Treatment of kaolin with sulfuric acid is carried out in a pressure cooker with a pressure of 2 × 15 5 Pa for 2 - 3 h , with an 8 - 10% H 2 SO 4 solution and an excess, and the Fe and residual acid are washed away after treatment. About 90% of the Fe 2 O 3 in the kaolin is removed. A mixture of concentrated sulfuric acid and ammonium sulfate in a ratio of 1:2 is used. 100 °C The kaolin was treated for 2 hours , the suspension was filtered and washed with sulfuric acid, and titanium and iron impurities were removed. 0.1 - 0.5% hot solution of oxalic acid or sodium oxalate, the surface of the particles can occur in finely divided kaolin iron-titanium compound is dissolved and removed. Table 3 lists the results of treatment of kaolin with oxalic acid and its salts. According to the data, the bleaching research of kaolin in foreign countries has made new progress, such as adding ammonium chloride to the kaolin powder and heating it to 200 . 300 °C It reacts with iron in kaolin, and 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 Â Â Â 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 |
7 , biological iron removal
Different kinds of microorganisms ( bacteria, fungi, etc. ) have the ability to dissolve iron from iron oxide ( limonite, goethite, etc. ) , the dissolution of microorganisms and the formation of organic acids and other metabolites acting as complexing agents. Related, it is also related to the reduction of iron by enzymatic and non-enzymatic hydrolysis. The iron impurities contained in the kaolin can be removed by utilizing the ability of the microorganism to dissolve iron. A two-step treatment method has been developed: first, a culture solution ( ie, a leaching agent ) is prepared , and the leaching agent is a strain. 30 °C It is cultivated under the nutrient medium. The nutrient medium contains 3 g of NH 4 NO 3 , 1 g of KH 2 PO 4 , 0.5 g of MgSO 4 · 7H 2 O and unequal amounts of molasses per liter of natural water. The initial medium pH of about 7, such microorganisms on the surface of the water or the generation, depending on the required incubation time and the initial concentration of the culture medium in a method syrup, typically 5 - 14 days, when the syrup concentration is higher than the initial 150g At /1 , the final pH is always less than 2 , and the concentration of organic acid in the leaching agent is greater than 40g /1 . The sum of the content of oxalic acid and citric acid accounts for more than 95% of the total organic acid content, and the same leaching effect can be obtained by acidifying with a hydrochloric acid leaching agent containing the same amount of organic acid to pH=0.5 . After the leaching agent is prepared, 90 °C The kaolin was leached with a leaching agent. The kaolin of 11 different varieties was used in the experiment. The Fe 2 O 3 content ranged from 0.65% to 1.49% , and the Al 2 O 3 content was 32% to 35.2% , respectively. The form of matter, mainly goethite, is present in the kaolin lattice, and the remaining iron is infiltrated from the outside and contaminates the kaolin mycelium. Stirring strength test using 400 - 600r / min, the optimum concentration of pulp 20--25% the processing time is 2 - 5h. The results are shown in Table 4, it can be seen from the table, after leaching agent treatment, Fe 2 O 3 content of from 0.65 - 1.49% can be reduced to 0.44 - 0.75%, the whiteness of from 55 - 87 to 86 to improve - 92 Only a small amount of aluminum is leached from the kaolin along with the iron. Extending the leaching period 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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