Basic Study on the Remediation Technology
4
Conclusion
439
We examined a method for purifying mercury contaminated soils by heating the
soils at low temperatures.
1. Mercuric sulfide evaporates at temperatures below 583.5 °C (the physical and
chemical sublimation point of mercury) when it is heated in minerals, such as
standard sand.
2. When mercuric sulfide is dispersed in minerals, such as in standard sand, and
is heated, it evaporates at 200-300 0c. The same phenomenon was observed
when pure quartz sand was used. Therefore, we conclude that the evaporation
of heated mercuric sulfide was induced by the physical and chemical
charcateristics of the quartz.
3. The removal of mercuric sulfide from mercury-contaminated soils is
facilitated by adding iron chloride (FeCI2.4H20) to and then heating the soils.
4. The efficiency of the mercuric sulfide evaporation reaction generated by heat
and the additon of iron chloride to contaminated soils and the amount of iron
chloride to be added to the soils is greatly affected by heating temperature. As
our test results show, the percentage of mercury removed increased with an
increase in heating temperature. At a heating temperature of 300°C,
regardless of soil type, at least 99% of the mercuric sulfide can be removed;
the amount of iron chloride that should be added is equal to or slightly greater
than the amount of mercury mol contained in the soil. We conclude that this
is due to the dramatic physical change that occurs to iron chloride when it is
heated to 250°C.
5. According to references, when iron chloride is heated to 200-250 °C in air, it
becomes denatured and converts to iron oxide and hydrogen chloride gas.
Therefore, when iron chloride is heated in air, bivalent iron can be converted
to trivalent iron, allowing an oxidation-reduction atmosphere to be forcefully
made and a reaction between it and the mercuric sulfide to be generated.
Our test results also suggest that coexisting silicas have an important function
in the removal of mercuric sulfide through heating. Given these two points, we
consider the reactions we observed in our tests to be oxidation-reduction
reactions in the soil, reactions in which the characteristics of the silica, such as
quartz, and the denaturation of iron chloride by heating, were utilized.
References
Aguilera NH, Jackson ML (1953) Iron oxide removal from soils and clays. Soil Science Society of
America Proceedings, vol 17. The Soil Science Society of America, Wisconsin, pp 359-364
Akagi H, Nishimura H (1991) Speciation of mercury in the environment. In: Suzuki T et al. (eds)
Advances in mercury toxicology. Plenum Press, New York, pp 53-76
Akagi H, Fujita Y, Takabatake E (1975) Solid-photosensitized methylation of inorganic mercury in
aqueous acetic acid solutions. The Chemical Society of Japan, Tokyo, pp 1273-1279
4
Conclusion
439
We examined a method for purifying mercury contaminated soils by heating the
soils at low temperatures.
1. Mercuric sulfide evaporates at temperatures below 583.5 °C (the physical and
chemical sublimation point of mercury) when it is heated in minerals, such as
standard sand.
2. When mercuric sulfide is dispersed in minerals, such as in standard sand, and
is heated, it evaporates at 200-300 0c. The same phenomenon was observed
when pure quartz sand was used. Therefore, we conclude that the evaporation
of heated mercuric sulfide was induced by the physical and chemical
charcateristics of the quartz.
3. The removal of mercuric sulfide from mercury-contaminated soils is
facilitated by adding iron chloride (FeCI2.4H20) to and then heating the soils.
4. The efficiency of the mercuric sulfide evaporation reaction generated by heat
and the additon of iron chloride to contaminated soils and the amount of iron
chloride to be added to the soils is greatly affected by heating temperature. As
our test results show, the percentage of mercury removed increased with an
increase in heating temperature. At a heating temperature of 300°C,
regardless of soil type, at least 99% of the mercuric sulfide can be removed;
the amount of iron chloride that should be added is equal to or slightly greater
than the amount of mercury mol contained in the soil. We conclude that this
is due to the dramatic physical change that occurs to iron chloride when it is
heated to 250°C.
5. According to references, when iron chloride is heated to 200-250 °C in air, it
becomes denatured and converts to iron oxide and hydrogen chloride gas.
Therefore, when iron chloride is heated in air, bivalent iron can be converted
to trivalent iron, allowing an oxidation-reduction atmosphere to be forcefully
made and a reaction between it and the mercuric sulfide to be generated.
Our test results also suggest that coexisting silicas have an important function
in the removal of mercuric sulfide through heating. Given these two points, we
consider the reactions we observed in our tests to be oxidation-reduction
reactions in the soil, reactions in which the characteristics of the silica, such as
quartz, and the denaturation of iron chloride by heating, were utilized.
References
Aguilera NH, Jackson ML (1953) Iron oxide removal from soils and clays. Soil Science Society of
America Proceedings, vol 17. The Soil Science Society of America, Wisconsin, pp 359-364
Akagi H, Nishimura H (1991) Speciation of mercury in the environment. In: Suzuki T et al. (eds)
Advances in mercury toxicology. Plenum Press, New York, pp 53-76
Akagi H, Fujita Y, Takabatake E (1975) Solid-photosensitized methylation of inorganic mercury in
aqueous acetic acid solutions. The Chemical Society of Japan, Tokyo, pp 1273-1279