How to remove iron impurities in kaolin and increase their whiteness
The types of pigment ions are different, and the reagents and methods used are different:1, the surface of the adsorbed kaolinite is Fe3+, that is, when iron exists in the form of Fe2O3, the reaction of Fe3+ with Na2S2O4 is reduced to two valent iron salt, which is removed by rinsing and filtering;2, when the adsorption ion is Fe2+, that is iron in the form of FeS2, the oxidant should be used and its reaction, the oxidation of soluble ferrous sulfate and ferric sulfate, so that it can be washed away colorless oxides;3, the majority of samples containing both Fe3+ and Fe2+, the oxidation reduction combined bleaching method, first with the oxidant and reducing agent will become Fe2+ Fe3+ its reduction to Fe2+. Removed by rinsing, filtering, etc.
The two stage bio bleaching method refers to: firstly, Aspergillus niger in shake flask cultivation fermentation, 10 days or so, organic acids accumulated to a certain amount, then separate, the addition of kaolin can also achieve iron removal and whitening effect. The two stage biological bleaching method not only overcomes the above-mentioned shortcomings of in-situ biological bleaching, but also achieves the highest concentration of organic acids (especially oxalic acid) at suitable pH.
In situ biological bleaching refers to the addition of kaolin at the initial stage of fermentation.
