Multivariate optimization of process parameters in the synthesis of calcined Ca‒Al (NO₃) LDH for defluoridation using 3³ factorial, central composite and Box–Behnken design

ABSTRACT

Response surface methodology was applied for the first time in the optimization of the preparation of layered double hydroxide (LDH) for defluoridation. The influence of three vital process parameters (viz. pH, molar ratio and calcination temperature) in the synthesis of the adsorbent ‘Calcined Ca‒Al (NO₃) LDH’ was thoroughly examined to maximize its fluoride scavenging potential. The process parameters were optimized using the 3³ factorial, face centered central composite and Box–Behnken designs and a comparative assessment of the methods was conducted. The maximum fluoride removal efficiency was achieved at a calcination temperature of approximately 500ºC; however, the efficiency decreased with increasing pH and molar ratio. The outcome of the comparative assessment clearly delineates the case specific nature of the models. A better predictability over the entire experimental domain was obtained with the 3³ factorial method, whereas the Box–Behnken design was found to be the most efficient model with lesser number of experimental runs. The desirability function technique was performed for optimizing the response, wherein face centered central composite design exhibited a maximum desirability. The calcined Ca‒Al (NO₃) LDH, synthesized under the optimum conditions, demonstrated the removal efficiencies of 95% and 99% for the doses of 3 g L⁻¹ and 5 g L⁻¹, respectively.

Keywords:

• 3³ factorial design
• Box–Behnken design
• defluoridation
• face centered central composite design
• layered double hydroxide