Al Hydroxide Research Articles

Phosphorus × Other Plant Nutrient Interactions, Reaction Products, Anion Exchange and Phosphate Fixation in Soil and Strategies to Increase Availability of the Native and Applied P to Crop Plants-A Mini Review and Critique

Phosphorus is a major plant nutrient obtained from non-renewable phosphate rock, which is not much available in India. Over and above in this its recovery efficiency in crops hardly exceeds 15-20 per cent. Utmost care is therefore required in its use. Phosphorus applied to soil gets fixed by the formation of insoluble reaction products by reacting with Fe and Al in acid soils and with calcium in saline and alkaline soils. Two techniques used for identification of reaction products are X-ray diffraction and solubility product principle. In addition, phosphate ions are also held on Fe and Al hydroxides by anion exchange. The reaction products identified are variscite and strengite minerals in acid soils and dicalcium phosphate and hydroxy apatite in calcareous soils. Methods to increase phosphorus recovery by crops include: 1) addition of organic matter to soils; 2) addition of sulphur to compost or to ground rock phosphate or directly to soil and use of phosphorus solubilising organisms including VAM/AM along with ground rock phosphate.

Replication of Small Ruminant Lentiviruses in Aluminum Hydroxide-Induced Granulomas in Sheep: a Potential New Factor for Viral Dissemination.

Aluminum (Al)-based salts are widely used adjuvants in ruminants and other species to strengthen the immune response elicited against vaccine antigen(s). However, they can lead to the formation of long-lasting granulomas composed of abundant activated macrophages. Small ruminant lentiviruses (SRLV) are widely distributed macrophage-tropic retroviruses that cause persistent infections in sheep and goats. Infected monocytes/macrophages and dendritic cells establish an inflammatory microenvironment that eventually leads to clinical manifestations. The aim of this work was to study the effect of Al-induced granulomas in the replication and pathogenesis of SRLV. Eleven adult, naturally SRLV-infected sheep showing clinical arthritis were distributed in vaccine (n = 6), adjuvant-only (n = 3), and control (n = 2) groups and inoculated with commercial Al-based vaccines, Al hydroxide adjuvant alone, or phosphate-buffered saline, respectively. In vitro studies demonstrated viral replication in Al-induced granulomas in 5 out of 10 sheep. Immunohistochemistry (IHC) evinced granular, intracytoplasmic SRLV presence in macrophages within granulomas. Viral sequences obtained from granulomas, blood monocytes, and other tissues were highly similar in most animals, suggesting virus circulation among body compartments. However, notable differences between isolated strains in granulomas and other tissues in specific animals were also noted. Interestingly, the B2 subtype was the most commonly found SRLV genotype, reaching a wider body distribution than previously described. Recombination events between genotypes B2 and A3 along the gag region were identified in two sheep. Our results indicate that Al-hydroxide-derived granulomas may represent an ideal compartment for SRLV replication, perhaps altering natural SRLV infection by providing a new, suitable target tissue.IMPORTANCE Granulomas are inflammation-derived structures elicited by foreign bodies or certain infections. Aluminum adjuvants included in vaccines induce granulomas in many species. In sheep, these are persistent and consist of activated macrophages. Small ruminant lentiviruses (SRLV), which are macrophage-tropic lentiviruses, cause a chronic wasting disease affecting animal welfare and production. Here, we studied the occurrence of SRLV in postvaccination granulomas retrieved from naturally infected ewes after vaccination or inoculation with aluminum only. SRLV infection was confirmed in granulomas by identification of viral proteins, genomic fragments, and enzymatic activity. The infecting SRLV strain, previously found exclusively in carpal joints, reached the central nervous system, suggesting that occurrence of SRLV in postvaccination granulomas may broaden tissue tropism. SRLV recombination was detected in inoculated animals, a rare event in sheep lentiviruses. Potentially, virus-host interactions within granulomas may modify viral pathogenesis and lead to more widespread infection.

