Organo-mineral Complexes Research Articles

Soil Indicators of Paleoenvironmental Conditions in the South of the East European Plain in the Quaternary Time

Climatic conditions are an important factor affecting mineralogical and chemical compositions of soils and paleosols with the formation of paleosol archives that reflect major stages of the evolution of biogeosphere systems in the Quaternary period. In the steppe zone of the south of the East European Plain, two types of the “time capsules” storing information on paleoecosystems and paleoclimate of the Quaternary period are found. First, these are loess/paleosol complexes in coastal zone of the Sea of Azov and in the North Caucasus; their environmental records extend back into the Pleistocene for about 800 ka. Second, these are Holocene paleosols of archeological sites; they are buried under kurgans constructed in different periods of the Middle and Late Holocene. The completeness and reliability of paleoenvironmental reconstructions depend on the chosen study objects. For quantitative reconstruction of the environmental parameters in the past, independent methods based on the assessment and interpretation of soil solid-phase properties—magnetic. mineralogical, geochemical, isotopic, etc.—are to be applied. Detailed mineralogical study of paleosols coupled with the analysis of their organomineral complexes and variations in the concentrations of biophile and lithophile elements significantly increase the reliability of soil indicators of the paleoclimatic conditions. The sets of soil indicators obtained from the study of Holocene paleosols and loess/paleosol sequences in the Sea of Azov region allow us to estimate parameters of the paleoenvironment: paleotemperature, paleoprecipitation, and aridity of the climate.

Does Particulate Organic Matter Fraction Meet the Criteria for a Model Soil Organic Matter Pool?

There is a well-recognized need for improved fractionation methods to partition soil organic matter into functional pools. Physical separation based on particle size is widely used, yielding particulate organic matter (POM, i.e., free or “uncomplexed” organic matter > 50 μm) as the most labile fraction. To evaluate whether POM meets criteria for an ideal model pool, we examined whether it is: 1) unique, i.e., found only in the > 50 μm fraction and 2) homogeneous, rather than a composite of different subfractions. Following ultrasonic dispersion, sand (> 50 μm) along with coarse (20–50 μm) and fine (5–20 μm) silt fractions were isolated from a silt loam soil under long-term pasture at Lincoln, New Zealand. The sand and silt fractions contained 20% and 21% of total soil C, respectively. We adopted a sequential density separation procedure using sodium polytungstate with density increasing step-wise from 1.7 to 2.4 g cm−3 to recover organic matter (light fractions) from the sand and silt fractions. Almost all (ca. 90%) the organic matter in the sand fraction and a large proportion (ca. 60%–70%) in the silt fractions was recovered by sequential density separation. The results suggested that POM is a composite of organo-mineral complexes with varying proportions of organic and mineral materials. Part of the organic matter associated with the silt fractions shared features in common with POM. In a laboratory bio-assay, biodegradability of POM varied depending on land use (pasture > arable cropping). We concluded that POM is neither homogeneous nor unique.

Anticancer activity of Yashada Bhasma (bioactive nanoparticles of zinc): A human pancreatic cancer cell line study.

Background:Pancreatic ductal adenocarcinoma is the fourth leading cause of cancer-related mortality. Efforts to improve cancer treatment through nanotechnology are at the developmental stage, and it will be gracious if the drug with anticancer property itself is a nanoparticle. Bhasma is organomineral complexes which are bioactive nanoparticles. Yashada Bhasma (incinerated processed zinc) is widely used in Ayurveda for various diseases, and there are evidence that ZnO nanoparticles are promising antitumor agent. However, no studies have been conducted on the effectiveness of Yashada Bhasma in pancreatic cancer.Materials and Methods:Two types of test drugs, Parada Marita Yashada Bhasma (PMY) and Vanaspati Jarita Marita Yashada Bhasma (JMY), were prepared as per the guidelines of pharmaceutics of Ayurveda. Particle size analyses of Yashada Bhasma and Zeta potential study was carried out initially. Further human pancreatic cancer cell line (MIA PaCa-2) study was done using in vitro sulforhodamine B assay, keeping adriamycinas control. After 48 h of incubation, antiproliferative effects were assessed.Results:JMY and adriamycin showed dose-dependent growth inhibition of cancer cells. Both Yashada Bhasma samples showed a cytostatic effect at this concentration.Conclusion:The study leads to new avenues for cancer treatment by developing such unique and highly effective bioactive nano-sized therapeutic agent.

