Cinética dos contaminantes e otimização da estabilização por solidificação de lodo de curtume.

Abstract

The tannery sludge is classified as a Class I – hazardous solid residue. It compromises the environment due to the presence of chromium (Cr3+), sulfides (S2-) and high amounts of organic matter. In this research, the tanning sludge was subjected to a solidification stabilization process, aiming to determine the kinetic decay rate of the contaminants and to optimize the stabilization process by solidification of the tannery sludge. The experimental design comprised two factors and two replicates, resulting in 18 treatments, which used percentage of tannery sludge (5%, 15% and 25%) and curing time (7, 28 and 90 days) as variables. An evaluation of the material stabilized by solidification was carried out with the criteria of integrity/durability and immobilization of contaminants. The variance analysis allowed us to obtain a process optimization of the tannery sludge treatment, the mass balance and a retention efficiency of the stabilized material contaminants. Finally, the contaminants kinetics were analyzed taking into account the tannering time and percentage. The present work is different from previous ones because it presents three important scientific contributions regarding the tannery sludge treatment. The first one is focused on the optimization of the solidification stabilization process, in which was found an ideal balance between tannering time and percentage. The second is related to the rate of the contaminants kinetic decay. The third one is related to the mass balance and an edition of the S/S process of the contaminants present within the tanning sludge. As a result of the study it was found that, an optimization of the responses to minimize and/or maximize as variables of the S/S process responses, achieved with shorter cure duration and lower sludge percentage. According to a desirable function all the treatments were approved in the integrity/durability tests and immobilization of the contaminants, converting it from a Class I (dangerous) to a Class II (non-hazardous) residue. The parameters related to the durability and integrity obtained their optimization with different optimum points. The best responses to the environmental control in the leached and solubilized extracts were attributed to the combined treatments with the lowest tannering rate and percentage of tannery sludge. The research concluded that it was possible to determine the kinetics of tannery sludge contaminants in the optimization of the S/S process. Thus, a reduction in the kinetic detoxification rate of the environmental contaminants in the leached and solubilized extracts was attributed to treatments combined with a smaller percentage of tannery sludge and varied tannering time. The solidification stabilization process used to treat the tannery sludge was efficient as it promoted the attenuation of contaminants converting it from a hazardous to a non-hazardous residue.