Remoção de metais utilizando composto humico proveniente do tratamento de lodo de esgoto industrial e tabaco de cigarro contrabandeado em reator

Abstract

One of the problems that has been widely explored and of interest to many researchers is the contamination of environmental matrices by potentially toxic metals. In this sense, adsorption has been shown to be a promising alternative due to its high efficiency and low cost. The main objective of this work was to apply as adsorbent the humic compost (HC) obtained from composting in reactor of smuggled cigarette tobacco (SCT) and industrial sewage sludge (ISS) in the removal of metals: lead (Pb+2), cadmium (Cd+2) and total chromium (Cr) of aqueous solutions. The removal capacity of the material was investigated using batch procedure, and experimental parameters such as pH, adsorbent concentration, initial concentration of metals and contact time were investigated. The results showed that the adsorbent concentration of 3 g L-1 was sufficient to saturate the available binding sites of the three evaluated metals (Pb+2, Cd+2 and total Cr). For Pb+2 the maximum removal (82%) was reached at pH 5.0 and 240 minutes time. The maximum adsorption capacity for Pb2+ was 21.544 mg g -1 , calculated by the Sips equation, and the kinetics were better adjusted using the pseudo second order model. Cd+2 showed maximum removal (92%) at pH 5.0, and the time required to reach equilibrium was 120 minutes. The maximum adsorption capacity for Cd2+ was 28.546 mg g -1 , calculated by the Sips equation, and the kinetics were better adjusted using the pseudo second order model. For total Cr, pH 3.0 and time of 120 minutes were necessary to reach maximum removal (72%). The maximum adsorption capacity for total Cr was 14.92 mg g -1 , calculated by the Sips equation, and the kinetics was better adjusted using the Elovich model. The removal process for each metal was characterized by Infrared Spectroscopy and Field Emission Scanning Electron Microscopy (FEG) coupled with EDX (X-ray Dispersive Energy) microanalysis, where it was observed that hydroxyl, carbonyl and carboxyl groups are mainly responsible for metal removal, and in addition a possible ion exchange mechanism between Pb+2, Cd+2 and total Cr with Na+ , K+ , Ca+2 may occur. The leaching test allowed to evaluate the chemical stability of metals on the compost when in contact with aqueous solutions, confirming the immobilization of contaminants. As a complement to mono-metal removal, a multi-metals removal study under different pH conditions was developed to evaluate the behavior of the species on the adsorbent. The results confirmed that there is no compromise in metal adsorption and/or metal competition for active adsorbent surface sites. Finally, HC was applied as adsorbent of potentially toxic metals in rivers and lakes of Ponta Grossa region. The results showed that the compost produced by the treatment of SCT and ISS, besides having a low cost, presented a high removal efficiency and can be applied as a new adsorbent of Cd+2.