Sastav organsko-mineralnih kompleksa koji migriraju u zemljištu tipa Umbric Albeluvisols Abruptic

Sastav organsko-mineralnih kompleksa koji migriraju u zemljištu tipa Umbric Albeluvisols Abruptic

Roles of soil organic carbon and iron oxides on aggregate formation and stability in two paddy soils

Knowledges of aggregate stability and formation depending on soil organic carbon (SOC) and iron oxides are essential to the conservation of soil structure. In this work, the effects of SOC and different forms of iron oxides on the stability of aggregates of paddy soils were determined by applying the Le Bissonnais (LB) and extractions method by water, oxalate (OA), dithionite–citrate–bicarbonate (DCB), or hydrogen peroxide (H2O2). Two topsoils (0–20 cm) were selected based on two levels of SOC and iron oxides, high SOC (22.1 g kg−1)–low iron oxides (S1) and low SOC (8.50 g kg−1)–high iron oxides (S2) paddy soils from subtropical China. For the fast-wetting (FW) test, the percentage of 2–0.25 mm (34.0%) and >2 mm (42.2%) aggregate fractions were highest in S1 and S2, respectively. Both the soils had a >2 mm fraction that was above 60% under the slow-wetting (SW) and stirring after prewetting (WS) test. The free Fe oxide (Fe(DCB)) could increase in aggregate stability when SOC contents were low in S2. All three chemical extractions considerably decreased the >2 mm fractions (35.5–87.5%), and consequently increased the <0.053 mm fractions. The S1 soil presented the lower mean weight diameter (MWD) after DCB extractions, whereas it was no significantly different after OA or DCB extraction in S2 soil, indicating that Fe(DCB) had a greater effect on the stability of aggregates than amorphous Fe oxide (Fe(OA)) in the S1 soil, but both had the same effect for S2. The H2O2 treatment destructed>2 mm and 2–0.25 mm aggregates intensively, indicating that SOC was the major binding agent for aggregates of these sizes. The SOC was a key agent influencing soil aggregation not only in macro-aggregates (>0.25 mm) but also in micro-aggregates (0.25–0.053 mm) in the S1. The formation of aggregates in S1 was attributed to its higher content of organo-mineral complexes because the contents of SOC (3.30–11.2 g kg−1) were higher in >0.053 mm aggregates compared with S2 after H2O2 extractions. Fe oxides were the key agents for <0.25 mm aggregates formation. The MWD of the FW treatment was found to have a significant positive correlations with Fe(DCB), and MWD of the WS treatment proved significant positive correlations with SOC and Fe(OA) oxide, indicated that SOC and Fe oxides improved aggregate stability against external force collapse. This implies that the differential roles of SOC and Fe oxides in mechanisms of aggregate formation and stability in two paddy soils.

Humus composition and humification degree of humic acids of alpine meadow soils in the northeastern part of the Qinghai–Tibet Plateau

