The removal and desorption of two toxic dyes from aqueous solution by hydroxylated hematite sand: Kinetics and equilibrium

M. Abbaz

Abstract


The adsorption/desorption properties of hematite sand (HS) for removal of two toxic dyes have been tested in aqueous solution by batch process. HS was prepared by a simple, economic and environmentally friend method. The raw sand and HS were characterized. Toluidine blue (TB) and crystal violet (CV) were selected as a toxicity model. Fe2O3 (85%) is the major constituent of HS identified by XRF and higher number of hydroxyl group on the surface revealed by FTIR. The effect of adsorbent dose, contact time, pH solution and ionic strength was investigated. The adsorption of two basic dyes increased at high pH values (pHZPC=5.4 for HS). The dye adsorption was influenced significantly by the presence of inorganic salt (KCl). The best fitted equilibrium and kinetic model for two dyes were found to be Langmuir and pseudo-second order, respectively. Intra-particle diffusion is not the only speed-controlled step. The maximums monolayers capacities of TB and CV were 1.60×10-5 and 2.65×10-5 mol.g-1, respectively with the optimal equilibrium time of 60 min at room temperature and pH 10. In the batch desorption process, 0.2 M NH4Cl achieved better performance for both dyes desorption and the HS can be effectively reused for four cycles consecutively.


Keywords


hematite sand; toluidine blue; crystal violet; adsorption; toxic dye; desorption

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