Adsorption of phosphate in aqueous solution by ash from the fruit peel of Caryocar coriaceum Wittm: adsorption characteristics and 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 e ciency in the removal of phosphate (PO 4 3− ) 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°Cin an oxidative atmosphere. The XRF and EDS analysis of PPA after contact with an aqueous PO 4 3− solution con rmed an increase of PO 4 3− content from 1.5-3.7%, thus con rming the adsorption of PO 4 3− . The Elovich and Langmuir models adequately described the kinetics and the equilibrium state of the process, respectively. The highest PO 4 3− adsorption capacity was approximately 79.50 mg g − 1 at 10°C. PO 4 3− adsorption by pequi peel ash is a spontaneous, favorable and exothermic process with structural changes. The highest removal e ciency was 97.08% for a PO 4 3− concentration of 100 mg L − 1 . Therefore, PPA has shown potential as an excellent natural bioadsorbent.The pequi fruit (Caryocar coriaceum WITTM) can be widely found in the Cariri region (state of Ceará, Brazil), where it plays an important socioeconomic role. The extraction of pequi generates a large amount of waste, especially peels, which are not used and cause discomfort, bad smell, slurry and the propagation of disease vectors.Pequi peels (PP), which are an agricultural waste, can be used as raw material for the production of bioadsorbents able to remove contaminants from aqueous solutions, as they are easy and cheap to obtain.