Mercury recovery from acidic mercury solution using electrodeposition

Mercury, a heavy metal, can seriously harm human bodies and the environment due to its characteristics of high toxicity, biological enrichment, and long-range migration. The non-ferrous metal smelting industry is one of the main sources of atmospheric mercury pollution in China. Therefore, controlling atmospheric mercury emissions from non-ferrous smelting plants is very important. The wet cleaning process has been widely applied in the purification of smelting flue gas because of its advantages such as a high removal efficiency, stable operation, and low cost. During the wet purification process, thiourea is usually added because it can reduce the oxidation potential of mercury and react with mercury to form stable coordination ions, resulting in the high-efficiency removal of mercury from high-sulfur smelting flue gas. However, mercury recovery from scrubbing solutions containing mercury and thiourea obtained from the wet cleaning process is difficult. In this study, a novel technology to recover mercury from the thiourea mercury solution via electrodeposition was proposed and investigated. The linear potential scanning method was applied to obtain the reduction potential of mercury. It was determined that the optimal potential of the mercury electrodeposition process should be controlled between −0.55 V and −0.45 V because the presence of ferric ions, copper ions, and sulfite ions did not seriously affect the electrodeposition of mercury. Controlled potential electrolysis was employed to efficiently recover mercury from thiourea mercury solution, and the effects of key parameters, including electrolyte type and concentration, electrolyte temperature, stirring rate, and electrolytic time, on the mercury recovery efficiency were explored. The optimal process conditions are as follows: a cathode material of copper sheet, electrolyte of 0.24 mol·L⁻¹ Na₂SO₄, electrolyte temperature of 30–40 ℃, stirring speed of 100–300 r·min⁻¹, ${\rm{SO}}^{2-}_{3}$ concentration of 8 mmol·L⁻¹, and electrolytic time of 5 h. Under the optimal process conditions, the mercury recovery efficiency mercury is over 98%. The electrolytic products on the cathode are elemental mercury, and the corresponding purity is over 99%.