Effects of particle size and mineral crystallinity on formation of Zn[sbnd]Al layered double hydroxides (LDH) on aluminum (oxyhydr)oxides

The widespread usage of zinc oxide nanoparticles (ZnO NPs) inevitably leads to its release in nature and interaction with environmental minerals. To reveal ZnO NP retention by natural aluminum (Al) minerals as layered double hydroxide (LDH) in the environments, the effects of Al (oxyhydr)oxide particle size and crystallinity on ZnAl LDH formation were investigated during ZnO NP interaction with seven different Al (oxyhydr)oxides at neutral and alkaline pHs. Dissolution kinetics displayed a decrease of dissolved Zn2+ and Al(OH)4− concentrations in a dual-solid system (ZnO and Al minerals) relative to a single-solid one (ZnO or Al minerals), suggesting a potential transformation of mixture solids. Diffraction, spectroscopic, and microscopic analyses indicated that Al (oxyhydr)oxide particle size and crystallinity had obviously impacted on ZnAl LDH formation. The composition percentage of ZnAl LDH in solid products followed the order of amorphous Al hydroxides (89.90% and 86.41% Zn species as ZnAl LDH at pH 7 and 10, respectively) > 5 nm γ-Al2O3 (41.62% and 49.62%) > 35 nm γ-Al2O3 (14.77% and 19.03%) > large size Al (oxyhydr)oxides (below 13.00%), including 70 nm γ-Al2O3, corundum, boehmite, and gibbsite. ZnAl LDH formation was regulated mainly by Al (oxyhyro)oxide crystallinity and particle size via changing Al oxide dissolution at pH 10 and Zn2+ adsorption at pH 7, whereas solution pH controlled the crystallinity of the formed ZnAl LDH. A dissolution-interaction-coprecipitation pathway was proposed to elucidate the mechanism of ZnAl LDH formation. The findings highlight the importance of substrate mineral size and crystallinity for ZnAl LDH formation in environmental settings.

Phosphorus concentration and availability in raw organic waste and post fermentation products

The aim of the study was to determine the mobility of phosphorus forms in raw organic waste and from the solid and liquid fractions of digestate. To achieve the purpose of this study, the components (including livestock manure, agricultural waste, food waste, sewage sludge) and their post fermentation products were considered. Subsequently, the effect of the fermentation process on the mobility of phosphorus forms in post-fermentation fractions (solid and liquid) was investigated. Then, the evaluation of the fertilising potential of digestate fractions was assessed.The available organic and inorganic phosphorus forms were determined according to the Standards in Measurements and Testing (SMT) Programme extraction protocol and according to the acid molybdate spectrophotometric method.It has been shown that phosphorus in digestates occurred mainly in inorganic forms with Fe, Al, Mn, Mg and Ca ions. Its proportion in relation to total phosphorus ranged from 80 to 90%. The lowest phosphorus content was found in digestate from the fermentation of agricultural and food waste (fruit and vegetables), while digestate from livestock manure and sewage sludge fermentation was rich in phosphorus. It was shown that the solid fractions of digestate represented from 30 to 70% of highly labile phosphorus (i.e. phosphorus with organic matter and in bonds with Al, Fe, Mg and Mn oxides and hydroxides) in relation to total phosphorus. However, the share of labile phosphorus forms in the liquid fraction of digestates was much higher and accounted for 80–90% of the total phosphorus.

Phosphate solubilization from adsorbents and precipitates by different AVAIL polymers

AbstractLess than 40% of phosphate fertilizer applied to soils is typically taken up by the intended crop within the year of application because of strong soil retention. AVAIL polymers are fertilizer additives that were commercially developed to enhance availability of fertilizer phosphate. Knowledge of underlying mechanisms of phosphate solubilization would help to optimize the effectiveness of these polymers for different soils. This study compared different types and levels of AVAIL polymers in solubilizing (ad)sorbed and precipitated phosphate to gain insights into the mechanisms involved. Varying inputs of four newer forms of polymers and the original AVAIL (Original) were co‐reacted with one level of phosphate (ad)sorbed on ferrihydrite or noncrystalline Al hydroxide in batch (ad)sorption experiments or with Fe and Ca phosphate precipitates in dissolution experiments. Dissolved phosphate increased with increasing levels of co‐added polymers reacted with (ad)sorbents or phosphate precipitates. Across input levels evaluated, the Original AVAIL generally solubilized more phosphate from ferrihydrite than any of the new formulations. The Original and the new Liquid 2 formulation equally solubilized the greatest phosphate from Fe phosphate, whereas Liquid 2 solubilized more phosphate from Al hydroxide and Ca phosphate. (Ad)sorption and dissolution results implied competitive (ad)sorption and complexometric dissolution as key mechanisms. Our results suggest that the effectiveness of AVAIL polymers in soils depends on the level of added polymer charge relative to phosphate adsorption capacities or the types of phosphate minerals present.

