Separation Science and Technology, Vol.32, No.1-4, 373-386, 1997
Extraction and Precipitation Chemistry for Mercury Recovery from Aqueous Wastes
This paper describes an extraction-precipitation process to recover mercuric chloride from aqueous solutions. The process is a modification of a dicarboxylic acid recovery process that exploits the enhanced solubility of mercuric chloride in organic solvents loaded with water. Mercuric chloride in ethyl acetate has a solubility enhancement of 1.34 moles mercuric chloride per mole of water added to the solvent, consistent with previously reported phase behavior. Solubility enhancement is also reported for formates, in contrast to previously reported results. For example, propyl formate showed 2.91 moles mercuric chloride per mole water enhancement. The modified process described in this paper relies on (1) favorable liquid-liquid equilibrium (mercuric chloride distribution into ethyl acetate or into propyl formate), (2) favorable liquid-solid equilibrium with enhanced solute solubility on addition of a minor constituent (water), and (3) preferential vaporization of the minor constituent from the solid slurry (relative volatility of water in mercuric chloride loaded ethyl acetate is four). Enhanced solubilities for zinc(II) chloride(3.46) and mercury(II) iodide(1.10) in isopentyl acetate indicate a potential application of the process for the recovery of other metal halides from aqueous wastes.