Presented paper

IMWA2019 Students work

Thermodynamic Study Of The Adsorption Performance Of Spent Coffee Beans For The Removal Of Cadmium From Coal Tailing Leachates

Fosso-Kankeu, Elvis; Weideman, Reinhardt; Moyakhe, Dumisane; Waanders, Frans; Campbell, Quentin
North-West University, South Africa

Coal mining operations are notorious for producing large amounts of tailings wastes which are disposed of in the form of a slurry on tailings dams. This inadvertently contributes towards environmental problems. Heavy metals are one of the most common pollutants that originate from solid mine waste disposal facilities which in turn can leach into ground water supplies, leaving it contaminated and unsuited for human consumption. Cadmium occurs in unison with metalliferous ores and can cause severe damage to agricultural soils and drinking water supplies in the vicinity of mining sites. The removal of cadmium from polluted water sources is therefore important to restore usable water for human activities.

An attractive method for metal removal from wastewater is adsorption whom performance depends on the type of adsorbent. Biochar has been recently considered for the removal of heavy metals from wastewater for several reasons. Benefits of using biochar include its low production costs, availability of a wide range of feedstock, diversity of the biochar with each type of feedstock and the mechanical and thermal stability of the char. Spent coffee grounds have no commercial value and are usually sent to compost facilities for disposal. This makes spent coffee beans an abundant feedstock available for the production of biochar. For the first time, surfactant impregnation for surface modification of spent coffee-based biochar produced through hydrothermal method has been carried for improved adsorption of cadmium from coal tailing leachates.

In this study spent coffee beans was transformed into biochar using a hydrothermal method where after it was pre-treated through surfactant impregnation to enhance its adsorption capacity. The non-treated and pre-treated biochars were characterized using FTIR spectroscopy and SEM-EDS analyses, which revealed a successful preparation of biochar with the potential for adsorption. The adsorption potential and mechanism was predicted using thermodynamic study.

The adsorption of cadmium on the pre-treated (PT) biochar was found to occur spontaneously while it was the case for the non-treated (NT) biochar. For both adsorbents, the adsorption of the cadmium was endothermic in nature due to the large positive enthalpy values, confirming that the adsorption of cadmium on NT biochar and PT biochar occurred through a chemisorption mechanism.

It could be therefore concluded that the pre-treated biochar showed potential as an adsorbent and could be considered for implementation in the treatment of metal polluted effluents.