Facile Synthesis of Three‐dimensional Hierarchical Ni3S2@CoAl‐LDHs Nanosheet Arrays and Their Efficient Hydrogen Evolution

AbstractDesigning an electrocatalyst with optimized structure and performance is vital for the electrolysis of water to produce hydrogen. Herein, a three‐dimensional (3D) hierarchical composite electrode material is proposed for alkaline hydrogen evolution reaction (HER), consisting of Co−Al hydroxides (CoAl‐LDHs) nanosheets decorated with vertically aligned nickel sulfide (Ni3S2) arrays (Ni3S2@CoAl‐LDHs/NF). The as‐obtained electrocatalyst displays a minimum overpotential of 175 mV at 10 mA cm−2 toward HER. Electrochemical impedance spectroscopy and Tafel slope further reveals outstanding kinetics in the electrolysis process. The catalytic performance of the electrode can still maintain 90 % capacity after 1000 CV cycles. The outstanding properties of the composite material benefits from its unique 3D hierarchical structure, which promote plentiful active sites and faster electronic transfer rate. This work sheds lights on the current research of noble‐metal‐free electrocatalysts and the design of overall water splitting.

Diffusion dialysis and extraction integrated system for recovery of cobalt(II) from industrial effluent

This paper presents multistage hydrometallurgical separation of Co(II) from wastewater, achieved in an integrated system containing diffusion dialysis (DD) to decrease the acidity of the industrial effluent – pregnant leach solution (PLS), followed by precipitation of Al(III), Fe(III) and Cr(III) hydroxides, selective extraction of Co(II) with bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272), stripping of Co(II) from the loaded organic phase to form an electrolyte. DD results indicate that minimum metal ion content in the dialysate and high concentration of H+ (1.5−3 M) can be achieved by conducting the process at a low flow rate, but for a longer time. The feed after DD was effectively purified by precipitation of Cr(III), Al(III) hydroxides, and some admixtures of Cu(II) and Fe(III) to ensure that those metals will not disturb the liquid-liquid extraction of Co(II) at pH 5.2. High distribution ratio values for Co(II) extraction mean that ions of this metal can be selectively separated from the remaining ions present in the feed, especially Ni(II), and transported to the organic phase. The application of H2SO4 solution and the dialysate as stripping phases indicates that the dialysate more efficiently stripped most of the metal ions from the extract, thus forming Co(II) rich electrolyte for further electrodeposition of the metal. Finally, Co(II) electrowinning from a model stripping solution was investigated and the preliminary results showed that good quality metallic cobalt can be deposited.

A Physicochemical Model of Gold Transformation in the Wastes of Processed Pyrite–Polymetallic Ores (Salair Ridge, Russia)

Abstract —Gold-bearing dumps of processed pyrite–polymetallic ores of the Ursk ore field (Novo-Urskoe and Beloklyuchevskoe deposits, Salair Ridge) have been studied. Physicochemical modeling of the gold behavior in wastes allowed us to describe quantitatively the gold precipitation process in different horizons of the dumps. In the upper part of the sulfide-rich section, sulfide minerals undergo intense oxidation accompanied by the dissolution of structural and surface-bound gold. Gold redeposition on the pyrite surface (sorption reduction barrier) as a result of electrochemical processes is accompanied by the formation of heavy-metal sulfates and barite. Under the sorption barrier, there is a loose leaching horizon with high humidity, where gold is present in pore solutions as thiosulfate, hydrosulfide, and hydroxo complexes; its content reaches 68 mg/L. In the middle part of the section, composed of compact siliceous sandstones (hardpan), high-grade (up to 973‰) gold forms through the disintegration of thiosulfate complexes, but its content decreases to 10-6 mg/L (lithologic reduction barrier). No visible gold was found in the lower part of the section (soil bed), but its high contents (up to 0.35–0.42 g/L) might be due to the sorption by organic high-molecular compounds, such as humic acids. The morphology and chemical composition of native gold from the gold-containing dumps of processed pyrite–polymetallic ores have been first studied. It is shown that the gold surface has traces of supergene transformations, e.g., gold nano- and microparticles as sponge overgrowth on the gold or barite particle surface or as newly formed gold phases in Fe, Mn, and Al hydroxide films.