ABSTRACT The characteristics of humus composition are important for understanding the mechanism of carbon storage in the Qinghai–Tibet Plateau. The aim of this study was to characterize the quality of soil organic matter (SOM) in this region. Soil samples from four soil profiles in fenced study sites in the alpine grassland were collected at altitudes of 4200, 4000, 3800, and 3400 m, along the southwest facing slope in the Qilian Mountains. The humus composition and humification degree of the humic acid (HA) were determined by two methods: (1) extraction with 0.5% sodium hydroxide (NaOH) followed by 0.1 M sodium pyrophosphate (Na4P2O7) (OH-PP method); and (2) treating once with 0.1 M hydrochloric acid (HCl) followed by extracting with 0.5% NaOH (Cl-OH method). Physico-chemical analysis revealed higher exchangeable cation content and higher base saturation ratios could be related to slightly acidic to neutral soils, which could be regarded as calcium (Ca)-rich soils. The amounts of combined-form HAs obtained by HCl pretreatment (HACl – HAOH; ∆HACl) were remarkably higher than those extracted with Na4P2O7 (HAPP), indicating that the combined form of HAs is mainly Ca. In addition, the proportion of HAPP in the total HAs extracted with both NaOH and Na4P2O7 (HAOH + HAPP) obtained in the OH-PP method increased with soil depth and decreasing elevation, indicating that HAs associated with aluminum (Al) and iron (Fe) were distinguished in the subsoils of lower elevation. Therefore, the formation of the organo-mineral complex may contribute to stabilizing SOM in the Qinghai–Tibet Plateau. Moreover, Type A-HA with the highest degree of humification was obtained from the deeper horizons with the Cl-OH method and almost all horizons by extraction with Na4P2O7 in the OH-PP method. Further studies using various spectroscopic analyses are necessary to elucidate the chemical properties of SOM in this region.

PROPERTIES OF MODIFIED CONCRETE FOR SPECIAL PURPOSE STRUCTURES

Purpose. The paper is aimed at developing the scientific fundamentals of new-generation monolithic concrete technology for special purpose structures by controlling the processes of structure formation of a modified cement system under natural hardening conditions. Methodology. The kinetics of interaction between the cement system and aggregates was evaluated by microcalorimetry. The measurements were carried out continuously for 24 hours after preparation of the mixture. The differential and integral characteristics of the heat release of the solidifying system were recorded. Investigation of the rheological properties of concrete mixtures was carried out on the mixtures with 10...15 cm consistency. The microhardness of contact layers was investigated on concrete cubes with dimensions from 20×20×20 to 50×50×50 mm. When determining the structural characteristics, x-ray phase and differential-thermal analyzes of the concrete cement matrix were used. Infrared spectroscopy was used to determine the effect of physicochemical modification on the cement system. Tensile creep was studied over a wide load range from 0.2 R t to 0.8 R t . Findings. It is determined that the reason for changing the concrete properties of natural hardening is the change in its hygrometric and thermal state, as well as the harmonic fluctuations of these environmental factors. The hygrometry of concrete depends on the thermal moisture conditions of the environment, the type and composition of concrete, the massiveness of concrete elements. An analysis of these factors and experimental data made it possible to establish the exponential dependence of the change in the hygrometric state of monolithic natural hardening concrete. The change in the moisture state of concrete makes it possible to predict its volumetric deformations. Originality . For the first time, the features of the structure formation of a modified cement system are established, consisting in the fact that magnesium chloride hydrate crystals grow rapidly in the space between hydrated clinker minerals, and the resulting mechanical cohesion defines the development of initial strength and rigidity. Since the free growth of crystals is hampered by a lack of space, the crystals mutually intergrow, forming a dense structure, contributing to the growth of strength. The developed organo-mineral modifying complex provides disperse reinforcement of the cement matrix of concrete. Practical value . The obtained dependences of structural concrete stresses make it possible to analyze their effect on the structure of modified concrete: to determine the probability of formation around the filler particles of the plastic flow zone, the material microcrack formation zone, the crack initiation period, the microcrack onset conditions, and the change of elasticity modulus of the material caused by microcracks in its structure. Disperous modification of cement matrix allows to obtain durable concrete of special purpose with design operational properties. The developed binder disperse modification technology, the established features of the structure formation mechanism for the modified cement system, as well as the use of the principle of congruence of a complex of technological influences to the physico-chemical processes of hydration of clinker minerals allowed developing the scientific fundamentals for the special purpose concrete technology. This helps to expand the use of modified concrete in various types of construction.

