Optimization of cristal violet adsorption by calcium silicate waste material

Abstract

In this study, calcium silicate waste material was used as adsorbent of crystal violet in batch mode. The calcium silicate was synthesised from fluosilicic acid (FSA), which is a by-product of phosphoric acid manufacture. The obtained calcium silicate was characterised by X-ray fluorescence spectroscopy. The response surfaces, through the Box-Behnken model were used to model and optimize various adsorption parameters namely, the initial concentration of CV (A: 10–100 mg/L), the contact time (B: 5–50 min), the dose of adsorbent (C: 1–5 g/L) and the pH (D: 3–10). The removal efficiency of CV (97.86%), after statistical analysis, was obtained under the following optimal conditions: an adsorbent dose of 3.349 g/L, an initial CV concentration of 58 mg/L, a pH of 6.87 and a contact time of 30.49 min. The study of the four factors effects highlighted a positive effect on the removal of crystal violet. The interactions between adsorption time (B) and pH (D) and between adsorbent dose (C) and pH (D) were significantly important. However, an intermediate situation was noticed in the case of the interaction between adsorbent dose (C) and crystal violet concentration (A), where the lines cannot be considered parallel but do not cross each other in the analysed area either. The analysis of the residues showed that they are normally distributed and fluctuate in a random pattern. The adsorption kinetics were well described by the pseudo second order model and the equilibrium data were in agreement with the Langmuir isotherm model with a maximum adsorption capacity of 277.78 mg/g.