Production of fusion with sodium peroxide is generally used in carbon ferrochrome acidification specimen at high temperature, and then analyzed. Thus, when the respective elements in the high carbon ferrochrome are separately measured, a large amount of time is wasted in the melt acidification pretreatment of the sample. To this end, it is proposed to determine the content of chromium, phosphorus and manganese in high carbon ferrochrome by systematic analysis. Table 1 High carbon ferrochrome standard chromium measurement results ( n = 6 ) % Standard number standard value Measurement average standard deviation RSD BH0310-3 58.37 58.5 0.14 0.24 BH0310-4 61.74 61.75 0.35 0.57 GBW1424 68.75 68.76 0.32 0.46 FeCr67C9.5 68.08 68.07 0.37 0.55 Table 2 High carbon ferrochrome standard phosphorus measurement results ( n = 6 ) % Standard number standard value Measurement average standard deviation RSD FeCr55C1000 0.022 0.0225 0.0007 3.14 GBW01424 0.025 0.0253 0.0012 4.75 BH0310-4 0.049 0.049 0.0014 2..95 BH0310-3 0.073 0.073 0.0028 3.87 Table 3 High carbon ferrochrome standard manganese measurement results ( n = 6 ) % Standard number standard value Measurement average standard deviation RSD FeCr67C9.5 0.19 0.19 0.007 3.72 BH0310-3 1.3 1.29 0.021 1.64 BH0310-4 0.51 0.508 0.019 3.76 FeCr55C1000 0.34 0.342 0.012 3.51 When the sample is melted with sodium iron oxide by iron shovel, it should be heated and baked in a low temperature electric furnace to a burnt yellow color, and then transferred to a high temperature furnace at 700 ° C for melting. Otherwise, the moisture in the sodium peroxide flux is likely to splash out when exposed to high temperatures, causing the analysis to fail. When ammonium persulfate is used to oxidize chromium, the acidity of the solution has a great influence on the analysis results. When the acidity is large, the oxidation of chromium is slow; when the acidity is small, the precipitation of MnO 2 is easy to precipitate. It is generally considered that the acidity is preferably 4 to 8 mL of concentrated sulfuric acid or phosphoric acid in a 100 mL solution.
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After alkali-melting acidification of the sample, the determination of the amount of chromium by the ammonium ferrous sulfate titration method and the determination of the amount of phosphorus by the molybdenum sulfate-reduced molybdenum blue method have been reported. This law has been improved on this basis:
(1) After hot water leaching, the heating and boiling decomposition H 2 O 2 process is omitted, and after direct neutralization with sulfuric acid, a small amount of trivalent which may be reduced by H 2 O 2 is oxidized with ammonium persulfate in the presence of the catalyst silver nitrate. Chromium is hexavalent.
(2) After caustic acidification, directly add perchloric acid and hydrochloric acid to chrome, and then develop color with ammonium molybdate barium sulfate, and measure the amount of phosphorus by molybdenum blue light method. The above two improvements make the determination procedure of chromium and phosphorus simple, fast, accurate, and the analysis period is greatly shortened. The remaining test solution can also be used to determine the amount of manganese by ammonium persulfate silver salt oxidative spectrophotometry.
First, the instrument and reagent 721 spectrophotometer.
Sodium peroxide: solid;
Sulfuric acid: 1+1;
Phosphoric acid: Ï about 1.70g / mL;
Manganese sulfate solution: 4%;
Silver nitrate solution: 1%;
Ammonium persulfate solution: 15%;
Sodium chloride solution: 5%;
N - benzoo-aminobenzoic acid indicator: 0.2%;
Ammonium ferrous sulfate standard solution: 0.08 mol / L;
Perchloric acid: Ï about 1.67g / mL;
Hydrochloric acid: Ï about 1.19g / mL;
Sodium bisulfite solution: 10%;
Ammonium molybdate solution: Weigh 20g of ammonium molybdate dissolved in 200mL of warm water, add 700mL of sulfuric acid (1+1) while stirring, then dilute to 1000mL with water, shake well;
Barium sulfate solution: Weigh 1.5g of barium sulfate dissolved in 200mL of water, dilute to 1000mL with water, shake;
Color developer solution: when used, take 25mL ammonium molybdate solution, 10mL barium sulfate solution and 65mL water, mix;
EDTA solution: 5%.
