Chemical Forms Of Mn Research Articles

Study on phase evolution and promoting the pozzolanic activity of electrolytic manganese residue during calcination

Electrolytic manganese residue (EMR) is a harmful by-product in the electrolytic manganese industry. Calcination is an efficient method for disposing EMR. In this study, thermogravimetric-mass spectrometry (TG-MS) combined with X-ray diffraction (XRD) was used for analysing the thermal reactions and phase transitions during calcination. The pozzolanic activity of calcined EMR was determined by the potential hydraulicity test and strength activity index (SAI) test. The leaching characteristics of Mn were determined by TCLP test and BCR SE method. The results showed that MnSO4 was converted into stable MnO2 during calcination. Meanwhile, Mn-rich bustamite (Ca0.228Mn0.772SiO3) was converted into Ca(Mn, Ca)Si2O6. The gypsum was transformed into anhydrite and then decomposed into CaO and SO2. Additionally, the organic pollutants and ammonia were completely removed following calcination at 700 °C. The leaching concentration of Mn decreased from 819.9 mg L−1 to 339.6 mg L−1 following calcination at 1100 °C. The chemical forms of Mn were transformed from acid-soluble fraction to residual fraction. The pozzolanic activity tests indicated that EMR1100-Gy maintained a complete shape. The compressive strength of EMR1100-PO reached 33.83 MPa. Finally, the leaching concentrations of heavy metals met the standard limits. This study provides a better understanding for the treatment and utilization of EMR.

The potential of Paulownia fortunei seedlings for the phytoremediation of manganese slag amended with spent mushroom compost

The use of phytoremediation was an efficient strategy for the restoration of mine slag and the addition of modifier was favorable for improving the phytoremediation efficiency. Herein, spent mushroom compost (SMC) was added in manganese (Mn) slag to reveal the phytoremediation potential of Paulownia fortunei seedlings. The transportation, subcellular distribution and chemical forms of Mn in P. fortunei, the diurnal variation of photosynthesis and antioxidant enzyme activities in P. fortunei leaves were measured to reveal the effect of SMC (mass ratios of 10%, M+) on the phytoremediation of Mn slag. Results showed that the addition of SMC increased the accumulation content of Mn by 408.54% due to the increased biomass of P. fortunei seedlings. After SMC amendment, the maximum net photosynthetic rate (Pn) increased and the superoxide dismutase (SOD) activities decreased significantly (p<0.05), which was beneficial to the tolerance of leaves to Mn stress. SMC amendment maintained the cell structural integrity of P. fortunei seedlings observed by transmission electron microscope (TEM). Additionally, SMC amendment decreased the damage level of Mn to the cell of P. fortunei seedlings by using function groups (-CH3 and -COOH) to bond Mn in the cell walls and vacuoles. SMC amendment reduced the Mn toxicity to P. fortunei seedlings and improved the phytoremediation capacity.

Integrative study of subcellular distribution, chemical forms, and physiological responses for understanding manganese tolerance in the herb Macleaya cordata (papaveraceae)

Macleaya cordata is a perennial herb, a candidate phytoremediation plant with high biomass and manganese (Mn) tolerance. To study the mechanism underlying its Mn adaptability, Mn2+ at various concentrations (0, 1000, 5000, 10000, 15000, and 20000 μM) were applied to M. cordata to investigate the subcellular distribution and chemical forms of Mn, as well as the resulting physiological and biochemical changes by pot culture experiment under natural light in a greenhouse. According to our results, Mn level in M. cordata increased with exogenous Mn concentrations; and Mn contents in different tissues exhibited a leaf > root > stem pattern. Meanwhile, biomass and the level of photosynthetic pigments increased at lower Mn concentrations but declined as Mn concentration further ascended. Subcellular distribution analysis revealed that Mn was sequestered in cell wall and vacuole; in addition, it was incorporated into pectates and protein, phosphates, and oxalates. These findings revealed a possible effective strategy for M. cordata to reduce Mn mobility and toxicity. Moreover, a continuous boost in the level of malondialdehyde was observed with Mn gradient; whereas contents of soluble proteins and proline, and the activities of superoxide dismutase and peroxidase were initially increased and then dropped. Altogether, these results indicated that most Mn was trapped in the cell wall and soluble fractions in low toxicity forms such as pectates and protein, phosphates, and oxalates. These strategies, that is functioning cooperatively with the well-coordinated antioxidant defense systems and the non-enzymatic metabolites, confer strong resistance to Mn in M. cordata.

