Electroleaching: a mobile cleanup process for mercury contaminated materials

To date, there is no satisfactory technique known for simultaneous remediation of materials contaminated with mercury and other metals. In the case of mercury-polluted tailings from Brazilian gold-mining areas, there is the opportunity to extract mercury and traces of gold hydrometallurgically, thus making the remediation process cost-effective. Hydrometallurgical techniques are widely used in ore treatment, whereas solid remediation applications are rare. This chapter outlines two variants of an electroleaching process and gives an overview of its thermodynamic fundamentals. Model calculations are presented as well as results from laboratory experiments. The leaching agent, hypochlorous acid, can be produced by electrolytic oxidation of a sodium chloride solution. After leaching, the leachate is treated electrolytically to deposit the metals in the elemental form and to regenerate the leaching agent for recirculation. The leaching mechanism is a mercury oxidation and a complexation of mercuric ions by chloride ions, forming, for example, a tetra-chloro-mercurate-complex. The main process parameters, such as pH, Eh and element concentrations, control the speciation of mercury. It is illustrated how leaching efficiency and electrolytical mercury deposition are both dominated by the mercury species in solution. The electroleaching could be conducted in two different reaction systems: (1) as a 1-reaction process with an in-suspension production of the leaching agent (EL-IS) and (2) as a 2-reactor process with an in-line production (EL-IL). While the more costly EL-IL is capable of recovering mercury sufficiently (>99% removal rate) even from highly contaminated German industrial samples, the EL-IS is the best solution for less contaminated Brazilian gold-mining residues. After treatment, the mercury concentration is lower than 1 mg/kg and more than 82% of the residual gold can be recovered. (orig.)SIGLEAvailable from TIB Hannover: RA 3251(98/E/54) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman