on the yield and nutrient uptake of soybean following surface application and/or incorporation of different types of slag, in comparison to lime, on a tropical, acidic soil under a no-till system. The trial was performed in Botucatu, SP, Brazil. Six soil-acidity corrective materials were incorporated or surface-applied, including steel slag, ladle slag, stainless-steel slag, wollastonite, dolomitic lime, and calcined dolomitic lime, plus a negative control. Each material dose was calculated to raise the base saturation to 70%. Slags can be applied in a no-tillage system with efficiency similar to that of lime for the neutralization of soil acidity, for adequate nutrition and yield of the soybean crop. Slags and limes showed similar effects on increased pH, decreased Al³⁺concentration, and increased base saturation up to the 0.40 and 0.20-m soil layers at 12 and 23 months, respectively, after the application of treatments, regardless of surface or incorporated application. The by-product application has an additional advantage, depending on the type of slag, that is the provision of phosphorus and/or silicon.
Three main lignocellulosic components (lignin, cellulose and hemicellulose) are major plant cell walls. Their content in biomass crops, for example, MD2 pineapple waste will affect the heating values (HHV) if uses as a feedstock for the solid biofuel (biocoke). The aim of this paper is to identify the amount of lignocellulosic content in the MD2 pineapple waste and its effect on heating value. The experiment and parameters setup were carried out by following the chemical composition determination of standard methods. The process involved the sample preparation and treatment process by using NaOH and sodium chlorite for bleaching purposes. The effect of a percent of the lignocellulosic content in the MD2 pineapple waste before and after bleaching process towards heating value was studied. From the result, lignocellulosic in leaves (Cellulose 30 wt%, Hemicellulose 37 wt% and Lignin 22 wt%) showed the similarities (slightly higher and lower) content compared to the stem (Cellulose 46 wt%, Hemicellulose 29 wt% and Lignin 17 wt%) and root (Cellulose 42 wt%, Hemicellulose 32 wt% and Lignin 19 wt%). The majority of the leaves for the whole non-woody plant will give the cumulative effects since the quantity of stem and root is only about 15 % of the total weight of the plant. The cellulose and hemicellulose produce different thermal stability due to their different chemical structure even though they are both polysaccharides. From the data, all parts of MD2 pineapple has high cellulose and hemicellulose content. The hemicellulose can indicate the ignition temperature and time to ignite of the biocoke product produce by MD2 pineapple waste same goes to the cellulose content. The decomposition of lignin from start to end of the burning process can be an indicator that the biocoke product produces from MD2 pineapple waste can withstand up until 900 °C or above with some additional reactor or chemical that can enhance its thermal properties.
There is increasing evidence that the origins of organic acids (OAs) are as important as their roles and pathways of production. This review focuses on information about challenges associated with various aspects of OA production and release in the soil with the primary intention of harmonising different views to enable better understanding of this topic.A considerable body of work devoted to the understanding of origins, roles and dynamics of OAs in soil has been critically scrutinised for their various positions in this review. Organic acids in the soil originate from a variety of sources that may include plant roots, microorganisms and organic decomposition. Although OA synthesis in the soil environment may reflect a natural response of biological systems to biotic and abiotic stresses, they also play crucial roles in physiochemical processes such as mineralisation and solubilisation of poorly available and complex minerals as well as contribution to the carbon cycle and detoxification of metals. However, these roles are conceivably a pooled effect of soil OAs interacting with other factors (soil type, soil pH, microbes and other metabolites). The key challenge to elucidate and unravel the dynamics of OAs in the soil lies with the ability to explain and understand how OAs are released in the rhizosphere alongside other important metabolites, which perhaps influence the dynamics.
Approximately 21 million tons of steel industry slag are produced each year in the United States, and many productive commercial uses of slag have been developed (e.g., road bed, fill material). However, because slag contains heavy metals at concentrations that are higher than in most soil, questions have been raised regarding the need to evaluate the potential human health and environmental hazards associated with current applications. To enhance general understanding of the physical and chemical characteristics of this material, slag samples from 58 active mills with blast furnaces, basic oxygen furnaces, and/or electric arc furnaces were examined. This study profiles the major and minor constituents of slag from each furnace type and reports the leachability of metals from slag under neutral and acidic conditions. Particle size distributions and partitioning coefficients (Kd) are also reported. Although concentrations of metals in slag are elevated relative to concentrations in soil, the metals in slag are tightly bound to the slag matrix and not readily leached. This study represents the most complete characterization of steel industry slag currently produced in North America, encompassing mills that collectively produce over 47% of steel industry slag. These data provide insights that may be useful for evaluating the marketability of steel industry slag and for human and ecological health risk assessment of environmental applications.
Background and aims
Alkaline soils, characterized by high pH, are representative of degraded regions throughout the world. Studying germination in relation to alkalinity can contribute to understanding how species cope with such conditions. Although the effects of pH have been widely studied, it is unknown whether germination response to pH gradients created with buffer solutions is representative of the conditions experienced in alkaline soils. Our aims were to (1) determine if high pH gives an accurate assessment of the effects of alkaline soils on germination, and (2) identify the inhibitory factors for germination in alkaline soils.