Zeta potential of roots determined by the streaming potential method in relation to their Mn(II) sorption in 17 crops

To compare the zeta potentials of roots of 17 crops measured with streaming potential method and to test feasibility of this method for different plants. In addition to zeta potentials, surface charge and cation exchange capacity (CEC) of plant roots were measured independently. Mn(II) chemical forms sorbed on the roots were separated using sequential extraction. There was a significant positive correlation between the zeta potential, CEC and negative charge of plant roots, indicating that the zeta potentials of plant roots as measured by streaming potential method were reliable. The roots of legumes carried greater negative charge than did non-legumes, which was responsible for more exchangeable and complexed Mn(II) sorbed on legume roots. In the infrared spectroscopy, the intensity of absorption peaks of legume roots was higher than that of non-legume roots. This indicated a higher concentration of functional groups on the roots of legumes than those of non-legumes, which was the main reason for the greater CEC and more negative zeta potential of legume roots and their higher sorption of Mn(II) when compared with non-legume crops. Surface charge properties of plant roots determined their sorption capacity for Mn(II) and chemical forms of Mn(II) on the roots.

Distribution of Manganese(II) Chemical Forms on Soybean Roots and Manganese(II) Toxicity

Distribution of chemical forms of manganese(II) (Mn(II)) on plant roots may affect Mn(II) absorption by plants and toxicity of Mn(II) to plants at its high level. The chemical forms of Mn(II) on soybean roots were investigated to determine the main factors that affect their distribution and relationship with Mn(II) plant toxicity. Fresh soybean roots were reacted with Mn(II) in solutions, and Mn(II) adsorbed on the roots was differentiated into exchangeable, complexed, and precipitated forms through sequential extraction with KNO3, EDTA, and HCl. The exchangeable Mn(II) content on the roots was the highest, followed by the complexed and precipitated Mn(II) contents. Mn(II) toxicity to the roots was greater at pH 5.5 than at pH 4.2 due to the larger amount of exchangeable Mn(II) at higher pH. The cations Al3+, La3+, Ca2+, Mg2+, and NH4+ competed with Mn(II) for cation exchange sites on the root surfaces and thus reduced exchangeable Mn(II) on the roots, in the order Al3+, La3+ > Ca2+, Mg2+> NH4+. Al3+ and La3+ at 100 μmol L−1 decreased exchangeable Mn(II) by 80% and 79%, respectively, and Ca2+ and Mg2+ at 1 mmol L−1 decreased exchangeable Mn(II) by 51% and 73%, respectively. Organic anions oxalate, citrate, and malate reduced free Mn(II) concentration in solution through formation of complexes with Mn(II), efficiently decreasing exchangeable Mn(II) on the roots; the decreases in exchangeable Mn(II) on the roots were 30.9%, 19.7%, and 10.9%, respectively, which was consistent with the complexing ability of these organic anions with Mn(II). Thus, exchangeable Mn(II) was the dominant form of Mn(II) on the roots and responsible for Mn(II) toxicity to plants. The coexisting cations and organic anions reduced the exchangeable Mn(II) content, and thus they could alleviate Mn(II) toxicity to plants on acid soils.

Chemical forms in soil and availability of manganese and zinc to soybean in soil under different tillage systems

