There are three types of potassium chloride products: I am a special industrial use of potassium chloride, which is suitable for electrolysis of potassium hydroxide, potassium chlorate, and other industrial use of potassium chloride Π, suitable for a variety of potassium fertilizer production and chemical industry. Class III agriculture uses potassium chloride, which is suitable for the application of compound fertilizer or directly as fertilizer.
The potassium chloride described in this paper is suitable for compound fertilizer or directly used as fertilizer. It exists in the form of white or red crystal, and its main component is potassium oxide. In the detection of potassium oxide content of potassium chloride products, attention should be paid to the following aspects:
Temperature control is the primary condition of solution preparation
According to 6.6 of general sampling rules for chemical products (GB / T 6678-2003), the number of sampling units shall be determined in the test. The sampler takes samples from one corner of the bag mouth to 3 / 4 of the bag depth, evenly mixes the collected samples, and reduces them to the sample quantity to be measured by quartering method. Because potassium chloride fertilizer has strong water absorption, it should be carried out as soon as possible when preparing samples. After sample preparation, weigh 5g sample, take 0.001g precision, add 150ml water. Then, the sample is heated under constant stirring and boiled for 5 minutes. After cooling to 20 ℃, transfer the sample to a 500 ml volumetric flask. This is a key link. For the convenience of some inspectors, they did not set the volume when the water temperature reached 20 ℃, but when the water temperature reached 20 ℃, the result was very high. When the water temperature is below 20 ℃, the result is very low. Two constant volumes result in two errors. Therefore, accurate test temperature is the key to the accuracy of test results. Compare the test results when the water temperature is higher than 20 ℃ with the test results when the water temperature is 20 ℃, as shown in Table 1.
Influence of detergent and distilled water on test results
The determination method of potassium oxide content is the same as iso2051:1976 determination of potassium chloride content of potassium for industrial use weight method of potassium tetraphenylborate. In the weak alkaline medium, the alkaline solution and washing solution of sodium tetraphenylborate (NAB (C6H5) 4) directly affect the test results. Because the preparation of sodium tetraphenylboron is very unstable, it is easy to produce turbidity. If turbidity is found before use, filter with medium speed filter paper first, otherwise the test result is too high. Washing liquid and distilled water have different effects. Some inspectors think that it is troublesome to replace the detergent with distilled water when preparing the detergent, and the test results will be relatively low. The comparison between the original results of distilled water and the correct results of detergent is shown in Table 1.
Washing step is the key
In the test, there is a problem that the end-point of washing is not clear after the test solution is filtered. According to the provisions of potassium chloride in GB 6549-1996, the supernatant is extracted and filtered first, and then the precipitate is transferred to the filter with the washing solution (i.e. potassium chloride solution). , room temperature saturated potassium tetraphenylboron solution). The above washing solution is washed and precipitated for about 12 times, and each time about 5ml of washing solution is washed. If the inspector does not clean enough times, the pink material can be clearly seen on the dry crucible, which is the color of the material produced by the uncleaned sodium hydroxide and phenolphthalein, which will eventually lead to high potassium content. Therefore, the washing time should not be less than 12 times. Compare the original result of less than 12 times of washing with the correct result of no less than 12 times, as shown in Table 1.
In conclusion, in the detection of potassium chloride products mainly composed of potassium oxide, several key links should be paid full attention to to avoid and overcome various factors that may cause errors, so as to ensure the accuracy of the detection results.