To treat kaolin with sulfuric acid, it should be kept in a pressure cooker with a pressure of 2×155Pa for 2-3 hours. Use 8-10% H2SO4 solution and excess. After treatment, remove Fe and residual acid. In this way, the kaolin can be removed. 90% Fe2O3. The mixture was treated with a mixture of concentrated sulfuric acid and ammonium sulfate in a ratio of 1:2 at value="100" unitname="°C" w:st="on">100 °C for 2 h, the suspension was filtered and washed with sulfuric acid. Titanium and iron impurities can be removed. The hot titanium solution of 0.1 to 0.5% of oxalic acid or sodium oxalate can be used to dissolve and remove the iron-titanium compound which is present on the surface of the finely divided kaolin particles. Table 3 lists the results of treatment of kaolin with oxalic acid and its salts. According to the data, the bleaching research of foreign kaolin has made new progress, such as adding ammonium chloride to the kaolin powder, heating to 200-value="300" unitname="°C" w:st="on" When it is >300 ° C, it reacts with iron in kaolin. After cooling, the product is leached with dilute HCl to be bleached. However, it is still in the experimental stage, and bleaching is carried out under high temperature and airtight conditions.
Table 3 Test results of treatment of kaolin with oxalic acid and its salts
| Mineral sample | Fe 2 O 3 content (%) | TiO 2 content (%) | ||
| Before treatment | After processing | Before treatment | After processing | |
| No.1 | 0.36 | 0.19 | 0.50 | 0.47 |
| No.2 | 1.22 | 0.49 | 0.72 | 0.51 |
| No.3 | 0.83 | 0.40 | 1.11 | 0.71 |
Biological removal of different types of microorganisms (bacteria, fungi, etc.) has the ability to dissolve iron from iron oxide (limonite, goethite, etc.), and the dissolution of microorganisms acts as a complexing agent. The organic acid in the spoon is related to the formation of other metabolites, and also related to the reduction of iron by enzymatic hydrolysis and non-enzymatic hydrolysis. By using the ability of the microorganism to dissolve iron, the iron impurities contained in the kaolin can be removed. A two-step process has been developed: first prepare a culture solution (ie, a leaching agent), and the leaching agent places the strain at a value="30" unitname="°C" w:st="on">30°C. Cultured in a nutrient medium. The nutrient medium contains 3 g of NH4NO3, 1 g of KH2PO4, 0.5 g of MgSO4·7H2O, and no equivalent amount of molasses per liter of natural water. The initial pH of the medium is about 7, and the microorganisms are formed on the surface or in water. The time required for the culture depends on the initial concentration of the syrup in the culture method and medium, usually 5-14 days, when the syrup is initially When the concentration is higher than value="150" unitname="g" w:st="on">150g/1, the final pH value is always less than 2, and the concentration of organic acid in the leaching agent is greater than value="40 " unitname="g" w:st="on">40g/1. The sum of the content of oxalic acid and citric acid accounts for more than 95% of the total organic acid content. It can also be obtained by acidifying with hydrochloric acid to pH=0.5 in a synthetic leaching agent containing the same amount of organic acid. Take the effect. After the leaching agent is prepared, the kaolin is leached with leaching agent at value="90" unitname="°C" w:st="on">90°C. The test uses 11 different kinds of kaolin, the Fe2O3 content is from 0.65% to 1.49%, etc., Al2O3 content is 32% to 35.2%, iron is in the form of hydroxide, the most important is goethite, which is in the form of inclusions in the kaolin lattice, and the rest of the iron It is infiltrated from the outside and contaminates the kaolin mycelium. The test used stirring intensity of 400-600r/min, the optimal concentration of pulp was 20-25%, and the treatment time was 2-4h. The results are shown in Table 4. It can be seen from the table that after the leaching agent treatment, the Fe2O3 content can be reduced from 0.65-1.49% to 0.44-0.75%, and the whiteness is increased from 55-87 to 86-92. Only a portion of the aluminum is leached from the kaolin along with the iron. Extending the leaching cycle can leaching more iron in the kaolin, but at the same time causing the aluminum to dissolve strongly, so the general leaching time should be properly controlled.
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