Methods
Using Leymus chinensis seeds, germination was tested over a gradient of pH solutions prepared using Tris (50 mM and 100 mM) and H2O buffers and eight germination media prepared from non-alkaline and alkaline soils with different pH and electrical conductivities (EC). Additionally, solutions of 10–100 mM NaCl, Na2SO4, Na2CO3 and NaHCO3 were used to determine the main ions inhibiting seed germination.
Results
H2O-buffered pH had no effect on seed germination, and seed germination was much lower at all pH levels in 50 mM Tris–HCl solutions (pH 7.0–10.35) than in the H2O control (pH 7.05). No seeds germinated in 100 mM Tris–HCl buffers irrespective of the pH. In alkaline germination media (pH 10.04–10.61), high germination was obtained only at low EC. The rank order of the inhibitory effect of salts was Na2CO3 > NaHCO3 > NaCl > Na2SO4.
Conclusions
Buffer solutions used to simulate alkaline environments did not provide a reliable indicator of the effects of alkaline soils on seed germination. High pH of alkaline soil had no negative effects, and results suggest that salt composition and concentration, especially CO3 2− and HCO3 −, are key inhibitors.
This research aims to investigate the effect of using electric arc furnace (EAF) steel slag as coarse aggregate in concrete. Properties of fresh and hardened concrete were evaluated for five concrete mixtures with different grades (30, 50 and 70 MPa), and the inclusion of supplementary cementing materials (SCM) such as fly ash class F (FA) and silica fume (SF). EAF steel slag beneficially affected the engineering properties (i.e. physical, mechanical and durability) of the produced concrete. Also, it would be more beneficial if the grading of the produced EAF steel slag is controlled and adjusted to better improve the quality of the produced concrete.
Root colonization by Bacillus amyloliquefaciens is directly related to bacterial growth, chemotaxis, biofilm formation, and the interaction with host plant root exudates. In this study, root exudates were collected from two tomato plant varieties that supported bacterial cell division and induced the B. amyloliquefaciens T-5 chemotactic response, even at the concentration of 10 μg ml−1. Root exudates also induced biofilm formation, but lower than control treatment. In addition, five organic acids were identified in the root exudates and subsequently evaluated. Malic acid, citric acid, succinic acid and fumaric acid significantly induced the chemotaxis response and swarming motility. Maximal chemotactic response and swarming motility were induced by malic acid, and all the organic acid did not have a significant effect on biofilm formation. Furthermore, these organic acids promoted the B. amyloliquefaciens T-5 recruitment under gnotobiotic conditions, increasing the rhizosphere bacterial population. This data suggested that tomato root colonization by B. amyloliquefaciens T-5 was influenced by organic acids secreted by roots. This study expands our understanding of B. amyloliquefaciens T-5 colonization on tomato roots under natural conditions and reflects the significance of B. amyloliquefaciens T-5 strain as biocontrol agent which will be useful for preparing formulations for the better control of plant wilt diseases.
Agricultural practices mostly influence methane (CH4) emissions from rice field, which must be controlled for maintaining the ecosystem balance. No-tillage farming with chemical amendments having electron acceptors could be an effective mitigation strategy in CH4 emissions from irrigated rice (Oryza sativa L.) field. An experiment was conducted in Korean paddy field under tillage and no-tillage farming practices with silicate iron slag amendments (1–4 Mg ha−1) for suppressing CH4 emissions and maintaining rice productivity. It was found that CH4 emissions from the no-tillage rice field significantly decreased as compared to that of tilled field, irrespective of silicate amendments. The total seasonal CH4 flux from the control tillage and control no-tillage plots were recorded 38.1 and 27.9 g m−2, respectively, which were decreased by 20% and 36% with 4 Mg ha−1 silicate amendment. Silicate fertilization (4 Mg ha−1) with no-tillage system decreased total seasonal CH4 flux by 54% as compared to that of control tillage plot. This is most likely due to the higher concentrations of active iron and free iron oxides in the no-tilled rice field as compared to that of tilled field under silicate fertilization, which acted as electron acceptors and contributed to decrease CH4 emission. In addition, the improved soil porosity and redox potential, rice plant growth parameters such as active tillering rate, root volume and porosity, etc. in combination increased the rhizosphere oxygen concentrations and eventually suppressed CH4 emission during the rice growing season. The leaf photosynthetic rate was significantly increased with 4 Mg ha−1 silicate amendment, which ultimately increased grain yield by 18% and 13% in the tilled and no-tilled rice field, respectively. CH4 flux showed a strong positive correlation with the availability of soil organic carbon, while there were negative correlations with soil porosity, soil pH, soil Eh, and the content of active iron and free iron oxides in soil.
