Electrolytic treatment of mercury-loaded activated carbon from a gas cleaning system

Characterization and treatment of artisanal gold mine tailings

The solid waste generated by artisanal gold mining, with high mercury and gold contents, can be found in several areas in the South America. The present study focused on the tailings of an artisanal gold mine area located in the Brazilian northeastern. Samples of the mine tailings were taken and used to perform a physical and chemical characterization study using X-ray diffraction, scanning electron microscopy, neutron activation, X-ray fluorescence, induced coupled plasma-mass spectrometry, among others analytical methods. The results indicate that the material is composed mainly by quartz and goethite, the characteristic size of the particles (d(50)) is about 150 microm, and the density is close of that of quartz. The main constituents are silicon, iron, and aluminum. The tailings gold content is of about 1.8 mg/kg and the mercury content is of about 10 mg/kg. A remarkable feature of this solid waste is that the gold and mercury are both concentrated in both the fine and the coarse particles, but not in particles of intermediary size. Leaching studies indicated that the tailings are stable in weak organic acids, but soluble in alkaline and aired cyanide solutions, in which 89% of gold and 100% of mercury are extracted in 24 h. Electroleaching experiments, performed using sodium chloride as electrolyte, indicated that mercury and gold are extracted simultaneously and the recovery of both metals can be as high as 70% in 4 h. In addition, chromium, nickel, and lead are found in relatively large amounts in the solution, which indicate an effectively action of the electroleaching method to clean up solid wastes contaminated with metals.

An electrochemical system for removing and recovering elemental mercury from a gas stream

The impending EPA regulations on the control of mercury emissions from the flue stacks of coal-burning electric utilities has resulted in the development of numerous advanced mercury control technologies such as sorbent injection and in-situ mercury oxidation. Although these technologies can effectively remove mercury from a flue stack they share, along with many other technologies, the common shortcoming of intermedia pollution transfer i.e. the traffic of mercury from the air phase to the solid phase and the subsequent generation of residue for landfill. This work addresses the need for an integrated system of mercury removal and recovery from flue stack gases and from the environment. The research explored the capture of elemental mercury from the gas phase at ambient temperature on an electrically conductive porous sorbent. The mercury loaded sorbent was regenerated at the anode in an electrochemical cell and the oxidized mercury recovered at the cathode as solid elemental mercury. Activated carbon cloth was selected as the most suitable sorbent as it had the highest mercury adsorption capacity of the sorbents tested and was electrically conductive. Direct and indirect electro-oxidation were shown to remove 95% and 100%, respectively, of the elemental mercury from the carbon cloth. After regeneration the carbon cloth was reused without any loss in mercury adsorption capacity. More than 99% of the mercury stripped from the cloth during regeneration was recovered at the cathode.