Stabilization and Solidification of Elemental Mercury for Safe Disposal and/or Long-Term Storage

Abstract

ABSTRACT A simple and highly effective stabilization/solidification (S/S) technology of elemental mercury using only sulfur with paraffin is introduced. First, elemental mercury is mixed with an excess of sulfur powder and heated to 60 °C for 30 min until elemental mercury is converted into mercuric sulfide (HgS black, metacinnabar) (Step 1). Then, metacinnabar with additional sulfur is poured into liquid paraffin (Step 2). Finally, the mixture is melted at 140 °C and settles to the bottom of the vessel where it cools and solidifies under the layer of liquid paraffin (Step 3). The proposed S/S method with sodium sulfide nonahydrate (Na2S·9H2O) as an additive is also tested for comparison. The average toxicity characteristic leaching procedure test values are 6.72 μg/L (no additive) and 3.18 μg/L (with additive). Theses concentrations are well below the Universal Treatment Standard (25 μg/L). Effective diffusion coefficient evaluated from accelerated leach test and average headspace concentration of Hg vapor after 18 hr are 3.62 × 10−15 cm2/sec, 0.55 mg/m3 (no additive) and 5.86 × 10−13 cm2/sec, 0.25 mg/m3 (with additive). IMPLICATIONS The simple treatment method for elemental mercury by stabilization/solidification introduced in this study will benefit the United Nations Environmental Programme (UNEP) Mercury Programme initiating a project to reduce the global mercury supply and address the safe and long-term storage of mercury. In addition, it will also provide an option and possible solution to the compliance of the recently passed law individually by the European Union and the United States banning the sale of toxic mercury abroad in 2011 and 2013, respectively.