Potassium Fluosilicate Volumetric Method for Determination of Silica Content in Phosphate Rock

Abstract

The invention discloses a method for determining the content of silica in a phosphorus rock by potassium fluosilicate volumetric technology. The method comprises the following steps: processing a sample according to the prescription of the potassium fluosilicate volumetric technology in GB / T1873-1995 until a potassium fluosilicate form precipitate is obtained, filtering and washing the precipitate, adding a potassium chloride-ethanol eluent II into the precipitate and a paper pulp, adding a bromothymol blue-phenol red indicator, performing neutralization by using a sodium hydroxide standard titration solution while stirring, repeatedly scrubbing a cup wall until a stable bright purple color is formed, adding neutral boiling water regardless of reading, uniformly stirring the obtained solution, performing titration with the sodium hydroxide standard titration solution, adding the neutral boiling water when the obtained solution becomes purple, uniformly stirring the obtained solution, performing titration with the sodium hydroxide standard titration solution until an end point characterized by a stable bright purple color is reached, and calculating the silica content according to the titration volume of sodium hydroxide. The method has the advantages of reduction of the influences of the temperature on the hydrolysis of the precipitate, improvement of the accuracy and the stability, strong operability, and good safety and reliability.

Description

technical field [0001] The invention belongs to the field of chemical detection and analysis, and in particular relates to a method for measuring the silicon dioxide content in phosphate rock by adopting the potassium fluorosilicate volumetric method. Background technique [0002] In the national standard of the People's Republic of China, the determination of the silicon dioxide content of phosphate rock includes gravimetric method and volumetric method, among which the volumetric method is simple, fast and widely used. The principle of the potassium fluorosilicate volumetric method is: the sample is melted with potassium hydroxide, leached in water, acidified, and potassium chloride and potassium fluoride are added to the nitric acid solution to precipitate the silicic acid in the form of potassium fluorosilicate, which is filtered and washed. , remove the free acid, hydrolyze with neutral boiling water to generate hydrofluoric acid, use bromothymol blue-phenol red as indi...

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Problems solved by technology

The disadvantage of precipitation hydrolysis is that the hydrolysis reaction of potassium fluorosilicate precipitation is an endothermic reaction. The higher the temperature during hydrolysis, the more favorable the reaction is. It should be titrated immediately after adding neutral boiling water. When it is lower than 70 ° C, the fluorine silicon Potassium acid hydrolysis reaction speed is slow, the end point is unstable, and the measurement result is low. It is necessary to ensure that the temperature of the solution is greater than 70°C after the titration is completed.

In order to overcome the influence of temperature on the precipitation hydrolysis, the predecessors took several measures: (1) rapid titration after hydrolysis to speed up the titration speed, such as the discussion on the accuracy of the determination of silicon dioxide by potassium fluorosilicate volumetric method, (Huang Mingqing, Dai Guangfu , Building Materials Development Orientation, 2008.8,39-40), this method is more suitable for phosphate rock samples with low silica content, but for phosphate rock samples with high silica content, with the precipitation hydrolysis endothermic, titration The added sodium hydroxide solution increases and the titration time prolongs, especially in winter, when the temperature drops more, it is difficult to ensure that the solution temperature is above 70°C after the titration is completed; (2) after hydrolysis, continue to heat the polyethylene beaker with liquid to boiling, and then titrate, this method, because the polyethylene beaker cannot be heated with an open flame, and has poor thermal conductivity, it takes a long time to be heated to boiling, which reduces the analysis speed; (3) place the polyethylene beaker on a low-temperature electric heating Carry out insulation titration on the plate or in the water bath, such as the matters needing attention in the determination of silicon in ferrosilicon by potassium fluorosilicate volumetric method, (Wang Zhiqiang, Deng Yuhua, Industrial Science and Technology 2010 (39) 4:50-51), this method can Ensure that the temperature of the solution is above 70°C after the titration, but it requires high labor intensity for the analyst and increases the risk factor of the analysis

Because it is difficult to effectively guarantee the hydrolysis temperature, the stability of the measurement results is reduced, which limits the stability and accuracy of the results of the potassium fluorosilicate volumetric method

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