The Attenuation of Heavy Metals from Landfill Leachates by Bunter Sandstone and Chalk

Abstract

Extensive quarrying in the Chalk and Triassic Sandstones,
which are the two largest aquifers in the U.K., has produced a need
for reclamation. Infilling these quarries with waste materials will
create a potential pollution hazard to underground water supplies.

Laboratory experiments were set up to investigate the
natural chemical processes by which the heavy metals and alkaline
earth metals in landfill leachates may be attenuated by movement
through these rocks. Results obtained indicate that carbonate
precipitation is the most important mechanism in heavy metal uptake
by the Bunter Sandstone, although cation exchange on clays and a
possible two stage uptake by iron sesquioxides also play significant
roles. Precipitation of the metals as carbonates was found to
govern heavy metal mobility in Chalk groundwater.

Further experiments to compare heavy metal uptake by, both
rock types in the absence and presence of the other common
constituents of leachate and under varying pH conditions were made.
The leachate constituents tested were the alkaline earth metals,
ammonium, chloride and short chain carboxylic acids. The results
of those experiments showed that the initial solution pH has little
importance due to the buffering capacity of the Bunter Sandstone.
Neither alkaline earth metals nor chloride had any adverse effects
on heavy metal uptake. Metal uptake is decreased in the presence of
ammonium ions and by increasing concentrations of the carboxylic
acids, with acetic acid having greatest effect.

The conclusions reached imply that heavy metals are unlikely
to contribute seriously to groundwater contamination in either the
Bunter Sandstone or Chalk provided that an adequate unsaturated zone
is left beneath the fill to maintain aerobic conditions.

Date of Award	1982
Original language	English