Chemical forms of Mn and Zn in the soil and its availability to soybeans grown in a Latosol for 12 years under different tillage systems were studied. The effects of these systems on Mn complexation by soil humic acid (HA) were also evaluated. The field experiment was carried out in a randomized block (three blocks) split-plot experimental design. The main treatments consisted of four tillage systems and the secondary, of three soil sampling depths (0.00–0.05m, 0.05–0.10m and 0.10–0.20m). The tillage systems were no tillage (NT), conventional tillage (CT), minimum tillage (MT) and NT with scarification, every three years. The results presented refers to the last 2 years of the experiment, 2000 and 2001. In average numbers, the Zn content of the 0.00–0.05m layer was lower in soil under CT (2mgkg−1), compared to the other tillage systems (NT and NT with scarification=2.7 and MT=2.8mgkg−1). In general, Zn percentages in exchangeable, organic, oxides and residual forms were not modified by the tillage systems. In turn, the Mn content of the soil surface layer under the NT was higher than in the soil under CT. Mn contents extracted with DTPA were 11 and 5.2mgkg−1 in the soil under NT and CT, respectively. The Mn contents extracted with Mehlich I, Mehlich III and HCl in the soil under CT were 20.8, 8.7 and 16.8mgkg−1, respectively. In the soil under NT, the contents extracted with the same extractors were 27.9, 15 and 29.2mgkg−1. In the surface layer, higher Mn percentages in the organic fraction were found in the soil under NT (19.2%) and NT with scarification (15.9%) than in soil under CT (11.8%). The Mn content of this layer was also positively correlated with the soil organic matter, but none of the extractors used (DTPA-TEA pH 7.3, HCl 0.1molL−1, Mehlich I and III) properly assessed the levels of Mn and Zn available to plants, suggesting the need for further studies. It was not observed presence of Mn in the HA samples by electron paramagnetic resonance (EPR). Since the digestion by nitro-perchloric acid of the HA samples showed the presence of Mn in these samples, it strengthens the hypothesis that Mn was bound to the HA in the form of stable complexes (covalent bonds), since this form of Mn cannot be detected by EPR. During soybean cultivation, Mn concentrations in the leaves did not vary with the tillage methods and were near or below the range considered adequate for the crop. Furthermore, visual symptoms of Mn deficiency in the leaves were observed in the initial stages of plant development, regardless of treatment. This suggests the need for new correlation and calibration studies for micronutrients in Brazil, especially for soils cultivated under the NT.

The role of chemical speciation, chemical fractionation and calcium disruption in manganese-induced developmental toxicity in zebrafish (Danio rerio) embryos

Manganese (Mn) is an essential nutrient that can be toxic in excess concentrations, especially during early development stages. The mechanisms of Mn toxicity is still unclear, and little information is available regarding the role of Mn speciation and fractionation in toxicology. We aimed to investigate the toxic effects of several chemical forms of Mn in embryos of Danio rerio exposed during different development stages, between 2 and 122h post fertilization. We found a stage-specific increase of lethality associated with hatching and removal of the chorion. Mn(II), ([Mn(H2O)6]2+) appeared to be the most toxic species to embryos exposed for 48h, and Mn(II) citrate was most toxic to embryos exposed for 72 and/or 120h. Manganese toxicity was associated with calcium disruption, manganese speciation and metal fractionation, including bioaccumulation in tissue, granule fractions, organelles and denaturated proteins.

Manganese species migration in soil at the Sabine National Wildlife Refuge, Louisiana.

A modified sequential extraction procedure was employed to speciate the chemical forms of Mn in sediment using flame atomic absorption spectrophotometry. Concentrations were determined in five different fractions for each sample (Mn in the exchangeable form, bound to carbonates, bound to Mn/Fe oxides, bound to organic matter and in the residual form). The determinations were made for sediments obtained from the Sabine National Wildlife Refuge while a marshland reclamation project was being conducted. Sediment samples were taken from Ship Channel dredge spoils (thought to be contaminated), an old reclamation site, a new reclamation site and a reference site. The results indicated that the Ship Channel sediments were not contaminated, but revealed an Mn "pumping" model, which proposes that additional Mn added to a similar site is concentrated near the surface soil layers by environmental conditions, which may be a cause of the observed slow recovery of vegetation at one of the more recently developed sites.

Evaluation of Sampling and Analytical Errors in the Determination of Manganese in Soils

Sampling variances and analytical variances were estimated in a study of five chemical forms of Mn in nine soil types from a greenhouse experiment. A sampling and analytical quality control scheme and a robust analysis of variance were used for this purpose and proved appropriate. The resulting statistics were then subjected to an assessment of analytical precision and sampling precision according to certain criteria. The results showed that the sampling variances and analytical variances in this experiment were good enough to describe the natural geochemical variances.