Factors contributing to aggregate stability at different particle sizes in ultisols from Southern China

The main objective of this study was to investigate the effects of abiogenic and biogenic factors, and their interaction, on aggregate stability determined at different particle sizes. Soil samples with the same land use pattern were collected and fractioned into five aggregate sizes: 10–15 mm, 5–10 mm, 2–5 mm, 0.25–2 mm, and < 0.25 mm. Contents of iron/aluminum (Fe/Al) oxides, soil organic carbon (SOC), clay, and mean weight diameter (MWD) values for aggregates at different sizes were determined. The respective contributions of these factors were further estimated using path analysis. The results showed that SOC contents in A horizon declined with the increase of aggregate size. Highest amorphous iron oxide (Feo) contents were observed in 0.25–2 and 2–5 mm aggregates, but highest amorphous aluminum oxide (Alo) contents were found in 5–10 mm aggregates. Abiotic factors (Fe/Al oxides, clay) played a more important role in determining the formation of < 0.25 mm aggregates, whereas both abiotic and biotic factors play an effective role in stabilizing larger aggregates (0.25–2, 2–5, 5–10, and 10–15 mm). The organo-mineral complexes played a certain role in the stability of soil aggregates, especially the larger aggregates. We conclude that abiotic and biotic factors play variable roles in soil aggregates at different sizes, and more studies are needed to better assess their respective roles to improve our understanding of soil aggregation.

Impact of agricultural fertilization practices on organo-mineral associations in four long-term field experiments: Implications for soil C sequestration

Soil organic carbon (SOC) associated with minerals is considered to be one of the most fundamental long-term SOC storage strategies, but little research has integrated the organo-mineral complexes regulated by long-term fertilization. Here, soil samples under three fertilization treatments (Control, no fertilization; NPK, chemical nitrogen, phosphorus and potassium fertilization; NPKM, NPK plus manure) from four 23–34 years long-term field experiment sites across China were examined. Chemical analyses indicated that vigorous iron (Fe) mobilization could be regulated by long-term fertilization regimes. Meanwhile, Fe K-edge X-ray absorption near-edge fine structure (XANES) demonstrated that compared to NPK treated soils, NPKM treated soils contained significantly higher concentration of poorly crystalline ferrihydrite. Results from both the Fourier transform infrared combined with two-dimensional correlation spectroscopy analyses (FTIR-2DCOS) and C 1 s X-ray photoelectron spectroscopy (XPS) revealed that aliphatic carbohydrate might play an important role in binding exogenous Fe(III) in all tested four soils. In addition, greater amounts of aromatic C (the most resistant soil C fraction) were under long-term treated NPKM than NPK soils. Furthermore, multiple regression analyses showed a significantly positive relationship between poorly crystalline Fe minerals and SOC or aromatic C. Such relationships indicated that aromatic functional groups had been attached to the poorly crystalline Fe minerals, which could also be protected from being transformed to the crystalline counterpart. In conclusion, results from our integrated spectroscopic analyses have evidenced greater improvement of both poorly crystalline Fe minerals and aromatic C in organically fertilized than in chemically fertilized soils.

Protection of extractable lipid and lignin: Differences in undisturbed and cultivated soils detected by molecular markers

Understanding formation of organo-mineral association is crucial for soil organic matter (SOM) stabilization. To remove reactive minerals from un-disturbed natural soil (NS) and two cultivated soils (dry-farming soil, TD, and terrace paddy soil, TP), a 10% HF/1M HCl treatment was applied. The mineral protection of different molecular SOM structures before and after cultivation was compared by using markers for lipid and lignin. The removal of reactive mineral increased the lipid extractability in TD and NS similarly, indicating that the cultivation did not reduce the mineral protection; this is attributable to fertilizer application and amorphous Fe oxide enrichment. In TP, the extent of lipid protection was lower than in TD, demonstrating that the protection depends on the type of cultivation. In contrast to lipids, lignin-derived phenols decreased over 80% after acid treatment. Furthermore, the ratios of acid to aldehyde in vanillyl ((Ad/Al)V) of TD and TP were much higher than in NS, indicating an increased oxidation of lignin in cultivated soils. During acid treatment, two distinct layers of soil particles were identified: an organic matter (OM)-enriched layer (LOM), and a non-reactive mineral-enriched layer (LNR) with hardly detectable OC content. However, up to 50% of lipids were detected in LNR, indicating that lipids did not selectively interact with reactive mineral particles. In TD and TP, (Ad/Al)V values were higher in LOM than in LNR, indicating a strong interaction of oxidized lignin in LOM. Therefore, the protection of lignin, especially highly oxidized lignin, can depend more on reactive minerals than lipid. Promoting the formation of organo-mineral complexes is the primary strategy for soil management, especially for highly oxidized OM.

