Estudo do potencial de remoção de metais por calcário dolomítico, escama de peixe e resina catiônica visando o tratamento da água residuária da indústria de baterias

Abstract

This work focused on the characterization of an effluent of a recycling and recovery industry of automotive batteries and on the feasibility evaluation of different materials, a biosorbent (fish scales - FS), a mineral (dolomite - DL) and a commercial material (cationic resin - CR) combined use in the removal of heavy metals. The studied materials were physico-chemically and morphologically characterized (pHpzc, MEV-EDS, FTIR and XRD) before and after their use in the removal processes in order to understand the structural modifications of the materials. In addition, the elemental composition of the liquid and solid phases after the treatment process were evaluated by TXRF analysis. The effluent presented an extremely acidic characteristic (pH = 1) and the incidence of heavy metals above the legislation discharging limits (Fe, Zn and Pb). Due to the structural characteristics and its respective functional groups, each adsorbent material presented different functional groups and different behavior in solution, which led to different removal and neutralization capacities. The CR presented the highest removal capacity of the metallic ions, mainly governed by an ion exchange process. Whilst the FS and DL presented lower removal capacities following complex simultaneous phenomena such as dissolution, complexation, precipitation and adsorption. On spite of that, the FS and DL presented a great neutralization capacity (i.e. pH elevation of the extremely acidic medium), related to the leaching of its alkaline constituents. By considering the generation of chemical sludge as a key factor in the work, aiming its mitigation and the better quality of the treated effluent, it was verified that the sequential application of these materials in hybrid process could be a promising and feasible alternative, by taking advantage of the particular characteristics of each material both in the neutralization and heavy metals’ removal. In this way, the use of DL, FS and CR in combined hybrid processes was evaluated, initially in batch system. Amongst the evaluated ones, the DL-CR hybrid process, in which the dolomite was used for the effluent neutralization up to pH = 5 followed by CR for the metallic ions removal presented better results. Therefore, the DL-CR hybrid process showed the highest percentages of metal removal (99, 73 and 100%, respectively, for Fe, Zn and Pb), as well as the lowest generation of chemical sludge by the end of the processes. In addition, the pre-neutralization (pH = 5 achieved by the DL) provided greater chemical stability of the CR. Subsequently, the DL-RC hybrid process was employed in fixed bed, evaluating the possibility of adsorption-desorption cycles aiming at the resin reuse and recovery of heavy metals. Different affinities of each metal ions by the RC for the multicomponent system (Pb> Fe> Zn) were identified, which were associated with the properties of each species as radius of hydration, valence and electron affinity. The possibility of the RC use in recycle was verified, in which similar removal capacities to the previous cycle and compatible with the levels of disposal of legislation - in terms of concentration of heavy metals as well as pH - was reached. These results demonstrate the potential of the hybrid treatment process, however, the fixed bed operating conditions such as bed height and volumetric flow still can be optimized in order to maximize mass transfer efficiency in the bed. Therefore, considering that the DL-RC hybrid process was able to overcome the treatment drawbacks of such type of effluent, due to its extremely acidic character and the complex multicomponent composition of heavy metals in solution, the process can be considered viable in technical and operational terms. In general, the cooperative use between DL and RC in hybrid process presents a remarkable potential in the neutralization and treatment of heavy metals from the battery recycling industry.