Cadmium (II) removal from aqueous solution using magnetic spent coffee ground biochar: Kinetics, isotherm and thermodynamic adsorption

Abstract

Spent coffee grounds are a waste generated in large amounts by the food industry producing instant coffee. While it is used as animal feed, mostly spent coffee grounds are burned. In this study, The spent coffee grounds were modified to be magnetic in order to remove cadmium (II) ion. The magnetic solids are easy to separate from water with a magnet. The biochar was prepared at 400 °C. Several factors that affect the adsorption were studied, such as adsorbent dosage, contact time, initial metal ion concentration and effect of solution pH. At the optimum conditions (the adsorbent dosage 0.1 g l−1, pH 7, time 30 min and the initial concentration 40 mg l−1), the percentage removal of Cd(II) was ∼96%. The surface morphology of the adsorbent showed iron particles with a cubical shape on the adsorbent, with 3–20 μm average diameter. The adsorption data was well fit by a pseudo-second order and a Langmuir isotherm, with the maximum adsorption capacity 10.42 mg/g. The adsorption process was spontaneous and endothermic. The main goal of the study is to re-use the spent coffee grounds waste and use low-cost adsorbent for cadmium (II) removal in aqueous solution. The magnetic biochar was easily manipulated by external magnetic fields after treatment. With good adsorbent performance of the magnetic biochar, spent coffee grounds could be used to treat Cd(II) contamination.