Engineering of clay lining system for landfills using bio-material to improve its adsorption of Pb2+
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Lead (Pb), a heavy metal that can leach from landfills, is one of the most lethal heavy metals to
man. A clay modified with sawdust, a waste from processing wood, was investigated for its
potential to prevent Pb2+ from lead-containing wastes disposed at landfills from contaminating
groundwater and thereby protect public health. The chemical and mineralogical composition of the
clay, and microstructural analysis of the clay and sawdust-modified-clay were determined. The
effects of sawdust on the suitable use of the modified clay as a landfill liner was investigated by
carrying out specific gravity, Atterberg’s limits, compaction, unconfined compressive strength
(UCS) and permeability tests. Batch equilibrium adsorption test was used to evaluate the sorption
of Pb2+ on the clay and sawdust-modified-clay at varying initial concentrations and contact times.
The clay, which is classified as a clay of high plasticity (CH), has low permeability and strength.
The modification of the clay with increasing percentages of the sawdust altered its geotechnical
properties by: reducing its plasticity, specific gravity, maximum dry unit weight, and UCS; and
increasing its optimum moisture content and permeability. The admixing of the clay with 8%
sawdust, by weight of the soil, provided a modified clay whose geotechnical properties satisfy
standard requirements for use as landfill liner materials. The batch adsorption test results indicate
that the application of the sawdust successfully improved the Pb2+ adsorption capacity of the clay.
The Pb2+ adsorption capacity of the clay and sawdust-modified-clay increased with increasing
initial concentration. The batch studies also show that optimal Pb2+ adsorption of 91% was
achieved by the sawdust-modified-clay, when the initial Pb2+ concentration of 100 mg/L in the
solution was used and after a contact time of 120 minutes. The Freundlich isotherm provided a
better fit for the description of the adsorption process at equilibrium than the Langmuir isotherm
while the pseudo-second-order kinetic model is the best representation of the adsorption rate.
Consequently, sawdust is recommended as a low-cost modifier of clay for use in liner system for
the containment Pb2+ while also preventing the nuisance associated with improper disposal of
sawdust.
Keywords
T Technology (General), TA Engineering (General). Civil engineering (General)