Utilization of a natural ecosystem bio-waste; leaves of Arundo donax reed, as a raw material of low-cost eco-biosorbent for cadmium removal from aqueous phase

Arundo donax reed grows in a natural ecosystem in Wadi Shueib in Jordan and is also grown in constructed wetlands built for domestic wastewater treatment. The utilization of leaves of excessive A. donax reed as an ecosystem bio-waste for the removal of Cd2+ from aqueous solutions was investigated. Effects of pH (3.5 to 7.5), contact time (10 to 360 min), adsorbent dose (2.5 and 5 g l−1), and adsorbate concentration (5 to 50 mg l−1) at an ionic strength of 0.01 M NaNO3 on adsorption efficiency and capacity were studied in batch adsorption experiments. Cadmium removal percentage of 92% occurred in 20 mg l−1 Cd solutions at pH 5.5 containing 5 g l−1 powdered leaves of A. donax. Cadmium removal percentage increased to 97% with decreasing the adsorbent dose to 2.5 g l−1. The adsorption process was relatively fast and equilibrium was attained at 120 min contact time. The equilibrium adsorption capacity of A. donax leaves increased from 1.96 to 18.80 mg g−1 with increasing initial Cd concentration from 5 to 50 mg l−1. The kinetic process of Cd2+ adsorption onto leaves of A. donax obeyed the pseudo-second-order kinetic model (R2 > 0.9995) indicating that chemisorption is the rate-limiting step. Although Freundlich and Langmuir isotherm models described well the experimental data, equilibrium isotherm data were best described by Freundlich model (R2 0.990 and 0.978, respectively). The monolayer adsorption capacity was 27.9 mg g−1. A. donax leaves can be potentially used as a raw material of low cost eco-biosorbent for treating Cd-contaminated water systems.