Adsorption performance of activated charcoal from castor seed cake prepared by chemical activation with phosphoric acid

Abstract

Castor seed cake is an interesting material from which to make activated charcoal (AC). The present research aimed to produce and characterize AC from castor seed cake by activation with phosphoric acid. Experimental conditions included two concentrations of activating agent (20 and 40%), two temperatures (400 and 800 °C) and two times (60 and 180 min), in a factorial experiment with two replicates for each treatment, totalizing 16 observations. One control treatment produced AC at 600 °C and 120 min. Scanning electron microscopy, BET surface area analysis, and adsorption tests with methylene blue were performed, and point-of-zero charge and mesoporosity were determined. Langmuir and Freundlich models were adjusted to explain adsorption. Results showed type IV isotherms. Best activation results were achieved at 800 °C, 60 min, and 40% phosphoric acid. The Langmuir model had the best fit, and experimental results demonstrate the technical viability of producing AC with good adsorption properties. Despite of having a maximum surface area not so high as the commercial ACs, the maximum adsorption capacity for methylene blue of the AC produced from castor cake exceeded the values reported in the literature for those products.