Production of Alpha-Alumina from Black Aluminum Dross Using NaOH Leaching Followed by Calcination

The aim of this work is to produce α-alumina particles from aluminum (Al) dross via leaching–precipitation–calcination processes. In the leaching test, the effects of parameters such as the temperature, NaOH concentration, and time were investigated based on the Taguchi approach. In addition, the effect of the particle size on the Al extraction rate was determined. The Al extraction rate ranged from 78.64% to 93.11% and from 78.35% to 91.99% for ground dross and as-received dross, respectively. In the precipitation test, the pH of the leachate solution was decreased using HCl to remove Al ions as Al hydroxide precipitate. The precipitate was calcined at 1000°C to 1200°C for 270 min. The morphological and polymorphic properties of the products were characterized by scanning electron microscopy, atomic force microscopy, and x-ray diffraction analysis. The experimental findings indicated that the calcination temperature and stabilization time were critical for producing α-alumina particles rather than other polymorphs.

Effectiveness of dredging on internal phosphorus loading in a typical aquacultural lake

Intensive aquaculture significantly affects the global phosphorus (P) cycle and enhances eutrophication in inland waters. Sediment dredging efficiently removes P-rich sediments from shallow-water eutrophic lakes. However, studies on the effects of sediment dredging on the internal P loading of aquacultural lakes are still lacking. Moreover, the migration and transformation processes of labile P and the mechanisms of sediment P release are unclear. To evaluate dredging effectiveness, we employed two in situ high-resolution sampling techniques to simultaneously measure sediment labile P and porewater soluble reactive P (SRP) and Fe (II) at the millimeter scale. Dredging effectively reduced surface sediment CaP contents and organic matter (OM) below the sediment-water interface (SWI). Moreover, dredging decreased the SRP diffusion flux across the SWI in summer. After dredging, FeP (P bound to Fe, Al, and Mn oxides and hydroxides) and OP (organic P) contents increased by 136% and 48% in the newly formed deposited layer (140 mm thick), respectively. The increased bioavailable P content significantly enhanced the capability of sediment solids to resupply labile P to porewater SRP. The stronger positive correlation between porewater soluble Fe (II) and SRP suggests that Fe redox cycling regulated internal P release. Our results suggest that dredging effectiveness will weaken over time due to the re-deposition of active P, which in turn increases the risk of sediment P release. To curb the release of sediment P, we recommend the implementation of additional in situ restoration techniques that improve the oxide layer of surface sediments and reduce sediment suspension.

VARIATIONS OF WATER QUALITY ALONG ACIDIC RIVERS IN VOLCANIC AREAS OF EASTERN JAPAN

There are many acidic rivers in Japan, due to acid mine drainage (AMD) and drainage from acidic hot springs. Low pH values and relatively high concentrations of heavy metals and other trace elements are often detected in the acidic rivers. In this study, water quality parameters including pH and concentrations of major cations and anions, heavy metals, and other trace elements were investigated in nine acidic river basins located in volcanic areas of Eastern Japan. The study included both untreated river basins and basins where neutralization treatment is carried out. Variations of water quality along two acidic river basins and the mechanisms controlling the variations in water quality were also discussed. Generally, the pH values ranged from 1.31 to 5.45 in the nine river basins. Positive effects from neutralization treatment were observed along the Agatsuma river basin where pH values markedly increased and the concentrations of As, Pb, F, Fe, and Al dramatically decreased. In comparison, along the untreated Nagase river basin, the pH values gradually increased and the concentrations of As, Pb, F, Fe, and Al steadily decreased, mainly due to the dilution effect caused by mixing with other rivers. In these two river basins, harmful elements such as As, Pb, and F were probably coprecipitated with Fe and Al hydroxides. The sediments deposited in the Nagase river bed and Lake Inawashiro may therefore contain much higher concentrations of harmful elements including As, Pb, and F as were previously reported on the Shinaki Dam of the Agatsuma river basin.

