Remoção de P-Nitrofenol por processos adsortivos utilizando carvão ativado produzido a partir de subprodutos agroindustriais (caroço de pêssego e coroa de abacaxi)

Abstract

The p-nitrophenol is a toxic contaminant present in wastewater and effluents from several industrial sectors. Even at low concentrations, its presence is an obstacle to the reuse of water in other processes and the release of effluents containing p-nitrophenol affects human health and biota in a harmful way. Given the above, this study aimed to evaluate the removal of p-nitrophenol present in synthetic effluent through adsorptive processes using activated carbon produced from agro-industrial underproducts of peach stones (prunus persica) and pineapple crown (ananas comosus). Activated carbon production yields (72.03% for peach stones and 61.24% for pineapple crown) were calculated and their characterizations were performed. The activated carbon were considered to have a relevant surface area (912.31 and 857.92 m2.g-1, respectively for activated carbon of peach stones and pineapple crown), being considered mesoporous. Preliminary experimental tests on the adsorptive processes in question resulted in greater adsorptive capacities in the acidic pH range (2 to 6). The adsorption was considered fast and favorable, occurring mainly in the first 20 minutes and for the study of the initial concentration of the adsorbent (C0 = 1.0 g.L-1) good values of adsorptive capacity were obtained (88.4 and 83.9 mg.g-1) and removal percentage equally high 88.4% and 83.9% for peach stones and pineapple crown coals, respectively. A factorial design 24 was carried out for each adsorbent in order to evaluate the influences of the variables calcination temperature used during the production of activated carbon (350, 450 and 550 ºC), granulometry of the adsorbent (<0.6; 0.6 to 0 , 8 and 0.8 to 1.0. Mm), stirring speed (0; 75 and 150 rpm) and temperature of the experiment (10; 20 and 30 ºC), aiming to optimize the adsorption and find the best parameters of the process. For the initial concentration of the contaminant equal to 100 mg.L-1, the highest adsorptive capacities were 97.65 mg.g-1 (peach stones activated carbon) and 93.15 mg.L-1 (pineapple crown activated carbon) obtained at granulometry levels <0.6 mm, stirring at 150 rpm, calcined at 550 ºC and at the temperature of the experiment equal to 30 ºC for peach stones coal and 10 ºC for pineapple crown coal. The adsorption kinetics revealed that, for the two coals studied, the pseudo-second order model is the one that best fits the experimental data and for the intraparticle diffusion model the stage that limits the adsorptive process is the instantaneous initial stage. The study of equilibrium and adsorption isotherms presented the Freundlich model as the one that best fits the experimental data for the adsorbents in question, referring to the heterogeneous nature of the coals surface. Desorption tests revealed low rates and rates of recovery of the contaminant requiring more comprehensive studies and optimizations. In general, the activated carbon produced showed good adsorptive capacity and good efficiency in removing p-nitrophenol from synthetic effluents. Future studies and the continuity of the investigative steps may frame the industrial use of the activated carbon produced.