FEASIBILITY OF PbS NPs SYNTHESIS COUPLED TO A BIOREMEDIATION SYSTEM FOR ACID MINE DRAINAGE TREATMENT

摘要

Nowadays, there is much attention to the development of protocols for the synthesis of nanocrystalline semiconductors, such as PbS and other metal sulphides, since they are emerging as a new class of materials with several recognized environmental applications, namely as photocatalysis and as additives to solar panels.The use of Sulphate-Reducing Bacteria (SRB) for the bioremediation of metals and sulphate in highly contaminated effluents, such as Acid Mine Drainage (AMD), is well documented. The biological reduction of sulphate in the presence of metal ions leads to their precipitation as metal sulphides. However, depending on the metal and sulphate concentrations, these processes may generate excess sulphide, which may in turn pose an environmental issue that needs to be addressed.In this context, the use of the surplus sulphide to synthesize useful materials, such as semiconductor metal sulphide nanoparticles (NPs) and nanocomposites, is of particular environmental relevance, as this will not only improve the remediation system from an economical point of view, but it also allows overcoming the problems generated by the excess of toxic H_2S produced by SRB.This paper describes the successful synthesis of nanocrystalline PbS and PbS/TiO_2 nanocomposites, coupled to a continuous bioremediation system for AMD treatment, at room temperature and atmospheric pressure, yielding near complete metal precipitation. According to Transmission Electron Microscopy (TEM) analysis, the particles obtained are in the range of 20 to 50 nm in size, for both the PbS nanoparticles and the PbS/TiO_2 composites. This AMD bioremediation system with coupled synthesis of NPs presents obvious advantages in terms of economy and safety, due the production of functional materials from a toxic waste. Moreover, the simplicity of the process here described presents an attractive route for the synthesis of metal sulphide NPs, such as PbS NPs and the respective TiO_2 nanocomposites.