Preparation And Characterization Of Acid Treated And Na-Modified Sericite

Sericite is a kind of important industrial mineral raw materials with excellent physical and chemical properties. It has been widely applied in industrial fields such as paper making, ceramics, coatings, rubber, plastics and cosmetics. Polymer/sericite nanocomposites can not only farthest exert outstanding characteristics of sericite but also add new functions. So the preparation of polymer-layered silicate (PLS) nanocomposite based on sericite is an important means to improve the application values of sericite and realize high-level utilizations. However, the structure of sericite is firmly stabilized, it is hard to directly prepare PLS nanocomposite.Sericite raw material was calcined beforehand and its structure was activated to some extent. Then it was further modified through acid treatment and Na-exchange treatment. Influences of acid treatment on aluminum dissolution and interlayer negative charge of sericite structure were studied. Cation exchangeability was obtained by Na-exchange treatment. Optimum process conditions were determined by orthogonal experiments and single-factor experiments. The products were characterized and the action mechanisms were discussed.Relatively large amount of Al³⁺ cations were dissolved from heat-treated sericite using nitric acid. The dissolution amount reached around 30mg/g at the optimal processing conditions of concentration of nitric acid solution 5mol/L, reaction temperature 95℃, agitation speed 4h and solid-liquid ratio 3%. Results of XRD analyses show that the structure of sericite was distorted but not collapsed, and part of interlayer spacing was expanded. Results of ²⁷Al NMR analyses indicate that both 4-fold and 6-fold aluminum in the structure were dissolved. Because the cations in interlayer and layer were dissolved, the net negative charge reduced from 1.00 to 0.78. And this was proved by the Zeta potentials of sericite before and after acid-treated.Certain cation exchangeability was gained by Na-exchange treatment of acid-treated sericite. Optimum process conditions were determined: concentration of NaCl solution 6mol/L, reaction temperature 95℃, agitation time 1h and repeated for 3 times. Optimal CEC value reached 29.07mmol/100g. The distortion degree was larger than that of acid-treated sericite, but the structure of sericite was still integrated.Researches on the processing conditions by orthogonal and single-factor experiments indicate that acid treatment and Na-exchange treatment are ion exchange reaction. The dissolution amount of Al³⁺ cations and other cations increased with increasing H⁺ cations with enough activation energy. The hydration energy of Na⁺ cations are relatively low and its exchangeability is excellent. The CEC value of Na-exchanged products increased with increasing concentration of Na⁺ cations that can efficiently exchange K⁺ cations in the solution.