Insurance powder reduction method
Using sodium dithionite as a reducing agent, in an acidic medium, the reaction formula is:
According to the oxidation-reduction reaction formula, it can be concluded that:
It can be seen that the electrode potential of the SO42-/S2O42-electric pair increases as the pH of the solution decreases. When the acidity of the solution is sufficiently high, the electrode potential of Fe3+/Fe2+ is independent of pH. However, when the pH of the solution gradually increases, it is due to Fe3+. The hydrolysis occurs at this time on the ferroelectric converted to Fe (OH) 3, / Fe2 +, which [Fe (â…¢) / Fe ( Il)] is:
From the above formula, the relationship between the electrode potential and the pH value of the solution can be obtained. When pH=1.53, the maximum value is reached, and when pH=6.45, it is the smallest. When the pH value is more than 6.45, since the reduced product of iron is Fe(OH)2:, it cannot be removed by filtration. Therefore, when dithionite is used as the reducing agent, the acidity of the reaction medium should be at pH=1.53-6.45. The acidity is too small, the electrode potential difference between the two is small, the reaction speed is slow and incomplete, the acidity is too large, the acid consumption is large, and the stability of the dithionite is lowered, and the easy separation is released. The pH value of the solution is controlled at about 3 should. In addition, since the insurance powder is easily decomposed and its reducing ability is reduced, the reaction is as follows:
These side reactions waste both reagents and product quality, and if not washed in time, the product will turn yellow. To solve the above drawbacks, an appropriate amount of a chelating agent is usually added, such as oxalic acid, citric acid, EDTA, poly-phosphate, hydroxylamine salts, chelating ion may be dissolved in water, with the exclusion of the filtrate, bleaching with fast speed, the advantages of good effect.
2. Acid leaching hydrogen reduction method
This is a combined pickling and reducing bleaching process, the basic principle is the use of aluminum powder or zinc powder as reducing agent, hydrochloric acid, sulfuric acid, oxalic acid medium, using the active metal in an acidic solution continuously displaced continuously H2 :, The resulting H2 changes the colored insoluble in the kaolin to soluble Fe2+ and is removed with the filtrate. The reaction formula is as follows:
For low brightness kaolin coal-based hydrogen reduction method employed pickling iron, calcining method in addition to the sulfur, to maximize the whiteness of the product.
3. Flotation method
Kaolin pulping is added with lime powder as adsorbent, and Fe2O3 is adsorbed from the slurry solution onto the lime carrier. The carrier can adhere to the bubble by its own hydrophobicity and the hydrophobicity caused by the reliable collector to obtain the iron-containing carrier. Foam products and in-tank products containing kaolin concentrates to separate Fe2O3 from kaolin. Due to the effects of carrier adsorption, absorption, crystal mixing, enthalpy, agglomeration, etc., as well as the influence of the pH of the medium, the addition time and location of the carrier on the adsorption flotation, the Fe2O3 in the kaolin can be reduced by 0.72% by adsorption flotation. Up to 0.5% or less.
4. Oxidation method
Pyrite and organic matter contained in kaolin sometimes require oxidation by bleaching. The ferrite in a reduced state is oxidized to a ferrous ion dissolved in water by a strong oxidizing agent in an aqueous medium; at the same time, the dark organic matter is oxidized to become a colorless oxide which can be washed away by water. Commonly used oxidants are sodium hypochlorite, hydrogen peroxide, potassium permanganate, chlorine, ozone and the like.
5. Microbial iron removal and whitening method
Thiobacillus ferrooxidans is one of the most commonly used bacteria in mineral microbial processing, which oxidizes pyrite and other sulfide minerals. The low cost, low environmental pollution, and no influence on the physicochemical properties of kaolin are a new whitening method for kaolin.
to sum up
The choice of the kaolin bleaching process depends on the type and mode of occurrence of the dyeing material in the raw material. Iron is the most common dyeing material in kaolin. The effect of reducing the complexation with sodium dithionite is better. The carbon and organic dyeing materials are treated by high temperature calcination. However, for the bleaching of complex coal-based kaolin, further research is needed to determine a reliable and economically sound method.
Conveyor Section,Conveyor Belt Section,Sections Of Conveyor,Roller Conveyor Sections
Vitrans Automation Equipment Co.,Ltd , https://www.vitrans-conveyor.com