Wood biochar impacts soil phosphorus dynamics and microbial communities in organically-managed croplands

Biochar (a carbon-rich product from pyrolysis of organic materials) addition to agricultural soils has been proposed as a novel technology for enhancing soil C storage and fertility; however, few studies have evaluated the effects of biochar on nutrients from an integrated perspective. Previous studies have demonstrated that biochar has the potential to improve bioavailable phosphorus (P) of sandy soils in organic farming systems; yet the underlying mechanisms remain poorly understood. We hypothesized that the unique characteristics of wood biochar could induce changes in soil microbial communities, which would subsequently drive biotic controls on soil P availability through microbial solubilization and/or mineralization and that this would be reflected in microbial P gene expression. To test this hypothesis, we determined the abundance and diversity of bacterial and fungal communities as related to microbial communities in sandy soils of organically-managed farmlands amended with locally produced wood biochar. A series of soil biochemical properties and genes encoding synthesis of phosphatase and those encoding the production of small molecular weight organic acids (involved in metal chelation and P solubilization) were directly quantified to help understand soil P mobilization following biochar addition. Three months after the application of wood biochar, the bioavailability of soil P was found to be elevated and a shift towards a bacterial dominated community was observed. Contrary to our hypothesis; however, the abundance of genes dictating soil phosphatase synthesis or organic acids production remained unaltered following biochar amendment. We suggest that the shift in P bioavailability could be controlled by abiotic mechanisms such as biochar-induced surface organic matter stabilization or adsorption/desorption of P associated with organo-mineral complexes. Although there was no specific molecular evidence of soil microorganism-mediated P mobilization, locally produced wood biochar had a positive effect on surface soil P bioavailability which could benefit agricultural soil health and ecosystem service delivery in organic farming systems.

Experimental Research on the Photodegradation of the Organic Compounds of Natural Waters

The photodegradation of organo-mineral complexes in natural conditions was studied using samples of soil and swamp waters to study the effect of sunlight on the composition and properties of organic matter and metal forms dissolved in natural waters. The total contents of certain aliphatic and aromatic carboxylic acids increased in the samples after irradiation. Photodegradation of organic matter of the natural waters with the high Fe content is accompanied by the formation of colloidal particles (Fe hydroxides). The number of negatively-charged complexes of Ni, Cu, Zn, and Cd increased under insolation in swamp waters and decreased in soil waters.

Experimental research of photodegradation processes of organic compounds of natural waters

In order to study the effect of sunlight on the composition and properties of dissolved organic matter and metal forms in natural waters, the process of photodegradation of organo-mineral complexes in field conditions with samples of soil and swamp waters was studied. Total content of certain aliphatic and aromatic carboxylic acids increased in the studied samples after irradiation. Photodegradation of organic matter of the natural waters that are rich in iron is accompanied by formation of colloidal particles (Fe hydroxides). The amount of negatively-charged complexes of Ni, Cu, Zn and Cd increases during the insolation in swamp waters and decreases in soil waters.

Guanidine-Containing Organomineral Complexes as Biocide Additives to Polymeric Composites

Obtaining and using polymeric composite materials with biocide properties is of considerable practical interest both for making construction materials stable against biological corrosion and for improving the sanitary-epidemiological situation. The method suggested for obtaining biocide polymeric composites is based on using new guanine-containing polymers immobilized on montmorillonite as biocide additives. Macromolecular compounds based on guanidine polymers are characterized by high biocide efficiency and low toxicity, and their use as organomineral complexes with montmorillonite can rule out washing-out of the additive from the composite and improve the distribution of the additive in the composite. Methods are suggested for obtaining organomineral complexes in a wide range of compositions. It is shown that composites based on polyethylene and the additives have high biocide efficiency toward micromycetes and gram-positive and gram-negative bacteria.

