Utilização de carvão ativado de produção de sílica biogênica para adsorção de fenol e tratamento de água produzida de petróleo

Abstract

This study aimed to present viable alternatives for the treatment of produced water (PW) using a purification method to convert sodium silicate-impregnated activated carbon (CA- SodSi), obtained at no cost as a byproduct of biogenic silica production, into an effective adsorbent - modified activated carbon (MAC). PW is a highly complex effluent composed of many potentially toxic substances, such as metal ions and phenolic compounds. As it is generated in large volumes, the applicability of new and effective methods for PW treatment is often limited by cost. In this context, a simple acid-base purification protocol was developed to ensure the economic viability of the proposed adsorbent application, and its performance was tested for the removal of phenol from aqueous medium and total organic carbon (TOC) in effluent from an oil platform. This contaminant was defined as the target pollutant for all evaluations. The produced material was extensively characterized, in all its complexity, by various analytical techniques, revealing a substantial surface area exceeding 1000 m2 g−1. The working conditions for the kinetic experiments were determined from preliminary tests, with an optimal adsorbent dosage of 1g L−1 and pH 6 being defined - approximately the same natural pH of PW. The kinetic tests demonstrated that the material was able to effectively remove the contaminant even with increasing concentration, reaching an adsorption capacity of up to 22 mg g−1 and maximum removal of 88% in up to 150 min. The inverse effect was observed with increasing temperature during the equilibrium tests, with higher temperatures disfavoring the process and the best results being found at up to 298 K. Regarding the kinetic mathematical models of Pseudo-first-order and Pseudo-second-order (PPO and PSO) and isotherms (Freundlich, Sips, Liu, Redlich-Peterson and Radke-Prausnitz), of which the best fit was found for PSO, Sips and Liu. This also allowed the thermodynamic behavior of the process to be defined, which was favorable, spontaneous and exothermic. The material's regeneration and reuse capacity was also verified, achieving results superior to the averages reported in the literature, where 15 effective adsorption cycles were achieved. Finally, the application to PW consolidated the effectiveness of the material, where it achieved 73% TOC removal from the sample in 150 min. Thus, the use of inherently carbonized activated carbon during silica production is an economically viable and attractive solution for the removal of phenol and TOC from PW, presenting adsorption capacity and removal percentage values superior to other methodologies employed.