Removal of Heavy Metals From Wastewater
By Adsorption on Sand
A. NETZER, Research Scientist
P. WILKINSON, Research Assistant
Water and Wastewater Treatment Research Subdivision
Canada Centre for Inland Waters
Burlington, Ontario, Canada
INTRODUCTION
The increase in public awareness of the hazards of heavy metals and their effects on the
environment and public health has prompted governments to implement legislation
requiring treatment of heavy metal bearing effluents at source.
Active research into heavy metal removal from wastewaters has shown treatment
methods such as ion-exchange, electro deposition, reverse osmosis, chemical precipitation,
ultra-filtration, and chemical oxidation and reduction to be usable.
This paper deals with the removal of heavy metals from wastewater using sand and is
part of a larger study dealing with heavy metal removal from wastewaters utilizing novel
treatment methods. Some treatment methods evaluated include metal oxidation using
ozone gas, a combined treatment process utilizing lime and ozonation, metal adsorption on
activated carbon, adsorption of metals using discarded automotive tires, and preliminary
studies using zeolites, silica gels, activated alumina, and polyeurethane foams.
The merits and advantages of using sand in water and wastewater treatment as a filter
and support medium are well documented in the literature (1,2). Both slow and rapid sand
filtrations are capable of achieving bacterial and turbidity reductions and a certain degree of
color removal by a complex mechanism involving straining, adsorption, flocculation,
sedimentation and biological assimilation.
More recently, considerable interest has been aroused in the possibilities of using soil
and sand to remove heavy metals from water and wastewaters.
Kowal (3), in his study on the composition of deposits retained in rapid sand filters,
observed the adsorption of trace amounts of gold, molybdenum and vanadium on the sand
particles. He also found that lead did not adsorb at all.
Using a calcerous soil material composed predominately of 80% sand and the
remainder gravel and clay. Lehman and Wilson (4) noted that the concentrations of iron,
nickel, zinc, lead, and cadmium in domestic sewage effluents were considerably reduced
after percolation through the soil material contained in lysimeters eight feet in length and
one foot in diameter. For iron. lead, and cadmium, around 98% removals were attained
after percolation through the first 3" of the column material, and greater than 95% removals
were observed for manganese, nickel, copper, and zinc in the final effluent.
These removals were attributed primarily to a combination of ion-exchange,
adsorption, and biological uptake.
Wentink and Etzel (5) achieved greater than 98% reduction for chromium, zinc, and
copper by passing solutions containing up to 300 mg/1 of each of these metals through
various columns of clay loam. Also, they determined the exchange capacity of the soils
tested, and by demonstrating that re-exchange with ammonium ions is possible, they
concluded that the dominant removal mechanism was ion-exchange. Furthermore, these
investigators found that there was no leaching of the exchanged ions from the soils when
either tap or distilled water was used as a leachate.
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