From nanofiltration membrane permeances to design projections for the remediation and valorisation of acid mine waters

Acidic Mine Waters (AMWs) are characterised by high acidity (pH < 3) as H2SO4 and elevated contents of metals (Al, Fe, Cu, Zn), including rare earth elements (REEs). Due to the exhaustion of minable REE containing-minerals, AMWs are increasingly regarded as an alternative source of REEs. Among the different alternatives for the pre-concentration of AMWs required to make the REE extraction possible, nanofiltration (NF) membranes emerge as a promising technology because they not only successfully reject multivalent ions (metals), allowing its concentration in the retentate stream, but also permit the transport of monovalent ones, such as H+ and HSO4−, allowing the recovery of sulphuric acid in the permeate. Despite this potential of NF, there is still a lack of modelling tools for predicting the performance of NF membranes because of its dependence on solution composition, membrane properties and interaction between both. In this study, a prediction tool based on the Solution-Electro-Diffusion model (including the effect of solution composition) was developed and experimentally validated for the application of two polyamide-based NF membranes (NF270 and Desal DL) for the recovery of REEs and H2SO4 from three different synthetic solutions mimicking AMWs (pH 1.0, 60 mg/L REEs and, 25–600 mg/L Al, Cu, Ca and Zn) differing in their Fe concentration (0–2125 mg/L). Metals were effectively rejected (>98%), whereas H2SO4 was transported across the membrane (H+ rejections <30%). The mathematical model was able to predict the performance of both membranes as well as the potential scaling events associated with Fe and Al hydroxides and hydroxy-sulphates.

Change in Arsenic Leaching from Silty Soil by Adding Slag Cement

Cementitious materials are commonly used to reinforce the bearing capacity of silty soils. However, there is very little data about how changes in arsenic (As) leaching from silty soils caused by the addition of cementitious materials. Therefore, batch leaching tests were conducted using As-bearing silty soil under different pH conditions. The pH was adjusted by changing the amount of slag cement added or the concentration of sodium hydroxide. This allows us to evaluate the effects of cement on As leaching. In addition, two different additives were applied to reduce As migration. The results show that high concentration of calcium ion (Ca2+) in leachates of soil-cement mixture has a significant effect in reducing the mobility of As even under hyperalkaline pH conditions. Arsenic immobilized by Ca2+ was observed in two patterns. The first mechanism was the help of Ca2+ to reduce the negative electrical potential on the surface of (hydr)oxide minerals under high pH conditions, thereby reducing the mobility of As by adsorption and coagulation of fresh precipitates of Fe and Al hydroxides. The second was the precipitation of calcium carbonate. This precipitate either directly adsorb/co-precipitate As or lower the concentration of strong competing ion, silica, both of which reduced the As mobility. When Ca- or Mg-based additive was added to the silty soil-cement mixture, As concentration in the leachate decreased. These findings are useful in developing sustainable soil-cement reinforcement techniques to avoid contamination.

Geographical variations in arsenic contents in rice plants from Latin America and the Iberian Peninsula in relation to soil conditions

Arsenic is a ubiquitous, toxic element that is efficiently accumulated by rice plants. This study assessed the spatial variability in the total As (tAs) contents and organic and inorganic forms in different types of rice, plant parts (husk, stem, leaves and phytoliths) and residues. Samples were collected in different countries in Latin America (Ecuador, Brazil and Peru) and the Iberian Peninsula (Spain and Portugal). The tAs content in commercial polished rice from the Latin American countries was similar (0.130-0.166mgkg-1) and significantly lower than in the rice from the Iberian countries (0.191 ± 0.066mgkg-1), and together, the tAs concentration in brown rice (236 ± 0.093mgkg-1) was significantly higher than in polished and parboiled rice. The inorganic As (iAs) content in rice was similar in both geographical regions, and the aforementioned difference was attributed to dimethylarsinic acid (DMA). The relative abundance of organic species increased as the tAs content in rice grain increased. A meta-analysis of our and previously reported data confirmed the negative correlation between iAs/tAs and tAs. At low tAs concentrations, inorganic forms are dominant, while at higher values (tAs > 0.300mgkg-1) the concentration of organic As increases substantially and DMA becomes the dominant form in rice grain. On the contrary, inorganic arsenic was always the dominant form, mainly as arsenate [As(V)], in leaves and stems. The presence in soils of high concentrations of amorphous Fe and Al oxides and hydroxides, which are capable of strongly adsorbing oxyanions (i.e. arsenate), was associated with low concentrations of As in rice plants. In addition, the presence of high concentrations of As(V) in stems and leaves, low concentration of As in phytoliths, and the As associated with organic matter in stems and husk, together suggest that rice plants take up more As(V) than As(III).

