Estudo de adsorção do íon Pb2+ por apatitas sintéticas

Abstract

The industry employs lead in many processes, mainly due to its easy use in metal alloys, generating large amounts of waste. It has high toxicity and is harmful to all biological activity, has a large cumulative capacity in organisms, is capable of inhibiting the activity of some enzymes, blocking the action of calcium and interacting with fundamental proteins. Several techniques are employed in the decontamination of these industrial wastes, such as ion exchange, reverse osmosis, electrodialysis, and chemical precipitation, however, these processes are complex, expensive, and often of low efficiency. In this way, adsorption processes have been studied as alternative means, possessing high efficiency and low cost for the treatment of these residues. This work aims to study the use of apatites such as hydroxyapatite (HAP), Ca10(PO4)6(OH)2, synthesized from eggshells as a precursor of calcium at pH 5-7 and at pH 10-12, in comparison with HAP control, synthesized from the use of calcium hydroxide Ca(OH)2 PA, at pH 5-7 and at pH 10-12, in order to verify the effectiveness of the use of eggshells as source of calcium. In order to verify its efficiency for the removal of lead (Pb2+) present in synthetic aqueous medium, solutions with concentrations of 10 ppm and 20 ppm were used, simulating real situations of environmental contamination. The apatites used as adsorbent in this work were synthesized in previous works, the materials had already been characterized by X-ray diffractometry, confirming the formation of HAP as the majority phase. The adsorbent HAP synthesized at pH 5-7 presented pH(PCZ) of 7.12 and the one synthesized at pH 10-12 presented pH(PCZ) of 7.55. In the infrared spectroscopy the interactions caused by the presence of lead in the HAP structure were observed. In the kinetic study, it was found that the equilibrium time for HAP synthesized at pH 5-7 was 5,0 minutes in solutions of 20 ppm in Pb2+ and 60,0 minutes in 10 ppm solutions in Pb2+. For HAP synthesized at pH 10-12 was 5,0 minutes in solutions of 10 ppm in Pb2+, and 60,0 minutes in 20 ppm solutions in Pb2+. The mathematical fit for all samples resulted in the pseudo-second order model, with determination coefficient very close to 1. The HAP synthesized from eggshells as a source of calcium as a precursor of synthesis were shown to be highly efficient in the removal of lead, reaching values very similar to those obtained in the adsorption tests employing HAP control.