Taguchi optimization for water defluoridation by thermally treated biosorbent developed from the waste snail shells

Abstract

Developing adsorbents from waste materials for water defluoridation is gaining vast interest to help cost-effective and sustainable water treatment. The current study attempts to develop a new adsorbent from the waste snail shells by thermal treatment (900 °C ± 5 °C for 3 hours), and the experiments were carried out to investigate its feasibility for fluoride removal. The process parameters were optimized using L 16 orthogonal array of Taguchi technique to acquire the maximum F − removal. The sorption capacity of 10.417 mg/g and a maximum F − removal of 90.41% was achieved for snail shell sorbent at pH: 7 ± 0.1, snail shell dose: 10 g/L, agitation time: 60 minutes, the temperature: 313 K ± 1 K, and initial F − : 15 mg/L. ANOVA indicates the process variable’s contribution toward F − removal in descending order as initial F- (42.32%) > pH (27.09%) > dose (11.23%) > time (9.71%) > temperature (9.65%). The Freundlich isotherm and a second order kinetic model were best fitted for F − sorption onto snail shell sorbent. Thermodynamic constants revealed spontaneous and endothermic sorption onto snail shell sorbent. The surface morphology, functional groups, and crystallinity of the sorbent were studied with SEM, FTIR, and XRD analysis. The sorption–elution study with 0.1 NaOH indicates the reusability of the adsorbent up to 4 cycles. Conclusively, the waste-derived adsorbent from the waste snail shells is found potentially quite feasible for water defluoridation, adds commercial value to the waste material, and helps in cleaner production through proper waste utilization.