Aplicação de carvão ativado de casca de arroz na remoção de ferro e níquel do chorume de aterro sanitário

Abstract

In the present work, the prospects of dealing with various environmental problems in the South region of Brazil were demonstrated, turning a local residual of rice peel into an effective adsorbent, which was then applied for the treatment of real waste from sanitary landfills. The heterogeneity of Landfill Leachate (LL), consisting of numerous organic and inorganic pollutants from the physical, chemical and biological degradation of urban solid waste, has potential for pollution and negative effects on the environment when untreated. This study focused on the reuse and characterization of treated rice husk activated charcoal (AC-T), prepared after simple purification process carried out in situ of activated charcoal impregnated with sodium silicate (AC-SS), residual from Oryzasil's silica production, to reduce the total iron (Fe) and nickel (Ni) content in post-membranes samples. The growing global production of agro-industrial waste stimulates the demand for alternative methods of value-adding. Among the materials with the highest production on a global scale, the rice husk stands out. This solid waste is one of the main problems with regard to the inorganic waste produced. In this sense, the utilization of this material is shown as a means of reuse and recovery of the residues of the rice husk. The waste from the landfill was collected in post-membrane systems and characterized in July 2022, revealing high concentrations of iron (Fe) and nickel (Ni), in addition to its high content of organic matter. The membrane set in the secondary stage reduced 72 and 69% of the Fe and Ni ions in the current landfill treatment system. The adsorption unit is needed to further reduce the concentration of Fe and Ni to meet the requirements required by current world resolutions. The AC-T was characterized according to its zero-load point and by XRD, SEM, FTIR, BET and TGA/DSC, and analysed its application in LL and regeneration. After characterization, a mesoporous material was obtained with amorphous structure, structured and homogeneous surface, existence of oxygenated functional groups on the surface, pores with an average size of 3.68 nm and specific surface area of 752.97 m2 g -1 . The adsorption capacities of Fe and Ni were evaluated at different pH values (1; 2; 3; 4; 5 and 6) with initial concentration of synthetic solutions (15 mg L-1 ) for each of the metals. Subsequently, pH 3 (altered due to metal precipitation to higher pH) and 6 (natural of the solution) were fixed for synthetic solutions of Fe and Ni, respectively, with concentrations of 5, 10, 15, 20 and 25 mg L-1 for the construction of kinetics and adsorption isotherms. Balance data were obtained in 308 K barrel experiments, applying 0.05 g of adsorbent in 50 mL of synthetic Fe and Ni solutions. Batch adsorption experiments have been employed to remove both metals, and the results revealed a rapid mass transfer process that allows the selective removal of Fe and Ni after 10 and 120 min related to meeting the legislation in force in the countries. The pseudosecond order model demonstrated greater ability to describe the kinetics of total removal of iron and nickel. Langmuir's model was most suitable to describe the system's equilibrium, achieving maximum adsorption capacity of 252.30 and 201.63 mg g-1 (308 and 328; and 328 K) for iron and total nickel, respectively. The thermodynamic behavior expressed that the process is spontaneous and favorable, with endothermic nature. The application of the AC-T under real conditions and temperature of 308 K pointed to adsorption capacities of 0.71 and 0.025 mg g-1 , removal rates of 43.51 and 88.79% in 10 and 120 min for Fe and Ni, respectively, to meet the conditions of the world legislation, and maximum adsorption and removal capacity of 1.33 and 0.025 mg g-1 , 81.53 and 91.03 % in 180 min for iron and total nickel, all results obtained by the Langmuir model. The adsorption capacity did not significantly decrease after 5 consecutive cycles, and the metals were recovered by acid leaching. The final disposal efficiencies obtained have shown that, due to the remarkable efficiency of the process, the treated effluent meets various world environmental legislation for use in irrigation. Thus, by using the convincing methods optimized here it is possible to refer to the solution of three environmental problems at once.