Adsorption of phosphate in aqueous solution by ash from the fruit peel of Caryocar Coriaceum WITTM: Characteristics and adsorption behavior

Abstract High phosphate concentrations in water may disturb the ecological balance, deteriorate water quality, cause water eutrophication and affect the smart and sustainable use of water in human activities. With that in mind, the goal of this work was to study the adsorptive capacity of pequi peel ash (PPA) and its efficiency in the removal of phosphate (PO43−) from aqueous solutions, while measuring the kinetics, equilibrium and thermodynamics of the process. The pequi is the fruit of the species Caryocar coriaceum WITTM and is widely found in the Cariri region, in the state of Ceará, Brazil. The processing of this fruit generates a large amount of waste, especially the fruit´s peel, which lacks any further use. These peels were used and tested in this study as raw material for the production of a bioadsorbent. PPA were produced at 500°C in an oxidative atmosphere. The XRF and EDS analysis of PPA after contact with an aqueous PO43− solution confirmed an increase of PO43− content from 1.5–3.7%, thus confirming the adsorption of PO43−. The Elovich and Langmuir models adequately described the kinetics and the equilibrium state of the process, respectively. The highest PO43− adsorption capacity was approximately 79.50 mg g− 1 at 10°C. PO43− adsorption by pequi peel ash is a spontaneous, favorable and exothermic process with structural changes. The highest removal efficiency was 97.08% for a PO43− concentration of 100 mg L− 1. Therefore, PPA has shown potential as an excellent natural bioadsorbent.