Study of the Zeolitization Process of Fly Ash Using an Orthogonal Array of Taguchi Experimental Design

Zeolitization of fly-ash by a direct route and a fusion method (two-step process) was studied using an orthogonal array of Taguchi experimental design. The effect of different processing conditions, such as type and concentration of the mineralizing agent, fusion and crystallizing temperatures and times and stirring speed, on the quantity of the zeolitic phase obtained, were evaluated. By means of a variance analysis, the contribution of the processing conditions to the response variable (content of zeolitic phase, wt%) was evaluated. According to the results, the statistical significant processing conditions that show a stronger effect on the zeolite content were the type of mineralizing agent and crystallizing temperature. The optimal conditions for obtaining 5 types of zeolites were also determined. The type of zeolite depends mainly on the nature of the mineralizing agent. When using the direct method potassium hydroxide (KOH) was the optimal mineralizing agent, leading to a material with 77 wt% of zeolitic phase. On the other hand, when using the fusion method the optimal alkaline agent was sodium hydroxide (NaOH) reaching up to 91 wt% of zeolitic material.