Organic matter protection by kaolinite over bio-decomposition as suggested by lignin and solvent-extractable lipid molecular markers

The formation of organo-mineral complexes is essential in organic matter (OM) stabilization. However, limited studies have been conducted to systematically examine the mineral influence on the decomposition of plant residuals at a molecular level. In this study, pine needles and chestnut leaves were mixed with kaolinite at the weight ratio of 5:1. The controls were plant tissues without kaolinite. All the samples were incubated in the laboratory for one year. Molecular markers, including lignin-derived phenols (e.g. Vanilly units, syringyl units and cinnamyl units) and solvent-extractable lipids (e.g. n-alkanoic acid, n-alkanols and n-alkanes), were analyzed. The concentrations of lignin-derived phenols and lipid compounds were higher in the presence of kaolinite than without kaolinite. Lower degradation indexes, such as (Ad/Al)V (ratio of vanillic acid to vanillin) and CPI (carbon preference index of n-alkanoic acid and n-alkanes), were found in the kaolinite system. These results indicate that kaolinite reduced the OM decomposition. The addition of kaolinite also stabilized some carbohydrates from plants. Furthermore, the degradation of OM led to the generation of persistent free radicals, indicated by electron paramagnetic resonance (EPR) signals. The EPR signals were higher with than without kaolinite. We hypothesize that the adsorption of semiquinone or quinone radicals on kaolinite may limit their reaction with other OM moieties and thus extended their lifetimes. In addition to embedding OM in soil aggregates, our results provide direct evidence of another mineral protective mechanism of soil OM.

Variation in the Molecular Structure and Radiocarbon Abundance of Mineral-Associated Organic Matter across a Lithosequence of Forest Soils

Soil mineral assemblage influences the abundance and mean residence time of soil organic matter both directly, through sorption reactions, and indirectly, through influences on microbial communities. Though organo-mineral interactions are at the heart of soil organic matter cycling, current models mostly lack parameters describing specific mineral assemblages or phases, and treat the mineral-bound pool as a single homogenous entity with a uniform response to changes in climatic conditions. We used pyrolysis GC/MS in combination with stable isotopes and radiocarbon abundance to examine mineral-bound soil organic matter fractions from a lithosequence of forest soils. Results suggest that different mineral assemblages tend to be associated with soil organics of specific molecular composition, and that these unique suites of organo-mineral complexes differ in mean residence time. We propose that mineralogy influences the composition of the mineral-bound soil organic matter pool through the direct influence of mineral surface chemistry on organo-mineral bond type and strength in combination with the indirect influence of soil acidity on microbial community composition. The composition of the mineral-bound pool of soil organic matter is therefore partially dictated by a combination of compound availability and sorption affinity, with compound availability controlled in part by microbial community composition. Furthermore, results are suggestive of a preferential sorption of N-containing moieties in Fe-rich soils. These bonds appear to be highly stable and confer extended mean residence times.

Soil structure and soil organic matter in water-stable aggregates under different application rates of biochar

Soil structure and soil organic matter in water-stable aggregates under different application rates of biochar

Dissolved Organic Carbon in Leachate after Application of Granular and Liquid N-P-K Fertilizers to a Sugarcane Soil.

