The Effect of Particle Size, Activation Type and Contact Time of Cocoa Pod Husk (Theobroma Cacao L.) Activated Carbon on Artificial Waste Chromium Adsorption Capability

Abstract

Cocoa (Theobroma cacao L.) is among the top commodities in Indonesia but the economic value is only limited to seeds, and pod husk is considered a waste. Cocoa pod husk contains cellulose, hemicellulose, and lignin, suggesting great potential as activated carbon. In this study, the cocoa pod husk activated carbon used varied in various sizes, namely particles passing through a 20 mesh sieve and retained by a 40 mesh sieve (20/40), particles passing through a 50 mesh sieve and retained by a 70 mesh sieve (50/70), particles passing through a 90 mesh sieve and retained by a 120 mesh sieve (90/120), and particles passing through a 150 mesh sieve and retained by a 200 mesh sieve (150/200). The carbon was then chemically activated using 0.8 M phosphoric acid (H₃PO₄), soaked for 8 hours, and physically activated using an oven at 110°C for 1 hour. The activated carbon was contacted with chromium (Cr(VI)) for 6 hours, 12 hours, and 24 hours. The results showed that, based on the atomic absorption spectroscopy test, the best Cr(VI) adsorption occurred in the adsorbent with a 150/200 mesh particle size variation, which chemically activated with a contact time of 24 hours. The adsorbed Cr(VI) content was 992.02 ppm with an adsorption efficiency of 99.20%. Correspondingly, an iodine number test of 850.23 mg/g was obtained on activated carbon with a particle size of 150/200 mesh, which was chemically activated. The scanning electron microscope analysis results showed a porous, rough, and distributed activated carbon surface.