1. What is the standard of potassium fertilizer content
Potash fertilizer is a fertilizer with potassium as the main nutrient, so the content of potassium in potassium fertilizer is one of the criteria for judging its quality 1. Generally speaking, the content of potassium in potash fertilizer is calculated by the content of potassium oxide, so what is the standard of potassium fertilizer content?
There are many types of potash fertilizers. Different types of potash fertilizers have different potassium content. It is understood that in general potash fertilizers, the content of potassium chloride is greater than or equal to 60%, and the content of potassium sulfate is greater than or equal to 50%. , the potassium nitrate content is greater than or equal to 46%, most of the potassium in other compound potassium fertilizers is mixed with the above fertilizers, and the specific content is shown on the package label.
In terms of the content standard of potassium fertilizer, taking potassium chloride as an example (agricultural type), the standard of the quality fraction of potassium chloride of superior grade is ≥60.0%, and the mass fraction of water is ≤2.0%; one The standard of mass fraction of potassium chloride of equivalent product is ≥57.0%, and the mass fraction of moisture is ≤4.0%; the standard of mass fraction of potassium chloride of qualified product is ≥55.0%, and the mass fraction of moisture is ≤6.0%.
II. Determination formula of potassium content in potassium fertilizers
Potassium is one of the three elements of plant nutrition, and potassium fertilizer is also one of the three widely used in agriculture. One of the fertilizers, the potassium tetraphenylborate gravimetric method is the most widely used for the determination of potassium content in potash fertilizers in my country. This method has the characteristics of accurate determination results, but it takes a long time.
The determination principle of potassium tetraphenylborate gravimetric method is: in weak alkaline medium, use sodium tetraphenylborate solution as precipitant to precipitate potassium ions in the sample solution to generate white potassium tetraphenylborate The precipitate was filtered, washed, dried and weighed. The potassium content in the fertilizer was calculated based on the sediment quality. The reaction formula is:
K++Na[B(C6H5)4] →K[B(C6H5)4] ↓+ Na+
III. Potassium content in potassium fertilizer Determination method of
1. Preparation of sample solution
Weigh the sample (sample prepared according to GB/T8571) About 2g-5g (containing about 400mg of potassium oxide), accurate to 0.0002g, put it in a 250mL conical flask, add about 150mL of water, heat and boil for 30min, cool, quantitatively transfer it to a 250mL volumetric flask, dilute with water to the mark, and mix well , dry filtration, discard the initial filtrate 50mL.
2. Test solution treatment
Draw 25mL of the above filtrate into a 250mL beaker, add 20mL of EDTA solution (40g/L) Add 40mL), add 2-3 drops of phenolphthalein indicator (5g/L ethanol solution), dropwise add sodium hydroxide solution (400g/L) until the red color just appears, and then add 1mL in excess, cover with a watch glass, and keep in good ventilation. Slowly heat and boil in the cabinet for 15 minutes, then cool down. If the red color disappears, adjust it to red with sodium hydroxide (400g/L). (If the sample contains cyanamide or organic matter, before adding the EDTA solution, add bromine water and activated carbon for treatment: add 5 mL of 5% bromine water solution, boil and decolorize the solution until it has no bromine color, if it contains other colors , evaporate the volume of the solution to less than 100mL, add 0.5g of activated carbon after cooling and stir it fully to make it adsorb, then filter and wash, and wash with about 5mL of water each time, the number of times is 3-5 times, and collect all the filtrate).
3. Precipitation and Filtration
Under constant stirring, add sodium tetraphenylborate precipitant ( 15g/L), the addition amount is 0.5mL of precipitating agent for every 1mg of potassium oxide, and the excess is 7mL, continue to stir for 1min, let stand for more than 15min, and filter the precipitate into No. 4 pre-constant weight at 120 ℃ In the glass crucible filter, wash the precipitate with sodium tetraphenylborate washing solution (1.5g/L) 5-7 times, each time about 5mL, and finally wash twice with water, each time about 5mL.
4. Drying
Put the crucible containing the precipitation in a drying oven at 120℃±5℃, dry for 1.5h, take it out and put it to dry Cool in the container and weigh.
5. Do a blank test
The analysis steps and reagent dosage are the same as the above steps, except that no test solution is added.
6. Calculation results and data processing
The potassium content of the sample is represented by the mass fraction of potassium oxide X (K2O) (%), and the calculation formula is:
X(K2O)=[(m2-m1)*0.314/m0*(25/250)]*100=(m2-m1)*131.4/m0
where m2 is the mass of the precipitate obtained from the test solution, m1 is the mass of the precipitate obtained by the blank test, m0 is the mass of the sample, and 0.314 is the coefficient of the mass of potassium tetraphenylborate converted to the mass of potassium oxide.
When the mass fraction of potassium in the determination result is less than 10.0, the allowable difference in parallel determination is 0.20%, and the allowable difference in different laboratories is 0.40%; when the mass fraction of potassium is 10.0-20.0, the allowable difference in parallel determination is 0.40%. The difference is 0.30%, and the allowable difference in different laboratories is 0.60%; when the mass fraction of potassium is greater than 20.0, the allowable difference in parallel determination is 0.40%, and the allowable difference in different laboratories is 0.80%. Take the arithmetic mean of the parallel measurement results as the measurement result.
