Preparation And Performance Of Functional Pigments And Fillers Using Bauxite Tailings

Bauxite tailings with the characteristics of a large amount of the output, fine grain size and complex components, whether it can been reasonably recycled relates to the promotion of new technology of " beneficiation-Bayer ". High iron content and being impracticable for removing iron from bauxite-tailings by conventional methods limit its application in refractory and building materials. Therefore, as fillers in polymer should be more promising directions. However, its deeper color limits its large-scale applications, so need to find a simple and economic method to whiten bauxite tailings.According to the facts that iron phosphate being white or yellow white, bauxite tailings were whitened by using the process route of phosphoric acid to react with bauxite tailings and then the reaction products being calcined for removal carbon. The addition amount of phosphoric acid and calcination temperature is the key factors to affect on the whiteness of bauxite tailings. The effects of calcination temperature on whiteness largely depend on the amount of phosphoric acid phosphate:the whiteness of bauxite tailings almost can't been improved through the calcination in the insufficient dosage of phosphoric acid; while, the whiteness firstly increase, reach the maximum of72%at550℃, then decrease with calcination temperature in sufficient dosage of phosphoric acid conditions.The phosphate coated with most particles of whitening bauxite tailings meliorate the superficial acid and alkali nature of particles of bauxite tailings, so less effect on the thermal stability of polyvinyl chloride(PVC), but it still significantly influences the thermal degradation and combustion performance of PVC. The whitening tailings reduced the degradation temperature of PVC, weakened release quantity of volatile gases HCl and aromatic compounds benzene, increased the activation energy and frequency factor of degradation reaction, and reduced the mass loss in the first degradation stage of polyvinyl chloride when PVC degraded in argon; The whitening tailings reduced the temperatures of the first degradation stage and the third stage of PVC, improved the temperature of the second degradation stage, weakened the release volume of toxic gases HC1and aromatic compounds benzene, reduced the mass loss of the second degradation stage, decreased the activation energy and frequency factor of the first degradation stage, and increased the activation energy of the second degradation stage when PVC degraded in air. The whitening tailings decreased the total smoke released, total heat released and the ratio of mass loss and shorten the ignition time when PVC combusted.The whitening bauxite tailings were modified by using surface chemical reaction of dry method and wet chemical method. The modification effect of the wet chemical method is better than the one of dry method at the same modifier being used. The modification effect of mixture of different modifier used is better than the one of a single modifier used under the same other modification conditions. In experiment, the largest activation index obtained is80%, when modifier ratio of0.4:1.6and wet chemical method were used. The dispersion of the modified whitening tailings in PVC and the interface bonding condition were improved, the influences on mechanics properties of matrix was reduced after the bauxite tailings modification.Aluminum tri-polyphosphate was synthesized from bauxite tailings and phosphoric acid when P/Al molar ratio of2.5, condensation temperature of300℃and condensation time of8h. Talc, zinc oxide and wollastonite were respectively used to modify the aluminum tripolyphosphate in order to meliorate the pH value of aluminum tripolyphosphate. The possibility of using modified aluminum tripolyphosphate as an anticorrosive pigment was also investigated by routine method and electrochemical impedance spectroscopy. Zinc oxide modified aluminum tripolyphosphate has the best corrosion resistance. Steel board dipping in the saturated solution of zinc oxide modified aluminum tripolyphosphate for48h occured only non-proliferation of pitting corrosion. The impedance of steel board with coating with zinc oxide modified aluminum tripolyphosphate pigment was108Ω.cm-2in first immersion stage, down to6.5×107Ω.cm-2at immersion of20days and increase to7×107Ωcm-2up to immersion for40days.