To assess the mobilities of Pb, Cd, and Zn from a contaminated soil, the effects of redox potential and pH value on metal solubilities were investigated. Both redox potential and pH were found to greatly affect heavy metal solubility in the soil. Results showed that the soil suspension under continuous oxygen aeration for 21 days resulted in increases of redox potential from 290 to 440 mV and pH value from 6.9 to 7.0, respectively. Soluble concentrations of Pb, Cd, and Zn varied with time, and were all lower than 1 mg kg–1. When the soil suspension was aerated with nitrogen, final redox potential was –140 mV and pH value of 7.1. The soluble metal concentrations were slightly higher than those aerated with oxygen. The equilibrium solubility experiments were conducted under three different pH values (3.3, 5.0, 8.0) and three redox potential (325, 0, –100 mV). Results showed that metals were sparingly soluble under alkaline conditions (pH = 8.0). Metal solubilities were higher when under slightly acidic conditions (pH = 5.0), and increased drastically when pH was kept at 3.3. When solubilities were compared under same pH values, it was observed that metal solubilities increased as redox potential decreased. Generally speaking, acidic and reducing conditions were most favorable for metal solubilization, and the effect of pH was more significant than that of redox potential. It was proposed that heavy metals were mostly adsorbed onto Fe-Mn oxyhydroxides. The pH-dependent metal adsorption reaction and the dissolution of Fe-Mn oxyhydroxides under reducing conditions was the mechanism controlling the release of heavy metals from soils.
Basic oxygen furnace steel slag is the most common steel slag in China. In this study, the hydration properties of this kind of steel slag were investigated. Steel slag was ground separately to 458 m2/kg as well as 506 m2/kg. Different hydration conditions were set by changing the temperature or pH value. Hydration exothermic rate was measured within 4 days. Non-evaporable water content, hydration products and hardened paste morphologies were investigated at 1, 3, 7, 28 and 90 days. The results showed that the hydration process of steel slag was similar with that of cement. However, its hydration rate was much lower than cement. The hydration rate of steel slag at the early age could be accelerated by raising the fineness of particles, curing temperature or alkalinity of solution. However, raising the pH value of solution had little efficiency for the later hydration of steel slag and raising curing temperature even had negative influence on its later hydration. CSH gel and Ca(OH)2 were the main hydration products of steel slag. A part of C3S and C2S crystal in steel slag had very low activity and unhydrated after 90 days. RO phase was almost inert. The interface between the particles of RO phase and CSH gel was a weak region in the system.
Ectomycorrhiza-forming fungi (EMF) alter the nutrient-acquisition capabilities of vascular plants, and may play an important role in mineral weathering and the partitioning of products of weathering in soils under nutrient-limited conditions. In this study, we isolated the weathering function of Suillus tomentosus in liquid-cultures with biotite micas incubated at room temperature. We hypothesized that the fungus would accelerate weathering by hyphal attachment to biotite surfaces and transmission of nutrient cations via direct exchange into the fungal biomass. We combined a mass-balance approach with scanning electron microscopy (SEM) and atomic force microscopy (AFM) to estimate weathering rates and study dissolution features on biotite surfaces. Weathering of biotite flakes was about 2–3 orders of magnitude faster in shaken liquid-cultures with fungus compared to shaken controls without fungus, but with added inorganic acids. Adding fungus in nonshaken cultures caused a higher dissolution rate than in inorganic pH controls without fungus, but it was not significantly faster than organic pH controls without fungus. The K+, Mg2+ and Fe2+ from biotite were preferentially partitioned into fungal biomass in the shaken cultures, while in the nonshaken cultures, K+ and Mg2+ was lost from biomass and Fe2+ bioaccumulated much less. Fungal hyphae attached to biotite surfaces, but no significant surface changes were detected by SEM. When cultures were shaken, the AFM images of basal planes appeared to be rougher and had abundant dissolution channels, but such channel development was minor in nonshaken conditions. Even under shaken conditions the channels only accounted for only 1/100 of the total dissolution rate of 2.7 × 10−10 mol of biotite m−2 s−1. The results suggest that fungal weathering predominantly occurred not by attachment and direct transfer of nutrients via hyphae, but because of the acidification of the bulk liquid by organic acids, fungal respiration (CO2), and complexation of cations which accelerated dissolution of biotite. Results further suggest that both carbohydrate source (abundant here) and a host with which nutrients are exchanged (missing here) may be required for EMF to exert an important weathering effect in soils. Unsaturated conditions and physical dispersal of nutrient-rich minerals in soils may also confer a benefit for hyphal growth and attachment, and promote the attachment-mediated weathering which has been observed elsewhere on soil mineral surfaces.
A novel colorimetric and fluorescent chemosensor based on a rhodamine 6G phenylurea conjugate showed highly selective and sensitive recognition toward acetate ions in H(2)O-CH(3)CN (1:1, v/v) with fluorescence intensity change and also clear color change from pink to colorless in the presence of Fe(III) ions.