The Study On The Electrochemical Anodic Oxidation Of Sulfide

Sulfide is present in a wide range of industrial wastewater such as tannery and paper mill wastewater and hydrogen sulfide is a particularly troublesome gas in the oil industry and in the natural gas. It is toxic, jeopardizes the health and threatens the life of humans. Sulfide is corrosive and odorous and for these reasons often requiring removal from the aqueous or gaseous phase before discharge into the environment. Electrochemical processes, which utilize electrons, are more advantageous than processes which consume chemicals, under otherwise comparable conditions. Recently, the electrochemical approach was proposed for wastewater sulfide removal, in which sulfide can be directly oxidized at an anode.In this paper, the anodic oxidation processes of the sulfide in solution have been studied by self-made cell reactor, these experiments employ graphite electrode as the working electrode, the stainless steel electrode as the cathode. The electrochemical measure methods such as the cyclic voltammetry and linear sweep voltammetry combined with XRD, SEM have been used to investigate the mechanism and the products of the anodic oxidation processes of sulfide, and the influences of environmental factors on the oxidation processes have been studied. Experimental results showed that:In the scanning process of the polarization curve, the oxidation peak of S2- was observed at --0.1V, the current value declined with the increase of the potential value after the current peak, the S2- were oxidized to sulfur deposited on the surface of the graphite electrode and caused the passivation of anode. Electrolysis Na2S in the alkaline solution at the potential of-0.1 V, the analysis results show that the products of the anode oxidation contain both sulfur and polysulfide; it can be observed from the cyclic voltammetry that the anodic oxidation of S2-at a low potential is irreversible reaction.In the processes of the electrolysis, the concentration of Na2S and NaOH in the anodic electrolyte, the type of impurity ions and temperature had considerable influences on the oxidation processes of the S2-. Increasing concentration of Na2S is beneficial to the formation of polysulfide; appropriate alkalinity can reduce the oxidation potential and promote the formation of polysulfide; increasing temperature increases rate of reactions, higher temperature improves the dissolution of sulfur and alleviate passivation of anode. Scanning rate in the polarization curve and cyclic voltammogram effects both number and position of the current peaks in the oxidation area of S2-. In the process of electrolyzing Na2S at constant potential, electrolytic potential, temperature, alkalinity and additives all effect the conversion of S2-. The determination results of conversion rate of S2- in different experimental conditions show that the optimal parameter of removing S2- by electrochemical process is:the anode electrolytic potential is-0.1V; the reaction temperature is 60℃; the additive is NaOH; the concentration of NaOH in the electrolyte is 0.1mol/L. Electrolyze Na2S in the above electrolysis conditions for 12 hours, the conversion rate of S2- can be up to 87.5%.