Development and characterization of multifunctional carbon fabric‐reinforced polymer composites incorporated with inorganic flame retardants

AbstractCarbon fabric‐reinforced polymer (CFRP) composites were incorporated with novel, environment‐friendly and, low‐cost inorganic flame‐retardant (FR) materials. Synergistic properties of potash alum (KA) and magnesium hydroxide (MH) were obtained by infusing these materials in the carbon woven fabric with diglycidial ether of bisphenol‐A epoxy (EP) matrix through resin infusion technology. Composite samples EP80%MH20% and EP80%MH15%KA5% showed Underwriter Laboratories 94 (UL94) V‐2 rating, EP80%MH10%KA10% and EP80%MH5%KA15% showed UL94 V‐1 rating, and EP80%KA20% showed UL94 V‐0 rating. Flame retardancy of EP was improved with increasing concentration of KA up to UL94 V‐0 while a high concentration of MH improved flame retardancy only up to UL94 V‐2 rating, which is not suitable for the material. Flexural modulus and flexural strength of EP were decreased with increasing concentration of KA and MH because both FR created the distance between the EP chains and hence imparted ductility. Thermogravimetric analysis showed an increase in char residue with increasing KA concentration. The char residue of EP100% (without FR materials) was 16.5 wt%, which increased to 71.2 wt% for EP80%KA20%. CFR samples were prepared with the given FR materials and it was seen that reduction in mechanical properties was compensated with the help of CFRP.

Green synthesis of aluminum-hydrochar for the selective isomerization of glucose to fructose

Hydrochar microspheres supported Al catalysts with hierarchically porous structure (Al/HPHMs) for glucose to fructose isomerization were fabricated. Superior catalytic selectivity (93.3%) and fructose yield (32.6%) were achieved in aqueous under 160 °C for 20 min. Hierarchically porous structure was formed after KHCO3 and K2CO3 activation and the roles of KHCO3 and K2CO3 in controlling the Al phase and tailoring morphology of hydrochar supported Al were evaluated. The major active sites were characterized as Al hydroxides including β-Al(OH)3, γ-Al(OH)3, γ-AlO(OH), Al-C-O linkages. Active sites by KHCO3 activation with high contents of Al-C-O and Al(OH)3 have better selectivity. Oxygen-containing functional groups including aluminum‑oxygen groups on the hydrochar microspheres have contributed to the formation of hydrogen bond and π-π interactions between glucose and Al species. Green process synthesized aluminum-hydrochars have potential for their application as a variety of stable, recyclable, and efficient catalysts for lignocellulosic biorefining.

Mining Activities and the Chemical Composition of R. Modonkul, Transbaikalia

The Dzhidinsky orefield is located in the Zakamensky district of Buryatia. It is characterized by a high concentration of mineralization in a small area. The ores of the Dzhidinsky economic deposits are complex. This ore field includes Pervomaiskoye Mo, Kholtosonskoe W, and Inkurskoe W deposits. The catchment basin of the river Modonkul is located in the Dzhidinsky orefield. Mineral resource industry waste is a real threat to the city Zakamensk. Currently, the waste of deposits is located at the floodplain terrace and the watershed of the river Modonkul. In this work, the impact of the drainage mine and tributary Inkur on the formation chemical composition of the river Modonkul is studied. The 80 samples of water and suspended matter were taken from a surface of 0–0.5 m on seven sites. Physical and chemical parameters were measured at the sampling sites, and chemical composition was analyzed in the laboratory. In the natural background of the river, the major cations are, in decreasing order, Ca2+ &gt; Mg2+ &gt; Na+ + K+, and major anions are, also in decreasing order, HCO3− &gt; SO42− &gt; Cl−. Along the river, the chemical type of water changes from bicarbonate to sulfate across the sulfate-bicarbonate or bicarbonate-sulfate class and from calcium-magnesium across sodium-calcium-magnesium reverse calcium-magnesium group. Total dissolved solids (TDS) increase by a factor of 4.0–4.7 between the upper and mouth of the river. The dissolved and suspended loads were studied in the mixing zone of acid mine and river water. The different hydrochemistry characteristics may result from Fe, Al, and Mn hydroxide precipitation. The pH values and dissolved oxygen cycles could change the uptake of heavy metals on suspended iron and manganese oxides, and the mechanism of removing it in water. River particulates have the potential of regulating heavy metal inputs to aquatic systems from pollution. The ore elements or the heavy metals are removed from the water in two ways: by the runoff of Modonkul and the sedimentation of suspended material at the bottom. The inflow of mine water into the Modonkul river leads to the rare earth elements (REEs) composition with negative cerium and positive europium anomalies.

