Removal of cyanide from wastewater by adsorption onto pistachio hull wastes: Parametric experiments, kinetics and equilibrium analysis

Many waste materials have been evaluated for their efficacy in removing different classes of contaminants from water and wastewater in order to improve the cost-effectiveness of adsorption. In the present study, pistachio green hull wastes were investigated as a potential adsorbent for the removal of cyanide from a synthetic wastewater. The effects of a selection of the most significant parameters (pH, adsorbent dose, cyanide concentration and contact time) were initially evaluated based on the percentage of cyanide removed from the wastewater. At an optimum pH of 10, over 99% removal of 100 mg/L cyanide was obtained for an adsorbent dose of 1.5 g/L after a 60 min contact time. Kinetic evaluation indicated that the adsorption of cyanide ions onto the pistachio hulls clearly followed the pseudo-second order rate reaction. The equilibrium assessment illustrated that the Langmuir model is the best fit for the experimental data, which attains a maximum adsorption capacity of 156.2 mg/g. The sorption of cyanide ions onto the introduced adsorbent was inferred to be a chemosorption process with intraparticle diffusion as the most important step controlling the overall process rate. Accordingly, the pistachio hull waste is introduced as an efficient and low-cost adsorbent for removal of different concentrations of cyanide from water and wastewater.