The progressive decline of soil organic matter (SOM) threatens the sustainability of arable cropping worldwide. Residue removal and burning, destruction of protected microsites, and the acceleration of microbial decomposition are key factors. Desorption of SOM by ammonia-based fertilizers from organomineral complexes in soil may also play a role. A urea- and molasses-based liquid fertilizer formulation and a urea-based granular formulation were applied at recommended and district practice rates, respectively, to soil leaching columns, with unfertilized columns used as controls. The chemistry of leachate collected from the columns, filled with two sandy soils differing in recent cropping history, was monitored over eight successive wet-dry drainage events. The pH, electrical conductivity, and concentration and species of N in leachate was compared with the concentration and aromaticity of dissolved organic C (DOC) to indicate if salt solutions derived from the two fertilizers extracted SOM from clay mineral sites. Cation exchange capacity and exchangeable cations in the soil were monitored at the start and end of the trial. Fertilizer application increased DOC in leachate up to 40 times above the control, but reduced aromaticity (specific ultraviolet light absorbance at 253.7 nm). Dissolved organic C was linearly proportional to leachate NH-N concentration. Exchangeable Ca and Mg in soil from fertilized columns at the end of both trials were significantly lower than in unfertilized soil, indicating that ammonium salt solutions derived from the fertilizers extracted cations and variably charged organic matter from soil mineral exchange sites. Desorption of organic matter and divalent cations from organomineral sites by ammonia-based fertilizers may be implicated in soil acidification.

Initiation of soil formation in weathered sulfidic Cu-Pb-Zn tailings under subtropical and semi-arid climatic conditions

Field evidence has been scarce about soil (or technosol) formation and direct phytostabilization of base metal mine tailings under field conditions. The present study evaluated key attributes of soil formation in weathered and neutral Cu-Pb-Zn tailings subject to organic amendment (WC: woodchips) and colonization of pioneer native plant species (mixed native woody and grass plant species) in a 2.5-year field trial under subtropical and semi-arid climatic conditions. Key soil indicators of engineered soil formation process were characterized, including organic carbon fractions, aggregation, microbial community and key enzymatic activities. The majority (64–87%) of the OC was stabilized in microaggregate or organo-mineral complexes in the amended tailings. The levels of OC and water soluble OC were elevated by 2–3 folds across the treatments, with the highest level in the treatment of WC and plant colonization (WC+P). Specifically, the WC+P treatment increased the proportion of water stable macroaggregates. Plants further contributed to the N rich organic matter in the tailings, favouring organo-mineral interactions and organic stabilization. Besides, the plants played a major role in boosting microbial biomass and activities in the treated tailings. WC and plants enhanced the contents of organic carbon (OC) associated with aggregates (e.g., physically protected OC), formation of water-stable aggregates (e.g., micro and macroaggregates), chemical buffering capacity (e.g., cation exchange capacity). Microbial community and enzymatic activities were also stimulated in the amended tailings. The present results showed that the formation of functional technosol was initiated in the eco-engineered and weathered Cu-Pb-Zn tailings under field conditions for direct phytostabilization.

Biochar aging in contaminated soil promotes Zn immobilization due to changes in biochar surface structural and chemical properties

Adding biochar to Zn-contaminated soil can immobilize excess Zn and promote plant biomass growth. This was seen previously over the course of a 180-day planted pot trial involving two types of biochar (cattle manure, CM, and grain husk, GH) in a Zn-contaminated soil. Both biochars alleviated Zn-induced phytotoxicity to Ficus by immobilizing Zn and reducing its uptake by the plant, but to different extents. The aim of the current study was to delve into the in-soil mechanisms involved in biochar-mediated Zn immobilization. Biochar particles were excavated from the pot soils. Fresh and aged biochar particles were examined by high-resolution scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), field-emission electron probe micro-analyzer (EPMA), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The physical and chemical properties of the biochars had changed over the 180 days. SEM-EDS and EPMA indicated that organo-mineral micro-agglomerates had formed on biochar surfaces and in pores. Some of the Zn immobilized by the biochars was bound in the organo-mineral complexes of these agglomerates. XPS and FTIR showed that the complexes had a high concentration of oxygenated functional groups which facilitated Zn binding and encapsulation. The micro-agglomerates were similar in structure and composition to those observed on biochars having resided for much longer times in soils, or having been subjected to accelerated aging. Overall, Zn immobilization by the CM biochar was greater than by the GH biochar, due to its higher alkalinity, higher concentration of available negatively charged groups, and greater accretion of organo-mineral layers. These findings are suggestive that biochar-assisted phytorestoration of heavy metal-contaminated soils can be optimized through selection of biochar having such traits. It is hypothesized that metals may be continually taken up in such micro-agglomerates, since they continue to form over the lifetime of the biochar in the soil.