Removal of Methylmercury(II) Chloride from Waste Water by Flotation Method Using N-Phenyl-N'-amidinothiourea as a Collector

Abstract

Removal methylmercury (II) chloride (MMC) from waste water was carried out by flotation method using N-amidinothiourea derivatives (N-methyl-N'-amidinothiourea, N-ethyl-N'-amidinothiourea and N-phenyl-N'-amidinothiourea) as collectors for MMC and sodium dodecylbenzenesulfonate (DBS) as a surfactant. Hg atom in MMC combines by coordination with sulfur containing group in the collectors and forms cationic complexes. Resulting complexes and an anionic surfactant DBS make new chemical species and then MMC complexes are removed by the flotation.
Among these N-amidinothiourea derivatives, N-phenyl-N'-amidinothiourea (Ph-ATU) is the most effective collector for MMC in the flotation.
Effects of pH, concentrations of DBS and Ph-ATU and coexisting salts on the removal of MMC were studied. Optimum pH is If waste water contains enough DBS to make bubbles continuously, the percentage removal of MMC increases with increasing concentration of Ph-ATU. When concentrations of coexisting salts: sodium chloride, calcium chloride and magnecium chloride, were less than 50-100 ppm, no effects of these salts on the flotation of MMC were observed.
Under the condition of 1 ppm of MMC, 100 ppm of DBS, 25 ppm of Ph-ATU, pH 5.5 and 80 ml/min of gas (N₂ gas) flow rete, MMC was removed from waste water to the level of 1 ppb by the flotation. From these results, Ph-ATU can practically be used as a collector of MMC in the flotation.