Optimisation of acid pre-treatment parameters in silica extraction process from cassava periderm

Abstract

Silica nanoparticles have been synthesized from various agricultural wastes using different routes. Most of the routes involve acid pretreatment of agricultural wastes to improve yield of silica qualitatively and quantitatively. In order to optimize the diverse conditions of this treatment, effects of acid concentration, temperature and time of the leaching process was studied using factorial design. Cassava periderm was dried and leached using various degrees of acid concentrations (0.5–2.5 M), temperatures (25–75 °C) and time (30–150 min). Two-level factorial design was used using Design Expert software. Weight loss measurement and chemical analysis of the leachates and residues were obtained. Atomic emission spectroscopy was used to study the leaching efficiencies of the various treatment conditions. Scanning Electron Microscopy, Energy Dispersive X-Ray Spectroscopy, X-Ray Florescence and X-Ray Diffractometry were carried out on the residues. Regression models were generated from weight loss and leaching efficiency data obtained from experimental results. Both linear and polynomial models were obtained for the various chemical species with high coefficient of determinations (62.06–99.99%) and good predictability of their leaching behaviours. The optimum treatment condition obtained was 1.59 M of HCl at 45 ± 5 °C for 85 min. The models showed that concentration and time are significant factors during leaching of cassava periderm. Temperature was observed to be significant for leaching of reactive metals like Mg and Al. Hence, leaching of agricultural wastes prior to silica extraction improves the purity of silica substantially.