Adsorptive performance of chemically treated olive pomace for the removal of crystal violet from aqueous solutions: characterisation, optimisation, regeneration and isotherm studies

Olive oil industry produces a large quantity of solid effluent (olive pomace OP) which can be used to get an economic profit. At the same time, crystal violet has been stated as a recalcitrant dye that perseveres in environment for extended time and bearings noxious influences in environment. In this work, olive pomace (OP) was treated by sodium hexametaphosphate (SHMP) and used as a low cost and eco-friendly biosorbent (SHMP-OP) for the removal of crystal violet (CV) from aqueous solutions. The prepared adsorbent characterised thru infrared spectroscopy (FT-IR), X-ray diffraction analysis (XRD) scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX) and zero-point charge (pH_zpc). In the batch adsorption process, the effect of different factors like pH, adsorbent amount, initial dye concentration, temperature and contact time, on the removal of CV dye from aqueous solutions using SHMP-OP was examined. The results showed that maximum dye adsorption was found at pH 7 after equilibrium contact time of 50 min with a biosorbent dosage of 120 mg at temperature of 25°C. Langmuir and Freundlich isotherms were applied for the interpretation of experimental data. The isotherm studies showed that Langmuir was found to be best fitted with 271.003 mg/g maximum adsorption capacity. Also, successful desorption study using 0.5 mol/L of HCl has greatly promoted the spent adsorbent to be further used up to four consequent adsorption/desorption cycles. These results revealed that SHMP-OP is effective, eco-friendly and low-cost biomaterial for CV removal from aqueous media.