Mining and hydrometallurgical industries produce large amounts of hazardous metal sulfate solutions as a by-product which can be recycled and exploited to produce valuable and advanced materials. Here, for the first time, extracellular polymeric substances of Bacillus licheniformis were applied as biosurfactants to synthesize quantum dots of cadmium sulfide from pure artificial and impure industrial cadmium sulfate solutions. The bacterial biopolymers stabilized the generated crystalline nuclei as colloidal dots and prevented their further growth or agglomeration. In order to discover the composition and size distribution of the produced particles, characterization was performed by X-ray diffraction (XRD), and transmission electron microscopy (TEM). Results showed that the particles biosynthesized from the pure solutio were nano-sized cubic crystals of CdS with the dimensions of 2 to 10 nm. The same product was also derived from the impure industrial solution. The outcomes of this study indicate the feasibility of cadmium or probably other metal recovery from industrial solutions and wastewaters in the form of valuable metal sulfide nanoparticles.
