Cáscara de cacao modificada químicamente con h2so4 para la recuperación selectiva de cadmio en solucionas acuosas

Abstract

In the present research, an adsorbent material was obtained from cocoa shell, chemically modified with sulfuric acid, with the aim of increasing its adsorption capacity for heavy metals such as cadmium in aqueous solutions. Contamination by heavy metals poses a significant risk to humans, making it important to seek sustainable alternatives to help mitigate this issue. The study consisted of several experimental stages, including the collection and preparation of cocoa shell, drying, grinding, chemical modification with sulfuric acid, determination of the zero charge potential, and characterization of the obtained material using methods such as infrared spectroscopy (FTIR) to identify functional groups and evaluate the regenerability of the material through adsorption-desorption cycles using nitric acid as an eluent. The zero charge potential of the material was determined to be at a pHpzc = 2.23, which allowed for the adsorption process to capture cadmium at higher pH levels. This is crucial for managing aqueous solutions containing cadmium, as above the pHpzc, the surface of the material treated with sulfuric acid favored the adsorption of cationic heavy metals like Cd²⁺. In the adsorption-desorption process, the bioadsorbent showed an adsorption capacity of 0.8444 mg of Cd in the first cycle and 0.7635 mg of Cd in the second cycle. During desorption with HNO₃, 0.7738 and 0.6951 mg of Cd were desorbed for the first and second cycles, respectively. FTIR analysis determined the presence of new functional groups in the CCA, such as carboxylic acids, alkanes, alkenes, and alkyl halides, which were not present in cocoa powder. This can be attributed to the chemical reactions produced by treatment with sulfuric acid, which may have introduced new functional groups, modified existing ones,or eliminated others. The study of sulfuric acid-modified cocoa shell demonstrated a significant capacity to retain cadmium, and its regenerability with nitric acid is highly efficient, allowing it to be reused in multiple cycles. The modification added functional groups that enable the adsorption of Cd²⁺, highlighting the potential of cocoa shell as a sustainable resource for the bioremediation of water contaminated by heavy metals.