Forty soils from top layer (0-20 cm) were sampled in different regions of China and Kjeldahl, HF-Kjeldahl and double treatment methods were used to determine total N, total N plus fixed ammonium, and total N and the r...Forty soils from top layer (0-20 cm) were sampled in different regions of China and Kjeldahl, HF-Kjeldahl and double treatment methods were used to determine total N, total N plus fixed ammonium, and total N and the residual fixed ammonium left in soil after determination of total N, respectively, to evaluate if Kjeldahl’s method could include the fixed N by soil minerals. The fixed N by soil minerals was measured by Silva-Bremner procedure to make comparison. Results showed that total N determined by Kjeldahl’s method averaged 1.622 g kg-1, while that by HF- Kjeldahl’s method 1.633 g kg-1, and that by double procedure 1.666 g kg-1. Obviously results obtained by the last two methods, particularly the double treatment method, were higher than Kjeldahl’s, showing that Kjeldahl’s method could not or not fully release N fixed by 2:1 minerals in soil, and therefore the determined results would not be the true “total N” for soils that contained large amount of the fixed N. The mineral fixedN averaged 166 mg kg-1, accounting for 10.1% of the total N while the residual fixed N amounted to 30.4 mg kg-1, equivalent to 1.9% of the total N or 18.3% of the total fixed N. The residual fixed N was correlated neither to organic matter nor to total N, but closely related to the total fixed N with a correlation coefficient of 0.598 (n=40), showing that the fixed N was the sole source of the residues. Soils having high residues of the fixed N were just those containing high fixed N, and soils containing high fixed N were just those containing high amount of 2:1 minerals. As a result, Kjeldahl’s method could not give a true value of the total N for such soils. However, for those containing small or little amount of 2:1 minerals, there was no significant difference in results measured by these methods.展开更多
A novel method for the preparation of single-phase ammonium dimolybdate with industrial ammonium molybdate was studied. Various in- fluential factors were evaluated in the paper, including reaction temperature, reacti...A novel method for the preparation of single-phase ammonium dimolybdate with industrial ammonium molybdate was studied. Various in- fluential factors were evaluated in the paper, including reaction temperature, reaction time, initial molybdenum concentration, initial NH_3 /Mo molar ratio, and stirring speed. Under the optimum experimental conditions, the crystallization rate of product is 85.23%. The X-ray diffraction (XRD) analysis and chemical analysis show that the product is single-phase ammonium dimolybdate, and no impurity phases exist. The scanning electronic microscope (SEM) image reveals uniform particle size, good particle dispersion, and no agglomeration between particles. Meanwhile, the final pH value of acidification was investigated. The total molybdenum recovery can reach up to 99.40%, and the main phases of acidification product are the same as those of raw material with the final pH value of 1.5. This determines that the acidification product can be used as a raw material to produce single-phase ammonium dimolybdate.展开更多
基金the National Natural Sci。ence Foundation of China(30230230,30070429 , 40201028)
文摘Forty soils from top layer (0-20 cm) were sampled in different regions of China and Kjeldahl, HF-Kjeldahl and double treatment methods were used to determine total N, total N plus fixed ammonium, and total N and the residual fixed ammonium left in soil after determination of total N, respectively, to evaluate if Kjeldahl’s method could include the fixed N by soil minerals. The fixed N by soil minerals was measured by Silva-Bremner procedure to make comparison. Results showed that total N determined by Kjeldahl’s method averaged 1.622 g kg-1, while that by HF- Kjeldahl’s method 1.633 g kg-1, and that by double procedure 1.666 g kg-1. Obviously results obtained by the last two methods, particularly the double treatment method, were higher than Kjeldahl’s, showing that Kjeldahl’s method could not or not fully release N fixed by 2:1 minerals in soil, and therefore the determined results would not be the true “total N” for soils that contained large amount of the fixed N. The mineral fixedN averaged 166 mg kg-1, accounting for 10.1% of the total N while the residual fixed N amounted to 30.4 mg kg-1, equivalent to 1.9% of the total N or 18.3% of the total fixed N. The residual fixed N was correlated neither to organic matter nor to total N, but closely related to the total fixed N with a correlation coefficient of 0.598 (n=40), showing that the fixed N was the sole source of the residues. Soils having high residues of the fixed N were just those containing high fixed N, and soils containing high fixed N were just those containing high amount of 2:1 minerals. As a result, Kjeldahl’s method could not give a true value of the total N for such soils. However, for those containing small or little amount of 2:1 minerals, there was no significant difference in results measured by these methods.
基金supported by the National Natural Science Foundation of China(No.51072233)
文摘A novel method for the preparation of single-phase ammonium dimolybdate with industrial ammonium molybdate was studied. Various in- fluential factors were evaluated in the paper, including reaction temperature, reaction time, initial molybdenum concentration, initial NH_3 /Mo molar ratio, and stirring speed. Under the optimum experimental conditions, the crystallization rate of product is 85.23%. The X-ray diffraction (XRD) analysis and chemical analysis show that the product is single-phase ammonium dimolybdate, and no impurity phases exist. The scanning electronic microscope (SEM) image reveals uniform particle size, good particle dispersion, and no agglomeration between particles. Meanwhile, the final pH value of acidification was investigated. The total molybdenum recovery can reach up to 99.40%, and the main phases of acidification product are the same as those of raw material with the final pH value of 1.5. This determines that the acidification product can be used as a raw material to produce single-phase ammonium dimolybdate.
