Decomposition Of Potassium Feldspar In NaOH Sub-molten Salt And Its Deep Processing

Potassium feldspar, rich in potassium, silicon and aluminum, is extensively distributed with large reserve. It was focused on the topics of its deep processing and high value application in recent years. In this thesis, the potassium feldspar was decomposed by NaOH sub-molten salt method under low temperature. The resulting decomposed filtrate and residues were used to prepare the white carbon black, hydrophobic silica and composite titanium dioxide powder, respectively.As the sub-molten salt medium, high concentration of NaOH solution was used to decompose potassium feldspar powder. The effect of various processing conditions on the dissolution rate of K+was investigated. The results indicated that the dissolution ratio of K+was higher than98%when the concentration of NaOH was60%(wt), the reaction temperature was160℃, liquid-solid ratio was4:1and reaction time was140minutes. Sodalite was obtained from the reaction solution during the decomposition process. Furthermore, a preliminary exploration of kinetics of the decomposition process was performed. It was confirmed that the decomposition rate of potassium feldspar powder was in accordance with the shrinking core model with constant particle size. The reaction was controlled by the internal diffusion through ash layer at the initial stage of the reaction. The apparent activation energy was110.42kJ/mol under the temperature of80～140℃.With the resulting decomposed filtrate as the reactant, the white carbon black was produced by the precipitation method. The acidity of the system was adjusted by adding hydrochloric acid or carbon dioxide, and the dispersity of the product was improved by adding surfactant and dispersant. The results showed that the product has excellent performance when the filtrate’s pH was adjusted by HCl to5. The silica content was93.26%, whose BET surface was622.65m2/g and whiteness was94.3%. In addition, the aluminate coupling agent and stearic acid were used as modifiers to prepare hydrophobic silica, and the effect of several processing conditions on modification was studied. The modification effects of the aluminate coupling agent and aluminate-stearic acid mixture were compared. The contact angle of the hydrophobic silica powder was larger than130°, and it showed good dispersity in organic solvents. The resulting decomposed residue powder as the inner core was coated by titanium dioxide with the liquid mechanical force chemical method. The effect of processing conditions on the properties of residue/TiO2powder was investigated. It was showed that the1:1(wt%) of residue/TiO2product was obtained under the condition of grinding speed was1400r/min, slurry concentration was30%, TiO2disperse time was30minutes, the ball/material ratio was5:1(wt%), and composite time was50minutes. Under this condition, the covering power was17.20g/m2, which was87.21%of the pure titanium dioxide; the whiteness was98.0%, which was nearly equal to pure titanium dioxide; the oil absorption value of the product was32.74g/100g. These results revealed that the product could replace part of titanium dioxide as white pigment since its good performance.