Development of Alumina Modified Laterite Material for Fluoride Removal from Contaminated Water
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Date
August, 2016
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Abstract
Fluoride in groundwater is a threat to the provision of potable water to our rural
communities because continuous consumption of water contaminated with fluoride
could lead to dental fluorosis or even in extreme cases, skeletal fluorosis. Many
fluoride removal techniques have been suggested but most of them have been found
not to be practical and sustainable in Ghana as they are either expensive or need
highly skilled personnel to operate. The need for a local adsorbent which is less
expensive and effective for fluoride removal is of much relevance. Laterite has been
identified as a local adsorbent which is readily available and not expensive.
However, there have been debates among researchers about the effectiveness of
laterite to remove fluoride. This study investigated the characteristics of three (3)
laterites from three locations of the Upper East Region for fluoride removal. These
areas are Agamolga, Balungu and Dua. Chemical and mineralogical analyses
performed using X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD) methods
showed varying amounts of iron oxide/hydroxide (goethite/hematite), silica and
kaolinite. Scanning Electron Microscopy (SEM) combined with Energy Dispersive
X-ray (EDX) showed that the minerals are intimately associated. Isoelectronic Point
(IEP) value was influenced by the mineral composition with the larger IEP value
corresponding to higher iron oxide/hydroxide content.
The study measured the responses of the different laterites to fluoride uptake under
different conditions of pH, temperature, particle size of adsorbent and initial
concentration of fluoride solution. The responses showed that Agamolga and
Balungu laterites could remove fluoride better than Dua laterite mainly due to the
chemical and mineralogical constituents of these two laterites as compared to Dua
laterite which has high silica content. To improve the adsorption capacity of the
iv
laterite for fluoride uptake, an alumina modified laterite (AML) was developed using
Balungu laterite. The effect of treatment temperature and application to different
conditions of fluoride uptake was investigated including adsorbent dosage, initial
fluoride concentrations, solution pH and fluoride uptake in the presence of other
competing anions. The response of AML to the different experimental conditions
shows that the material is capable of removing fluoride to a level below the WHO
recommended limit of 1.5 mg/L. At a dosage of 4% solids, AML could remove
fluoride from 10±0.2 to 0.42 mg/L without any pH adjustment within 35 minutes.
The results indicated that the adsorption characteristics of AML were not
significantly affected in the pH range of 6-9 and this means pH adjustment of the raw
water is unnecessary. The results also showed that there was an improvement on the
adsorption capacity as the raw laterite assumed an adsorption capacity of 0.55 mg/g
whereas the AML material assumed a value of 0.69 mg/g. The results also showed
little or no significant change in fluoride adsorption by AML in the presence of other
competing ions such as chloride, sulphate, phosphate, bicarbonate and nitrates.
Description
A Thesis submitted to the Department of Materials Engineering, Kwame University of Science and Technology in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY (MATERIALS ENGINEERING)
Keywords
Alumina modified laterite, Fluoride, Contaminated water