Experimental Study of Mercury Removal and Electrolytic Regeneration by Ca(ClO)2 Solutions

Abstract

The trace element mercury (Hg0) released from fossil fuel combustion in thermal power plants is difficult to be collected by pollution control equipment as its high volatility, high volatility and low solubility. The removal of Hg0 is the most critical part of mercury removal technology. The existing technologies of mercury removal include activated carbon adsorption, fly ash adsorption, calcium-based adsorbent adsorption, and wet scrubbing method. While these existing technologies have some disadvantages, like high absorbent consumption, high absorption cost and existence of secondary pollution. Much attention has been devoted to the development of new mercury removal technology in recent years. In this study, the Ca(ClO)2 solution was proposed for the absorption of elemental mercury as its strong oxidizing property and low expenditure. The chemical reaction mechanism, reaction kinetics and reaction thermodynamic in both absorption and regeneration processes were explored, which verified the feasibility of mercury removal and absorbent regeneration. Effects of solution concentration, absorption temperature and solution pH value on absorption performance of Ca(ClO)2 solution were investigated in micro bubbling reactor. The experimental results revealed that acid environment (pH = 1–5) and high solution concentration were beneficial to mercury removal. A high removal efficiency (over 90%) and a low outlet mercury concentration (below 0.01mg·m3) was obtained under optimal experimental parameters (with the pH value of 3, the solution concentration of 15 mmol·L−1 and the temperature of 25 °C). The performance of electrolytic regeneration in Ca(ClO)2 rich solutions were carried out, and the effect of electrolysis time on current efficiency and energy consumption in electrolytic regeneration processes were specifically studied. The regeneration results showed that the oxidation reaction of Cl− with a series of other oxidation reactions will occur at the anode, and the reduction reaction of Hg2+ will occur at the cathode. The results verified the feasibility of the electrolytic regeneration of Ca(ClO)2 rich solution using an ion-exchange membrane insulating the catholyte and the anolyte. The Ca(ClO)2 solution is a promising absorbent for elemental mercury which can accomplish the cyclic utilization of solution and the reuse of mercury.