Removal of lithium from aqueous solution by spent coffee ground activated biochar

Each year, 1.6 billion tons of food waste are generated, and this is predicted to increase to 2.1 billion tons by 2030 resulting in an enormous solid waste management concern. Out of the many food wastes, beverage waste, spent coffee grounds (SCG) almost 15 million tons, on a wet basis, go to waste. This waste can be used for beneficial reuse, such as conversion to carbon rich activated carbons and biochars, which can subsequently be used as a water treatment adsorbent. Worldwide, but especially in Middle East and North Africa (MENA), one of the largest sources of wastewater is the "produced water" from the gas and oil industries containing several pollutants, such as lithium (Li+). Out of all the metal pollutants, the recovery of Li+ is of great interest due to its valuable use in industries. Its removal also reduces health risks associated with its accumulation in agricultural irrigation. Therefore, this study focuses on the production of activated biochar from a waste biomass, namely, spent coffee grounds (SCG) and conducts a batch adsorption test to remove Li+ from a synthetic aqueous solution. In this study, SCG was activated using two reagents, potassium hydroxide (KOH) and phosphoric acid (H3PO4), in the presence of two catalysts, bentonite and potassium phosphate (K3PO4), and without any catalyst. The SCG activated biochar at three different temperatures was characterised and the activated biochar at 600 °C showed a high adsorption capacity by removing 35–80 mg/g of Li+ at different concentrations of synthetic solution ranging from 200 to 500 mg/L. More than 95% of Li+ was removed by SCG activated biochar within 2 h contact time demonstrating the activated biochar produced from SCG is a sustainable and cost effective adsorbent.