Sonochemical dissolution of cinnabar (alpha-HgS).

To investigate the sonochemical dissolution of cinnabar, sulfur oxidation products (S(ox)) and dissolved Hg(II) released into the aqueous solution were determined. Detected S(ox), in the presence of ultrasound suggests that dissolution of cinnabar occurred. Terephthalic acid (TA) used to scavenge *OH in bulk solution formed from sonication showed that oxidative dissolution occurred in both the bulk solution and the interfacial areas of cavitation bubbles. Dissolved S(-II) was not detected, and SO4(2-) was the main S(ox) indicating that the formation of S(-II) from cinnabar by physical and thermal effects of sonication was the rate-limiting step. Hg(Il) released was much lower than S species measured. Hg(II) adsorption isotherms indicated that dissolved Hg(II) adsorbed back onto the remaining cinnabar particles lowering Hg(II) release. Ultrasound significantly reduced cinnabar particle size and increased surface area, leading to higher Hg(ll) adsorption. In addition, the cinnabar surface isoelectric point (IEP) increased after sonication, indicating adsorption of Hg(II) and/ or mineral phase transformation from cinnabar to metacinnabar. The presence of humic acid (HA) and ultrasound enhanced cinnabar dissolution and greatly increased the dissolved Hg(ll) concentration due to the synergistic effects of ultrasound and HA.