Abstract
Advanced wastewater-treatment techniques such as adsorption are essential in the removal of non- biodegradable toxic wastes from water. In this study, the use of South African coal fly ash, an industrial byproduct, has been investigated as a potential replacement for the current costly adsorbents used for removing heavy metals from wastewater. We utilised coal fly ash for the adsorption of cobalt(II) ions from synthetic petrochemical wastewater and characterised its performance. A two-level three-factor full-factorial design was successfully employed for experimental design and analysis of the results. The combined effects of pH, initial concentration and adsorbent dose on cobalt(II) removal were assessed using response surface methodology. Although the focus was on removal of cobalt(II), the adsorption was carried out in the presence of phenol and other heavy metal ions using the batch technique. The applicability of the Freundlich and Langmuir models to the equilibrium data was tested. Consequently, the equilibrium data was found to conform more favourably to the Freundlich isotherm than to the Langmuir isotherm; in this case, the coal fly ash had a maximum adsorption capacity of 0.401 mg/g for cobalt(II). We conclude that South African coal fly ash, as a natural, abundant and low-cost adsorbent, might be a suitable local alternative for elimination of cobalt(II) from aqueous solutions.
Highlights
The removal of recalcitrant contaminants, such as cobalt, from wastewater is essential as they pose a serious health and environmental hazard
The objectives of the present study were to investigate the feasibility of using South African coal fly ash for the removal of cobalt(II) from synthetic petrochemical wastewater, to model the adsorption process of cobalt(II) and to investigate the interactive effects of process parameters such as adsorbent dose, solution pH and initial concentration on the adsorption capacity of coal fly ash towards cobalt(II) ions using response surface methodology
Characterisation of coal fly ash Adsorption is a surface phenomenon and the rate and extent of adsorption are functions of the specific surface area of the adsorbent used, i.e. the portion of the total surface area that is available for adsorption
Summary
The removal of recalcitrant contaminants, such as cobalt, from wastewater is essential as they pose a serious health and environmental hazard. Severe effects of acute cobalt poisoning in humans include asthmatic symptoms and damage to the heart, thyroid and liver. Current studies related to the method of removing cobalt from wastewater have drawn broad interest and show that cobalt removal from wastewater cannot be adequately achieved using secondary adsorption methods.[1] advanced wastewater-treatment methods, such as ion exchange,[2] precipitation,[3] membrane separation[4] and electrolysis,[5] must be used to remove recalcitrant waste such as cobalt Most of these methods are costly and require high levels of expertise; these methods are not applied by many end-users. Adsorption technology has gained a wider application due to its inherent low cost, simplicity, versatility and robustness
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