AbstractMercury causes many problems in the processing of hydrocarbons in oil and gas industries. It is a toxic metal and can lead to disastrous failure of processing plants leading to explosions and loss of life. With many of the hydrocarbon processing plants now approaching 30 years in operation they are coming to the end of their economic life and need to be decontaminated as part of their decommissioning process. Here the problem is that mercury can “hide” inside pipelines and flanges, increasing the difficulty of plants decommissioning and recycle. Economical and applicable chemical decontamination i.e. dissolution of elemental Hg should be studied to eliminate this problem to avoid mercury exposure to worker and environment.
In this study, wet-based chemical approaches using KI/I2 solutions were studied for the recovery of mercury as part of plant cleaning and decommissioning. The influence of solution concentration, molar ratio of KI:I2, pH, temperature was investigated in this experiment. To see whether KI can be substituted by other halide salts i.e. NaBr, KBr, NaCl, KCl, mixed oxidative trihalide solutions were studied to learn its efficiency of mercury dissolution. After oxidation/dissolution of Hg0 to Hg2+, the obtained mercury(II)-containing solution need a further treatment to concentrate and capture mercury from aqueous solutions via commercial 2,4,6-Trimercapto-s-triazine, trisodium salt (TMT-15) or Purolite S924/S920 ion exchange resin, thus ensuring no mercury is left in wastewater. The operating variables of dosage, initial mercury concentration, contact time, pH and temperature were studied.
Results indicated that KI/I2 solution was efficient on mercury dissolution, 100 mg elemental mercury could be completely dissolved in 10 ml of 4% (0.053/0.16 M I2/KI) w/v KI/I2 solution in 10 h at room temperature, mercury concentration was achieved of 0.050±0.002 mol/l. For bromide/iodine solution, a mercury concentration of 0.051±0.001 mol/L and 0.051±0.001 mol/L was achieved by 10 ml 0.0504/0.6531 M NaBr/I2 and 0.0510/0.5630 M KBr/I2 solution, respectively. Dissolved mercury ions were effectively removed from the aqueous solutions using S924 and S920 resin or TMT-15, producing solutions that had very low mercury contents ([Hg] ~ 0.02 g/L). A dosage of 30% molar excess (0.7 g) of TMT-15 can reduce 10 g/L mercury to 0.028±0.025 g/L with a contact time of 1 h. The resins S924 and S920 showed good removal of mercury after 4~6 h contacting, with an extraction efficiency of 84.28±0.71% and 99.16±1.91% respectively.
|Date of Award
|04 Dec 2017
|Martin Atkins (Supervisor) & John Holbrey (Supervisor)