442
). Thiiming et al.
volume of mercury vapours, which requires sophisticated condensation systems
to assure no leak to the atmosphere.
A voiding these disadvantages of thermal remediation, wet extraction processes
are becoming more and more interesting. This work presents a contribution to
the extraction and recovery of mercury from mercury-bearing materials. The
main goal of the present work is to provide an improved and economical process
for the hydrometallurgical extraction and recovery of mercury that can be
applied to low, and to some extent, to high mercury content residues.
There is not enough information in the literature regarding hydrometallurgical
recovery of mercury from residues (US PTO 1993); There are, however, extensive
works on the environmental problems which are caused by mercury. The lack of
information on recovery processes is due largely to the chemistry of the mercurywater system, and the lack of very low solubility compounds which could be used
to reduce mercury concentrations in solution. In addition, there is the problem
that mercury forms strong complexes with many ligands, but this is, at least, an
advantage when considering the possibilities of chemicals for leaching mercury
from residues.
2
The Electroleaching Process
The process described here is called electroleaching because electrolysis is
employed for generating the leaching agent.
The leaching process takes place by the action of hypochlorous acid or
hypochlorite ions, generated during the electrolysis of:
1. A suspension made up of residue in an aqueous sodium chloride solution (insuspension production of leaching agent: EL-IS, Fig. 1).
2. An aqueous sodium chloride solution in a separate electrolysis cell (in-line
production of leaching agent: EL-IL, Fig. 2).
The leaching agent generation is the result of the oxidation of chloride ions to
chlorine gas, which in contact with the aqueous solution produces hypochlorous
acid and/or hypochlorite ions, depending on the solution pH. In the situation
where sodium chloride is used as the electrolyte, the reaction occurring at the
anode is
.
2CI B Cl2 + 2e
and the reaction taking place at the cathode is
2H2 0 + 2e B 20H + H2 ·
In a cell in which the anode and cathode products are not separated, there is a
measuring process which can result in
Cl2 + 20H B CIO + H2 0 + CI
). Thiiming et al.
volume of mercury vapours, which requires sophisticated condensation systems
to assure no leak to the atmosphere.
A voiding these disadvantages of thermal remediation, wet extraction processes
are becoming more and more interesting. This work presents a contribution to
the extraction and recovery of mercury from mercury-bearing materials. The
main goal of the present work is to provide an improved and economical process
for the hydrometallurgical extraction and recovery of mercury that can be
applied to low, and to some extent, to high mercury content residues.
There is not enough information in the literature regarding hydrometallurgical
recovery of mercury from residues (US PTO 1993); There are, however, extensive
works on the environmental problems which are caused by mercury. The lack of
information on recovery processes is due largely to the chemistry of the mercurywater system, and the lack of very low solubility compounds which could be used
to reduce mercury concentrations in solution. In addition, there is the problem
that mercury forms strong complexes with many ligands, but this is, at least, an
advantage when considering the possibilities of chemicals for leaching mercury
from residues.
2
The Electroleaching Process
The process described here is called electroleaching because electrolysis is
employed for generating the leaching agent.
The leaching process takes place by the action of hypochlorous acid or
hypochlorite ions, generated during the electrolysis of:
1. A suspension made up of residue in an aqueous sodium chloride solution (insuspension production of leaching agent: EL-IS, Fig. 1).
2. An aqueous sodium chloride solution in a separate electrolysis cell (in-line
production of leaching agent: EL-IL, Fig. 2).
The leaching agent generation is the result of the oxidation of chloride ions to
chlorine gas, which in contact with the aqueous solution produces hypochlorous
acid and/or hypochlorite ions, depending on the solution pH. In the situation
where sodium chloride is used as the electrolyte, the reaction occurring at the
anode is
.
2CI B Cl2 + 2e
and the reaction taking place at the cathode is
2H2 0 + 2e B 20H + H2 ·
In a cell in which the anode and cathode products are not separated, there is a
measuring process which can result in
Cl2 + 20H B CIO + H2 0 + CI