RECOVERY OF MERCURY USING AN ELECTROCHEMICAL FLOW-BY REACTOR - PART IREACTION-RATE EXPRESSION FOR MERCURY DEPOSITION IN THE PRESENCE OF A SIDE REACTION

This paper analyses the deposition of the mercuric complexes from dilu te solutions of HgCln(2-n) and high concentrations of NaCl, taking int o account the reduction of O-2 as a simultaneous electrochemical react ion. Studies with a vitreous carbon rotating disk electrode were perfo rmed to determine the potential regions where the reactions take place and also to calculate the kinetic parameters under experimental condi tions. Reproducible results were obtained only when a mercury film was deposited on the vitreous carbon surface prior to each experiment. Po tentiodynamic polarizations were obtained from 5 x 10(-4) M Hg(II) sol utions and different NaCl concentrations ranging from 1 M to 4 M, in t he presence and absence of dissolved oxygen. The mercuric complex depo sition and the oxygen reduction proceeded via mixed control within the first 50 mV overpotential, followed by a diffusion control. After -0. 450 V vs see the H-2 evolution started. This reaction occurred at free vitreous carbon left between the liquid mercury droplets where the hy drogen overpotential is smaller. Kinetic parameters as well as the rea ction rate expression for mercury deposition from its chloride complex es were obtained. (C) 1997 Elsevier Science Ltd.