Second, the experimental part
(1) Preparation of test solution
0.5000 g of the sample was weighed into an iron crucible containing 5 g of sodium peroxide in advance, stirred and mixed, and then covered with 1 g of sodium peroxide, and the crucible was placed on a low-temperature electric furnace and baked to a burnt yellow color. Cover the lid, transfer it to a high temperature furnace and heat it to 700 ° C for 5 min. Remove it and cool it slightly. Place it in a 400 mL beaker containing 100 mL of hot water. Heat it to dissolve the melt in the crucible, rinse it with water and cover it. . Add sulfuric acid (1+1) to pH test paper until it is acidic, and excess 10mL sulfuric acid (1+1), heat and boil until the residue dissolves. If it is not completely dissolved, add sulfuric acid until the solution is clear (no residue on the bottom of the cup) If there is residue, the melt treatment is not complete. After cooling, transfer to a 250mL volumetric flask, dilute to the mark with water, and shake to a test solution.
(II) Determination of chromium by ammonium persulfate oxidation capacity method
Pipette 50 mL of the test solution into a 500 mL Erlenmeyer flask, add 12 mL of sulfuric acid (1+1), 8 mL of phosphoric acid, and dilute with water to a volume of about 200 mL of the test solution. Add 3 drops of manganese sulfate solution, 10mL silver nitrate solution, 15mL ammonium persulfate solution, and heat to boil until the chromium is completely oxidized to high-priced chromium (the test solution is magenta-colored magenta, indicating that the chromium has been oxidized to hexavalent). Continue to boil for 4-6 minutes to completely decompose the excess ammonium persulfate. Add 10mL of sodium chloride solution, heat to boil until the purple red disappears, if the residual purple does not disappear, add 3 ~ 5mL of sodium chloride solution, continue to boil until the silver chloride precipitates and sinks, the solution becomes clear. Remove a little cooling (avoid sudden cooling with running water, broken conical flask), cool to room temperature with running water, add 20mL sulfuric acid (1+1), titrate the solution with ammonium ferrous sulfate standard solution when yellowing green, add N - benzene 3 drops of the o-aminobenzoic acid indicator, continue to titrate until the solution rose disappears and turns to bright green as the end point. Calculate the chromium content as follows:
Cr%=T Cr ×V
Wherein T Cr - the standard solution of ferrous ammonium sulfate per milliliter corresponds to the percentage of chromium;
V - The number of milliliters of ammonium ferrous sulfate standard solution consumed when titrating the sample. [next]
(III) Determination of phosphorus by molybdenum blue light method
Pipette 50mL of test solution into a 200mL high-type beaker, add 20mL of perchloric acid, heat and evaporate to white smoke (when the cup bottom test solution is high-priced chrome yellow), add hydrochloric acid to volatilize the chromium (brown chromic chloride gas) After heating, the reduced chromium is oxidized, and then hydrochloric acid is repeatedly added dropwise to remove chromium, until the chromic acid brown vapor is no longer present, and the white smoke is further heated for 30 seconds to remove chlorine.
After taking off a little cooling, add 50mL of hot water to dissolve soluble salts (silicic acid insoluble in the test solution), boil, remove, filter with a cotton wool in a 250mL volumetric flask, wash the precipitate (silicic acid) and filter paper 4~ with warm water. 6 times, the precipitate was discarded, the filtrate was cooled to room temperature with running water, diluted with water to the mark, and shaken.
Pipette 25mL of the filtrate into a 100mL volumetric flask, add 10mL of sodium bisulfite solution, heat in a boiling water bath until the solution is colorless, remove, immediately add 25mL of color developer solution, then heat in boiling water bath for 10min, remove, Cool slightly, cool to room temperature with water, dilute to the mark with water, and shake well. The color developing solution was transferred to a 3 cm cuvette, and water was used as a reference solution, and the absorbance value was measured at a wavelength of 700 nm of a spectrophotometer.
Weigh 3 to 5 high-carbon ferrochrome standards with different phosphorus contents, measure the absorbance value by the same analytical method as the sample, and plot the working curve with the phosphorus content as the abscissa and the absorbance value as the ordinate.
(4) Determination of Manganese by Oxidation Spectrophotometry of Ammonium Persulfate Silver Salt
Pipette 50mL of test solution into a 200mL high-type beaker, add 20mL of perchloric acid, heat and evaporate to white smoke (when the cup bottom test solution is high-priced chrome yellow), add hydrochloric acid to volatilize the chromium (brown chromic chloride gas) Continue heating to oxidize the reduced chromium, then add hydrochloric acid repeatedly to remove chromium, until the brown gas no longer appears, continue to heat and boil white smoke to remove chlorine.
Remove a little cooling, add 30mL of hot water, heat near boiling to dissolve soluble salts. Filter with a cotton wool in a 150 mL Erlenmeyer flask, and wash the precipitate (silicic acid) and filter paper 4 to 6 times with hot water. Add 5mL sulfuric acid (1+1) and 3mL phosphoric acid to the filtrate. At this time, the volume of the test solution should be about 60mL (if the volume of the test solution is too large, it should be heated and evaporated). Add 5mL silver nitrate solution, 10mL ammonium persulfate solution, heat. Boil for 1 min, remove and cool slightly, then cool to room temperature with running water, transfer to a 100 mL volumetric flask, dilute to the mark with water, and shake well.
Part of the color developing solution was transferred to two 3 cm cuvettes, one of which was added with 2 drops of EDTA solution, and the purple color was removed as a blank solution. The absorbance value was measured at a wavelength of 530 nm of the spectrophotometer. The percentage of manganese was found from the working curve.
3 to 5 high-carbon ferrochrome standards with different manganese contents were weighed, and the absorbance values ​​were measured by the same analytical method as the sample, and the working curve was plotted with the manganese content as the abscissa and the absorbance value as the ordinate.
Third, the results and discussion
Chromium, phosphorus and manganese were tested by high carbon ferrochrome standard in this method. The comparison of the results is shown in Tables 1-3.
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Before the chromium is not completely oxidized to hexavalent chromium, the presence of HCl or Cl - is prevented in the test solution, and AgCl is precipitated by Ag + in CL - and AgNO 3 , causing the AgNO 3 to lose the action of the catalyst, and the analysis fails.
The N - benzoo-aminobenzoic acid indicator itself has a reducing property, and 2 to 3 drops can be added, and the result of multi-chrome analysis will be low. The chromium and trivalent iron in the test solution affect the determination of phosphorus, and the chromic acid is added to oxidize the chromium to high-valent chromium. The hydrochloric acid is repeatedly added dropwise to cause the chromium to form a brown chromic chloride gas to eliminate the interference of chromium. The interference of ferric iron can be removed by adding sodium bisulfite to boil.
When phosphorus is measured, a color developing agent is added, and under heating and boiling conditions, orthophosphoric acid and ammonium molybdate form phosphorus molybdenum yellow, which is then reduced to a phosphorus molybdenum blue complex by barium sulfate to improve the sensitivity of measuring phosphorus.
When measuring manganese, the chromium and ferric iron and chloride in the test solution interfere with the analysis of manganese. The addition of perchloric acid to oxidize the chromium to high-valent chromium, and the repeated addition of hydrochloric acid causes the chromium to form a brown chromic chloride gas to remove the interference, chlorine. The roots are also volatilized and removed when the perchloric acid emits white smoke. The addition of phosphoric acid can eliminate the interference with Fe 3+ to form [Fe(PO 4 ) 2 ] 3- colorless complex, and the presence of phosphoric acid enlarges the oxidation range of manganese. The formation of MnO 2 can be prevented, and the stability of permanganic acid can also be increased.
The experimental method is suitable for the combined determination of Cr, P and Mn in medium carbon ferrochrome and ferrochrome iron. The ferrochrome nitride sample entering Laigang is passed through 0.088mm mesh hole and the Cr is determined by this method. , P, Mn precision and accuracy are very high. Low-carbon, micro-carbon ferrochrome is converted to 20 mL of bromine- saturated hydrochloric acid to dissolve the sample, and 10 mL of perchloric acid is added to evaporate to white smoke, and the mixture is cooled, 50 mL of water is added, the salt is boiled, and the filter is filtered in a 250 mL volumetric flask with hot cotton. Wash with water 6-8 times, cool to room temperature, dilute to the mark with water, shake well. The following operations were combined with the determination of Cr, P, and Mn in high carbon ferrochrome.
Fourth, the conclusion
In this study, the high carbon ferrochrome sample was treated by the alkali fusion acidification method, and the effect was good. The use of the same mother liquor for the determination of chromium, phosphorus, manganese and other elements, reducing the pretreatment process of the sample, greatly shortening the analysis cycle, using this method to measure different levels of high carbon ferrochrome standards, the test results show that as long as The acidity and conditions of each element are controlled, the precision and accuracy of the method are very high, and the error of the analysis result is completely within the error range of the national standard. The method is feasible.