The process of bleaching diatomaceous earth

Abstract

[Solution] The subject of the invention is a method for bleaching diatomaceous earth, in which the diatomaceous earth is reacted with hydrochloric acid or with a mixture of hydrochloric and nitric acids at temperatures between 62°C and 108°C, after which the diatomaceous earth is filtered and dried.

Description

[Technical field]

[0001] The subject of the present invention is a method for bleaching diatomaceous earth. [Background technology]

[0002] Diatomite is a sedimentary rock of organic origin formed by the accumulation of organic remains or the precipitation of chemicals resulting from the physiological transformation of organisms, mainly single-celled algae (diatoms). Usually, diatomite forms as a deposit in cold water.

[0003] Diatomaceous earth consists primarily of amorphous SiO2 silica with some crystalline silica, although due to the presence of other living organisms, it may also contain detrital quartz, calcite, glauconite, argillaceous materials, and iron compounds. Diatomaceous earth has been used in many industries, for example, as a filtration material, bleaching agent, dehydrating agent, as a fire-resistant insulation material, as an absorbent for liquid fertilizers, disinfectants, and pesticides, in the manufacture of paints, varnishes, cosmetics, and in products intended to come into contact with food.

[0004] In the prior art, methods for bleaching diatomaceous earth are known which involve a calcination process in which the material is roasted to partially decompose the material while releasing water or other substances from its structure.

[0005] China Patent Publication No. 101486467 discloses a method for obtaining white diatomite. The claimed method includes calcining diatomite at a temperature of 700°C-1100°C for 4-8 hours, and the diatomite further has 3%-10% of an auxiliary agent, such as Na2CO3, CaCO3, NaCl, CaCl2, MgCO3, MgCl2, NaOH or a selected mixture.

[0006] US Patent No. 4,325,844 relates to an energy-efficient method of calcining diatomaceous earth, in which the diatomaceous earth is used to produce small beads containing 15% to 50% moisture, which are then calcined at temperatures between 923°C and 1290°C. Optionally, the calcined material can also contain a bleaching agent such as phosphoric acid, and the calcination process itself is carried out in a rotary tubular furnace.

[0007] China Patent Publication No. 1322673 discloses a method for purifying diatomaceous earth, in which the starting material is washed with sulfuric acid and heated at a temperature of 500°C to 550°C for 1 to 1.5 hours, followed by calcination at a temperature of 220°C to 280°C for 2 to 2.5 hours.

[0008] It is an object of the present invention to develop an energy efficient method for bleaching diatomaceous earth. Summary of the Invention [Means for solving the problem]

[0009] The subject of the invention is a method for bleaching diatomaceous earth, which involves heating the diatomaceous earth at high temperatures, characterized in that it comprises a step of reacting the diatomaceous earth with hydrochloric acid or with a mixture of hydrochloric and nitric acids at a temperature between 62°C and 108°C, followed by filtering and drying the diatomaceous earth.

[0010] Preferably the ratio of diatomaceous earth to hydrochloric acid is 1:1 w / v.

[0011] Preferably, the ratio of diatomaceous earth to the mixture of hydrochloric and nitric acid is 1:6 w / v.

[0012] Preferably, the concentration of hydrochloric acid is 35 to 38% by weight.

[0013] Preferably, the concentrations of hydrochloric acid and nitric acid are 35-38% by weight and 98-99.5% by weight, respectively.

[0014] Preferably, the volume ratio of hydrochloric acid to nitric acid in said mixture is 3:1.

[0015] Preferably, the reaction is carried out for 6 to 12 hours.

[0016] Preferably, the drying is carried out at a temperature of 60 to 80°C.

[0017] Preferably, the drying is carried out for 24 to 36 hours.

[0018] Diatomite bleaching was carried out on diatomite obtained from freshwater sediments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present invention is described in more detail in the embodiments, but these embodiments do not limit the scope of the present invention.

[0020] Working Example Wet method for bleaching diatomaceous earth 200g of amorphous diatomaceous earth was reacted with 200ml of 35% HCl or 900ml of a mixture of 35% HCl and 300ml of 98% HNO3. The reaction was carried out for 8 hours at temperatures ranging from 62°C to 108°C. After the reaction, the diatomaceous earth was dried at 75°C for 24 hours.

[0021] Color measurements were performed using the EnviSense NR60CP colorimeter in the CIELAB system (L * a * b * The results are shown in Table 1.

[0022] Comparative Example Dry method for bleaching diatomaceous earth Amorphous diatomite was subjected to calcination treatment in a flow of argon (tubular furnace) or air (muffle furnace). The samples were exposed to temperatures ranging from 750°C to 1000°C for 6 hours. The study was carried out in several configurations, as shown in Table 1.

[0023] Color measurements were performed using the EnviSense NR60CP colorimeter in the CIELAB system (L * a * b * The results obtained by the dry method are shown in Table 1. [Table 1] TIFF2025506602000002.tif110128ΔE - total color difference;ΔL - lightness difference;L - lightness;a - green to red-purple color;b - blue to yellow color;o Base diatomaceous earth - amorphous diatomaceous earth;Fractional diatomaceous earth - amorphous diatomaceous earth that has been subjected to a fractionation process and broken into fragments of a narrow particle size range.

[0024] It was concluded that the dry method of bleaching leads to the conclusion that the proper configuration of the samples placed in the tube furnace has a significant effect on the calcination process, resulting in a change in the luminescence of the diatomite, i.e. a decrease in the luminance value. The wet method using 35% HCl increased the luminance of the obtained samples (L = 92.97). The mixed acid of HCl and HNO3 used in this method increased the value of the L parameter to 94.11.

Claims

1. 1. A method for bleaching diatomaceous earth, comprising heating the diatomaceous earth at an elevated temperature, the method comprising: a) reacting diatomaceous earth with hydrochloric acid or with a mixture of hydrochloric and nitric acids at a temperature between 62°C and 108°C; b) filtering and drying the diatomaceous earth; The method of claim 1, further comprising:

2. 2. The method of claim 1, wherein the ratio of diatomaceous earth to hydrochloric acid is 1:1 w / v.

3. 2. The method of claim 1, wherein the ratio of diatomaceous earth to the mixture of hydrochloric acid and nitric acid is 1:6 w / v.

4. The method according to claim 1 or 2, characterized in that the concentration of hydrochloric acid is 35-38%.

5. The method according to claim 1 or 3, characterized in that the concentrations of hydrochloric acid and nitric acid are 35-38% and 98-99.5%, respectively.

6. 6. The method of claim 1, 3, or 5, wherein the volume ratio of hydrochloric acid to nitric acid in the mixture is 3:

1.

7. The method according to any one of claims 1 to 6, characterized in that the reaction is carried out for 6 to 12 hours.

8. The method according to any one of claims 1 to 7, characterized in that the drying is carried out at a temperature of 60 to 80°C.

9. The method according to any one of claims 1 to 8, characterized in that the drying is carried out for 24 to 36 hours.

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