Effect of the Mechanical and Thermal Prehistory of Precursors on the Zinc Spinel Synthesis

Thezinc spinel (gahnite) formation by a treatment of reaction mixtures of Zn and Al oxides, hydroxides, and salts was investigated. The influence of a preliminary mechanical activation by impact (planetary mill) and attrition (ball-ring mill) action as well as a microwave treatment was analyzed. The combined method consisting of a mechanical treatment of nitrates mixture in a planetary mill and the subsequent burning in a thermal kiln was considered as the most effective as it resulted in practically single product

Understanding phosphate sorption characteristics of mineral amendments in relation to stabilising high legacy P calcareous soil

In China, excessive phosphorus (P) application in protected vegetable fields has led to high legacy P stores. Soil amendment with alum or dolomite is one of many best management practices (BMPs) used to reduce P losses in calcareous soils. However, both the kinetics and mechanisms of P sorption and soil available P in amended soils are understudied. Herein, both aspects were looked at under controlled conditions. Firstly, a sorption study which coupled P concentrations with poorly-crystalline Al hydroxides and dolomite was conducted. Results from this batch experiment showed that P sorption on poorly-crystalline Al hydroxides was homogenous and occurred mainly via displacement of inner-sphere hydroxyl (Al–OH) instead of the formation of AlPO4. However, the amount of sorbed P reached maximum sorption of 73.1 mg g−1 and did not change with further increase in P concentration. It was observed that P adsorbed onto the dolomite surface at low P concentrations, whereas hydroxyl replacement and uneven cluster precipitation of Ca3(PO4)2 occurred at high P concentrations. A second 90 day incubation experiment investigated changes to soil available P and sorption-desorption across variable rates of amendments (0–50 g kg−1). Results showed that alum amendment at a rate of 50 g kg−1 decreased soil CaCl2–P and Olsen-P concentrations by 91.9% and 57.8%, respectively. However, Olsen-P increased when the dolomite rates were <20 g kg−1. Phosphorus sorption-desorption of the amended soil showed alum had higher P sorption efficiency than dolomite at low addition rates (<10 g kg−1). However, soil amended with high dolomite rates (>10 g kg−1) could sorb more P in comparison with alum when P concentrations were increased. The P status of the amended soil was closely connected to the P sorption mechanisms on mineral amendments, soil P concentrations and soil properties.

Phosphorus solubilization in the rhizosphere in two saprolites with contrasting phosphorus fractions

Little is known about the contribution of plants and microorganisms to the release of phosphorus (P) from minerals, despite the importance of P solubilization for plant nutrition and soil formation. Therefore, the aim of this study was to assess how plants affect P solubilization and the abundance of phosphorus-solubilizing bacteria (PSB) in the rhizosphere. We conducted an experiment in which we determined the release of P, Si, Fe, and Al from two contrasting saprolites (weathered rocks) that were kept in rhizoboxes with and without the grass Nassella trichotoma. In addition, we determined the pH and the concentration of organic acids in the solution over six weeks as well as the abundance and phylogeny of cultured PSB. In the strongly-weathered (SW) saprolite, a larger proportion of P was present in the NaOH-extractable P fraction, and thus was likely associated with Al and Fe oxides and hydroxides, than in the only moderately-weathered (MW) saprolite. The plants released more P, Si, and Fe from the MW saprolite than from the SW saprolite. In contrast, more Al was released from the SW saprolite than from the MW saprolite. The total P release was increased due to plants by a factor of 1591 in the MW saprolite and by a factor of 711 in the SW saprolite. P was preferentially released from the saprolites compared to Si. The release of elements went along with high consumption of protons, particularly in the MW saprolite, indicating high rates of mineral weathering. Citric acid, which can contribute to P solubilization, was present in the MW saprolite but not in the SW saprolite. The plants maintained a high abundance of PSB in the rhizoplane (surface of the roots) in the SW saprolite, but not in the MW saprolite, where concentrations of dissolved P were higher. In conclusion, the study shows that N. trichotoma strongly increased the release of P from saprolite and enriched PSB in the rhizosphere when growing in saprolite with low P availability. Taken together, our results suggest that plants can increase P solubilization by a factor of >1000 by preferentially releasing P from saprolite and preventing its (re-)adsorption and (re-)precipitation.