Novel applications of vacuum distillation for heavy metals removal from wastewater, copper nitrate hydroxide recovery, and copper sulfide impregnated activated carbon synthesis for gaseous mercury adsorption.

Hydrometallurgical processing of electronic waste produces copper (Cu)-containing wastewater. Recycling of Cu is thus crucial, as it reduces the Cu impact on the environment, and increases Cu sustainability in industry. Vacuum distillation provides excellent performance in both metals removal from aqueous solution, metal recovery, and metal impregnation to porous material. Thus, this work aimed to both utilize a vacuum distillation to remove heavy metals (Cu, Na, Ni, Zn and Fe) and recover copper nitrate hydroxide (Cu2NO3(OH)3) from Cu-containing wastewater in industrial applications (e.g., mordant agent in dyeing and pigment for glass), as well as prepare copper sulfide (CuS) impregnated activated carbon for mercury (Hg0) adsorption. The experimental results indicated a vacuum distillation metals removal efficiency of over 99.99 % at 60 °C and -72 cm Hg. Additionally, the copper nitrate hydroxide (Cu2NO3(OH)3) crystalline solid derived from the vacuum distillation process achieved 77 % purity, and the copper sulfide impregnated activated carbon (CuSAC) adsorbents were prepared by adding activated carbon (AC) during the vacuum distillation process. In adsorption tests, 50 % CuSAC exhibited the greatest gaseous mercury (Hg0) adsorption performance, and it was noted that a high adsorption temperature of 175 °C negatively impacted Hg0 adsorption of 50 % CuSAC due to mercury sulfide (HgS) decomposition. Furthermore, in a simulated flue gas (SFG) environment, Hg0 capture by CuSAC was shown to be slightly obstructed. In addition, mercury temperature-programmed desorption (Hg-TPD) identified that HgS was the dominant species among adsorbed Hg species of Hg-laden 50 % CuSAC, indicating that Hg0 capture of CuSAC was mainly facilitated by sulfur active sites. As such, the vacuum distillation technique proved to efficiently remove metals and leads to successful preparation of adsorbent for Hg. Therefore, the process is an effective treatment method for Cu-containing wastewater, and can be practically applied to capture or recycle Cu in the industry in the future.

Simultaneous aqueous Hg(II) adsorption and gaseous Hg0 re-emission inhibition from SFGD wastewater by using Cu and S co-impregnated activated carbon.

Seawater flue gas desulfurization (SFGD) has shown great effectiveness in the controlling of sulfur dioxide (SO2) emission and the removing of mercury (Hg) from flue gases of coal-fired power plants. Some problems pertaining to SFGD for Hg control, however, remain to be solved: (1) environmental impact from the discharge of Hg-containing seawater to the ocean, and (2) re-emission of gaseous Hg from the aeration tank to the atmosphere. This study synthesizes the copper/sulfur co-impregnated activated carbon (Cu-S-AC) to simultaneously capture aqueous Hg(II) and inhibit gaseous Hg0 re-emission from actual SFGD wastewater. Cu-S-AC exhibited greater Hg(II) adsorption than both raw activated carbon (AC) and sulfur-impregnated activated carbon (S-AC) at an initial Hg(II) concentration of higher than 8000 ng/L. The Hg(II) adsorption of Cu-S-AC was slightly greater at pH 7 and 8 than that under acidic conditions. The Hg(II) adsorption was well-fitted with both linear and Freundlich isotherms. The results of thermodynamic analyses veiled the endothermic and spontaneous adsorption of Hg(II) on Cu-S-AC. In addition, the pseudo-second-order equation provided the best correlation coefficient for the Hg(II) adsorption on Cu-S-AC. Notably, the increases of pH and temperature increased the Hg0 re-emission. Nevertheless, Cu-S-AC addition significantly inhibited the Hg0 re-emission (92%) from SFGD wastewater.