ABSTRACT
This work studies the adsorption capacity of laterite and iron oxide
nanoparticles for dissolved ions in solution and therefore its ability
to reduce conductivity of mine waste effluent. Three laterite samples
were prepared and used as adsorbents. The first laterite adsorbent was
used without any treatment, the second was heat treated and the third
was mixed with 15 % iron oxide nanoparticles of particle size 100 nm.
Laterite and nanoparticle characterization, pH and adsorption tests were
conducted to ascertain the composition of laterite and as-prepared iron
oxide nanoparticles, the adsorption capacity of the adsorbents and the
optimum conditions for adsorption. The X-ray diffraction. (XRD) results
of both pure and heat-treated laterite showed the main minerals present
to be: Quartz (SiO2), Alumina (Al3O4), Berlinite (AlPO4) and Hematite
(Fe2O3). The XRD results for synthesized iron oxide nanoparticles showed
the mineral Magnetite (Fe3O4). The adsorption results of heat-treated
laterite showed the highest adsorption capacity for total dissolved ions
at a pH range of 6.5 - 6.8. Laterite and nanoparticles composite had
the highest adsorption capacities for Ca and Mg ions.
CHAPTER ONE
BACKGROUND
1.1 Introduction
High quality water is a critical resource with invaluable
socio-economic and environmental value and significance worldwide. The
growing concern with water quality and increasing stringent
environmental regulation has brought focus on water recycling, water
treatment and minimization of water used in the mining and process
industries. Conventional treatments to meet allowable concentrations of
contaminants in water before discharge are being challenged due to
economics and cost factors in technology and selection. Effective
sustainable development must, therefore, ensure uncontaminated streams,
rivers, lakes and oceans (Nkwonta and Ochieng 2013). Under current
practice, water draining from process industries and base metal mines
frequently contain organic, inorganic and heavy metals at high levels.
When the contaminants in the effluents become higher than the set
standards, disposal becomes a challenge.
As process water from mineral processing accumulates or when the
water level overflows the depth of an open pit mine or an underground
mine, the water is pumped out of the mine to ensure safety and stability
or may be reused for process applications such as make-up water, dust
suppression or mill operations, grinding, leaching, and steam generation
depending on the water availability and quality. Nevertheless, it has
been observed that more than 70% of all pollutants from the mining
industry mostly contained in wastewaters are emitted into water bodies
(Doll, 2012). With the fast development in industries, a huge quantity
of wastewater is been produced and discharged into soils and water
systems. The removal of these contaminants before discharge is receiving
significant attention. There is, therefore, a growing necessity for
finding versatile and low-cost treatment technologies to mitigate these
contaminants. Currently, adsorption has emerged as a simple and
effective technique for water and wastewater treatment even though its
success largely depends on the development and improvement of materials
for efficient adsorption. Activated carbon, clay minerals, zeolites,
biomaterials and some industrial solid wastes materials have been used
as adsorbents for adsorption of dissolved ions and organics in
wastewater (Wang and Peng 2009).
In the past, membrane separation processes received much attention
and are been applied in different industries especially in wastewater
treatment (Mortazavi, 2008). These membrane processes which include:
reverse osmosis, nanofiltration, ultrafiltration and microfiltration are
effective (Dessouky and Ettouney, 2002) but considered to be very
expensive.
1.2 Problem Definition
The contamination of water by dissolved ions is a significant
worldwide problem (Nriagu and Pacyna, 1988) that warrants cost-effective
methods for the removal of the undesirable species. This excessive
pollution problem results from chemical substance and dissolved
constituents from the ore added to the water at concentrations higher
than established limits during processing. To make things worse, the
regulated discharge limits of industrial wastewater effluents are
getting more restrictive with time (Mortula and Shabani, 2012).
As inorganic components dissolve in water, one of the parameters that
changes significantly is conductivity. Conductivity is a measure of the
ability of water or an aqueous solution to carry an electric current.
The current flow in water depends on the presence and concentration of
ions in the water and therefore conductivity is often used as an
indirect estimate for dissolved solids content of a solution (Coury,
1999). High total dissolved solids (TDS) discharged to rivers and
streams can promote eutrophication, destroy sensitive ecosystems and
endangers aquatic species (e.g., the cutthroat trout and cui-cui fish)
in rivers and lakes (Mortensen et al., 2008). These water bodies can
also be rendered unwholesome for both animals and plant usage,
especially for people living in catchment areas, who do not only use
these waters for drinking but also for other domestic purposes.
In recent years, most mining companies in the Western Region of Ghana
have experienced relatively higher conductivity values of about 4000
µS/cm above Environmental Protection Agency (EPA) standard (≤ 1500µS/cm)
(US EPA, 2011) for process waters. Since large volumes of wastewater
are generated daily, high conductivity in the process water creates
discharge problems. Existing wastewater treatment technologies such as
oxidation, precipitation, alum coagulation/precipitation, reverse
osmosis, nanofiltration, ion exchange, demand high capital investment,
operation and maintenance cost (Lesmana et al., 2009).